Catalytic decomposition of sulfamethazine antibiotic and pharmaceutical wastewater using Cu- TiO2@ functionalized SWCNT ternary porous nanocomposite: Influential factors, mechanism, and pathway studies

In this study, photocatalysts made of Cu-TiO2@functionalized single-walled carbon nanotubes were prepared via a newly developed two-step (sol-gel/hydrothermal) process for the catalytic decomposition of sulfamethazine under natural solar irradiation. The properties of the photocatalysts were studied using BET, PL, FT-IR, XRD, TEM, TGA, FESEM, EDS, Raman, DRS, EIS, EDX and SAED tests. The TEM and FESEM images revealed a uniform distribution of Cu-doped TiO2 particles on the surface of the SWCNTs. The EIS and PL analysis indicated that photo-induced electrons were trapped by the SWCNTs and/or Cu oxidation states, which reduced electron-hole recombination. Photodecontamination was performed in a batch reactor, and the investigation of influencing factors indicated that sulfamethazine could be completely degraded at a Cu content of 4%, SWCNT content of 10%, pH of 7, catalyst loading of 0.9 g/L, and initial sulfamethazine concentration of 30 mg/L after 135 min solar irradiation. Kinetic studies revealed that the pseudo first-order kinetic model best fit the degradation of sulfamethazine under selected conditions. Trapping experiments indicated that O-center dot(2)- and (OH)-O-center dot reactive radicals, rather than h(+), were accountable for the decontamination process. The efficiency with which sulfamethazine was removed was evaluated in the presence of co-existing anions. The results revealed that the removal rate was considerably reduced by the addition of sulfate or chloride anions but only slightly reduced by the addition of phosphate or nitrate anions. A tentative mechanism and pathway for sulfamethazine degradation were formulated. The synthesized photocatalysts could be reused after five consecutive cycles of photodecontamination but with a slight reduction in removal rate (approximately 7%). An experiment involving pharmaceutical wastewater showed that photocatalytic decontamination eliminated 59.3% of TOC and 74.6% of COD after 390 min of solar irradiation.