Photocatalytic decolourisation of Reactive Red 4 dye by an immobilised TiO2/chitosan layer by layer system

The synergistic photocatalysis-adsorption processes by the immobilized TiO(2)/chitosan layer by layer system on a glass support (TiO(2)/CS/glass) were investigated for the decolourisation of Reactive Red 4 (RR4) dye solution. Effects of different reaction parameters such as TiO(2) loading, initial pH of the solution, visible light, dissolved oxygen and radical quenchers were studied. The decolourisation rate of RR4 by TiO(2)/CS/glass was more than 32 times faster than a single layer of TiO(2) but was highly dependent on the TiO(2) loading and the initial pH of the solution. A thin layer of TiO(2) and acidic conditions favoured the adsorption of RR4 at the TiO(2)/CS interface. The h(+)/OH() species that diffused from the TiO(2) layer into the TiO(2)/CS interface oxidised the chemisorbed RR4 anions at the interface, and the generated electrons were then transferred to the conduction band of TiO(2). Excess electrons in the conduction band of TiO(2) increased the number of superoxide ions produced and thus improved the photocatalytic decolourisation of RR4. Therefore, apart from the synergistic photocatalysis-adsorption processes, a charge transfer process was also found to be responsible for maintaining the efficiency, sustainability and reusability of the TiO(2)/CS/glass layer by layer system.