UiO-66-NH2@benzotrithiophene-based COF composites with core–shell structure for effective adsorption of dyes

Abstract

The treatment of wastewater containing organic dyes is an urgent environmental challenge, necessitating the development of advanced functional adsorbents. In this study, three covalent organic frameworks (COFs) with tailored pore sizes were synthesized from benzotrithiophene tricarboxaldehyde and different diamine linkers—benzidine, naphthalene-1,4-diamine, and p-phenylenediamine. These COFs were grown in situ onto UiO-66-NH₂ to construct core–shell MOF@COF composites. The materials were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Their adsorption performance toward Congo Red (CR), Rhodamine B (RB), and Malachite Green (MG) was systematically evaluated to clarify the influence of COF building units. The composites retained the chemical stability and hydrophobicity of the COF shell while overcoming the instability typical of pristine MOFs. Among them, UiO-66-NH₂@BTT–BZ-COF1 exhibited the highest adsorption capacities—2228.6 mg g⁻¹ for MG, 2037.2 mg g⁻¹ for RB, and 1503.7 mg g⁻¹ for CR—and could be reused for at least five cycles, demonstrating promising potential for dye removal applications.