A Synergistic NiCo2O4/g-C3N4@rGO Heterostructure via a Phytogenic Route for Phenol Abatement and Efficient Electrode Materials for Supercapacitor Applications

The nanoarchitectonic fabrication of multifunctional heterostructures that synergistically integrate photocatalytic environmental detoxification with electrochemical energy storage exemplifies an emerging frontier toward sustainable materials chemistry. Herein, a phytogenic-derived NiCo2O4/g-C3N4@rGO ternary heterostructure was synthesized to regulate electronic configuration, structural defects, and charge carrier transport through Ni/Co–O bonding and M–O–C interactions. The spectral and structural analyses revealed homogeneously distributed nanoparticles with an average crystallite size of ∼ 70 nm, a mesoporous heterostructure possessing a high specific surface area of 75.4 m2 g–1, a high defect density (nD = 1.74 × 1011 cm–2), a narrow optical bandgap (1.10 eV), and strong interfacial bonding with negative surface potential (ζ = −41.3 mV). Under natural solar radiation, the optimized heterostructure achieved 97% (4-NP), 96% (3-AP), and 92% (2,4-DNP) degradation of recalcitrant phenols, along with 71–81% total organic carbon (TOC) mineralization, subsequent pseudo-first-order kinetics, and stable activity over seven consecutive cycles. Statistical optimization via Box–Behnken design (BBD) recognized high predictive fidelity (R2 = 0.99), while GC–MS analysis elucidated a mineralization pathway primarily involving •OH and O2•– radicals. Electrochemical measurements revealed a pronounced supercapacitive response with dominant-diffusion contribution and enhanced surface contribution from corresponding individual components, with a specific capacitance of 1706 F g–1 at 4 A g–1 and significantly reduced charge-transfer resistance (Rct = 0.65 Ω), indicating improved accessibility of electroactive sites and favorable interfacial charge-transfer characteristics. The bifunctional heterostructure provides a promising platform for integrating various interfacial catalytic conversions with energy storage toward environmental remediation and energy conversion in the future.