Effectiveness of metal oxide catalysts for the degradation of 1,4-dioxane

1,4-dioxane, commonly used as a solvent stabilizer and industrial solvent, is an environmental contaminant and probable carcinogen. In this study, we explored the concept of using metal oxides to activate H₂O₂ catalytically at neutral pH in the dark for 1,4-dioxane degradation. Based on batch kinetics measurements, materials that displayed the most suitable characteristics (high 1,4-dioxane degradation activity and high H₂O₂ consumption efficiency) were ZrO₂, WO_x/ZrO₂, and CuO. In contrast, materials like TiO₂, WO₃, and aluminosilicate zeolite Y exhibited both low 1,4-dioxane degradation and H₂O₂ consumption activities. Other materials (e.g., Fe₂O₃ and CeO₂) consumed H₂O₂ rapidly, however 1,4-dioxane degradation was negligible. The supported metal oxide WO_x/ZrO₂ was the most active for 1,4-dioxane degradation and had higher H₂O₂ consumption efficiency compared to ZrO₂. In situ acetonitrile poisoning and FTIR spectroscopy results indicate different surface acid sites for 1,4-dioxane and H₂O₂ adsorption and reaction. Electron paramagnetic resonance measurements indicate that H₂O₂ forms hydroxyl radicals (˙OH) in the presence of CuO, and unusually, forms superoxide/peroxyl radicals (˙O₂⁻) in the presence of WO_x/ZrO₂. The identified material properties suggest metal oxides/H₂O₂ as a potential advanced oxidation process in the treatment of 1,4-dioxane and other recalcitrant organic compounds.

FTIR and surface poisoning results suggest 1,4-dioxane adsorbs to Lewis acid sites on metal oxide surfaces and is degraded by surface radical species.

Unpaired electrons as probes of catalytic systems

An overview is provided of the importance of molecular species containing unpaired electrons in catalytic systems, as revealed using ESR spectroscopy. The review aims to demonstrate the considerable extent of scientific progress that has been made in this broad topic during the past few decades. Studies of catalytically active surfaces, including zeolites, are surveyed, and the detection of radical species, formed as intermediates in their reactions, using matrix isolation and spin-trapping techniques. Radical cation formation in zeolites is discussed, and the employment of muon spin rotation and relaxation techniques to study the mobility of labelled radicals in various porous and catalytic media. Among the specific types of catalytic media considered are those for photocatalysis, water splitting, degradation of environmental pollutants, hydrocarbon conversions, fuel cells and sensor devices employing graphene. The review concludes with recent developments in the study of enzymes and their reactions, using ESR-based methods.