Role of Surface Oxygen Vacancies and Oxygen Species on CuO Nanostructured Surfaces in Model Catalytic Oxidation and Reductions: Insight into the Structure–Activity Relationship Toward the Performance

Abstract

Defect engineering, such as modification of oxygen vacancy density, has been considered as an effective approach to tailor the catalytic performance on transition-metal oxide nanostructured surfaces. The role of oxygen vacancies (O V ) on the surface of the as-prepared, zinnia-shaped morphology of CuO nanostructures and their marigold forms on calcination at 800 °C has been investigated through the study of model catalytic reactions of reduction of 4-nitrophenol and aerobic oxidation of benzyl alcohol. The O V on the surfaces of different morphologies of CuO have been identified and quantified through Rietveld analysis and HRTEM, EPR, and XPS studies. The structure− activity relationships between surface oxygen vacancies (O V ) and catalytic performance have been systematically investigated. The enhanced catalytic performance of the cubic CuO nanostructures compared to their as-prepared forms has been attributed to the formation of surface oxygen species on the reactive and dominant (110) surface that has low oxygen vacancy formation energy. The mechanistic role of surface oxygen species in the studied reactions has been quantitatively correlated with the catalytic activity of the different morphological forms of the CuO nanostructures.

Optical Asymmetry and Structural Complexity in Hierarchically Organized Chiral CuO Nanostructures: Insight into the Geometric and Crystallographic Effects on Cooperative Chirality

“…The peaks ranging from 615 to 415 cm −1 have been attributed to the various Cu−O stretching vibrations of all CuO nanostructures, as illustrated in the IR spectra (Figure 1B). The peaks positioned at 1571, 1647, 1354, and 3400 cm −1 were ascribed to the symmetric and asymmetric C�O stretching modes of the adsorbed tartrate anions, C−OH, and broad bands of adsorbed water, respectively, 17 that Specifically, a disappearance of the ν asymm COO stretch associated with the native ligands at 1530 cm −1 is observed, along with the appearance of a vibrational feature at 1567 cm −1 , tentatively assigned to a νCOO stretch for bound Dtartaric acid. Notably, this vibrational feature differs from the νCOO stretch associated with free D-tartaric acid at 1720 cm −1 .…”

“Click” Chemistry Assisted Synthesis of Magnetite‐CNT Nanohybrid Supported Gold Nanoparticles for Enhanced Catalytic Reduction of 4‐Nitrophenol

“…From these observations, it may be inferred that the reduction of 4-NP followed pseudo-first-order kinetics. [66] Therefore, the determination of the rate constant of the reaction in the presence of the catalysts was achieved by establishing a proportionate relationship between the absorbance of the primary species (namely, 4-nitrophenolate ions) and their corresponding concentrations. The rate constant of the reaction in the presence of Au NPs, Au/CNT, Fe 3 O 4 À CNT, and the ternary nanohybrid Au/Fe 3 O 4 À CNT was obtained using the following equation:…”

“…The dissociation is facilitated by the acid‐base interactions between gold and Fe 3 O 4 because of the acidic nature of Au NPs and the basic nature of oxygen vacancies present on the Fe 3 O 4 surface. The basic nature of oxygen vacancies on transition metal oxide‐based surfaces has already been well established [66] . Also, Fe 3 O 4 support plays an important role in the preferential adsorption of 4‐NP on the surface of Au/Fe 3 O 4 through the nitro group enabling the chemoselectivity.…”

“…The basic nature of oxygen vacancies on transition metal oxide-based surfaces has already been well established. [66] Also, Fe 3 O 4 support plays an important role in the preferential adsorption of 4-NP on the surface of Au/Fe 3 O 4 through the nitro group enabling the chemoselectivity. Moreover, Strong adsorptive contacts between CNT and 4-NP because of the π-π interactions between 4-NP molecules and the highly polarizable graphene sheets of CNT played an additional role in the catalytic activity of the Au/Fe 3 O 4 À CNT nanohybrid.…”

Carbon Dots as a Fluorescent Probe for Appraising Morphology‐Dependent Free‐Radical‐Scavenging Properties of CuO Nanostructures

“…The CuO nanostructures have been reported to exhibit efficacy as antioxidant since they demonstrate the ability to scavenge the free radicals. [2] The dual oxidation states of copper (Cu 1 + /Cu 2 + ) at the surface of the basic CuO accelerates the redox reactions with the reactive oxygen species (ROS; such as: superoxide; hydrogen peroxide; hydroxyl radical; hydroxyl ion), [3,4] which gets generated from molecular oxygen during any aerobic metabolic process, and helps in their removal. This facilitates the inhibition of "oxidative stress" that would otherwise harm the aerobic life forms due to imbalance created between the rates of production and removal of ROS in the biological cells.…”