Preparation of TiO2/graphene composite with appropriate N-doping ratio for humic acid removal

Abstract

Humic acid (HA), which contains abundant carboxyl groups and hydroxyl groups, is one of the major constituents of dissolved organic matter. The increase of HA in natural waters worldwide has caused great trouble in water treatment and water health. Photocatalysis is a promising technology for degrading HA. In this study, graphene oxide, TiO2 and different amounts of urea (nitrogen source) were mixed to dope nitrogen into TiO2 and RGO simultaneously and form N-TG to remove HA from aqueous solution. To confirm the effect of the N-doping and determine the best N-doping ratio for N-TG, various characterization and HA removal tests using different samples were conducted, we found the best N-doping ratio is ~1.46 at.%. The influences of the initial HA concentration, temperature and pH on HA removal performance were measured and discussed, notably, temperature range of 25–35 °C and neutral solution are more fitable for HA removal. HA removal is in the synergistic effect of adsorption and degradation. The presence of RGO almost doubles the adsorption ability of the composite, which does have a significant improvement on HA removal efficiency. Pretreated in darkness has an extra 2% improvement on HA removal efficiency.