Composite polymer hydrogels as draw agents in forward osmosis and solar dewatering

We report here on new composite polymer hydrogel particles with light-absorbing carbon particles incorporated within them that can be used as draw agents in the forward osmosis process of desalination. These hydrogels are synthesized by free-radical polymerization of different monomers (e.g. sodium acrylate, N-isopropylacrylamide or their mixtures) and the crosslinker N,N′-methylenebisacrylamide with light-absorbing carbon particles. We have previously shown that hydrogel particles are able to draw pure water through forward osmosis membranes, and then the water can be removed by pressure or heating, or a mixture of both. The incorporation of light-absorbing particles leads to natural, enhanced heating and dewatering of the composites compared to neat hydrogels during such irradiation with light. However, it is also advantageously found that these composite polymer hydrogels exhibit higher swelling ratios, and thus produce higher water fluxes in the FO process. Furthermore, with the increasing loadings of carbon particles, the water recovery rates from the swollen composite hydrogels are found to be greatly enhanced.