Fabrication of two-dimensional Zn/Cd-based metal-organic frameworks and their heterostructures as efficient photocatalysts for the degradation of industrial dyes

Heterostructures of metal-organic frameworks (MOFs) and metal oxides have currently been explored for their application in heterogeneous photocatalysis for wastewater remediation. We have developed two new heterostructures fabricated by integration of the [Zn(apca)₂]_n (Zn–MOF) and [CdCl₂(apca)]_n (Cd–MOF) over the hexagonal-faced surface of ZnO synthesized by template-assisted method and abbreviated as Zn/Cd–MOF@ZnO. The as-synthesized heterostructures were characterized by employing morphological (FE–SEM), thermal (TGA), and spectral techniques (FT–IR, UV–Vis, XPS, and PXRD). Their performance for the degradation of hazardous industrial dyes (methylene blue (MB), malachite green (MG), and methyl violet (MV)) has been explored. The response in terms of photodegradation efficacy, (89.4%, 90%) MB, (90.7%, 94.5%) MG, and (90.1%, 92.5%) MV was recorded in the presence of Zn–MOF@ZnO and Cd–MOF@ZnO heterostructures, respectively, at optimal conditions (pH–7, catalyst dose–0.6 g/L, and dye concentration–5 mg/L). The rate constant values for Zn–MOF@ZnO and Cd–MOF@ZnO heterostructures are (0.0247 min⁻¹, 0.0315 min⁻¹) MB, (0.0312 min⁻¹, 0.0359 min⁻¹) MG, and (0.0278 min⁻¹, 0.0372 min⁻¹) MV, respectively. These heterostructures are found to be promising photocatalysts as compared to pristine metal oxides owing to their synergistic effect. Moreover, the heterostructures have low band gap energy and high surface area which results in offering more active sites for carrying out photocatalytic reactions and enhancing the efficiency of catalysts. Furthermore, the fabricated photocatalysts demonstrate excellent stability and recyclability over five experimental cycles.

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