Sporopollenin supported ionic liquids biosorbent for enhanced selective adsorption of 2,4-dinitrophenol from aqueous environment

This study attempts to bring about a facile approach to selectively adsorb 2,4-dinitrophenol (2,4-DNP) from an aqueous system using sporopollenin supported ionic liquid (SpIL) biosorbent, namely sporopollenin supported methylimidazolium (Sp-MIM). Spompollenin acts as the host with the accessible chamber, while methyl-imidazolium acts as the active site that binds 2,4-DNP from the aqueous system. Methylimidazolium, being chemically immobilized onto sporopollenin, simultaneously ensures that the ionic liquid does not leach into the aqueous environment while providing increased affinity and selectivity towards 2,4-DNP. The solid samples were characterized using conventional solid-state testing techniques such as FTIR, C-13 CP/MAS solid-state NMR, FESEM-EDX spectroscopy, TGA, and BET/BJH analysis. While UV-Visible spectroscopy was used to study the adsorption parameters. Based on the study, methylimidazolium's immobilization onto sporopollenin increased pore size distinctly from 5.06 nm to 44.94 nm, thereby reporting definitive mesoporous structure with a pronounced affinity towards 2,4-DNP, determined via a series of analyte screening. Adsorption parameter exploration revealed 15 mg of Sp-MIM was able to adsorb 84% of 2,4-DNP from 20 ppm concentrated aqueous solution within 15 min of contact under acidic condition (pH 4) and could be reused up to 5 cycles without any loss to adsorption percentage. The affinity of Sp-MIM towards 2,4-DNP was further explored employing computational calculations using molecular docking and quantum mechanics, both of which support the presence of pi-pi interaction and hydrogen bonding between Sp-MIM and 2,4-DNP.