Article

A model for analyzing the performance of photocatalytic air cleaner in removing volatile organic compounds

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Abstract

A photocatalytic oxidation (PCO) reactor model was developed to analyze the removal of volatile organic compounds (VOCs) in indoor air. Two parameters, the fractional conversion, ε, and the number of mass transfer units (NTUm), were found to be the main parameters influencing the photooxidation performance of PCO reactors. The factors of affecting the effect of removing VOCs of PCO reactor are discussed. The predicted photocatalytic reaction rate coefficient, fractional conversion, ε, and NTUm for a typical PCO reactor agreed well with experimental data. The study shows that the effectiveness—NTU method used for heat exchangers is also an effective tool for designing PCO reactors and for evaluating their VOC removal effect.

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... He found that the product of volumetric flow rate and conversion rate, which represent the overall rate of VOC removal, reaches an asymptote with the velocity increasing. Zhang et al. (2003) developed a PCO reactor model. They found that two parameters, the number of the mass transfer unit, NTU m , and the fractional conversion, ε, were the main parameters influencing the photooxidation performance of a PCO reactor. ...
... When h m (z, ξ) and K(z, ξ) are independent of location ξ, this model can be simplified to the model of Yang et al. (2004); when independent of both z and ξ, this model can be simplified to the model of Zhang et al. (2003). The advantage of the present model is that it can be used to analyze the VOC removal performance of three-dimensional PCO reactors, in particular to those with inner extended surfaces and spatially dependent mass transfer rate coefficient and reaction rate coefficient. ...
... However, if the VOC concentration difference in the PCO reactor is not high, the influence of VOC concentration to St m can be neglected, just as the situation of the influence of temperature to the heat transfer. Zhang et al. (2003) found that when the VOC concentration is low (lower than 2 ppmv), NTU m remains almost constant in a series of experiments with various VOC concentrations. Therefore, it is justified to assume that St m is independent of the VOC concentration if the concentration is low (as is the case in most practical situations). ...
... He found that the product of volumetric flow rate and conversion rate, which represent the overall rate of VOC removal, reaches an asymptote with the velocity increasing. Zhang et al. (2003) developed a PCO reactor model. They found that two parameters, the number of the mass transfer unit, NTU m , and the fractional conversion, ε, were the main parameters influencing the photooxidation performance of a PCO reactor. ...
... When h m (z, ξ) and K(z, ξ) are independent of location ξ, this model can be simplified to the model of Yang et al. (2004); when independent of both z and ξ, this model can be simplified to the model of Zhang et al. (2003). The advantage of the present model is that it can be used to analyze the VOC removal performance of three-dimensional PCO reactors, in particular to those with inner extended surfaces and spatially dependent mass transfer rate coefficient and reaction rate coefficient. ...
... However, if the VOC concentration difference in the PCO reactor is not high, the influence of VOC concentration to St m can be neglected, just as the situation of the influence of temperature to the heat transfer. Zhang et al. (2003) found that when the VOC concentration is low (lower than 2 ppmv), NTU m remains almost constant in a series of experiments with various VOC concentrations. Therefore, it is justified to assume that St m is independent of the VOC concentration if the concentration is low (as is the case in most practical situations). ...
Chapter
Indoor air cleaning has been proved to be an efficient way to reduce indoor harmful VOCs. Many advanced technologies have been studied for the quick and economical removal of VOCs from indoor air. This chapter introduced photocatalytic oxidation (PCO) and room-temperature thermal catalytic oxidation (TCO). The principle of PCO was introduced, and then a general model was developed for analyzing the VOCs removal performance by PCO. The enhancement of PCO performance was analyzed based on the general model. The unwanted by-products during the PCO reaction process were observed online and qualitatively identified. We also introduce various kinetic models for TCO. The experimental results show that a kinetic model with a bimolecular Langmuir-Hinshelwood mechanism and temperature effect best fit the data. The activation energy of the TCO reaction for formaldehyde was then obtained. In summary, the great potential of the combination of PCO, TCO, and adsorption will advance indoor air cleaning in the future.
... Many tests have been carried out at the laboratory scale in order to evaluate the de-polluting potential of numerous photo-catalysts: TiO 2 , SnO 2 , WO 3 , CeO 2 , ZnO, etc. Then numerous photocatalytic reactors have been developed for the treatment of VOCs in air streams to improve indoor air quality inside houses, offices, factories [7]... This has led to the commercialisation of indoor air photocatalytic cleaners [8,9]. Later, larger scale experiments have been carried out, firstly in semi-confined places such as tunnels and canyon streets, then outside in open field, aiming at determining effects on outdoor air quality [10,11,12,13,14,15]. ...
... In a PCO reactor generally the contaminated air is drawn into the system by a fan. It passes over the reactor bed where it is adsorbed on the TiO 2 catalyst and treated with UV-light until it is completely broken down to gaseous products, mainly CO 2 and H 2 O. Several types of PCO reactors have been developed, and they can be divided in 3 categories: plate, honey-comb or tubular [9]. • efficient and powerful UV lamps, the less expensive and with the longest lifespan, • an internal framework (generally metallic) to which the UV lamps are fixed, • and an opening for discharging the purified air. ...
Conference Paper
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In order to decrease their time return on investment, all the solar chimney power projects (SCPP) describe alternative income sources like: certificates for carbon dioxide (CO2) compensation, farming under the greenhouse, tourism, R&D centres, telecommunications... Other synergies could arise from photo-catalysed oxidation of atmospheric methane (CH4) and from CO2 capture. From all the long lived and globally mixed greenhouse gases (GHG), CO2 and CH4 account respectively for 63 and 18% of the total radiative forcing.
... A device allowing to activate a photocatalyst with sunlight and to put into contact the pollutant is called a photoreactor. Zhang et al. (2003) described the three principal photocatalytic reactor (PCR) types employed in laboratory research, as shown in Fig. 3: plate, tubular, and honeycomb. As lower pressure drops, larger volumes, and large surface areas are needed, annular reactors and honeycomb monoliths are the most common PCRs. ...
... A SCPP also has an inlet, an outlet, and a very large transparent side (the canopy) exposed to freely available sunlight Fig. 3 Principal PCR types according to Zhang, et al. (Zhang et al. 2003) a) flat, b) tubular and c) honeycomb irradiation 12 h/day and is crossed by a gigantic air stream. Coating the inner part of its greenhouse collector with transparent photocatalysts, and/or adding a bed of photocatalysts on the ground, under this very large area exposed to UV and visible light irradiation might allow to use this modified SCPP as a giant PCR for N 2 O mitigation by photocatalytic reduction. ...
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Even if humans stop discharging CO2 into the atmosphere, the average global temperature will still increase during this century. A lot of research has been devoted to prevent and reduce the amount of carbon dioxide (CO2) emissions in the atmosphere, in order to mitigate the effects of climate change. Carbon capture and sequestration (CCS) is one of the technologies that might help to limit emissions. In complement, direct CO2 removal from the atmosphere has been proposed after the emissions have occurred. But, the removal of all the excess anthropogenic atmospheric CO2 will not be enough, due to the fact that CO2 outgases from the ocean as its solubility is dependent of its atmospheric partial pressure. Bringing back the Earth average surface temperature to pre-industrial levels would require the removal of all previously emitted CO2. Thus, the atmospheric removal of other greenhouse gases is necessary. This article proposes a combination of disrupting techniques to transform nitrous oxide (N2O), the third most important greenhouse gas (GHG) in terms of current radiative forcing, which is harmful for the ozone layer and possesses quite high global warming potential. Although several scientific publications cite “greenhouse gas removal,” to our knowledge, it is the first time innovative solutions are proposed to effectively remove N2O or other GHGs from the atmosphere other than CO2.
... There are several studies focused on the removal of volatile organic compounds (VOCs), with attention paid to the reaction mechanism [17][18][19], reactor design [20,21], effect of process parameters such as flow rate, UV intensity [22,23], humidity [24,25] or large scale studies including photocatalytic de-polluting efficiency in indoor car parks [26] or simulated street canyons [27]. For the determination of photocatalytic activity in the gaseous phase, acetaldehyde is often used as a model compound [28][29][30][31]. ...
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This work deals with the preparation of TiO 2 nanoparticulate layers of various mass (0.05 mg/cm ² to 2 mg/cm ² ) from three commercial nanopowder materials, P90, P25 and CG 300, their characterisation (profilometry, BET and SEM) and evaluation of their photocatalytic activity in the gaseous phase in a flow-through photoreactor according to the ISO standard (ISO 22197-2). Hexane was chosen as a single model pollutant and a mixture of four compounds, namely acetaldehyde, acetone, heptane and toluene was used for the evaluation of the efficiency of simultaneous removal of several pollutants. A linear dependence between the layer mass and the layer thickness for all materials was found. Up to a layer mass 0.5 mg/cm ² , the immobilisation P90 and P25 powder did not result in a decrease in BET surface area, whereas with an increase in layer mass to 1 mg/cm ² , a decrease of the BET surface was observed, being more significant in the case of P90. The photocatalytic conversion of hexane was comparable for all immobilised powders up to a layer mass of 0.5 mg/cm ² . For higher layer mass, the photocatalytic conversion of hexane on P25 and P90 differ; the latter achieved about 30% higher conversion. In the case of the simultaneous degradation of four compounds, acetaldehyde was degraded best, followed by acetone and toluene; the least degraded compound was heptane. The measurement of released CO 2 revealed that 90% of degraded hexane was mineralised to CO 2 and water while for a mixture of 4 VOCs, the level of mineralisation was 83%. Graphical abstract
... Previous work demonstrated that the flat plate reactors are not suitable for high air throughput. Zhang et al. found that the number of mass transfer units is one of the main parameters influencing the photooxidation performance of the reactor [104]. To overcome this barrier, several types of reactors have been proposed towards process intensification. ...
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The development of clean and sustainable teleology is vital to treat the critical environmental pollutants. In the last decade, the use of photocatalytic reactors has been widely reported for organic pollutants degradation. From photocatalysis’s application in environmental remediation, the primary technical issue to scientists is always the efficiency. The enhanced photocatalytic efficiency is mainly depended on the materials improvement. However, the design of photoreactors lags behind the development of photocatalysts, which strongly limit the widespread use of photocatalysis technology in environmental remediation. The nanoparticles separation, mass transfer limitation, and photonic efficiency have always been problematic and restrict the high photocatalytic efficiency of photoreactors. To overcome these bottleneck problems, the most popular or newfangled designs of photoreactors employed in air and water treatment has been reviewed. The purpose of this review is to systematize designs and synthesis of innovative TiO2-based photoreactors and provides detailed survey and discussion on the enhanced mechanism of photocatalytic performance in different TiO2-based photoreactors. The most studied photoreactors are the following: packed bed reactor, film reactor and membrane reactor, which have some limitations and advantages. A comprehensive comparison between the different photocatalytic performance of TiO2-based photoreactors is presented. This work aims to summarize the progress of TiO2-based photoreactors and provides useful information for the further research and development of photocatalysis for water and air purification.
... Some developed models or parameters have attempted to simplify the experimental parameters. Zhang et al. (2003) developed a concise model to evaluate the VOC removal (NTU model) by assuming that the photocatalytic reaction is a first-order reaction. ...
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Photocatalytic oxidation (PCO)-based air filters are gaining attention owing to their capacity for indoor pollutant removal. This review summarized the application of ultraviolet-photocatalytic oxidation (UV-PCO) in heating, ventilation, and air conditioning (HVAC) systems, including the modeling studies, reactor designs, the influence of operational conditions, with emphasis on the common issue of byproduct generation, and the resulting indoor byproduct exposure levels. As a result, the concentrations of the typical byproducts for the most challenging pollutants were relatively low, except for the PCO of ethanol. Hence, UV-PCO is not recommended for buildings with high ethanol concentrations. Based on the formation of the formaldehyde, a new exposure-based evaluation standard for UV-PCO was developed to evaluate the feasibility of integrating UV-PCO reactors into an HVAC system. Then, applying the newly developed evaluation standard on a developed database (data size: 174) from the literature, 32.5% of the cases were identified as suitable for HVAC system applications in residential and commercial buildings, and all cases could be used for industrial buildings. Finally, a case study was conducted to develop a support vector machine (SVM) classification model with good accuracy, and challenging compound types, inlet concentrations, and air velocity were found to be the main parameters affecting the applicability of UV-PCO.
... Aerogel insulation sheets are made up of fibrous reinforcement and silica aerogel [59]. A house has a lot of gases produced from inside such as cooking food, burners, paints and furniture [61]. These harmful particles and gases may be absorbed by efficient porous materials, aerogels have excellent absorption capacity to mitigate the toxic gases owning to its relatively large specific surface area [59]. ...
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Smart materials have played significant contribution towards the development of buildings. There are various smart materials which can change their properties and behavior under the influence of external catalyst or stimulus. Such materials are changing the face of traditional engineering materials. Smart materials can be utilized individually as well as it can be incorporated with existing materials to enhance their desirable properties. Smart materials are widespread across all the domains of human inventions due to its multidisciplinary applications. Some of these materials are relatively new while some are being used from a very long time. Hence it suffices to say that the recently developed smart materials still require research. The general classification of smart material is illustrated in this review paper. The paper intends to identify the various types of available smart materials and also illustrated the application of such materials in the various fields of civil engineering. Further, the potential benefits and downsides are also discussed along with their applicability under different conditions. Some innovative materials are also discussed which can bring potential revolution in the construction industry. The impact or the benefits related to sustainability also discussed in this review paper.
... Currently, the most widely used photocatalyst for purification is TiO 2 . Depending on the type and the level of concentration of the treated pollutants, the generation of harmful intermediate products and derivatives should be considered [20,21]. ...
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In this study, we propose a new design for a microchannel filter. The closed indoor environments with which we interact daily are sources of diseases for the respiratory system of human beings. Recommendations for the design of microchannel filters for indoor air purification are proposed, implementing low-cost microequipment technology (MET) for the manufacture of the elements that constitute a microfiltration system. For the microchannel filter production, we proposed to use MET, which is a miniaturization technology and can reduce manufacturing costs. The microchannel filter was 3.75 cm in radius with a thickness of 3 mm. It had a triangular profile and a helical trajectory. It was designed, manufactured, and tested for two profile dimensions. The main purpose was to reduce the pressure drop of the air flow through the filter. We described the air flow simulation for the microchannel filter using SolidWorks. A prototype microchannel filter was constructed, which underwent manufacturing tests. It is possible to clean the microchannel using water flow, which allows us to maintain the filtration quality within an optimum range of contaminant removal.
... Also the aerogels are capable to the efficient removal of many pollutants from indoor environment such as: chloride from tap water, hydrocarbons (CH3CHO and CH3CHO) from cigarettes, NOx and SOx from incomplete burning of gas, VOC from organic solvents, formalin from paints and furniture who are responsible for health problems [55]. Aerogel-prepared nanocrystals of MgO, CaO, and Al2O3 with specific surface area of up to 500 m 2 ·g -1 , have shown remarkably high capacity to destructively adsorb VOCs under the atmospheric pressure and temperature [56]. ...
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In this paper data regarding the utilization of aerogel as a promising material for thermal insulation of the residential and commercial buildings are presented. Also, research work and developments in synthesis, properties and characterization of silica aerogels will be addressed. Aerogel is a synthetic porous ultralight material derived from a gel in which the liquid component of the gel has been replaced with a gas. The result is a solid with extremely low density and low thermal conductivity. Sol-gel is the most used method of preparation. Aerogel melts at 1200ºC and the thermal conductivity is almost 0. Is a solid material with the smallest density because contains about 99.8% air. This material has almost unlimited potential, believing that they might find application in most human activities and areas. Aerogel insulation is a good choice because nearly neutralizes all three methods of heat transfer: convection, conduction and radiation. The resistance to convective transfer is given by the fact that air does not circulate in the material structure. The resistance to thermal transfer by conduction is given by the majority of gaseous components. If using a carbon based gel, a high resistance to radiation transfer is obtained. Therefore, the most used aerogel for thermal insulation is the silica aerogel with carbon as nanostructured material. The high price makes it currently inaccessible and less used material. But, inevitably, the aerogel will quickly become one of the most attractive materials in the future.
... is the concentration of R, k is the rate constant and n is the order of the reaction, n is equal to 0, 1, etc. [105][106][107]. Kinetic models including the influencing factors need to be developed. ...
Article
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Emission of volatile organic compounds (VOCs) is one of the major contributors to air pollution. The main sources of VOCs are petroleum refineries, fuel combustions, chemical industries, decomposition in the biosphere and biomass, pharmaceutical plants, automobile industries, textile manufacturers, solvents processes, cleaning products, printing presses, insulating materials, office supplies, printers etc. The most common VOCs are halogenated compounds, aldehydes, alcohols, ketones, aromatic compounds, and ethers. High concentrations of these VOCs can cause irritations, nausea, dizziness, and headaches. Some VOCs are also carcinogenic for both humans and animals. Therefore, it is crucial to minimize the emission of VOCs. Among the available technologies, the catalytic oxidation of VOCs is the most popular because of its versatility of handling a range of organic emissions under mild operating conditions. Due to that fact, there are numerous research initiatives focused on developing advanced technologies for the catalytic destruction of VOCs. This review discusses recent developments in catalytic systems for the destruction of VOCs. Review also describes various VOCs and their sources of emission, and kinetics of catalytic destruction.
... To date, most studies considered mass balance of species in either gas or solid phase and only a few models presented mass balance in both phases [75,146]. In this context, some authors (for example Zhang et al. [152], Boulinguiez et al. [149], Biard et al. [153] and Tomašić et al. [146]) introduced a simple 1D mass conservation equation, in which mass transfer happens through gas boundary layer near catalyst surface and pore diffusion has been assumed negligible due to very thin catalyst layer. Considering the aforementioned facts, they implemented following mass balance in the gas phase (Eq. ...
Article
Photocatalytic oxidation (PCO) has a great potential to eliminate various gaseous pollutants even at low concentrations. Numerous studies have been carried out to improve the effectiveness and performance of this technology. In addition, the development of appropriate models can enhance the understanding of reactor performance and the evaluation the intrinsic kinetic parameters that enable the scale up or re-design of more efficient large-scale photocatalytic reactors. This paper reviews recent research works on mathematical modeling of gas phase photocatalytic reactors and analyses different key factors that can enhance pollutants decomposition performance. First, the fundamental of the photocatalytic oxidation process and degradation reaction mechanism are briefly described. Then, to study kinetics of reaction, this paper focuses on Langmuir-Hinshelwood equation, which is by far the most common kinetic model that takes both adsorption and reaction processes into account. Moreover, an overall mass balance that contains advection, diffusion, and reaction rate terms, is analyzed to obtain a comprehensive mathematical model. In the end, the influence of key operating parameters (e.g. flow rate, catalyst surface area and porosity, and catalyst thickness) on the photocatalytic process and removal efficiency of the reactor are discussed.
... The main disadvantages of these systems include the highenergy consumption of the fans, heat losses, and the dependency on the outdoor air quality (OAQ). To ensure a healthy IAQ, an interesting strategy is to combine ventilation and air purification (Zhang et al. 2003). Of the advanced air purification methods, photocatalytic oxidation (PCO) is a promising technique for integration into heating, ventilation, and air conditioning (HVAC) systems Mo et al. 2009b;Paz 2010;Destaillats et al. 2012). ...
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... Heterogeneous photocatalysis with TiO2 as catalyst is a rapidly developing field in environmental engineering. In the past decade, the removal of trace levels of inorganic and organic contaminants in air through a photocatalytic process has received much attention because of this technology is potentially suitable for air purification in office buildings and residences [15,16]. Coating photocatalyst modified concrete materials on the external surface of buildings may be a good supplement to conventional technologies to treat the gaseous exhaust emission [17,18]. ...
Article
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... In this sense, it is possible to demonstrate, based on other authors, that the mass transfer phenomena did not produce effects on the reaction speed on the studied conditions of this work. Zhang et al. [72] were able to demonstrate that reaction rate constants were smaller than the mass transfer coefficients. For these results, speeds were above 0.60 m s −1 , so the authors concluded that mass transfer effects were not important under those conditions. ...
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For the photocatalytic degradation of the hydrogen sulphide (H2S) in the gas-phase it was developed a rectangular reactor, coated with acrylic paint supported on fiber cement material. The surface formed by the paint coverage was characterized structural and morphologically by scanning electron microscopy with energy dispersive X-ray and X-ray diffraction analysis. The flow rate and the inlet concentration of H2S were evaluated as operational performance parameters of the reactor. Removal efficiencies of up to 94% were obtained at a flow rate of 2 L min-1 (residence time of 115 s) and inlet concentration of 31 ppm of H2S. In addition, the H2S degradation kinetics was modelled according to the Langmuir-Hinshelwood (L-H) model for the inlet concentrations of 8-23 ppm of H2S. The results suggest that flow rate has a more important influence on photocatalytic degradation than the inlet concentration. It is assumed that H2S has been oxidized to SO 4 2 - , a condition that led to a deactivation of the photocatalyst after 193 min of semi-continuous use.
... Controlled conditions refer to process parameters such as flow rate, irradiance, UV wavelength, etc. Uncontrolled parameters depend on features of the air stream to be treated, such as the type of pollutants, concentrations, and air humidity. In the literature, studies for the development of kinetic models are generally performed at ppmv levels of VOCs [15][16][17][18][19], which are higher than typical indoor air VOC concentrations. It was the case of a previous study performed in the laboratory and already published [20]. ...
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The photocatalytic degradation of toluene in indoor air conditions was performed in a closedloop multi-pass photocatalytic reactor using the Box-Behnken experimental design methodology. The objective of this work was to rigorously determine a kinetic model in order to understand the behavior of the reactor in real indoor air conditions and to relate the kinetic parameters to physical and chemical mechanisms. Three main parameters were studied: initial toluene concentration, light irradiance and air stream velocity. The experimental results were used to calculate the single-pass removal efficiency for different operating conditions and to establish a relationship between the single-pass removal efficiency, light irradiance and air stream velocity. This relationship was integrated into an overall reaction rate law based on the Langmuir-Hinshelwood mechanism. The kinetic model obtained was then validated for various experimental conditions.
... Several types of photocatalytic reactors (PCR) are used for laboratory research: they can be classified in 3 main categories (Zhang et al., 2003) as shown in Fig. 12: plate, honey-comb or tubular. Annular reactors and honeycomb monoliths are the most common among fixed-bed designs because of their lower pressure drops and higher volumes. ...
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In order to mitigate the effects of climate change, a lot of research has been devoted to reduce carbon dioxide (CO2) emissions, develop capture and storage technologies (CCS), as well as direct carbon dioxide removal (CDR) from the atmosphere. The 2014 "Summary for Policymakers" of the Intergovernmental Panel on Climate Change 5th report (working group III) preponderantly mentions CCS and CDR.Although many scientific publications cite "greenhouse gas removal", to our knowledge none of them has yet proposed innovative solutions to effectively remove greenhouse gases other than CO2 from the atmosphere. This article proposes a combination of disrupting techniques to transform or destroy the halogenated gases in the atmosphere, which are harmful for the ozone layer, and possess high global warming potential as well as long atmospheric lifetimes.
... Iako su mnogi autori prouèavali utjecaj relativne vlaÞnosti na ukupnu brzinu fotooksidacije razlièitih organskih spojeva, interpretacije utjecaja relativne vlaÞnosti na uèinkovitost fotokatalitièkih reakcija se jako razlikuju. 28,36,43,44,59,60 Prema nekim tumaèenjima u podruèju malih poèetnih koncentracija hlapljivih organskih spojeva vlaga djeluje kao promotor, dok u podruèju visokih koncentracija hlapljivih organskih spojeva vlaga inhibira fotokatalitièku reakciju. Prema tome vrlo je vaÞno odrediti optimalnu vrijednost relativne vlaÞnosti. ...
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The use of heterogeneous photocatalysts for the abatement of environmental problems has received increased attention during the last three decades. The photocatalyst used in most of these studies was titanium dioxide. This fact relates to the unique physical and chemical properties of titanium dioxide and similar semiconductor materials, such as ZnO, MgO, WO3, Fe 2O3, CdS, etc. that may be utilized for a wide range of potential applications. Specifically, upon ultraviolet irradiation these materials exhibit photocatalytic activity that enables the oxidative destruction of a wide range of organic compounds and biological species on their surface. In addition, these materials may also exhibit photocatalytically induced superhydrophilicity that converts the hydrophobic character of the surface to hydrophilic when exposed to UV light. This causes the formation of uniform water films on the surface of these materials, which prevents the adhesion of inorganic or organic components and thus retains a clean surface on the photocatalyst. Photocatalytic materials may be deployed on surfaces of various substrates, such as glass, ceramics or metals to provide layers that exhibit photocatalytic activity when they are exposed to light. Excitation of a photocatalyst leads to the creation of electrons and holes in the semiconductor material. Furthermore, these electrons and holes interact with molecules adsorbed on the semiconductor and can induce charge transfer process that results in the degradation of the adsorbate. The commercial potentials of heterogeneous photocatalysis are huge, including medical applications, application in the field of architecture (particularly for the cultural heritage purposes, facade paints, etc.), automotive and food industries (cleaner technologies, non-fogging glass and mirrors, product safety), textile and glass industry, as well as in environmental protection (water and air purification and disinfection). After the discovery that the photocatalytic degradation of organic compounds is generally more efficient in the gas phase than in the liquid phase, and the fact that the treatment cost may be significantly lower than that of the water phase photocatalytic treatment, the scientific interest has shifted towards the application of photocatalysis for air treatment. This paper describes the basics of heterogeneous photocatalysis, mainly on TiO 2 and the application of photocatalytic processes for air treatment purposes. Review of more interesting practical application of heterogeneous photocatalysis for the treatment of polluted air is presented. Special efforts are made to describe the technical aspects of the photocatalytic processes and to characterize different photocatalytic reactors in use for air treatment.
... Many pollutants are released into the indoor environment, including chloride from tap water, hydrocarbons (CH 3 CHO and CH 3 CHOH) from cigarettes, formalin ( preservative) from furniture and paints, NO x and SO x from the incomplete burning of gas and VOC from organic solvents. Some allergies and respiratory problems, such as asthma, are exacerbated by airborne contaminants and their conversion into non-toxic compounds is an effective route for their removal [26]. The first stage of this process is the rapid adsorption of the contaminants by a multi-porous material. ...
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Aerogels are a special type of solid material with nanometre-scale pores <1/3000th the width of a human hair. Porosity is in excess of 90%, in some cases as high as 99.9%, and densities can be as low as 3 kg/m3. Aerogels are essentially ‘puffed-up sand’ and are often termed ‘frozen smoke’. Their thermal conductivity (0.014 W/m K at room temperature) is the lowest of any solids, and they also have good transparency. The acoustic properties of aerogels make them effective insulators against noise, and aerogels have the lowest refractive index, and dielectric constant of all solid materials. The unusual properties of aerogels open the way to a new range of opportunities for their application in buildings. This paper provides information on their unique features and reviews the potential applications for aerogels in buildings as well as latest developments in the field.
... Generally, in fixed-bed reactors, the fluid flow regime allows achieving high conversion per unit mass of catalyst; and the low pressure drop enables such systems to be operated at reduced operating costs. Several types of photocatalytic reactors have been developed, and they can be divided into three main categories [196,231]: plate, honeycomb and tubular. Among fixed-bed designs, honeycomb monoliths and annular reactors are the most common because of their higher volumes and lower pressure drop [196]. ...
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Hydrogen and synthesis gas (syngas) production from water and carbon dioxide as well as fuel processing for fuel cells and for transport applications have great potential in addressing major challenges in the area of energy. This review highlights recent progress and future trends on energy storage via carbon-neutral fuels made from water, carbon dioxide and renewable energies. The various electrochemical, thermochemical and photochemical energy conversion technologies for dissociation of H2O or/and CO2 are reviewed and discussed systematically.
... Mass transfer based models for the determination of kinetic parameters were developed by several researchers [8,9]. A mechanistic method to understand the interacting effects of reaction area, mass transfer, kinetic reaction rate and other influencing factors was developed by Zhang et al. [10]. Their method is based on two parameters, the 'number of mass transfer units' NTU, and the fractional conversion, e, for describing the performance of PCO reactors. ...
... This problem is simplified by assuming that the photocatalytic reaction is a first-order reaction with a constant reaction rate coefficient (this assumption was validated experimentally as described in Section 3). Many authors have rejected the L-H expression in favour of a first-order model (Wang and Chou 2000;Sattler and Liljestrand 2003;Zhang et al. 2003;Zou et al. 2006;Yu et al. 2006a). For this assumption, the mass balance equation that describes the decay rate of the concentration within the chamber with air cleaner operating can be expressed by Eq. 3 (Yu et al. 2006a;Gao and Zhang 2010): ...
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Nowadays, a large proportion of photocatalytic oxidation (PCO) devices are being implemented in heating, ventilation and air-conditioning systems. However, no systematic studies have been carried out regarding the influence of inlet air preconditioning. To analyse the impact of the inlet air-conditions into photocatalytic efficiency, a simulated air-conditioning duct with flowing gas through inside was designed. Isobutylene was chosen as the target VOCs. The concentration in the gas phase was monitored using a photoionization detector. The influence of flow rate, relative humidity and temperature on the VOC removal efficiency was analysed. Experimental results were presented in terms of gas-removal efficiency (η) and clean air delivery rate (CADR) and analysed on a kinetic basis. From them, the weight of each parameter in the global process has been determined, from bigger to smaller contribution, flow>temperature>relative humidity. Also, the relevance of the inlet air conditions has been illustrated in a model room in order to determinate the time necessary to obtain a threshold value accomplishing with enough air quality and the energy consumption of the device. Additionally, the photocatalytic decontamination has been assimilated to the "air exchange rate", a parameter commonly used in indoor air quality studies. The results show that preconditioning of air can improve the efficiency of photocatalytic devices and bring important energy savings.
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Urban air pollution has become a pressing challenge in recent times, demanding innovative solutions. This review delves into the potential of Solar Chimney Power Plants (SCPPs) as a sustainable approach to mitigating air pollution. The idea of mitigation of pollution may be an added advantage to the use of SCPPs in practice. Recent advancements, such as the integration of photocatalytic reactors (PCRs) for the elimination of greenhouse gases (GHGs), emphasizing the importance of addressing non-CO2 GHGs like CH4 and N2O are analyzed. The novelty of this review is that it not only focuses on the shifting and removal of particulate matter but also on the removal of greenhouse gases. Numerous case studies, ranging from filter-equipped SCPPs to Solar-Assisted Large-Scale Cleaning Systems (SALSCSs), are reviewed, providing a comprehensive understanding of their design, performance, and potential benefits. This review serves as a guide for researchers and policymakers, emphasizing the need for multifaceted approaches to address the intricate nexus of air pollution, renewable energy generation, and climate change mitigation.
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This work develops a mathematical and a numerical model based on Langmuir-Hinshelwood kinetics and mass transfer theory for photocatalytic NO removal. The mathematical model employs the resistance-in-series theory, whereas the...
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The photocatalytic oxidation (PCO) kinetics of volatile organic pollutants generally fit the L-H model. In this paper, we reviewed the recent research in proposed kinetic models based on L-H models. However, besides the flow rate and the initial concentration, light intensity, relative humidity, the photoreactor-related coefficients, the convective mass transfer coefficients, electron-hole pair recombination rate and intermediate by-production also play an important role in the photocatalytic oxidation reactions. Methods to identify the rate-determining step using those kinetic models were then discussed. The applicability of L-H model under various experimental conditions, such as photoreactor parameters, light sources and the properties of VOCs and photocatalysts, was also investigated.
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Over the last decades, fighting global warming has become the most important challenge humanity has to face. Therefore technologies of carbon dioxide capture, sequestration and recycling are equally important in order to tackle the global climate change stakes. Among recycling technologies, photocatalytic processes reducing CO 2 with H 2 O back to fuels or to other useful organic compounds, have the potential to be part of a renewable energy system. Indeed these processes can help to control CO 2 emissions and eventually eliminate CO 2 in excess. This perspective paper describes a large size device, able simultaneously: to proceed to direct air capture (DAC) of CO 2 ; to transform part of it into useful chemicals, like hydrocarbons or syngas; and to produce renewable energy, thus preventing future CO 2 emissions. Synergies between solar chimney power plants (SCPPs) and semiconductor photocatalysis in order to create giant photocatalytic reactors for artificial photosynthesis are discussed, as well as scale economies for unconventional carbon capture directly from the atmosphere. This paper presents a carbon negative emission technology obtained by coupling SCPPs with DAC systems which allows many scale economies, and also synergies to proceed to solar-to-chemical energy-conversion process by photocatalytic reduction of atmospheric CO 2 under sunlight.
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The utilization of solar irradiation to supply energy or to initiate chemical reactions is already an established idea. If a wide-band gap semiconductor like titanium dioxide (TiO2) is irradiated with light, excited electron–hole pairs result that can be applied in solar cells to generate electricity or in chemical processes to create or degrade specific compounds. Recently, a new process used on the surface of TiO2 films, namely, photoinduced superhydrophilicity, is described. All three appearances of the photoreactivity of TiO2 are discussed in detail in this review, but the main focus is on the photocatalytic activity towards environmentally hazardous compounds (organic, inorganic, and biological materials), which are found in wastewater or in air. Besides information on the mechanistical aspects and applications of these kinds of reactions, a description of the attempts and possibilities to improve the reactivity is also provided. This paper would like to assist the reader in getting an overview of this exciting, but also complicated, field.
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Hollow fiber membrane contactors are used in air dehumidification. The benefit of this technology is that the liquid desiccant is not in a direct contact with the process air; therefore, the problem of liquid droplets crossover is prevented. The equations governing the heat and moisture transfer from the air to the liquid, through the membranes, are described. An analytical solution is obtained for the dimensionless differential equations, with which the dehumidification effectiveness could be estimated by simple algebraic calculations. It provides a convenient yet accurate tool for the component design and system optimization. The model is validated by experiments. The effects of varying operating conditions on system performance are investigated. It is found that the total number of transfer units for sensible heat and the overall Lewis number are the most dominant parameters influencing heat and mass transfer. [DOI: 10.1115/1.4003900]
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Mass transfer is key to understanding and controlling indoor airborne organic chemical contaminants (e.g., VVOCs, VOCs and SVOCs). In this paper, we first introduce the fundamentals of mass transfer, and then present a series of representative works from the past two decades, focusing on the most recent years. These works cover: (1) predicting and controlling emissions from indoor sources, (2) determining concentrations of indoor air pollutants, (3) estimating dermal exposure for some indoor gas phase SVOCs, and (4) optimizing air purifying approaches. The mass transfer analysis spans the micro-, meso- and macro-scales, and includes normal mass transfer modeling, inverse problem solving and dimensionless analysis. These representative works have reported some novel approaches to mass transfer. Additionally, new dimensionless parameters such as the Little number and the normalized volume of clean air being completely cleaned in a given time period were proposed to better describe the general process characteristics in emissions and control of airborne organic compounds in the indoor environment. Finally, important problems that need further study are presented, reflecting the authors' perspective on the research opportunities in this area. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
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Reduced energy consumption and increased indoor environmental quality are the two main/major goals when constructing green buildings. Nanoscale catalysts and reactive sorbents have the potential to improve indoor air quality and operational efficiency. This work illustrates applications of these advanced materials for in room air cleaning devices. Catalysts attached to walls and those incorporated into packed beds have demonstrated potential performance in simulation studies. Operational results are also presented using the OdorKlenz-Air cartridge.
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Double-skin sheet reactor (DSSR) attracts attention in recent years due to the simple design and high mass transfer, but its application to photocatalytic CO2 reduction with immobilized catalyst is still a new trial. In this paper, the three-dimensional models describing the photocatalytic CO2 reduction in DSSR by means of solar energy were developed and numerically simulated, on the basis of the transient and continuous solar light distributions. A performance evaluation approach was proposed to guide the structural optimization of DSSR in photocatalytic CO2 reduction. The effects of operation parameters and reactor structures on CH3OH concentration were analyzed and discussed. The results show that the outlet CH3OH concentration of 2.68 × 10−4 mol m−3 in DSSR is much greater than that of 1.77 × 10−5 mol m−3 in optical fiber monolith reactor under the same conditions. It increases as both the inlet water vapor concentration ratio and day-average light flux increase, but decreases with increasing the inlet velocity, all of which are beneficial to the CH3OH productivity. The CH3OH concentration will decrease with the increase of the number of parallel-flow channels, but increase thanks to the rise in the width–height ratio and inserting flow guiding pieces, which are recommended for higher CH3OH concentration in the design of DSSR.
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The sol-gel method was used for the synthesis of BiVO4 hollow nanospheres by employing carbon spheres as a hard template. CuO loaded composite photocatalysts were prepared by impregnation. The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Brunauer-Emmett-Teller (BET), Tafel polarization curves (Tafel), linear sweep voltammetry (LSV), monochromatic incident photon to current conversion efficiency (IPCE), and UV-Vis diffuse reflectance spectroscopy (UV-Vis-DRS). We found that the BET surface area of the BiVO4 hollow nanospheres (10.24 m2?g-1) was 5.20 times that of the amorphous form of BiVO4 (1.97 m2?g-1). A p-n heterojunction was formed between CuO and BiVO4. Samples with 5% CuO exhibited optimal photoelectrochemical performance. They had a higher corrosion current density (12.33 times as much as that of the BiVO4 hollow nanospheres), and a smaller band gap (2.30 eV). Toluene was chosen as a model pollutant to evaluate the removal capacity and the CO2 mineralization rate of volatile organic compounds under visible light. The samples doped with 5% CuO exhibited optimal visible-light photocatalytic activity, with an 85.0% toluene degradation efficiency and a 12.0% mineralization rate in 6 h.
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In the commercialisation of photocatalytic air purifiers, the performance as well as the cost of the catalytic material plays an important role. Where most comparative studies only regard the photocatalytic activity as a decisive parameter, in this study both activity and cost are taken into account. Using a cost-effectiveness analysis, six different commercially available TiO2-based catalysts are evaluated in terms of their activities in photocatalytic degradation of acetaldehyde as a model reaction for indoor air purification.
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Aerogel is a kind of synthetic porous material, in which the liquid component of the gel is replaced with a gas. Aerogel has specific acoustic properties and remarkably lower thermal conductivity (≈0.013 W/m K) than the other commercial insulating materials. It also has superior physical and chemical characteristics like the translucent structure. Therefore, it is considered as one of the most promising thermal insulating materials for building applications. Besides its applications in residential and industrial buildings, aerogel has a great deal of application areas such as spacecrafts, skyscrapers, automobiles, electronic devices, clothing etc. Although current cost of aerogel still remains higher compared to the conventional insulation materials, intensive efforts are made to reduce its manufacturing cost and hence enable it to become widespread all over the world. In this study, a comprehensive review on aerogel and its utilization in buildings are presented. Thermal insulation materials based on aerogel are illustrated with various applications. Economic analysis and future potential of aerogel are also considered in the study.
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Photocatalytic degradation of trace acetone and acetaldehyde in air on TiO2 was studied. The results show that 390 mg/m3 of acetone and 413 mg/m3 of acetaldehyde can be completely degraded into CO2 and H2O in a short time under illumination by UV-lamp with power of 11 W and in the presence of water vapor and O2 in air. The effect of calcining temperature and time of TiO2 on activity was investigated. The effects of amount of photocatalysts, O2 on the rate of photocatalytic degradation were also studied.
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The gas-phase photocatalytic destruction of 17 VOCs over illuminated titanium dioxide was investigated using a plug flow reactor with the following experimental conditions: 200 ml min−1 flow rate, 23% relative humidity, 21% oxygen and an organic compound concentration range of 400–600 ppmv. At steady state, high conversion yields were obtained for trichloroethylene (99.9%), isooctane (98.9%), acetone (98.5%), methanol (97.9%), methyl ethyl ketone (97.1%),t-butyl methyl ether (96.1%), dimethoxymethane (93.9%), methylene chloride (90.4%), methyl isopropyl ketone (88.5%), isopropanol (79.7%), chloroform (69.5%) and tetrachloroethylene (66.6%). However, the photodegradation of isopropylbenzene (30.3%), methyl chloroform (20.5%) and pyridine (15.8%) was not so efficient. Carbon tetrachloride photoreduction was investigated in the presence of methanol as an electron donor. It was observed that the presence of methanol results in higher degradation rates. No reaction byproducts were detected for all VOCs tested under the experimental set-up and conditions described. Also, long-term conversion was obtained for all tested compounds. Catalyst deactivation was detected with toluene only, but the activity was restored by illuminating the catalyst in the presence of hydrogen peroxide. The capacity of the process to destroy different classes of volatile organic compounds present in the atmosphere was demonstrated.
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Indoor air pollution caused by volatile organic compounds (VOCs) may affect the health and well-being of inhabitants. Uptake and release of these compounds by and from indoor materials alter their concentrations in indoor air: uptake will lower peak concentrations, whereas subsequent (slow) release at lower concentration levels will prolong the presence of VOCs in indoor air. An experimental set-up has been implemented where indoor materials are placed as a “membrane” separating two air compartments. Both compartments – consisting of Field and Laboratory Emission Cells FLECs – are constantly flushed with air, one air stream containing a mixture of 20 VOCs, and concentrations in both compartments are measured after 1 h. Ten materials usually covering extensive surfaces indoors were consecutively exposed to the vapour mixture at concentration levels typically found in indoor environments. Under the chosen experimental conditions, five of these materials exhibited a permeability high enough that VOCs could be detected on the other side. Mass transport of VOCs into and through indoor materials has therefore been confirmed by experiment. The set-up allows for a quick screening of indoor materials with respect to their sorption capacity and permeability.
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Utilities of hybrid photocatalyst consisting of TiO2 and an adsorbent such as activated carbon in photoinduced mineralization of organic substances of very dilute present concentrations are demonstrated for the photodecomposition of propionaldehyde in air atmosphere, and propyzamide and bromoform dissolved in water. The substrates of target were adsorbed on the adsorbent support, and then a high concentration environments of the substrate was formed around the loaded TiO2, resulting in an increase in the photodestruction rate. Evidences for the diffusion of propionaldeyde adsorbed on the mordenite support to the loaded TiO2 are presented. Merits of the use of the adsorbents as the support for TiO2 loading is discussed.
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The effect of temperature, water vapor concentration, and ethylene concentration on the photooxidation of ethylene on titania was investigated. Ultraviolet radiation from a black-light lamp together with a glass-plate reactor were used to develop intrinsic oxidation rates. Ethylene oxida tion rates decreased significantly as the water vapor concentration was increased from 1000 ppmv for the three temperatures (2, 27, and 48 °C) investigated. The influence of water vapor on the reaction rate derived from the low adsorption of ethylene due to its low adsorption affinity relative to water. Over the range of water vapor concentration of 1000−25000 ppmv, ethylene oxidation rates increased as the temperature increased. An Arrhenius plot of the measured ethylene oxidation rates indicated an apparent activation energy of 3.4 kcal/mol. A Langmuir−Hinshelwood expression displaying an explicit temperature dependence was used to correlate the entire set of rate data. Based on this correlation, an enthalpy of adsorption for ethylene of −2.6 kcal/mol was found.
Article
The effects of humidity and sub-parts-per-million by volume contaminant levels on the photooxidation of formaldehyde and toluene are presented. UV radiation from a black-light lamp and a titania-coated glass-plate reactor were used to develop kinetic oxidation rates. The data indicated that competitive adsorption between water and the two contaminants has a significant effect on the oxidation rate. A simple differential design model is developed and validated using data from two ceramic foam photocatalytic reactors. The utility of rate data developed from the glass-plate reactor as the basis for reactor design models is demonstrated.
Article
A first-principles mathematical model describes performance of a titania-coated honeycomb monolith photocatalytic oxidation (PCO) reactor for air purification. The single-channel, 3-D convection–diffusion–reaction model assumes steady-state operation, negligible axial dispersion, and negligible homogeneous reaction. The reactor model accounts rigorously for entrance effects arising from the developing fluid-flow field and uses a previously developed first-principles radiation-field submodel for the UV flux profile down the monolith length. The model requires specification of an intrinsic photocatalytic reaction rate dependent on local UV light intensity and local reactant concentration, and uses reaction-rate expressions and kinetic parameters determined independently using a flat-plate reactor. Model predictions matched experimental pilot-scale formaldehyde conversion measurements for a range of inlet formaldehyde concentrations, air humidity levels, monolith lengths, and for various monolith/lamp-bank configurations. This agreement was realized without benefit of any adjustable photocatalytic reactor model parameters, radiation-field submodel parameters, or kinetic submodel parameters. The model tends to systematically overpredict toluene conversion data by about 33%, which falls within the accepted limits of experimental kinetic parameter accuracy. With further validation, the model could be used in PCO reactor design and to develop quantitative energy utilization metrics.
Article
Photocatalyzed oxidation of acetone (70-400 mg/m3) in air was carried out using near-UV illuminated TiO2 (anatase) coated on the surface of a ceramic honeycomb monolith. Considerable adsorption of acetone and water was noted on the catalyst coated monolith; these uptakes were described with a Langmuir adsorption isotherm for acetone and a modified BET adsorption isotherm for water. The acetone photocatalyzed disappearance kinetics on the TiO2 were determined with initial rate differential conversion, recycle reactor data and were analyzed using a Langmuir-Hinshelwood rate form coupled with a reactant mass balance including appreciable acetone monolith adsorption. The model, with parameters evaluated from initial rate data, is then shown to satisfactorily predict reactor behavior at all conversions. These kinetics and design results, together with earlier literature for photocatalytic oxidation of alkanes, 1-butanol, toluene, trichloroethylene, and odor compounds, indicate a potential for use of the photocatalytic monolith configuration for removal of all major classes of air contaminants.
Article
Nanoscale TiO2 catalysts prepared using a sol–gel method exhibit higher initial activity than commercially available P-25 TiO2 for the photocatalytic oxidation of toluene. Unlike P-25 TiO2, nonporous, nanoscale TiO2 catalysts are composed mainly of mesopores with pore sizes in the range of 35–44 nm. Calcination at 420°C leads to agglomeration of nanoscale TiO2 particles, formation of rutile, a decrease in pore capacity, and an enlargement of the mesopores. Catalysts treated at such a temperature display relatively low activity. Results of competitive adsorption of water and toluene on TiO2 samples confirm that TiO2 has a highly hydrophilic surface, which intrinsically suppresses the oxidation rate of toluene at high water content in the feed stream. Severe deactivation of TiO2 catalysts is due to the accumulation of partially oxidized intermediates, such as benzaldehyde and benzoic acid, on active sites. Complete recovery of catalytic activity requires a regeneration temperature above 420°C. Using platinum loaded on TiO2 results in lower oxidation rates of toluene, but facilitates the removal of poisonous intermediates from the deactivated TiO2 surface. Kinetic studies of the deactivation process indicate that the adsorption of poisonous intermediates in the initial stage of the photocatalytic reaction is almost irreversible. The initial oxidation rates on the catalysts are proportional to their surface areas. The surface concentration of illuminated active sites on TiO2 catalysts is estimated to be 0.85–0.96 μmol/m2.
Article
Trichloroethylene in solution with air is oxidized rapidly in the presence of irradiated titanium dioxide. Dichloroacetyl chloride (DCAC), which is formed as an intermediate during the trichloroethylene reaction, also undergoes photocatalytic oxidation. This paper describes the kinetics of these reactions and how operating conditions influence the observed reaction rates. Annular photocatalytic reactors with thin films of titanium dioxide catalyst were used to make kinetic measurements. Observations of the reaction rate of trichloroethylene were made while varying parameters such as catalyst loading, feed flow rate, feed composition, and ultraviolet light energy. The observed reaction rates are higher by several orders of magnitude than those previously reported in the literature, and an expression for the prediction of rate as a function of reactant partial pressure is provided. The rate of reaction of the DCAC intermediate is also discussed. Air is shown to be an optimum oxidant, and an optimum humidity is established. The reaction is shown to proceed indefinitely under dry conditions, supporting the existence of a chlorine radical propagated surface reaction.
Article
Persistent indoor air contaminants, those originating from emissions by interior furnishings, occupants, and materials of construction, typically exist in concentrations below 100 parts per billion (ppb) on an individual basis. The total of distinct contaminants may number in the hundreds with an equivalent accumulated concentration of one part per million. This study investigated the effects of humidity and trace (sub-ppmv) contaminant levels on the oxidation rates of formaldehyde, toluene, and 1,3-butadiene. The evaluation also included variations in UV intensity and flow residence time. UV intensities from inexpensive mercury fluorescent lamps, those which are expected to be employed in a practical photocatalytic purifier, are in the mW/cm2 range. For this reason, the study included UV intensities in that range. The reactor element used in the study was a low pressure drop alumina reticulate, wash-coated with Degussa P25 titania. The data indicated that the reaction was first-order for the three reactants at the sub-ppmv level. An important finding was that competitive adsorption between water and trace (sub-ppmv) contaminants has a significant effect on the oxidation rate. The dependencies of humidity and contaminant concentrations on the oxidation rates are explained as being the results of competitive adsorption on available hydroxyl adsorption sites and of changes in hydroxyl radical population levels.
Article
Concentrations of 15 VOCs including 1,3-butadiene, benzene, and styrene were measured in a wide range of urban microenvironments, viz: homes, offices, restaurants, pubs, department stores, coach and train stations, cinemas, libraries, laboratories, perfume shops, heavily trafficked roadside locations, buses, trains, and automobiles. For most target VOCs-including 1,3-butadiene and benzene-mean concentrations at heavily trafficked roadside locations were exceeded by those in automobiles and were comparable to those in pubs and train stations. With regard to indoor-outdoor relationships in homes, this study revealed higher mean indoor concentrations, no correlation between simultaneously measured indoor and outdoor concentrations, and significantly different patterns of diurnal variation. Thus-in poorly ventilated buildings-indoor emission source strength is considered a more significant influence on VOC concentrations than infiltration of outdoor air. In the six smoking homes studied, environmental tobacco smoke (ETS) was found to make a substantial contribution to concentrations of 1,3-butadiene. This finding was based on the significantly higher concentrations detected in smoking compared to nonsmoking homes, the significant correlation between 1,3-butadiene concentrations and those of 3-ethenylpyridine (an ETS marker), factor analysis, and the results of a source apportionment exercise based on ratios of 1,3-butadiene to 3-ethenylpyridine.
Photocatalytic elimination of harmful gases in air
  • Y W Tao
  • M Y Zhao
  • S F Chen
  • X Liang
Tao, Y.W., Zhao, M.Y., Chen, S.F., Liang, X., 1997. Photocatalytic elimination of harmful gases in air. Journal of Catalyst 7, 345–347 (in Chinese).
ASHRAE Research Project 1134-RP: Evaluation of Photocatalytic Air Cleaning Capability: A Unfinished business: a comparative assessment of environmental problems Characterizing air emissions from indoor sources
  • D T Tompkins
Tompkins, D.T., 2001. ASHRAE Research Project 1134-RP: Evaluation of Photocatalytic Air Cleaning Capability: A Literature Review and Engineering Analysis Final Report. US EPA, 1987. Unfinished business: a comparative assessment of environmental problems, EPA report EPA-230/2-87-025, US Environmental Protection Agency, Washington, DC. US EPA, 1995. Characterizing air emissions from indoor sources. EPA Report EPA/600/F-95/005, US Environmen-tal Protection Agency, Washington, DC. Yoneyama, H., Torimoto, T., 2000. Titanimum dioxide/ adsorbent hybrid photocatalysts for photodestruction of organic substances of dilute concentrations. Catalysis Today 58, 133–140.
Unfinished business: a comparative assessment of environmental problems
  • Us Epa
US EPA, 1987. Unfinished business: a comparative assessment of environmental problems, EPA report EPA-230/2-87-025, US Environmental Protection Agency, Washington, DC. US EPA, 1995. Characterizing air emissions from indoor sources. EPA Report EPA/600/F-95/005, US Environmental Protection Agency, Washington, DC.
ASHRAE Research Project 1134-RP: Evaluation of Photocatalytic Air Cleaning Capability: A Literature Review and Engineering Analysis Final Report
  • D T Tompkins
Tompkins, D.T., 2001. ASHRAE Research Project 1134-RP: Evaluation of Photocatalytic Air Cleaning Capability: A Literature Review and Engineering Analysis Final Report.
TiO2 photocatalysis for indoor air applications
  • Obee
Characterizing air emissions from indoor sources
  • Us Epa
Photocatalytic elimination of harmful gases in air
  • Tao