LED-assisted sonocatalysis of sulfathiazole and pharmaceutical wastewater using N,Fe co-doped TiO2@SWCNT: Optimization, performance and reaction mechanism studies

N-Fe co-doped titania was anchored on the functionalized single-walled carbon nanotubes (NFeTFC) through two-step sol-gel and ultrasonic-assisted hydrothermal synthesis and integrated with LED visible light (LED) and ultrasonic (US) waves as a sono-photocatalyst. The properties of fabricated catalysts were investigated via XRD, Raman spectroscopy, FT-IR, PL, EIS, TGA, BET, TEM, FESEM, EDX, EDS-Dot-Mapping, and UV-vis techniques. These analyses demonstrated the successive deposition of N and Fe atoms on the FSWCNT surfaces covered by TiO2. FESEM and TEM micrographs showed uniform coverage of FSWCNT with TiO2 nanoclusters. The PL results indicated that the introduction of dopants and FSWCNT into the TiO2 structure, acts as electrons traps and/or electron sink which prevents the electron/hole recombination and also enables TiO2 to be active in a visible light region. The investigation of effective sono-photocatalytic operational parameters confirmed that the complete removal of sulfathiazole (SUTZ:40 mg/L) can be accomplished at pH:7.0, NFeTFC: 0.7 g/L, US power: 250 W and light intensity: 150 W/m(2), over 90 min reaction time. SUTZ sono-photocatalytic decontamination kinetic was followed by pseudo-first order kinetic model. Trapping studies illustrated that O-2 and OH radicals are the main reactive species through decontamination process. The as-prepared composite could be recovered and reused after seven consecutive-cycles of SUTZ decontamination with an insignificant reduction in performance. For a typical real wastewater, over 88 and 79 % of COD and TOC, respectively were eliminated by NFeTFC/LED/US within 225 min treatment. A great enhancement was observed by integrating US to the photocatalysis process and also a great positive synergy index of 0.54 was achieved for coupling individual of processes of photolysis, sonolysis and adsorption.