Photocatalytic performance of biochar-modified TiO2 (C/TiO2) for ammonia-nitrogen removal.

Abstract

Biochar-modified TiO2 (C/TiO2) was prepared by a sol-gel method in this study to improve the photocatalytic capacity for ammonia-nitrogen (NH3-N) removal from aqueous solutions. The results showed that biochar was successfully modified on TiO2 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/TiO2 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/TiO2 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 TiO2. SEM-EDS and BET analyses displayed that C/TiO2 had a larger surface area and more pores than the raw materials. XRD spectroscopy illustrated that C/TiO2 had typical characteristic peaks of anatase-TiO2 and presented a good photocatalytic degradation performance. It was confirmed from XPS and FT-IR analyses that -COOH groups were present in C/TiO2 and originated from biochar modification, and these enhanced the photocatalytic performance. Through radical quenching experiments, it was found that superoxide radicals (˙O2-) played a dominant role in NH3-N photocatalytic reactions with hydroxyl radicals (˙OH) and valence band holes (h+) playing a synergistic role. N2 was the main degradation product after 6 h NH3-N photocatalytic degradation, which was much larger than NO3-/NO2- (both almost undetected) and NH3 (ca. 2 times lower than N2). The new composite C/TiO2 has potential for ammonia-nitrogen degradation in wastewater treatment and favorable for treating sewage sludge.