Volatile organic compounds (VOC) are one of most common air pollutants. There are high health risks associated with the exposure to VOCs in indoor environments. VOC emissions may result from the use of cleaning products, paints, furniture and building materials. Heterogeneous photocatalysis has been shown to provide significant potential for VOC degradation. However, the approaches to be used for the required photocatalyst immobilization in scaled and highly efficient photoreactors are still not well established. Furthermore, there is a lack of reported photonic efficiencies and a shortage of required methods to establish these efficiencies.
Immobilization of a TiO2 aeroxide photocatalyst was accomplished in the present study using a new automatized spray coating method. Careful manipulation of coating variables, including slurry droplet size
, gives a homogeneous nanoparticle agglomerate coating on a stainless steel mesh. The homogeneity of the spray coated immobilized TiO2 was characterized using SEM and local gravimetric measurements. Furthermore, the high performance of the immobilized photocatalyst was established in a 55 liter Photo-CREC Air Reactor. This Photo-CREC-Air Reactor is equipped with 8 near-UV lamps of 15 watts each and a stainless steel coated mesh (1).
The spray coated immobilized TiO2 performance was studied using acetone photodegradation. It was observed that complete mineralization of acetone was achieved for 24 to 49 µmol/L concentrations in 1-2 h. Acetaldehyde was the main intermediate species present. The valuable finding that the spray coated immobilized TiO2 gave 20.1 µmol/g-min initial photoconversion rates versus the 5.59 µmol/g-min for a previously developed brush dispersion coated TiO2 (1) was demonstrated. Furthermore the absorbed photons on the spray coated immobilized TiO2 were calculated using macroscopic radiation balances. These macroscopic radiation balances accounted for incident, scattered and transmitted near-UV radiation. On this basis, Quantum Yields (QY) and Photochemical Thermodynamic Efficiency Factors (PTFE) were calculated with these efficiencies being at the promising levels of 0.65 (65%) and 0.082 (8.2%) respectively.
(1) Garcia-Hernandez, J. M., et al., “Energy Efficiencies in a Photo-CREC-Air Reactor: Conversion of Model Organic Pollutants in Air,” Ind. Eng. Chem. Res. 51 (16), pp 5715-5727 (2012).