Nowadays necessities for the green synthesis of nanoparticles are enlarged because of its neutral toxicity and eco-friendly advantages. In this present study, we have explored the rapid biosynthesis of AgNPs at room temperature by the fresh leaf aqueous extract of Anacardium occidentale. Aqueous extracts were prepared at different temperatures 60, 80 and 100°C. Formation of silver nanoparticles (AgNPs) was confirmed by surface plasmon resonance (SPR) peak observed around 400-420 nm in UV-Visible spectra. Among the extracts prepared, 80°C extract showed good shift in UV-Visible spectrum during Cr(VI) detection and a good linear relationship was found between the absorbance ratio (A 510 /A 400 ) against 100 mM-1 lM concentration of Cr(VI). Cr(VI) was confirmed by the red shift of SPR position from 400 to 510 nm. Detection limit of our prepared probe is 1 lM and this simple technique exhibiting high selectivity to Cr(VI) over other tested heavy metal ions. Finally, efficient 80°C extract synthesized AgNPs were characterized by XRD, SEM and TEM. XRD characterization confirmed its face centered cubic structure and confirmed that the prepared AgNPs are crystalline in nature. TEM and SEM characterization results revealed that the AgNPs are in spherical nature. The size of AgNPs was found to be 40-60 nm.

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Mixed transition-metal oxides are emerging electrode materials, because of their higher electrochemical performances. In the present work, single-metal oxides, binary-metal oxides, and ternary mixed-metal oxides (MMOs) of zinc oxide (ZnO), nickel oxide (NiO), and copper oxide (CuO) are successfully prepared by simple gel-combustion process. The structure and properties of MMOs are of great interest, because of the opportunity to tune their properties for better multifunctional performance than single and binary metal oxides. The crystal structure, functional group, surface morphology, and binding energy of all of the single, binary, and ternary MMOs are studied through X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDX), high-resolution transmission electron microscopy (HR-TEM) and X-ray photoelectron microscopy (XPS), respectively. The entire electrochemical studies are also performed using cyclic voltammetry (CV), galvanostatic charge−discharge (GCD), and electrochemical impedance spectroscopy (EIS). From the electrochemical study, the ZnO−NiO−CuO MMOs electrode was found to possess pseudocapacitor-type features and shows an outstanding specific capacitance of 1831 F g −1 at a current density of 1 A g −1 , which is higher than that of single and binary metal oxides. The fabricated asymmetric (ASC) device [ZnO−NiO−CuO MMOs || r-GO] exhibits maximum specific capacitance of 118 F g −1 at the current density of 1 A g −1 . Hence, it leads to the supercapacitance property of maximum storage response; the ASC device possessed the excellent retentivity of (89.97%) up to 10 000 repeated cycles. The ASC device reveals a maximum specific power of 5672 W h kg −1 with a specific energy of 15.7 W h kg −1 with a high current density of 10 A g −1 . This finding shows that the ZnO−NiO−CuO MMOs can be used as potential electrode material and might have promising applications in high-performance energy storage devices.

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