(195a) Donnan Membrane Principle: It's Application In Developing Hybrid Nanosorbents

Donnan membrane equilibrium arises from the inability of ions to diffuse out from one phase into the other in a heterogeneous system. This principle was judiciously exploited to formulate a new class of hybrid sorbents developed at Lehigh University. Hybrid anion exchange resins (HAIX) dispersed with nanoparticles of iron oxide, popularly known by the brand name ArsenXnp, use the Donnan membrane principle to achieve high sorption capacity for environmentally important ligands like arsenic. As a result of a counter-ion inclusion effect that may be derived from the principle, concentration of anions inside an anion exchanger far exceeds those in the bulk solution. Hydrated ferric oxide (HFO) nanoparticles have high selectivity towards dissolved arsenic species which predominantly remain as oxy-anions in natural waters. However, the nanoparticles are needed to be encapsulated in a suitable host material before their field application. The hybrid anion exchange resins not only provide support as a host material for the HFO nanoparticles dispersed inside, it also provide a synergistic effect of concentrating the target arsenic anions inside the resin phase so that the effective overall adsorption capacity of the hybrid sorbent is greatly enhanced. Moreover, the hybrid sorbents are regenerable and reusable, making the process of arsenic removal cost-effective. The arsenic selective hybrid nanosorbents have been successfully used in Indian subcontinent and USA. Field results of sustainable arsenic removal in remote villages in India shall also be presented.