Photocatalytic degradation of bisphenol-A by nitrogen-doped TiO2 hollow sphere in a vis-LED photoreactor

Abstract

Photocatalytic degradation and mineralization of bisphenol-A (BPA) by a novel photocatalyst, nitrogen-doped TiO2 hollow sphere (NhT), under blue, green and yellow lights emitted by light emitting diodes (LEDs) were investigated. The photocatalyst was synthesized through polystyrene spheres templating and treatment with ammonia to extend its light absorption properties to 550nm (Eg=2.26eV) and meanwhile possess high porosity and specific surface area. Nitrogen incorporation was confirmed through XPS analysis indicating the presence of O–Ti–N or Ti–O–N linkages in the photocatalyst material. The NhT exhibited significant increase of BPA degradation and mineralization under blue, green and yellow lights as compared to the undoped TiO2 hollow sphere, powder TiO2, and Hombikat UV100. The photocatalytic degradation of BPA increased with pH, and the rate was the highest even at pH>pKa1 of BPA (i.e., pH 9.6). At circumneutral pH, 90% of BPA was degraded in 2h under irradiation of blue light with NhT, while TOC removal was 66% after 6h of irradiation. The main aromatic intermediates formed were identified with GC/MS and LC/MS/MS as 4-hydroxyacetophenone, 4-isopropylphenol, 4-isopropenylphenol and isopropanolphenol. The pathways for BPA degradation under visible light appear to agree with those with UV/TiO2.