Synthesizing nanomaterials at the expense of solar energy and the associated energy generation have utmost significance as far as environmental sustainability is concerned. Here, sunlight-assisted combustion synthesis of a nanoscale metal oxide (CeO2) is reported. The sunlight, as a clean renewable energy source, is used for the first time to initiate the exothermic combustion reaction and to introduce oxygen vacancies into the CeO2. The current synthesis setup controls the environmental problems of gas evolution, usually associated with the conventional method, and thus maintains the green pathway. Additionally, for comparison, CeO2 nanoparticles are also synthesized using the conventional solution combustion method (CeO2-CSC). It is found that the CeO2 synthesized using sunlight-assisted combustion (CeO2-SAC) possesses a smaller particle size, a higher concentration of oxygen vacancies, and a narrower band gap than the CeO2-CSC. Therefore, CeO2-SAC demonstrates higher photocatalytic performance in converting CO2 to CH3OH (0.702 μmol h–1 g–1) than the CeO2-CSC (0.397 μmol h–1 g–1), thus pointing toward environmentally benign photocatalytic CO2 reduction.

A simple, eco-friendly, and biomimetic approach using Thymus vulgaris ( T . vulgaris ) leaf extract was developed for the formation of ZnO-Ag nanocomposites (NCs) without employing any stabilizer and a chemical surfactant. T . vulgaris leaf extract was used for the first time, in a novel approach, for green fabrication of ZnO-Ag NCs as a size based reducing agent via the hydrothermal method in a single step. Presence of phenols in T . vulgaris leaf extract has served as both reducing and capping agents that play a critical role in the production of ZnO-Ag NCs. The effect of silver nitrate concentration in the formation of ZnO-Ag NCs was studied. The in-vitro Antimicrobial activity of NCs displayed high antimicrobial potency on selective gram negative and positive foodborne pathogens. Antioxidant activity of ZnO-Ag NCs was evaluated via (2,2-diphenyl-1-picrylhydrazyl) DPPH method. Photocatalytic performance of ZnO-Ag NCs was appraised by degradation of phenol under natural sunlight, which exhibited efficient photocatalytic activity on phenol. Cytotoxicity of the NCs was evaluated using the haemolysis assay. Results of this study reveal that T . vulgaris leaf extract, containing phytochemicals, possess reducing property for ZnO-Ag NCs fabrication and the obtained ZnO-Ag NCs could be employed effectively for biological applications in food science. Therefore, the present study offers a promising way to achieve high-efficiency photocatalysis based on the hybrid structure of semiconductor/metal.

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