Light‐responsive bilayered hydrogel for freshwater production from surface soil moisture

Abstract

The search and the utilization of alternative water resources to produce freshwater are highly important to the water shortage, especially in arid and desert regions. In these areas, the surface soil moisture (SSM) can be a promising water source, whereas its extraction and following release remain challenging. In this study, a light‐responsive bilayered hydrogel (LRBH) is designed to produce freshwater from SSM, which is obtained by the copolymerization of N‐isopropylacrylamide (NIPAM) and acrylic acid (AA) and in‐situ surface polymerization of polypyrrole (PPy). By careful optimization of the ratio of NIPAM and AA, the water absorption capacity of LRBH is significantly improved with the water absorption of 4.4 g/g even in the sandy soil with an extremely low water content (~3 wt%). The PPy in the top layer of the LRBH can absorb solar light to heat the hydrogel at daytime so that the temperature of the hydrogel can quickly rise above the lower critical solution temperature of LRBH. As a result, the freshwater is quickly expelled from the LRBH. Under simulated solar light irradiation, 68.6% of all absorbed water within LRBH can be released within 20 min. The current study provides an effective and facile strategy for SSM capture and suitable systems for the generation of freshwater in arid or desert regions.

Sustainable Hierarchical-Pored PAAS–PNIPAAm Hydrogel with Core–Shell Structure Tailored for Highly Efficient Atmospheric Water Harvesting

“…Combined with the XPS results, it further indicated that PDA was attached to the hydrogel surface. Besides, we found that the N–H peak shifted from 1558 to 1546 cm –1 through the infrared spectra of PP 2 and PDA 2 @PP 2 –Cl, indicating the existence of hydrogen bonding between polydopamine and the hydrogel …”

“…Besides, we found that the N−H peak shifted from 1558 to 1546 cm −1 through the infrared spectra of PP 2 and PDA 2 @ PP 2 −Cl, indicating the existence of hydrogen bonding between polydopamine and the hydrogel. 28 3.4. Solar Thermal Conversion Efficiency.…”

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 .…”

End‐group controlling aqueous solution properties in star‐shaped poly(2‐hydroxyethyl acrylate) and poly(2‐hydroxyethyl acrylate)‐b‐poly(N‐isopropylacrylamide) polymers

“…Hence through the development of intelligent materials, many alternatives can be proposed to respond to these priority needs. For example, PNIPAM‐based materials are developed for treatment, purification, recovery, desalination, 8–11 or; generating clean water 12…”