Kinetic and catalytic analysis of mesoporous metal oxides on the oxidation of Rhodamine B

In this study, we demonstrate the synthesis and catalytic activity of different mesoporous transition metal oxides, silica (SiO ₂ ), copper oxide (CuO), chromium oxide (Cr ₂ O ₃ ), iron oxide (Fe ₂ O ₃ ) cobalt oxide (Co ₃ O ₄ ), cerium oxide (CeO ₂ ) and nickel oxide (NiO), on the oxidation of a pollutant dye, Rhodamine B (RhB). These metal oxides were synthesized by inverse micelle formation method and characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), adsorption-desorption isotherms (BET) and H ₂ -temperature programmed reduction (TPR). UV–vis spectrophotometry was used to monitor the time-resolved absorbance of RhB at λ _max = 554 nm. Mesoporous copper oxide was calcined at different final heating temperatures of 250, 350, 450 and 550 °C, and each mesoporous copper oxide catalyst showed unique physical properties and catalytic behavior. Mesoporous CuO-550 with the smallest characteristic path length δ proved to be the catalyst of choice for the oxidation of RhB in aqueous media. We observed that the oxidation of RhB in aqueous media is dependent on the crystallite size and characteristic path length of the mesoporous metal oxide. The Langmuir-Hinshelwood model was used to fit the experimental data and to prove that the reaction occurs on the surface of the mesoporous CuO. The thermodynamic parameters, E _A , ΔH ^# , ΔS ^# and ΔG ^# were calculated and catalyst recycling and reusability were demonstrated.