Photocatalytic degradation of Orange G using sepiolite-TiO2 nanocomposites: Optimization of physicochemical parameters and kinetics studies

Abstract

Highly photoactive nanocomposites Sep-TiO2 with various ratios of Ti/Sep were prepared by a novel microwave-hydrothermal method and were compared for their photocatalytic activity. The catalyst with the Ti/Sep ratio of 40 mmol/g showed the highest photodegradation activity on account of its relatively intact sepiolite structure and more anatase active sites. The effects of operational conditions, including photocatalyst amount, initial dye concentration and pH on photocatalytic degradation performance were analyzed and optimized, which demonstrated low and negligible photodegradation efficiency in the presence of sepiolite only and in the absence of photocatalyst, respectively. The photocatalytic degradation kinetics under different reaction conditions was elucidated by modeling. The results showed that the photocatalytic degradation of Orange G could be described by the modified Langmuir-Hinshelwood model. The photocatalytic degradation process fits into first-order kinetics for most of the operational parameters, while follows zero-order kinetics for the condition of high dye concentration. The apparent rate constants kapp for each degradation reaction were calculated by fitting the model to experimental data and the highest value was obtained at catalyst dosage 0.8 g/L, initial dye concentration 10 mg/L and pH = 3. Moreover, the recycling experiments confirmed the stability of the catalyst.