Effect of inorganic ions on the photocatalytic degradation of humic acid

Abstract

The article studies on the effects of six inorganic ions (Ca2+, Mg2+, Cl−, SO42−, H2PO4−, and HCO3−) on titanium dioxide (TiO2)-based photocatalytic degradation of humic acid (HA). We focus on the effects of the inorganic ions on HA characters, adsorption of HA on TiO2 and photocatalytic degradation of HA. The results indicate that Ca2+ and Mg2+ with HA can form complexes which can decrease the solubility of HA, and then increase the HA adsorbed on TiO2. However, the complex is more difficult to be degraded than HA. The effects of Cl− and SO42− are closely related to their influences on HA solubility. The solubility changes of HA to some extent can enhance the adsorption of HA on TiO2, and promote the photocatalytic degradation. Nevertheless, great solubility decreasing of HA can weaken the photocatalytic degradation. HCO3− and H2PO4− can inhibit the photocatalytic degradation process seriously, because HCO3− and H2PO4− are the strong scavengers of hydroxyl radicals, and can weaken the adsorption of HA on TiO2 due to adsorption competition.