Preparation and photocatalytic degradation of methylene blue using a sulfanilic acid-functionalized NiO/GO ternary composite with electrochemical evaluation

A NiO/GO/SA ternary nanocomposite was successfully synthesized <i>via</i> co-precipitation and demonstrated multifunctional performance. Structural analysis confirmed uniform NiO distribution on wrinkled GO sheets with sulfanilic acid functionalization, yielding reduced crystallite size (∼18-22 nm), high crystallinity (83%), and strong interfacial bonding, as verified by Raman, FTIR, and XPS. Elemental mapping further validated the integration of Ni, O, C, S, and N functionalities, which contribute to the composite's synergistic properties. The photocatalyst exhibited excellent visible-light activity against methylene blue, achieving 96% degradation with pseudo-first-order kinetics (<i>k</i> = 0.032 min^-1) and 82% TOC mineralization after 210 min. Radical scavenger studies confirmed hydroxyl and superoxide radicals as the dominant species. The composite outperformed several reported ternary systems and retained >85% efficiency after five reuse cycles, demonstrating both activity and stability. Electrochemical studies showed pseudocapacitive behavior with reversible Ni²⁺/Ni³⁺ redox transitions, low charge-transfer resistance (∼0.4 kΩ), and high capacitance of 650 F g^-1 at 5 mV s^-1, maintaining 275 F g^-1 at 50 mV s^-1. These results highlight NiO/GO/SA as a promising material for wastewater treatment and energy storage, with potential improvements achievable through further interface engineering and defect modulation.