Photo-catalytic degradation of sulfamethoxazole from aqueous solutions using Cu-TiO2/ CQDs hybrid composite, optimisation, performance and reaction mechanism studies

Cu doped TiO2 decorated with carbon quantum dots (CQDs), called Cu-doped TiO2/CQD, was synthesised as a photocatalyst, and then used in the degradation of sulfamethoxazole (SMX) antibiotic. The properties of the synthesised catalyst were determined by FT-IR, XRD, FESEM, TEM, EDX, BET and UV-Vis DRS analysis. These analyses showed successful doping of TiO2 with Cu coated by CQDs. Variable parameters such as different CQDs ratios, photocatalyst dosage, initial concentration of SMX, pH and intensity of visible light were investigated. The best removal efficiency of SMX was obtained at initial concentration = 20 mg/L SMX, photocatalytic dosage = 0.8 g/L, pH = 6, visible light intensity = 75 W/m(2) and CQDs ratios in the composite = 4% wt during 60 min reaction time. The photocatalytic degradation kinetic of SMX fitted well with the pseudo-first-order kinetic model. Experiments showed that HO center dot and O-2(center dot -) were active species in the photocatalytic destruction of SMX and O-2(center dot -) had more inhibiting effects in the SMX degradation process. The synthesised photocatalyst was used for six cycles with a slight reduction in the SMX degradation efficiency. TOC removal efficiency was 81% at optimal condition.