Arc-discharge-enabled synthesis of multiphase Bi-based/g-C₃N₄ heterojunctions for photocatalytic pollutant degradation and hydrogen evolution

• DC arc discharge decorated multiphase Bi-based components directly on g-C 3 N 4 sheets. • BGW2 heterojunction achieved 98% methylene blue removal within 60 min. • BGW2 produced 1116 μmol g −1 h −1 H 2 , nearly five times higher than pure g-C 3 N 4 . • Multi-heterojunction design enhanced visible light absorption and charge separation. • BGW2 showed stable cycling, coupling dye degradation with green H 2 production. Photocatalytic systems for pollutant degradation and hydrogen production require efficient interfacial charge separation under solar irradiation. In this work, Bi-containing nanostructures and their g-C₃N₄-coupled hybrid heterojunctions were synthesized via an electrical arc discharge method in deionized water and g-C₃N₄-dispersed solutions, followed by controlled aging at 80°C to promote the formation of mixed Bi-based phases. XRD analysis revealed the progressive transformation of initially formed Bi/Bi(OH) 3 into oxide and oxycarbonate phases, including Bi 2 O 3 , Bi 2 O 2 CO 3 , and (BiO) 4 CO 3 (OH) 2 , uniformly distributed within the g-C 3 N 4 matrix. FTIR spectroscopy confirmed the coexistence of Bi–O bonds, carbonate groups, and heptazine structural units. XPS analysis of the Bi₂O₃/Bi₂O₂CO₃/(BiO)₄CO₃(OH)₂/g-C₃N₄ (BGW2) sample showed Bi exclusively in the Bi³⁺ oxidation state, indicating the formation of oxide and oxycarbonate domains while preserving g-C₃N₄ integrity. BGW2 exhibited an enhanced BET surface area of 42.0 m 2 g −1 and a hierarchical sheet-like morphology decorated with Bi-based nanostructures. Optical studies demonstrated improved visible-light absorption and suppressed charge-carrier recombination. BGW2 achieved 98% degradation of methylene blue within 60 min, effective removal of RhB (91%) and MO (81%), while exhibiting a hydrogen evolution rate of 1116.07 μmol g⁻¹ h⁻¹ under visible light, nearly five times higher than pristine g-C₃N₄. Excellent stability over repeated cycles further confirmed the strong multifunctional photocatalytic performance of BGW2.