Interfacial solar evaporation for water production: from structure design to reliable performance

Interfacial solar evaporation based on Janus films: An effective strategy to improve salt tolerance and antifouling performance

Solar-powered flow-through catalytic evaporator for high-performance water desalination and synergistic pollutant degradation

Boosting extraction of Pb in contaminated soil via interfacial solar evaporation of multifunctional sponge

Solar interfacial evaporation (SIE) emerges as a pivotal technology for addressing global freshwater scarcity and advancing sustainable development. Gel materials, distinguished by their inherent hydrophilicity and porous architecture, have garnered significant interest for SIE applications. First, this review elaborates on the compelling advantages of gels for SIE, stemming from their low thermal conductivity, reduced evaporation enthalpy, good hydrophilicity, tunable porous structure, adjustable mechanical properties, facile processability, and multifunctional integration capabilities. Subsequently, it focuses on strategies to enhance the performance of gel-based evaporators, specifically addressing the achievement of photothermal stability, mechanical robustness, salt resistance, interfacial stability and antibiofouling stability through rational structural design and exploitation of intrinsic gel properties to realize optimal evaporation performance. Scalable applications of gel-based SIE, including water treatment, auxiliary power generation, atmospheric water harvesting, and metal extraction, are highlighted. Finally, conclusions and perspectives outline current challenges and future research directions for gel-based SIE at both theoretical and practical levels.

Solar interfacial evaporation based oil/water separation from emulsion using a wood-melamine/calcium alginate composite structure

Most thermodynamic modeling of hydrogels is built on Flory's theories for the entropy of mixing and rubber elasticity, and Donnan's equilibrium conditions if polyelectrolyte polymer and mobile ions are involved. The entropy of mixing depends on the number of solvent and polymer molecules while the configurational entropy depends on the volume the polymer occupied. Flory's theory treated these two entropy terms in the Gibbs free energy on an equal basis: using the molecular numbers as the variable. I argue that the molecular number and volume are two independent thermodynamic variables and reformulate Flory's classical hydrogel thermodynamic model by minimizing the Helmholtz free energy of a combined system consisting of the hydrogel and its environment. This treatment enables us to unequivocally state that the osmotic pressure is the thermodynamic pressure of the solvent inside the hydrogel and to unambiguously write down the chemical potential of each species. The balance of the chemical potentials of the mobile species, including both the solvent and the mobile ions gives a set of equations that can be simultaneously used to solve for the equilibrium volume of the hydrogel, the osmotic pressure, and the Donnan potential, including their coupling. The model is used to study the thermodynamic properties of both pure and salty water in non-electrolyte and electrolyte hydrogels such as (1) the latent heat of evaporation, (2) the ability of hydrogels to retain water and to absorb water from the atmosphere, (3) the use of hydrogels for desalination via solar or forward osmosis, (4) the antifouling characteristics of hydrogels, and (5) melting point suppression and boiling point elevation, and solubility of salts in hydrogels. These properties are of interest in solar-driven interfacial water evaporation for desalination and wastewater treatment, atmospheric water harvesting, and forward osmosis. The reformulated thermodynamic framework will also be useful for understanding polymer electrolytes and ion transport in electrochemical and biological systems.

Production of fresh water based on a renewable energy source is one of the most important global challenges for mankind due to ever-accelerating climate changes. Solar thermal evaporation shows promise for overcoming the water scarcity problem by utilizing solar energy, the most abundant and clean energy source. To enhance the performance of solar evaporators, interfacial solar evaporators have been introduced, which harness solar energy onto the water surface. To enable energy conversion and water evaporation at the interfaces of a solar evaporator, multi-scale heat and water transport have been investigated. Furthermore, various light-absorbing materials and system configurations have been studied to achieve the theoretical maximum performance. The fundamental physics of the interfacial solar evaporator, including thermal and water transport, and a broad range of interfacial solar evaporator devices in terms of the fabrication techniques and its structures are reviewed.

A 3D Corncob-based interfacial solar evaporator enhanced by environment energy with salt-rejecting and anti-corrosion for seawater distillation

Solar-powered atmospheric water harvesting (AWH) with metal-organic frameworks (MOFs) has been recognized as an attractive way to alleviate water shortage stress in rural arid areas given the naturally abundant solar energy. However, the existing solar-powered AWH technologies only allow a singular water production mode: either solar heating-driven AWH which usually results in rather poor water productivity due to the limited availability of sufficient sunlight or conductive heating-driven all-day AWH with significantly improved water productivity but requiring additional electricity provided with a photovoltaic module. This greatly limits the flexibility in managing AWH based on climate conditions, water productivity, and energy cost. Herein, a sandwich-structured MOF monolith (denoted as CACS) with dual heating capacity, localized solar heating (LSH) and electrical heating (LEH), is presented. Compared with LSH, the use of LEH leads to more rapid and uniform heating of CACS monoliths, thereby driving a significantly enhanced water desorption efficiency with faster kinetics. Using the CACS monolith as an AWH sorbent, a new type of atmospheric water harvester is developed and able to produce water in multiple working modes: LSH-, LEH-, and LSH-/LEH-driven AWH, thereby enabling flexible AWH on demand: direct use of sunlight for LSH-driven AWH during the sunlight-sufficient day and/or LEH-driven all-day AWH powered by a photovoltaic module particularly during the sunlight-absent/-insufficient time (night or cloudy day). When working at the LSH-/LEH-driven AWH mode, the resulting prototype delivers 1.4 LH2O kgMOF-1 day-1 of water productivity with 2.3 kW·h L-1H2O of energy consumption, corresponding to 5.4 times higher water productivity than the LSH-driven AWH working mode alone and 17.9% of energy saving at the cost of 22.2% of water productivity reduction compared with the LEH-driven AWH working mode alone. The current work, therefore, demonstrates a novel solar-powered AWH strategy that enables all-day water production with flexible choices on AWH working modes in terms of climate conditions, desired water productivity, and energy cost.

The lack of freshwater has been threatening many people who are living in Africa, the Middle East, and Oceania, while the discovery of freshwater harvesting technology is considered a promising solution. Recent advances in structured surface materials, metal-organic frameworks, hygroscopic inorganic compounds (and derivative materials), and functional hydrogels have demonstrated their potential as platform technologies for atmospheric water (i.e., supersaturated fog and unsaturated water) harvesting due to their cheap price, zero second energy requirement, high water capture capacity, and easy installation and operation compared with traditional water harvesting methods, such as long-distance water transportation, seawater desalination, and electrical dew collection devices in rural areas or individual-scale emergent usage. In this contribution, we highlight recent developments in functional materials for "passive" atmospheric water harvesting application, focusing on the structure-property relationship (SPR) to illustrate the transport mechanism of water capture and release. We also discuss technical challenges in the practical applications of the water harvesting materials, including low adaptability in a harsh environment, low capacity under low humidity, self-desorption, and insufficient solar-thermal conversion. Finally, we provide insightful perspectives on the design and fabrication of atmospheric water harvesting materials.

The global scenario of water shortage and pollution has necessitated the use of advanced water treatment and desalination technologies. Solar interfacial evaporation has shown promising results for clean water generation but depends on the sunlight intensity, which changes over time and climatic conditions. Furthermore, the solar-driven interfacial evaporation cannot operate in the dark and is susceptible to salt deposition. Here, we have explored the Joule heating effect in laser-induced graphene (LIG)-based Joule heaters (JHs) for interfacial water evaporation under different applied voltages. The effect of stacking of Joule heaters has been explored and found to give an enhanced evaporation rate with less spatial footprint and energy consumption. The evaporation rate in a single-layer LIG JH reached ∼5 kg·m–2·h–1 under the application of 10 V. The JH area and its stacking effect on evaporation rate, spatial footprint, and energy consumption were investigated. An increase in evaporation rate by seven times and reduction of electrical energy consumption by three times has been demonstrated by three levels of stacking compared to its equivalent triple-area LIG JH. The enhanced performance of the stacking configuration could be due to the enhanced heat transfer from the bottom JH to the upper JH, thermal concentration, and reduced thermal losses to the environment. The single-layer LIG JH also gave ∼2 kg·m–2·h–1 evaporation rate under natural sunlight and environmental conditions, showing potential for solar interfacial evaporation. The JHs also showed excellent resistance to salt deposition with self-salt-cleaning capability under the tested conditions. These compact stacked JH systems could be integrated with renewable energy, which can be operated in the presence and absence of sunlight. Such compact JH systems with a lesser spatial footprint, enhanced evaporation rate, and reduced energy requirement can help in providing constant water evaporation for various applications.

Sorbent-coupled radiative cooling and solar heating to improve atmospheric water harvesting

Solar interfacial evaporation technology has the advantages of environmentally conscious and sustainable benefits. Recent research on light absorption, water transportation, and thermal management has improved the evaporation performance of solar interfacial evaporators. However, many studies on photothermal materials and structures only aim to improve performance, neglecting explanations for heat and mass transfer coupling or providing evidence for performance enhancement. Numerical simulation can simulate the diffusion paths and heat and water transfer processes to understand the thermal and mass transfer mechanism, thereby better achieving the design of efficient solar interfacial evaporators. Therefore, this review summarizes the latest exciting findings and tremendous advances in numerical simulation for solar interfacial evaporation. First, it presents a macroscopic summary of the application of simulation in temperature distribution, salt concentration distribution, and vapor flux distribution during evaporation. Second, the utilization of simulation in the microscopic is summed up, specifically focusing on the movement of water molecules and the mechanisms of light responses during evaporation. Finally, all simulation methods have the goal of validating the physical processes in solar interfacial evaporation. It is hoped that the use of numerical simulation can provide theoretical guidance and technical support for the application of solar-driven interfacial evaporation technology.

Engineering hydrogels towards next-generation multifunctional interfacial solar evaporators beyond seawater desalination

Interfacial solar evaporators (ISEs) for seawater desalination have garnered enormous attention in recent decades due to global water scarcity. Despite the progress in the energy conversion efficiency and production rate of ISE, the poor portability of large-area ISE during transportation as well as the clogging of water transport pathways by precipitated salts during operation remain grand challenges for its fielded applications. Here, we designed an ISE with high energy conversion efficiency and shape morphing capability by integrating carbon nanotube (CNT) fillers with a light-responsive shape memory polymer (SMP, cross-linked polycyclooctene (cPCO)). Utilizing the shape memory effect, our ISE can be folded to an origami with 1/9 of its original size to save space for transportation and allow for on-demand unfolding upon sunlight irradiation when deployed in service. In addition, the ISE is equipped with a real-time clogging monitoring function by measuring the capacitance of the electric double layer (EDL) formed at the evaporator/seawater nanointerface. Due to its good energy conversion efficiency, high portability, and clogging monitoring capability, we envisage our ISE as a promising selection in solar evaporation technologies.