Catalytic performance of Ni-Doped Co/La2O3 for degradation of malachite green by hetero-Fenton-like oxidation and sonocatalysis processes

Abstract

In this research, we investigated the performance of La₂O₃, Co/La₂O₃, and Ni-doped Co/La₂O₃ catalysts for the degradation of malachite green (MG), which is used as a model of wastewater refractory pollutants, under different reaction conditions (light irradiation or its absence, hetero-Fenton-like processes, without and with H₂O₂, and sonocatalytic degradation as intensifying energy). The catalysts were characterized using XRD, FTIR, and SEM-EDX. The results indicate that cobalt significantly influenced the microstructure and catalytic activity of the samples. The Ni-doped Co/La₂O₃ sample demonstrated a higher rate of catalytic degradation activity compared to the pure Co/La₂O₃ sample when reacting with H₂O₂. This degradation adhered to second-order and parabolic model reaction kinetics. Our kinetic studies revealed that at low initial concentrations of dye (8.22 × 10⁻⁵ M), the degradation efficiency over La₂O₃ by H₂O₂ exceeded 84.9 % (k = 0.4744 min^-0.5) for the parabolic diffusion model R² ≈ 1. The synergistic effect of sonocatalysis in the removal of MG increased the efficiency between 1.5 and 3.8 times. NiCo/La₂O₃ exhibited a better sonocatalytic degradation effect on the MG solution without and with H₂O₂, and the degradation reached 96.3 % (k = 0.5468 L.mg⁻¹.min⁻¹) within 40 min with R² = 0.9812. The second-order and parabolic model described the experimental data well, and the reusability up to five cycles also showed no loss of catalytic activity. The obtained results are among the best reported in the literature for this reaction in comparison to related catalysts.