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Titanium Dioxide based Heterogeneous and Heterojunction Photocatalysts for Pollution Control Applications in the Construction Industry
Abstract
With increasing urbanization and industrialization there is an upsurge in air pollution that demands immediate attention. The use of nanomaterials to alleviate air pollution is gaining importance. Certain nanomaterials can photocatalytically act on air pollutants such as oxides of nitrogen (NOx), sulfur (SOx), and carbon (CO2), thereby bringing down their concentration locally. Titanium Dioxide (TiO2), its composites, and TiO2 based Z/S scheme heterojunction photocatalysts are a few such nanomaterials. The band-gap of TiO2 in solid-state (3.2 eV) makes it a good photocatalyst in the ultraviolet region and its composites in the visible light region of the spectrum. Metropolitan cities are densely filled with high-rise buildings and the exteriors of these buildings, which are largely exposed to the atmosphere, can be utilized to coat these nano materials to enable photocatalytic reduction of air pollutants in the surrounding atmosphere. The nano photocatalysts can either be applied as coatings on the existing buildings or incorporated into the construction materials during construction. In this review article, an attempt is made to cover the application of photocatalysts in the construction industry starting from the working principle (mechanism) of heterogeneous and heterojunction photocatalysts, their advantages and disadvantages, methods of synthesis, pollution control applications, with emphasis on the methods of incorporating the photocatalysts into construction materials and also as a coating on existing buildings, the set up required to evaluate NOx reduction and the factors that affect the NOx reduction. The current status of pollution control applications in the construction industry and the authors perspective on the application of heterojunction photocatalysts in construction industry are highlighted.
... In this sense, titanium dioxide (TiO 2 ) is an n-type semiconductor and is one of the most promising photocatalytic semiconductors due to its non-toxicity, high chemical and physical stability, very acceptable biocompatibility, and natural abundance [8]. Moreover, it has proved wide photocatalytic applications, such as sterilization, H 2 generation, water decontamination, application in solar cells, and for CO 2 reduction [9]. In fact, by 2010, TiO 2 production had increased to 5000 tons, and it is projected to keep on increasing until at least 2025 with greater reliance upon nanosized TiO 2 [10]. ...
This study describes the preparation of TiO2-modified Bi2O3 photocatalysts with different TiO2 contents, synthesized via an in situ hydrothermal method. The powder samples were characterized by XRD, SEM, TEM, FTIR–ATR, UV–Vis, XPS, and N₂ physisorption analysis. The photocatalytic activity of the TiO2-modified Bi2O3 was studied for the removal of methyl orange (MO) and methylene blue (MB) under different reaction conditions. The TiO2-modified Bi2O3 photocatalysts exhibited superior photocatalytic activity compared to the pristine samples of TiO2 and Bi2O3. The BiT16 sample achieved degradation rates of approximately 93.9% and 98.2% for MO and MB, respectively, within 120 min of reaction at 30 ppm. These results are attributed to the band gap values, differences in textural features, TiO2 content, and the reduction in the recombination process of e⁻/h⁺ pairs in the Bi2O3–TiO2 composites. Reaction kinetics were determined using the Langmuir–Hinshelwood mechanism, and during the third photoreaction cycle, the TiO2-modified Bi2O3 (BiT16) achieved photocatalytic degradation rates of 65.6% for MO and 70.5% for MB.
... Despite the numerous advantages, more photosensitization is needed to harvest not only UV light but also the larger visible light portion of the light Processes 2025, 13, 163 4 of 26 spectrum and increase its capability to generate more radicals efficiently. To increase the photosensitivity of titania, efforts such as doping [20], creation of heterojunctions [41], and dye sensitization [42] have been implemented. These efforts are vital in reducing reliance on the use of UV electric lamps that consume power. ...
Increasing water pollution by bio-recalcitrant contaminants necessitates the use of robust treatment methods. Individual treatment methods are not effective against these emerging organic pollutants due to their stability in the environment. This has necessitated the use of advanced integrated systems such as photocatalytic membranes. Synergy in the reactive photocatalytic membranes effectively degrades the emerging organic pollutants. This review presents the state of the art in the synthesis and application of photocatalytic membranes in water and wastewater treatment. The study critically evaluates pertinent aspects required to improve the performance of photocatalytic membranes, such as tailored material synthesis, membrane fouling control, improved photocatalyst light absorption, use of visible light from sunlight, enhanced reaction kinetics through synergy, and regeneration and reuse. Previous studies report on the effectiveness of photocatalytic membranes in the removal of organic contaminants in synthetic and actual wastewater. As such, they show great potential in wastewater decontamination; however, they also face limitations that need to be addressed. The review identifies the challenges and provides a way forward in increasing the photoactivity of titanium oxide, fouling mitigation, scalability, improving cost effectiveness, enhancing membrane stability, and other aspects relevant in scaling up efforts from the lab scale to industrial scale.
... In this sense, titanium dioxide (TiO2) is an n-type semiconductor and is one of the most promising photocatalytic semiconductors due to its non-toxicity, high chemical and physical stability, very acceptable biocompatibility, and natural abundance [8]. Moreover, it has proved wide photocatalytic applications, such as sterilization, H2 generation, water decontamination, application in solar cells and for CO2 reduction [9]. In fact, by 2010, TiO2 production had increased to 5,000 tons, and it is projected to keep on increasing until at least 2025 with greater reliance upon nanosized TiO2 [10]. ...
The current study reports the preparation of TiO₂-modified Bi₂O₃ photocatalysts with different TiO₂ contents, synthesized via an in-situ hydrothermal method. The powder samples were characterized by XRD, SEM, TEM, FTIR–ATR, UV-vis, XPS, and N₂ physisorption analysis. The photocatalytic activity of the TiO 2 -modified Bi 2 O 3 was studied for the removal of methyl orange (MO) and methylene blue (MB) under different reaction conditions. Our study showed that the TiO 2 -modified Bi 2 O 3 photocatalysts exhibited superior photocatalytic activity compared to the pristine samples of TiO 2 and Bi 2 O 3 . The BiT16 sample achieved degradation rates of approximately 93.9% and 98.2% for MO and MB, respectively, within 120 minutes of reaction at 30 ppm. These results are closely related to the band gap values, differences in textural features, TiO 2 content, and the reduction in the recombination process of e⁻/h⁺ pairs in the Bi 2 O 3 –TiO 2 composites. Reaction kinetics were determined using the Langmuir–Hinshelwood mechanism, and during the third photoreaction cycle, the TiO 2 -modified Bi 2 O 3 (BiT16) achieved photocatalytic degradation rates of 65.6% for MO and 70.5% for MB.
... These challenges can be managed by merging TiO 2 with other materials to form hybrid structures, such as WO 3 /TiO 2 , MoO 3 /TiO 2 , ZrO 2 /TiO 2 , ZnO/ TiO 2 , and Fe 2 O 3 /TiO 2 . However, most of the previously reported metal oxides (e.g., ZrO 2 , MoO 3 , and WO 3 ) are expensive, and their preparation is complex (Meda et al., 2022). ...
This study synthesized a ferric oxideenanographite (NG) nanocomposite (Fe 2 O 3 @NG) from waste toner powder through carbonization. Subsequently, a TiO 2 /Fe 2 O 3 @NG nanohybrid was fabricated using the solegel technique to improve the photocatalytic degradation of dyes. TiO 2 /Fe 2 O 3 @NG nanocomposites were prepared at TiO 2 :Fe 2 O 3 @NG ratios of 2:1 (Ti:T-21), 1:1 (Ti:T-11), and 1:2 (Ti:T-12). The porosity, morphology, surface chemistry, and chemical interactions between TiO 2 , Fe 2 O 3 , and graphite in the prepared TiO 2 /Fe 2 O 3 @NG nanocomposites were characterized using the BrunauereEmmetteTeller (BET) method and microscopic and spectroscopic analyses. The TiO 2 /Fe 2 O 3 @NG nanohybrid exhibited a reduced bandgap (2.4e2.9 eV) and enhanced charge carrier separation through charge transfer at the junction of the hetero-structured TiO 2 /Fe 2 O 3 @NG nanohybrid. Preliminary experiments revealed that Ti:T-21 was the most effective photocatalyst for degrading acid blue-25 (AB-25) compared to Ti:T-11, Ti:T-12, sole TiO 2 , and Fe 2 O 3 @NG. This study also investigated the impacts of catalyst dose and initial dye concentration on the AB-25 photocatalytic degradation. Notably, 97% of 5-mg/L AB-25 was removed using 1.25-g/L Ti:T-21 at an unmodified pH of 6.4 within 120 min. Furthermore, Ti:T-21 exhibited remarkable recyclability in its immobilized form, achieving degradation ratios of 74.7%e71.8% over five consecutive runs, compared to removal efficiencies of 85.0%e62.3% in the suspended mode. Trapping experiments identified hydroxyl radicals, holes, and superoxide as the principal reactive radicals. The TiO 2 /Fe 2 O 3 @NG/light system was effective in disintegrating and mineralizing other synthetic dyes such as Congo red, methylene blue, and methyl red, indicating its potential for industrial-scale degradation of authentic dye wastewater. The utilization of waste toner for water treatment is highlighted as a strategy to promote environmental sustainability, foster a circular economy, and contribute to pollution remediation.
... In the latter region, TiO 2 is transparent and has a high recombination rate, which hinders its commercial use [6]. The setback can be solved by either doping with other metal ions or nonmetals that produce more states in the conduction band gap region [7]; they include Al 3+ , Cu 2+ , Mn 2+ , Fe 3+ , and Zn 2+ , N, S, and C, respectively, or addition of a dye. ...
Fe-doped TiO2 nanoparticles (F-T NPs) were synthesized using the sol-gel method where different molar concentrations (0, 1, 2, 3, 5, 7, 9, and 10%) of Iron (iii) nitrate were added to a constant amount of the metal precursor TetraisopropylOrthotitanate (TTIP) solution, the solvent precursor ethanol and refluxing agent diethanolamine at the ratios of 1:6:1 respectively. The gel formed was annealed at 500°C in a muffle furnace for 2h. Fourier Transform Infrared (FTIR) showed Fe-O symmetrical stretching vibration for the 5% doping and above and Ti-O-Fe asymmetrical stretching vibration at wavenumber 668 cm-1 and 1033cm-1, respectively. Fe-O stretching vibration confirms substitution doping. The crystallite size was calculated using the Debye Scherer equation; 2% F-T NPs had the largest crystallite size at 16.45 nm, and 7% F-T NPs had the least size at 10.95 nm, a decrease of 2.80 nm from the 0% F-T NPs. X-ray diffraction spectra showed a merging of peaks at planes 105 and 211. The peak at plane 204 is found to diminish, and the growth of another peak at 2θ (64.28°). Optical analysis was studied using UV-Vis, where the Tauc plot estimated the calculated band gap (Eg). It was the least at 7% F-T NPs with a value of 4.41 eV, and 5% F-T NPs were found to have the highest value of 4.86 eV.% Transmittance is directly proportional to the optical band gap. Scanning Electron Microscope showed improved agglomeration and aggregation with a dense and smooth particle. Energy Dispersive Spectroscopy confirmed the presence of Fe, Ti, and O in the F-T NPs.
... Titanium and its alloys have been extensively studied since the early 1950s due to their broad range of applications across various industries, including aviation, space, shipbuilding, chemical, defense, construction, and medicine industries [1][2][3][4][5][6][7][8][9][10]. The versatility of titanium alloys stems from their ability to be tailored through variations in chemical composition and phase structure [11]. ...
This study presents a comparative analysis of the corrosion resistance of nitrided layers on conventional Grade 2 titanium alloy and those produced by direct metal laser sintering (DMLS). Low-temperature glow-discharge nitriding of the tested materials was carried out using conventional glow-discharge nitriding (so-called nitriding at the cathode potential—TiN/CP) and with the use of an “active screen” (nitriding at the plasma potential—TiN/PP). The TiN + Ti2N + Ti(N) layers were characterized by their microstructure, nanohardness profile distribution, surface topography, and corrosion resistance. The reduction in the cathodic sputtering phenomenon in the process using the active screen allowed the creation of surface layers that retained the topography of the base material. The parameters of the glow-discharge treatment led to grain growth in the printed substrates. This did not adversely affect corrosion resistance. The corrosion resistance of nitrided layers on the printed titanium alloy is only slightly lower than that of layers on the conventional Grade 2 alloy. Iron precipitates at grain boundaries facilitate increased nitrogen diffusion, resulting in reduced nitrogen concentration in the surface layer, slight changes in corrosion potential values, and increased nitrogen concentration in the Ti(N) diffusion layer.
... Titanium dioxide (TiO 2 ) is commonly employed in the photodegradation of EMPs due to its high stability, insolubility, cost-effectiveness, abundance, and unique catalytic performance [6,7]. However, wide bandgap and fast recombination of electron-hole pairs obstruct the way towards the largescale application of the photocatalysis process using TiO 2 [8,9]. The wide bandgap of TiO 2 restrains the exploitation of solar light energy and makes the excitation only take place under UV light which constitutes only 5 % of solar energy [10]. ...
... These challenges can be managed by merging TiO 2 with other materials to form hybrid structures, such as WO 3 /TiO 2 , MoO 3 /TiO 2 , ZrO 2 /TiO 2 , ZnO/ TiO 2 , and Fe 2 O 3 /TiO 2 . However, most of the previously reported metal oxides (e.g., ZrO 2 , MoO 3 , and WO 3 ) are expensive, and their preparation is complex (Meda et al., 2022). ...
This study synthesized a ferric oxide–nanographite (NG) nanocomposite (Fe2O3@NG) from waste toner powder through carbonization. Subsequently, a TiO2/Fe2O3@NG nanohybrid was fabricated using the sol-gel technique to improve the photocatalytic degradation of dyes. TiO2/Fe2O3@NG nanocomposites were prepared at TiO2:Fe2O3@NG ratios of 2:1 (Ti:T-21), 1:1 (Ti:T-11), and 1:2 (Ti:T-12). The porosity, morphology, surface chemistry, and chemical interactions between TiO2, Fe2O3, and graphite in the prepared TiO2/Fe2O3@NG nanocomposites were characterized using the Brunauer–Emmett–Teller (BET) method and microscopic and spectroscopic analyses. The TiO2/Fe2O3@NG nanohybrid exhibited a reduced bandgap (2.4 to 2.9 eV) and enhanced charge carrier separation through charge transfer at the junction of the hetero-structured TiO2/Fe2O3@NG nanohybrid. Preliminary experiments revealed that Ti:T-21 was the most effective photocatalyst for degrading acid blue-25 (AB-25) compared to Ti:T-11, Ti:T-12, sole TiO2, and Fe2O3@NG. This study also investigated the impacts of catalyst dose and initial dye concentration on the AB-25 photocatalytic degradation. Notably, 97% of 5-mg/L AB-25 was removed using 1.25-g/L Ti:T-21 at an unmodified pH of 6.4 within 120 min. Furthermore, Ti:T-21 exhibited remarkable recyclability in its immobilized form, achieving degradation ratios of 74.7% to 71.8% over five consecutive runs, compared to removal efficiencies of 85.0% to 62.3% in the suspended mode. Trapping experiments identified hydroxyl radicals, holes, and superoxide as the principal reactive radicals. The TiO2/Fe2O3@NG/light system was effective in disintegrating and mineralizing other synthetic dyes such as Congo red, methylene blue, and methyl red, indicating its potential for industrial-scale degradation of authentic dye wastewater. The utilization of waste toner for water treatment is highlighted as a strategy to promote environmental sustainability, foster a circular economy, and contribute to pollution remediation.
... These slightly superior pore sizes in Fe 3 Al alloy (Table 3) may be due to the higher Fe concentration in the base material, i.e., higher current densities were reported, and hence, larger pore diameters are prone to be formed. Namely, the registered current density values in conventional TSA of the studied Fe 3 Al alloy are about ten times higher (100-120 mA cm −2 ) (Fig. 1a) than those reported on Al alloys (10-20 mA cm −2 at 15-20 V and 20-25 °C in TSA electrolytes) [37][38][39] . ...
It has recently been found that the anodizing of FeAl alloys allows the formation of iron-aluminum oxide layers with interesting semiconducting properties. However, the lack of systematic research on different anodizing regimes is hampering their full exploitation in numerous photoelectrochemical-related applications. This study address, for the first time, the systematic effect of the electrolyte composition on the formation of self-ordered oxide films by anodizing on cast Fe 3 Al alloy. The Fe 3 Al alloy was anodized in 3 electrolytes with different water-ethylene glycol (EG) ratios (pure water, 25 vol.%-EG, and 50 vol.%-EG solutions) at a constant tartaric-sulfuric acids concentration, different voltages (10–20 V) and treatment times (2–60 min). After anodizing, all anodic oxide layers were annealed at 900 °C to form semiconductive iron-aluminum crystalline phases. Conventional techniques were used to systematically ascertain the morphological (SEM/EDS, XRD, eddy-current measurements) and semiconductive (UV–VIS reflectance spectroscopy) properties of these oxide layers. The results confirmed the formation of homogeneous and self-ordered anodic oxide layers at 10 and 15 V, regardless of the electrolyte composition. Namely, anodic films formed in electrolytes containing EG showed lower pore sizes, growth rates, and film thicknesses than those anodic films formed in the aqueous-based electrolyte. The annealing post-treatment results in different Fe-Al oxides (Fe x O y , FeAl 2 O 4 , etc.) with superior band gap values than those for non-annealed films.
... An efficient and affordable method should be capable of converting organic pollution into non-toxic compounds and complete oxidation of pollutants [10], hence potent methods like the Advanced oxidation processes (AOPs) have gained ground. Among the various AOPs, photocatalysis has been vastly studied over the last 30 + years due to its success in non-selective degradation of various organic compounds, high efficiency, and the potentials of sunlight use as an free source of renewable energy [11,12]. ...
... The secondary sector includes industry and construction, where the burning of fossil fuels from industry and dust from construction are major contributors to air pollution. The rapid growth of the construction industry has promoted the development of industries, such as steel and cement, which not only directly affect urban air quality but also indirectly contribute to an increase in air pollution [32]. The severity of pollution levels in the cities of the region can be seen from the early raw data. ...
In this paper, based on the traditional grey multivariate convolutional model, the concept of a buffer operator is introduced to construct a single-indicator buffered grey multivariate convolutional model applicable to air quality prediction research. The construction steps of the model are described in detail in this paper, and the stability of the model is analyzed based on perturbation theory. Furthermore, the model was applied to predict the air quality composite index of the “2 + 26” Chinese air pollution transmission corridor cities based on different socioeconomic development scenarios in a multidimensional manner. The results show that the single-indicator buffered grey multivariate convolutional model constructed in this paper has better stability in predicting with a small amount of sample data. From 2020 to 2025, the air quality of the target cities selected in this paper follows an improving trend. The population density, secondary industry, and urbanization will not have a significant negative impact on the improvement of air quality if they are kept stable. In the case of steady development of secondary industry, air quality maintained a stable improvement in 96.4% of the “2 + 26” cities. The growth rate of population density will have an inverted U-shaped relationship with the decline in the city air quality composite index. In addition, with the steady development of urbanization, air quality would keep improving steadily in 71.4% of the “2 + 26” cities.
... In addition, during the calcination process, Bi 3+ easily combines with O 2 to form Bi 2 O 3 (Ren et al., 2015). Therefore, p-type semiconductor Bi 2 O 3 and n-type semiconductor TiO 2 are selected to construct heterojunction, which is helpful for the effective separation of photogenerated carriers and the improvement of photocatalytic activity (Meda et al., 2022;You et al., 2021). ...
The p-n heterojunction Bi2O3/TiO2 catalysts with different mass ratios of Bi2O3 were prepared by the sol–gel method. Under simulated solar irradiation, the photocatalytic degradation effects of Bi2O3, TiO2, and p-n heterojunction Bi2O3/TiO2 on acid red 18 (AR18) were evaluated. The characterizations show that the diffraction peaks were all anatase phase and Bi2O3 was evenly distributed on the surface of TiO2. With the increase of Bi2O3 content, the band gap of the composites gradually decreased. When the dosage of catalyst (Bi2O3 mass ratio was 10%) was 0.5 g/L and the initial concentration of dye was 50 mg/L, the photocatalytic experiment was carried out under a xenon lamp (500 W), the p-n heterojunction formed by Bi2O3 and TiO2 improved the performance of the photocatalyst and showed good catalytic performance under acidic conditions. Compared with TiO2 and Bi2O3, when the mass ratio of Bi2O3 was 10%, the photocatalytic degradation performance of the material was the best, and the degradation rate of AR18 could reach 99.76% after 210 min illumination.
... Comparing the positions of the composite peaks, it can be seen that the C 1s orbitals in ZnO-C have electrons, loss of electrons in C 1s orbitals in MnO2. It can be seen from the high-resolution diagram e of O 1s that ZnO-C is in the O 1s peak at 529.98 eV and 531.48 eV, MnO2 is in the O 1s peak at 529.28 eV, 530.88 eV, 531.9 eV, and ZnO-C/MnO2 is in the O2 − [45] at 529.38 eV, 531 eV, and 532.8 eV. Figure 5b is a high resolution XPS map of Zn 2p. The binding energies of ZnO-C at 1021.28 eV and 1044.58 ...
Unlike many studies on the preparation of Z-scheme heterojunctions by doping precious metals, in this paper we first prepared a core-shell material obtained by C doping in ZnO and then composite with MnO2 to form a heterojunction; that is, a low-cost and highly catalytic ternary composite catalyst was prepared by a simple hydrothermal reaction. Meanwhile, a large amount of experimental data have enabled the heterostructure type as well as the mechanism of photocatalytic performance to be fully demonstrated. It is proven that C as an intermediate medium achieves electron transport while making up the deficiency of ZnO, and constitutes an all-solid state Z-scheme heterojunction, which enables the rapid transfer of photogenerated electron pairs and visible light irradiation to the stream to improve the photocatalytic performance of the composite photocatalyst. In terms of examination of degradation performance, this catalyst showed a high photodegradation rate of tetracycline hydrochloride (TC) of 92.6% within 60 min, and the surface ZnO-C/MnO2 catalysts also showed good degradation effect on practical petrochemical wastewater in CODcr degradation experiments.
... The mixing of TiO2 with construction materials such as cement could lower the air pollutant concentrations [221]. TiO2-based photocatalysts can also be applied as coatings on the interiors of buildings to improve air quality [222]. ...
TiO2 is seen as a low cost, well-known photocatalyst; nevertheless, its sluggish charge kinetics does limit its applications. To overcome this aspect, one of the recent approaches is the use of its composites with graphene to enhance its photoactivity. Graphene-based materials (nanosheets, quantum dots, etc.) allow for attachment with TiO2 nanostructures, resulting in synergistic properties and thus increasing the functionality of the resulting composite. The current review aims to present the marked progress recently achieved in the use of TiO2/graphene composites in the field of photocatalysis. In this respect, we highlight the progress and insights in TiO2 and graphene composites in photocatalysis, including the basic mechanism of photocatalysis, the possible design strategies of the composites and an overview of how to characterize the graphene in the mixed composites. The use of composites in photocatalysis has also been reviewed, in which the recent literature has opened up more questions related to the reliability, potential, repeatability and connection of photocatalytic mechanisms with the resulting composites. TiO2/graphene-based composites can be a green light in the future of photocatalysis, targeting pollution remediation, energy generation, etc.
... The important issue in the photocatalytic process is providing sufficient semiconductor to that antibiotics can be effectively destroyed by sunlight [14,15]. In recent years, various transition metalbased semiconductors, such as zinc oxide (ZnO) [16,17], iron oxide (Fe 3 O 4 ) [18,19], titanium dioxide (TiO 2 ) [20,21], cobalt oxide (Co 3 O 4 ) [22,23], zinc sulfide (ZnS) [24], and cadmium sulfide (CdS) [25] have been prepared and applied for photocatalytic process. Among the mentioned nanostructures, cobalt oxide-based nanomaterials have been found more attention. ...
How to cite this article Mohammed H T., Alasedi K K., Ruyid R. et al.. ZnO/Co Due to the widespread use of antibiotics in geese, water contamination by antibiotics has become a major problem. Photocatalyst semiconductors can play an important role in removing these pollutants from the aquatic environment by using sunlight. In this work, ZnO/Co 3 O 4 nanocomposites as a new magnetic semiconductor is introduced to remove the antibiotics azithromycin and ciprofloxacin. First, the nanocomposite is synthesized by a simple co-precipitation method. Then, the crystalline and morphological properties of the prepared nanocomposite are identified by X-ray powder diffraction (XRD) and scanning electron microscope (SEM) methods. Also, the magnetic properties of the sample are analyzed by vibrating-sample magnetometer (VSM) technique. Because the photocatalytic properties of semiconductors directly depend on their optical properties and energy gap, the optical properties of the prepared nanocomposite are fully studied by the UV method. Photocatalytic results showed that the prepared nanocomposite could significantly remove antibiotics from the wastewater. The prepared nanocomposite degraded 84.5 % and 71.7% of ciprofloxacin and azithromycin in 80 minutes under visible light respectively. 504 H. T. Mohammed et al. / Photocatalytic Activity of ZnO/Co 3 O 4 Nanocomposites J Nanostruct 12(3): 503-509, Summer 2022
Uncontrolled urbanisation and continued population growth are increasing air pollution levels and the burden of chronic respiratory diseases. The transport sector is responsible for a quarter of total emissions. A shift towards sustainable transport solutions is needed to reduce high concentrations of air pollutants that are harmful to human health. This review examines the role of urban planning and transport on respiratory health. A literature review was conducted on the challenges facing urban planning and urban design to reduce air pollution and prevent chronic respiratory diseases. The main search sources were via Science Direct, Pub Med and The Lancet journal, using keywords such as “sustainable urban mobility”, “urban planning”, “air pollution”, “chronic respiratory diseases”, “green infrastructure” and “15-minute city”. The recent literature shows that there are no definitive results on how the built and natural environment contributes to the worsening of chronic respiratory diseases. There are a variety of factors and parameters that interact with respiratory diseases and vary from study to study. However, the 15-minute city concept, walkable neighbourhoods and green infrastructure have been proposed for their benefits to human health and well- being. These urban planning approaches promote active mobility and reduce pollution from transport. As mentioned it is important to adhere to the strict air quality guidelines set by the World Health Organization and European Union. So, integrated policies for sustainable cities require cooperation and participation of all stakeholders in decision- making. Having a holistic approach, strategies can be implemented to mitigate the effects of air pollution aimed at health-promoting urban planning
Renewable fuel and environmental remediation are of paramount importance in today's world due to escalating concerns about climate change, pollution, and the finite nature of fossil fuels. Transitioning to sustainable...
Air pollution poses a severe health hazard in Bangladesh, contributing to approximately 173,500 deaths in 2019. This review examines the pervasive impact of PM2.5 and PM10 pollutants emanating from sources like brick kilns, vehicles, and biomass burning, surpassing safe thresholds. These pollutants are linked to widespread respiratory diseases, cardiovascular complications, and elevated mortality rates among the population. Despite regulatory efforts, persistent challenges underscore the urgent need for cleaner technologies, sustainable urban planning, and heightened public awareness campaigns. Effective global and national strategies are crucial to mitigate these health risks and foster sustainable development in Bangladesh and globally. Bangabandhu Sheikh Mujib Med. Coll. J. 2024;3(2):101-106
Till today, air pollution is one of the leading causes of global burden of diseases. According to the World Health Organization, more than 13.7 million people died in 2016 as a result of living and working in unhealthy environments. Transportation, manufacturing, construction, petroleum refining, mining, and other practices that are parts of the ongoing industrialization and urbanisation mechanisms, deplete natural resources and generate substantial amounts of hazardous wastes that pollute the air and severely affecting public health and environmental stability. In this context, stringent and comprehensive mitigation measures should be adopted which in turn results in better environment quality and improve public health circumstances. Nanotechnology is an emerging field of science which uses nanomaterials for treatment of polluted air matrices. Due to their distinctive surface characteristics, nanoscale materials have the ability to remove a variety of contaminants from the environment. This chapter will discuss about the public health and economic burden due to air pollution followed by the implications of science and technology in the form of nanotechnology to mitigate air pollution for better public health.
This chapter explores the ethical and safety dimensions of employing nanomaterials. Delving into the intricate interplay between technological advancements and responsible practices, it scrutinizes potential risks associated with nanomaterial applications. Addressing concerns regarding toxicity, environmental impact, and human health, the chapter navigates through regulatory frameworks and ethical guidelines. Emphasizing the need for transparent communication, it advocates for a balanced approach that fosters innovation while safeguarding societal well-being. The chapter serves as a comprehensive guide for researchers, policymakers, and stakeholders navigating the evolving landscape of nanotechnology, promoting a responsible and ethically sound integration of nanomaterials into diverse domains
With the advancements in nanotechnology, the interaction between nanotechnology, society and environment has increased. Nanotherapeutics and nanopharmaceuticals have allowed facilitation of earlier and more precise diagnosis, reduced side effects, improved targeted therapies and efficacy of drugs. Likewise, nanotechnology has helped in improving the quality of environment by solving issues of air pollution, water remediation and waste management with the help of nanoproducts such as nanofilters, nanophoto catalysts, nanoadsorbents and nanosensors. Moreover, nanopesticides, nanofood, anti-bacterial nanopackaging, nanofertilizers and many other products have helped food and agriculture sector to grow. There are innumerable products on shelf based on nanotechnology impacting almost every sector. However, nanotechnology like any other technology if used unchecked and unregulated can be a cause of social, environmental, legal and ethical concerns. Therefore, it is crucial to consider these challenges in addition to the promises and opportunities nanotechnology has to offer. This review has highlighted the immense importance of nanotechnology by discussing its applications especially in medicine, environmental sciences and food and agriculture sectors. Closely studying these aspects will allow us to discover gaps, obstacles and potential solutions for responsible nanotechnology development and deployment. Understanding these concerns and challenges is also critical for policymakers, researchers, industrialists and society as a whole in order to promote ethical practices and informed decision-making. This review will help to contribute to the continuing discourse and raise ethical awareness in the field of nanotechnology thence minimizing the harm while maximizing the benefits.
Offering unprecedented opportunities to revolutionize healing and healthcare, this chapter delves into the cutting-edge advancements in nanocoatings tailored specifically for medicinal applications, presenting a comprehensive overview of their potential to enhance healing processes and improve health outcomes. A major focus of this chapter is on the multifaceted roles of nanocoatings in medicinal contexts. These include drug delivery systems, wound healing, antimicrobial coatings, and tissue engineering scaffolds, among others. Furthermore, it discusses the challenges and regulatory considerations associated with the integration of nanocoatings into clinical practice. By exploring the latest research findings, this chapter provides valuable insights into how nanocoatings are poised to transform the landscape of medicinal applications. It underscores their potential to revolutionize healing processes, mitigate health-related challenges, and pave the way for a healthier future.
Coatings provide underlying item surfaces or bulk materials with protection, enhancement, and/or additional usefulness and attributes. Since materials can be modified or enhanced to possess different properties such as mechanical, thermal, or chemical to improve urban built environment functions, nanotechnologies have been widely included in functional coatings in recent years. Recent studies on functional coatings for green and smart buildings are summarized in this review paper. These comprised phase change materials, photocatalytic, hydrophilic, hydrophobic, solar reduction, and solar utilization coatings. This study offers a thorough overview of functional coating methods, from the production of raw materials through their application to building components.
Herein, the synthesis, characterization, and reduction properties of 2D TiO2 aerogel powder decorated with BiVO4 (TiO2/BiVO4) were investigated for versatile applications. First, 2D TiO2 was prepared via lyophilization and subsequently modified with BiVO4 using a wet impregnation method. The morphology, structure, composition, and optical properties were evaluated using transmission electron microscopy (TEM), X-ray diffractometry (XRD), laser-induced breakdown spectroscopy (LIBS), and diffuse reflectance spectroscopy (DRS), respectively. Significantly enhanced photocurrent densities (by 3–15 times) were obtained for TiO2/BiVO4 compared to those of pure TiO2 and BiVO4. The reduction of toxic Cr(VI) to Cr(III) was assessed, including the effect of pH on overall photocatalytic efficiency. Under acidic conditions (pH ∼ 2), Cr(VI) reduction efficiency reached 100% within 2 h. For photocatalytic CO2 reduction, the highest yields of CH4 and CO were obtained using TiO2/BiVO4. A higher efficiency for both applications was achieved because of the better separation of the electron-hole pairs in TiO2/BiVO4. The excellent stability of TiO2/BiVO4 over repeated runs highlights its potential for use in versatile environmental applications. The efficiency of TiO2/BiVO4 is due to the interplay of the structure, morphology, composition, and photoelectrochemical properties that favour the material for the presented herein photocatalytic applications.
The widespread use of organic dyes in industrial applications consistently endangers the eco-system health. The photocatalytic degradation of organic wastewater has been recognized as a highly promising strategy for combating this environmental issue. Herein, A series of bimetallic Co²⁺Cr³⁺LDH anchored AgCl as excellent solar-light-responsive Ag-decorated staggered nano-heterojunctions were constructed using a facile sono-precipitation method and their performance toward degradation of various azo dyes were investigated. Ag-AgCl-CoCrLDH(3:1)-PU exhibited excellent photocatalytic activity by degrading acid orange 7, eosin Y, rhodamine B, methylene blue, and methyl orange with respective efficiencies of 100.0, 98.4, 94.0, 88.7, and 86.2%. The photocatalyst characteristics were determined using XRD, FESEM, TEM, EDX, BET-BJH, FTIR, and UV-vis DRS techniques. The DRS analysis of Ag-AgCl-CoCrLDH(3:1)-PU photocatalyst (Eg = 2.37 eV) revealed that the introducing of LDH in the heterostructure, along with the SPR effect of Ag particles, increased the visible light absorption capacity. Furthermore, the staggered band gap accelerated charge carrier transformation, resulting in a lower recombination rate. Based on the BET-BJH results, integration of LDH combined with ultrasound irradiation increased the SBET and pore volume (Vp) to 19.5 m²/g and 0.052 cm³/g, respectively (compared to bare Ag-AgCl-PU with SBET and Vp of 3.4 m²/g and 0.004 cm³/g, and non-sonicated Ag-AgCl-CoCrLDH(3:1)-P with SBET and Vp of 16.8 m²/g and 0.016 cm³/g). The FESEM and TEM images clearly displayed the significant influence of sonication on well dispersion and de-agglomeration of nanoparticles. Subsequently, the reusability of nanophotocatalyst was examined, and a possible degradation mechanism was suggested.
Preparation of TiO2 nanoparticles (NPs) and X-ray diffraction (XRD).and scanning electron microscopy (SEM) analysis of the nanoparticles. The synthesis of TiO2 nanoparticles was carried out consuming the sol-gel and direct precipitation methods. The TiO2 nanoparticles were calcined for 2 hours at temperatures of 200°C. X-Ray diffraction.(XRD) and scanning electronic microscopy were used to explore the structural, morphological, and chemical aspects of produced TiO2 nanoparticles in the second half (SEM). The range of 90 nm, the average crystallite sizes and particle sizes of catalyst nanoparticles were estimated. In this example, however, the crystallite size as determined by particle size was 50 nm. The structural analysis of TiO2 nanoparticles using XRD patterns revealed that anatase is the predominant phase and mixed phases are present in all of them.
Reasonable design of efficient hierarchical photocatalysts has gained significant attention. Herein, a step‐scheme (S‐scheme) core‐shell TiO2@ZnIn2S4 heterojunction is designed for photocatalytic CO2 reduction. The optimized sample exhibits much higher CO2 photoreduction conversion rates (the sum yield of CO, CH3OH, and CH4) than the blank control, i.e., ZnIn2S4 and TiO2. The improved photocatalytic performance can be attributed to the inhibited recombination of photogenerated charge carriers induced by S‐scheme heterojunction. The improvement is also attributed to the large specific surface areas and abundant active sites. Meanwhile, S‐scheme photogenerated charge transfer mechanism is testified by in situ irradiated X‐ray photoelectron spectroscopy, work function calculation, and electron paramagnetic resonance measurements. This work provides an effective strategy for designing highly efficient heterojunction photocatalysts for conversion of solar fuels.
Inspired by natural photosynthesis, constructing inorganic/organic heterojunctions is regarded as an effective strategy to design high‐efficiency photocatalysts. Herein, a step (S)‐scheme heterojunction photocatalyst is prepared by in situ growth of an inorganic semiconductor firmly on an organic semiconductor. A new pyrene‐based conjugated polymer, pyrene‐alt‐triphenylamine (PT), is synthesized via the typical Suzuki–Miyaura reactions, and then employed as a substrate to anchor CdS nanocrystals. The optimized CdS/PT composite, coupling 2 wt% PT with CdS, exhibits a robust H2 evolution rate of 9.28 mmol h−1 g−1 with continuous release of H2 bubbles, as well as a high apparent quantum efficiency of 24.3%, which is ≈8 times that of pure CdS. The S‐scheme charge transfer mechanism between PT and CdS, is systematically demonstrated by photoirradiated Kelvin probe measurement and in situ irradiated X‐ray photoelectron spectroscopy analyses. This work provides a protocol for preparing specific S‐scheme heterojunction photocatalysts on the basis of inorganic/organic coupling. The construction of a CdS/PT inorganic/organic S‐scheme heterojunction not only leads to efficient charge separation and transfer, but also increased redox ability and enhanced stability for photocatalytic hydrogen evolution.
Exploring photocatalysts to promote CO2 photoreduction into solar fuels is of great significance. We develop TiO2/perovskite (CsPbBr3) S-scheme heterojunctions synthesized by a facile electrostatic-driven self-assembling approach. Density functional theory calculation combined with experimental studies proves the electron transfer from CsPbBr3 quantum dots (QDs) to TiO2, resulting in the construction of internal electric field (IEF) directing from CsPbBr3 to TiO2 upon hybridization. The IEF drives the photoexcited electrons in TiO2 to CsPbBr3 upon light irradiation as revealed by in-situ X-ray photoelectron spectroscopy analysis, suggesting the formation of an S-scheme heterojunction in the TiO2/CsPbBr3 nanohybrids which greatly promotes the separation of electron-hole pairs to foster efficient CO2 photoreduction. The hybrid nanofibers unveil a higher CO2-reduction rate (9.02 μmol g-1 h-1) comparing with pristine TiO2 nanofibers (4.68 μmol g-1 h-1). Isotope (13CO2) tracer results confirm that the reduction products originate from CO2 source.
The NOx degradation performance of nano-TiO2 as a coating material for the road environment was evaluated in this research. The nano-TiO2 coating materials for both road surface and roadside were prepared by using anatase nano-TiO2, activated carbon powder, silane coupling agent and deionized water. The impact of varying amounts of coating material and silane coupling agent were evaluated. The road environment of NOx degradation was simulated by the photocatalytic test system designed by the research team. For the road surface coating, the photocatalytic degradation experiments of NO under different radiation intensities were carried out. The results show that the material has good photocatalytic degradation performance, and the proper amount of silane coupling agent can enhance the bonding performance of the material and asphalt mixture. For the roadside coating, sodium dodecylbenzene sulfonate was selected as the surfactant to carry out the photocatalytic degradation experiment of NO2 with different dosages of surfactant. The results showed that when the mass ratio of nano-TiO2 and surfactant was about 1:2, the catalytic degradation effect of the material was the best.
The photocatalytic mixed crystal nano-TiO2 particles were incorporated with concrete by means of the internal doping method (IDM) and spraying method (SPM) in this paper. To evaluate the photocatalytic degradation efficiency of mixed crystal nano-TiO2 concrete, the methyl orange (MO) was chosen to simulate pollutants. The physicochemical characteristics and photocatalytic performance of mixed crystal nano-TiO2 concrete prepared by above two different methods were experimentally investigated under UV irradiation and solar irradiation. Furthermore, the effects of two key influential factors including pollutant concentration and irradiation condition were also analyzed and discussed. Experimental results indicate that the nano-TiO2 concrete prepared by the spraying method (SPM) exhibits maximum photocatalytic degradation efficiency of 73.82% when the sprayed nano-TiO2 slurry concentration is 10mg/L. The photocatalytic degradation efficiency of unpolished nano-TiO2 concrete is much higher than that of polished nano-TiO2 concrete under the same exposure time of UV irradiation. Moreover, the photocatalytic degradation efficiency of nano-TiO2 concrete decreases with the increase of pollutant concentration. The irradiation condition has an obvious influence on the photocatalytic degradation efficiency of nano-TiO2 concrete. In the aspect of applications, the practical recommendations for the nano-TiO2 concrete with self-cleaning capacity were presented according to the experimental results.
Nitric oxide generated from various sources like car combustion is one of the most surrounding pollutants. Titanium dioxide considered an environmentally friendly active photocatalytics that can be used with building materials safely and effectively to react with nitric oxides in the presence of UV radiation from sunlight.
To study the possibility for the reduction of air pollutants two strategies were adopted. First one included mixing of micro particles of TiO2 with cement paste in two percentages: 3% and 6%. In the second one mortar substrates were coated with micro TiO 2 (mT) aqueous solution by either dipping or spraying coating method. A laboratory test procedure was adopted to assess the performance of the prepared photoactive specimens. The specimens were subjected to NO gas and there efficiency in gas removal was monitored with time.
Results showed that coating strategy was more effective than mixing strategy in term of gaseous pollutants removal. The comparison between the two coating methods showed that the dipping method reached 98.08 % removal capacity and was better than spring method which reached 87.69 % only.
In spite of their positive role in the framework of circular economy, waste-to-energy processes are responsible for the emissions of a large number of air pollutants. Although this sector has made significant improvements in the air pollution control of primary emissions, the role of other sources (i.e. secondary emissions) has been often neglected. This paper aims at investigating the contributions of primary and secondary emissions expected from a waste gasification plant that is planned for the construction in an Alpine valley. The results from this analysis show that secondary emissions would play a significant role in the overall emissive footprint of the plant, contributing to 29% and 10%, respectively, of the overall emissions of dusts and total organic carbon. In the light of such results, secondary emissions would require an appropriate monitoring approach, which should complement the existing monitoring protocols for primary emissions.
To alleviate the heavy burden on landfilling, construction and demolition wastes (C&DWs) are recycled and reused as aggregates in cementitious materials. However, the inherent characteristics of recycled fine aggregates (RFA), such as the high crushing index and high-water absorption, magnify the reusing difficulty. Nevertheless, attributing to the high porosity and high level of calcium hydroxides existing in the old mortar, RFA is featured with a high specific surface area and a high alkalinity. These features are useful to augment the total photo-degradation of SO2 by nano-TiO2 (NT) intermixed mortar, leading RFA to be an excellent potential carrier to load nano-TiO2 and prepare the composite photocatalyst. Hence, this study proposed to load NT onto the surface of RFAs and river sands (RSs) (the control) by the soaking method, preparing composite photocatalysts denoted as NT@RFA and NT@RS, respectively. The prepared composite photocatalysts were then utilized as sands in photocatalytic mortar to evaluate for SO2 degradation. Experiments identified a 50% higher amount of NT was loaded onto the surface of FRA relative to the control. This higher loading amount plus higher alkalinity ultimately translated into a higher photocatalytic activity. In addition, the mortar containing NT@RFA exhibited 46.3% higher physiochemical absorption and 23.9% higher photocatalytic activity than that containing NT@RS. In addition, the durability, embodied by the reuse and anti-abrasive properties, of NT@RFA exceeded that of NT@RS. The overall findings reveal that the NT@RFA not only garners beneficial effect from the high porosity but also generates positive effect from the high alkalinity. Though a number of studies deal with building materials with NT, this study is the first to load NT onto RFA and prepare composite photocatalysts which were then used as fine aggregates in building materials. Consequently, this study proves the potential high-added-value reusability of RFA in green construction materials and provides a low-cost, high-efficiency approach to degrade atmospheric SO2.
Applications of heterogeneous photocatalytic processes based on semiconductor particles in cement-based materials have received great attention in recent years in enhancing the aesthetic durability of buildings and reducing global environmental pollution. Amongst all, titanium dioxide (TiO2) is the most widely used semiconductor particle in structural materials with photocatalytic activity because of its low cost, chemically stable nature, and absence of toxicity. Utilization of TiO2 in combination with cement-based materials would plunge the concentration of urban pollutants such as NOx. In fact, cementitious composites containing TiO2 have already found applications in self-cleaning buildings, antimicrobial surfaces, and air-purifying structures. This paper aims to present a comprehensive review on TiO2-based photocatalysis cement technology, its practical applications, and research gaps for further progression of cementitious materials with photocatalytic activity.
Nanoparticles are defined as ultrafine particles sized between 1 and 100 nanometres in diameter. In recent decades, there has been wide scientific research on the various uses of nanoparticles in construction, electronics, manufacturing, cosmetics, and medicine. The advantages of using nanoparticles in construction are immense, promising extraordinary physical and chemical properties for modified construction materials. Among the many different types of nanoparticles, titanium dioxide, carbon nanotubes, silica, copper, clay, and aluminium oxide are the most widely used nanoparticles in the construction sector. The promise of nanoparticles as observed in construction is reflected in other adoptive industries, driving the growth in demand and production quantity at an exorbitant rate. The objective of this study was to analyse the use of nanoparticles within the construction industry to exemplify the benefits of nanoparticle applications and to address the short-term and long-term effects of nanoparticles on the environment and human health within the microcosm of industry so that the findings may be generalised. The benefits of nanoparticle utilisation are demonstrated through specific applications in common materials, particularly in normal concrete, asphalt concrete, bricks, timber, and steel. In addition, the paper addresses the potential benefits and safety barriers for using nanomaterials, with consideration given to key areas of knowledge associated with exposure to nanoparticles that may have implications for health and environmental safety. The field of nanotechnology is considered rather young compared to established industries, thus limiting the time for research and risk analysis. Nevertheless, it is pertinent that research and regulation precede the widespread adoption of potentially harmful particles to mitigate undue risk.
Photocatalysis is a multifunctional phenomenon that can be employed for energy applications such as H2 production, CO2 reduction into fuels, and environmental applications such as pollutant degradations, antibacterial disinfection, etc. In this direction, it is not an exaggerated fact that TiO2 is blooming in the field of photocatalysis, which is largely explored for various photocatalytic applications. The deeper understanding of TiO2 photocatalysis has led to the design of new photocatalytic materials with multiple functionalities. Accordingly, this paper exclusively reviews the recent developments in the modification of TiO2 photocatalyst towards the understanding of its photocatalytic mechanisms. These modifications generally involve the physical and chemical changes in TiO2 such as anisotropic structuring and integration with other metal oxides, plasmonic materials, carbon-based materials, etc. Such modifications essentially lead to the changes in the energy structure of TiO2 that largely boosts up the photocatalytic process via enhancing the band structure alignments, visible light absorption, carrier separation, and transportation in the system. For instance, the ability to align the band structure in TiO2 makes it suitable for multiple photocatalytic processes such as degradation of various pollutants, H2 production, CO2 conversion, etc. For these reasons, TiO2 can be realized as a prototypical photocatalyst, which paves ways to develop new photocatalytic materials in the field. In this context, this review paper sheds light into the emerging trends in TiO2 in terms of its modifications towards multifunctional photocatalytic applications.
The science on the anthropogenic airborne aerosols impacting the World Heritage marble monument, the Taj Mahal, at Agra, has been studied in the light of modern physico-chemical approaches. The study is an effort to understand unrecognized airborne species which were found on the surface of the Taj Mahal monument. These species have been analyzed in the light of current analytical methods to impart characterization features and their possible impacts on the surface of the marble. Chemical constituents of these substrates, which were incorporated over the top surface of the monument, have been identified. Interestingly, the carbon particulates which were found on the micro level, popularly called “particulate matters”, have now been identified in the nano domain entity, which is chemically more reactive, and have been found on the surface of the monument. Because of their high chemical activity, these nano carbons have a newer chemistry in the presence of air and sunlight, generating several reactive oxygen species (ROS). These ROS are capable of responding to complicated chemical reactions on the surface of the marble in association with deposited cyanophyceae and other deposits of plant origin, causing rapid degradation. This study provides the nature of the onslaught of such monuments exposed under the prevalent smoggy environmental scenario.
To address the increasing air pollution caused by vehicle exhaust, environment-friendly pavement materials that possesses exhaust-purifying properties were prepared using common cement concrete and porous cement concrete as the base of photocatalyst nano-titanium dioxide (TiO2), respectively. Firstly, Fe³⁺-doped TiO2 powder was prepared by applying planetary high-energy ball milling in order to improve the efficiency of the semiconductor photocatalyst for degrading vehicle exhausts. Two nano-TiO2, namely the original and modified nanomaterials, were adopted to produce the photocatalytic cement concretes subsequently. The physicochemical properties of the modified powder, as well as the mechanical and photocatalytic properties of TiO2-modified concrete, were characterized using a suite of complementary techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), compressive strength and degradation efficiency tests. The results show that the ball milling method not only successfully doped Fe³⁺ into catalysts but also caused significant changes in: (1) decreased particle sizes, (2) more amorphous morphology, (3) decreased percentage of the most thermodynamically stable crystal facet, and (4) increased percentage of other high gas sensing crystal facets. Both the original and modified nano-TiO2 can improve the concrete strength while the strengthening effect of modified nanomaterials is superior. It is pronounced that the photocatalytic property of the modified nano-TiO2 is much better than that of the original nano particles, and the degradation rate of porous concrete is also better than common concrete when exposed to the same photocatalyst content. In a comprehensive consideration of both mechanical performance and degradation efficiency, the recommended optimum dosage of TiO2 is 3% to 4% for exhaust-purifying concrete.
In this study, mortar specimens were prepared with a cement:sand:water ratio of 1:3:0.5, in accordance with standard EN196-1. Portland CEM I 52.5 R grey (G) and white (W) cements were used, together with normalised sand and distilled water. Different amounts of TiO2 photocatalyst were incorporated in the preparation of the mortar samples. The effect of the addition of TiO2 was studied on mechanical properties of the mortar and cement including compressive and flexural strength, consistency (the flow table test), setting time and carbonation. Characterization techniques, including thermogravimetry, mercury porosimetry and X-ray diffraction spectroscopy (XRD), were applied to study the physico-chemical properties of the mortars. It was shown that adding the photocatalyst to the mortar had no negative effect on its properties and could be used to accelerate the setting process. Specimen photoactivity with the incorporated photocatalyst was tested for NOx oxidation in different conditions of humidity (0% RH and 65% RH) and illumination (Vis or Vis/UV), with the results showing an important activity even under Vis radiation.
Due to the anthropogenic pollution, especially the environmental crisis caused by air pollutants, the development of air pollutant degradation photocatalyst has become one of the major directions to the crisis relief. Among them, titania (titanium dioxide, TiO2) family materials were extensively studied in the past two decades due to their strong activity in the photocatalytic reactions. However, TiO2 had a drawback of large bandgap which limited its applications, several modification techniques were hence developed to enhance its catalytic activity and light sensitivity. In recent years, other metal oxide based materials have been developed as replacements for TiO2 photocatalysts. In this review, background information and developments from pure TiO2 to chemically modified TiO2-based materials as photocatalysts were discussed in detail, which covered their basic properties and their role in the air pollutant removal. It also proposes to solve the shortcomings of TiO2 by developing other metal oxide-based materials and predict the future development of TiO2 materials in future environmental applications. Keywords: TiO2, Photocatalyst, Doping, Photocatalytic oxidation, Air pollutant, VOCs
This article reviews the efforts of the last two decades to deNOxify the atmospheric environment with TiO2-based photocatalytic materials supported on various cementitious-like substrates. Prior to undertaking this important aspect of applied photocatalysis with metal-oxide emiconductor photocatalysts, however, it is pertinent to describe and understand the fundamentals of Heterogeneous Photocatalysis. The many attempts done in a laboratory setting to degrade (deNOxify) the major components that make up the NOx, namely nitric oxide (NO) and nitrogen dioxide (NO2), but most importantly the efforts expended in deNOxifying the real environment upon depositing titania-based coatings on various model and authentic infrastructures, such as urban roads, highway noise barriers, tunnels, and building external walls among others, are examined. Both laboratory and outdoor experimentations have been performed toward NOx being oxidized to form nitrates (NO3−) that remain adsorbed on the TiO2-based photocatalytic surfaces (except in tunnels—indoor walls) but get subsequently dislodged by rain or by periodic washings of the infrastructures. However, no serious considerations have been given to the possible conversion of NOx via photocatalytic reduction back to N2 and O2 gases that would restore the atmospheric environment, as the adsorbed nitrates block the surface-active sites of the photocatalyst and when washed-off ultimately cause unduly damages to the environment.
Titanium dioxide has been widely studied for its ability to photocatalytic and applications have high performance for photovoltaic applications. In this paper TiO2 nanoparticle was investigated for the degradation of methylene blue under UV light in various pH condition. The TiO2 nanoparticle was characterized by SEM and XRD. The results showed that TiO2 nanoparticle has the structure of anatase and have a particle size of 27 nm. The photocatalytic activity of TiO2 nanoparticle show that the degradation of methylene blue under UV light have dye removal of 97% dye was degraded in 3 h, but the degradation of methylene blue without UV light have dye removal of 15% dye was degraded in 3 h. It indicated that The photocatalytic activity of TiO2 nanoparticle could occur if there the UV light. If not UV light the photocatalytic activity cannot occurs, the degradation of Methylene Blue 15% is not a photocatalytic activity but it is adsorption of Methylene Blue by TiO2 nanoparticle. The photocatalytic activity of TiO2 nanoparticle has pH-sensitive. The photocatalytic activity of TiO2 nanoparticle in acid condition (pH 4.1) is 40%, in neutral condition (pH 7.0) is 90%, and in base condition (pH 9.7) is 97%. The highest photocatalytic activity occurs in base condition, it causes in base condition OH- can be direct reaction with a hole to produce hydroxyl radical (OH*).
The application of photocatalysts in concrete technology is by now a well-established concept. However, despite the great opportunities for air quality improvements to be derived from the considerable concrete surfaces exposed to the atmosphere, particularly in cities where air quality is greatly affected by vehicle exhaust and industrial emissions, photocatalytic concretes are still not in mainstream application. With current levels of NOx pollution considerably exceeding EU legislative guidelines in urban centres throughout the industrialised world, it is important to consider what the issues are. The likely barriers to more widespread implementation are likely to include cost effectiveness, which needs to be related to photocatalyst impact, but the challenges in measuring impact on air quality directly are complex. This paper seeks to place photocatalytic efficiencies into context, comparing performances of the conventional photocatalyst dispersion in surface mortar coatings with that of photocatalysts supported on surface exposed aggregates. The nature and impact of catalyst binding to the aggregate is also discussed.
Photocatalytic CO2 conversion into solar fuels has been a promising strategy to utilize abundant solar energy and alleviate greenhouse effect. Herein, a series of polydopamine-modified TiO2 (TiO2@PDA) hollow spheres were fabricated by in situ self-polymerization of dopamine to systematically investigate the effect of PDA wrapping on the photocatalytic CO2 reduction activities of TiO2. Among all TiO2@PDA composite photocatalysts, the highest value of methane yield (1.50 μmol h⁻¹ g⁻¹) was achieved with 0.5% PDA, which was 5 times than that of pure TiO2 (0.30 μmol h⁻¹ g⁻¹). The improvement of photocatalytic activity and methane selectivity was ascribed to the enhanced light absorption, promoted CO2 adsorption capacity, increased reduction power of photogenerated electrons, as well as efficient separation and transfer of photogenerated charge carriers induced by the S-scheme heterojunction between TiO2 and PDA. This work provides a facile surface modification method with cost-effective polymer materials in photocatalytic CO2 conversion.
This work deals with the photocatalytic degradation of NOx gases by cement mortars with variable nano-TiO2 concentrations and at different environmental conditions (flow rate, UV-A radiation and relative humidity). The TiO2-added mortar samples were kept in controlled room at 25±2 °C and RH of 60±5% for 2 years to assure complete cement hydration. Moreover, fresh and hardened state properties were also evaluated. In fresh state, the higher the amount of nano-TiO2 in the mix, the lower the workability of the mortar. For flexural strength, there was a small increase in the values, but not enough to indicate a change in the performance of the mechanical properties of the mortars. In photocatalytic tests, results showed that the higher the NOx flow rate, the lower was the performance on NOx degradation and the higher was the degradation rate. Efficiency values up to 80% NOx degradation were verified in the experiments. When the relative humidity was raised, NOx degradation efficiency and rate decreased. Finally, for higher UV-A radiation intensity, the photocatalysis efficiency is enhanced. Even being statistically significant, the nano-TiO2 concentration in the cement mortars was less influent on the photocatalysis reaction when compared to environmental conditions.
The significance of photocatalysts is unquestionable, and scientists are devoted to improving their photocatalytic efficiency. To solve the high recombination rates of photogenerated electron-hole pairs and their low reduction and oxidation abilities in a single photocatalyst, heterojunction manipulation is urgently required. Two mainstream heterojunctions—type-II and Z-scheme heterojunctions—have been widely acknowledged. However, we soberly reflect the charge-transfer mechanism from many perspectives and are finally aware of the fundamental challenges they face. To ensure a correct understanding, it is necessary to share our analysis with others. Moreover, step-scheme (S-scheme) heterojunctions, consisting of a reduction photocatalyst and an oxidation photocatalyst with staggered band structure, are introduced to avoid misinterpretation. The differences in the charge-transfer mechanism between S-scheme, type-II, and Z-scheme heterojunctions are highlighted. Finally, limitations and the future research direction of S-scheme photocatalysts are discussed.
Titanium dioxide (TiO2) has been used in building materials to produce products that do not require major maintenance and also contribute to improve air quality and extend the life of buildings. Thus, this research evaluated the effects of incorporation of this substance into cement mortars in the process of degradation of sulfur dioxide (SO 2), one of the largest atmospheric pollutants. Mortars were developed at a weight ratio of 1:3 (cement: sand), incorporating 2.5%, 5%, 7.5% and 10% of TiO 2 relative to the cement weight. Mortars were evaluated in their fresh state (consistency and bulk density) and hardened (dry bulk density, water absorption by capillarity, open porosity and flexural and compressive strength). The samples were exposed to an accelerated aging SO 2 (pollutant) chamber, then moistened and exposed to ultraviolet radiation. For this exposure of the samples, two Light Emitter Diodes (LEDs) with wavelengths covering the UV-A range were used: UV (380-420 nm) and blue (420-493 nm). Fourier Transform Infrared measurements were also performed in three stages, which were: (1) before contamination , (2) after SO 2 contamination and (3) after radiation exposure. The nano TiO 2 incorporation in the mortars contributed to the increase in open porosity and favored the increase in dry bulk density of mortars this was due to the filler effect. In addition, there was an increase in both the compressive strength and the flexural strength for mortars with addition, compared with the reference mortar. It can be concluded that the incorporation of TiO 2 improved the physical, mechanical and photocatalytic properties, and enabled the decontamination of mortars due to the action of the SO 2 pollutant.
The photocatalytic degradation of trichloroethylene and nitric oxide (model volatile organochloride and inorganic compounds) by two commercial TiO2-based cementitious materials at the laboratory scale was studied. TiO2 P25 was selected as the benchmark photocatalyst. The materials were characterized by N2 adsorption–desorption, TGA, SEM–EDX, and XRD, and the hydrophobic/hydrophilic nature of the cement surface was determined through contact angle measurements. Preliminary photoactivity tests in which a glass plate was covered with photocatalytic material were performed. Moreover, the photocatalytic activities of asphalt plates (approximately 1 cm thick) covered with either of the photoactive cementitious materials were also evaluated. A notable improvement in the photocatalytic activity from the first to the second photocatalytic run was observed because sample conditioning with airflow and UV-A irradiation led to the elimination of species (carbonates) that were adsorbed at active TiO2 sites, ensuring stability under operating conditions. The cementitious samples completely photooxidized the organochloride compound but presented reduced photoefficiency for nitric oxide oxidation. The results obtained when the materials were deposited on glass and asphalt showed the crucial influences of the sample loading and the nature of the substrate on nitric oxide photooxidation. Using TiO2 P25 led to the complete conversion of nitric oxide but also to the formation of a large amount of nitrogen dioxide. On the other hand, one of the photoactive asphalts exhibited a nitric oxide conversion rate of 32%, which was lower than that achieved with pure TiO2-P25, but using this material did not lead to the release of nitrogen dioxide. When tested according to the ISO 22197-1:2007 standard, the selected photocatalytic asphalt removed 29% of the NO and 22% of the NOx under more demanding operating conditions.
Herein, two-dimensional (2D) TiO2 mesoporous nanosheets with three to four C3N4 layers grown in situ are employed to design a core–shell 2D/2D van der Waals heterojunction (TiO2/C3N4). Edge-terminated zero-dimensional (0D) Ti3C2 MXene quantum dots (TCQD) are subsequently integrated in the C3N4 surface via electrostatic interactions. The constructed 2D/2D/0D TiO2/C3N4/Ti3C2 composite heterojunction photocatalyst exhibits enhanced CO2 reduction activity compared to TiO2, C3N4, TiO2/C3N4, C3N4/Ti3C2 for CO and CH4 production. A step-scheme (S-scheme) charge transfer mechanism operates for the prepared samples during CO2 reduction, as authenticated by in situ X-ray photoelectron spectroscopy and electron paramagnetic resonance analysis. This study provides a paradigm of a rational structural design for regulating the number and type of heterointerfaces and further insights into the mechanism of multijunction photocatalysts.
Titanium dioxide (TiO2) has been the semiconductor most used in photocatalytic pavement due to its chemical and physical properties. However, the use of zinc oxide (ZnO) as an alternative material to TiO2 has gained ground in the scenario of heterogeneous photocatalysis, mainly for aqueous medium. This nano-product has characteristics suitable for application in advanced oxidative processes, in addition to having lower market cost compared to TiO2. This study presents the results of the efficiency of NOx degradation of concrete blocks produced with ZnO under different environmental conditions. A comparison of the efficiency of ZnO with TiO2 was also performed, resulting in mathematical models of the photocatalytic cost/performance of nanomaterials. The results showed that ZnO presents lower efficiency when compared to TiO2, being less susceptible to flow rate and more sensitive to UV-A radiation. The application of ZnO as photocatalyst in pavement is only feasible when the market price of ZnO is much lower than that of TiO2.
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.
The use of titanium dioxide (TiO2) photocatalytic nanoparticles as road coating to trap and decompose air pollutants provides a promising technology to mitigate the harmful effects of vehicle emissions. However, there are few studies on computational fluid dynamics (CFD) simulations of the effect of NOx photocatalytic oxidation in street canyon with TiO2 nanoparticles as pavement coating. This study develop a CFD model with photocatalytic oxidation (PCO) reaction implemented for numerical simulation of NOx abatement in an urban street canyon with TiO2 coating, considering the effects of relative humidity (RH) (10–90%), and irradiance (10–40W ⋅ m⁻²). Results show that TiO2 coating road can effectively reduce nitrogen oxide (NOx) concentration in the street canyon. The average nitric oxide (NO) and nitrogen dioxide (NO2) concentrations in street canyon with TiO2 coating road were reduced by 3.70% and 4.31%, respectively, comparing with street canyon without TiO2 coating. The irradiance and relative humidity had great effect on PCO reaction in street canyon with TiO2 coating road. When the irradiance increased from 10W ⋅ m⁻² to 40W ⋅ m⁻², average NO conversion rose from 1.35% to 3.70%, and average NO2 conversion rose from 2.43% to 4.31%. The average conversion of NO and NO2 decreased from 5.11% to 2.54% and from 5.60% to 3.25%, respectively, when the relative humidity is varied from 10% to 90%. Results are useful to transport planners and road engineers who need to reduce NOx concentrations in urban streets travelled by fossil fuel-powered vehicles. Method of the study can be considered by future research faced with different pavement construction and traffic environment.
Titanium dioxide (TiO2) nanoparticles have been incorporated in cementitious composites to achieve photocatalytic (PC) functions such as self-cleaning and air purifying functions. This study experimentally investigates the effect of TiO2 nanoparticles and fly ash on the nitrogen oxides (NOx) abatement rate and efficiency of Engineered Cementitious Composites (ECC) that has retained strain-hardening properties and tensile ductility. Emphasis is placed on understanding the fundamental mechanisms through research on the microstructures and chemical environment of the composite material. A first-order chemical reaction model is applied to analyze the PC reaction rate and residual NOx concentration. Test results indicate that the PC reaction rate and efficiency increase with the TiO2 content from 0 to 5%, and the fly ash to cement ratio from 0 to 2.2. Using the low-calcium fly ash further increases the PC reaction rate and efficiency. The microstructure change originated from different fly ash contents and types are closely related to PC efficiency changes. This study advances the fundamental knowledge for engineering the cementitious composites to achieve the optimal PC functions.
Nanoparticles have appeared as valuable outcomes of nanotechnology because of their unique physicochemical characteristics based on variable shape, size, and surface properties. Among transition metal oxide‐based nanoparticles, titanium dioxide (TiO2) nanoparticles have demonstrated significant potential owing to their fascinating properties and utilization in water treatment, fabrication of energy devices, soil remediation, paint and paper productions, and as additives in food and cosmetic products. In nanobiotechnology and nanomedicine, the admirable photocatalytic ability, biocompatibility, and low toxicity of TiO2 nanoparticles have been exploited for genetic and tissue engineering, manufacturing healthcare products, bioimaging, and the treatment of certain diseases such as cancer. In this chapter, we highlighted from basic to advance properties of TiO2 nanoparticles that are responsible for their usage in numerous applications as a potential candidate. The various facile techniques for the preparation of TiO2 nanoparticles are discussed in detail, which help to understand the modification strategies of these nanoparticles for practical applications. Finally, we also provided introductions to the applications of TiO2 nanoparticles in various fields including nanomedicine and nanobiotechnology.
Photocatalytic materials are potentially an effective remediation technology for indoor air purification. Here, we assess the impact of photocatalytic paint’s porosity on indoor nitrogen oxides (NOx) and nitrous acid (HONO) levels. We observed that the porosity of photocatalytic paints plays a paramount role for the NO2 removal. The increase of porosity from PVC 53 % to PVC 80 % leads to an increase of the geometric NO2 uptake coefficient from (3.3±0.5)·10-6 to (2.7±0.1)·10-5. At the same time, high quantity of HONO formed by NO2 conversion on photocatalytic paint is emitted in the air. The formation of HONO which is considered as a harmful compound and a major player in the oxidative capacity of indoor air is reduced as the paint porosity increases. Based on these results, further optimizations should be considered for future commercialization of photocatalytic paints aimed for indoor applications.
LaNiO3/TiO2 step-like composite heterojunction photocatalysts were synthesized via a facial in-situ sol‐gel method with different calcination temperatures. The crystal structure and performance of synthetic photocatalyst are characterized by X‐ray diffraction (XRD), transmission electron microscope (TEM), UV‐vis absorption spectroscopy and X-ray photoelectron spectroscopic spectroscopy (XPS). The results illustrate that binary structure of LaNiO3/TiO2 step-scheme heterojunction can be obtained at a calcination temperature of 700 °C, and it extends light‐absorption to the visible region. Moreover, the LaNiO3/TiO2 shows superior photocatalytic efficiency with respect to methyl orange (MO) degradation under visible light irradiation for 75 min, the degradation rate in MO solution of 10 mg/L and 20 mg/L are respectively 2 times and 3 times higher than pure LaNiO3. The synthetic photocatalyst also performed effective photocatalytic ability of antibiotic ciprofloxacin under visible light, and the degradation efficiency is higher than pure TiO2 and LaNiO3. Enhancement of organic degradation activity can be attributed to improvement of the electron-hole pairs separation rate caused by the formation of S-scheme heterostructure.
Two factors are key in the design of a TiO2 photocatalyst for building materials that meets the requirements for environmental applications: the TiO2 light absorption restricted to UV and its poor adhesion to the substrates. In this work, two strategies of TiO2 modification, nitrogen doping and AuNPs deposition, were combined in order to promote the TiO2 photoactivity under solar radiation. By the other hand, the Au/N–TiO2 photocatalysts were incorporated in a silica sol allowing their application by spray on three different building material substrates (limestone, granite and concrete), where the sol spontaneously produced Au/N–TiO2/SiO2 well-adhered coatings. The samples photoactivity was evaluated by dye degradation tests and NO abatement measurements. The obtained results demonstrated that the AuNPs considerably enhanced the photoactivity of N–TiO2, doubling the amount of NOx removed under UV–visible light. In addition, the role of the substrate and the TiO2/SiO2 ratio of the coating were also investigated. The coatings practically triplicated their depolluting effectiveness on concrete in comparison with their application on limestone. A direct correlation between the TiO2 loading and the photoactivity was observed, increasing NOx abatement by a factor of 1.3 when the Au/N–TiO2 loading of the coating was raised from 10 to 25%. However, the Au presence can induce evident colour modifications of the treated substrates that can limit the product application on certain substrates.
The transfer/separation of interfacial charge carriers relies heavily on the appropriate interfacial contact of heterojunction. In-situ heterojunction will be an effective way for enhancing charge transfer rate since the tight interface, which is conductive to promote the photoelectrochemical or photochemical activity. Herein, 0D/2D SnO2/SnS2 novel Step-scheme (S-scheme) heterojunctions have been successfully constructed by solvothermal method and in-situ oxidation technique through controlling the annealed temperature in N2/H2 atmosphere. The SnS2 nanosheets annealed at 400 °C (SS-400) reveals the highest photocurrent density (0.33 mA cm⁻²) at 1.23 V vs. RHE under AM 1.5G, that is approximately of 1.9 and 1.2 times than SS-300 (0.17 mA cm⁻²) and SS-500 (0.27 mA cm⁻²), respectively. The SS-400 shows the hydrogen and oxygen evolution of 5.5 and 2.7 μmol cm⁻²h⁻¹, and the corresponding faradaic efficiencies are about 89.4% and 87.7%, respectively. The mainly enhanced reason of SS-400 is that appropriate amount of 0D SnO2 nanoparticles generated on the surfaces and edges of 2D SnS2 nanosheets fabricate the in-situ of S-scheme heterojunctions, which are accelerating the recombination of carriers with relatively weaker redox capacity and promoting the separation of carriers with relatively stronger redox capacity. Meantime, the barrier factor, internal electric field, coulomb interaction, and applied bias factors can also promote the recombination of carriers with weak redox capacity (electrons of SnO2 and holes of SnS2). This work will provide a novel thought for designing and constructing the mechanism of S-scheme heterojunctions for photoelectrochemical water splitting.
Au/N-TiO2 photocatalysts with enhanced photoactivity thanks to nitrogen doping and gold nanoparticles (AuNPs) controlled deposition onto titania have been obtained bymeans of a simple and innovative one-pot synthesis promoting synergetic activity between these two approaches. The activity of the materials under study was evaluated by methylene blue and NOx degradation tests as models of environmental remediation processes for water purification and air depollution. The use of a deposition-precipitation method employing urea allows obtaining Au/N-TiO2 photocatalysts containing 0.3 at.% of nitrogen and 0.5 wt% of gold. The results obtained confirmed that the presence of both, nitrogen and AuNPs, enhanced the TiO2 photoactivity increasing the photodegradation of the dye and NOx in a factor of 4.5 and 1.7, respectively. In particular, the AuNPs enabled the photoactivity under visible light and improved substantially the selectivity of the NO degradation process.
The photocatalysts here proposed maintain their properties as they are integrated into a silica matrix producing a product with potential use for the coating of different substrates, such as building materials for application in urban areas and fabrics or foams for the photocatalytic filters production.
This study brings new understanding of the interaction of nitrogen oxides (NOx) with cement-based materials, necessary for optimizing these materials for NOx sequestration. The masses of nitrites and nitrates produced through NOx uptake in cement-based materials are quantified for both plain portland cement pastes (OPC) and nano TiO2-doped OPC. Both nitrite and nitrate were bound within plain OPC, with a nitrite:nitrate ratio of 1:2. This intrinsic NOx sequestration capacity is attributed to the microstructural features and alkalinity of cement-based materials. The capacity is increased by 360%, with a lower nitrite:nitrate ratio of 1:1.3, in TiO2-doped OPC. The increase in NOx uptake and the change in nitrite:nitrate ratio is attributed to the microstructural differences and activation of photocatalytic reactions that are associated with TiO2 addition. Comparing NO x exposure with and without UV on TiO2-doped OPC shows that photocatalytic activities have greater influences on NOx uptake than microstructural differences induced by TiO2 addition.
This research carried out the NO2 degradation performance and asphalt pavement performance of SBS modified asphalt with different content (0%, 1%, 2%, 5%, 10%) of nano-TiO2, and the impact of cationic surfactant were evaluated as well. The nano-TiO2 modified asphalt was prepared for Dynamic Shear Rheometer (DSR) test, Bending Beam Rheometer (BBR) test, Rolling Thin Film Oven Test (RTFOT) and Pressure Aging Vessel (PAV) test. And the high temperature performance, low temperature performance and aging properties were evaluated. Results show that the nano-TiO2 increased the rutting resistance of asphalt in high-temperature especially when the content increased from 0% to 1%, and it did not have a significant impact on low temperature cracking resistance. Secondly, this research developed an innovative photo-reactive and measuring system, and simulated the NO2 degradation environment based on field data of varies typical roadway sections. Then, this research conducted photo-catalytic degradation test of NO2 for asphalt mixture with 5% nano-TiO2 content. The analysis shows that there are reversible reaction between NO2 and N2O4, and results indicated that the asphalt mixture has exhibited NO2 degradation effects. This research provided a deep understanding for the road performance and engineering application of nano-TiO2 modified asphalt mixture.
The potential of TiO2-based photocatalysts in mitigating the effects of environmental pollutants is evident in the scientific literature but the large-scale implementation of photocatalytic concretes still appears limited, despite the current global concerns over urban NOx pollution. Improvements in cost-effectiveness are required to enhance the case for a photocatalyst-modified infrastructure and this must address catalyst efficiency, catalyst loading and performance durability. This paper compares photocatalytic efficiencies of supported TiO2 on mortar surfaces with the more conventional TiO2 dispersed in mortar. The influences of environmental conditions, such as NO concentration and flow rate, UVA light intensity and relative humidity, on photocatalytic performance are also investigated using photonic efficiency as an indicator. The supported TiO2 shows greater degradation of NOx (De-NOx), at about 9 times higher than TiO2 powder dispersed in the mortar, ca. 150 times higher utilization efficiency, than that of TiO2 in traditional photocatalytic mortar (with 5% loading).
The appropriate interfacial contact of heterojunction photocatalysts plays a critical role in transfer/separation of interfacial charge carriers. Design of two-dimensional (2D)/2D surface-to-surface heterojunction is an effective method for improving photocatalytic activity since greater contact area can enhance interfacial charge transfer rate. Herein, ultrathin 2D/2D WO3/g-C3N4 step-like composite heterojunction photocatalysts were fabricated by electrostatic self-assembly of ultrathin tungsten trioxide (WO3) and graphitic carbon nitride (g-C3N4) nanosheets. The ultrathin WO3 and g-C3N4 nanosheets were obtained by electrostatic-assisted ultrasonic exfoliation of bulk WO3 and a two-step thermal-etching of bulk g-C3N4, respectively. The thickness of ultrathin WO3 and g-C3N4 nanosheets are 2.5–3.5 nm, which is equivalent to 5–8 atomic or molecular layer thickness. This ultrathin layered heterojunction structure can enhance surface photocatalytic rate because photogenerated electrons and holes at heterogeneous interface more easily transfer to surface of photocatalysts. Therefore, the obtained ultrathin 2D/2D WO3/g-C3N4 step-scheme (S-scheme) heterojunction photocatalysts exhibited better H2-production activity than pure g-C3N4 and WO3 with the same loading amount of Pt as cocatalyst. The mechanism and driving force of charge transfer and separation in S-scheme heterojunction photocatalysts are investigated and discussed. This investigation will provide new insight about designing and constructing novel S-scheme heterojunction photocatalysts.
Human exposure to volatile organic compounds and NO2 can lead to health problems, therefore strategies to mitigate against the risks are required. Abatement and sensing are approaches which could both neutralise and monitor these species thus providing a safer environment and warning occupants of harmful levels. This paper presents pure TiO2 and TiO2/graphene hybrids synthesized through a sol-gel route. Electron optical, helium ion microscopy, X-ray diffraction and spectroscopic methods have been applied to elucidate the physical and chemical behaviour. NO2 sensing properties of TiO2/graphene hybrids formed by the addition of graphene to the reaction vessel prior to initiating the sol gel reaction followed by annealing (GTiO2S), and an alternative manufacturing method involving the addition of graphene to TiO2 nanoparticles which had already been annealed (GTiO2M) were compared and evaluated. A conductometric sensor based on TiO2/graphene prepared using material GTiO2S showed a higher response to NO2 compared to sensors based on pure TiO2 and TiO2/graphene prepared with material GTiO2M. Under UV irradiation generated by a low power LED, the sensor showed a remarkably enhanced response to 1750 ppb NO2, about double the response in the dark, and a limit of detection of about 50 ppb of NO2 (Signal/Noise = 3). Photocatalytic tests to assess the degradation of NOx showed that TiO2/graphene hybrids using material GTiO2S were the most active amongst the whole series of TiO2-based materials. Our data highlights the unique characteristics of material GTiO2S TiO2/graphene and the suitability for multi-purpose applications in the field of environmental monitoring and remediation. The capability of the material for both sensing and abatement of NOx could be exploited to offer a safer environment through providing a warning of the presence of NOx whilst also reducing levels.
Immobilized composite powders of titania with various carbon content were tested with respect to their efficiency of degradation of impurities in air (toluene, acetaldehyde, NO) under UVA illumination in a single-pass flow-through reactor and ISO conditions. Addition of active carbon (AC) to titania resulted in increased conversion efficiencies of some pollutants. In the case of toluene as a test pollutant, an AC/TiO2 ratio of 0.23 in the photocatalyst led to 47% conversion efficiency (against 36% without carbon). The presence of water in the gaseous reaction mixture was found to be essential for the degradation reactions to occur with an optimum at 50% RH. In gas phase degradation experiments with NO, a carbon to titania ratio of 0.7 led to the best results. For long time irradiation, accumulation of one of the reaction products, HNO3, in the catalyst layer was noticed resulting in a lower production of NO2. Photocatalytic removal of acetaldehyde was not improved by carbon loading; pure titania showed already a conversion efficiency of 75%. In general, although carbon loading helped in adsorption and preconcentration of pollutants, light absorption by carbon counteracted this effect.
Environmental and energy problems have drawn much attention due to the rapid population growth and the accelerated economic development. For instance, photocatalysis, "a green technology", plays an important role in solar energy conversion owing to its potential to solve energy and environmental problems. Recently, many efforts have been devoted to improve the visible‐light photocatalytic activity using titanium dioxide as photocatalyst due to its wide range of applications in energy and environment fields. However, the fast charge recombination and the absorption edge in the UV range limits the photocatalytic efficiency of TiO2 under visible‐light irradiation. Many investigations have been carried out in order to overcome the limitations of TiO2 and therefore enhance its photocatalytic activity under visible light. The present literature review focuses on different strategies used to promote the separation efficiency of the electron‐hole pairs and to shift the absorption edge of TiO2 to the visible region. Current synthesis techniques used to elaborate several nanostructures of TiO2 based material, recent progress in enhancing visible photocatalytic activity and the different photocatalysis applications will be discussed. Based on the studies reported in the literature, we believe that this review will help in the development of new strategies to further improve the visible light photocatalytic performance of TiO2 based materials.
Although high energy TiO2 nanocrystals (HE-TiO2-NCs) with exposed (0 0 1) facets shows superior photoreactivity in oxidation of organic pollutants, they are suffering from the problem of hard to be collected in recycling use. In this paper, high photoreactive HE-TiO2-NCs decorated TiO2 nanofibers (TiO2-NFs) were fabricated by electrospinning the mixture of TiOF2 cubes and tetrabutyl titanate (TBT) followed by calcination. We systematically studied the dependence of calcination temperature on microstructure and photocatalytic property toward acetone oxidation. It was found that heat treatment of the TiOF2 embedded TiO2 nanofibers results in the formation of HE-TiO2-NCs decorated TiO2-NFs (HE-TiO2-NCs/TiO2-NFs). The addition of TiOF2 not only improves the crystallization, but also prevents the anatase-to-rutile phase transformation of TiO2-NFs, and 600 °C-calcined HE-TiO2-NCs/TiO2-NFs sample (TF600) shows the highest photoreactivity under UV irradiation with an acetone oxidation rate of 97.2 ppmh⁻¹, 4.2 times higher than pristine TiO2-NFs sample (T600) that was prepared under similar conditions but without the addition of TiOF2. TF600 sample also exhibits increased visible photoreactivity in oxidation of NO when compared with T600 sample. The enhanced photoreactivity of HE-TiO2-NCs/TiO2-NFs was attributed to the combined effects of fluoride-induced enhancement of crystallization, formation of oxygen vacancy (Vo) and the production of a direct Z-scheme homojunction between HE-TiO2-NCs and TiO2-NFs.
Nanoparticles are highly efficient additives for modification of cement products, even at small concentrations (≤1%). The main modifications are (typical ranges shown, though great variability has been observed): reduction of set time (by 1–2 h) and diffusivity (by 4–75%), and increase of strength (by 5–25%), and thermal durability (0–30% increase in residual strength). These modifications were attributed to the unique reactivity of nanoparticles associated with their small size and large surface area. The paper reviews documented observations of SiO2, Al2O3, Fe2O3, TiO2, CaCO3, and clay nanoparticles, and discusses effective modification mechanisms and commercial application challenges, including cost and dispersion.
The properly designed semiconductor photocatalysts are promising materials for solving the current serious energy and environmental issues because of their ability of using sunlight to stimulate various photocatalytic reactions. Especially, the constructed direct Z-scheme photocatalysts, mimicking the natural photosynthesis system, possess many merits, including increased light harvesting, spatially separated reductive and oxidative active sites, and well-preserved strong redox ability, which benefit the photocatalytic performance. This review concisely compiles the recent progress in the fabrication, modification, and major applications of the direct Z-scheme photocatalysts; the latter include water splitting, carbon dioxide reduction, degradation of pollutants, and biohazard disinfection. It finishes with a brief presentation of future challenges and prospects in the development of direct Z-scheme photocatalytic systems.
TiO2-based Z-scheme photocatalysts have attracted considerable attention because of the low recombination rate of their photogenerated electron–hole pairs and their high photocatalytic efficiency. In this review, the reaction mechanism of Z-scheme photocatalysts, recent research progress in the application of TiO2-based Z-scheme photocatalysts, and improved methods for photocatalytic performance enhancement are explored. Their applications, including water splitting, CO2 reduction, decomposition of volatile organic compounds, and degradation of organic pollutants, are also described. The main factors affecting the photocatalytic performance of TiO2-based Z-scheme photocatalysts, such as pH, conductive medium, cocatalyst, architecture, and mass ratio, are discussed. Concluding remarks are presented, and some suggestions for the future development of TiO2-based Z-scheme photocatalysts are highlighted. © 2017 Dalian Institute of Chemical Physics, the Chinese Academy of Sciences