Nanoparticles of BiVO₃/g-C₃N₄ heterojunctions embedded two semiconductor of matching band gap energy was employed for photodegradation of amaranth dye and evolution of huge amount of hydrogen gas. A simple thermal decomposition of urea is efficient route for producing g-C₃N₄ nanosheets. In ultrasonic bath of power intensity 150 Watt, BiVO₃ nanoparticles were deposited homogeneously on g-C₃N₄ surface. The localization of BiVO₃ nanoparticles on the corners of g-C₃N₄ sheets was proved with HRTEM analysis. With increasing BiVO₃ contents to 10 wt%, the photocatalytic hydrogen evolution rate reach a maximum value of 6.8 mmolg⁻¹h⁻¹ which is ten fold higher than that of bare g-C₃N₄. The sonicated nanocomposites were characterized by XRD, N₂-adsorption-desorption isotherm, HRTEM, XPS, DRS and PL. The influence of radiation power of ultrasound waves on the dye degradation and the amount of hydrogen evolved was established. The production of charge carriers with high reductive and oxidative power through step S-scheme mechanism is primary cause for the exceptional photocatalytic efficiency of the nanocomposites. The charge migration through step S-scheme mechanism rather than type (II) heterojunction mechanism was established by the PL measurements of terephthalic acid and the trapping scavengers experiments. Nanocomposite with 10 wt% BiVO₃ possesses a superior reactivity for six consecutive cycles reveal the high stability of the as-synthesized sample.