Comparative Optimization of Photocatalysis and Adsorption of Methylene Blue Using Aluminum Doped Magnetic Iron Oxide by Central Composite Design

Abstract

Water pollution still remains a major issue in developing countries due to poor disposal systems. Therefore, this study was to optimize methylene blue removal from aqueous solutions through adsorption and photocatalysis methods using aluminium-doped magnetic iron oxide. The synthesis of aluminium-doped magnetic iron oxide (AlFe3O4) as an adsorbent and photocatalyst was successfully prepared using the co-precipitation method. The removal efficiency of the AlFe3O4 was evaluated as a function of two input parameters, viz., catalyst/ adsorbent dose (0.1-0.5 g) and contact time (20-100 min) by using central composite design (CCD) adopted from response surface methodology (RSM). Using removal and degradation efficiency as responses, a 13 run experiment matrix was generated by the CCD to investigate the interaction effects of the two input factors. From the results, a linear model was generated for the two treatment methods of adsorption and photocatalytic processes, which didn't show good predictability of results agreeable to the experimental data. The analysis of variance (ANOVA) showed the selected models for adsorption and degradation were significant (P <0.05) with poor coefficients of determination (R 2 ) values of 0.6323 and 0.6535, respectively.The highest efficiency of MB removal for the adsorption process (59.68%) and the photocatalysis process (49.02%) were obtained in optimum conditions of adsorbent/photocatalyst = 0.23g, contact time = 38.96 min, and MB concentration = 40mg/l. The kinetic studies showed that the adsorption data fitted well to a pseudo-first-order kinetic model, whereas the photocatalysis data fitted well to a pseudo-second-order kinetic model.