Photocatalytic 4-nitrophenol degradation and oxygen evolution reaction in CuO/g-C3N4 composites prepared by deep eutectic solvent-assisted chlorine doping.

Anion doping into the oxygen site as a new plan for tuning the physical and chemical properties of metal oxides and adjusting their catalytic behavior has been studied. Herein, we report a Cl- anion-doped CuO (Cl-CuO) preparation method using deep eutectic solvents (DESs) as a green solvent, and the Cl-CuO/g-C3N4 heterostructure was successfully prepared in various weight ratios via a simple ultrasonication and mixing method for the oxygen evolution reaction (OER) in acidic media and the photocatalytic degradation of 4-nitrophenol. Cl- was doped into the CuO crystal lattice, as revealed by the XRD and XPS studies. The as-prepared Cl-CuO/g-C3N4 (1 : 2) exhibited a low overpotential of 0.77 V on the glassy carbon electrode with a current density of 33 mA cm-2 at 2.4 V for OER in an acidic solution. Also, about 92% degradation of 20 ppm of 4-nitrophenol was achieved for Cl-CuO/g-C3N4 (1 : 2) in 100 minutes under the irradiation of a 35 W Xe arc lamp. We also evaluated the effect of thermal energy on degradation kinetics by tuning the temperature, which led us to the quantification of various thermodynamic parameters. To the best of knowledge, this is one of the new methods of green synthesis to fabricate photocatalysts for energy and environmental studies.