Sewage sludge ash-based thermo-responsive hydrogel as a novel draw agent towards high performance of water flux and recovery for forward-osmosis

Thermo-sensitive hydrogels for forward osmosis with NIR light-induced freshwater recovery

“…5(d), the network size in NSPPH-9 to NSPPH-22 gradually became larger with the addition of NPs and gradually exhibited a certain heterogeneous network with pore sizes of different shapes and sizes, which effectively improved water diffusion during absorption and is one of the possible reasons for the increasing trend of water flux in the hydrogels. 18 On the other hand, in both NSPPH-19 and NSPPH-22, we were surprised to find a more compact crosslinked network hidden in the pore structure (Fig. S15†).…”

“…[50][51][52][53] The presence of NPs is also reported to confer a hierarchical network structure to the hydrogel, thus facilitating the transport of water molecules in the network and improving hydrophilicity. 18 Fig. 6(a) shows that when the feed solution was 2000 ppm NaCl, the initial water flux of the hydrogel without NPs (PPH) was only 0.36 LMH, and with the increase of NP doping, the water flux showed an obvious trend of a gradual increase in the first hour, and with the FO process, the water flux of all samples showed a gradual decrease.…”

“…Table 1 summarizes the water recovery rate of various hydrogels under different heating conditions and at different times published in the literature. 1,2,[17][18][19][21][22][23][24]26,27,29,30,32 The water recovery rate varies greatly depending on the hydrogel compositions and water recovery conditions in the FO system. Hence, our method can achieve high water recovery rates in a short time and under mild conditions compared to other works.…”

“…1 Subsequently, a large amount of work on thermo-sensitive hydrogels for desalination, especially in the field of forward osmosis (FO), has been reported. 2,[19][20][21][22][23][24][25][26][27][28] These works can be broadly classified into two categories: the first is different hydrogel compositions, such as the poly(ionic liquid) hydrogels (PTVBP-C6-5/5) developed by Liu et al 24 and the electroresponsive hyaluronic acid/poly(vinyl alcohol) (HA/PVA) hydrogels prepared by Zhang et al 31 The second category is composite/hybrid hydrogels, such as reduced graphene oxide (rGo) composite hydrogels prepared by Wang et al 22 for water recovery under sunlight and sewage sludge ash (SSA) composite hydrogels prepared by Pan et al 18 for significantly improving the swelling rate of hydrogels. The incorporated components endow the hydrogel with various composite functions.…”

Quick-Release Antifouling Hydrogels for Solar-Driven Water Purification

“…One approach to reducing the energy needed for sustainable water production is to use thermoresponsive hydrogels, specifically poly­( N -isopropylacrylamide) (PNIPAm), which exhibits an accessible lower critical solution temperature (LCST). − Near the LCST at ∼33 °C, PNIPAm-based hydrogels can absorb and release liquid water via hydrophilic/hydrophobic switching. The low LCST for water releasea temperature readily achievable using natural sunlight as the heating sourcedistinguishes PNIPAm from other materials requiring high energy consumption. − PNIPAm-based technologies have shown promise in wastewater purification, − desalination, − and moisture harvesting. − Nevertheless, conventional PNIPAm (C-PNIPAm), characterized by a closed-pore structure, suffers from a slow response rate above the LCST due to the formation of a dense skin layer, which acts as a barrier that entraps absorbed water and reduces the water release rate . Thus, current solar-driven hydrogel-based water purification systems can produce only a few gallons of water per day, well below the recommended use of ∼15–40 gallons per person .…”