Synthesis of new hybrid composite based on TiO2 for photo-catalytic degradation of sulfamethoxazole and pharmaceutical wastewater, optimization, performance, and reaction mechanism studies

In this study photo-catalytic degradation of sulfamethoxazole (SMX) from aqueous solutions using carbon quantum dot (CQD)-decorated Cu-TiO2 was investigated. The as-prepared photo-catalyst samples were characterized by various FTIR, XRD, FE-SEM, TEM, EDX, BET, and DRS techniques. The investigation of effective photo-catalytic operational parameters confirmed that the complete removal of SMX (20 mg/L) can be accomplished at pH: 6.0 and light intensity: 75 mW/cm(2) over a 30-min reaction time. DRS analysis demonstrated adding CQD to the Cu-TiO2 reduced its bandgap energy from 2.97 to 2.90 eV. The photo-catalytic degradation kinetics of SMX fit well with the pseudo-first-order model. The radical trapping experiment indicates that HO center dot and O-2(center dot-) active species were more effective species for SMX degradation, and the higher inhibition effect on the SMX degradation efficiency was assigned to O-2(center dot-) ions. The water matrix species-inhibited effect in SMX removal was as follows: SO42- > Cl- > NO3- > CO3- > no ions. The synthesized photo-catalyst could be recycled after six consecutive cycles of SMX degradation with an insignificant decrease in performance. The total organic carbon (TOC) analysis suggested the mineralization of SMZ by composite photo-catalysts. The minimum inhibitory concentration (MIC) for Escherichia coli remained at 12.5 mg L-1 SMX. A possible mechanism and pathway of SMX degradation in the photo-catalytic system was presented.