Photocatalytic Degradation of Azo Dyes Using Au:TiO₂, γ-Fe₂O₃:TiO₂ Functional Nanosystems

We report photocatalytic degradation studies on Navy Blue HE2R (NB) dye on significant details as a representative from the class of azo dyes using functional nanosystems specifically designed to allow a strong photocatalytic activity. A modified sol–gel route was employed to synthesize Au and γ-Fe₂O₃ modified TiO₂ nanoparticles (NPs) at low temperature. The attachment strategy is better because it allows clear surface of TiO₂ to remain open for photo-catalysis. X-ray diffraction, Raman and UV-VIS spectroscopy studies showed the presence of gold and iron oxide phases along-with the anatase TiO₂ phase. TEM studies showed TiO₂ nanocomposite particles of size ∼10–12 nm. A detailed investigation on heterogeneous photocatalytic performance for Navy Blue HE2R dye was done using the as-synthesized catalysts Au:TiO₂ and γ-Fe₂O₃:TiO₂ in aqueous suspension under 8 W low-pressure mercury vapour lamp irradiation. Also, the photocatalytic degradation of Amranth and Orange G azo dyes were studied. The surface modified TiO₂ NPs showed significantly improved photocatalytic activity as compared to pure TiO₂. Exposure of the dye to the UV light in the presence of pure and gold NPs attached TiO₂ catalysts caused dye degradation of about ∼20% and ∼80%, respectively, in the first couple of hours. In the presence of γ-Fe₂O₃ NPs attached TiO₂, a remarkable ∼95% degradation of the azo dye was observed only in the first 15 min of UV exposure. The process parameters for the optimum catalytic activity are established which lead to a complete decoloration and substantial dye degradation, supported by the values of the Chemical Oxygen Demand (COD) ∼93% and Total Organic Carbon (TOC) ∼65% of the treated dye solution after 5 hours on the employment of the UV/Au:TiO₂/H₂O₂ photocatalytic process.