TiO₂ as an effective nanocatalyst for photocatalytic degradation of humic acid in water environment

Photocatalysis with TiO₂ is used to remove humic acid (HA) in a water environment under UVA and UVC light. The effects of operating parameters, including light intensity, HA concentration, catalyst dose, and contact time are investigated at neutral pH conditions. Results show that HA degradation increases with increasing contact time and light intensity and decreases with increasing HA concentration. Increasing catalyst dose increases the HA degradation up to an optimum value. At pH 7 with an initial HA concentration of 14 mg/L, UVA light of 0.236 mW/cm² and catalyst dose of 0.3 g/L, 100% efficiency of the HA degradation can be achieved in 3 h. Under identical experimental conditions with UVC light of 0.284 mW/cm², the efficiency of HA degradation also reaches 100%. Based on total organic carbon (TOC) analysis, the mineralization of HA is found to be lower than the degradation of HA. A negligible amount of TOC on the catalyst surface confirms that HA removal is due to photocatalysis. Moreover, a higher degree of mineralization of HA is found under UVA light although degradation is better under UVC light. This indicates that TiO₂ under UVA light has relatively low selectivity to degrade different compounds, including various intermediates from HA degradation.