Enhanced photocatalytic activity of biogenically synthesized CuO nanostructures against xylenol orange and rhodamine B dyes

In the present article we report the Tamarindus indica L extract mediated biogenic green synthesis of CuO nanostructures. The synthesis consisted of reacting mixtures of copper salt solution and fruit extract at elevated temperatures. Heating under hydrothermal conditions for a very short duration (1 h) and under normal conditions for several hours were employed. The role of the heat treatment method on the growth of the nanostructures and their photocatalytic properties has been investigated. To the best of our knowledge, no one else has reported such a rapid synthesis of CuO nanostructures biogenically employing plant extracts. Moreover, no one else has reported the synthesis of CuO nanostructures such as nanosheets using fruit extracts of Tamarindus indica L. X-ray diffraction (XRD) and selected area electron diffraction (SAED) results reveal that the CuO nanostructures grow in the monoclinic and cubic phases. Morphological studies indicate the material grown under short duration (hydrothermal conditions) predominantly consists of nanosheets (similar to 27 nm thick) while that grown with prolonged heating consists of granular nanoparticles (diameter similar to 19 nm), both agglomerated as spherical structures. Thermogravimetric results show good thermal stability of the nanostructures even at high temperatures. Optical properties indicate the material is visible light active and possesses an indirect energy band gap similar to 1.7 eV. Photoluminescence (PL) spectra of the nanostructures showed prominent emission at similar to 700 nm and a small amount of emission around 400 nm. The color coordinates of the nanoparticles determined from the PL data were located in the blue region of the Commission internationale de l'eclairage (CIE) diagram. Surface area analysis revealed mesoporous nature of the nanostructures. The nanosheets exhibit larger surface area (35.4 m(2)/g) than the granular nanoparticles (22.6 m(2)/g). The microspheres made of agglomerated nanosheets were used to carry out the photocatalytic degradation of rhodamine B (RhB) and xylenol orange (XO) dyes under UV-Visible light illumination. The nanosheets exhibited strong photocatalytic behavior and photodegraded 96% of RhB and 87% of XO in 150 and 90 min of light illumination, respectively. The photocatalyst showed good stability during the photocatalytic reactions. High activity and better stability of the nanosheets indicate the photocatalysts have potential ability to get commercialized.