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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.

We report a molecular fluorophore-based concept for the first time, to explain the quenching mechanism of the blue-emissive N-doped carbon dots (NCDs) exhibiting molecular fluorescence (quantum yield = 37%), synthesized through microwave-assisted pyrolysis of malic acid and urea (in 1:3 mole ratio), which has been devised as a fluorescent probe for the sensitive and selective detection of picric acid (PA). A linear Stern–Volmer plot for the fluorescence quenching of NCDs in the PA detection has been observed in the concentration range of 0–1.6 μM, and the limit of detection (LOD) is found to be 33 nM (7.56 ppb). Furthermore, molecular fluorescence in NCDs has been realized to originate from a putative pyridinic (2-pyridone moiety)-type molecular fluorophore, which has been manifested by the inferences drawn from HRMS, 1H NMR, 13C NMR, and XPS studies. The chemical structure of the molecular fluorophore was further validated by correlating the simulated absorption and emission spectra of the molecular fluorophore generated by TD-DFT, with those obtained from NCDs’ experimental data. The underlying photophysical property involved in the simultaneous occurrence of FRET and ET quenching mechanism has been illustrated based on the molecular fluorophore, along with the conventional approach. Here, the role of the molecular fluorophore in the NCDs has been demonstrated as a donor in the ET process involving the NCDs–nitroaromatics pair, where the acid–base interaction between the acceptor (nitroaromatics) and donor has been considered as the essence of the ET process.

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