The removal of volatile organic compounds by Pt/TiO2-based thermocatalyst and TiO2-based photocatalytic air purification system

Abstract

Formaldehyde (FA) and toluene are the most common volatile organic compounds (VOCs) present in indoor environment. The International Agency for Research on Cancer (IARC) has classified FA as group 1 human carcinogen, therefore their abatement is highly needed. Among various VOCs removal techniques, the (thermo/photo) catalytic oxidation is a highly useful option to convert VOCs to harmless by-products such as carbon dioxide and water. In particular, TiO2-based composite catalysts have displayed significantly higher catalytic activities with good chemical stability. Therefore, in this thesis work, diverse approaches have been used to develop an effectual TiO2 composite-based catalytic air purification (AP) system. As the first approach, the TiO2-supported Pt catalyst (Pt/TiO2) was used for the thermocatalytic degradation of binary mixture between FA and toluene at ppb levels in a tube reactor system. Specifically, the practical applicably of Pt/TiO2 thermocatalyst was acessed against FA/Toluene in relation to the key process variables (e.g., temperature, flow rate, catalyst mass, VOC concentration, and relative humidity). The 1 wt.%-Pt/TiO2-R (the ‘R’ suffix means thermal reduction pre-treatment using 10% H2) achieved 100% conversion of FA (500 ppb) and toluene (100 ppb) mixture at 130°C. These findings may provide information lacking in the current literature on the purification of VOCs gas mixtures at ppb levels. In the second approach, a mini-scale photocatalytic air purifier (AP) system was built by modifying a porous honeycomb (HC) filter (i.e., through the fabrication of TiO2 photocatalyst on HC filter). The variables of synthesis conditions (e.g., sonication time, concentration of catalyst solution, coating repetition, and calcination temperature/time) were controlled and adjusted to upgrade the photocatalytic oxidation potential of modified TiO2 photocatalytic ceramic filter (PCF) against gaseous FA. The results showed that repetition of the catalyst coating (4 times) over ceramic filter under sufficient solution concentration (3g/L) of TiO2 can help enhance the photocatalytic oxidation efficiency of AP against gaseous FA to achieve 100% degradation. Furthermore, calcination at 450°C for over 5 h resulted in higher photocatalytic performance by increasing the proportion of anatase phase in TiO2 by contributing to the photocatalytic activity of TiO2 under ultraviolet light with the values of QY (3.2E-03 molecules photon-1), STY (3.1E-05 molecules photon-1 mg-1), and FOM (8.6E-05 L mol g-1 J-1 h-1). As such, the use of dip coating methods is an important option for the filter fabrication to enhance the performance. As a results, the proposed catalytic technologies for VOC removal will provide better insights for practical air purification systems.