Oxides of copper have been investigated for decades due to their unique semiconductor and optical properties. The review of literature revealed that very few reports are available on the synthesis of copper oxide nanoparticles using microorganisms and plant extracts. In this paper, we have reported the synthesis of copper oxide nanoparticles (CuO) using tea leaf and coffee powder extracts under microwave irradiations. The synthesis was carried out by irradiating metal salt and the extracts of tea and coffee in 1:3 ratio in a microwave at 540 W for 7-8 min. The synthesized nanoparticles were characterized by Scanning electron microscope, X-ray diffraction, UVvisible spectroscopy and Fourier transform infrared spectroscopy. The antibacterial activity of these nanoparticles was tested against six human pathogenic microbes. It was interesting to find that these nanoparticles possess remarkable antibacterial activity against two human pathogenic bacteria. Moreover, the use of environmentally benign materials for the synthesis of CuO nanoparticles offers numerous benefits of eco-friendliness and compatibility for pharmaceutical and other biomedical applications.

Graphene quantum dots (GQDs) as a new series of nanomaterials have drawn great attention in recent years owning to their unique properties. Here we report the single-step synthesis of GQDs using pyrolysis of citric acid which produced GQDs at different pH. The effect of different pH was studied in detail to optimize the conditions of the formation of GQDs. UV-Visible absorption and normalized fluorescence spectra were applied to analyze the optical properties of GQDs. The particle size distribution of the GQDs in case of varying pH was determined to optimize the synthesis conditions. The surface morphology and microstructures were studied by atomic force microscope (AFM).

With an increasing awareness of green and clean energy, zinc oxide-based solar cells were found to be suitable candidates for cost-effective and environmentally friendly energy conversion devices. In this paper, we have reported the green synthesis of zinc oxide nanoparticles (ZnONPs) by thermal method and under microwave irradiation using the aqueous extract of tomatoes as non-toxic and ecofriendly reducing material. The synthesised ZnONPs were characterised by UVÀvisible spectroscopy (UVÀvis), infra-red spectroscopy, particle size analyser, scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction study (XRD). A series of ZnO nanocomposites with titanium dioxide nanoparticles (TiO 2 ) and graphene oxide (GO) were prepared for photovoltaic application. Structural and morphological studies of these nanocomposites were carried out using UVÀvis, SEM, XRD and AFM. The currentÀvoltage measurements of the nanocomposites demonstrated enhanced power conversion efficiency of 6.18% in case of ZnO/GO/ TiO 2 nanocomposite.

Alumina nanoparticles (AlNP) were synthesized from aluminium nitrate using extracts of tea, coffee and triphala-a well known herbal plant as well as a nontoxic and eco-friendly green material. The synthesis was carried out taking 1:4 ratio of metal salt and these extracts under microwave irradiations at 540 W, which gave better yield of nanoparticles. Water was taken as solvent medium. The formations of AlNP were initially monitored by the colour changes occurring in the reaction mixture during the incubation period. As synthesized nanoparticles were characterized by scanning electron microscope (SEM), UV-Visible (UV-Vis) spectroscopy and Fourier transform infrared spectroscopy (FTIR). The AlNP were found to be spherical in shape in case of tea and coffee extracts with a size of 50-200 nm and to be oval shaped in case of triphala extract with an average size of 200-400 nm. The formation of AlNP with the microwave-assistance using these plant extracts has proved to be very faster than any other methods. In addition, excellent reproducibility of these nanoparticles, without the use of any additional capping agent or stabilizer will have great advantages in comparison with microbial synthesis, avoiding all the tedious and hygienic complications.

We have reported the green synthesis of silver nanoparticles (AgNPs) using the aqueous extract of Sapodilla (Manilkara zapota) fruit as nontoxic and eco-friendly reducing material. The synthesized AgNPs were characterized and used for preparing nanocomposites with GO and PEDOT:PSS. We have compared the performance of polymer cells based on poly­(3,4 ethylenedioxy-thiophene):poly­(styrenesulfonate) (PEDOT:PSS) with AgNPs incorporated in graphene oxide (GO). The constructed structure of the solar devices was ITO-AgNPs-GO-PEDOT:PSS-Al. We have investigated the influence of polymer as a hole extraction layer and GO as electron extraction layer on the performance of bulk heterojunction polymer solar cells. The maximum power conversion efficiency (PCE) was found to be 3.98% under illumination of 100 mW/cm2.