Enhanced photocatalytic degradation of sulfamethoxazole by visible-light-sensitive TiO2 with low Cu addition

• The visible-light-driven Cu–TiO2 at low Cu loading was successfully prepared.
• The distribution of copper ions was even on TiO2 and the dominant species was CuO.
• The rate constants of SMX by Cu–TiO2 were 2–13 times higher than that of P25 TiO2.
• The Cu–TiO2 could be recycled for at least 4 cycles under visible light irradiation.

In this study, the one-pot microwave-assisted impregnation method was developed to prepare the visible-light-sensitive Cu–TiO2 at low mass ratios of 0.006–0.063 wt% for the enhanced photocatalytic degradation of sulfamethoxazole (SMX) under visible light irradiation. The electron probe microanalysis and X-ray absorbance near-edge spectroscopic results indicated that the distribution of copper ions was even on TiO2 nanoparticles and the dominant species of copper element was CuO. The photodegradation efficiency and rate of SMX by Cu–TiO2 increased positively upon increasing Cu loading from 0.006 to 0.045 wt% Cu and then decreased when further increasing the Cu mass loading to 0.063 wt%. The pseudo-first-order rate constants for SMX photodegradation by Cu–TiO2 were in the range 0.0103–0.0506 min−1, which were 1.9–13.1 times higher than that of pure Degussa P25 TiO2. The photodegradation efficiency and rate of SMX can be maintained in the pH range of 5–9, and the release of Cu ions in the solution was only few μg/L, which indicates the stability of Cu–TiO2 during the photocatalytic reaction in aqueous solutions. In addition, the Cu–TiO2 could be recycled for at least 4 cycles and maintained the highly stable photoactivity toward SMX degradation under visible light irradiation. Results obtained in this study clearly demonstrate that low mass loading of Cu(II) onto TiO2 can effectively shorten the route of electron transfer and can serve as the efficient visible-light-driven photocatalysts for photodegradation of SMX and other pharmaceutical products.

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