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Examines the synthesis of template-free zeolite nanocrystals by using in situ thermoreversible polymer hydrogels. Physical properties and thermogelation mechanism of zeolites; Schematic representations of synthesis of template-free zeolite nanocrystals.

The swelling properties of hydrogels as draw agents have been identified as one of the key parameters in determining the performance of polymer hydrogel-driven forward osmosis process. We report here a new strategy to improve the swelling property of hydrogels by the introduction of structural inhomogeneity and compressive forces in an ionic hydrogel for the purpose of increasing forward osmosis water flux. This is achieved by incorporating a hydrophobic, elastic polyester (PET) hollow microfiber into an ionic hydrogel under a compressive force during the preparation of the composite hydrogel monolith. The forward osmosis water flux of the composite hydrogels increased with increasing the microfiber loading and compression pressure. The composite hydrogel with 50 wt% PET microfiber loading and 18 kPa compression pressure demonstrated the highest flux. The water flux of poly(NIPAM-co-SA)-PET microfiber composite prepared under 18 kPa compression (PN5S5-PET-0.5/0.5-18) and poly(sodium acrylate)-PET microfiber composite (PSA-PET-0.5/0.5-18) reached 3.0 and 5.0 LMH in the first 10 min, respectively, when their swelling ratio is 4. The water flux of the composites was twice as high as the pure hydrogel. The composite hydrogels were also better at maintaining high water fluxes for a long period. The water flux of PSA-PET-0.5/0.5-18 decreased from 3.5 to 1.4 LMH after 24 h forward osmosis test. The combination of hydrophilic ionic hydrogel and hydrophobic PET microfiber resulted in an extended, porous structure within the hydrogel because of their different wettability, while an additional relaxation force was preserved in the composites because of the compression pressure applied during the preparation. Both of these worked together to enhance the FO water flux and maintain it for an extended long period. [ABSTRACT FROM AUTHOR]

The feasibility of bilayer polymer hydrogels as draw agent in forward osmosis process has been investigated. The dual-functionality hydrogels consist of a water-absorptive layer (particles of a copolymer of sodium acrylate and N-isopropylacrylamide) to provide osmotic pressure, and a dewatering layer (particles of N-isopropylacrylamide) to allow the ready release of the water absorbed during the FO drawing process at lower critical solution temperature (32 °C). The use of solar concentrated energy as the source of heat resulted in a significant increase in the dewatering rate as the temperature of dewatering layer increased to its LSCT more rapidly. Dewatering flux rose from 10 to 25 LMH when the solar concentrator increased the input energy from 0.5 to 2 kW/m2. Thermodynamic analysis was also performed to find out the minimum energy requirement of such a bilayer hydrogel-driven FO process. This study represents a significant step forward toward the commercial implementation of hydrogel-driven FO system for continuous production of fresh water from saline water or wastewaters. [ABSTRACT FROM AUTHOR]