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Atmospheric NOx removal: Study of cement mortars with iron- and vanadium-doped TiO 2 as visible light–sensitive photocatalysts
Abstract
Mortars made with Portland cement, two different calcium aluminate cements and air lime were chosen to incorporate photocatalytic additives, because they have large exposed surfaces that boost the photochemical oxidation (PCO) of atmospheric pollutants such as nitrogen oxides. TiO2 as reference catalyst, and two doped titania, Fe-TiO2 and V-TiO2, which were expected to increase the sensitivity of the additives towards the visible light, were studied. Cementing matrices, particularly air lime and high alumina cement mortars, yielded significant amounts of NO removal under the three illumination conditions studied (UV, solar and visible light), with high selectivity response for NO abatement (up to 60–80%) and low NO2 release. The presence of calcium carbonate has been shown to have a synergistic effect, enhancing the PCO of these mortars under different light sources.
... Characterized by their macro to micro porous structure [6,7], they emerge as promising substrates for TiO 2 -based photocatalysts. The process schematic and reaction equation for the photocatalytic conversion of NO x by TiO 2 in cementitious materials is shown in Fig. 1 [8,9]. Upon exposure to UV light, the surface of TiO 2 undergoes a process in which photogenerated electrons (e -) and holes (h + ) interact with O 2 and OHpresent in the environment. ...
... Namely, TiO 2 has a high cost as the concrete additive, and due to the wide band gap caused by the quantum size effect, its responsiveness is largely confined to ultraviolet (UV) light [8], which makes it almost inactive when UV incidence is not available. Furthermore, the NO x removal efficiency of TiO 2 is compromised due to the rapid recombination of photogenerated electron-hole pairs [9]. In order to tackle these issues, supplementary materials featuring unique surface properties are typically incorporated onto TiO 2 for modification. ...
... Specifically, 1 g of H 3 BO 3 was dissolved in a 50 mL solution containing Fig. 1. Schematic diagram of photocatalytic conversion of NO x by TiO 2 [8,9]. 20 mL of deionized water and 30 mL of ethanol and ultrasonic-dispersed for 1 h. ...
In this paper, an advanced photocatalyst, B-TiO 2 /MgAl-CLDH, was synthesized and applied in cement mortar. The photocatalytic NO x degradation ability of cement mortar containing B-TiO 2 /MgAl-CLDH under different initial NO x concentrations and flow rates was investigated. The results show that B-TiO 2 /MgAl-CLDH has stronger visible light absorption, lower recombination rate of electron-hole pairs and narrower optical band gap than commercial nano-TiO 2 (P25), resulting in enhanced NO x removal efficiency. Specifically, the maximum NO x degradation ratio of B-TiO 2 /MgAl-CLDH is 23.4% within 30 min, which is about 5 times that of P25. For pho-tocatalytic mortar, the initial NO x concentration (from 1.0 ppm to 2.0 ppm) and flow rate (from 1 L/min to 3 L/ min) were positively correlated with NO x removal amount, while negatively correlated with NO x removal ratio. Based on the internal molecular diffusion properties of NO x , Langmuir-Hinshelwood and the power law kinetic models were used to predict the NO x degradation ability of photocatalytic mortar. The modeling of NO x degradation process presents a reliable prediction of the NO x removal ability of photocatalytic mortar, serving as a valuable tool for assessing the mortar's NO x removal effectiveness for policymakers and engineers.
... Independent to the varieties, TiO2 is the most widely used catalyst due to the stability of its chemical structure, low toxicity, biocompatibility, high reactivity, electrical, physical and optical properties, ease of synthesis and low cost [2,7,16]. The photocatalytic process starts with the exposure to UV-A (photons), which makes an electron (e − ) from the valence band move towards the conduction band, leaving a hole (h + ) in the valence band [7,18,19]. This is only produced if the activation light contains photons with equal or higher energy than its band gap (Eg), energy difference between the valence and conduction bands. ...
... To ensure that the magnitude of the photocatalytic effect is retained, several strategies have been designed such as the use of metal doping (W, Fe and V) on titanium dioxide. This strategy allows increasing the sensitivity to visible light and consequently increasing the pollutant removal efficiencies, without the need to incorporate a higher concentration of nanoparticles [12,18,22]. According to Petronella et al., [23], the combination of metal nanoparticles such as Ag and Au with semiconductors such as TiO2 allows to increase the photocatalytic efficiency due to their electrical and optical properties. ...
... UV exposure generated O2 vacancies, whereby Ti4 + ions are transformed into Ti3 + ions, increasing the affinity for water molecules. It should be noted that the greater the roughness of the nanocrystal surface the greater the selfcleaning properties at this scale [18,43]. However, this relationship does not occur at a greater scale, i.e., with the roughness of the photocatalytic surface. ...
Since the early seventies with the work of Akira Fujishima on photocatalytic and super-hydrophilic properties of titanium dioxide (TiO2), also known as the Honda-Fujishima effect, pho-tocatalysis has been investigated and progressively implemented in cement-based materials towards the development of self-cleaning, air-purifying and antiseptic materials, buildings and infrastructure. Although important achievements have been obtained at the laboratory scale, their real scale application has had some limitations mainly due to the low efficiencies obtained during adverse environmental conditions. Therefore, this article presents the challenges and opportunities of using of titanium dioxide in cement-based materials towards the development of truly efficient sustainable building materials. First, TiO2 photocatalysis and its incorporation in cementitious materials are presented. Second, self-cleaning, air-purifying and antimicrobial properties are discussed in terms of the lab and pilot project results. Third, conclusions regarding the different multifunctional properties are given towards the real application of TiO2 photocatalysis. Particularly, complementary technologies and strategies are presented in order to increase the above-mentioned multifunc-tional properties.
... Shen et al. produced a photocatalytic ultrasmooth concrete containing nano-TiO 2 , which can effectively degrade methylene blue (Shen et al., 2015). To enhance the photocatalytic efficiency of TiO 2 , Pérez-Nicolás et al. used TiO 2 doped with iron and vanadium as a visible light-sensitive photocatalyst to remove NO x in the atmosphere (Pérez-Nicolás et al., 2017). It was found that the mortar with two doped TiO 2 photocatalysts (Fe-TiO 2 and V-TiO 2 ) enhances NO removal under visible light, and that the use of the Fe-TiO 2 dopant was the most effective (Pérez-Nicolás et al., 2017). ...
... To enhance the photocatalytic efficiency of TiO 2 , Pérez-Nicolás et al. used TiO 2 doped with iron and vanadium as a visible light-sensitive photocatalyst to remove NO x in the atmosphere (Pérez-Nicolás et al., 2017). It was found that the mortar with two doped TiO 2 photocatalysts (Fe-TiO 2 and V-TiO 2 ) enhances NO removal under visible light, and that the use of the Fe-TiO 2 dopant was the most effective (Pérez-Nicolás et al., 2017). In addition, Sood et al. synthesized Sr-doped TiO 2 nanoparticles by hydrothermal and ultrasonic methods and found that Sr doping greatly improves the photocatalytic efficiency of TiO 2 , with an excellent photodegradation rate of 96% observed within 60 min (Sood et al., 2015). ...
... This means that only 3-5% sunlight can be used by the TiO 2 -mediated photocatalytic system. One of the methods used to overcome this problem is to adjust the band gap of TiO 2 through surface modification, doping, etc. (Li et al., 2018;Pérez-Nicolás et al., 2017;Sood et al., 2015). Another effective method is to prepare a new photocatalyst with a suitable band gap (Li et al., 2018). ...
A new method using MoS2 nanoflowers to prepare cement paste for degradable dyes is proposed. In this study, MoS2 nanoflowers were synthesized and applied to improve the hydration rate and dye degradation performance of cement. The effects of MoS2 on the hydration, strength, microstructure, hydration products, and dye degradation performance of the cement system were systematically studied. The main conclusions of this study are as follows: (1) MoS2 nanoflowers (0.5 wt% and 1 wt%) show a nucleation effect and can promote early cement hydration. The promotion effect of MoS2 in the later stage of hydration is not as remarkable as in the early stage; (2) Although MoS2 does not change the type of cement hydration products, it slightly affects the amounts produced. After adding MoS2, the cumulative pore volume is slightly reduced; (3) Compared to a plain specimen, the MoS2-blended cement specimen shows a better degradation effect on rhodamine 6G. The presence of MoS2 in the cement paste promotes the photobleaching effect for rhodamine 6G degradation.
... Furthermore, modification with a surfactant influenced the visible light photocatalytic activity, as was confirmed by the diffuse reflectance spectra of modified samples, indicating visible light absorption. In other work, Pérez-Nicolás et al. obtained TiO 2 modified with iron and vanadium as additives to cement mortar [163]. An improvement in visible light-induced photocatalytic activity in NO removal was observed for modified samples in comparison with a reference pristine titania-containing sample. ...
... Another important factor, not often considered, which can influence photocatalytic NO x removal efficiency is the type of binding matrix. Pérez-Nicolás et al. used four different binders to prepare mortars containing unmodified titania and modified (Fe-TiO 2 , V-TiO 2 ) components: Portland Cement (PC), which is considered in most studies; high alumina cement (HAC); low alumina cement (LAC); and dry slaked lime [163]. The highest activity in NO removal under UV and visible light was observed for the lime and HAC mortars. ...
... Another aspect discussed was the availability of calcium carbonate in HAC and lime mortars. CaCO 3 can participate in a reaction with nitric acid (as a final product of NO photodegradation) to form calcium nitrates, which can be more easily removed from the surface of the photocatalyst, thus enhancing the photocatalytic reaction efficiency [163]. Different observations were reported by Lackhoff et al. [32]. ...
The intensive development of construction in recent years and the increasing demands on the durability and service life of buildings have increasingly made the construction industry pay attention to new materials solutions based on nanotechnology. One of such solutions is the use of titanium dioxide with photocatalytic and antibacterial properties in building materials. Although this solution has been known for decades, there are few articles that review the latest trends in this area. Compared to other literature studies, this article pays particular attention to the possibility of modifying nanotitania to expand its photocatalytic properties and analyses the effects of these alterations on the self-cleaning, smog-abating and antibacterial properties of building materials, mainly cement-based composites. It is complemented by a section dedicated to the mechanical and durability properties of pristine and functionalized TiO2-modified building materials, taking into account dispersion methods, rheological and mechanical parameters as well as resistance to external factors.
... The band gap of TiO 2 is relatively large (3.0-3.2 eV) and therefore it is active under UV light below 400 nm in wavelength, which appears at low intensity in the ambient urban environment. Therefore, a shift in the band gap to a lower energy, within the visible range (which accounts for 43% of incoming solar radiation, compared with 3-5% for UV), that is still great enough to initiate the oxidation of NOx, would increase the activity of the surface under ambient conditions [95,96]. A large amount of research has aimed at increasing the efficiency of light harvesting under solar excitation, whilst preserving or improving the fraction of electron hole pairs that do not recombine [97]. ...
... Doping the TiO 2 surface, or forming a nano-composite with other species, such as noble metals, metal-oxides and carbon, is generally aimed at increasing the activity of the material, chiefly through shifting the band gap towards the visible region and preventing electron/hole recombination. There has been extensive research into this, with studies investigating doping with Fe [96,98,99], Fe 2 O 3 [100], Cu [98] , Sn [101], Zn [102], Zn-S [103], Au-N [104], Al 2 O 3 [105], Pd [88,106], Pt [107], Pt/Au [108], Ag [109,110], g-C 3 N 4 [111,112], graphene [113], Sn and Ce/Mn-graphene [114], other forms of carbon [53,115] and minerals from clay [116]. Many of these have previously been summarised in tables in Martinez et al. [98,101]. ...
... With the optimal support, the NO 2 production which occurs during NO oxidation, can be suppressed. For example, concrete can be produced with high specific surface area porosity in the correct size region to adsorb NO 2 and so suppress the NO 2 produced when large amounts of NO are oxidised [79,96]. Other materials with high porosity, such as zeolites can also serve this purpose [127]. ...
NOx is a pervasive pollutant in urban environments. This review assesses the current state of the art of photocatalytic oxidation materials, designed for the abatement of nitrogen oxides (NOx) in the urban environment, and typically, but not exclusively based on titanium dioxide (TiO2). Field trials with existing commercial materials, such as paints, asphalt and concrete, in a range of environments including street canyons, car parks, tunnels, highways and open streets, are considered in-depth. Lab studies containing the most recent developments in the photocatalytic materials are also summarised, as well as studies investigating the impact of physical parameters on their efficiency. It is concluded that this technology may be useful as a part of the measures used to lower urban air pollution levels, yielding ∼2% NOx removal in the immediate area around the surface, for optimised TiO2, in some cases, but is not capable of the reported high NOx removal efficiencies >20% in outdoor urban environments, and can in some cases lower air quality by releasing hazardous by-products. However, research into new material is ongoing. The reason for the mixed results in the studies reviewed, and massive range of removal efficiencies reported (from negligible and up to >80%) is mainly the large range of testing practices used. Before deployment in individual environments site-specific testing should be performed, and new standards for lab and field testing should be developed. The longevity of the materials and their potential for producing hazardous by-products should also be considered.
... Various problems regarding environment and human health were caused by the vehicular combustion (e.g. NO x ), including intensification of greenhouse effect, acid rain, ozone depletion, respiratory and lung diseases [1][2][3]. Many methods have been proposed to control or mitigate the air pollution issues, and photocatalytic technology using nanomaterials (e.g. ...
... Many methods have been proposed to control or mitigate the air pollution issues, and photocatalytic technology using nanomaterials (e.g. TiO 2 ) has been proved effective to purify air pollution caused by vehicle emissions [1,4]. The traffic exhaust tends to accumulate on the pavement surface, especially on those with heavy traffic, dense population and buildings [2]. ...
... Fan et al. [2] prepared TiO 2 -asphalt composite specimen by spraying TiO 2 powder suspension on glassfiber mats treated with emulsified asphalt, which exhibited outstanding NO removal performance. Similar conclusions were also obtained by Perez-Nicolas et al. [1] and Wang et al. [10]. Instead of using spraying methods, Chen and Liu [11] prepared dispersion by adding surface modified TiO 2 powder into penetrant and penetrated it into porous asphalt specimens. ...
Photocatalyst titanium dioxide (TiO2) has been widely applied on asphalt and concrete pavements to mitigate the air pollution caused by traffic exhaust. In general, most of the TiO2 used in previous studies was pure anatase, which only exhibited excellent photocatalytic activity under ultraviolet (UV) light. Thus, N-doping method was selected to improve the photocatalytic activity, especially under visible light. Additionally, the TiO2 suspension was commonly used on the pavements comparing with other application methods. However, the Nano-TiO2 particles with great surface area-to-volume ratio and surface energy have a strong tendency to agglomerate in the suspension, which has significantly negative effects on the photocatalytic activity. Thus, the objective of this study was to enhance the photocatalytic performance of mortar specimens containing TiO2 by preparing optimum N-doped TiO2 and suspensions using both single-factor and orthogonal experimental design. Methylene blue (MB) decomposition results indicated that the optimum N-doped TiO2 was prepared with 1% N-dosage at 700 °C for 5 h. X-ray diffractometer (XRD) pattern results implied that the phase transformation from anatase to rutile occurred around 700–800 °C and anatase transferred to rutile completely at 900 °C. Absorbance results showed that the optimum suspension was prepared with following conditions: ultrasonic power 100 W, ultrasonic time 120 min, silica sol concentration 0.5%, and sodium hexametaphosphate (SHMP) dosage of 0.3%. Lastly, NO decomposition test was conducted to investigate the effects of TiO2 implementation methods and environmental factors on the photocatalytic performance of mortar specimens. The NO decomposition results showed that the optimum suspension could significantly improve the photocatalytic performance of specimens. Meanwhile, the NO decomposition percentage decreased with the increasing flow rate and NO concentration.
... incorporated into blends of construction materials [4]. Innovative solutions, intensively investigated so far, include research activities addressed to effectively activate TiO 2 under visible light. ...
... Innovative solutions, intensively investigated so far, include research activities addressed to effectively activate TiO 2 under visible light. Examples of well-performing building materials exhibiting multi-purpose aspects due to the effective combination of TiO 2 with capable dopants were proposed previous studies [4,5]. ...
... Our research is addressed towards this direction. Having studied the specific features and durability of lime mortars and plasters in the conservation of historic masonry, the adopted scenario presented here included the synthesis of TiO 2 doped with iron (Fe), its activation under visible irradiation, and further incorporation in lime coatings [4]. The choice of Fe is based on a multi-criterial decision, taking into account: (a) its presence in construction materials and the induced compatibility; (b) the low cost and its occurrence in a number of compounds; (c) its color, which could provide colored ochre surfaces; (d) its capability to be embedded into the TiO 2 crystalline structure due to the similar radii of Ti 4+ (0.68 Å) and Fe 3+ (0.68 Å); and finally (e) the enhancement of the TiO 2 photocatalytic activity, as Fe 3+ ions play a crucial role in this procedure, functioning as hole and electron scavengers. ...
Iron-doped TiO2 nanoparticles, ranging in Fe concentrations from 0.05 up to 1.00% w/w, were synthesized through a simple sol-gel method. Fourier-transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), Ultraviolet-Visible (UV-Vis) spectroscopy, nitrogen adsorption-desorption isotherms, X-ray photoelectron spectroscopy (XPS), and X-ray absorption near-edge structure spectroscopy (XANES) were used to characterize the synthesized nanoparticles. The characterization of the Fe-doped TiO2 nanoparticles revealed the predominant presence of anatase crystalline form, as well as the incorporation of the Fe3+ ions into the crystal lattice of TiO2. The photocatalytic assessment of the Fe-doped TiO2 nanoparticles indicated that the low iron doping titania (0.05 and 0.10% w/w) have a positive effect on the photocatalytic degradation of Methyl Orange under visible radiation. Moreover, FTIR monitoring of calcium hydroxide pastes enriched with low Fe-doped TiO2 revealed enhancement of carbonation at both early and later stages. Improved photocatalytic performance and increased lime carbonation, observed in lime coatings with low Fe-doped TiO2 admixtures, established them as invaluable contributors to the protection of the built environment.
... The Ti 2p spectra of A-TiO 2 showed two characteristic peaks around 459.39 eV and 465.07 eV. Whereas, P25 depicted the Ti2p characteristic peaks around the binding energies of 458.41 eV and 464.31 eV, which can be attributed to Ti 2p 3/2 and Ti 2p 1/2 , respectively, of Ti 4+ [50]. A major shift (465.07 ...
... Despite the notable difference (almost six times) in density, the extent of photoactivity only reduced by 50%. It is presumed that complex interactions between cement and A-TiO 2 NPs, along with physical properties of mortar contributed towards the improved removal of NO [37,50]. Park et al. [43] prepared TiO 2 from flocculation of dye wastewater and their TiO 2 performed at par with commercial P25 for the removal of atmospheric NO x , since the apparent density of their TiO 2 was not very high when compared with P25. ...
... The Ti 2p spectra of A-TiO2 showed two characteristic peaks around 459.39 eV and 465.07 eV. Whereas, P25 depicted the Ti2p characteristic peaks around the binding energies of 458.41 eV and 464.31 eV, which can be attributed to Ti 2p3/2 and Ti 2p1/2, respectively, of Ti 4+[50]. A major shift (465.07 ...
The purpose of the study was to effectively treat algae bloomed water while using a Ti-based coagulant (TiCl4) and recover photoactive novel anatase TiO2 from the flocculated sludge. Conventional jar tests were conducted in order to evaluate the coagulation efficiency, and TiCl4 was found superior compared to commercially available poly aluminum chloride (PAC). At a dose of 0.3 g Ti/L, the removal rate of turbidity, chemical oxygen demand (COD), and total phosphorus (TP) were measured as 99.8%, 66.7%, and 96.9%, respectively. Besides, TiO2 nanoparticles (NPs) were recovered from the flocculated sludge and scanning electron microscope (SEM), energy dispersive X-ray spectroscope (EDX), and X-ray diffraction (XRD) analysis confirmed the presence of only anatase phase. The recovered TiO2 was found to be effective in removing gaseous CH3CHO and NOx under UV-A lamp at a light intensity of 10 W/m2. Additionally, the TiO2 mixed mortar blocks that were prepared in this study successfully removed atmospheric nitrogen oxide (NOx) under UV irradiance. This study is one of the first to prepare anatase TiO2 from flocculated algal sludge and it showed promising results. Further research on this novel TiO2 concerning internal chemical bonds and shift in the absorbance spectrum could explore several practical implications.
... In addition, enhancement of photocatalytic performance can be achieved by increasing the surface area of the support material and catalyst particles [25], as well as by the presence of chemical interaction between them [36,37]. The use of materials providing high porosity of concrete will contribute to more intensive adsorption of NO 2 [38,39]. The formation of a basic medium type (pH) on the concrete surface facilitates the oxidation of NO 2 to nitrates [40]. ...
... The formation of a basic medium type (pH) on the concrete surface facilitates the oxidation of NO 2 to nitrates [40]. This process can be regulated by introducing various additives such as lime, alumina and CaCO 3 [28,38]. ...
The modern rhythm of human life leads to well-known problems, which are air, water and soil pollution and climate warming. An increase in the power of industries and vehicles leads not only to atmospheric pollution by-products of incomplete fuel combustion but also to various microscopic particles that form aerosols, which carry an obvious danger to human health and also pollute the buildings’ facades. An environmentally friendly building material with a hybrid method “Nano-titania gradient” was developed. This method consists of forming a gradient of n-TiO2 particles concentration in the composite since the physical properties of the composite are always inextricably linked to the geometry. To increase the efficiency of the photocatalytic process, a method of surface sensitization of titanium dioxide with the use of graphene oxide was proposed, which contributed to an increase in the overall photosensitivity. Thus, the decomposition of nitrogen oxide by volume with the modified surface increased by 27% in comparison with the classic titanium dioxide, and the decomposition of volatile organic substances increased by 32%. It was found that for the facade plate made with surface-sensitized TiO2, the process of self-cleaning is completed after 3 h after the irradiation start. The modern rhythm of human life leads to well-known problems, which are air, water and soil pollution and climate warming. Using the theory of percolation, the concentration range of the photocatalyst content was calculated. To facilitate the material, waste cellulose was introduced. To increase the efficiency of the photocatalytic process, a method of surface sensitization of titanium dioxide (SS TiO2) with the use of graphene oxide was proposed. The analysis of the experimental-statistical models of the compressive strength shows that the optimum content of TiO2 was in the range from 0.8 to 1.1%, and cellulose from 0.4 to 0.8%, the optimum content of SS TiO2 was in the range from 0.7 to 1.1%, and cellulose from 0.4 to 0.8%. Analysis of the experimental and statistical model of the bending strength shows that the optimal content of TiO2 and SS TiO2 was in the range of 0.6 to 1.0%, and cellulose from 0.4 to 0.8%. When studying the structure of composites, it was found that titanium dioxide was sorbed on the surface of swollen cellulose fibers and remained there after the process of cement hydration. The effectiveness of the method of surface sensitization of titanium dioxide by combining it with graphene oxide was shown. Thus, the decomposition of nitrogen oxide by volume with the modified surface increased by 27% in comparison with the classic titanium dioxide, and the decomposition of volatile organic substances increased by 32%. It was found that for the facade plate made with surface-sensitized TiO2, the process of self-cleaning was completed after 3 h after the irradiation start.
... Under atmospheric conditions, the NO and NO2 uptake coefficients were determined in the range of 5×10 −5 at a surface deposition velocity of about 0.5 cm/s. The NOx removal capacity of photocatalytic blocks of cement, based on mortars made with Portland cement, two different calcium aluminate types of cement, and air lime, and at least a few TiO2 additives (TiO2 as reference catalyst, and two doped titania, Fe-TiO2, and V-TiO2), was investigated [112]. A high NOx abatement (up to 60-80%) with good selectivity was observed for air lime and high alumina cement (HAC) mortar-based photocatalytic cement under the three illumination conditions (UV, solar, and visible light). ...
... Under atmospheric conditions, the NO and NO 2 uptake coefficients were determined in the range of 5 × 10 −5 at a surface deposition velocity of about 0.5 cm/s. The NO x removal capacity of photocatalytic blocks of cement, based on mortars made with Portland cement, two different calcium aluminate types of cement, and air lime, and at least a few TiO 2 additives (TiO 2 as reference catalyst, and two doped titania, Fe-TiO 2 , and V-TiO 2 ), was investigated [112]. A high NO x abatement (up to 60-80%) with good selectivity was observed for air lime and high alumina cement (HAC) mortar-based photocatalytic cement under the three illumination conditions (UV, solar, and visible light). ...
Titanium dioxide (TiO2) has been extensively investigated in interdisciplinary research (such as catalysis, energy, environment, health, etc.) owing to its attractive physico-chemical properties, abundant nature, chemical/environmental stability, low-cost manufacturing, low toxicity, etc. Over time, TiO2-incorporated building/construction materials have been utilized for mitigating potential problems related to the environment and human health issues. However, there are challenges with regards to photocatalytic efficiency improvements, lab to industrial scaling up, and commercial product production. Several innovative approaches/strategies have been evolved towards TiO2 modification with the focus of improving its photocatalytic efficiency. Taking these aspects into consideration, research has focused on the utilization of many of these advanced TiO2 materials towards the development of construction materials such as concrete, mortar, pavements, paints, etc. This topical review focuses explicitly on capturing and highlighting research advancements in the last five years (mainly) (2014-2019) on the utilization of various modified TiO2 materials for the development of practical photocatalytic building materials (PBM). We briefly summarize the prospective applications of TiO2-based building materials (cement, mortar, concretes, paints, coating, etc.) with relevance to the removal of outdoor/indoor NOx and volatile organic compounds, self-cleaning of the surfaces, etc. As a concluding remark, we outline the challenges and make recommendations for the future outlook of further investigations and developments in this prosperous area.
... Vehicle exhaust emissions can reduce lung function, thereby increasing the risk of respiratory diseases [3][4][5]. NO x emitted from vehicle exhaust is a major contributor to air pollution, posing significant hazards to human health and the environment [6][7][8][9]. Furthermore, previous studies have suggested that nitrogen dioxide (NO 2 ) is linked to a higher occurrence of diabetes and cardiovascular diseases [10,11]. ...
Nano-TiO2 combined with cement slurry can be utilized to degrade nitrogen oxides (NOx) in vehicle exhaust, making it an excellent photocatalytic material for air purification. In practice, environmental factors can significantly affect the photocatalytic performance. In this study, a vehicle exhaust test system was developed, and the test methods and evaluation criteria for the degradation test are provided. This study investigated the photocatalytic degradation of NO2 using nano-TiO2 cement slurry through laboratory tests. The effects of temperature, relative humidity, ultraviolet (UV) radiation flux, cement slurry thickness, surface dust adherence, and the number of water rinsing cycles were examined. Additionally, nano-TiO2 cement slurries were applied to an expressway toll station. The results showed that the efficiency of photocatalytic degradation was significantly influenced by temperature and UV radiation flux, while the thickness of the cement slurry had minimal impact. The photocatalytic degradation efficiency was negatively correlated to the relative humidity, when the relative humidity of the cement slurry specimens was high. This is because the excess water (H2O) competes with NO2 for adsorption. The photocatalytic performance of the samples was significantly reduced by surface dust and rain erosion, as both led to a decrease in the amount of nano-TiO2 participating in the reaction. Furthermore, the photocatalytic material has wide-ranging potential applications. The findings of this study would support the promotion of environmentally friendly roads as a strategy to combat air pollution.
... This evaluation was carried out under two different lighting conditions: strictly visible radiation (with the use of a coloured glass filter (FGL420, Thorlabs, Newton, NJ, USA), which completely cuts off wavelengths shorter than 410 nm) and UV-VIS illumination. A 300 W Osram Ultravitalux lamp was used as the light source [75]. The lamp's nominal irradiance at a distance of 0.5 m after 1 h was measured to be 41.4 Wm −2 (780-400 nm), 13.6 Wm −2 (400-315 nm), and 3.0 Wm −2 (315-280 nm). ...
The aim of this study was to develop versatile coatings that can protect the stone surfaces of Architectural Heritage. Two different 3D media, namely superhydrophobic (SPHB) and hydro-oleophobic (OHB), were utilized as host matrices for nanostructured photocatalysts (Bi2O3-ZnO 8/92). These photocatalysts were sensitive to visible light to enhance their efficiency when exposed to sunlight. To prevent the nanophotocatalyst from clumping together in the 3D media, non-ionic dispersant additives (Tween20, TritonX-100, and Brij35) were incorporated. The optimized suspensions were then applied to various substrates such as sandstone, limestone, and granite. The effectiveness of the coatings was assessed by evaluating the hydrophobicity, oleophobicity, and photocatalytic activity of the coated substrates. The Bi2O3-ZnO photocatalyst exhibited higher activity in the SPHB medium compared to the OHB medium. To simulate real-life conditions, the coated substrates were subjected to accelerated weathering tests to predict their durability. Despite a significant reduction in their thickness, the coatings demonstrated sustained hydrophobic efficiency and self-cleaning capability after the accelerated ageing tests.
... Therefore, the incorporation into building materials of special additives responsible for the elimination of these detrimental factors remains a significant challenge. Besides having self-cleaning properties, such materials can also combat smog (for example, by removing NO x from the air [6]). To provide such functions, the additives must have photocatalytic properties. ...
Carbon-modified titanium(IV) oxide with improved photocatalytic properties under visible light was used as an admixture for cement composites. For this purpose, two commercially available titanium(IV) oxides differing in crystallographic form, and two synthesized for the experiment from titanyl sulfate hydrate and titanium(IV) isopropoxide were used as starting materials, with ethylene glycol as the carbon source. The effect of carbon modification on the surface of titania was to increase the BET surface area, which resulted in a greater tendency of TiO2 nanoparticles to aggregate and agglomerate, higher water adsorption on the oxide surface, and lower temperature stability. Nevertheless, electrokinetic studies demonstrated the stability of modified titanium(IV) oxides in alkaline media, and the increased BET surface area led to a significant increase in their activity in a photodegradation reaction, especially in the visible light range in the case of oxides containing a higher content of the anatase form. The photocatalytic properties of titanium(IV) oxides were maintained after incorporation into the cement matrix. For composites with carbon-modified titania admixtures an improvement in photocatalytic activity was higher in the UV than in the visible light range. In general, modification of titanium(IV) oxide with carbon did not significantly affect the mechanical and durability properties of the cement composites. For both modified and unmodified oxides, a reduction in heat during hydration of the cementitious binder and increases in flexural and compressive strengths were observed at later curing times. This is related to the presence of TiO2 nanoparticles, which, being additional active centers, contribute to the initiation of C–S–H phase growth and refinement of the composite structure, as confirmed by the increased proportion of micro- and nanopores. An additional effect of introducing titanium(IV) oxide, especially the anatase variety, into the cement matrix was an improvement in the antibacterial properties of the composite.
... Atmospheric pollution caused by vehicles is an increasing problem that influences the public health. The vehicle combustion will result in acid rain, greenhouse effect, human diseases, and ozone depletion [17]. Measures have been introduced to control the effect of the air pollution. ...
Cement-asphalt pavements are widely used in transport infrastructure. Multifunctional pavement is a novel concept that can improve the functionalities, durability, and serviceability of the pavement for smart transport. The self-healing, self-sensing, photocatalytic, and thermochromic capacities of cement-asphalt concrete are significant components of multifunctional pavements. The self-healing function can extend the service life of pavements with improved durability. The concept of self-sensing concrete has been proposed and widely investigated for structural health monitoring. The photocatalytic function helps reduce pollution caused by vehicle gas emission. The thermochromic function can be used to detect the temperature of asphalt concrete pavements. Previous studies mainly focused on the individual components and performance of these functionalities in cement-asphalt concrete. To achieve these multifunctionalities, various carbon nanomaterials can be added to the cementitious-asphalt concrete, such as carbon black (CB), carbon nanofiber (CNF), carbon nanotubes (CNTs), graphene nanoplate (GNP), and others. However, more and more attentions have been paid to the pavements with integrated multifunctionalities. The functional concrete has been applied to the smart transport system, such as pavement, railway, bridge, and tunnel for infrastructure health monitoring and traffic-flow monitoring. This paper comprehensively reviews the recent developments of multifunctional technologies as well as the potential applications of these novel technologies. The related findings will be useful for future research on multifunctional pavements and their applications for smart transport.
... Therefore, for reducing NOx in urban areas, controlling NOx emitted through road mobility sources or using road facilities is effective. Among various road facilities, those composed of concrete, such as boundary stones, bagged and sacked concrete, and crash walls, have large surface areas; therefore, the use of infrastructure composed of functional concrete is an efficient method of reducing roadside NOx [7]. ...
Fine dust, recently classified as a carcinogen, has raised concerns about the health effects of air pollution. Vehicle emissions, particularly nitrogen oxide (NOx), contribute to ultrafine dust formation as a fine dust precursor. A photocatalyst, such as titanium dioxide (TiO2), is a material that causes a catalytic reaction when exposed to light, has exceptional characteristics such as decomposition of pollutants, and can be used permanently. This study aimed to investigate NOx reduction performance by developing ecofriendly permeable concrete with photocatalytic treatment to reduce fine dust generated from road mobile pollution sources. Permeable concrete specimens containing an activated loess and zeolite admixture were prepared and subjected to mechanical and durability tests. All specimens, including the control (CTRL) and admixture, met quality standard SPS-F-KSPIC-001-2006 for road pavement. Slip resistance and permeability coefficient also satisfied the standards, while freeze–thaw evaluation criteria were met only by CTRL and A1Z1 specimens. NOx reduction performance of the permeable concrete treated with TiO2 photocatalyst was assessed using ISO standard and tank chambers. NOx reduction efficiency of up to 77.5% was confirmed in the permeable concrete specimen with TiO2 content of 7.5%. Nitrate concentration measurements indirectly confirmed photolysis of nitrogen oxide. Incorporating TiO2 in construction materials such as roads and sidewalks can improve the atmospheric environment for pedestrians near roads by reducing NOx levels through photocatalysis.
... Fan y colaboradores prepararon una muestra asfáltica compuesta de TiO 2 rociando polvo de TiO 2 en suspensión sobre esteras de fibra de vidrio tratadas con asfalto emulsionado, y reportaron un excelente desempeño en la remoción de NO x (Fan et al., 2017). Pérez-Nicolás y colaboradores recrearon casi el mismo experimento, pero sin la fibra de vidrio y obtuvieron conclusiones similares (Pérez-Nicolás et al., 2017). Por otro lado, en lugar de usar métodos de rociado, Chen y colaboradores agre-garon polvo de TiO 2 modificado en la superficie de un asfalto poroso (Chen y Liu, 2010). ...
En las grandes áreas metropolitanas del mundo se está generando una alta concentración de contaminantes atmosféricos, producto del creciente número de vehículos, fábricas, industrias y construcciones, los cuales están propiciando serios problemas de calidad del aire, de salud pública y de deterioro estructural. Para abordar estos problemas, el uso, en los últimos años, de los materiales de construcción fotocatalíticos ha surgido como una nueva tecnología alternativa para remediar la contaminación de la atmósfera urbana, mantener la estética y la funcionalidad de las infraestructuras. Las grandes áreas superficiales expuestas al sol de cualquier infraestructura proporcionan las condiciones óptimas para la aplicación de materiales fotocatalíticos. El gran interés por esta tecnología ha alentado la creación de diversos materiales de construcción inteligentes con propiedades fotocatalíticas, al incorporarles nanopartículas de TiO2. Por ese motivo, hoy en día se dispone de una gran variedad de productos, tales como pinturas, vidrio, estucos, pavimentos, cementos, entre muchos otros, cuya aplicación se ha promovido recientemente. El propósito del presente trabajo es hacer una revisión integral del proceso fotocatalítico, sus propiedades y sus aplicaciones en la industria de la construcción, así como de los problemas y limitaciones de esta tecnología.
... indicate that the removal of air pollutants can be achieved by photo-catalytically active TiO2 mixed into cementitious products [28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45]. However, this approach is costly and time-consuming, given the catalyst deactivation, the need to have UV illumination to activate TiO2, and the overall inefficiency of bulk modification of concrete as the only surface located catalytic particles can be activated by light. ...
Concrete is by far the most abundant material produced by humanity in both volume and weight. It is not surprising that it is also a significant source of solid waste that ends up in landfills. Based on EPA data, the Construction and Demolished (C&D) concrete waste accounts for 70% of all the construction materials in landfills. Moreover, cement manufacturing emits approximately 20% of all industrial oxides of nitrogen (NOx)emissions leading to a negative impact on human health and the environment. This report will provide an overview of concrete production, the environmental challenge in the cement industry and put forward a policy recommendation to address climate change using innovative technological approaches.
... These nitrates are subsequently removed by rain or periodic washing of the photocatalytic devices [28,29]. Thus, the generic mechanism proposes the decomposition of NO into NO − 3 through the pathway NO → HNO 2 → NO 2 → NO − 3 [30]. ...
The effect of Dean flow on the performance of a curved channel reactor in terms of fluid flow and mass transfer characteristics was numerically evaluated. Laminar multi-component gas flow considering the photocatalytic NOx degradation as model reaction was investigated using a validated three-dimensional computational fluid dynamics (CFD) model. The curved channel device was compared with a conventional straight channel reactor, considering the same catalytic area and cross-section. The results showed that the velocity profile was distorted from its original symmetrical shape, and the maximum velocities shifted towards the outer-side wall for De > 120.1, due to the influence of centrifugal acceleration in the radial direction. The curved channel reactor resulted in higher mass transfer coefficients compared to the straight channel device. The higher mass transfer enhancement factor (γ ~ 1.8) was obtained for AR = 1 and Re = 725.5. However, this condition imposed a pressure drop 3 times higher the straight channel device. The reactor’s performance was also represented by an association of ideal reactors (PFR and CSTR). The NO conversion in the curved channel device was equivalent to the behavior of a CSTR (n = 1.5) due to the Dean flow contributions favoring the mixing. Additional analyzes regarding the influence of the radius of curvature were carried out in a U-shaped reactor. Finally, an analysis of dimensionless numbers (P é clet and Damköhler) corroborated the results found numerically. Therefore, this study can provide insights into the design and analysis guidelines for curved channel reactors.
... The environmental pollution problems faced by the city restrict the sustainable development of the city [1][2][3]. Industrial waste gas and wastewater, automobile exhaust and runoff pollution endanger the urban environment and the health of the people [4,5]. Photocatalytic cement-based materials are effective in alleviating urban pollution and have been widely concerned by researchers [6,7]. ...
In this paper, Ag-TiO2 photocatalysts with different Ag contents (1 mol%–5 mol%) were prepared and applied to cement mortar. The photocatalytic performance of Ag-TiO2 and photocatalytic cement mortar under UV light and simulated solar light was evaluated. The results showed that Ag loading on the surface of TiO2 could reduce its band gap width and increase its absorbance in the visible region, and 2% Ag-TiO2 had the highest photocatalytic activity under UV light, the degradation rate of methyl orange (MO) was 95.5% at 30 min, and the first-order reaction constant k was 0.0980 min−1, which was 61.7% higher than that of TiO2, and 5% Ag-TiO2 had the highest photocatalytic activity under solar light, the degradation rate of methylene blue (MB) was 69.8% at 40 min, and the first-order reaction constant k was 0.0294 min−1, which was 90.9% higher than that of TiO2. The photocatalytic mortar prepared by the spraying method has high photocatalytic performance, The MO degradation rate of sample S2 under UV light was 87.5% after 120 min, MB degradation rate of sample S5 under solar light was 75.4% after 120 min. The photocatalytic reaction conforms to the zero-order reaction kinetics, which was 1.5 times–3.3 times higher than that of the mixed samples and has no effect on the mechanical properties of mortar.
... This triggers a series of reactions involving NO x , O 2 and H 2 O, which can be simplified as shown in Eqs. 2 and 3 [26]. Ultimately, the reaction forms adsorbed nitric acid or nitrate anions, which will adhere to the surface until washed off by water [26,27]. ...
This study presents our solution of an active nitric oxides (NOx) control method for large traffic tunnels. A titanium dioxide (TiO2) coated carrier material is assessed using lab-based photocatalysis experiments, leading to a coating with high photocatalytic activity (deposition speed of 1.4 cm/s for nitrogen monoxide, NO). The coating is tested on several carrier materials to maximize the interaction between the reactive surface and the pollution molecules in the air. Several reactor prototype geometries and carrier materials are simulated and tested on a pilot plant scale. A coated PU-foam with 3 cm thickness and porosity of five pores per inch proved to be the most effective carrier material, while a reactor design with vertically flowed stacks of the foam carrier is capable of optimally exploiting the potential of the photocatalytic coating for high volume flows. With data from on-site measurements of the atmospheric conditions and pollution in the highway tunnel ‘Rudower Höhe’ in Berlin, Germany, we could build a simulated tunnel setup of our reactors within the tunnel. An estimate based on these simulations assumes a reduction potential of 25% of the NOx mass generated in the tunnel. In conclusion, actively vented TiO2 surfaces are controversial yet could achieve high removal rates while simple to clean or exchange.
... They can contribute to various environmental problems and have health consequences [2]. There are several methods to reduce NO x , in particular photochemical oxidation by the use of photocatalysts [3]. ...
The development of new modified cement-based materials is increasingly becoming a necessity for improving the durability and surface performance of building materials. Titanium dioxide (TiO2) photocatalyst has been widely used in building materials science due to its ability to break down pollutants. Zinc oxide (ZnO) is often considered a substituent for TiO2 because of its photocatalytic and photoluminescent properties. A new inorganic nanocomposite photocatalyst, based on titanium and zinc oxides, is introduced in this work in order to study its compatibility with High Performance Concrete (HPC). This research aims to study the mechanical and photocatalytic behavior of mixtures based on nanoparticles in HPC. The study of the efficiency in the nitrogen oxides (NOx) degradation of modified HPC in TiO2 and ZnO with different percentages is studied. The studies have shown that the introduction of titanium dioxide in HPC presents a significant efficiency for the NOx degradation and a positive effect on the mechanical properties than zinc oxide, and thus represents potential contribution to sustainability of concrete structures.
... No oxidation of NO has been observed during this test, indicating that no photolysis phenomenon has been occurred. The treated sample with S0T0Cu photocatalyst showed the same NO oxidation behaviour as observed by the untreated sample, indicating that without photocatalyst NOx cannot be reduced and confirming the ability of TiO 2 photocatalyst in oxidizing NOx [57,58]. ...
As a consequence of human activities, today, we are exposed to high pollution levels that cause building materials damage and many diseases. The application of TiO2 as coating on building materials has proven the efficiency of self-cleaning and air de-pollution. However, its performance is limited due to its absorption being exclusively located at UV light. In this study, Cu-TiO2 photocatalysts were integrated into silica sol–gel synthesis to manufacture new long-lasting term coatings with self-cleaning and air purification properties for concrete-based building materials. The enhancement of TiO2 photoactivity by incorporating Cu into its network has been clearly demonstrated. The self-cleaning and air de-polluting efficiency were assessed using methylene blue (MB), soot and NO, respectively, indicating that the presence of Cu promotes the TiO2 performance. For low doping levels, by increasing the copper loading, the TiO2 photoactivity increased. The highest efficiency was obtained by the photocatalyst containing 5% copper, which shows maximum destruction of methylene blue and soot of 95% and 50% within 60 min and 168 h of irradiation, respectively. However, higher copper loading led to a decrease in its performance, reaching a total degradation of MB and soot of 90% and 45% after 60 min and 168 h of irradiation, respectively, for the sample containing 15% of copper loading.
... With the development of nanoscience, a large number of industrial nanomaterials have been developed and applied to daily life and production, such as the nano-TiO 2 (nTiO 2 , negatively charged) and nano-C eO 2 (nCeO 2 , positively charged). They have been widely used in various fields, for instance, building materials (Pérez-Nicolás et al. 2017), medical applications (Cesmeli and Biray 2019), nitrite reduction (Troutman et al. 2020), organic matter degradation (Gomes et al. 2017;Khammar et al. 2020), remediation of heavy metal pollution (Dai et al. 2019;Yin et al. 2019), and stuff. Inevitably, nanoparticles (NPs) would be released into groundwater environments in each process of use (Malakar and Snow 2020). ...
Nanomaterials are threatening the environment and human health, but there has been little discussion about the stability and mobility of nanoparticles (NPs) in saturated porous media at environmentally relevant concentrations of surfactants, which is a knowledge gap in exploring the fate of engineered NPs in groundwater. Therefore, the influences of the anionic surfactant (sodium dodecylbenzene sulfonate, SDBS), the cationic surfactant (cetyltrimethylammonium bromide, CTAB), and the nonionic surfactant (Tween-80) with environmentally relevant concentrations of 0, 5, 10, and 20 mg/L on nano-TiO2 (nTiO2, negatively charged) and nano-CeO2 (nCeO2, positively charged) transport through saturated porous media were examined by column experiments. On the whole, with increasing SDBS concentration from 0 to 20 mg/L, the concentration peak of nTiO2 and nCeO2 in effluents increased by approximately 0.2 and 0.3 (dimensionless concentration, C/C0), respectively, because of enhanced stability and reduced aggregate size resulting from enhanced electrostatic and steric repulsions. By contrast, the transportability of NPs significantly decreased with increasing CTAB concentration due to the attachment of positive charges, which was opposite to the charge on the medium surface and facilitated the NP deposition. On the other hand, the addition of Tween-80 had no significant influence on the stability and mobility of nTiO2 and nCeO2. The results were also demonstrated by the colloid filtration theory (CFT) modeling and the Derjaguin-Landau-Verwey-Overbeek (DLVO) interaction calculations; it might promote the assessment and remediation of NP pollution in subsurface environments.
... The neutralization of products (NO 2 and nitrates) formed by the photocatalysis generally could be achieved on alkaline-earth metal via the the retention of NO 2 and nitrates to promote the removal of NOx. [26][27][28][29] Further, it is worth mentioning that the decorated CaCO 3 extends the π bonds of CN to deviate from the planes and steers the random transfer of carriers in this research. Specifically, CaCO 3 as a "transit hub" could provide extra active sites to accelerate the adsorption/activation of reactants and also expedite the spatial separation of charge carriers, which is beneficial to boost the generation of ROS for highly efficient NO removal and NO 2 suppression. ...
Photoinduced reactive oxygen species (ROS)‐based pollutant removal is one of the ideal solutions to achieve the conversion of solar energy into chemical energy and thus to address environmental pollution. Here, earth‐abundant CaCO3 decorated g‐C3N4 (g‐C3N4 labeled as CN, CaCO3 decorated g‐C3N4 sample labeled as CN‐CCO) has been constructed by a facile thermal polymerization method for safe and efficient photocatalytic NO removal. The decorated CaCO3 as “transit hub” extends the π bonds of CN to deviate from the planes and steers the random charge carriers, which thus provides extra active sites and expedites spatial charge separation to facilitate adsorption/activation of reactants and promote formation of ROS participating in the removal of pollutant. Furthermore, boosted generation of ROS regulates the photocatalytic NO oxidation pathway and thus increases the selectivity of products. NO prefers to be directly oxidized into final product (nitrate) rather than toxic intermediates (NO2), which is well demonstrated by theoretically simulated ROS‐based reaction pathways and experimental characterization. The present work promotes the degradation of pollutant and simultaneously suppresses the formation of toxic by‐product, which paves the way for ROS‐based pollutant removal.
... Subsequently, specific NOx degradation reactions occur. Then, the generic mechanism can be described according to Eqs. (9) to (12) [63]. ...
This article provides a comprehensive review of the photoreactors for gas-phase reaction focusing on process intensification and recent computer simulations. This review selected two photocatalytic gas-phase reactions, namely the oxidation of organic compounds (VOCs) and the degradation of nitrogen oxides (NOx). It was also discussed the two photocatalytic gas-phase reactions’ importance from a scientific and social perspective. Therefore, heterogeneous photocatalysis was applied, and it excelled itself as a promising technology for gas-phase reaction applications. However, despite the numerous advances in photocatalytic processes in recent times, there are still several challenges in their development for this technology to achieve high performance. Mass transfer and low quantum efficiency (photon transfer) are some of these challenges becoming a significant concern for the design of new photoreactors or the improvement of existing ones. Different types of photocatalytic reactors have already been designed, examined, and simulated, seeking to maximize the pollutant-catalyst contact (enhancing mass transfer) and to maximize the lighting efficiency throughout the catalyst surface (enhancing photon transfer). The process intensification has been highlighted in the development of photoreactors to ensure the improvement in mass and photons transfer. Here, we will address the monolithic photoreactors, photocatalytic membrane reactors, and photo-microreactors, in which each photoreactor has its advantages and drawbacks. CFD-based models, combined with the design of the photoreactors, are essential since they can successfully predict the performance of various geometric configurations and identify the limitations to the photon and the mass transfer with only validated virtual prototypes. From this perspective, this review presents the state-of-art of photocatalytic air treatment providing examples such as the VOCs oxidation and NOx degradation. Furthermore, this review also reports a literature exam of three different types of photoreactor designs presenting their advantages and limitations regarding the mass and the photons transfer focusing on photocatalytic process intensification. Also, it is presented a discussion of the recent applications of photocatalytic reactor modeling using computational fluid dynamics (CFD) for the gaseous pollutant degradation.
... One of the most effective methods is the use of photocatalysis, which is performed due to the course of various chemical processes under the influence of light; the degradation of facade pollution (dust, mold, bacteria, etc.) occurs [1][2][3]. Various substances are oxidized to carbon dioxide and water on the surface of the photocatalyst under the action of ultraviolet radiation. The advantage of this method is not only cleaning the surface, but also air cleaning [4,5]. ...
The increasing urbanization of urban areas poses the challenge of the development of materials capable of self-cleaning from organic pollutants formed. Previous papers substantiated the possibility of the coating of titanium oxide as the main agent of the photocatalytic method of cleaning structural materials on silica raw materials in order to increase the degree of its distribution in the volume of cement matrix and, as a result, increase its efficiency.It is obvious that a silica substrate will affect the processes of structure formation during hardening of a cement matrix. During the research, the processes of phase transformations of cement stone modified with silica raw materials of natural and technogenic origin were studied. As a result, the influence of siliceous modifiers on the strength characteristics of the cement stone was determined, which allowed ranking them according to the degree of decrease in efficiency as follows: technogenic raw materials; natural raw materials of silicate composition; natural raw materials of aluminosilicate composition. Quantitative assessments of the degree of efficiency showed the irrationality of using aluminosilicate composition as a silica modifier of natural raw materials, which is explained by its low pozzolanic activity.
... Different types of illumination were applied: UV-vis and strictly visible (guaranteed by the use of a cut-off filter) radiation. Illumination source was a Osram Ultravitalux 300 W lamp, according to the specifications of intensities reported elsewhere (Pérez-Nicolás et al. 2017). ...
Unique multifunctional coatings, comprising a 3D superhydrophobic agent and two nanostructured photocatalysts (solar-light sensitive 50/50 and 10/90 TiO 2-ZnO nano-heterostructures), compatible with the inorganic substrates of the Built Heritage, have been designed. The synthesized nanoparticles showed an enhanced photocatalytic activity (tested by NO degradation) as compared with the raw TiO 2 and ZnO materials. Dispersing agents were used to optimize the coatings, avoiding agglomeration of the photocatalytic nanoparticles and increasing the stability of the suspensions. Four distinct dispersions were optimized and applied as coatings onto stony materials used in the Built Heritage, such as sandstone, lime mortar, granite and limestone. Their effectiveness was assessed by assessing hydrophobicity of the surfaces (static water contact angle), photocatalytic activity and self-cleaning as well as water vapour permeability of the treated specimens. These transparent coatings demonstrated high compatibility with the construction materials of the Architectural Heritage and showed a synergistic effect rendering a minimized water absorption, self-cleaning ability evidenced by the reduced adsorption of soiling deposits and a reasonable degradation of any trace that might be adsorbed, as well as a protecting hydrophobic environment for the photocatalyst.
TiO2-based building materials possess air purification, self-cleaning, and sterilization functionalities, making them innovative green building materials with significant potential for future energy-saving and emission-reduction applications. However, the transition from laboratory-scale to practical applications poses substantial challenges in improving the photocatalytic efficiency and stability of TiO2-based building materials. In recent years, researchers have made considerable efforts to enhance their efficiency and stability. This paper provides a concise overview of the photocatalytic principles employed in buildings for air purification, discusses preparation techniques for TiO2-based building materials, explores strategies to improve their efficiency, outlines key factors influencing their performance in practical applications, analyzes limitations, and discusses future development trends. Finally, we propose recommendations for further research on photocatalytic buildings and their real-world implementation as a valuable reference for developing highly efficient and stable photocatalytic building materials. The aim of this paper is to guide the application of TiO2-based photocatalysts in green buildings towards creating more efficient and stable low-carbon buildings that support sustainable urban growth.
The dispersion containing black TiO2 photocatalyst was prepared and sprayed onto the concrete's surface to achieve a black TiO2-based photocatalytic concrete paving Eco-block, and its photocatalytic NO removal ratio is...
TiO2-based building materials have air purification, auto-cleaning and sterilization functions, and these innovative green building materials have great potential for energy-saving and emission reduction applications in the future. However, there are still great challenges in improving photocatalytic efficiency and stability from laboratory to practical applications. In recent years, researchers have done a lot of work to improve the efficiency and stability of TiO2-based building materials. This paper briefly discussed the air purification principle by photocatalytic building, and the preparation techniques of TiO2-based building materials and the strategies to improve the efficiency of TiO2. Moreover, this paper has outlined the key factors that affect the photocatalytic building performance in practical applications, and analyzed the limitations and future development trends. Finally, we proposed some suggestions for further research on photocatalytic buildings and its application in practice, aiming to provide an efficient reference for developing highly efficient and stable photocatalytic building materials. The aim of this paper is to provide effective guidance for the application of TiO2-based photo-catalysts in the field of green buildings, helping to develop more efficient and stable low-carbon buildings for the development of sustainable cities.
A photocatalyst that can adsorb particulate matter (PM) with an electric charge is a popular method for PM reduction. Some commonly used photocatalysts comprise single metal oxides such as TiO2 and ZnO, which could be utilized under ultraviolet (UV) region. However, because UV region constitutes a very small part of the total wavelength of sunlight, technology needs to be developed that allows the utilization of the visible region as well. Herein, we developed a new organic material that activated under not only UV region but also visible region by utilizing methylene blue (MB) with TiO2. To make the TiO2–MB film adsorb well, we discuss various solvents, concentration controls, and even coating methods. By conducting NO removal test, we showed that it is possible to reduce the PM more effectively by using TiO2–MB film than that achieved using TiO2 alone.
This work aims to perform an experimental study to examine the long-term photocatalytic performance of TiO2-incorporated cementitious systems under carbonation exposure and the effect of the incorporation of different mineral admixtures (metakaolin or calcite) on the time-dependent photocatalytic performance stability of the cementitious systems. To do this, TiO2-containing mixtures were produced by replacing cement with different mineral admixtures (metakaolin or calcite) at a mass percentage of 15 and 30 % of total powder material. Produced specimens were kept under two different environmental conditions [95 ± 5 % relative humidity (RH) and 20 ± 2 °C (Curing Condition I), and 65 ± 5 % RH, 50 ± 5 °C and %4 CO2 (Curing Condition II)]. Photocatalytic activity of the specimens was assessed by determining NOx degradation rate (%), NO degradation rate (%), NO2 formation rate (%) and system selectivity (%) via photocatalytic degradation tests. To assess the microstructural, physical and chemical properties of the specimens, mercury intrusion porosimeter (MIP) and thermogravimetry (TG/DTG) analyses were used. The results indicated that metakaolin incorporation into the cement-based systems enhanced the long-term photocatalytic performance of the specimens. For Curing Condition II, a better time-dependent performance stability was achieved from the mixture with higher metakaolin incorporation rate. Calcite incorporation into the cement-based systems also improved the time-dependent photocatalytic performance of the mixtures, which was more pronounced for the high calcite incorporation rate. While the carbonation mechanism determined the time-dependent photocatalytic performance of the metakaolin-incorporated mixtures, the presence of defects in the matrix because of the calcite incorporation determined that of the calcite-incorporated mixtures.
There is an upsurge in air pollution due to urbanization and industrialization across the globe. This calls for immediate action. Large exterior surfaces of high-rise buildings and civil infrastructure can be utilized to one’s advantage by applying nanocoatings that are capable of alleviating the concentration of air pollutants in the surrounding atmosphere. Few nanomaterials with their photocatalytic property can degrade some of the air pollutants such as oxides of Nitrogen (NOx) and Sulfur (SOx) to their respective non-harmful counterparts thereby bringing down the concentration of actual pollutants. Most of the metropolitan cities which have high-rise buildings are the ones that have more
concentration of pollutants. Therefore, these buildings can be employed for coating Nanomaterials on the exterior surface of these buildings. Nano photocatalysts can be either incorporated onto a surface as a coating or into the outer layer of the building
during construction. The most commonly used semi-conductor nano-photocatalyst for this purpose is Nano Titanium Dioxide (TiO2) or its composites, such as silica-doped TiO2. This review paper consolidates various methods of synthesizing TiO2 and its
composites, their characterization, different methods of incorporating nanomaterials onto construction materials, and degradation mechanisms.
Air quality is one of the main factors having incontestable effect on the quality of life of every being on earth. In addition to its effect on the public health, low air quality also has an indispensable negative effect on the society, environment, and economy as it requires rigorous efforts to be made for proper reduction and/or elimination. Because of the rapidly increasing urban population and industrial activities, the incremental trend in the air pollution, which is one of the world’s major problems nowadays, will most likely continue in the future since the release of greenhouse gases into the atmosphere is also expected to continue at an increasing pace as a consequence of the progressive man-made activities. Among various air pollutants, toxic nitrogen oxide (NOx) is of special interest recently as the release of NOx from the industrial organizations and vehicles has reached serious levels, especially in crowded cities. In an effort to adequately tackle the increased levels of NOx, researchers have looked into several solutions and realized that light irradiated from different types of sources [ultraviolet (UV), visible, solar light, etc.] activates the photocatalytic reactions reducing the pollutiveness of NOx and large surface areas of building members in contact with different light sources offer a unique opportunity for the elimination of detrimental effects of NOx through stimulation of photocatalytic reactions. Given the widespread utilization of cementitious systems in the construction industry, numerous ongoing and completed studies focusing on the use of various photocatalytic materials (photocatalysts) within the cementitious systems can be found. The main focus of these studies is to develop new-generation multi-functional cementitious composites with air cleaning feature without compromising the mechanical features and cost of production. In order to equip cementitious systems with the air cleaning feature, titanium dioxide (TiO2) is a very commonly used semiconductor photocatalyst. The commonness of utilization of TiO2 in cementitious systems is originated from the material’s high efficiency in oxidization of NOx, chemical/photochemical stability, chemical inertness in the absence of irradiation, safety, comparative cost-effectiveness, and nontoxicity. In this chapter, a comprehensive review about the mechanism/properties/advantages of TiO2-based photocatalytic multi-functional cementitious composites with air purification capability is presented.
Environmental air pollution is a major concern for society at present. Due to increasing road traffic, the presence of nitrogen oxides gases (NO x ) in urban areas exceeds the recommended limits for human health, as the harmful NOx are responsible for thousands of early deaths worldwide. The heterogeneous photocatalytic oxidation (PCO) assists as a simple, easy, efficient, and advanced method to be implemented in urban architecture in order to combat NOx pollution. The first successful applications have been obtained with the use of TiO 2 ‐based building materials. In the last few years, research on DeNO x materials has largely increased with the aim of finding the best photocatalyst, considering the efficiency, sustainability, and cost as key parameters. With the aim of increasing the light harvesting ability and selectivity in the PCO process for the photocatalyst, a wide range of new oxide nanomaterials are being studied, from the new functionalization of titania to new metal oxides/compounds (BiOI, Bi 2 MoO 6 , ZnO, SnO 2 , Fe 2 O 3 , LDHs, …). Apart from the inherent light activity ability of each compound, strategies considering changes in micro/nano‐morphology, doping, electronic heterojunctions, or oxygen vacancy engineering, among others, are successfully implemented in the search of enhanced DeNO x photocatalysts. The latest advances in this field are presented and critically discussed in relation to the current state‐of‐the‐art and emerging perspectives for future development.
This paper explores the effect of the inclusion size of titanium dioxide (TiO2) particles on a variety of performance properties of cementitious systems via experimental studies. In addition to comprehensive microstructural analysis including pore size distribution and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX) analyses, particular consideration was given to the effect of particle size distribution (PSD) of TiO2 particles on mechanical and photocatalytic properties and hydration kinetics of cementitious systems. Nano-sized, submicron-sized and micron-sized anatase-phase TiO2 powders were utilized as photocatalysts at a dosage of 5% by total weight of powder material. In addition to the single use of TiO2 particles with three different size ranges (nano, submicron and micron), they were also used in combination by adjusting their PSDs with three different PSD moduli (q): 0.1, 0.5, and 0.9. Test results show that techniques for achieving optimal microstructural characteristics of cementitious systems also help design and improve their performance in favor of multifunctionality. As a result of PSD optimization of TiO2 particles with three different size ranges, which was significantly influential on the microstructure of the cementitious systems, superior photocatalytic degradation results were obtained from mixtures containing lower amounts of nano-sized TiO2 particles. Cementitious composites with denser microstructure showed lower performance in terms of being able to maintain photocatalytic degradation capability for a prolonged period, whereas the opposite was the case for compressive strength.
In this work the hybrid CFD-ANN-GA method is proposed as a tool for the analysis and optimization of micro-photocatalytic reactors, taking NOx abatement as a case study. Initially, a 3D CFD model of the microreactor allowed the investigation of the effects of residence time, light intensity, relative humidity and initial NO concentration on the performance of the photocatalytic reaction. Then, an artificial neural network (ANN) was implemented to predict the overall conversion of NO in the micro device. Different ANN structures were developed using data from 256 CFD simulations, and the best structure was chosen based on the performance factors MSE, RMSE and R². Moreover, a genetic algorithm (GA) was used to find the optimal operating conditions that maximize the NO conversion. The best ANN model consisted of a feed-forward back-propagation structure with three layers and 11 neurons in the hidden layer (4:11:1), logsig-logsig transfer function and training through the Levenberg-Marquardt algorithm. This network presented a high predictivity (R² = 0.9997), and it was used for optimization by GA to determine the optimum conditions. Based on the optimization results, full NO conversion (100%) was achieved when the residence time, light intensity, relative humidity and initial concentration were 2.12 s, 10 W·m⁻², 10%, and 2.09×10⁻⁸ kmol·m⁻³, respectively. Furthermore, the most influential variable on the NO conversion prediction was the residence time, with a relative importance of 48.97%. The ANN was then modified to yield two outputs: NO consumption rate and pressure drop. All parameters were kept the same, except the number of neurons in the hidden layer (17). GA was then applied to a multi-objective optimization, aiming to maximize the NO consumption rate while minimizing the pressure drop in the system. The optimal set of operating conditions in this scenario was found based on a Pareto front analysis.
Nitrogen oxides (NO x ), especially nitric oxide (NO) and nitrogen dioxide (NO2), play a major role in atmospheric chemistry and air pollution. They constitute a major environmental and health concern as they are toxic compounds and also facilitate the formation of ozone and acid rain. As a consequence, increasingly stronger regulations and policies are in place enforcing actions to reduce emissions and to lower the overall pollutant levels. Recent studies and events have shown that emission standards are frequently exceeded as well as emission treatment systems not being as efficient as they are claimed to be. Apart from reducing the emissions directly at the emission source, which appears to be more difficult than anticipated, semiconductor photocatalysis presents an appealing alternative capable of removing NO x and other air pollutants from the air once they have already been released and dispersed. Additionally, photocatalysis needs neither maintenance nor external reagents because the only requirements are sunlight, water, and molecular oxygen, which are already present in outdoor conditions.
This chapter will summarize the basic principle and mechanism of photocatalytic NO x abatement, including studies on the reaction pathways and intermediate products, highlighting the principal challenges of the technique. Additionally, recently reported strategies of improving the activity, spectral response, and selectivity of the photocatalysts are reviewed. As the intended applications are functionalized building materials, the specific challenges of coating the photocatalysts onto or integrating them into the matrices of these building materials are addressed. Finally, a collection of results from field tests and simulations are reported to estimate the efficacy of the technology in real-world scenarios.
Removing NO2 from cement kilns can have tremendously beneficial effects on the environment and human health. Sequestering NO2 in demolished concrete is an innovative, cost-effective, and sustainable approach to remove NO2 flue-gas from cement kilns and other industrial plants to minimize their environmental impact. Another notable advantage of this approach was signified by our recent discovery of NO2 sequestered Recycled Concrete Aggregate (NRCA) acting as a corrosion inhibitor when recycled backed into new concrete. This paper focuses on NO2 sequestration by the waste concrete at elevated temperatures that are representative of those found in the cement kilns flue gas exhaust. The gas-phase uptake experiments were performed for 1, 2, and 20-years old concrete samples to reflect the variable age of NRCA. The mechanistic studies of NO2 adsorption to concrete surfaces at 27 oC, 150 oC, and 250 oC temperatures that simulate flue gas temperatures were obtained by time-resolved Diffuse Reflectance Infrared Fourier Transform spectroscopy (DRIFTs) and gas-phase analysis. The results showed that NO2 sequestration increased with an increase in temperature. Most importantly, the 20-year-old concrete still had significant uptake capacity, which shows that aged waste concrete can be used to reduce air pollution and then recycled back into new concrete structures to prevent corrosion. These findings were also supported by TGA, BET, and XRD results. The XRD data indicated a presence of alite, belite, ettringite, portlandite, and dolomite, where the increased fractions of portlandite and hydrates were correlated to higher NO2 uptake. Moreover, the BET results indicated notable changes in the microstructure of the concrete at elevated temperatures, which also contributed to changes in the NO2 uptake capacity of concrete.
In this study, graphitized carbon nitride photocatalysts were successfully prepared by using the desulfurized waste liquid extracting salt from coking plants. The NOx removal efficiency of g-C3N4 synthesized using ammonium thiocyanate (NH4SCN), ammonium thiosulfate ((NH4)2S2O3) and ammonium sulfate ((NH4)2SO4) with different mass ratios were evaluated. The results showed that due to the addition of (NH4)2S2O3 and (NH4)2SO4 a large amount of sulfur-containing gas was released during pyrolysis, which significantly increased the specific surface area and pore volume of the photocatalysts. The release of sulfur-containing gas also resulted in the incorporation of sulfur, and due to this doping process the band gap of the photocatalyst was widened to 2.94 eV, thus enhancing its visible light response. C vacancies were formed in the hepazine ring, which increased the electron density around the N–(C)3 bridge bond and formed an electron trapping center, thus inhibiting the recombination of charge carriers. The photocatalysts had increased O2 adsorption capacity and increased number of amino groups on their surface. This facilitated the rapid generation and consumption of reactive oxygen species, inhibited the accumulation of NO2 on the surface, reduced the production of NO2, thus improving the NOx removal efficiency of the photocatalysts. The principle of using “waste for waste control” was achieved, and a new method for nitrogen oxide removal was provided.
The present review article is aimed at analysing the different aspects of titania-modified building materials towards environmental remediation. The possibility of degradation of different toxic environmental pollutants like VOCs and NOx by the titania-modified paints, cements and other building materials has been discussed. The major role of titania resides in its photocatalytic activity that renders the materials’ potent for degrading these obnoxious compounds. The application of TiO2 both in small and in large scale and the mutual relationship of the amount of TiO2 with the amount of main building block constituents are discussed in detail. Application of daylight or lamplight, energy, time, and atmospheric conditions has also been dealt with. This review article solely focuses on titania-incorporated building blocks and is an endeavour to propagate a new horizon for our future pollution-free perspectives. Several environmental and product-related parameters that affect the efficacy of these modified matrices have been taken up. The present scenario in the industrial fields has also been assessed. Finally, a critical view is also presented that highlights the shortfall and areas open for further research and development in this particular field.
The utilization of recycled concrete as an adsorbent to sequester NO2 without additives or catalysts is an innovative, cost-effective, and sustainable approach to capture NO2 from targeted industrial facilities. This paper presents the mechanical and durability performance of ordinary portland cement (OPC) concrete containing NO2 sequestered recycled concrete aggregate (NRCA). NRCA was used as a partial replacement for natural fine aggregate at 20% and 40% rates by volume. The incorporation of NRCA in concrete resulted in increased compressive strength, decreased water-permeable porosity, and reduced chloride ion migration. Moreover, test mixtures comprising 40% NRCA showed a significant chloride binding capacity compared to control concrete mixtures. Furthermore, high replacement rates of NRCA noticeably enhanced the resistance to chloride-induced corrosion of steel in concrete or at least was on par with the performance of a commercially available calcium nitrite-based corrosion inhibitor.
This work continues EPR investigation of photocatalytic systems based on vanadium modified titanium dioxide (anatase) surface containing various concentrations of VO2+ paramagnetic centers (PCs). Three different types of the isolated PCs are revealed on the surface of V–TiO2 nanoparticles and quantitatively characterized. Time-dependent transitions among these PCs were observed and kinetic behavior was described using new theoretical approach and the developed numerical calculation procedure. The slow-process kinetic rate constant has been calculated from EPR data.
Bismuth oxybromide (BiOBr) was synthesized in aqueous medium in presence of EDTA as structure-directing agent following a simple coprecipitation method at 23 °C and by microwave irradiation at 110 °C. The physicochemical properties of BiOBr (morphology, specific surface area, energy band gap and photocatalytic activity) were modified using different EDTA concentrations. Nanoparticles of BiOBr with {1 1 0} crystallographic exposed facets were obtained as a peculiar feature of the synthesis followed. The photocatalytic activity of BiOBr was evaluated in the oxidation reaction of nitric oxide (NO) in gaseous phase under UV–Vis and visible irradiation. An enhancement in the NO conversion degree was reached for BiOBr synthesized by coprecipitation with an EDTA/Bi molar ratio of 0.6. This sample showed a NO conversion degree of 94%, a selectivity to nitrate ions of 98%, a good stability after four cycles of irradiation and sample was able to retain its high photocatalytic activity under humidity conditions (70% RH). The use of different chemical scavengers revealed that superoxide radical (O2•-) was the main reactive specie in the mechanism of the photocatalytic reaction. BiOBr photocatalyst was successfully incorporated in two formulations of ceramic coatings to develop prototypes of building materials with active surface for the photocatalytic elimination of NOx gases from the air.
In a quest for a cleaner planet and to have alternative forms of energy generation apart from the fossil-based power supply, fuel cell technology has emerged as an alternative energy source for usage across all economic sectors. The application of this age-old technology is found in alkaline (AFC), molten carbonate (MCFC), phosphoric acid (PAFC), polymer electrolyte membrane (PEMFC) and solid oxide (SOFC) fuel cells. These fuel cells are named based on the type of electrolyte employed in their applications and the fuel of choice for energy generation is hydrogen. This fuel can be used in its pure form or extracted from other sources such as methanol, water and syngas. Ammonia in its liquefied and gaseous forms may be used as a non-carbonaceous fuel for the hydrogen source in some of these fuel cell technologies due to its safety, lower price, ease of storage and transportation. In this review, all the fuel cells will be investigated in their capability of using ammonia as a direct fuel. The role of earth abundant metal catalysts in comparison to TiO 2 was evaluated in terms of molecular orbital theory and in the decomposition of organic compounds and other material into nitrogen and hydrogen products under the visible light radiation. The p-orbital participation in earth abundant metals or metal oxides doping, emerged as a strong contribution to bandgap attenuation.
Herein, we prepared composite photocatalysts (CP) by loading nano-TiO2 (NT) on recycled clay brick sands (RCBS) and recycled glass (RG). CPs are denoted as [email protected] and [email protected], respectively. The [email protected] was used to partially replace [email protected] and the combined CPs were then used to replace common river sand (RS) in photocatalytic mortar. Micrographs coupled EDS exhibit both [email protected] and [email protected] successfully carry NT on their surfaces; whilst the amount of carrying is measured by analytical balance as 0.0048 g per gram of RCBS and 0.0013 g per gram of RG. Once some [email protected] is replaced by [email protected], the rheological behaviour is improved due to the smooth surface of the latter. However, compressive strength is not evidently lifted by [email protected] because the weak bonding between [email protected] and surrounding cementitious materials even though [email protected] relative to [email protected] has a higher hardness. However, the [email protected] by 25% weight replacement over [email protected] contributes to an enhanced NOx removal since a mutual promotion effect that [email protected] receives enough refracted light to activate photocatalysts in deep pores while [email protected] obtains enough room to accommodate final products caused by photocatalysis and enhances the anti-abrasion capacity. Finally, the combined use of [email protected] and [email protected] increases NOx removal by ~18.8%; and at the same saves NT usage by ~80% relative to the traditional NT (5% NT by wt. of cement) intermixing approach. Thereby, this study provides a cost saving approach to by construction wastes prepare environmentally friendly photocatalytic mortar with higher photocatalytic efficiency.
This study presents an experimental overview for the development of photocatalytic materials based on geopolymer binders as catalyst support matrices. Particularly, geopolymer matrices obtained from different solid precursors (fly ash and metakaolin), composite systems (siloxane-hybrid, foamed hybrid), and curing temperatures (room temperature and 60 °C) were investigated for the same photocatalyst content (i.e., 3% TiO2 by weight of paste). The geopolymer matrices were previously designed for different applications, ranging from insulating (foam) to structural materials. The photocatalytic activity was evaluated as NO degradation in air, and the results were compared with an ordinary Portland cement reference. The studied matrices demonstrated highly variable photocatalytic performance depending on both matrix constituents and the curing temperature, with promising activity revealed by the geopolymers based on fly ash and metakaolin. Furthermore, microstructural features and titania dispersion in the matrices were assessed by scanning electron microscopy (SEM) and energy dispersive X-ray (EDS) analyses. Particularly, EDS analyses of sample sections indicated segregation effects of titania in the surface layer, with consequent enhancement or depletion of the catalyst concentration in the active sample region, suggesting non-negligible transport phenomena during the curing process. The described results demonstrated that geopolymer binders can be interesting catalyst support matrices for the development of photocatalytic materials and indicated a large potential for the exploitation of their peculiar features.
The InVO4/TiO2 heterojunction system has been prepared by means of a practical impregnation method in alcoholic media. The obtained photocatalysts were characterized by several techniques, such as X-ray powder diffraction (XRD), UV-vis diffuse reflectance spectroscopy (DRS) and electron microscopy (SEM/TEM). Also, nitrogen adsorption-desorption isotherms were employed in order to determine the surface area (BET) and pore-size distribution (BJH) of the samples. We have observed that the addition of InVO4 did not provide changes in the structural and textural properties of TiO2 but substantially improved its photocatalytic properties. The best photocatalytic performance for the degradation of phenol was achieved for TiO2 with 0.5 wt.% loading of InVO4. From these results it can be inferred that the effective separation of the charge carriers produced an improvement in the photocatalytic performances of the InVO4/TiO2 heterojunction photocatalysts. In the same way, a possible mechanism is discussed in order to explain the enhanced photoactivity under UV-vis irradiation.
The beneficial and harmful effects of human exposure to solar ultraviolet radiation (UV-R) are topics that arouse great interest not only among physicians and scientists, but also the general public and the media. Currently, discussions on vitamin D synthesis (beneficial effect) are confronted with the high and growing number of new cases of non-melanoma skin cancer and other diseases of the skin and eyes (harmful effect) diagnosed each year in Brazil. However, the lack of scientific knowledge on the UV-R in Brazil and South America leads to adoption of protective measures based on studies conducted in Europe and USA, where the amounts of UV-R available at surface and the sun-exposure habits and characteristics of the population are significantly different from those observed in Brazil. In order to circumvent this problem, the Brazilian Society of Dermatology recently published the Brazilian Consensus of Photoprotection based on recent studies performed locally. The main goal of this article is to provide detailed educational information on the main properties and characteristics of UV-R and UV index in a simple language. It also provides: a) a summary of UV-R measurements recently performed in Brazil; b) a comparison with those performed in Europe; and, c) an evaluation to further clarify the assessment of potential harm and health effects owing to chronic exposures.
This paper describes the environmental performance of a mixed phase coating (photocatalytic nanolime) manufactured from a colloidal nano-structured calcium hydroxide in alcohol (nanolime) combined with titanium dioxide. While nanolime is used as a consolidant in the field of cultural heritage and titanium dioxide is used as a photocatalytic material for self-cleaning coatings and environmental pollution control within the construction industry both materials are often used separately. We report in this paper an approach to combine both materials for the development of a photocatalytic nanolime coating. The photocatalytic effect of titanium dioxide on the carbonation of nanolime and its influence on the degradation processes in polluted environments is explored. A suspension of 25g/l of nanolime in ethanol and 7.4% wt/vol titanium dioxide was applied to specimens of Bath stone. For comparison, additional specimens were treated only with the nanolime. The specimens were exposed to oxides of nitrogen and sulphur under 30% relative humidity (RH) for 120 hours. Exposure was carried out under both, UV and daylight. After exposure, the effect of titanium dioxide on the carbonation of nanolime and on the degradation processes was investigated using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS) and X-ray photo electron spectroscopy (XPS). Results were evaluated considering the dissolution processes of the two oxides in water, and modelled using PHREEQC. Results show that the nanolime and the photocatalytic nanolime coatings promote the reaction of SO2. In addition, the photocatalytic effect of the anatase form of titanium dioxide promotes the formation of a surface layer of calcium sulphate and inhibits carbonation of calcium hydroxide. That was attributed to the oxidation of sulphur dioxide to sulphur trioxide by hydroxyl radicals which led to the formation of sulphuric acid.
A study was conducted on the development of lime based grouts for consolidation of renders and plasters detached from the support. The aim is to develop grouts that should be compatible with the preexisting materials and allow the restoring of the adherence of coatings to the background. Special attention was paid to the rheological behaviour of the grouts and to other features of the fresh state. The role of components such as binders, aggregates and admixtures used in the formulations was tested through an outlined series of mechanical and physical tests. In terms of hardened state properties, a set of basic requirements (related to strength and capillarity) were evaluated and a test for adhesion loss measurement was developed in order to test the ability of developed grouts to restore adhesion of coating layers. The rheological behaviour was evaluated through a distinct procedure, which involved the test with a specific speed profile (dwell profile). The dwell profile allows studying the rheological behaviour along measuring time, making possible to observe changes in rheological parameters in mortar suspensions, through the measurement of flow curves along the time test. The dwell profile allowed obtaining the rheological parameters (viscosity and yield stress) according to the Bingham model. Grouts based on lime, fine sand and metakaolin together with the right amount of water and admixtures were developed and adjusted in order to be used in consolidation works of old renders.
Self-cleaning glass can be realized utilizing photo-induced hydrophilicity of titanium dioxide. In order to understand the photo-induced hydrophilic self-cleaning effect, it is necessary to understand the relationship between the mutual effect of photohydrophlicity and photocatalysis. In this paper, the relationship between hydrophilicity, photocatalysis and the self-cleaning effect is investigated. It is found that the TiO2/SiO2 surface can have more hydrophilic activity and less photocatalytic activity, or vice versa by adding different amount of SiO2. It is the synergetic effect of hydrophilicity and photocatalysis that improves and maintains the self-cleaning effect. SiO2 addition increases the acidity which results in the increase of the hydroxyl content in the composite films, with the consequence that the hydrophilicity and photocatalytic activity are increased during UV irradiation thus enhances the self-cleaning effect.
The ability of calcium aluminate cement (CAC) to encapsulate toxic metals (Pb, Zn and Cu) was assessed under two curing conditions. Changes in the consistency and in the setting time were found upon the addition of the nitrates of the target metals. Both Pb and Cu caused a delay in CAC hydration, while Zn accelerated the stiffening of the mortar. Compressive strengths of the metal-doped mortars, when initially cured at 60°C/100% RH, were comparable with that of the free-metal mortar. Three different pore size distribution patterns were identified and related to the compounds identified by XRD and SEM. Sorbent capacities of CAC for the toxic metals were excellent: a total uptake was achieved for up to 3wt.% loading of the three metals. In this way, CAC mortars were perfectly able to encapsulate the toxic metals, allowing the use of CAC for waste management as proved by the leaching tests.
Increased photocatalytic activity of NiO and SnO2 was achieved by coupling and supporting of them onto clinoptilolite nanoparticles (NC) via calcination of Ni(II)-Sn(IV) - exchanged NC in photocatalytic degradation of metronidazole (MZ) aqueous solution. XRD, XRF, FTIR, SEM, X-ray mapping, DRS, TEM, BET Cyclic voltammetry and electrochemical impedance spectroscopy techniques (EIS) were used for characterization of samples. Red shift occurred in bang gap energies of the coupled semiconductors with respect to monocomponent one. This p-n hetero-junction forms a depletion layer in the semiconductors interface with negative and positive charges, causing considerable enhancement in the photocatalytic activity. The calcined catalyst at 600 °C for 4h showed the best photocatalytic activity and charge transfer efficiency (in EIS results). The mole ratio of SnO2/NiO affects the degradation activity of the catalysts and the best activity were was obtained for the NiO1.1–SnO2(6.7)/NC (NS5-NC) catalyst at pH 3, 1.2 g L⁻¹ of the catalyst and 2 mg L⁻¹ of MZ. SnO2 played electron sink role and the photogenerated electrons migrate from more negative Cb-NiO (E= -3.0 V) to Cb-SnO2 (E=-0.3 V vs SHE). Initial pH of MZ solution was changed from 6.20 to 4.73 during 180 min that confirms formation of Oxalic acid and Maleic acid.
Decoration of silver nanoparticles (Ag-NPs) on surface of α-SnWO4 nanosheets has been achieved by a microwave-assisted deposition method. The as-synthesized products are structurally characterized by x-ray diffraction (XRD) and transmission electron microscopy (TEM). The results illustrate that Ag-NPs are evenly anchored onto α-SnWO4 surface to form close heterojunction and the amount of Ag nanoparticles grown on α-SnWO4 nanosheets can be well controlled by tuning Ag⁺ concentration. The photocatalytic properties of Ag-NPs/α-SnWO4 composites are evaluated by degrading methyl orange (MO) under visible-light irradiation. Ag-NPs/α-SnWO4 composites exhibit better photocatalytic properties than that of pure α-SnWO4, and Ag-NPs/α-SnWO4 (5 mol% Ag) presents the best photocatalytic activity, whose photodegradation efficiency of MO is about 97% within 70 min. In addition, the obtained samples demonstrate good recyclability. The enhanced photocatalytic properties was attributed to synergistic effect between Ag-NPs and α-SnWO4 nanosheets, which can increase absorption of visible light enabled by surface plasma resonance (SPR) of Ag-NPs and facilitate the separation of photogenerated electron-hole pairs.
Supported Fe2O3/TiO2 nanocomposites were prepared for the first time by a plasma-assisted route and successfully tested in photocatalytic NOx abatement driven by solar illumination. In particular, a sequential low-temperature (<100 °C) plasma enhanced-chemical vapor deposition (PE-CVD)/radio frequency (RF) sputtering approach was used to fabricate Fe2O3/TiO2 nanocomposites with controlled composition and morphology. The preparation process was accompanied by a thorough multi-technique investigation carried out by complementary techniques, including X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), field emission-scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and atomic force microscopy (AFM). The results evidenced the formation of high purity nanocomposites, in which TiO2 content could be tailored by controlled variations of the sole sputtering time, and characterized by an intimate Fe2O3/TiO2 contact, of key importance to exploit the chemical and electronic coupling between the two oxides. The obtained nanomaterials were tested in NO photo-oxidation activated by sunlight, showing a remarkable activity in NOx (NO + NO2) removal and a high selectivity (>60%) in their conversion to nitrate species. Overall, the present performances candidate the present photocatalysts as valuable materials for next-generation technologies aimed at the abatement of harmful gaseous pollutants.
A novel Mo, Fe, and N triple-doped rutile TiO2 nanopowder was synthesized with simple HNO3 assisted hydrothermal treatment. Powders synthesized were characterized by using x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), and Brunauer-Emmett-Teller (BET) surface area analysis techniques. Mo doping initiated the formation of a structure composed of a mixture of anatase and rutile with some modifications in morphology; but Mo, Fe, and N triple-doped titania powders are composed of entirely rutile structures. XPS analysis confirmed that Mo dissolved in the structure, replacing Ti atoms and forming some MoO3 partially crystallized nano regions on the surface. Existence of Fe in the TiO2 crystal lattice was confirmed by ICP analysis. Fe doping had an influence on the crystal structure and morphology. N was found to be dissolved in the co-doped structure by HNO3 catalyzer autogenously. Methylene blue degradation testing and band gap measurements were performed by using UV-Vis photospectroscopy and diffuse reflector apparatus in order to evaluate the photocatalytic performance of the powders. Dopant elements decreased band gap energy steadily. An enhanced photoactivity was reached by Mo, Fe, and N triple-doping as compared with that of undoped, and mono doped TiO2 powders under UV-light irradiation. Possible reasons for the enhancement in photocatalytic activity are outlined.
Concrete materials are ubiquitous in the developed world due to their versatility and cost-effectiveness as a construction material, but their great potential for increased functionality remains underdeveloped. As supports for photocatalysts, these structures offer viable solutions for the reduction of atmospheric pollutant concentrations, the source of which is often associated with urbanisation and the built infrastructure. This paper addresses (i) the photocatalytic mechanisms applicable to atmospheric depollution, (ii) the influence of doping, and (iii) the application of TiO2-based photocatalysts to concrete. Modifications to TiO2 will be discussed which can improve its activation in visible light and, in the treatment of NOx, improve catalytic selectivity towards nitrate rather than the more toxic NO2. The influence of the chemistry of cements on catalyst performance during both concrete placement and in service will also be addressed and some attention will be given to alternative strategies for
Photocatalytic cementitious material (PCM) was prepared by porous magnesium oxychloride cement (PMOC) and TiO2 photocatalyst. Influences of PMOC substrate surface microstructure on TiO2 loading and photocatalytic performance had been investigated. The results revealed that loading effect mostly depends on PMOC substrate surface microstructure which could be controlled by its curing age. Appropriate interlaced microstructure enhanced TiO2 dispersity, loaded mass and adsorption capability. PCM-14d specimen (14-day curing before TiO2 loading) had the best photocatalytic performance, which could completely purify toluene (200 ppm) within 80 min. Practical simulation experiment indicated that PCM-14d specimen was 1.3 times better than nickel foam based photocatalytic material.
A novel process for solidification/stabilization of EMR and simultaneous reusing it as resource was proposed. A new type of photocatalytic cement materials (TiO2-EMR cement) was developed by coating TiO2 onto EMR-cement. The sol–gel dip-coating method was investigated to prepare the TiO2-EMR cement materials. Degradation of methyl orange (MO) was selected to assess the self-cleaning activity of the cement samples. The influence of calcination temperature, coating cycles, leaching property, especially utilization cycles was systematically investigated. The results indicated that the maximum MO degradation of 94.2% was achieved. Furthermore, the photocatalytic activity of the cement coated with TiO2 can be regenerated by calcination at 500 °C for 2 h and used repeatedly. In addition, leaching toxicity of the prepared cement can meet the national standards. Therefore, the results obtained in this study established a technical suitability of reuse electrolytic manganese residue as raw material for self-cleaning cement materials.
Titanium dioxide (TiO2) is a photocatalyst which can accelerate the oxidation of nitrogen oxides (NOx) and other pollutants under ultraviolet (UV) radiation. In this study, a new method to coat TiO2 onto asphalt pavements was developed with the aim to enhance the NOx decomposition efficiency and durability of the coating material for asphalt pavements. In this method, pulverized TiO2-cement mortar is used as the spreading material, which is bonded to asphalt pavement surface by epoxy resin. The composition of the TiO2-cement mortar was optimized in terms of its mechanical properties. The long-term NOx degradation efficiency, abrasion resistance, and skid resistance of the spreading material were measured after it was subjected to 300 min polishing by the advanced Aachen Polishing Machine (APM). It was concluded that durable NOx degradation efficiency can be achieved by the developed method and the method is feasible for practical implementation.
Ti0.9V0.1O2-δ catalysts were prepared by flame synthesis to improve low temperature activity for selective catalytic reduction (SCR) of NO with ammonia. The influence of different synthesis conditions (precursor concentration and axial distance of stagnation plate) was investigated. The activities of these catalysts were performed by temperature programmed reaction (TPR). These catalysts were characterized by surface area measurement, XRD, TEM, Raman spectroscopy, XPS, H2-TPR and NH3-TPD. The results showed that the Ti0.9V0.1O2-δ catalysts synthesized with 304 ppm precursor concentration, exhibited small particle size and high SCR activity. The particle size of Ti0.9V0.1O2-δ generally increased as the axial distance of stagnation plate. The samples prepared with stagnation plate placed 20 mm beneath the nozzle were most active, which might be caused together by strong interaction between vanadia species and titania surface, high redox properties and abound Brønsted acid sites. Sample Ti0.9V0.1O2-δ (304-20) showed excellent H2O-resistant performance.
The utility of carbonaceous materials for hybrid semiconductor photocatalysts has been rapidly increasing in recent years due to the synergetic effect via interfacial charge transfer reactions. In this study, we prepared a novel graphdiyne–ZnO nanohybrid by the hydrothermal method and examined its photocatalytic properties on the degradation of two azo dyes (methylene blue and rhodamine B). Interestingly, the graphdiyne–ZnO nanohybrids showed superior photocatalytic properties than that of the bare ZnO nanoparticles as evidenced by the absorption spectra and total organic carbon analyses. Moreover, the rate constant of graphdiyne–ZnO nanohybrids is nearly 2-fold higher compared to that of the bare ZnO nanoparticles on the photodegradation of both azo dyes. Further, a plausible mechanism for the enhanced photocatalytic properties of the graphdiyne–ZnO nanohybrids has been discussed. This work on the development of graphdiyne-based semiconductor photocatalysis can provide new insights into the design of novel hybrid photocatalysts for potential applications in the environmental remediation sectors.
In this paper, an enhanced visible-light photocatalytic oxidation (PCO) of NO (∼400ppm) in the presence of the graphitic carbon nitride (g-C3N4) treated by the alkaline hydrothermal treatment is evaluated. Various g-C3N4 samples were treated in different concentrations of NaOH solutions and the sample treated in 0.12molL(-1) of NaOH solution possesses the largest BET specific surface area as well as the optimal ability of the PCO of NO. UV-vis diffuse reflection spectra (DRS) and photoluminescence (PL) spectra were also conducted, and the highly improved photocatalytic performance is ascribed to the large specific surface area and high pore volume, which provides more adsorption and active sites, the wide visible-light adsorption edge and the narrow band gap, which is favorable for visible-light activation, as well as the decreased recombination rate of photo-generated electrons and holes, which could contribute to the production of active species. Fluorescence spectra and a trapping experiment were conducted to further the mechanism analysis of the PCO of NO, illustrating that superoxide radicals (O2(-)) play the dominant role among active species in the PCO of NO.
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A series of semiconductor photocatalysts based on transition metals (M' = V, Cr, Fe, Co, Mn, Mo, Ni, Cu, Y, Ce, and Zr) incorporated TiO2 (Ti/M' = 20 atomic ratio) materials have been synthesized by adopting a one-step liquid flame aerosol synthesis technique. The resulting materials were explored for the destruction of acetonitrile in gas phase under visible light irradiation at ambient conditions. Our H-2-TPR studies revealed the formation of Me-O-Ti bonds, which suggest the strong interaction of dopant metal-TiO2 in all the as-synthesized materials. The reduction peaks in Cr-doped TiO2 shifted to much lower temperatures, due to the increase in the reduction potential of titania and chromium. The strong interaction (formation of Cr-O-Ti bonds) is the main reason that the Cr/TiO2 is an active photocatalyst in visible light. Our XPS studies suggest that the relative atomic percentage value of Ti3+/Ti4+ characterized by XPS was significantly high for our flame-made Cr/TiO2 nanoparticles (Ti3+/Ti4+ = 0.89, 32.9%), whereas, other samples demonstrated poor atomic percentage value of Ti3+/Ti4+ (Ti3+/Ti4+ = 0.08-0.32). The existence of Ti3+ species with narrow band gap is highly beneficial for the promotion of visible light-induced photocatalytic activity. The position of the Cr 2p peaks shifted to lower binding energies in Cr-doped TiO2 nanoparticles. The electrons migrate from the TiO2 nanoparticles to chromium species, which reveals a strong interaction between Cr and TiO2 nanostructure in the interface of flame-made nanoparticles. Conversely, Mn3+ species combined with TiO2 because its surface metal dispersion was kept high after TiO2 loading. However, Mn3+ incorporated catalyst was inactive because of the small energy driving force for electrons to detrap from Mn2+. The UV-vis spectroscopy results of M'-doped TiO2 (M' = Fe, Cr, V, Co, Ce, and Ni) materials showed augmentation of light absorption in the visible range. The Cr, V and Fe (Ti:M' atomic ratio = 20:1) titania aerosol catalysts reduced the bandgap energy of TiO2 to 2.9 eV under visible light irradiation. Among all of the catalysts we tested, the transition metals (M' = Cr, Fe, and V) incorporated materials have shown an impressive catalytic performance in visible light. Among all the catalyst tested, Cr-doped titania demonstrated a superior catalytic performance and the rate constant is about 8-19 times higher than the rest of the metal doped catalysts. Their catalytic performances are correlated with the UV-vis spectrum of each synthesized catalyst to reveal the specific role played by each metal ion. Published by Elsevier B.V.
Self-cleaning materials have gained considerable attention for both their unique properties and practical applications in energy and environmental areas. Recent examples of many TiO2-derived materials have been illustrated to understand the fundamental principles of self-cleaning hydrophilic and hydrophobic surfaces. Various models including those proposed by Wenzel, Cassie-Baxter and Miwa-Hashimoto are discussed to explain the mechanism of self-cleaning. Examples of semiconductor surfaces exhibiting the simultaneous occurrence of superhydrophilic and superhydrophobic domains on the same surface are illustrated, which can have various advanced applications in microfluidics, printing, photovoltaic, biomedical devices, anti-bacterial surfaces and water purification.
