3D Photothermal Cryogels for Solar-Driven Desalination

Abstract

This paper reports the fabrication of photothermal cryogels for freshwater production via the solar-driven evaporation of seawater. Photothermal cryogels were prepared via in situ oxidative polymerization of pyrrole with ammonium persulfate on preformed poly(sodium acrylate) (PSA) cryogels. We found that the pyrrole concentration used in the fabrication process has a significant effect on the final PSA/PPy cryogels (PPCs), causing the as-formed polypyrrole (PPy) layer on the PPC to evolve from nanoparticles to lamellar sheets and to consolidated thin films. PPC fabricated using the lowest pyrrole concentration (i.e., PPC10) displays the best solar-evaporation efficiency compared to the other samples, which is further improved by switching the operative mode from floating to standing. Specifically, in the latter case, the apparent solar evaporation rate and solar-to-vapor conversion efficiency reach 1.41 kg m –2 h –1 and 96.9%, respectively, due to the contribution of evaporation from the exposed lateral surfaces. The distillate obtained from the condensed vapor, generated via solar evaporation of a synthetic seawater through PPC10, shows an at least 99.99% reduction of Na while all the other elements are reduced to a subppm level. We attribute the superior solar evaporation and desalination performance of PPC10 to its (i) higher photoabsorption efficiency, (ii) higher heat localization effect, (iii) open porous structure that facilitates vapor removal, (iv) rough pore surface that increases the surface area for light absorption and water evaporation, and (v) higher water-absorption capacity to ensure efficient water replenishment to the evaporative sites. It is anticipated that the gained know-how from this study would offer insightful guidelines to better designs of polymer-based 3D photothermal materials for solar evaporation as well as for other emerging solar-related applications.

Self-Assembly of a Graphene Oxide Liquid Crystal for Water Treatment

“…Very recently, solar-driven interfacial evaporation has aroused great interest. − An indispensable component in such a system is solar absorber materials, and GMs are competitive candidates on account of their broadband absorption and excellent photothermal properties. , Thanks to their light weight, our LCI-GMs float directly at the air–water interface, thus spontaneously setting up two-dimensional water pathways that help suppress heat loss and boost photothermal conversion efficiency by the establishment of a local heating zone close to the gas–liquid interface . As shown in Figure S15a–d, the temperature at the air–water interface in the system with LCI-GM or H-GM (approximately 68 °C) is higher than the temperature of the bulk water (approximately 50 °C), whereas the system without a solar absorber has nearly the same temperature at both locations (approximately 38.5 °C).…”

Recent developments of hydrogel based solar water purification technology

“…A representative polymer solar absorber is polypyrrole (PPy), which has been reported in recent studies. 25,75,130,137–148 For instance, Zhao et al 25 introduced PPy into a PVA-based hydrogel network and achieved a high evaporation rate of 3.2 kg m −2 h −1 with an excellent energy conversion efficiency of 94%. In the next year, the same group reported a PPy/chitosan/PVA hydrogel platform that exhibited an enhanced solar vapor generation capacity of 3.6 kg m −2 h −1 .…”

Avant‐Garde Solar–Thermal Nanostructures: Nascent Strategy into Effective Photothermal Desalination

“…Recently, Loo and colleagues reported 3D photothermal cryogels consisting of poly(sodium acrylate) (PSA)/polypyrole (PPy) for photothermal desalination. [ 141 ] The superior performance attributed to the following features: i) greater solar absorption characteristics, ii) enhance localized heating phenomena, iii) open porous channel to simplify vapor discarding, iv) rough pore morphology, which synergistically ameliorated solar absorption and steam production, and v) improved absorption of water ( Table 3 ).…”