Forward osmosis using electric-responsive polymer hydrogels as draw agents: Influence of freezing-thawing cycles, voltage, feed solutions on process performance

Recently, many materials have been evaluated as draw agents for forward osmosis (FO) processes. In the present work, it is the first attempt to regard electric-responsive polymer hydrogels as draw agents in an FO process. Electric-responsive hyaluronic acid/polyvinyl alcohol (HA/PVA) polymer hydrogels have been prepared by repeated freezing-thawing. Polymer hydrogels with different freezing-thawing cycles were designated as HA-PVA-3, HA-PVA-5, HA-PVA-7, and HA-PVA-9, respectively. The effects of freezing-thawing cycle, voltage, and concentrations of the feed solution on the FO process were examined, while the as-prepared polymer hydrogels were used as draw agents. By using HA-PVA-5, HA-PVA-7, and HA-PVA-9 polymer hydrogels as draw agents and deionised water as the feed solution in FO process, the initial water fluxes reached 1.2, 0.91, and 0.9 L m−2 h−1, respectively. When the voltage of the electric field was 0, 3, 6, and 9 V, the total water fluxes produced by HA-PVA-5 polymer hydrogels in 24 h reached 17.27, 20.95, 25.49, and 26.47 L m−2, respectively. When the different concentrations of sodium chloride was used as feed solutions, the total water fluxes produced by HA-PVA-5 polymer hydrogels at a voltage of 6 V in 24 h were recorded at 22.66, 15.77, and 12.41 L m−2 for 2000, 5000 and 8000 ppm, respectively. Compared with the other published studies which also adopted polymer hydrogels as draw agents in FO process, the fluxes in our article are desirable. In addition, salt reverse diffusion of the draw agent can be avoided and the complexity of the operation can be minimized when the electric-responsive hydrogels are employed as draw agents in FO process.