A novel and greener approach for shape controlled synthesis of gold and gold–silver core shell nanostructure and their application in optical coatings

• Design of a new simple and environmental friendly method employing the fish scale extract of Labeo rohita.
• Anisotropic, polyhedral and spherical gold nanostructures were formed by varying the reaction parameters.
• Bimetallic core–shell gold–silver nanostructures (spherical and oval shaped) were formed.
• The anisotropic gold nanotriangles were utilized in optical coatings.
• Gold nanotriangles were found to block the IR radiation and lower the temperature by almost 5 °C.

Green and facile synthetic methods have gained marvellous fame for the production of polyhedral, anisotropic and spherical gold, and gold–silver bimetallic nanostructures. The useful pivotal characteristics of a green procedure are the usage of environment benign solvent medium, reducing and stabilising agents, and shorter reaction time. We describe here a novel, and greener method for the production of gold and gold–silver core shell nanostructures using aqueous fish scales extract of the Labeo rohita. The effect of various reaction parameters, such as temperature and concentration for the synthesis of the nanostructures were studied. Results indicated that triangular and decahedron gold nanostructures were formed at a lower temperature (40 °C) and concentration (10%). While, icosahedral and spherical gold nanostructures were produced at a comparatively higher temperature (100 °C) and concentration (40%). The study also revealed that the core–shell bimetallic nanostructures with different morphologies (spherical and oval-shape) were formed at different ratios of chloroaurate and silver nitrate solution. Thus, the present study indicated a simple shape controlled synthesis of gold and gold silver core–shell nanostructures. The synthesised gold nanotriangles were coated over the glass substrate and found to be highly efficient in absorbing infra-red radiations for potential architectural applications. Therefore, the study demonstrated the facile usage of gold nanotriangles for optical coatings. The present strategy depicted the dual functional ability of the fish scale extract as reducing and stabilising agents. This strategy also eliminates the usage of hazardous chemicals, toxic solvents and harsh reducing and stabilizing agents.

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