(533q) Cationic Dye Adsorption on Metal Organic Framework: An Equilibrium Study

Environmental pollution is a huge concern which is complicated by different types of pollutants present in aqueous streams. The pollutants include toxic organics, dyes, heavy metal ions, pharmaceutical compounds, etc. In this study, we focus on dyes present in textile industry effluents. These dyes, even at low concentrations cause coloring of water streams leading them to lose their aesthetic appeal. Further, sunlight penetration in water bodies is hindered leading to disruption in the marine ecosystem. These dyes are difficult to be broken down by biological processes and, hence, suitable alternatives are required. Adsorption is the preferred choice owing to its economy, simplicity in design and operation and ability to be effective even at very low concentrations. Adsorbent materials are a hotbed of immense research activity where there is considerable scope for synthesizing materials with pollutant capacity enhancement and rapid uptake. A new class of adsorbents termed as Metal Organic Frameworks (MOF) is gaining popularity in recent times. These classes of adsorbents have been found to be having high BET surface area, tuneable porosity and functionality which enable in deep removal of toxic pollutants in aqueous streams.

In the present work, a functionalized MOF (MIL-101-SO₃H¹) was synthesized hydrothermally and characterized for its physico-chemical properties such as BET surface area, morphology, surface composition and point of zero-charge. MIL-SO₃H (MILS) was used to adsorb a cationic dye viz. basic yellow. Optimal conditions for enhanced equilibrium capacities were identified using Design of Experiments (DoE). The adsorption capacity was found to be 320 mg/g at pH 6, temperature 25 °C, and dosage of 1 g/L. The equilibrium data was fitted to Simple Hill’s Model (SHM), a statistical physics-based model which gives considerable insight into the interaction between adsorptive and adsorbent. The adsorption process was found to be exothermic with enthalpy of adsorption of -29.37 kJ/mol. The adsorption mechanism was revealed to be an electrostatic interaction between the cationic dye and the SO₃^- group present on the functionalized MOF. Kinetic studies were also carried out with this MOF at the optimal conditions.

References:

1. Ma, L., Xu, L., Jiang, H. & Yuan, X. Comparative research on three types of MIL-101(Cr)-SO 3 H for esterification of cyclohexene with formic acid. RSC Adv. 9, 5692–5700 (2019).