Efficient degradation of methyl orange via multilayer films of titanium dioxide and silicotungstic acid

We report layer-by-layer (LbL) assembly of TiO2 and H4SiW12O40 (SiW12) multilayer film on silicon wafers and glass slides for photocatalytic degradation of methyl orange (MO). The photocatalytic efficiency of the obtained multilayer film increases along with the decrease of pH and salt concentration of the incubation solution. The results show that MO can be almost removed in pH 2.0 solution without salt addition in the first 60 min incubation when MO concentration is lower than 15 mg/L. Different salts show an apparent inhibitory effect on photocatalytic degradation of MO with the order of ZnCl2 > KCl > NaCl > LiCl. The TiO2/SiW12 multilayer film maintains photocatalytic activity even after five degradation cycles. The reaction of MO photodegradation accords with an apparent first-order dynamics.