Self‐Assembled Nanofibrous Hydrogels with Tunable Porous Network for Highly Efficient Solar Desalination in Strong Brine

Abstract

Hydrogel‐based solar evaporators (HSEs) emerged as energy‐efficient designs for water purification due to the reduced vaporization enthalpy in the hydrated polymeric network. However, it remains challenging for HSEs to achieve stable performance in desalination, partly due to the tradeoff between desired evaporation dynamics and salt tolerance. Here, composite hydrogels with tunable self‐assembled nanofiber networks are exploited for the engineering of solar evaporators with both high evaporation performance and resistance to salt accumulation. The nanofibrous hydrogel solar evaporators (NHSEs) present an intrinsic open network with high porosity, above 90%, enabling continuous water channels for efficient mass transfer. Theoretical modeling captures the complex nexus between microstructures and evaporation performance by coupling water transfer, thermal conduction, and vaporization enthalpy during evaporation. The mechanistic understanding and engineering tuning of the composites lead to an optimum configuration of NHSEs, which demonstrate a stable evaporation rate of 2.85 kg m−2 h−1 during continuous desalination in 20% brine. The outstanding performance of NHSEs and the underlying design principles may facilitate further development of practical desalination systems.

Versatile GO/ANFs Aerogel for Highly Efficient Solar-Powered Water Purification in Wide Environments

“…For long-term use, salt tolerance is another key factor in solar evaporation. , During long-term operation under solar irradiation, the salt content on the evaporator surface would unavoidably rise, causing salt crystals to accumulate on the solar absorber surface. − As shown in Figure d, all NaCl solutions with different concentrations evaporated faster than 2.17 kg m –2 h –1 . In order to verify the excellent salt rejection of the GO/ANFs aerogel, the evaporation was carried out under high salinity brine (20 wt %).…”

Hydrogel-Based Interfacial Solar-Driven Evaporation: Essentials and Trails

“…However, more research is needed to bridge the gap between the current state of research and implementation on a larger scale. In contrast to the 20–50 m 2 effective area of seawater desalination reverse osmosis membrane elements used in commercial large-scale applications, the hydrogel employed for interfacial solar-driven evaporation is currently limited to laboratory scales of 1–100 cm 2 [ 64 , 77 , 84 ]. The emergence of hydrogels provides a possibility for the development of ISDE systems, as highly adjustable hydrogels can be used to reduce evaporation enthalpy, control water flow rate, minimize heat loss, resist pollution, enhance stability, etc.…”

“…An effective strategy to address this challenge is by diluting the salt concentration at the evaporation interface. Xu et al [ 84 ] developed a high-porosity nanofiber-based hydrogel substrate with a continuous microchannel structure to promote rapid water transport to the evaporation interface, achieving efficient mass transfer and thus preventing salt accumulation ( Figure 4 a). However, due to contact with free water with higher thermal conductivity, the thermal energy at the evaporation interface might dissipate, affecting evaporation efficiency.…”

“… ( a ) The scheme of a high-porosity nanofiber-based hydrogel with a continuous microchannel structure for preventing salt accumulation. Reprinted with permission from ref [ 84 ]. Copyright 2023 Wiley-VCH Verlag GmbH.…”

Foaming photothermal inks for direct-ink writing: hierarchical design and enhanced solar-powered interfacial evaporation

“…40,41 In order to streamline complex manufacturing processes, there is a significant demand for the one-step synthesis of monolithic 3D interfacial SGs endowed with the capacity to govern hierarchically porous structures and to modulate the associated heat and mass transfer. 42–53 Considerable research efforts have been dedicated to crafting 3D material platforms that are durable, lightweight, scalable, capable of floating and resistant to overturning. 54–56 Despite the rapid and scalable fabrication of porous photothermal foams using diverse foaming techniques, the realization of a sophisticated and well-aligned microarchitecture with inherent anisotropic properties has remained elusive.…”