Increasing photocatalytic activity of magnetite NPs with the inclusion of methyl orange and Evans blue functional groups in the photoactivation of acid sites

Abstract

In this paper, The photocatalytic reactions of methyl orange (MO) and Evans Blue (EB) are conducted on four distinct magnetite nanoparticles (NPs) samples. This study investigates, for the first time in literature, the impact of the inclusion of chromophores and auxochromes in the photoactivation of Brönsted and Lewis’s acid sites on the photocatalytic activity. In so doing, free functional groups of MO and EB that are not photodegraded have been analyzed using FTIR spectroscopy. This analysis leads to infer photoactivated acid site densities. FTIR analysis of initial residual solutions of MO and EB revealed lower contents of free functional groups of EB compared to MO. Based on this finding, it would be expected that EB would demonstrate better photodegradation due to the lower contents of its functional groups. However, the obtained results contradicted this assumption, indicating an opposite behavior. Moreover, FTIR analysis of final residual solutions revealed that functional groups of MO were highly photodegraded compared to EB. Also, calculated MO photodegradation capacities, yields, and kinetics constants were found to be higher than those of EB. This suggests that parameters other than band gap energy may control the photoactivation of Brönsted and Lewis’s acid sites and thus photocatalytic activity. Indeed, functional groups are involved in increasing the photocatalytic activity. The higher contents of MO functional groups lead to better increasing the photocatalytic activity of magnetite NPs.