Mesoporous Cu-Doped Manganese Oxide Nano Straws for Photocatalytic Degradation of Hazardous Alizarin Red Dye.

The present work reports the photocatalytic degradation of alizarin red (AR) using Cu-doped manganese oxide (MH16-MH20) nanomaterials as catalysts under UV light irradiation. Cu-doped manganese oxides were synthesized by a very facile hydrothermal approach and characterized by energy dispersive X-ray spectroscopy, powder X-ray diffraction, scanning electron microscopy, Brunauer-Emmett-Teller analysis, UV-vis spectroscopy, and photoluminescence techniques. The structural, morphological, and optical characterization revealed that the synthesized compounds are nanoparticles (38.20-54.10 nm), grown in high mesoporous density (constant C > 100), possessing a tetragonal phase, and exhibiting 2.98-3.02 eV band gap energies. Synthesized materials were utilized for photocatalytic AR dye degradation under UV light which was monitored by UV-visible spectroscopy and % AR degradation was calculated at various time intervals from absorption spectra. More than 60% AR degradation at various time intervals was obtained for MH16-MH20 indicating their good catalytic efficiencies for AR removal. However, MH20 was found to be the most efficient catalyst showing more than 84% degradation, hence MH20 was used to investigate the effect of various catalytic doses, AR concentrations, and pH of the medium on degradation. More than 50% AR degradation was obtained for all studied parameters with MH20 whereas the pseudo-first-order kinetic model was found to be the best-fitted kinetic model for AR degradation with k = 0.0015 and R2 = 0.99 indicating a significant correlation between experimental data.

Catalytic Oxidation of Toluene into Benzaldehyde and Benzyl Alcohol Using Molybdenum-Incorporated Manganese Oxide Nanomaterials.

Oxidation of toluene (an organic pollutant), into useful chemical products, is of great interest nowadays. However, efficient conversion of toluene under mild and sustainable conditions is a thought-provoking task. Here, we report MnMoO4 nanomaterials (CH1-CH2), synthesized through a very facile solvothermal approach. Catalytic efficiencies of MnMoO4 nanomaterials were evaluated by direct oxidation of toluene via C-H activation. Toluene was converted into benzaldehyde and benzyl alcohol in the presence of H2O2 as an oxidant at 80 °C. The reaction parameters, that is, catalyst dose, time, and toluene concentration, were varied to obtain the optimal conditions for the oxidation process. The 40.62% maximum toluene conversion rate was obtained after 18 h of oxidation activity with 0.06 g of catalyst CH1. A maximum of 78% benzaldehyde selectivity was obtained with 0.06 g of catalyst CH1 after 18 h of toluene oxidation activity. Also, 62.33% benzyl alcohol selectivity was achieved using 0.1 g of catalyst CH1 after 1 h of activity. Several catalytic cycles were run with CH1 to evaluate catalyst reusability. Potential % toluene conversion was obtained for up to six cycles and their turnover frequencies were found to be 1.94-1.01 s-1. FTIR spectra of catalyst CH1 before and after recovery indicate no significant change. The good conversion rate of toluene and efficient selectivity toward benzaldehyde and benzyl alcohol indicates the robustness and high potential of these catalysts to oxidize toluene under a milder, greener, and hazardous chlorine-free environment.