Photocatalytic performance of titanium dioxide and zinc oxide binary system on degradation of humic matter

Application of photocatalysis using TiO2 or ZnO for the removal of natural organic matter (NOM) dates back more than two decades. Aiming to overcome the drawbacks of sole photocatalysts, use of multiphasic systems has received recent interest. ZnO/TiO2 binary oxide specimens were synthesized by a simple solid state dispersion method in different weight ratios of 1:1; 1:3; and 3:1 (ZT11, ZT13 and ZT31 respectively) and characterized by XRD, SEM, XPS, Raman, UV-DRS, PL and BET techniques. As a surrogate of NOM, humic acid (HA) was subjected to solar photocatalysis and degradation was followed by UV-vis and fluorescence spectroscopic tools along with dissolved organic carbon (DOC) contents. Photocatalytic degradation of HA was approximated to first order kinetic model. Referring to UV-vis parameters, ZT11 binary oxide expressed slightly higher photocatalytic performance with regard to TiO2, ZnO, ZT13 and ZT31 contrary to the mineralization extents as TiO2>ZT13 > ZT31 > ZT11 > ZnO. Excitation-emission matrix fluorescence (EEM) contour plots of the organic matrix displayed almost complete removal of humic-like and fulvic-like fluorophores upon use of sole TiO2 and ZnO. Regional distribution of the fluorophores were still evident with emergence of the new fluorophoric regions upon use of binary oxides. ZnO/TiO2 could be considered as an efficient photocatalyst for the degradation of humic acids under solar irradiation.