Unveiling of Interfacial Charge Carrier Dynamics in rGO Wrapped g-C₃N₄/SnO₂ Heterostructure for Enhanced Adsorption and Sunlight-Driven Photocatalysis

This work demonstrates the engineering of an rGO-wrapped g-C₃N₄/SnO₂ ternary heterojunction-based photocatalyst via a one-step in situ hydrothermal technique. The well-positioned CB edge of g-C₃N₄ and the VB of SnO₂ create a type-II heterojunction, making g-C₃N₄/SnO₂ a promising photocatalyst for efficient redox reactions. Further, the incorporation of rGO, with its high specific surface area, significantly enhances the density of active site availability of the resulting ternary rGO/g-C₃N₄/SnO₂ heterostructure. The reduced band gap and formation of the multiple heterojunctions improve the separation and migration efficiency of photogenerated charge carriers, making the rGO/g-C₃N₄/SnO₂ heterojunction highly effective for removing a diverse category of pollutants. A small dose of 0.3 mg/mL of the ternary heterostructure degrades 99.3% of RhB dye under the exposure of simulated solar light for 40 min. Remarkably, the ternary heterostructure exhibits exceptional photodegradation efficiency for a mixture of dyes (MB + RhB + MO) with a high concentration of 30 mg/L, achieving removal rates of 99.99%, 71.4%, and 71%, respectively, within 40 min of irradiation. Moreover, first- and second-order in addition to the intraparticle diffusion models were used to determine the rate constants and equilibrium adsorption capacities of the rGO/g-C₃N₄/SnO₂ heterostructure, uncovering the underlying adsorption mechanisms. To comprehend the mechanistic intricacies underlying photocatalysis, a charge transfer process at the multiple interfaces has been thoroughly discussed using the experimentally determined values of work function and band edge positions from ultraviolet photoelectron spectroscopy and Mott-Schottky analysis, respectively. Eventually, the scavenger's study affirms that the photogenerated e^--h⁺ pairs, superoxide anion, and hydroxyl free radicals all play an active role in the photodegradation process.