A Multifunctional Zn(II) Metallohydrogel for Anionic Dye Adsorption and Catalytic CO₂ Fixation

A multiresponsive Zn(II) metallohydrogel was synthesized by utilizing a new amino-acid-based gelator Na₂HL {H₃L = l-2-(3,5-di<i>tert</i>-butyl-2-hydroxybenzylamino) pentanedioic acid}. The ligand was characterized by IR and NMR spectroscopy and high-resolution mass spectrometry (HRMS). The Zn(II)-metallogel was characterized using rheology, MALDI-TOF, FTIR, FESEM, TEM, AFM, BET, PXRD, and TGA techniques. The metallogel exhibited a self-healing and self-sustaining nature. Adsorption and catalytic properties of the metallogel were explored, indicating its multifunctional nature. Xerogel, the dried form of gel, displayed excellent uptake of Congo red (CR), an anionic dye (128.2 mg/g). Kinetics, isotherm, and thermodynamic aspects of CR adsorption were investigated at pH 7 and room temperature (27 °C). Adsorption isotherm and kinetic studies suggested that the adsorption process followed the Langmuir adsorption model and pseudo-second-order kinetics. Selective adsorption of a dye from a mixture of dyes was also studied. The xerogel was also employed as an efficient heterogeneous catalyst in the chemical fixation of carbon dioxide with epoxide under solvent-free conditions.