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• g-C 3 N 4 is modified with Gd species and then integrated with WO 3. • Characterization techniques suggested intimate contact between the components. • S-scheme heterojunction was established through computational studies. • Superoxide and hydroxyl radicals dominated the degradation mechanisms. Modifying the surface structures of g-C 3 N 4 through interfacial coupling with other semiconductors has been spotlighted as an efficient approach for improving photocatalytic efficiency. With the surge of S-scheme heterojunctions, the research is intensified towards designing this kind of composite for energy-environmental-related applications. In this context, a new approach involving surface modifications of g-C 3 N 4 through Gd species and integrating with monoclinic-WO 3 via a wet chemical approach to form S-scheme heterojunctions is investigated. The characterization results attested that the adopted protocol promotes the better dispersion of Gd species over the g-C 3 N 4 surface and rigidly integrates with WO 3. The optical response of the composite spanned a significant portion of the visible region in the solar spectrum. The computational studies and the findings of the Mott-Schottky plot collectively suggested that the position of band edges qualifies for the formation of S-scheme heterojunction. The results derived from photocurrent response measurements and photoluminescence technique attribute to the effective charge carrier separation in the heterostructure. The rate constant of Gd-g-C 3 N 4 /WO 3 was 1.48 × 10−2 min−1 which was approximately 4.35 and 2.27 times greater than that of WO 3 (0.34 × 10−2 min−1) and g-C 3 N 4 /WO 3 (0.65 × 10−2 min−1) respectively. Furthermore, RhB degradation in the presence of scavengers validated the participation of superoxide and hydroxyl radicals in the degradation mechanisms. This was possible only when the conduction band electrons of WO 3 recombined with the valence band holes of Gd-modified g-C 3 N 4. The present work helps to understand the S-scheme heterojunction formation between surface-modified g-C 3 N 4 and metal oxides and retain the involvement of energetic charge carriers in the desired redox reactions. [ABSTRACT FROM AUTHOR]