Background and aims: Clean air is one of the most important components of health and sustainable development. Every person breathes about 10 kg of air per day and if it contains pollutants, it will have a serious impact on their health. Indoor air quality (IAQ) is one of the major health issues that have been addressed in recent years with changes in lifestyle patterns. Usually, due to the increased time of presence and activity in these environments and reduced air exchange with the outdoor environment, indoor air quality is poorer than outdoor environments. Toluene is a Volatile organic compound with widespread applications. VOCs has a high vapor pressure and high emission rate to environment. Due to its adverse effects on human and environment health, they must be controlled before discharging to the environment. Photo catalytic oxidation process is one of the environment-friendly and effective methods for the remove the organic compounds from the air which likely to be better in combination with other methods such as adsorption. Through the process of PCO, UV radiation adsorption on TiO­₂ is associated with forming electron and holes from electron escape. The resulted electrons have got high levels of oxidation power and act as a strong oxidant producing superoxide ion. The resulted holes have good oxidation potential; with superoxide ions, they make good conditions for oxidation of most organic compounds to less hazardous compounds such as carbon dioxide and aqueous vapor. The most important limitation of Photo catalytic oxidation process is the dependence of the contaminant removal on the surface chemistry and the residence time of the contaminant on the photo catalyst surface. The most important limitation of the adsorption method is the decrease in adsorption removal efficiency and elimination capacity due to the filling of the adsorption sites.
According to this, by combining adsorption and photo catalytic oxidation, it is possible to increase the time of contaminant presence at photo catalytic oxidation sites and to enhance the surface chemistry and on the other hand, to restore the adsorption sites. This study is conducted with the aim at examining the effects of combination Activated carbon and Titanium dioxide (TiO2) on the toluene removal efficiency.
Methodology: In order to prepare samples, 5g of TiO2 and 5g of TiO2 and 1g of activated carbon dissolve in separate 100 ml distilled water under vigorous stirring. The surface modification was done by dip-coating method. The efficiency of the photocatalytic oxidation of toluene is evaluated in two separate reactors exposed to ultraviolet light. Additionally, to investigate the effect of initial concentration of toluene and airflow rate on the photocatalytic removal efficiency in photocatalytic and photocatalytic-adsorption beds, the RSM method was used to design experiments.
Also, Scanning Electron Microscopy was used to determine catalysts surface morphology. First, to obtain the adsorption capacity in both reactors, with the UV lamp being off, the considered concentrations were added to the reactors in 2-5 L/m airflows. Then, adsorption capacity of adsorption beds were evaluated according to the time needed for the outlet concentration to reach 10% of the inlet amount, as the fraction point of the adsorbent and saturated capacity.
Next, to compare the removal efficiency of toluene in the two reactors, the lamps were immediately turned on; concentrations were gradually decreased and when the outlet concentration was balanced, the data was collected.
Results: Images from an electron microscope of surfaces of the two catalysts showed that the distribution of nanoparticles on glass wool was similar and the particle size in the non-combined catalyst were smaller than 95 n