BaMoO4 nanocatalyst for oxidation of methylene blue: Preparation, characterizations, and process modeling using the response surface methodology

Barium molybdate BaMoO₄ nanocatalyst, a tetragonal distorted scheelite (β) form, was successfully synthesized via thermal decomposition of an oxalate complex (prepared beforehand and then characterized using Fourier transform infrared spectroscopy (FTIR) and thermal gravimetric analysis (TGA)) under controlled temperature conditions of 700°C. Its characterization was performed by using X-ray diffraction (XRD), Raman spectroscopy (RS), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). Its catalytic efficiency was assessed through Methylene Blue (MB) oxidation with hydrogen peroxide as a model reaction. Its process parameters, the initial pH value of the MB solution (4.5- 11), and contact time (30- 300 min), were optimized by using central composite design (CCD) adopted from Response Surface Methodology (RSM) to minimize process cost and reaction time. The analysis of variances (ANOVA) reveals that the CCD model was valid, and predicted values for MB oxidation efficiency were in good agreement with experimental values for MB (R²= 0.9989 and Adj-R² A= 0.9955). The maximum oxidation of MB was achieved at over 96 % under optimal conditions: solution pH of 10.78, initial MB concentration of 5 ppm, catalyst amount of 0.1 g/L, and a reaction time of 75 minutes. The experimental data were well-described by a pseudo-first-order kinetic model. In summary, the successfully synthesized BaMoO₄ nanocatalyst has high catalytic activity.