N, Cu co-doped TiO2@functionalized SWCNT photocatalyst coupled with ultrasound and visible-light: An effective sono-photocatalysis process for pharmaceutical wastewaters treatment

In this study, N-Cu co-doped TiO2 was decorated on the single-walled carbon nano-tube (marked as N-Cu co-doped TiO2@CNTs) via two-step sol-gel/hydrothermal synthesis method for the first time as a novel photocatalyst in coupling with ultrasound (US) waves. The catalyst properties were characterized via BET, Raman, FESEM, TEM, FTIR, XRD, EIS, PL, TGA, UV-Vis DRS, EDX and EDS dot mapping. These techniques confirmed the successful doping of both N and Cu elements on the CNTs impregnated with TiO2 nanoparticles. The investigation of effective operational parameters demonstrated that the total removal of sulfamethoxazole (SMXZ) could be achieved under pH of 6.0, catalyst dosage of 0.8 g/L, light intensity of 200 W, US power of 200 W, and initial SMXZ concentration of 60 mg/L within 60 min. SMXZ degradation kinetics over sono-photocatalytic process were in a good agreement with pseudo-first-order model. Quenching experiments illustrated that HO center dot and O2(center dot-) active species were more effective species for SMXZ degradation. The synthesized sono-photocatalyst could be recycled after six consecutive cycles of SMXZ degradation with an insignificant decrease in perfor- mance. A tentative mechanism and pathway for SMXZ were formulated. Pharmaceutical wastewater was treated through the optimum degradation conditions which showed that the sono-photocatalytic degradation eliminated 93% of COD and 89% of TOC within 180 min.