Study on the Indoor Volatile Organic Compound Treatment and Performance Assessment with TiO₂/MCM-41 and TiO₂/Quartz Photoreactor under Ultraviolet Irradiation

Abstract

Volatile organic compounds (VOCs) are the cause of indoor air pollution and are readily emitted from furniture and cleaning agents. In Taiwan, the concentrations of indoor VOCs range roughly from 1 to 10 ppm. It is important to effectively reduce indoor VOC emissions and establish the implementation of long-term, low-cost, controlled techniques such as those found in the ultraviolet/titanium dioxide (UV/TiO₂) control systems. This study evaluates the performance of a photoreactor activated by visible irradiation and packed with TiO₂/quartz or TiO₂/mobile catalytic material number 41 (MCM-41). The photocatalysts tested include commercial TiO₂ (Degussa P-25) and synthesized TiO₂ with a modified sol-gel process. The UV light had a wavelength of 365 nm and contained an 8-W, low-pressure mercury lamp. Reactants and products were analyzed quantitatively by using gas chromatography with a flame-ionization detector. It is important to understand the influence of such operational parameters, such as concentration of pollutant, temperature, and retention time of processing. The indoor concentrations of VOCs varied from 2 to 10 ppm. Additionally, the temperatures ranged from 15 to 35 °C and the retention time tested from 2 to 8.2 sec. The results show that quartz with TiO₂ had a better photoreductive efficiency than quartz with MCM-41. The toluene degradation efficiency of 77.4% with UV/TiO₂/quartz was larger than that of 54.4% with the UV/TiO₂/MCM-41 system under 10-min reaction time. The degradation efficiency of the UV/TiO₂ system decreased with the increasing concentrations of indoor VOCs. The toluene degradation efficiency at 2 ppm was approximately 5 times greater than that at 10 ppm. The photoreduction rate of the VOCs was also evaluated with the Langmuir– Hinshewood model and was shown to be pseudo-first-order kinetics.