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.

Hydrothermal/solvothermal synthesis and treatment of TiO2 for photocatalytic degradation of air pollutants: Preparation, characterization, properties, and performance.

Photocatalytic oxidation (PCO) is a well-known technology for air purification and has been extensively studied for removal of many air pollutants. Titanium dioxide (TiO2) is the most investigated photocatalyst in the field of environmental remediation owed to its chemical stability, non-toxicity, and suitable positions of valence and conduction bands. Various preparation techniques including sol-gel, flame hydrolysis, water-in-oil microemulsion, chemical vapour deposition, solvothermal, and hydrothermal have been employed to obtain TiO2 materials. Hydro-/Solvothermal (HST) synthesis, focus of the present work, can be defined as a preparation method in which crystal growth occurs in a solvent at relatively low temperature (<200 °C) and above atmospheric pressure. This paper aims to provide a comprehensive and critical review of current knowledge regarding the application of HST synthesis for fabrication of TiO2 nanostructures for indoor air purification. TiO2 nanostructures are categorized from the morphological standpoint (e.g. nanoparticles, nanotubes, nanosheets, and hierarchically porous) and discussed in detail. The influence of preparation parameters including hydrothermal time, temperature, pH of the reaction medium, solvent, and calcination temperature on physical, chemical, and optical properties of TiO2 is reviewed. Considering the complex interplay among catalyst properties, a special emphasis is placed on elucidating the interconnection between various photocatalyst features and their impacts on photocatalytic activity.

Performance of ultraviolet photocatalytic oxidation for indoor air applications: systematic experimental evaluation.

Photocatalytic oxidation (PCO) is a promising technology that has potential to be applied in mechanically ventilated buildings to improve indoor air quality (IAQ). However, the major research studies were done in bench-top scale reactors under ideal reaction conditions. In addition, no study has been carried out on the investigation of the ozonation and photolysis effect using a pilot duct system. The objective of this study is the development of methodologies to evaluate the performance of PCO systems. A systematic parametric evaluation of the effects of various kinetic parameters, such as compound's type, inlet concentration, airflow rate, light intensity, and relative humidity, was conducted, and new interpretations were provided from a fundamental analysis. In addition, the photolysis effect under vacuum ultraviolet (VUV) irradiation for a variety of volatile organic compounds (VOCs) was examined for the first time in a pilot duct system. The performance comparison of ultraviolet C (UVC)-PCO and VUV-PCO was also discussed due to the presence of ozone. Moreover, the formation of by-products generated with or without ozone generation was fully compared to evaluate the PCO technology.

Adsorption performance of titanium dioxide (TiO2) coated air filters for volatile organic compounds.

The photocatalytic oxidation (PCO) technology as an alternative method for air purification has been studied for decades and a variety of PCO models indicate that the adsorption of reactants on the catalyst surface is one of the major physical and chemical processes occurring at a heterogeneous photocatalytic reaction. However, limited study explored the adsorption effect of a photocatalyst. This study carried out a systematic evaluation of adsorption performance of titanium dioxide (TiO(2)) coated fiberglass fibers (FGFs), TiO(2) coated carbon cloth fibers (CCFs), and original CCFs air filters at various relative humidity conditions for nine volatile organic compounds. TiO(2)/FGFs, TiO(2)/CCFs, and CCFs were characterized by SEM for morphology and N(2) adsorption isotherm for BET surface area and pore structure. A bench-scale adsorption test setup was constructed and adsorption tests were performed at various relative humidity conditions and four different injected concentrations for each compound. The isothermal adsorption curves at low concentration levels were obtained and they were well described by Langmuir isotherm model. It was noticed that there were significant differences between the adsorption behaviors and photocatalytic activities of TiO(2)/FGFs and TiO(2)/CCFs. It was concluded that adsorption performance is closely related to the characteristics of substrates and therefore, the development of a substrate with high adsorption ability is a promising trend for improving the performance of the UV-PCO technology.