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

Abstract

As an effective way to obtain freshwater resources, atmospheric water harvesting (AWH) technology has been a wide concern of researchers. Therefore, hydrogels gradually become key materials for atmospheric water harvesters due to their high specific surface area and three-dimensional porous structure. Here, we construct a core–shell hydrogel-based atmospheric water harvesting material consisting of a shell sodium polyacrylate (PAAS) hydrogel with an open pore structure and a core thermosensitive poly N-isopropylacrylamide (PNIPAAm) hydrogel with a large pore size. Theoretically, the mutual synergistic hygroscopic effect between the core layer and the shell layer accelerates the capture, transport, and storage of moisture to achieve continuous and high-capacity moisture adsorption. Simultaneously, the integration of polydopamine (PDA) with the hydrogel realizes solar-driven photothermal evaporation. Therefore, the prepared core–shell hydrogel material possesses great advantages in water adsorption capacity and water desorption capacity with an adsorption of 2.76 g g–1 (90% RH) and a desorption of 1.42 kg m–2 h–1. Additionally, the core–shell structure hydrogel collects 1.31 g g–1 day–1 of fresh water in outdoor experiments, which verifies that this core–shell hydrogel with integrated photothermal properties can capture moisture in a wide range of humidity without any external energy consumption, can further sustainably obtain fresh water in remote water-shortage areas.

Engineered Polymer Architectures for Thermo‐Responsive Desiccants in Dehumidification Applications

“…There has been a recent interest in using thermo-responsive polymers for removing water from the air. [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] Previous modeling work by Zeng et al [20] and Kocher et al [25] shows that the energy efficiency of desiccant-based dehumidification can be improved using thermo-responsive (TR) desiccants, which have a switchable hydrophilicity-to-hydrophobicity behavior that results in a temperature-dependent adsorption isotherm. [26][27][28][29] This hydrophilic-to-hydrophobic transition can be realized by TR polymers with a lower critical solution temperature (LCST)-these polymers are relatively hydrophilic/hydrophobic when the temperature is below/above the LCST, respectively.…”

“…[20] Experimental TR desiccant studies have primarily targeted atmospheric water harvesting applications. [10][11][12][13][14][15][16][17][18][19] These materials have been hypothesized to become a disruptive technology if water can be captured in the vapor form and then released as a liquid (which has some synthetic challenges discussed in Section 4.3). [30] However, these works focused on 1) the IPN polymer architecture at 2) specific RH values and temperatures, rather than exploring different polymer architectures and their performance over the full range of RHs and temperatures [10][11][12][13][14][15][16][17][18][19] needed in dehumidification applications (Section S1, Supporting Information).…”

“…[10][11][12][13][14][15][16][17][18][19] These materials have been hypothesized to become a disruptive technology if water can be captured in the vapor form and then released as a liquid (which has some synthetic challenges discussed in Section 4.3). [30] However, these works focused on 1) the IPN polymer architecture at 2) specific RH values and temperatures, rather than exploring different polymer architectures and their performance over the full range of RHs and temperatures [10][11][12][13][14][15][16][17][18][19] needed in dehumidification applications (Section S1, Supporting Information). Additionally, our simulations only consider polymers that both sorb and desorb water in the vapor phase (in contrast to sorbing as a vapor and desorbing as a liquid), as the only polymers that exhibited liquid water release showed poor cyclability and liquid water release is not necessary for improved efficiency.…”

“…Thus, the PNI-PAAm does not have enough chain mobility nor unbound water molecules to undergo an LCST-like response, thereby hindering Δu mean and the overall performance of the polymer. [16,18] To achieve control over both Δu mean and the LCST set point, all TR desiccant materials besides the homopolymer control sample discussed consist of a hygroscopic component, which promotes the moisture adsorption capacity to increase chain mobility, and a TR component, which enables the temperaturedependent isotherm shift. The specific materials used are detailed in Figure 5a.…”

“…There has been a recent interest in using thermo‐responsive polymers for removing water from the air. [ 10–24 ] Previous modeling work by Zeng et al. [ 20 ] and Kocher et al.…”