Photocatalytic performance of biochar-modified TiO(2) (C/TiO(2)) for ammonia–nitrogen removal

Biochar-modified TiO(2) (C/TiO(2)) was prepared by a sol–gel method in this study to improve the photocatalytic capacity for ammonia–nitrogen (NH(3)–N) removal from aqueous solutions. The results showed that biochar was successfully modified on TiO(2) and helped improve its photocatalytic performance for pollutant degradation. The removal capacity of ammonia–nitrogen on the synthesized photocatalyst performed well at pH 10 with 1 g L(−1) C/TiO(2) under both 60 (12.25 mg g(−1)) and 120 min (16.31 mg g(−1)) irradiation (xenon lamp, AM1.5, 25 A). Characterization of C/TiO(2) through scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectrometry (FT-IR) analyses showed the successful introduction of biochar on TiO(2). SEM-EDS and BET analyses displayed that C/TiO(2) had a larger surface area and more pores than the raw materials. XRD spectroscopy illustrated that C/TiO(2) had typical characteristic peaks of anatase-TiO(2) and presented a good photocatalytic degradation performance. It was confirmed from XPS and FT-IR analyses that –COOH groups were present in C/TiO(2) and originated from biochar modification, and these enhanced the photocatalytic performance. Through radical quenching experiments, it was found that superoxide radicals (˙O(2)(−)) played a dominant role in NH(3)–N photocatalytic reactions with hydroxyl radicals (˙OH) and valence band holes (h(+)) playing a synergistic role. N(2) was the main degradation product after 6 h NH(3)–N photocatalytic degradation, which was much larger than NO(3)(−)/NO(2)(−) (both almost undetected) and NH(3) (ca. 2 times lower than N(2)). The new composite C/TiO(2) has potential for ammonia–nitrogen degradation in wastewater treatment and favorable for treating sewage sludge.