Green combustion synthesis of multifunctional inorganic ZnO: Co2+ (1-11 mol%) nanoparticles: Electrochemical and photocatalytic applications

Aloe Barbadensis Miller (Aloe vera) gel fuel-assisted facile combustion synthesized novel ZnO:Co2+ nanoparticles were analysed for its multifunctional applications such as supercapacitors, sensors, and photocatalytic dye degradation. The PXRD pattern of ZnO was matched with DFT-based computational XRD pattern. The morphology of the prepared nanomaterial was tested using Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) techniques. Band gaps were estimated using the Kubelka-Munk function (KM function) using diffuse reflectance spectra (DRS). The band gap was found to be a minimum 1.90 eV for ZnO: Co2+ (7 mol%) nanoparticles. Electrochemical properties of ZnO: Co2+ (1-11 mol%) nanoparticles based modified carbon paste electrodes were studied in KCl electrolyte using cyclic voltammetry (CV), Electrochemical impedance spectroscopy (EIS) and Galvanostatic charge-discharge (GCD). Enhanced and optimized electrochemical performance in terms of specific capacitance was observed for ZnO: Co2+ (7 mol%) electrodes for supercapacitor application. EIS shows minimum ESR value of 72 omega and GCD shows 99 % cyclic stability over 1550 cycles for ZnO: Co2+ (7 mol%) electrode. Effect of low band gap on electrochemical properties were established and found that low band gap leads to high performance in electrochemical activities. Sensitive detection of paracetamol and glucose (1--7 mM concentration) was carried out using the ZnO: Co2+ (7 mol%) electrode, for electrochemical sensor application. Photocatalytic degradation of methylene blue (MB) & acid orange -8 (AO-8) dyes was carried out using ZnO: Co2+ (7 mol%) photocatalyst under sunlight including scavenging examinations. Under sunlight, 92.45 % of MB and 98.29 % of AO-8 dyes were degraded in 120 min. Overall, this paper reports, multifunctional applications (EDLC, Sensor and Photocatalysis) of toxic free green combustion synthesized ZnO: Co2+ (1-11 mol%) nanoparticles.