Photocatalytic degradation of Reactive Orange 16 dye using TiO2/PPy nanocomposites under simulated solar light

Abstract

It is well known that titanium dioxide is usually used as a photocatalyst due to its nontoxicity, low cost, and stability. Conductive polymer, polypyrrole (PPy) is also appropriate for photocatalytic application being stable and easy to synthesize. The aim of this study was to obtain TiO2/PPy composites reaching higher photocatalytic efficiency compared to pure TiO2. Therefore, TiO2 was synthesized by the hydrothermal route, while PPy was obtained by the chemical oxidative polymerization method. TiO2/x% PPy nanocomposites (x = 0, 0.5, 1, 1.5, 3, 5 wt.%) were prepared by hand-mixing of powders in agate mortar for 30 min in order to find the optimal PPy content. Obtained materials were characterized by XRD, FTIR, TG/DSC, FESEM, and UV-Vis methods while their photocatalytic activity was estimated towards degradation of Reactive Orange 16 dye (RO16). A kinetic study was performed and a detailed mechanism of RO16 photocatalytic degradation in the presence of TiO2/PPy composites was proposed based on scavenger tests. The results showed that, despite PPy addition, TiO2 was present in anatase form in all samples with sufficiently small crystallites (around 26 nm) and preserved structure with no significant deviations in unit cell parameters. The band gap energy decreased with increasing of PPy content, from 3.14 eV for pure TiO2 to 2.94 eV for TiO2/5% PPy. All the obtained nanocomposites demonstrated higher photocatalytic activity than pure TiO2, whereby TiO2/1% PPy nanocomposite was the most efficient by degrading 99.6% of the dye for 105 min under simulated solar light. Therefore, the amount of 1 wt.% should be consider as optimal amount of PPy in a composite. It is established that the photodegradation of RO16 using TiO2/PPy nanocomposites follows pseudo-first kinetic order. RO16 photocatalytic degradation mechanism in the presence of TiO2/PPy nanocomposites can be well described by direct Z-scheme heterojunction which has never been reported for TiO2/PPy system.