Evaluation of Activated Biocarbon Combined with Cobalt-Doped CuO Nanocomposite for Improving the Photocatalytic Degradation of Dye: Toward Sustainable Environmental, Biological, and Electrochemical Applications

In this study, a sustainable green synthesis route was developed to fabricate CuO, Co-doped CuO (Co-CuO), and a novel Activated Biocarbon-Co-doped CuO (ABC-Co-CuO) nanocomposite using Nelumbo nucifera (lotus) leaf extract. The key novelty of this study is the integrated use of lotus leaf extract as a bioreductant and lotus fiber biomass as a precursor of activated biocarbon (ABC) to create a multifunctional hybrid material. The primary objective was to design green and cost-effective nanocomposites with improved catalytic, electrochemical, and biological performance for multifunctional applications. ABC derived from lotus biomass significantly improved the physicochemical properties of the nanocomposites by increasing the surface reactivity and charge carrier mobility. The synthesized materials were comprehensively characterized using P-XRD, FE-SEM, FT-IR, HR-TEM, PL, UV-vis DRS, XPS, and BET analysis. XRD confirmed the monoclinic phase of CuO, while FE-SEM revealed mixed cubic and spherical morphology. The band gap was reduced from 3.34 eV (CuO) to 2.10 eV (ABC-Co-CuO), indicating enhanced visible light absorption due to Co doping and carbon integration. In the UV photocatalytic degradation of Brilliant Green dye (BG), ABC-Co-CuO (95.41%) showed a superior degradation rate compared to Co-CuO (75.95%) and CuO (63.62%). Electrochemical studies confirmed the superior performance of ABC-Co-CuO, exhibiting a high specific capacitance of 600 F/g at 10 mV s^-1 and a low solution resistance of 2.15 Ω, compared to 260 F/g and 3.02 Ω, respectively, for pure CuO. These results indicate that the composite materials have enhanced charge storage capacity and improved ionic conductivity, suggesting its potential in energy storage and electrocatalysis. The material also exhibited broad-spectrum antibacterial activity and antioxidant capacity comparable to those of ascorbic acid. This study introduces a new biomass-derived nanomaterial platform for multifunctional applications in environmental remediation, biomedical, and energy technologies, in line with sustainable development goals.