Graphitic carbon nitride impregnated niobium oxide (g-C₃N₄/Nb₂O₅) type (II) heterojunctions and its synergetic solar-driven hydrogen generation

Graphitic carbon nitride (g-C₃N₄) based catalysts are evolving in energy harvesting applications due to their robustness, nontoxicity, and most important photocatalytic efficiencies. In this work, we successfully engineered g-C₃N₄/Nb₂O₅ type (II) heterojunction via pulse sonochemical technique based on opposite charge-induced heteroaggregation on the surface. The agglomerated spherical Nb₂O₅ nanoparticles (NPs) having diameter 30-40 nm observed on the lamellar surface of g-C₃N₄ in FESEM images. The XRD and XPS analysis confirm the orthorhombic phase and formation of the g-C₃N₄/Nb₂O₅ heterostructure. The FTIR spectra of g-C₃N₄/Nb₂O₅ show characteristic poly-s-triazine bands from 1250 to 1650 cm^-1. Moreover, g-C₃N₄/Nb₂O₅ exhibited the lower bandgap value of 2.82 eV as compared to Nb₂O₅ (3.25 eV) with significant redshift and enhance visible light absorption. The Mott-Schottky (MS) analysis confirms the formation of heterojunction between g-C₃N₄ and Nb₂O₅, with significant band shifting toward lower hydrogen evolution reaction (HER) potential. The g-C₃N₄/Nb₂O₅ heterojunctions showed many folds enhanced photocurrent response from photoelectrochemical (PEC) water splitting, and the value reached to -0.17 mA/cm² with good stability and insignificant dark photocurrent at 1.0 V vs RHE. The electrochemical impedance spectroscopic (EIS) measurements further elucidate the suppression of photogenerated electrons/holes as the radius of the semicircle significantly decreased in case of heterojunction formation. The enhanced photocatalytic hydrogen generation by the heterostructures could be attributed to the effective formation of heterojunctions between the g-C₃N₄ and Nb₂O₅ semiconductors, causing the migration of the photogenerated electrons and holes, hence increasing their lifetimes.