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.