Stability of the Cu2ZnSnS4/TiO2 photocatalytic thin films active under visible light irradiation

The study investigates the long term stability and photocatalytic activity (up to 72 h) of the Cu2ZnSnS4/TiO2 thin film heterostructures, under simulated solar radiation, at low irradiance values (34 W/m(2)), using phenol and imidacloprid (c=10 ppm) as testing pollutants. High removal efficiencies correspond to both phenol (73%) and imidacloprid (57%) after 72 h of irradiation, while mineralization occurs slower, with efficiencies up to 42% for phenol, and less than 10% for imidacloprid, in agreement with the pollutant chemical structure. The stability of the photocatalysts in the aqueous pollutant solutions is investigated using VIS transmittance spectra, scanning electron microscopy, atomic force microscopy while photocatalyst leaching was evaluated based on surface composition analysis and atomic absorption spectroscopy. The processes affecting the photocatalyst surface and composition were discussed and the results were correlated with TiO2 layer morphology and porosity and pollutants' structure; promising results are outlined as low variation in the layers transmittance (after 72 h of testing: Delta T-600 < 15% for imidacloprid, Delta T-600 < 30% for phenol). The results recommend the use of Cu2ZnSnS4/TiO2 thin film photocatalyst for large-scale applications, involving organic pollutants removal from wastewaters, even at very low concentrations.