Photocatalytic degradation of organic micropollutants under UV-A and visible light irradiation by exfoliated g-CN catalysts.

In the present study, the photocatalytic performance of exfoliated graphitic carbon nitride (g-CN) catalysts, with enhanced properties and response in UV and visible light irradiation, was evaluated for the removal of selected contaminants i.e., diuron, bisphenol A and ethyl paraben. Commercial TiO Degussa P25 was also used as a reference photocatalyst. The g-CN catalysts demonstrated good photocatalytic activity which in some cases is comparable to TiO Degussa P25 leading to high removal percentages of the studied micropollutants under UV-A light irradiation. In contrast to TiO Degussa P25, g-CN catalysts were also able to degrade the studied micropollutants under visible light irradiation. For all the studied g-CN catalysts under both UV-A and visible light irradiation, the overall degradation rate decreases in the order of bisphenol A > diuron > ethyl paraben. Among the studied g-CN, the chemically exfoliated catalyst (g-CN-CHEM) showed superior photocatalytic activity under UV-A light irradiation due to its enhanced characteristics, such as pore volume and specific surface area and ~ 82.0 % in 6 min, ~75.7 % in 15 min and ~ 96.3 % in 40 min removals were achieved for BPA, DIU and EP, respectively. Under visible light irradiation, the thermally exfoliated catalyst (g-CN-THERM) demonstrated the best photocatalytic performance and the degradation ranged from ~29.5 to 59.4 % after 120 min. EPR data revealed that the three g-CN semiconductors generate mainly O, whereas TiO Degussa P25 generates both HO and O, the latter only under UV-A light irradiation. Nevertheless, the indirect formation of HO in the case of g-CN should also be considered. Hydroxylation, oxidation, dealkylation, dechlorination and ring opening were the main degradation pathways. The process proceeded without significant alterations in toxicity levels. Based on the results, heterogeneous photocatalysis using g-CN catalysts is a promising method for the removal of organic micropollutants without the formation of harmful transformation products.