Growth of nano metal oxide in surfactant-free microemulsion template and its catalytic mechanism simulation

Abstract

Nano metal oxides synthesized in surfactant-free microemulsion (SFME) exhibit excellent visible light catalytic performance while its growth process and catalytic mechanism are unclear. In this work, α-Fe2O3 synthesized in SFME was taken as a representative to investigate its growth process and the related mechanism. Rhodamine B (RhB) was selected as a typical pollutant, degraded by heterogeneous Fenton reaction system composed of the synthesized α-Fe2O3 and H2O2. Results reveal that under the controlled temperature and time, water in oil structure in SFME plays a critical role of micro-reactor, resulting in the formation of monodisperse spherical α-Fe2O3 with high surface area. Excess reaction temperature or time leads to Oswald ripening and other structures can be obtained. There are a large amount of free Fe3+ on the surface of the synthesized α-Fe2O3 and RhB can be efficiently degraded by 96.0% in 60 min. Simulation elucidates that free Fe3+ captures the electrons and catalyzes to form hydroxyl (·OH) and superoxide anion (O2·-) radicals. The variations of Gibbs free energy of the formation of ·OH and O2·- radicals are −320.8 and −164.4 kJ·mol−1, respectively, indicating that their generation on the surface of the synthesized α-Fe2O3 is spontaneous on thermodynamics. In addition, the stability, viability and versatility of this nanomaterial for the remediation of diverse organic pollutants are demonstrated. It is expected that this work would provide important information and inspiration for the synthesis of nanomaterials using SFME as a template.