A mesoporous SiO2 intermediate layer for improving light propagation in a bundled tube photoreactor

A photoreactor comprising a bundle of TiO2-coated quartz tubes was studied by varying its tube wall thickness and tube configuration as well as introducing a mesoporous SiO2 intermediate layer between the TiO2 coating and quartz tube. The bundled tube photoreactor (BTP) performance was assessed based on tube light propagation and photocatalytic degradation rate of ethylene. Increasing the tube wall thickness improved the tube light propagation and the degradation rate of ethylene. An array of eight 6-mm tubes was found to be the best BTP configuration in this work. The findings from varying the tube configuration suggested an effectively illuminated surface area as a second important parameter to consider when comparing different BTP performances. Introducing a mesoporous SiO2 intermediate layer with a thickness between 210 and 400 nm between the TiO2 coating and quartz tube improved not only the tube light propagation but also the ethylene photocatalytic degradation rate by up to 70%. This improvement was attributed to controlled light refraction from the quartz tube, which can be achieved under the conditions of frustrated total internal reflection.