Titanium Dioxide in gas-Phase Photocatalytic Oxidation of Aromatic and Heteroatom Organic Substances: Deactivation and Reactivation of Photocatalyst

Kinetic Aspects of Benzene Degradation over TiO2-N and Composite Fe/Bi2WO6/TiO2-N Photocatalysts under Irradiation with Visible Light

In this study, composite materials based on nanocrystalline anatase TiO2 doped with nitrogen and bismuth tungstate are synthesized using a hydrothermal method. All samples are tested in the oxidation of volatile organic compounds under visible light to find the correlations between their physicochemical characteristics and photocatalytic activity. The kinetic aspects are studied both in batch and continuous-flow reactors, using ethanol and benzene as test compounds. The Bi2WO6/TiO2-N heterostructure enhanced with Fe species efficiently utilizes visible light in the blue region and exhibits much higher activity in the degradation of ethanol vapor than pristine TiO2-N. However, an increased activity of Fe/Bi2WO6/TiO2-N can have an adverse effect in the degradation of benzene vapor. A temporary deactivation of the photocatalyst can occur at a high concentration of benzene due to the fast accumulation of non-volatile intermediates on its surface. The formed intermediates suppress the adsorption of the initial benzene and substantially increase the time required for its complete removal from the gas phase. An increase in temperature up to 140 °C makes it possible to increase the rate of the overall oxidation process, and the use of the Fe/Bi2WO6/TiO2-N composite improves the selectivity of oxidation compared to pristine TiO2-N.

Simultaneous removal of gaseous benzene and toluene with photocatalytic oxidation process at high temperatures under UVC irradiation

Organic air pollutants represent many different pollutants, including persistent toxic organics and volatile organic compounds (VOC). The VOC group includes about 150 different compounds, the majority of which are considered harmful and toxic to human health. Considering all these features, the removal of VOC is of great importance. According to the Industrial Air Pollution Control Regulation, VOCs in flue gases are classified, and the limit value for the most dangerous group is specified as 20 mg/m³ according to the degree of damage. From past to present, many different removal technologies have been developed and continue to be developed. Removal of pollutants at low concentrations by conventional methods is more inadequate than those above certain concentrations. Photocatalytic oxidation (PCO) is one of the technologies used for VOC removal recently. It has been determined that many different organic pollutants can be removed with this method. Within the scope of this study, the removal of benzene and toluene pollutants, which are two important VOCs frequently encountered in flue gases, by the photocatalytic oxidation method has been studied under UVC irradiation. In this study, a new photocatalyst by doping silver (Ag), a noble metal, and nickel (Ni), one of the transition metals, on TiO₂ nanoparticles was developed and a laboratory-scale reactor system was designed. Many experiments were carried out by changing the system parameters such as ambient temperature (120 °C, 150 °C, 180 °C), humidity (25% and 50%), and percentage of Ag and Ni doping on TiO₂ (0.5%, 1%, 2.5%, %5) and the most successful conditions for the removal of benzene and toluene contaminants were tried to be determined based on the results obtained. When all experiments carried out within the scope of this study were considered, the average removal efficiency for benzene was found as 89.33%, while the average removal efficiency for toluene was 88.23%. According to the obtained results, the most suitable conditions for the simultaneous removal of benzene and toluene pollutants with photocatalytic oxidation method under UVC light were determined as 120 °C temperature, 25% humidity, and 0.5% doping photocatalyst.