Photocatalytic degradation of organic micropollutants under UV-A and visible light irradiation by exfoliated g-C3N4 catalysts

In the present study, the photocatalytic performance of exfoliated graphitic carbon nitride (g-C3N4) catalysts, with en-hanced properties and response in UV and visible light irradiation, was evaluated for the removal of selected contami-nants i.e., diuron, bisphenol A and ethyl paraben. Commercial TiO2 Degussa P25 was also used as a reference photocatalyst. The g-C3N4 catalysts demonstrated good photocatalytic activity which in some cases is comparable to TiO2 Degussa P25 leading to high removal percentages of the studied micropollutants under UV-A light irradiation. In contrast to TiO2 Degussa P25, g-C3N4 catalysts were also able to degrade the studied micropollutants under visible light irradiation. For all the studied g-C3N4 catalysts under both UV-A and visible light irradiation, the overall degrada-tion rate decreases in the order of bisphenol A > diuron > ethyl paraben. Among the studied g-C3N4, the chemically ex-foliated catalyst (g-C3N4-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-C3N4-THERM) demonstrated the best photocatalytic performance and the degrada-tion ranged from-29.5 to 59.4 % after 120 min. EPR data revealed that the three g-C3N4 semiconductors generate mainly O2 & BULL;-, whereas TiO2 Degussa P25 generates both HO & BULL; and O2 & BULL;-, the latter only under UV-A light irradiation. Nev-ertheless, the indirect formation of HO & BULL; in the case of g-C3N4 should also be considered. Hydroxylation, oxidation, dealkylation, dechlorination and ring opening were the main degradation pathways. The process proceeded without sig-nificant alterations in toxicity levels. Based on the results, heterogeneous photocatalysis using g-C3N4 catalysts is a prom-ising method for the removal of organic micropollutants without the formation of harmful transformation products.