Metal organic framework-based ternary ZIF-8/ZnO/g-C3N4 heterostructures for improved adsorption and photocatalytic performance
摘要
The contamination of water by synthetic dyes poses a major environmental challenge, necessitating efficient remediation strategies. Photocatalytic degradation offers a promising, eco-friendly solution for removing such pollutants. In this study, a ternary composite comprising Zeolitic Imidazolate Framework-8 (ZIF-8), Zinc Oxide (ZnO), and graphitic carbon nitride (g-C3N4) was synthesized via a facile chemical method and applied for the degradation of Methylene Blue (MB) dye under UV and visible light. The materials were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and UV–Visible absorption spectroscopy, indicating crystalline phase formation, functional group presence, and enhanced visible-light absorption. Morphological analysis via scanning (SEM) and transmission (TEM) electron microscopy revealed a heterogeneous structure with interconnected nanosheets and agglomerated particles, indicating successful component integration with stable morphology. Energy-dispersive X-ray spectroscopy (EDX) revealed the presence of Zn, C, N, and O, validating the elemental composition of the composite. The composite exhibited a reduced band gap of 2.67 eV compared to pristine ZnO (3.2 eV, UV-active), g-C3N4 (2.7 eV, Visible active), and ZIF-8 (5.1 eV), facilitating efficient charge separation and extended light response. The ternary composite achieved 91% dye degradation within 60 min under visible light, while pure ZnO degraded only 70% under UV light which is attributed to improved charge carrier separation, extended light absorption, and strong interfacial interactions. The degradation kinetics followed a pseudo-first-order model, exhibited a significantly higher rate constant (k ≈ 0.045 min⁻1) compared to pristine ZnO (0.020 min⁻1). Moreover, the photocatalytic process involved oxidative breakdown of dye molecules rather than simple decolorization, consistent with the proposed S-scheme heterojunction mechanism. Unlike previously reported ZnO/g-C3N4 or MOF-based binary systems, the present work integrates ZIF-8 as a multifunctional porous scaffold within a ZnO/g-C3N4 S-scheme heterojunction, enabling simultaneous adsorption enrichment under visible-light irradiation. This rationally designed ternary architectures highlight the potential of ZIF-8-based ZnO/g-C3N4 photocatalysts as efficient materials for dye degradation and future wastewater treatment technologies.