DEPARTMENT OF Chemistry

 SYNTHESIS OF HIGH PERFORMANCE GRAPHENE/TiO₂ COMPOSITES FOR PHOTOCATALYTIC REMOVAL OF POLLUTANTS FROM WATER

MINOR RESEARCH PROJECT

MRP(S)-0315/12-13/KLMGO23/UGC-SWROdated29/03/13

Principal Investigator

Deepthi John

Assistant Professor

Department of Chemistry

Photocatalytic methods for environmental remediation have been an active field of research for over three decades. However, the effectiveness of this approach can be enhanced several-fold when the inorganic semiconductor active material is combined with other complementary components. In this study TiO₂-reduced graphene oxide (RGO) composites were prepared by a simple and environmentally benign one-step hydrothermal methodusing the titanium dioxide precursor TiCl₄ and graphene oxide (GO). Hydrolysis of TiCl₄ and mild reduction of GO were simultaneously carried out under hydrothermal conditions.The graphene nature of RGO in the composite was confirmed by X-ray diffraction (XRD), UV visible absorption spectroscopy, Raman spectroscopy and Transmission electron spectroscopy (TEM).

The photocatalytic performance of the TiO₂-RGO composites was evaluated for the photodegradation of Rhodamine B in an aqueous solution. The TiO₂-RGO nanocomposites exhibited much higher photocatalytic activity than pure TiO₂.The TiO₂-RGO nanocomposites exhibited much higher photocatalytic activity than pure TiO₂.The presence of RGO sheets as a two- dimensional (2D) platform for the deposition of titanium dioxide improved the adsorption of Rhodamine B.  As the graphene oxide in the composites has a very good contact with the TiO₂ nanoparticles it enhances the photo-electron conversion of TiO₂ by reducing the recombination of photo-generated electron–hole pairs. The effect of different amounts of graphene such as 1, 2, 5 and 10 wt% on the photocatalytic and adsorption efficiency was investigated. The photocatalytic efficiency is maximized at the optimal RGO content in the catalyst. The catalyst with a RGO-concentration of 5wt % (TiO₂−5 wt % RGO) shows the best catalytic activity both in UV and sun light. After 120min, 98% (in UV light) and 90%( in sun light)of RhB is photocatalytically degraded by the catalyst.The degradation in presence of TiO₂-RGO is about 20% more compared to TiO₂ in sun light where as in UV light the enhancement is only 10%.The comparative enhancement increases as the irradiation progresses. This is due to the inability of pure TiO₂ to get activated significantly in sun light while TiO₂-5wt%RGO continues to absorb light resulting in the formation of electron-hole pairs and subsequent activation of adsorbed oxygen. The comparative advantage of RGO incorporation is not that significant in UV irradiation because TiO₂ itself is very active in this region.  Higher pH favours the removal of Rhodamine B while increase in concentration of the dye decreases the % removal. There is an optimum for the catalyst loading beyond which the rate of degradation stabilizes or decreases. The reaction kinetics of the photo degradation of TiO₂ and TiO₂-RGO nanocomposite obeyed a Langmuir– Hinshelwood pseudo-first-order model.  The rate constant calculated for the composite (TiO₂-5wt%RGO) was 0.01865 min⁻¹, which is ∼2 times greater than that of TiO₂ (0.01027 min⁻¹). Under sun light irradiation the rate constant calculated for the composite was 0.01369 min⁻¹, which is ∼1.5times greater than that of TiO₂ (0.01093 min⁻¹).  A tentative mechanism for the photocatalytic degradation of the dye is proposed and discussed.