Surface-Functionalized Polydimethylsiloxane Sponges for Facile and Selective Recovery of Molybdenum from Aqueous/Acidic Solutions

Abstract

The present study fabricated two types of surface-functionalized polydimethylsiloxane sponges (amine-functionalized and extractant-impregnated), and investigated their applicability as a novel separation-recovery method for molybdenum ion (Mo(VI)) in aqueous and HNO₃ solutions. An amine-functionalized polydimethylsiloxane (PDMS) sponge was prepared using glycine hydrochloride as a functional ligand, called the Glycine-PDMS sponge, and bis(2-ethylhexyl) phosphate (HDEHP) and 2,2'-(Methylimino)bis(N,N-di-n-octylacetamide) (MIDOA) were used as extractants for the extractant-impregnated sponges, called the HDEHP-PDMS and MIDOA-PDMS sponges, respectively. The adsorption and desorption of Mo(VI) were demonstrated by facile soaking and squeezing of the sponges, which is unavailable in conventional adsorbents. Each PDMS sponge enabled selective Mo adsorption in aqueous and acidic solutions, and had different ligand and HNO₃ concentration dependence of the Mo(VI) adsorption capacities. The pseudo-second-order kinetic model was found to be applicable for the Mo(VI) adsorption process on the sponge surfaces. A regression analysis of the isothermal adsorption curves for Mo ions clarified that the adsorption of Mo ions onto all PDMS sponges occurs spontaneously, and that Mo(VI) adsorption mechanism is different depending on sponges; chemisorption for extractant-impregnated sponges and physisorption for an amine-functionalized, respectively. Furthermore, the squeezing of the Mo ion adsorbed PDMS sponges allowed the rapid desorption and recovery of Mo ions into eluent solutions such as deferoxamine B (DFOB) and H₂O₂ within a few minutes. These results prove that the novel PDMS sponge approach, enabling facile chemical-mechanical adsorption and desorption control of target elements, has great potential in various fields involving the environment, medicine, energy, and so on.