Polyol-grafted polysulfone membranes for boron removal: Effects of the ligand structure

Abstract

In this study, a series of polysulfone membranes grafted with polyol polymers have been synthesized and used for boron removal via complexation of the vicinal diol structure with boric acid. The membranes were prepared by non-solvent induced phase inversion of the chloromethylated polysulfone followed by surface-initiated atom transfer polymerization (ATRP). Three multi-hydric methacrylate monomers including 2,3-dihydroxypropyl methacrylate (HPMA), 3-(N-glucidol-N-methyl)amino-2-hydroxypropyl methacrylate (GMHP), and 2-(bis(2,3-dihydroxypropyl)amino)ethyl methacrylate (HAEM) were used. The membrane was characterized by ATR-FTIR, XPS, SEM, water contact angle (WCA) and water flux measurement. The effects of the ligand structure on the adsorption thermodynamics and kinetics were studied in detail. A series of polyol-grafted membranes with boron uptake ranging from 0.20 to 0.46mmol/g were obtained. The boron complexing efficiency of HAEM, GMHP and HPMA is calculated to be 222%, 175% and 62%, respectively. We believe the presence of the amino group, high vicinal diol content and the branched structure are all beneficial to the complexing efficiency. The adsorption isotherms conform to the Langmuir model and the adsorption kinetics obey the pseudo-second-order rate expression. Optimization of the ligand structure is helpful to increase the boron uptake but has limited benefits on the boron adsorption rate.