Surface-Engineered 2D Hybrid h -BN/ g -C3N4 Nanocomposite for High-Efficiency Adsorptive Removal of Heavy Metal Ions from Aqueous Media

Abstract Heavy metal contamination in water sources is a significant concern for environmental and human health, necessitating the development of efficient, cost-effective, and sustainable removal methods. In this study, a surface-engineered hexagonal boron nitride (h-BN)/g-C3N4 (BN−CN) nanocomposite was synthesized via in situ thermal polymerization and subsequently functionalized with cystine via epoxide-amine coupling to yield Cys-BN−CN. Comprehensive structural and surface characterizations (XRD, FTIR, BET, SEM/TEM, and zeta potential) validated the successful formation of the nanocomposite and the effective bio-functionalization, which resulted in a significant increase in the surface area and enhanced accessibility of active sites. Batch adsorption experiments demonstrated the superior efficacy of Cys-BN−CN as well as the hybrid BN−CN nanocomposite for the removal of Cd2+ and Pb2+ compared to pristine h-BN and g-C3N4. Kinetic model fitting reveals that the adsorption process is best described by the pseudo-second-order and Elovich models, while Weber−Morris intraparticle diffusion analysis indicated that adsorption proceeded through sequential external diffusion, intraparticle diffusion, and surface complexation. Under the optimized conditions (pH 7.0, 25 °C, adsorbent dosage of 0.2 g L−1, and an equilibrium time of 240 min), Cys-BN−CN achieved maximum Langmuir adsorption capacities of 365.04 mg g−1 for Pb2+ and 331.42 mg g−1 for Cd2+, while the equilibrium data were best described by the Freundlich and Redlich−Peterson isotherm models. Thermodynamic analysis confirmed that the process is spontaneous and endothermic, with an enhanced driving force post-cystine functionalization. Furthermore, the material displayed remarkable recyclability and improved selectivity in the presence of competing ions. These results position the 2D hybrid BN−CN and Cys-BN−CN as viable and sustainable candidates for advanced applications in heavy metal remediation.