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The different temperature drying processes were carried out at −60 °C, 15 °C, and 60 °C to control the nanosheet morphology of MXene matrix. The MXene electrode prepared at −60 °C (denoted as LT-Ti3C2Tx) produced more nanosheet arrays than those with drying temperatures of 15 °C and 60 °C (denoted as RT-Ti3C2Tx and HT-Ti3C2Tx MXene electrodes, respectively). The results of BET and electrochemical measurements show that the specific surface area and capacitance initially decrease and then increase with the change in nanosheet layers in MXene. Among these prepared electrodes, LT-Ti3C2Tx, with a well-controlled nanosheet array, showed outstanding specific capacitance (Cs) of 467.4 F g−1 at current density of 0.5 A g−1, and 98.13% stability after 5000 cycles. Furthermore, an LT-Ti3C2Tx // LT-Ti3C2Tx symmetric supercapacitor device (SSD) was assembled, employing the LT-Ti3C2Tx with a well-controlled nanosheet acting as both anode and cathode. The SSD exhibited high energy density of 5.67 Wh kg−1 at power density of 589.09 W kg−1, and long cycle life electrochemical stability of 99.9% after 5000 cycles. These promising results show that MXene electrodes prepared by low-temperature drying (i.e. –60 °C) may be useful for supercapacitor applications.

A self-grown copper sulfide@copper oxide (CuS@Cu2O) positrode synthsis by a hydrothermal method followed by 2 h of air annealing method (at 300 °C) from copper-foam (Cu-F) is envisaged as supercapattery electrode material in 0.1 M KOH electrolyte solution where remarkable capacities of 145, 134, 125, and 112 mA h g−1 at current densities of 1, 2, 3, and 4 A g−1, respectively, with about 80% retention ability after 2000 redox cycles, are obtained. The electrochemical performance obtained for self-grown CuS@Cu2O positrode is better than those reported previously for self-gown CuS, Cu(OH)2, and CuO electrode materials. An asymmetric supercapattery device fabricate using CuS@Cu2O as a positrode with Bi2O3 as negatrode, i.e., CuS@Cu2O//Bi2O3, demonstrates an energy density of 52 Wh kg−1 at a power density of 750 W kg−1 at 0.5 A g−1 which, when connected in series with another similar device, lightens a LED with its full-bright intensity, confirming a commercial potential of designed electrochemical supercapattery device.

Green synthesis of optically active silver nanoparticles (Ag) containing thin film on flexible plastic strip substrate has been carried using guava leaf extract. The properties of silver films were studied using UV–visible spectrophotometer, field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and energy dispersive X-ray (EDX) techniques. The silver thin films were used to detect Hg2+ ions in water with lower limit of concentration up to 20 ppm by visually observing the color change of the film from brown to cloudy white. UV–visible spectra indicated blue shift due to strong redox reaction between Ag and Hg2+ ions. Depending upon the time for the color change of the Ag films, the amount of Hg2+ ions in the water is determined. This method is found to be simple and rapid for detection of Hg2+ ions in the solution.