Synergistically enhanced selective adsorption of cationic dyes from aqueous solutions using porphyrin-confined zeolitic imidazolate framework

Abstract

Encapsulation of a free base meso-Tetra(4-carboxyphenyl)porphine ligand (TCPP) into the cavities of zeolitic imidazolate framework (ZIF-8) via the bottle-around-ship (BAS) approach generated an extremely selective reusable biomimetic adsorbent (TCPP@ZIF-8) for the elimination of hazardous cationic organic dyes. Entrapment in the MOF host prevents TCPP aggregation and provides a high surface area and protective environment for better TCPP dispersion, enhancing dye adsorption via electrostatic interaction. The appropriate synthesis of the adsorbent and the stability of the MOF throughout the modification were confirmed by multiple analyses. After being modified with TCPP, the adsorption efficacy of porous ZIF-8 is substantially increased, as seen by the significantly improved methyl violet (MV) cationic dye removal efficiency of TCPP@ZIF-8 (83.46 % and 41.67 mg/g at 10 mg dosage within 15 min) compared to ZIF-8 alone (23.83 % and 11.91 mg/g at 10 mg dosage within 15 min). The kinetic and isotherm studies revealed that adsorption adhered to pseudo-second-order (PSO) kinetics and the Langmuir isotherm, implies that the process is primarily governed by chemisorption and occurs as a monolayer on homogeneous adsorption sites. According to the reusing study, the stability of the adsorbent did not alter during the adsorption process, and the adsorbent could be easily recycled for use in consecutive cycles.