A novel NdWO3/g-C3N4 n–n heterojunction was prepared via a calcination method. The synergistic interaction between the NdWO3 and g-C3N4 catalysts has been investigated and characterized by using various analytical techniques. The band gaps and conduction band positions of NdWO3 and g-C3N4 samples were identified from ultraviolet–visible light (UV-Vis) absorption spectroscopy and Mott–Schottky results. The extended absorption in the visible region is due to the overlying of energy level bands between NdWO3 and g-C3N4 catalysts. The ternary NdWO3/g-C3N4 composite exhibited enhanced photocatalytic activity is due to the adequate utilization of light on the assembly of the n–n heterojunction and tight contact facilitates the interfacial charge transfer between NdWO3 to g-C3N4. The formation of the n–n heterojunction is confirmed from the open circuit potential measurements. The proposed mechanism for the enriched visible-light photocatalytic activity of the NdWO3/g-C3N4 n–n heterojunction was further supported and endorsed by photoluminescence, electrical impedance spectroscopy, and transient photocurrent response. Furthermore, the addition of hydrogen peroxide as an oxidant to the reaction system and flat band potentials was correlated with photocatalytic activity. Degradation product analysis was done using Liquid Chromatography Mass Spectroscopy techniques combined with UV–visible absorption spectrum. The results showed that the MB dye degradation is initiated by the removal of methyl groups in the molecule.

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