Photocatalytic degradation of paraquat dichloride over CeO2-modified TiO2 nanotubes and the optimization of parameters by response surface methodology

Abstract

Decontamination of water sources by one-dimensional (1D) nanostructured TiO₂ holds great potential due to their unique electronic and textural properties. In this study, CeO₂-modified TiO₂ nanotubes (Ce–TNTs) have been prepared by impregnation of CeO₂ on hydrothermally synthesized TiO₂ nanotubes (TNTs). The catalysts were characterized by XRD, HRTEM, EDX, STEM, EELS, DR-UV/VIS spectroscopy and nitrogen adsorption (NA) analyses. The photocatalytic activities of the synthesized Ce–TNTs were examined on the degradation of paraquat dichloride (PQ) under UV light. The modification of TNTs with CeO₂ led to an enhancement of the photocatalytic activity. Box–Behnken design (BBD) based on response surface methodology (RSM) was used to optimize three experimental parameters namely; CeO₂ ratio, calcination temperature and catalyst loading. ANOVA of the generated quadratic model yielded a coefficient of determination, R² of 0.9926 and probability, P < 0.0001, which confirms that the model is suitable for predicting the optimum degradation efficiency of PQ. Based on this model, the calcination temperature and CeO₂ ratio were the most significant parameters and the interactions between these parameters and the catalyst loading were also significant. The predicted optimum conditions that would give a maximum of 80.798% degradation of PQ in 4 h were 9.01% CeO₂ ratio, 760.49 °C calcination temperature and 0.38 g catalyst loading. Validation experiments were conducted in triplicate and an average of 80.27% degradation of PQ was achieved which is in agreement with 80.798% predicted. Under these optimum conditions, TOC analysis showed that 51.10% mineralization of PQ was achieved within 4 h. Therefore, this work further confirms that the photocatalytic treatment of organics-contaminated water can be designed and optimized by RSM.