Mechanisms of biochar enhanced CuO photocatalysts in the visible-light photodegradation of sulfamethoxazole.

CuO nanoparticles are decorated with biochars derived from spent coffee grounds (denoted as CuO/SCG) and applied as visible-light-active photocatalysts in the sulfamethoxazole (SMX) degradation. The physicochemical properties of CuO/SCG are identified by various spectral analysis, electrochemical and photochemical techniques. As a result, the CuO/SCG exhibits the higher removal efficiency of SMX than the pristine CuO under visible light irradiation. We can observe that CuO could be incorporated onto the SCG biochars with rich oxygen vacancies/adsorbed hydroxyl groups. In addition, the CuO/SCG has the lower charge transfer resistance, faster interfacial electron transfer kinetics, decreased recombination of charge carriers and superior absorbance of visible light. The construction of band diagrams for CuO/SCG and pristine CuO via UV-vis spectra and Mott-Schottky plots suggest that the band energy shifts and higher carrier density of CuO/SCG may be responsible for the photocatalytic activity enhancements. From the radical scavenger experiments and electron paramagnetic resonance spectra, the aforementioned energy shifts could decrease the energy requirement of transferring photoinduced electrons to the potential for the formation of active superoxide radicals (·O) via one and two-electron reduction routes in the photocatalytic reaction. A proposed degradation pathway shows that ·O and h are two main active species which can efficiently degrade SMX into reaction intermediates by oxidation, hydroxylation, and ring opening. This research demonstrates the alternative replacement of conventional carbon materials for the preparation of biochar-assisted CuO photocatalysts which are applied in the environmental decontamination by using solar energy.