Unraveling the Photoelectrochemical Properties of Bi₁₂NiO₁₉: A Novel p-Type Photocatalyst for Efficient Visible-Light Driven Dye Degradation

Bi₁₂NiO₁₉ was synthesized through a sol–gel technique employing citrate as a complexing agent. Structural confirmation via X-ray diffraction revealed a pure phase with an average crystallite size of approximately 32 nm. Optical analysis indicated a direct band gap of 2.38 eV, linked to Ni²⁺ (3d⁶) transitions, suggesting strong absorption in the visible spectrum. The material exhibited p-type conductivity and favorable charge transport characteristics, as evidenced by photoelectrochemical measurements. Mott–Schottky plots in 0.1 M Na₂SO₄ electrolyte identified a flat band potential of 0.67 V vs. SCE, with valence and conduction bands located at 0.87 V and –1.51 V vs. SCE, respectively, corresponding to O²⁻:2p and Bi³⁺:6p contributions. The photocatalytic activity of Bi₁₂NiO₁₉ was assessed for the degradation of Methyl Violet (MV) under visible-light exposure. A removal efficiency of 60% was achieved after 4 hours, primarily due to the formation of superoxide radicals (O₂•⁻). Kinetic studies followed a second-order reaction model with a photocatalytic half-life of 30 minutes. These results demonstrate the promise of Bi₁₂NiO₁₉ as a novel p-type photocatalyst for environmental remediation under visible light.