Polyzwitterionic Hydrogels for Highly Efficient High Salinity Solar Desalination

A system for efficient and sustainable cogeneration of water and electricity: Temperature difference induced by photothermal conversion and evaporative cooling

Solar energy, with its sustainable properties, has garnered considerable attention for its potential to produce green electricity and clean water. This paper proposes a multistage energy transfer co-generation system (MWCNTs-covered thermoelectric module with aerogel and cooler, AC-CTEM) combining power generation and evaporative cooling. On the light-absorbing surface, the hot side of a thermoelectric module is covered with a hydrophobic coating made of PDMS and MWCNT. The cold side transfers heat to the evaporation zone using a heat sink. Aerogel evaporators are cross-linked with chitosan and polyurethane, which reduces the enthalpy of evaporation and facilitates efficient interfacial evaporation to remove heat and return it to refrigeration. Additionally, with the addition of Fresnel lenses and wind energy to the enhancement device, the system achieved an evaporation rate of 3.445 kg m-2 h-1 and an open-circuit voltage of 201.12 mV under 1 kW m-2 solar irradiation. The AC-CTEM system also demonstrated long-term stability and effectiveness in treating various types of non-potable water. Furthermore, we demonstrated the practical utility of the system by successfully cultivating grass seeds and powering electronic equipment. The AC-CTEM system exemplifies a practical energy-saving approach for the development of highly efficient co-generation systems.

Improving diffusion kinetics of zinc ions/stabilizing zinc anode by molecular slip mechanism and anchoring effect in supramolecular zwitterionic hydrogels

The severe hydrogen evolution reaction and parasitic side reaction on Zn anode are the key issues which hinder the development of aqueous Zn-based energy storage devices. Herein, a polyacrylamide/carboxylated cellulose nanofibers/betaine citrate supramolecular zwitterionic hydrogels with molecular slip effects are proposed for enhancing Zn2+ diffusion and protecting Zn anodes. Non-covalent interactions within supramolecular hydrogels forms the skeleton for molecular slip and the strong coordination of carboxyl and amino groups with Zn2+ further facilitates the rapid Zn2+ transfer. Additionally, anchoring carboxyl and amino groups at the anode promotes the uniform deposition of Zn2+and protects Zn anode. On the basis of molecular slip mechanism and anchoring effect in the supramolecular zwitterionic hydrogels, Zn||Zn symmetric batteries undergo 800 h of stable electroplating stripping at a depth of discharge of 80 %. Zn||Cu asymmetric batteries exhibit an impressive average coulombic efficiency of 99.4 % over a remarkable span of 900 cycles at a current density of 15 mA cm-2. Furthermore, Zn||NH4V4O10 batteries successfully undergo over 1,000 cycles at a current density of 0.5 A g-1. Intrinsic ion diffusion mechanism of supramolecular hydrogel electrolytes provides an original strategy for the application of high-performance Zn-based energy storage devices.

Bioinspired Carbon-Silver Sulfide Scaffold with Synergistic Enhanced Light Capture and Anti-Biofouling Property for Stable Solar Steam Generation

Carbon material is a hot topic in solar evaporation. Due to the widely distributed microorganisms in natural water, biofouling has limited the actual application of solar evaporation material. Although carbon material lacks of nutrition for microbe, it is still vulnerable to biofouling because of the efficient pollutant adsorption property. However, current anti-biofouling design focuses on microbial control, neglects its influence on evaporators light absorption, that is usually a trade-off with evaporation efficiency. Herein, a bioinspired aligned carbon-Ag2S scaffold is introduced with synergistical enhanced light absorption (increased to 98.0% from 97.4%) and anti-biofouling property. The bioinspired aligned carbon-Ag2S scaffold exhibits a 1.87 kg m-2 h-1 evaporation rate under one sun, superior to pure carbon scaffold (1.78 kg m-2 h-1). It also maintains efficient light capture (-97.2%) and evaporation rate (1.73 kg m-2 h-1) after bacterial interference, avoiding sharp decline in light absorption (reduced to 83.3-87.6%) and evaporation performance (reduced to 1.24-1.28 kg m-2 h-1) which occurs in carbon scaffold due to biofouling. The carbon-Ag2S scaffold shows solid advantage in balancing light captures and biofouling control, compared to carbon-ZnO scaffold with conventional anti-biofouling design, which inhibits biofouling sacrificing light absorption (reduced to 89.8%) and evaporation performance (reduced to 1.41 kg m-2 h-1).

High-Performance Silicone Sponge Evaporators with Low Thermal Conductivity for Long-Term Solar Interfacial Evaporation and Freshwater Harvesting

Solar interfacial evaporation (SIE) has emerged as a highly promising approach for sustainable freshwater harvesting. However, maintaining a stable evaporation rate and achieving a high freshwater yield in high-salinity brines remain a significant challenge. In this study, we present the development of silicone sponge-based evaporators with a "free-salt" structure, designed to enhance the efficiency of SIE and freshwater collection. These evaporators, designated as PSS@Fe3O4/CNTs, were fabricated by grafting durable silicone onto a silicone sponge framework, followed by the incorporation of Fe3O4 nanoparticles and carbon nanotubes. The unique combination of exceptional photothermal properties and a controlled yolk-shell structure with low thermal conductivity enabled the PSS@Fe3O4/CNT evaporators to sustain a stable evaporation rate of 1.87 kg m-2 h-1 in real seawater over 200 h of continuous operation under 1 sun illumination. Importantly, no salt accumulation was observed on the evaporator surfaces, even when exposed to highly concentrated brines. In a closed system equipped with a condenser, these evaporators achieved freshwater production rates of 14.5 and 11.8 kg m-2 over 10 h from 10 and 20 wt % NaCl solutions, respectively, under 1 sun illumination. These values correspond to normalized production rates of 1.45 and 1.18 kg m-2 h-1, showcasing the consistent and efficient performance of the evaporators across varying salinity levels. Beyond salt rejection, the PSS@Fe3O4/CNT evaporators also demonstrated the ability to effectively remove various heavy metal ions (e.g., Cu2+ and Zn2+) and organic pollutants from contaminated water. This work provides valuable insights into innovative evaporator designs for efficient freshwater production from seawater and wastewater.

Making Interfacial Solar Evaporation of Seawater Faster than Fresh Water

Interfacial solar evaporation-based seawater desalination is regarded as one of the most promising strategies to alleviate freshwater scarcity. However, the solar evaporation rate of real seawater is significantly constricted by the ubiquitous salts present in seawater. In addition to the common issue of salt accumulation on the evaporation surface during solar evaporation, strong hydration between salt ions and water molecules leads to a lower evaporation rate for real seawater compared to pure water. Here a facile and general strategy is developed to reverse this occurrence, that is, making real seawater evaporation faster than pure water. By simply introducing specific mineral materials into the floating photothermal evaporator, ion exchange at air-water interfaces directly results in a decrease in seawater evaporation enthalpy, and consequently achieves much higher seawater evaporation rates compared to pure water. This process is spontaneously realized during seawater solar evaporation. Considering the current enormous clean water production from evaporation-based desalination plants, such an evaporation performance improvement can remarkably increase annual clean water production, benefiting millions of people worldwide.

Recent innovations in 3D solar evaporators and their functionalities

Interfacial solar evaporation (ISE) has emerged as a promising technology to alleviate global water scarcity via energy-efficient purification of both wastewater and seawater. While ISE was originally identified and developed during studies of simple double-layered two-dimensional (2D) evaporators, observed limitations in evaporation rate and functionality soon led to the development of three-dimensional (3D) evaporators, which is now recognized as one of the most pivotal milestones in the research field. 3D evaporators significantly enhance the evaporation rates beyond the theoretical limits of 2D evaporators. Furthermore, 3D evaporators could have multifaceted functionalities originating from various functional evaporation surfaces and 3D structures. This review summarizes recent advances in 3D evaporators, focusing on rational design, fabrication and energy nexus of 3D evaporators, and the derivative functions for improving solar evaporation performance and exploring novel applications. Future research prospects are also proposed based on the in-depth understanding of the fundamental aspects of 3D evaporators and the requirements for practical applications.

Spatial Confinement Engineered Gel Composite Evaporators for Efficient Solar Steam Generation

Recently, solar-driven interfacial evaporation (SDIE) has been developed quickly for low-cost and sustainable seawater desalination, but addressing the conflict between a high evaporation rate and salt rejection during SDIE is still challenging. Here, a spatial confinement strategy is proposed to prepare the gel composite solar evaporator (SCE) by loading one thin hydrogel layer onto the skeleton of a carbon aerogel. The SCE retains the hierarchically porous structure of carbon aerogels with an optimized water supply induced by dual-driven forces (capillary effects and osmotic pressure) and takes advantage of both aerogels and hydrogels, which can gain energy from air and reduce water enthalpy. The SCE has a high evaporation rate (up to 4.23 kg m-2 h-1 under one sun) and excellent salt rejection performance and can maintain structural integrity after long-term evaporation even at high salinities. The SDIE behavior, including heat distribution, water transport, and salt ion distribution, is investigated by combining theoretical simulations and experimental results. This work provides new inspiration and a theoretical basis for the development of high-performance interfacial evaporators.

Enhancing Solar Steam Generation of Hydrogels via Silver Nanoparticle-Doped Cellulose Nanofibers

Solar steam generation (SSG) is regarded as an efficient approach for harnessing solar energy to purify polluted or saline water. Herein, we demonstrate a hydrogel composed of cellulose nanofibers (CNFs), polyethylenimine (PEI), and reduced graphene oxide (rGO) that functions as an independent solar steam generator, which shows enhanced solar water evaporation efficiency by incorporating silver nanoparticles (AgNPs). It presented that the presence of AgNPs increases the photothermal conversion efficiency and thermal conductivity of the evaporator and reduces the enthalpy of evaporation. As a result, an outstanding water evaporation rate of 3.62 kg m-2 h-1 and a photothermal conversion efficiency of 96.25% are successfully obtained under one sun illumination. Also, the resulting hydrogel exhibits exceptional mechanical properties, as well as outstanding desalination and salt-resistant abilities during prolonged seawater desalination. In oil/water mixtures, the evaporation of the hydrogel decreases to 2.94 kg m-2 h-1, owing to the oil layer barrier. This work paves a reference approach to produce easily addressed cellulose nanofiber (CNF)-based hydrogel evaporators with significantly enhanced evaporation rates.

TpPa-1 COFs-Enhanced Zwitterion Hydrogel for Efficient Harvesting of Atmospheric Water

Zwitterionic hydrogel, serving as carriers for hygroscopic salts, holds significant potential in atmospheric water harvesting. However, their further application is limited by structural collapse in high-concentration salt solution and poor photothermal conversion performance. Herein, the graded pore structure of poly-3-[dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]azaniumyl]propane-1-sulfonate (PDMAPS) zwitterionic hydrogel/TpPa-1 covalent organic frameworks (COFs)/LiCl composite (named as PCL composite hydrogel) is proposed, which leads to the accelerated diffusion effect for water molecules. As a result, the vapor adsorption capacity of the optimal composite hydrogel (PCL-42) reaches 2.88 g g-1 within 12 hours under conditions of 25 °C and 90 % RH. Simultaneously, the maximum temperature of PCL-42 composite could reach 53.9 °C after 9 minutes under a simulated solar intensity of 1.0 kW m-2, releasing 91 % of the adsorbed water in 3 hours, providing a promising prospect for efficient solar-driven atmospheric water harvesting. One cycle could collect 7.55 g of fresh water under outdoor conditions, and the maximum daily water production may reach 2.71 kg kg-1. The reason lies in that TpPa-1 COFs lead hydrogel to form a gradient pore structure, which may accelerate the transport of water molecules, increase the loading capacity of LiCl and enhance the photothermal property.

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

Hydrogel-based interfacial solar-driven evaporation (ISDE) gives full play to the highly adjustable physical and chemical properties of hydrogel, which endows ISDE systems with excellent evaporation performance, anti-pollution properties, and mechanical behavior, making it more promising for applications in seawater desalination and wastewater treatment. This review systematically introduces the latest advances in hydrogel-based ISDE systems from three aspects: the required properties, the preparation methods, and the role played in application scenarios of hydrogels used in ISDE. Additionally, we also discuss the remaining challenges and potential opportunities in hydrogel-based ISDE systems. By summarizing the latest research progress, we hope that researchers in related fields have some insight into the unique advantages of hydrogels in the ISDE field and contribute our efforts so that ISDE technology reaches the finishing line of practical application on the hydrogel track.

Cost-Effective 3D-Printed Bionic Hydrogel Evaporator for Stable Solar Desalination

Solar desalination using hydrogel evaporators is an eco-friendly, highly efficient means with natural sunlight for sustainable freshwater production. However, it remains challenging to develop a cost-effective and scalable method to prepare salt-resistant hydrogel evaporators for stable desalination. Here, inspired by tree transpiration and hierarchical porous structure, a 3D-printed bionic hydrogel evaporator (3DP-BHE) is designed for long-term solar desalination. Commercialized activated carbon (AC) is introduced into biomass starch skeleton as a solar light absorber to build 3DP-BHE in a cost-effective fashion ($10.14 m-2 of total materials cost). The bionic tree leaf layer for 94.01% light absorption and timely vapor diffusion. The bionic tree trunk layer with 3D printed bimodal porous structure for water transfer, thermal isolation, and salt ions convection and diffusion. With the unique bionic structure, the 3DP-BHE achieves a stable evaporation rate of 2.13 kg m-2 h-1 at ≈90.5% energy efficiency under one sun (1 kW m-2). During the 7-day desalination of 10 wt.% brine, a steady evaporation rate of 1.98 kg m-2 h-1 is maintained with a record-high cost-effectiveness (195.3 g h-1 $-1) manner. This 3DP-BHE will open significant opportunities for affordable solar desalination systems on multiple scales, from individual households to off-grid communities.

A Polyzwitterionic@MOF Hydrogel with Exceptionally High Water Vapor Uptake for Efficient Atmospheric Water Harvesting

Atmospheric water harvesting (AWH) is considered a promising strategy for sustainable freshwater production in landlocked and arid regions. Hygroscopic salt-based composite sorbents have attracted widespread attention for their water harvesting performance, but suffer from aggregation and leakage issues due to the salting-out effect. In this study, we synthesized a PML hydrogel composite by incorporating zwitterionic hydrogel (PDMAPS) and MIL-101(Cr) as a host for LiCl. The PML hydrogel was characterized using various techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR), and thermogravimetric analysis (TGA). The swelling properties and water vapor adsorption-desorption properties of the PML hydrogel were also assessed. The results demonstrate that the MIL-101(Cr) was uniformly embedded into PDMAP hydrogel, and the PML hydrogel exhibits a swelling ratio of 2.29 due to the salting-in behavior. The PML hydrogel exhibited exceptional water vapor sorption capacity of 0.614 g/g at 298 K, RH = 40% and 1.827 g/g at 298 K, RH = 90%. It reached 80% of its saturated adsorption capacity within 117 and 149 min at 298 K, RH = 30% and 90%, respectively. Additionally, the PML hydrogel showed excellent reversibility in terms of water vapor adsorption after ten consecutive cycles of adsorption-desorption. The remarkable adsorption capacity, favorable adsorption-desorption rate, and regeneration stability make the PML hydrogel a potential candidate for AWH. This polymer-MOF synergistic strategy for immobilization of LiCl in this work offers new insights into designing advanced materials for AWH.

Vascular Bundle for Exceptional Water Confinement, Transport, and Evaporation

Nature, through billions of years of evolution, has constructed extremely efficient biosystems for transporting, confining, and vaporizing water. Mankind's ability to master water, however, is far from impeccable, and a sustainable supply of clean fresh water remains a global challenge. Here, we learn from Nature and prepare papyrus carbon (PC) from Egyptian papyrus paper as a sustainable solar desalination material. By taking advantage of the capillary pores from vascular bundles that are inherently built for transporting water in plants, PC achieves an evaporation rate of 4.1 kg m-2 h-1 in a passive single-stage device. Raman spectroscopy and thermal calorimetry show that the capillary pores pose a confinement effect to generate loosely hydrogen-bonded intermediate water, which substantially reduces the enthalpy of vaporization, allowing for exceptionally high energy efficiencies. The understanding is applicable to all nature-designed vascular plants and man-made separation and purification systems.

3D Cellular Solar Crystallizer for Stable and Ultra-Efficient High-Salinity Wastewater Treatment

Recent developed interfacial solar brine crystallizers, which employ solar-driven water evaporation for salts crystallization from the near-saturation brine to achieve zero liquid discharge (ZLD) brine treatment, are promising due to their excellent energy efficiency and sustainability. However, most existing interfacial solar crystallizers are only tested using NaCl solution and failed to maintain high evaporation capability when treating real seawater due to the scaling problem caused by the crystallization of high-valent cations. Herein, an artificial tree solar crystallizer (ATSC) with a multi-branched and interconnected open-cell cellular structure that significantly increased evaporation surface is rationally designed, achieving an ultra-high evaporation rate (2.30 kg m-2  h-1 during 2 h exposure) and high energy efficiency (128%) in concentrated real seawater. The unit cell design of ATSC promoted salt crystallization on the outer frame rather than the inner voids, ensuring that salt crystallization does not affect the continuous transport of brine through the pores inside the unit cell, thus ATSC can maintain a stable evaporation rate of 1.94 kg m-2  h-1 on average in concentrated seawater for 80 h continuous exposure. The design concept of ATSC represents a major step forward toward ZLD treatment of high-salinity brine in many industrial processes is believed.

Solar-powered simultaneous highly efficient seawater desalination and highly specific target extraction with smart DNA hydrogels

Obtaining freshwater and important minerals from seawater with solar power facilitates the sustainable development of human society. Hydrogels have demonstrated great solar-powered water evaporation potential, but highly efficient and specific target extraction remains to be expanded. Here, we report the simultaneous highly efficient seawater desalination and specific extraction of uranium with smart DNA hydrogels. The DNA hydrogel greatly promoted the evaporation of water, with the water evaporation rate reached a high level of 3.54 kilograms per square meter per hour (1 kilowatt per square meter). Simultaneously, uranyl-specific DNA hydrogel exhibited a high capture capacity of 5.7 milligrams per gram for uranium from natural seawater due to the rapid ion transport driven by the solar powered interfacial evaporation and the high selectivity (10.4 times over vanadium). With programmable functions and easy-to-use devices, the system is expected to play a role in future seawater treatment.

Recycling Graphite from Spent Lithium Batteries for Efficient Solar-Driven Interfacial Evaporation to Obtain Clean Water

Solar-driven interfacial evaporation technology is regarded as an attracting sustainable strategy for obtaining portable water from seawater and wastewater, and the recycle of waste materials to fabricate efficient photothermal materials as evaporator to efficiently utilize solar energy is very critical, but still difficult. To this purpose, graphite recovered from spent lithium-ion batteries (SLIBs) was realized using a simple acid leaching method, and a reconstructed graphite-based porous hydrogel (RG-PH) was subsequently fabricated by crosslinking foaming method. The incorporation of reconstructed graphite (RG) improves the mechanical characteristics of hydrogels and the light absorption performance significantly. The evaporation rate of optimized RG-PH can constantly reach 3.4278 kg m-2  h-1 for desalination under a one solar irradiation, and it also showed the excellent salt resistance in various salty water. Moreover, RG-PH has a strong elimination of a variety of organic contaminants in wastewater, including the typical volatile organic compound of phenol. This research shows the potential application of flexible and durable solar evaporators made from waste materials in purifying seawater and wastewater, not only contributing to carbon neutrality by recycling graphite from SLIBs, but also ensuring the cost-effectiveness harvest of solar energy for constantly obtaining clean water.

Multifunctional Solar Evaporator with Adjustable Island Structure Improves Performance and Salt Discharge Capacity of Desalination

Interfacial solar steam generation (ISSG) is the main method to get fresh water from seawater or wastewater. The balance between evaporation rate and salt resistance is still a major challenge for ISSG. Herein, a wood aerogel island solar evaporator (WAISE) with tunable surface structure and wettability by synthesizing poly(n-isopropylacrylamide)-modified multi-walled carbon nanotube photothermal layers. Compared to dense surface structure evaporators, interfacial moisture transport, thermal localization, and surface water vapor diffusion of WAISE are greatly promoted, and the evaporation rate of WAISE increased by 87.64%. WAISE allows for record performance of 200 h continuous operation in 20% NaCl solution without salt accumulation. In addition, the photo-thermal-electric device is developed based on WAISE with continuous water purification, power generation, and irrigation functions. This work provides a new direction for the development of multifunctional water purification systems.

Guiding Zn Uniform Deposition with Polymer Additives for Long-lasting and Highly Utilized Zn Metal Anodes

The parasitic side reaction on Zn anode is the key issue which hinders the development of aqueous Zn-based energy storage systems on power-grid applications. Here, a polymer additive (PMCNA) engineered by copolymerizing 2-methacryloyloxyethyl phosphorylcholine (MPC) and N-acryloyl glycinamide (NAGA) was employed to regulate the Zn deposition environment for satisfying side reaction inhibition performance during long-term cycling with high Zn utilization. The PMCNA can preferentially adsorb on Zn metal surface to form a uniform protective layer for effective water molecule repelling and side reaction resistance. In addition, the PMCNA can guide Zn nucleation and deposition along 002 plane for further side reaction and dendrite suppression. Consequently, the PMCNA additive can enable the Zn//Zn battery with an ultrahigh depth of discharge (DOD) of 90.0 % for over 420 h, the Zn//active carbon (AC) capacitor with long cycling lifespan, and the Zn//PANI battery with Zn utilization of 51.3 % at low N/P ratio of 2.6.

Water Activation in Solar-Powered Vapor Generation

Solar-powered vapor evaporation (SVG), based on the liquid-gas phase conversion concept using solar energy, has been given close attention as a promising technology to address the global water shortage. At molecular level, water molecules escaping from liquid water should overcome the attraction of the molecules on the liquid surface layer to evaporate. For this reason, it is better to reduce the energy required for evaporation by breaking a smaller number of hydrogen bonds or forming weak hydrogen bonds to ensure efficient and convenient vapor production. Many novel evaporator materials and effective water activation strategies have been proposed to stimulate rapid steam production and surpass the theoretical thermal limit. However, an in-depth understanding of the phase/enthalpy change process of water evaporation is unclear. In this review, a summary of theoretical analyses of vaporization enthalpy, general calculations, and characterization methods is provided. Various water activation mechanisms are also outlined to reduce evaporation enthalpy in evaporators. Moreover, unsolved issues associated with water activation are critically discussed to provide a direction for future research. Meanwhile, significant pioneering developments made in SVG are highlighted, hoping to provide a relatively entire chain for more scholars who are just stepping into this field.

Stable polyethylene glycol/biochar composite as a cost-effective photothermal absorber for 24 hours of steam and electricity cogeneration

Seawater desalination powered by solar energy is the most environmentally and economical solution in responding to the global water and energy crisis. However, solar desalination has been negatively impacted by intermittent sun radiation that alternates between day and night. In this study, sugarcane bagasse (SCB) was recycled via the pyrolysis process to biochar as a cost-effective solar absorber. Besides, polyethylene glycol (PEG) as a phase change material was encapsulated in the abundant pore structure of biochar to store the thermal energy for 24 hours of continuous steam generation. The BDB/1.5 PEG evaporator exhibited an evaporation rate of 2.11 kg m-2 h-1 (98.1% efficiency) under 1 sun irradiation. Additionally, the BDB/1.5 PEG evaporator incorporated by the TEC1-12706 module for continuous steam and electricity generation with a power density of 320.41 mW m-2. Moreover, 10 continuous hours of evaporation were applied to the composite demonstrating outstanding stability. The composite exhibited high water purification efficiency through solar desalination due to the abundant functional groups on the biochar surface. Finally, the resulting low-cost and highly efficient PCM-based absorber can be used on a wide scale to produce fresh water and energy.

Ultra-robust, high-adhesive, self-healing, and photothermal zwitterionic hydrogels for multi-sensory applications and solar-driven evaporation

Zwitterionic hydrogels have received considerable attention owing to their characteristic structures and integrating multifunctionality. However, the superhydrophilicity-induced poor mechanical properties severely hinder their potential applications. Besides, from the perspective of wide applications, zwitterionic hydrogels with integrated high mechanical properties, conductivity and multifunctionalities including self-adhesive, self-healing, and photothermal properties are highly desirable yet challenging. Herein, a new class of high-performance and multifunctional zwitterionic hydrogels are designed based on the incorporation of polydopamine-coated liquid metal nanoparticles (LM@PDA). Due to the efficient energy dissipation endowed by the isotropically extensible deformation of LM@PDA and the multiple interactions within the hydrogel matrix, the resultant hydrogels exhibited ultrahigh robustness with tensile strength of up to 1.3 MPa, strain of up to 1555% and toughness of up to 7.3 MJ m-3, superior or comparable to those of most zwitterionic hydrogels. The introduced LM@PDA also endows the hydrogels with high conductivity, versatile adhesion, autonomous self-healing, excellent injectability, three-dimensional printability, degradability, and photothermal conversion performance. These preferable properties enable the hydrogels promising as wearable sensors with multiple sensory capabilities for a wide range of strain values (1-500%), pressures (0.5-200 kPa) and temperatures (20-80 °C) with an impressive temperature coefficient of resistance (up to 0.15 °C-1). Moreover, these hydrogels can be also applied as solar evaporators with a high water evaporation rate (up to 2.42 kg m-2 h-1) and solar-thermal conversion efficiency (up to 90.3%) for solar desalination and wastewater purification. The present work can pave the way for the future development of zwitterionic hydrogels and beyond.

Constructing of efficient interface solar evaporator: In-situ colloid foaming strategy for solar desalination and visible light response sewage purification

The shortage of drinking water has become a global problem, coastal cities can make full use of abundant seawater resources by desalination technology to ease the contradiction between supply and demand. However, fossil energy consumption contradicts the goal of reducing carbon dioxide emissions. Currently, researchers favor interfacial solar desalination devices relying only on clean solar energy. Based on the structure optimization of the evaporator, a kind of device composed of a superhydrophobic BiOI (BiOI-FD) floating layer and CuO polyurethane sponge (CuO sponge) is constructed in this paper, with its design advantages presented in the following two aspects: 1. The novel BiOI-FD photocatalyst in the floating layer reduces the surface tension and realizes the degradation of the enriched pollutants, ensuring the device to achieve solar desalination and inland sewage purification; 2. CuO sponge can inhibit salt crystallization and realize the combination of the water transport and photothermal layers. Particularly, the photothermal evaporation rate of the interface device reached 2.37 kg m^-2 h^-1.The novel interface evaporator design will bring a new solution for solar desalination, sewage treatment and large-scale application.

Insight into the Charge-Ratio-Tuned Solar Vapor Generation of Polyion Complex Hydrogel/Coal Powder Composites

Solar-driven water purification has been deemed a promising technology to address the issue of clean water scarcity. However, traditional solar distillers often suffer from low evaporation rates under natural sunlight irradiation, while the high costs of the fabrication of photothermal materials further hinders their practical applications. Here, through the harnessing of the complexation process of oppositely charged polyelectrolyte solutions, a polyion complex hydrogel/coal powder composite (HCC)-based highly efficient solar distiller is reported. In particular, the influence of the charge ratio of polyanion-to-polycation on the solar vapor generation performance of HCC has been systematically investigated. Together with a scanning electron microscope (SEM) and the Raman spectrum method, it is found that a deviation from the charge balance point not only alters the microporous structure of HCC and weakens its water transporting capabilities, but also leads to a decreased content of activated water molecules and enlarges the energy barrier of water evaporation. As a result, HCC prepared at the charge balance point exhibits the highest evaporation rate of 3.12 kg m^-2 h^-1 under one sun irradiation, with a solar-vapor conversion efficiency as high as 88.83%. HCC also exhibits remarkable solar vapor generation (SVG) performance for the purification of various water bodies. In simulated seawater (3.5 wt% NaCl solutions), the evaporation rate can be as high as 3.22 kg m^-2 h^-1. In acid and alkaline solutions, HCCs are capable of maintaining high evaporation rates of 2.98 and 2.85 kg m^-2 h^-1, respectively. It is anticipated that this study may provide insights for the design of low-cost next-generation solar evaporators, and broaden the practical applications of SVG for seawater desalination and industrial wastewater purification.

Highly Efficient, Antibacterial, and Salt-Resistant Strategy Based on Carbon Black/Chitosan-Decorated Phase-Change Microcapsules for Solar-Powered Seawater Desalination

Solar-powered interfacial evaporation has been recognized to be a promising and sustainable technology for seawater desalination, in view of the challenge of freshwater scarcity and fossil energy storage. Nevertheless, current cutting-edge interfacial evaporation systems mostly ignore the issues of intermittent solar irradiation and bacterial contamination. We have hereby developed a novel type of an interfacial evaporator equipped with carbon black (CB)/chitosan (CS)-decorated phase-change microcapsules as a multifunctional photothermal material for solar-powered seawater desalination, based on a highly efficient, antibacterial, and salt-resistant multipurpose strategy. In the developed microcapsules, an n-docosane phase-change material (PCM) core was engulfed in a TiO₂ shell, followed by surface decorating a CB/CS nanocomposite layer. A high thermal energy-storage capacity of more than 140 J g^-1 was achieved, thanks to tight sealing of n-docosane as a PCM core in the perfect core-shell structured microcapsules. Moreover, a rational combination of CS and CB nanoparticles not only contributes an extremely high solar absorption efficiency of 95.04% and good wettability to the as-synthesized microcapsules, but also imparts outstanding antibacterial and salt-resistant abilities to them. These innovative designs enable the developed evaporator to gain a high evaporation rate of 2.58 kg m^-2 h^-1, along with an evaporation efficiency higher than 90% for consecutive and stable evaporation of seawater under intermittent solar illumination. Compared to conventional evaporators without a PCM, there is an increase by 1.03 kg m^-2 in the total water production of the develop evaporator under natural solar illumination for 8 h on a semicloudy day. The resultant evaporated water presents good vegetation compatibility to meet the requirement of crop growth for agricultural cultivation. This work provides a new pathway for designing and developing the high-performance interfacial evaporators with prominent antibacterial and salt-resistant abilities to produce purified water through solar-powered sustainable seawater desalination.

Tailorable Lignocellulose-Based Aerogel to Achieve the Balance between Evaporation Enthalpy and Water Transport Rate for Efficient Solar Evaporation

Solar-driven interfacial evaporation technology has become an effective approach to alleviate freshwater shortage. To improve its evaporation efficiency, the pore-size dependence of the water transport rate and evaporation enthalpy in the evaporator should be further investigated. Based on the transportation of water and nutrients in natural wood, we facilely designed a lignocellulose aerogel-based evaporator using carboxymethyl nanocellulose (CMNC) cross-linking, bidirectional freezing, acetylation, and MXene-coating. The pore size of the aerogel was adjusted by controlling its CMNC content. When the channel diameter of the aerogel-based evaporator increased from 21.6 to 91.9 μm, the water transport rate of the proposed evaporator increased from 31.94 to 75.84 g min^-1, while its enthalpy increased from 1146.53 to 1791.60 kJ kg^-1. At a pore size of 73.4 μm, the evaporation enthalpy and water transport rate of the aerogel-based evaporator achieved a balance, leading to the best solar evaporation rate (2.86 kg m^-2 h^-1). The evaporator exhibited excellent photothermal conversion efficiency (93.36%) and salt resistance (no salt deposition after three cycles of 8 h). This study could guide the development of efficient solar-driven evaporators for seawater desalination.

Superelastic 3D Assembled Clay/Graphene Aerogels for Continuous Solar Desalination and Oil/Organic Solvent Absorption

Superelastic, arbitrary-shaped, and 3D assembled clay/graphene aerogels (CGAs) are fabricated using commercial foam as sacrificial skeleton. The CGAs possess superelasticity under compressive strain of 95% and compressive stress of 0.09-0.23 MPa. The use of clay as skeletal support significantly reduces the use of graphene by 50%. The hydrophobic CGAs show high solvent absorption capacity of 186-519 times its own weight. Moreover, both the compression and combustion methods can be adopted for reusing the CGAs. In particular, it is demonstrated a design of 3D assembled hydrophilic CGA equipped with salt collection system for continuous solar desalination. Due to energy recovery and brine transport management promoted by this design, the 3D assembled CGA system exhibits an extremely high evaporation rate of 4.11 kg m-2  h-1 and excellent salt-resistant property without salt precipitation even in 20 wt% brine for continuous 36 h illumination (1 kW m-2 ), which is the best reported result from the solar desalination devices. More importantly, salts can be collected conveniently by squeezing and drying the solution out of the salt collection system. The work provides new insights into the design of 3D assembled CGAs and advances their applications in continuous solar desalination and efficient oil/organic solvent adsorption.