The effect of crystalline phase on the simultaneous degradation of phenol and reduction of chromium (VI) using UV/TiO2 photocatalysis

Abstract

Chromium (IV) contamination in industrial wastewater has been on the rise due to increased anthropogenic activities. Similarly, typical industrial wastewater contains high levels of phenol as a result of the direct disposal on phenol into industrial effluent or as degradation products from phenolic compounds. Both these contaminants have adverse effects to human health and the environment and it is therefore necessary to develop technologies to remove them in a sustainable manner. Photocatalysis using TiO2 catalyst activated by UV light is one such technology as it can either oxidize and mineralize organic pollutants or reduce heavy metals contaminants into a noble form. Degussa P25 TiO2 is normally used in photocatalysis due its ability to reduce electron-hole recombination. It has been theorized that the addition of organic compounds as hole scavengers during the photocatalytic reduction of Cr(VI) aids in the reduction efficiency. This study investigated the use of anatase-form TiO2 on the reduction of Cr(VI) in the presence of phenol and compared the results to similar work carried out by our group out Degussa P25 as catalyst. The anatase was shown to be an effective catalyst in the reduction of Cr(VI) with as much as 32 % reduction occurring at neutral pH with no phenol present. Adjusting the solution pH to 3 increased the percentage reduction to 40.7 % whilst addition of 100 ppm of phenol at pH 3 resulted in a 52.3 % Cr(VI) reduction. Comparison of the results obtained for anatase and Degussa P25 TiO2 at the same pH revealed approximately the same Cr(VI) reduction efficiencies with the Degussa P25 having a slight edge. This suggests that the nature of the crystal phase of the two TiO2 investigated does not significantly influence the reduction efficiency of Cr(VI) in the presence of phenol.