Photocatalytic degradation of orange II on the novel hetero-system WS2/TiO2 under UV light

Abstract

The photodegradation of orange II (OII) is successfully achieved on the new hetero-system WS2/TiO2 under UV illumination. The nano sized bi-functional catalyst is prepared by sol gel and calcined at ~450 °C. The X-ray diffraction shows noticeably broad peaks and TiO2 is therefore less crystallized with the anatase phase. The sensitizer WS2 presents a direct optical transition at 1.72 eV. The Mott–Schottky plot (C−2–V) is characteristic of n type conduction from which a flat band potential of 0.17 VSCE and a donor density of 5.30 × 1017 cm−3 are determined. An energy band diagram is established, predicting an electron transfer from WS2 to TiO2; the injection process is confirmed by the photocurrent measurements at different concentrations. Upon increasing the mass of WS2, the activity increases and the best performance occurs on 30 % WS2/TiO2. A conversion of 98 % is reported in aerated solution for OII concentration of 10 ppm in less than 90 min. The oxidation follows a first order kinetic with a rate constant of 4.8 × 10−2 min−1.