Photocatalyzed degradation on a TiO2-coated quartz crystal microbalance. Adsorption/desorption processes in real time in the degradation of benzoic acid and salicylic acid

The photocatalytic degradations of benzoic acid, phenol and salicylic acid were examined subsequent to in situ adsorption/desorption of the organic substrates on a TiO2-coated quartz crystal microbalance (QCM). The amount of substrate adsorbed from the bulk aqueous solution on the TiO2-coated QCM sensor was investigated at different pH under dark conditions. The order of adsorption was salicylic acid > phenol ∼ benzoic acid on the acidic side; phenol > benzoic acid > salicylic acid under neutral conditions; benzoic acid > phenol ∼ salicylic acid in alkaline media. Salicylic acid was an intermediate in the photodegradation of benzoic acid.