Solar degradation of an azo dye, acid red 1, by Ca–Ce–W–TiO2 composite catalyst

An electronically stable composite photocatalyst of the type Ti(1 − x − y)Ca(3x − y)Ce(2x − y)W(y/6)O2(1 − 2(y − x)) (at y < 2x and x + y < 1) with an enhanced solar photocatalytic activity was developed by doping TiO2 with Ca, Ce and W. The catalyst was prepared by sol–gel method and hydrothermally treated before used in the solar photocatalytic degradation of an azo dye, acid red 1 (AR1). To verify the effectiveness of the composite catalyst, two commercial photocatalysts; Degussa P25 and TiO2-Sigma product CAS No. 1317-70-0 were used in the solar degradation of AR1 for the purpose of comparison. The performance of the composite catalyst excelled that of TiO2-Sigma product, but was as good as Degussa P25 in terms of the solar photodegradation. Nevertheless, it has an added merit of quick settling out of solution (a quality which was lacking in Degussa P25) and could be reused. The reusability test proved that the catalyst was as good at the fourth cycle as at the first. Effects of pH and initial dye concentrations on the solar degradation of AR1 were also studied. The study revealed that while solution pH exerted a great influence on the degradation of the dye, initial dye concentrations did not. The chemical states of the catalysts were studied by XPS, while other characterizations were carried out by FT-IR, XRD, SSEM and BET.