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Dual-functional ZnO/g-C3N4 nanocomposites: effective adsorption - photocatalysis for both direct blue 71 and
Ngo Trung Hoc1, Nguyen Thi Hanh2, Le Dinh Tuan2
1Faculty of Materials Science and Engineering, Phenikaa University Duong noi Ward Hanoi 10000 Vietnam.
Abstract:
The ZnO/g-C3N4 nanocomposites (NCPs) were fabricated via a facile, one-step thermal decomposition of Zn(NO3)2·6H2O and urea. The successful chemical integration and composition of the NCPs were confirmed through FTIR and XPS analyses, while XRD patterns and HRTEM images revealed that interfacial interactions between the two phases induce lattice distortion at the ZnO surface. The BET and UV-vis absorption analyses demonstrated that the ZnO/g-C3N4 NCPs exhibit enhanced visible-light absorption alongside a significant increase in pore size and volume compared to pure ZnO. These synergistic structural and optical properties led to a marked improvement in adsorption - photocatalytic efficiency for Methylene Blue (MB) and Direct Blue 71 (DB 71). Under optimal conditions (catalyst weight: 0.03 g per 50 mL; dye concentration of 1.0 × 10-5 mol L-1 for MB and 25 ppm for DB 71), the ZnO/g-C3N4 NCPs achieved a superior removal efficiency of 98.2% for MB (at 55 °C and pH = 13) and 98.8% for DB 71 (at 25 °C and pH = 3) following 60 min of dark adsorption and 120-150 min visible-light irradiation. The NCPs achieved maximum adsorption capacities of 100.7 mg g-1 for MB and 154.08 mg g-1 for DB 71, performing optimally in alkaline and acidic media, respectively. Adsorption equilibrium data for both MB and DB 71 dyes correlated strongly with the Langmuir isotherm model, suggesting monolayer formation on a homogeneous adsorbent surface. The adsorption process is driven by a synergistic combination of molecular interactions - primarily physical adsorption - mediated by a network of electrostatic forces, π-π stacking, and hydrogen bonding. Furthermore, the photocatalytic degradation follows a Z-scheme mechanism, in which ˙OH radicals and h+ are identified as the primary active species for MB degradation, while ˙O2 - radicals are the dominant species in the degradation of DB 71. These results highlight the potential of the ZnO/g-C3N4 nanocomposite for high-performance applications in integrated adsorption-photocatalytic wastewater treatment.
