Photocatalytic Oxidation Reactor Research Articles

Framework for assessing collection-based photocatalytic oxidation systems in HVAC applications for bioaerosol control

We use a non-dimensional framework to examine the applicability of photocatalytic oxidation (PCO) to reduce bioaerosol concentration in heating, ventilation, and air conditioning (HVAC) systems. Two non-dimensional parameters: collection efficiency and dimensionless photon flux were used to evaluate the performance of two PCO reactor geometries: 1) honeycomb (HC) and 2) parallel plate (PP) since bioaerosol deposition and photon utilization are prerequisites for effective inactivation in collection based PCO systems. Collection efficiencies of the HC for bioaerosols (0.01–10 μm) were modeled by varying aspect ratios from 25 to 100, air velocities from 0.5 to 2 m/s, and charge numbers from 10 to 10000. The collection efficiencies and the photon fluxes of HC and PP were compared using prior literature studies. The modeling results show that larger bioaerosols (5–10 μm) have a higher collection efficiency than other aerosols for low velocities and longer channels. Larger aspect ratios (channels that are longer for a given diameter) are needed than those found in most commercial HC products, since the effects of gravitational settling and diffusion are inadequate for bioaerosol collection. Furthermore, using ionizers to increase the collection efficiency of PCO systems proved ineffective. The efficiency only increased 2 to 5 times for 0.01–1 μm bioaerosols for charge numbers on the order of 1000. These charge numbers may be impractical to obtain for this size range. PP requires longer channel lengths than HC to achieve the same collection efficiencies. However, the PP configuration has better photon utilization characteristics than HC.

Development of Fe/HNT and Fe/HNT-Al2O3 composite catalysts and application in successive treatment processes for pharmaceutical industry wastewater

The pharmaceutical industry wastewater (PIW) was treated by successive use of electro Fenton (EF) and photocatalytic oxidation (PcO) processes. Nano-particular powdered Fe/HNT (Iron/Halloysite nanotube) heterogeneous semiconductor catalyst was initially produced with Fe(OH)3 sludge modification precipitated after EF process. Thus, photocatalyst material was produced from the waste sludge and used in the PcO process. Photocatalyst Fe/HNT powder was immobilized on a three-dimensional (3D) reticulated Al2O3 ceramic support to enable rapid recovery of the catalyst from the PcO reactor system. Particle morphology and chemical configuration of the heterogeneous catalysts were analyzed with SEM (Scanning Electron Microscopy)-EDS (Energy-Dispersive X-ray spectrometry), UV-DRS (Ultraviolet Diffuse Reflectance Spectra) and XRD (X-ray diffraction). The Fe/HNT layer was calcined at three different temperatures (350, 450 and 600 °C). The optimum temperature was determined as 350 °C for better photocatalytic performance and practical reasons such as energy consumption. The successive use of EF + PcO processes for degradation of three different PIW samples was investigated by using two catalyst forms (nanoparticle and reticulated) and light sources (visible and sun light). The max TOC removal efficiency by EF + sun light-PcO (with Fe/HNT) successive treatment process was obtained as 78.4 %. Besides, the energy consumption value was calculated for optimum process state and calculated as 48.8 kWh/kg TOC at the EF + sun light-PcO (with Fe/HNT) successive treatment process.

Ozone-assisted degradation of 2-methoxyethanol in a prototype plug flow photocatalytic reactor

Airborne volatile organic compounds (VOCs) present an increasingly relevant health hazard addressed by the EU directive 2016/2284 requiring 40-% reduction in emissions of non-methane VOCs by 2030 in comparison to 2005. Advanced oxidation processes (AOPs) provide a solution for the VOC problem in industry. Among AOPs, pulsed corona discharge (PCD) and photocatalytic oxidation (PCO) are of particular interest in their synergy complementing each other’s strengths in energy-efficient manner. In the present study, air polluted with 2-methoxyethanol (2ME) was treated by using a prototype 21.3 L photocatalytic reactor for the pollutant degradation at its variable concentrations (6–50 ppm), irradiances (65–119 W m−2) and residence times (12–77 sec). Further combination of PCO reactor with forthcoming PCD requires studies in ozone photocatalytic degradation as a standalone byproduct and in combination with 2ME. The analysis of variable conditions resulted in singling out the PCO major restrictive parameters, also demonstrating the degradation enhancement, when both 2ME and ozone were present in air. The PCO treatment combined with ozone resulted in degradation of 2ME and ozone for 40 % and 95 %, respectively.

Facile synthesis of carbon layered TiO2 nanocomposite for high photocatalytic activity

A green synthesis route was designed to develop a visible-light-driven thin carbon layered titanium dioxide (CLT) nanocomposite using ascorbic acid as carbon precursor. The presence of a thin layer of carbon (CLT) on the TiO2 surface was observed from HR-TEM. The thickness of CLT is directly proportional to the concentration of carbon precursor, where this CLT acts a photosensitizer for harvesting the broad band of visible light spectrum. CLT nanocomposite (15.485 m2/g) showed an improved surface area of 1.4 times that of a commercial TiO2 (7.461 m2/g). The photocatalytic activity of CLT nanocomposite was investigated for the volatile organic compound destruction using p-xylene pollutant in a standard ISO photocatalytic oxidation reactor under daylight. The mechanism pathway of CLT nanocomposite was followed by the adsorption of chemical contaminants in the pores of CLT that precisely capture the contaminants capture and destruction on its surface. The electron-hole pair recombination rate of CLT nanocomposite was lower than the pristine TiO2 was evident from photoluminescence spectra. The antibacterial activity of CLT was also studied using E. coli as a model pathogen. This environmentally friendly photocatalyst CLT offers a novel route for good industrial utilization because of its low cost and mass production.

Optimization of photocatalytic oxidation reactor for air purifier design: Application of artificial neural network and genetic algorithm

Photocatalytic oxidation (PCO) is a promising approach for eliminating volatile organic compounds (VOCs) from indoor environments. The generation of toxic by-products, however, prevents this method becomes widely used. There is a lack of comprehensive model for the prediction of PCO removal efficiency and by-products generation, and its optimization. To address that, this study focusses on modeling and optimization of PCO based on artificial neural networks and genetic algorithms. The concentrations of target VOCs and three common by-products are estimated using the ANN model, which takes seven input parameters into account. They include; PCO type, number of PCO layers, air velocity, relative humidity, light intensity, and target VOC and its concentration. A number of ANN-based estimation concentration models are trained, validated, and tested using the experimental data from bench and pilot scale set-ups (a total of 260 data points). The best performance is achieved with a three-layer feed-forward back-propagation structure with 11 neurons in the hidden layer (7:11:4), tansig-purelin transfer function, and Levenberg-Marquardt (LM) as the training algorithm. The proposed ANN model could be trained to predict the concentration of different VOCs and formed by-products with a high accuracy (R2 of 0.99), which was further validated and tested with 0.98 and 0.97 precision, respectively. The relative importance of input parameters in the removal of target VOC and generated by-products showed that PCO media and type of target VOC were the most influential variables. Further, multi-objective optimization for maximizing removal efficiency and minimizing by-products showed that the optimal condition for PCO process is achieved when two layers of glass fiber-based PCO media is used as a photocatalyst, and the system is operating at air velocity of 0.91 m/s and relative humidity of 48.7%, and butyraldehyde concentration of 47.3 ppb.

Modeling of ternary mixture of VOCs in photocatalytic oxidation reactor for indoor air quality application

Photocatalytic oxidation (PCO) is an innovative method of removing volatile organic compounds (VOCs) from indoor air. PCO technology employs a semiconductor (such as TiO2) and ultraviolet light to decompose VOCs via successive oxidation processes and creates CO2 and H2O as the ultimate products of complete mineralization. The greatest drawback of this technology is, however, the production of hazardous by-products. The possible health risk posed by hazardous by-products inhibits the commercial adoption of PCO-based air purifiers in the indoor environment. Modeling is a powerful tool to address the chemical interaction and mass transfer phenomenon in the PCO reactor. This study presents the modeling of a ternary mixture of VOCs and generated by-products using a proposed degradation reaction pathway. A one-dimensional mathematical model by considering the axially dispersed plug flow and Langmuir-Hinshelwood (L-H) based reaction rate as well as linear source spherical emission model (LSSE) for the irradiation distribution on the media surface were used for modeling of VOCs and by-products. Three VOCs from different chemical groups (aldehyde, ketone, aromatic groups) were chosen as challenge compounds, and a commercial PCO filter (TiO2 coated on silica fiber felts) was considered as a photocatalyst. The model prediction was performed at different levels of concentration (0.1–1 ppm), relative humidity (15–70%), air velocity (0.016–0.1 m/s), and light intensity (7–23W/m2). Among generated by-products, aldehydes were the major by-products of VOCs in the PCO reactor. It was revealed that increasing concentration and irradiation, as well as decreasing relative humidity and velocity, increases by-product generation.

A Simple and Low-cost Photocatalytic Air Purification Test Method

The application of photocatalytic oxidation (PCO) in air purifiers (AP) to remove viruses, bacteria, and toxic gases in the air is intensively being studied, especially after the Covid-19 pandemic broke out. The testing method of PCO materials for AP purposes has been standardized through ISO 22197-4 (2013). However, the standard required a set of complex, high precision, and costly equipment. The present study demonstrates a simpler and low-cost test setup without compromising any accuracy in the overall result. The proposed test consists of a test chamber and mixing chamber, and sets of equipment installed in it. A 3D printer fabricated a PCO reactor, and TiO2 was coated on the surface. Formaldehyde (HCHO) is used as a sample pollutant to be observed, injected into the test chamber. Before the measurement of the concentration of HCHO, the intensity of UV A LED was measured. Then, the amount of formaldehyde concentration was monitored online by indoor air quality measurement equipment. The result shows that the intensity of UV light was enough to generate a photocatalytic oxidation reaction. After 20 minutes of reaction, the HCHO concentration inside the chamber was decreased around 21.76%.

Kinetic modeling of binary mixture of butyraldehyde and acetone with generated by-products in photocatalytic oxidation reactor

This research reports the development of a kinetic model to predict binary mixture degradation and by-product generation in a continuous flow Photocatalytic Oxidation (PCO) reactor. Butyraldehyde and acetone were chosen as a binary VOC mixture to validate the model using experiments conducted with a photocatalyst (TiO2 coated on silica fibers) under various concentration levels (0.1–1 ppm), concentration ratios of target compounds in the mixture (0.5–2), relative humidity levels (17–70%), irradiations (7–23.5 W/m2), and airflow rate (10–30 L/min). Formaldehyde, acetaldehyde, propionaldehyde, butyric acid, propionic acid, and acetic acid were detected as by-products, in which aldehydes had a higher quantity. Carbon balance analysis showed that butyraldehyde and binary mixtures mineralized into carbon dioxide at rates of 19% and 12.8%, respectively. Also, 24% of butyraldehyde and 10% of binary mixture were converted to by-products. Among three proposed scenarios for PCO reaction rate of butyraldehyde, the one including conversion of butyraldehyde directly towards propionaldehyde, acetaldehyde, and formaldehyde, provided the most accurate rate model (R2 = 0.98). Due to its faster reaction rate, butyraldehyde demonstrated a higher degradation efficiency than acetone in the binary mixture. At a constant butyraldehyde concentration, lowering the ratio of butyraldehyde/acetone to 0.5 resulted in the reduction of removal efficiency of butyraldehyde and an increase in concentration of acetaldehyde in air than other by-products. Conversely, enhancing this ratio to 2, led to improved removal efficiency of both butyraldehyde and acetone in the mixture and higher concentration of formaldehyde. Increases in air relative humidity level and velocity resulted in an increase in the outlet concentration of challenge compounds but reduced the formation of all by-products. However, raising the irradiation increased the degradation efficiency of butyraldehyde and binary mixture and, consequently, elevated the formation of by-products. The developed model was capable of properly predicting the concentration of the challenge compounds and their by-products in a binary mixture at different operating conditions.

Kinetic modeling and reaction mechanism of toluene and by-products in photocatalytic oxidation reactor

Photocatalytic oxidation (PCO) is an innovative and promising technology for removing VOCs from indoor environment. However, partial oxidation of reactants generates by-products that could be more harmful to human health than parent compound. This paper presents the development of a by-products predictive model for the estimation of generated by-products based on the degradation reaction pathway of toluene in PCO. A one-dimensional mathematical model by considering the axially dispersed plug flow and Langmuir-Hinshelwood (L-H)-based reaction rate as well as linear source spherical emission (LSSE) model for the irradiation distribution on the media surface was developed for the prediction of the by-products concentration. Toluene was tested in a continuous flow PCO reactor with a commercial PCO filter under various operating conditions; concentrations (0.05–1 ppm), relative humidities (17–67%), flow rates (10–30 L/min), and irradiance (7–23.5 W/m2). Several by-products from various chemical groups, including aldehyde, ketone, alcohol and light acid, were identified by analytical instruments. Aldehydes were the major by-products of toluene in PCO, in which light aldehydes (acetaldehyde and formaldehyde) had a higher concentration among others. The result of curve fitting using the proposed model showed a high accuracy of the model (with R-squared greater than 0.98) for parameters estimation. Kinetic analysis of toluene indicated that the rate coefficients followed the order of benzaldehyde > propionaldehyde > acetaldehyde > formaldehyde. Benzaldehyde and propionaldehyde had a greater value of the kinetic coefficient in PCO because of higher adsorption tendency towards TiO2. Changes in operating conditions highly affected generation of by-products and the developed model could predict the concentration of toluene and the by-products with acceptable accuracy. The carbon balance analysis at residence time of 0.24 s showed 16.6% of toluene mineralized into carbon dioxide and it increased at longer residence time. The health risk index (HRI) analysis of toluene and its by-products was performed and found out that formaldehyde was the most influential pollutant on HRI due to very low recommended exposure limit and higher generated concentration.

Kinetic and reaction mechanism of generated by-products in a photocatalytic oxidation reactor: Model development and validation

Photocatalytic oxidation is a promising technology to control air pollution. However, the formation of hazardous by-products hinders the commercialization application of this technology. This paper reports the development of a novel by-products predictive model considering the mass transfer of the pollutant in the gas phase and kinetic reaction in the solid phase. Two challenge compounds from ketone group (acetone and methyl ethyl ketone) were examined for model validation in a continuous Photocatalytic Oxidation (PCO) reactor with TiO2 coated on silica fiber felts. A possible reaction pathway for degradation of each challenge compound was proposed based on identified by-products using analytical methods (GC-MS and HPLC). Formaldehyde, Acetaldehyde, Propionaldehyde, Ethanol, and acetic acid were detected as by-products of the Acetone and Methyl Ethyl Ketone in the PCO reactor. Different possible reaction rate scenarios were evaluated to find the best expression fitted to experimental data at the steady-state condition. The obtained reaction coefficients were then used to validate the model under various operating conditions, namely concentration, relative humidity, irradiation, and velocity variations. Higher concentration and irradiation, as well as lower relative humidity and velocity, resulted in more by-products generation. It was also observed that with enhancing residence time, mineralization efficiency (or CO2 formation) and by-products generation increases through PCO reaction. The model validation provided acceptable accuracy for both steady-state and transient conditions. Finally, the Health Risk Index was used to investigate the implications of generated by-products on human health under varying operating conditions.

Modeling of photocatalytic oxidation reactor for methyl ethyl ketone removal from indoor environment: Systematic model development and validation

This paper describes the development of a model for predicting the performance of ultraviolet photocatalytic oxidation (UV-PCO) reactor for the removal of volatile organic compounds (VOCs) from indoor environment. The proposed model performance was validated at two stages. First, it was validated by comparing its performance with the prediction made by other models (inter-model comparison), and with experimental data from two different scales (pilot and bench) of UV-PCO reactors. A good agreement (with R2 = 0.98) between the developed model prediction and the experimental data was observed.Simulation of light intensity with linear source spherical emission model (LSSE) in bench-scale reactor showed a more uniform distribution than pilot-scale, due to longer distance of the lamp from the media in the bench-scale reactor. Beer-Lambert model demonstrated that light absorbed totally with one media, and adding extra media does not improve the PCO removal performance. Furthermore, Langmuir-Hinshelwood (L-H) rate expression by considering competitive effect of water and by-products with target compound was used. Formaldehyde and acetaldehyde were identified as the main by-products of the Methyl Ethyl Ketone (MEK) PCO reaction.A sensitivity analysis was performed to investigate the impact of three dimensionless parameters—Peclet (Pe), Stanton (St), and Damköhler (Da) numbers on the system performance. Simulation results indicated the UV-PCO process is mainly limited by the reaction rate at low removal efficiency. For higher removal efficiency, both the photochemical reaction rate and advective mass transfer have a significant impact on the system performance. The practical validation of the dimensionless model at two different scales of PCO reactor with same operating condition indicated that the proposed dimensionless model analysis can provide useful advice (qualitatively and quantitatively) for scale-up of PCO for the real application.

Modeling of gas-phase heterogeneous photocatalytic oxidation reactor in the presence of mass transfer limitation and axial dispersion

Mass transfer plays a critical role in the efficiency of photocatalytic oxidation (PCO) technology for air purification applications. There has been limited work on the exploration of mass transfer in the PCO reactor with the non-ideal flow. In this work, the performance of a continuous heterogeneous ultraviolet photocatalytic oxidation (UV-PCO) reactor was investigated and addressed under mass transfer limitation and axial dispersion. First, CFD modeling was used to determine the flow distribution in the reactor at various airflow rates. The residence time distribution (RTD) analysis with a tracer gas (CO2) was carried out for the experimental validation of the simulation model and good agreement between experimental and simulation data was achieved. Further, a quick and straightforward methodology employing an axial dispersion plug flow model was used to study the RTD. The proposed model could predict the residence time distribution of CO2 with high accuracy. Results of the RTD for CO2 in the presence and absence of a PCO filter (silica fiber felts (SFF) modified with TiO2) were almost identical due to the high porosity of the filter. The model was then used for the evaluation of the axial dispersion of methyl ethyl ketone (MEK) at different flow rates. Owing to a low value of the Peclet number (Pe < 100), the flow in the reactor deviated from an ideal plug flow and dispersion could not be ignored. The photocatalysis reaction of MEK by the SFF filter under the mass-transfer-controlled regime was further addressed. A steady-state mass balance equation was implemented for the assessment of the performance of the UV-PCO reactor in the presence of axial dispersion and mass transfer limitation. The mass transfer coefficient was calculated with the use of the developed model and a correlation for the Sherwood number was proposed to relate the mass transfer coefficient to the flow rate and fiber structure. The proposed correlation was assessed and compared with the other empirical formulas available in the literature.

Efficacy of photocatalysis and photolysis systems for the removal of ethylene under different storage conditions

Most fresh horticultural commodities are highly perishable and ethylene often plays an important role in their ripening and senescence process. Reduction of ethylene concentrations around these commodities may lead to the slowing down of metabolic processes, which could potentially extend their storage or shelf life. The objective of this work was to investigate photocatalytic oxidation (PCO) and vacuum ultraviolet light (VUV) photolysis for ethylene removal in fruit storage. The efficacy of both techniques for ethylene removal was analyzed under different storage conditions (initial ethylene concentration, oxygen, relative humidity and temperature). Ethylene removal in VUV photolysis was much faster than PCO with the reaction mechanism followed by Langmuir-Hinshelwood and first-order equations, respectively. Higher O2 concentration in the reactor favored both ethylene removal processes. However, high relative humidity impeded PCO and enhanced VUV photolysis efficacy of ethylene oxidation. Lowering the temperature from 21 °C to 1 °C showed no consistent trend of temperature effects on ethylene removal in the PCO process, whereas in VUV photolysis, reducing the temperature decreased ethylene removal significantly (p ≤ 0.05). Ethylene removal in a gas stream with a single pass through VUV photolysis reactor was 84.8% whereas it was only 14.9% in PCO reactor. Apple storage revealed that the ethylene concentration increased to 70 μL L−1 in 8 days at 1 °C. This concentration was brought down to 24 and 2.6 μL L−1 in storage chambers connected to PCO and VUV reactors, respectively. Further research efforts are needed to improve the performance of the reactors for the complete removal of ethylene in postharvest storage of fresh produce.

Photocatalytic treatment of VOC industrial emissions: IPA removal using a sensor-instrumented reactor

This work aims at evaluating the applicability of photocatalytic oxidation (PCO) for industrial emission treatment. A dedicated single-pass semi-industrial PCO reactor is designed and the PCO removal of isopropanol (IPA) is investigated under industrial conditions: (i) high IPA concentrations ranging from 1.8 to 14.6 ppm and (ii) high air flow rates ranging from 26 to 146 m3.h−1. The concentrations of upstream and downstream IPA and by-products are monitored, not only using analytical instruments (mass spectrometry), but also gas micro-sensors. This approach aims at assessing the aptitude of commercially available micro-sensors to monitor a semi-industrial PCO reactor, and estimating their ability to automate such a process for industry. First, the influence of the main process parameters has been addressed: (i) IPA concentration, (ii) total air flow rate, (iii) number of PCO stages and (iv) number of PCO media. Irrespectively of the process condition, IPA PCO does not lead to deactivation of the media; whereas IPA mineralization and side-products formation are directly impacted by the process parameters. The increase of IPA concentration and air flow rate inhibits IPA mineralization, while the increase of number of stages and media promotes IPA mineralization. It is evidenced that selected gas micro-sensors can provide a semi-quantitative monitoring of the process performances. The main limitations of sensors are (i) their resolution regarding the detection of concentration variations and (ii) their cross-sensitivity to various classes of VOCs. Nevertheless, some sensors could be relevant for the automation and control of the PCO process once a preliminary metrological validation with relevant analytical devices is performed.

Photocatalytic oxidation of dairy effluent with UV lamp or UV light-emitting diode module and biological treatment processes

The objective of this study was to develop a novel and simple-operated treatment system for refining dairy farm effluent after conventional dairy wastewater treatment system. Experimental results showed that average removal efficiency of COD, BOD, and SS in the effluents of a dairy farm was 72, 98, and 79%, respectively, using a combined photocatalytic and biological reactors. Removal efficiency of calculated conductivity value seems to be closely related to the removal efficiency of NH4+, PO43−, and Mg2+ when using the photocatalytic UV lamp reactor only. However, average removal efficiency of COD, BOD, and SS in the dairy farm effluent was 53, 62, and 62%, respectively, with the photocatalytic UV LED reactor. In summary, removal efficiency of BOD, COD, SS, and EC in photocatalytically treated dairy farm effluent with UV lamp reactor was higher than that with photocatalytic UV LED reactor. In addition, removal efficiency of COD and BOD with a combined photocatalytic and biological treatment system was higher than that using a photocatalytic oxidation reactor only. Thus, the combined system can provide dairy cattle farmers to refine and recycle their effluents.

Investigation of Photocatalytic Oxidation and Wet Absorption in a Combined System for Removal of Nitrogen Oxides

Background: One of the important achievements of the past decade was the rapid growth of industries and accordingly production of various chemical compounds. Objectives: This study presents a combined system of photocatalytic oxidation and absorption solution to remove nitrogen oxides from polluted air flow. Materials and Methods: The experimental system used in this study comprised a pollutant gas source, mixing chamber, photocatalytic oxidation reactor, wet absorption system, and finally a system for measuring nitrogen oxides. Firstly, by using photocatalytic property, nitrogen oxide was converted to nitrogen dioxide. Then, absorption system was used to absorb nitrogen dioxide into the sodium hydroxide solution. Results: Experimental results have shown that output of nitrogen oxide removal in the initial concentration of 200 ppm was 44% in the beginning of the process and then fixed at 15% during the rest of the process. Also, by changing the amount of zinc oxide nanoparticles from 4 to 8 mg/cm2, no considerable change was observed in the conversion rate of nitrogen oxide. In addition, while the weight percentage of the solution was 5%, the maximum removal of nitrogen dioxide happened. Conclusions: Application of zinc oxide as the photocatalyst can be effective in the removal process.

Visible-light photocatalytic oxidation of CO over plasmonic Au/TiO2: Unusual features of oxygen plasma activation

To seek an efficient activation of plasmonic Au/TiO2 photocatalysts, atmospheric-pressure cold plasmas of oxygen (OP) and argon (ArP) were employed to activate the Au/TiO2 coating samples on glass substrate and compared with the conventionally calcination. The activated samples were evaluated in a continuous-flow photocatalytic oxidation (PCO) reactor under visible light (λ>420nm) for CO removal from synthetic air and characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–vis spectroscopy, CO chemisorption and electron paramagnetic resonance (EPR). Although Au nanoparticles (NPs) of the three activation samples averaged at around 4nm by TEM, the OP and ArP samples exhibited the highest and lowest PCO activity, respectively. An unusual feature of oxygen plasma activation is high content of surface oxygen, which favors superoxide (O2−) formation by accepting hot electron generated from absorption of visible light through local surface plasmon resonance (LSPR) of Au NPs. The OP sample has the lowest metallic Au content but its cationic Au can be rapidly reduced to form numerous low-coordinated metallic Au around the interface between Au NPs and TiO2 support in the induction period, which is another unusual feature of oxygen plasma activation.

Solar Heterogeneous Photocatalytic Oxidation for Water and Wastewater Treatment: Problems and Challenges

Solar operation of heterogeneous photocatalytic oxidation reactors is looked at as a sustainable process for water and wastewater treatment, because it does not consume electric power and chemicals. However, there are still problems for technical-scale application. The problems addressed in this article are large area demand, water evaporation from open reactors and lack of simple photocatalyst recovery. An optimum solar reactor type is the parabolic compound collector reactor with borosilicate glass tubes. Challenges for further research are improvement in mass transfer as well as identification of novel photocatalysts which make use also of visible light, are efficient and stable, and are easy to be produced in an economically feasible way. Also the combination of photocatalysts with adsorbents is promising. Although membrane filtration processes have been successfully combined with solar photocatalytic oxidation and represent a safe barrier against spreading photocatalyst nanoparticles into the aquatic environment, more simple and less energy-consuming methods for photocatalyst recovery would be desirable.

Investigating the effect of gas flow rate and amount of zinc oxide nanoparticles on the efficacy of photocatalytic oxidation process of nitrogen oxide from waste airstream

Nitrogen oxides are one of the most important air pollutants in environment and industrythat due to the adverse health and environmental effects should be refined before discharging into the environment. The photocatalytic oxidation method of nitrogen oxide into nitrogen Dioxide for better absorption insolutions is a promising method for removing of nitrogen oxides. Laboratory system used in this study is included of a source of gas source, mixing chamber, photocatalytic oxidation reactor, measuring system for nitrogen oxidation. Zinc oxide nanoparticles which were simulated by UV-A radiation would be used for photocatalytic oxidation. Inlet concentration of nitrogen oxide and the amount of stabilized nanoparticles in reactor for converting nitrogen oxide into nitrogen dioxide has been investigated. Results showed that the amount of monotonic converting of nitrogen oxide into nitrogen dioxide in the amount of Nano-particles is stabilized 8mg/cm 2 for inlet concentration 100,150,200 ppm and respectively equivalent to 15, 26 and 32%. This study showed that increasing concentration of inletnitrogen oxide in system, reduce the capacity of photocatalytic oxidation for converting nitrogen oxide into nitrogen dioxide.

Acceleration of Trimethylamine Removal Process Under Synergistic Effect of Photocatalytic Oxidation and Surface Discharge Plasma Reactor

Removal of trimethylamine (TMA) from the air is experimentally investigated by combining photocatalysis with a DBD plasma reactor, at ambient temperature and atmospheric pressure. Many parameters are investigated in this work, such as flowrate, inlet concentration, relative humidity of effluent, and specific energy of discharge. By combining non‐thermal plasma and photocatalysis, a synergy effect on the removal efficiency of TMA has been observed under different experimental conditions. Moreover, we note that adding a photocatalyst in the zone of plasma inhibits ozone formation. The formation of by‐products due to TMA removal is also studied. The identified and analyzed by‐products are classified into four groups: intermediary products, carbon monoxide, carbon dioxide, and ozone and nitrogen oxides.