Plant leaves inspired sunlight-driven purifier for high-efficiency clean water production

Tree transpiration-inspired 3D-printed wastewater processors with hybrid nanocellulose for a broad range of oil-based effluents

The rise in industrial and domestic activities has led to increased oily wastewater generation and illicit discharge, posing a serious threat to clean water resources. Traditional water treatment methods, though scalable, consume fossil fuels and cause secondary pollution, necessitating safer, more efficient solutions. Here, we developed hybrid nanocellulose (HNC) inks by combining cellulose nanofibers (CNFs) and cellulose nanocrystals (CNCs) to fabricate advanced oily wastewater processors. These HNC inks enable 3D printing of tailored processor structures with high shape fidelity. By incorporating polydopamine (PDA) and chitin nanofibers (ChNFs), we created 3D-printed HNC scaffolds with exceptional hydrophilic-submerged oleophobicity and photothermal conversion properties. The HNC/PDA/ChNF (HAC) filter sheets achieved a 98.87 % separation efficiency and a high flux of 1646.96 L·m-2·h-1 for immiscible oil-water mixtures. For miscible mixtures, a 3D-printed C-HAC@HNC evaporator with a "bowl-shaped" layer achieved a 1.52 kg·m-2·h-1 evaporation rate and 96.61 % photothermal efficiency, excelling in oil-in-water emulsion treatment. It also demonstrated potential for seawater desalination and oily seawater purification, producing water that meets WHO drinking standards. This study offers innovative strategies for addressing critical challenges in water and energy resource management through efficient oily wastewater treatment.

Advancing Efficiency in Solar-Driven Interfacial Evaporation: Strategies and Applications

Solar-driven interfacial evaporation (SDIE) has emerged as a promising technology for addressing global water scarcity by utilizing solar-thermal conversion and evaporation at the air/material/water interface. The exceptional performance of these systems has attracted significant interest; it is imperative to establish rigorous and scientific standards for evaluating effectiveness, optimizing system design, and ensuring efficient practical applications. In this Review, we propose consensus criteria for accurately assessing system performance and guiding future advancements. We then explore the fundamental mechanisms driving system synergy, emphasizing how material compositions, microscopic hierarchical material structures, and macroscopic three-dimensional spatial architecture designs enhance solar absorption and photothermal conversion; balance heat confinement with water pathway optimization; manage salt resistance; and regulate enthalpy during vaporization. These matched coordination strategies are crucial for maximizing the target SDIE efficiency. Additionally, we investigate the practical applications of SDIE technologies, focusing on cutting-edge progress and versatile water purification, combined with atmospheric water harvesting, salt collection, electric generation, and photothermal deicing. Finally, we highlight the challenges and exciting opportunities for advancing research, emphasizing future efforts to integrate fundamental principles, system-level collaboration, and application-driven approaches to boost sustainable and highly efficient water and energy technologies. By linking system performance evaluation with optimization strategies for influencing factors, we offer a comprehensive overview of the field and a future outlook that promotes highly efficient clean water production and synergistic applications.

N, F Co-Doped Carbon Material Self-Supporting Cathode for High-Performance Lithium-Oxygen Batteries

The Li-O2 battery has emerged as a promising energy storage system due to its exceptionally high theoretical energy density of 3500 Wh kg-1. However, the sluggish kinetics associated with the formation and decomposition of discharge product Li2O2 poses several challenges in Li-O2 batteries, including excessive over-potential, limited rate performance, and reduced actual specific energy. Consequently, the development of cost-effective cathode catalysts with enhanced catalytic activity and long-term stability represents a viable approach to address these challenges. In this study, commercial melamine foam is utilized as a precursor material which was subjected to pyrolysis at elevated temperatures with PVDF to synthesize N, F co-doped self-supporting carbon cathode (NF-NSC). Remarkably, thanks to the synergistic effects of N, F heteroatomic in conjunction with the inherent three-dimensional reticular porous structure, NF-NSC exhibited enhanced electrochemical performance when utilized in Li-O2 batteries. Specifically, the NF-NSC cathode demonstrated an impressive discharge specific capacity of up to 35204 mAh g-1 alongside a low over-potential (0.86 V) and excellent cycling stability (146 cycles).

Interdisciplinary Hybrid Solar-Driven Evaporators: Theoretical Framework of Fundamental Mechanisms and Applications

The global water and energy crisis seems to be mitigated with promising prospects of emerging interdisciplinary hybrid solar-driven evaporator technology (IHSE). However, the lack of numeric standards for comparison between enormously reported systems and the synergistic effects of interdisciplinary hybridization remains a significant challenge. To entice researchers from various domains to collaborate on the design of a system for realistic, large-scale applications, this study provides a comprehensive overview of the interdisciplinary approaches to IHSE from the domains of physics, chemistry, materials science, and engineering, along with their guiding principles and underlying challenges. First, an in-depth analysis of IHSE with the basic scientific foundations and current advancements in recent years is discussed. Then, the physical principles/scientific principles alongside the overall system improvement enhancement techniques at the macro and micro scale are highlighted. Furthermore, the review analyzes the impact of significant physical factors that alter or restrict the efficiency of IHSE, as well as their connection and potential regulation. In addition, a comprehensive study of emerging sustainable applications for insight into the design and optimization of IHSE is provided for scientists from different fields. Lastly, the current challenges and future perspectives of interdisciplinary IHSE for large-scale applications are emphasized.

The liquid-vapor water generation characteristics of thermo-responsive polymer based on the multi-scale method

Thermo-responsive polymer is becoming a potential water purification and water harvesting material. To clarify the water diffusion characteristics, the desorption ratio of liquid water and water vapor for a poly (N-isopropylacrylamide) was researched by the multi-scale method. Firstly, macro and micro structures for the hydrogel with different water content were characterized. Second, the dynamic moisture preserving status of the hydrogel during the desorption process were tested. Thirdly, the dynamic liquid-vapor desorption rate was quantified. The macro volume of the polymer is of liner relationship with water content. During the desorption process, free and immobilized water transfers to immobilized and bound water. About 80% of the purified liquid water can be collected directly in closed environment, while the amount decreased to 21%-25% in air convection condition. The results suggested a heating method for improving liquid water collection rate with low energy cost for practical applications.

Black Phosphorus Tagged Responsive Strontium Hydrogel Particles for Bone Defect Repair

Hydrogel-derived implants have proven value in bone tissue regeneration, and current efforts have concentrated on devising strategies for producing functional implants with desired structures and functions to improve therapeutic outcomes. Herein, a novel black phosphorus (BP) tagged responsive strontium (Sr) hydrogel particles are presented for bone defect repair. By applying microfluidic technology, Sr and carboxymethyl chitosan, and BP are integrated into poly(N-isopropyl acrylamide) (pNIPAM) hydrogel matrix to generate such microparticles called pNBCSMs. Upon exposure to near-infrared irradiation, the pNBCSMs experience volume shrinkage and provoke the extrusion of the incorporated Sr, ascribed to the photothermal conversion ability of BP and the thermosensitivity of pNIPAM. In vitro and in vivo experimental results reveal that pNBCSMs subjected to near-infrared light display superior anti-inflammatory, anti-apoptotic, bacterial inhibitory, as well as osteogenesis-promoting effects, thereby effectively improving defective cranial bone repair. These features suggest that the proposed pNBCSMs can be promising candidates for bone repair.

2D Materials for Potable Water Application: Basic Nanoarchitectonics and Recent Progresses

Water polluted by toxic chemicals due to waste from chemical/pharmaceuticals and harmful microbes such as E. Coli bacteria causes several fatal diseases; and therefore, water filtration is crucial for accessing clean and safe water necessary for good health. Conventional water filtration technologies include activated carbon filters, reverse osmosis, and ultrafiltration. However, they face several challenges, including high energy consumption, fouling, limited selectivity, inefficiencies in removing certain contaminants, dimensional control of pores, and structural/chemical changes at higher thermal conditions and upon prolonged usage of water filter. Recently, the advent of 2D materials such as graphene, BN, MoS2, MXenes, and so on opens new avenues for advanced water filtration systems. This review delves into the nanoarchitectonics of 2D materials for water filtration applications. The current state of water filtration technologies is explored, the inherent challenges they face are outlines, and the unique properties and advantages of 2D materials are highlighted. Furthermore, the scope of this review is discussed, which encompasses the synthesis, characterization, and application of various 2D materials in water filtration, providing insights into future research directions and potential industrial applications.

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.

Sol-gel transition effect based on konjac glucomannan thermosensitive hydrogel for photo-assisted uranium extraction

Exploiting the intelligent photocatalysts capable of phase separation provides a promising solution to the removal of uranium, which is expected to solve the difficulty in separation and the poor selectivity of traditional photocatalysts in carbonate-containing uranium wastewater. In this paper, the γ-FeOOH/konjac glucomannan grafted with phenolic hydroxyl groups/poly-N-isopropylacrylamide (γ-FeOOH/KGM(Ga)/PNIPAM) thermosensitive hydrogel is proposed as the photocatalysts for extracting uranium from carbonate-containing uranium wastewater. The dynamic phase transformation is demonstrated to confirm the arbitrary transition of γ-FeOOH/KGM(Ga)/PNIPAM thermosensitive hydrogel from a dispersed state with a high specific surface area at low temperatures to a stable aggregated state at high temperatures. Notably, the γ-FeOOH/KGM(Ga)/PNIPAM thermosensitive hydrogel achieves a remarkably high rate of 92.3% in the removal of uranium from the wastewater containing carbonates and maintains the efficiency of uranium removal from uranium mine wastewater at over 90%. Relying on electron spin resonance and free radical capture experiment, we reveal the adsorption-reduction-nucleation-crystallization mechanism of uranium on γ-FeOOH/KGM(Ga)/PNIPAM thermosensitive hydrogel. Overall, this strategy provides a promising solution to treating uranium-contaminated wastewater, showing a massive potential in water purification.

Green Synthesis of Polyurethane Sponge-Grafted Calcium Alginate with Carbon Ink Aerogel with High Water Vapor Harvesting Capacity for Solar-Driven All-Weather Atmospheric Water Harvesting

Atmospheric water harvesting (AWH) technology is a new strategy for alleviating freshwater scarcity. Adsorbent materials with high hygroscopicity and high photothermal conversion efficiency are the key to AWH technology. Hence, in this study, a simple and large-scale preparation for a hygroscopic compound of polyurethane (PU) sponge-grafted calcium alginate (CA) with carbon ink (SCAC) was developed. The PU sponge in the SCAC aerogel acts as a substrate, CA as a moisture adsorber, and carbon ink as a light adsorber. The SCAC aerogel exhibits excellent water absorption of 0.555-1.40 g·g-1 within a wide range of relative humidity (40-80%) at 25 °C. The SCAC aerogel could release adsorbed water driven by solar energy, and more than 92.17% of the adsorbed water could be rapidly released over a wide solar intensity range of 1.0-2.0 sun. In an outdoor experiment, 57.517 g of SCAC was able to collect 32.8 g of clean water in 6 h, and the water quality meets the drinking water standards set by the World Health Organization. This study suggests a new approach to design promising AWH materials and infers the potential practical application of SCAC aerogel-based adsorbents.

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.

A critical review of sodium alginate-based composites in water treatment

The global freshwater crisis is a pressing issue, especially in areas with little rainfall and inner continental regions. The growing attention to water scarcity has induced increased interest in research on advanced water treatment technologies. As an abundant bioactive material in nature, sodium alginate (SA) has been widely used in water management due to its outstanding water absorption and holding ability, reversible swelling property, and pollutant adsorption performance. Building on this, progress made in using various modified forms of SA to access clean water is addressed in this review. Covering studies concern the adsorption and separation of pollutants in wastewater by SA-based absorbents and freshwater harvesting by SA-based collectors. This review explores SA-based composites' composition-structure-construction designs and emphasizes the impact of materials like inorganic materials, functional polymers, and porous matrices and how they can be exploited for water treatment. It also highlights the mechanisms of contaminants adsorption and freshwater desorption of SA-based composites. Finally, the shortcomings and future orientation of SA-based composites are proposed, including performance optimization, structural modification, application expansion, and mechanism in-depth investigation. This review aims to offer a theoretical basis and technical guidance for the use of natural materials to respond to the shortage of freshwater resources.

Solar interfacial evaporation devices for desalination and water treatment: Perspective and future

Water is an essential commodity for society, and alternate resources such as seawater and wastewater are vital for the future. There are various desalination technologies that can provide sufficient and sustainable water sources. Renewable energy-based desalination technologies like solar-based interfacial evaporation are very efficient and sustainable desalination methods. Solar-based interfacial evaporation has been a focus due to its efficient and easy-to-use methods. Still, research is needed for fouling resistance, scalable and low-cost materials, and devices for solar interfacial evaporation. Recent research focuses on the materials for evaporation devices, but various other aspects of device design and fabrication methods are also necessary to improve device performance. In this article, all the evaporator device configurations and strategies for efficient evaporator devices are compiled and summarized. The evaporator devices have been classified into eight main categories: monolayer, bilayer, tree-like design, low-temperature designs, 3D-Origami-based designs, latent heat recovery design, design with storage/batch process, and contactless design. It was found that a good absorber, well-engineered air-water interface, and bottom-layer insulation are necessary for the best systems. The current research focuses on the vapor production output of the devices but not on the water production from devices. So, the focus on device-based water production and the associated cost of the water produced is essential. This article articulates the strategies and various scalable and efficient devices for evaporation-based solar-driven desalination. This article will be helpful for the researchers in improving devices output and coming up with a sustainable desalination and water treatment.

Recent Advances of Green Electricity Generation: Potential in Solar Interfacial Evaporation System

Solar-driven interfacial evaporation (SDIE) has played a pivotal role in optimizing water-energy utilization, reducing conventional power costs, and mitigating environmental impacts. The increasing emphasis on the synergistic cogeneration of water and green electricity through SDIE is particularly noteworthy. However, there is a gap of existing reviews that have focused on the mechanistic understanding of green power from water-electricity cogeneration (WEC) systems, the structure-activity relationship between efficiency of green energy utilization in WEC and material design in SDIE. Particularly, it lacks a comprehensive discussion to address the challenges faced in these areas along with potential solutions. Therefore, this review aims to comprehensively assess the progress and future perspective of green electricity from WEC systems by investigating the potential expansion of SDIE. First, it provides a comprehensive overview about material rational design, thermal management, and water transportation tunnels in SDIE. Then, it summarizes diverse energy sources utilized in the SDIE process, including steaming generation, photovoltaics, salinity gradient effect, temperature gradient effect, and piezoelectric effect. Subsequently, it explores factors that affect generated green electricity efficiency in WEC. Finally, this review proposes challenges and possible solution in the development of WEC.

Nanocomposite Hydrogel Actuators with Ordered Structures: From Nanoscale Control to Macroscale Deformations

Flexible intelligent actuators with the characteristics of flexibility, safety and scalability, are highly promising in industrial production, biomedical fields, environmental monitoring, and soft robots. Nanocomposite hydrogels are attractive candidates for soft actuators due to their high pliability, intelligent responsiveness, and capability to execute large-scale rapid reversible deformations under external stimuli. Here, the recent advances of nanocomposite hydrogels as soft actuators are reviewed and focus is on the construction of elaborate and programmable structures by the assembly of nano-objects in the hydrogel matrix. With the help of inducing the gradient or oriented distributions of the nanounits during the gelation process by the external forces or molecular interactions, nanocomposite hydrogels with ordered structures are achieved, which can perform bending, spiraling, patterned deformations, and biomimetic complex shape changes. Given great advantages of these intricate yet programmable shape-morphing, nanocomposite hydrogel actuators have presented high potentials in the fields of moving robots, energy collectors, and biomedicines. In the end, the challenges and future perspectives of this emerging field of nanocomposite hydrogel actuators are proposed.

Interfacial Solar Evaporation: From Fundamental Research to Applications

In the last decade, interfacial solar steam generation (ISSG), powered by natural sunlight garnered significant attention due to its great potential for low-cost and environmentally friendly clean water production in alignment with the global decarbonization efforts. This review aims to share the knowledge and engage with a broader readership about the current progress of ISSG technology and the facing challenges to promote further advancements toward practical applications. The first part of this review assesses the current strategies for enhancing the energy efficiency of ISSG systems, including optimizing light absorption, reducing energy losses, harvesting additional energy, and lowering evaporation enthalpy. Subsequently, the current challenges faced by ISSG technologies, notably salt accumulation and bio-fouling issues in practical applications, are elucidated and contemporary methods are discussed to overcome these challenges. In the end, potential applications of ISSG, ranging from initial seawater desalination and industrial wastewater purification to power generation, sterilization, soil remediation, and innovative concept of solar sea farm, are introduced, highlighting the promising potential of ISSG technology in contributing to sustainable and environmentally conscious practices. Based on the review and in-depth understanding of these aspects, the future research focuses are proposed to address potential issues in both fundamental research and practical applications.

A novel scalable polycationic melamine sponge-based filtration matrix for continuous ultrafast adsorption of anionic pollutants

Effective capturing of anionic pollutants from wastewater under industrial operating conditions, which requires high processing flux and fast adsorption rate remains a challenge. Here, a commercially available melamine sponge (MS) with reticulated 3D macroporous structures was covalently modified with positively charged moieties using a single step functionalization under mild conditions. The developed novel polycationic melamine sponge (MS+) was formed by a nucleophilic addition reaction between glycidyltrimethylammonium chloride (GMTA) and MS, followed by a self-propagation of GMTA. The produced MS+ possessed strong electrostatic interactions with different anions such as Rose Bengal (RB) and phosphates (P) under a wide pH range (3-11). The MS+ exhibited promoted static adsorption efficiencies of 400 mg g-1 (P) and 600 mg g-1 (RB), within 5 min and 60 s, respectively. Furthermore, the MS+ showed high stability and recyclability for up to 15 cycles of uses, and the recycling process was environmentally friendly by using 1 M NaCl as a releasing solution. Benefiting from fast flow through the macroporous MS+ and highly positive charged skeleton, the MS+ was applied for rapid dynamic enrichment process of P from real manure wastewater with an enrichment factor of 4.4. Utilization of the MS+ as the substrate brings additional advantages such as low cost, availability, and flexibility to fit into existing filtration devices. The developed MS+ could be expanded for enrichments of other anionic species from various polluted water sources.

Boosting the Viable Water Harvesting in Solar Vapor Generation: From Interfacial Engineering to Devices Design

Continuously increasing demand for the life-critical water resource induces severe global water shortages. It is imperative to advance effective, economic, and environmentally sustainable strategies to augment clean water supply. The present work reviews recent reports on the interfacial engineering to devices design of solar vapor generation (SVG) system for boosting the viability of drinkable water harvesting. Particular emphasis is placed on the basic principles associated with the interfacial engineering of solar evaporators capable of efficient solar-to-thermal conversion and resulting freshwater vapor via eliminating pollutants from quality-impaired water sources. The critical configurations manufacturing of the devices for fast condensation is then highlighted to harvest potable liquid water. Fundamental and practical challenges, along with prospects for the targeted materials architecture and devices modifications of SVG system are also outlined, aiming to provide future directions and inspiring critical research efforts in this emerging and exciting field.

Mucus Transpiration as the Basis for Chronic Cough and Cough Hypersensitivity

Chronic cough is characterized by a state of cough hypersensitivity. We analyze the process of transpiration, by which water appears to evaporate from laryngeal and tracheal mucus as from the surface of a leaf, as a potential cause of cough hypersensitivity. In this process, osmotic pressure differences form across mucus, pulling water toward the air, and preventing mucus dehydration. Recent research suggests that these osmotic differences grow on encounter with dry and dirty air, amplifying pressure on upper airway epithelia and initiating a cascade of biophysical events that potentially elevate levels of ATP, promote inflammation and acidity, threaten water condensation, and diminish mucus water permeability. Among consequences of this inflammatory cascade is tendency to cough. Studies of isotonic, hypotonic, and hypertonic aerosols targeted to the upper airways give insights to the nature of mucus transpiration and its relationship to a water layer that forms by condensation in the upper airways on exhalation. They also suggest that, while hypertonic NaCl and mannitol may provoke cough and bronchoconstriction, hypertonic salts with permeating anions and non-permeating cations may relieve these same upper respiratory dysfunctions. Understanding of mucus transpiration and its role in cough hypersensitivity can lead to new treatment modalities for chronic cough and other airway dysfunctions promoted by the breathing of dry and dirty air.

Magnetic iron-based nanoparticles biogeochemical behavior in soil-plant system: A critical review

Increasing attention is being given to magnetic iron-based nanoparticles (MINPs) because of their potential environmental benefits. Owing to the earth abundance and high utilization of MINPs, as well as the significant functions of Fe in sustainable agriculture and environmental remediation, an understanding of the environmental fate of MINPs is indispensable. However, there are still knowledge gaps regarding the largely unknown environmental behaviors and fate of MINPs in soil-plant system. Thus, this review summarizes recent literature on the biogeochemical behavior (uptake, transportation, and transformation) of MINPs in soil and plants. The different possible uptake (e.g., foliar and root adsorption) and translocation (e.g., xylem, phloem, symplastic/apoplastic pathway, and endocytosis) pathways are discussed. Furthermore, drivers of MINPs uptake and transportation (e.g., soil characteristics, fertilizer treatments, copresence of inorganic and organic anions, meteorological conditions, and cell wall pores) in both soil and plant environments are summarized. This review also details the physical, chemical, and biological transformations of MINPs in soil-plant system. More importantly, a metadata analysis from the existing literature was employed to investigate the distinction between MINPs and other engineering nanoparticles biogeochemical behavior. In the future, more attention should be given to understanding the behavior of MINPs in soil-plant system and improving the capabilities of predictive models. This review thus highlights the main knowledge gaps regarding MINPs behavior and fate to provide guidance for their safe application in agrochemicals, crop production, and soil health.

Ultrathin Water Layer Conservation by "Nano-forest" in a Three-Dimensional Interface Regulates Energy Flow to Boost Solar Evaporation

Solar-driven interfacial evaporation technology utilizes materials to form a thin layer on the water's surface, absorbs sunlight on this layer, completes the light-to-heat conversion, heats up the water, and vaporizes it. This greatly reduces energy loss to bulk water and greatly improves the evaporation rate for producing clean water. Additionally, three-dimensional (3D) evaporators are increasingly being applied in this field, and the cold surface generated by the rapid evaporation in the 3D evaporator can utilize environmental heat to achieve a net energy gain for the system. Both strategies improve the evaporation rate of the system, but 3D materials typically have high water contents and cannot avoid energy flow into non-evaporated water. To address this, we introduce the advantages of interfacial evaporation into 3D evaporation by constructing an evaporator with a highly conductive copper core skeleton and an outer layer of ultrathin water and by reasonably constructing interconnected evaporation frameworks. Investigating and optimizing the mutual influence of the ultrathin water layer on the framework, an evaporator with 40 pores per inch (ppi) can reach a maximum of 24.4 kg·m-2 h-1, indicating that 3D interfacial evaporators with ultrathin water layers concentrate energy flow to stimulate high evaporation rates. This strategy will promote the development of photothermal evaporation technology.

Integrated Moist-Thermoelectric Generator for Efficient Waste Steam Energy Utilization

Industrial waste steam is one of the major sources of global energy losses. Therefore, the collection and conversion of waste steam energy into electricity have aroused great interest. Here, a "two-in-one" strategy is reported that combines thermoelectric and moist-electric generation mechanisms for a highly efficient flexible moist-thermoelectric generator (MTEG). The spontaneous adsorption of water molecules and heat in the polyelectrolyte membrane induces the fast dissociation and diffusion of Na⁺ and H⁺ , resulting in the high electricity generation. Thus, the assembled flexible MTEG generates power with a high open-circuit voltage (V_oc ) of 1.81 V (effective area = 1cm² ) and a power density of up to 4.75±0.4 µW cm^-2 . With efficient integration, a 12-unit MTEG can produce a V_oc of 15.97 V, which is superior to most known TEGs and MEGs. The integrated and flexible MTEGs reported herein provide new insights for harvesting energy from industrial waste steam.

Overflow Control for Sustainable Development by Superwetting Surface with Biomimetic Structure

Liquid flowing around a solid edge, i.e., overflow, is a commonly observed flow behavior. Recent research into surface wetting properties and microstructure-controlled overflow behavior has attracted much attention. Achieving controllable macroscale liquid dynamics by manipulating the micro-nanoscale liquid overflow has stimulated diverse scientific interest and fostered widespread use in practical applications. In this review, we outline the evolution of overflow and present a critical survey of the mechanism of surface wetting properties and microstructure-controlled liquid overflow in multilength scales ranging from centimeter to micro and even nanoscale. We summarize the latest progress in utilizing the mechanisms to manipulate liquid overflow and achieve macroscale liquid dynamics and in emerging applications to manipulate overflow for sustainable development in various fields, along with challenges and perspectives.

Quick-Release Antifouling Hydrogels for Solar-Driven Water Purification

Hydrogels are promising soft materials for energy and environmental applications, including sustainable and off-grid water purification and harvesting. A current impediment to technology translation is the low water production rate well below daily human demand. To overcome this challenge, we designed a rapid-response, antifouling, loofah-inspired solar absorber gel (LSAG) capable of producing potable water from various contaminated sources at a rate of ∼26 kg m^-2 h^-1, which is sufficient to meet daily water demand. The LSAG-produced at room temperature via aqueous processing using an ethylene glycol (EG)-water mixture-uniquely integrates the attributes of poly(N-isopropylacrylamide) (PNIPAm), polydopamine (PDA), and poly(sulfobetaine methacrylate) (PSBMA) to enable off-grid water purification with enhanced photothermal response and the capacity to prevent oil fouling and biofouling. The use of the EG-water mixture was critical to forming the loofah-like structure with enhanced water transport. Remarkably, under sunlight irradiations of 1 and 0.5 sun, the LSAG required only 10 and 20 min to release ∼70% of its stored liquid water, respectively. Equally important, we demonstrate the ability of LSAG to purify water from various harmful sources, including those containing small molecules, oils, metals, and microplastics.

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

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.

Surface Modification, Topographic Design and Applications of Superhydrophobic Systems

Superhydrophobic surfaces with expanded wetting behaviors, like tunable adhesion, hybrid surface hydrophobicity and smart hydrophobic switching have attracted increasing attention due to their broad applications. Herein, the construction methods, mechanisms and advanced applications of special superhydrophobicity are reviewed, and hydro/superhydrophobic modifications are categorized and discussed based on their surface chemistry, and topographic design. The formation and maintenance of special superhydrophobicity in the metastable state are also examined and explored. In addition, particular attention is paid to the use of special wettability in various applications, such as membrane distillation, droplet-based electricity generators and anti-fogging surfaces. Finally, the challenges for practical applications and future research directions are discussed.

Self-Propelled Structural Color Cylindrical Micromotors for Heavy Metal Ions Adsorption and Screening

Water contamination resulting from heavy metal ions (HMIs) poses a severe threat to public health and the ecosystem. Attempts are tending to develop functional materials to realize efficient and intelligent adsorption of HMIs. Herein, self-propelled structural color cylindrical micromotors (SCCMs) with reversible HMIs adsorption capacity and self-reporting property are presented. The SCCMs are fabricated by using platinum nanoparticles (Pt NPs) tagged responsive hydrogel of carboxymethyl chitosan (CMC) and polyacrylamide (PAM) to asymmetrically replicate tubular colloidal crystal templates (TCCTs). Owing to the self-propelled motion of the SCCMs, the enhancive ion-motor interactions bring significantly improved decontamination efficiency. Moreover, it is demonstrated that the SCCMs can realize quick and naked-eye-visible self-reporting during the adsorption/desorption process based on their responsive structure color variation and superior adsorption capacity. Thus, it is anticipated that such intelligent SCCMs can significantly facilitate the evolution of sensing assays and diverse environmental fields.

A Metal Ion and Thermal-Responsive Bilayer Hydrogel Actuator Achieved by the Asymmetric Osmotic Flow of Water between Two Layers under Stimuli

Shape-morphing hydrogels have drawn great attention due to their wide applications as soft actuators, while asymmetric responsive shape-morphing behavior upon encountering external stimuli is fundamental for the development of hydrogel actuators. Therefore, in this work, bilayer hydrogels were prepared and the shrinkage ratios (LA/LN) of the AAm/AAc layer to the NIPAM layer immersed in different metal ion solutions, leading to bending in different directions, were investigated. The difference in the shrinkage ratio was attributed to the synergistic effect of the osmolarity difference between the inside and outside of the hydrogels and the interaction difference between the ion and hydrogel polymer chains. Additionally, under thermal stimuli, the hydrogel actuator would bend toward the NIPAM layer due to the shrinkage of the hydrogel networks caused by the hydrophilic–hydrophobic phase transition of NIPAM blocks above the LCST. This indicates that metal ion and thermal-responsive shape-morphing hydrogel actuators with good mechanical properties could be used as metal ion or temperature-controllable switches or other smart devices.

A reconfigurable and magnetically responsive assembly for dynamic solar steam generation

Interfacial solar vapor generation is a promising technique to efficiently get fresh water from seawater or effluent. However, for the traditional static evaporation models, further performance improvement has encountered bottlenecks due to the lack of dynamic management and self-regulation on the evolving water movement and phase change in the evaporation process. Here, a reconfigurable and magnetically responsive evaporator with conic arrays is developed through the controllable and reversible assembly of graphene wrapped Fe₃O₄ nanoparticles. Different from the traditional structure-rigid evaporation architecture, the deformable and dynamic assemblies could reconfigure themselves both at macroscopic and microscopic scales in response to the variable magnetic field. Thus, the internal water transportation and external vapor diffusion are greatly promoted simultaneously, leading to a 23% higher evaporation rate than that of static counterparts. Further, well-designed hierarchical assembly and dynamic evaporation system can boost the evaporation rate to a record high level of 5.9 kg m^-2 h^-1. This proof-of-concept work demonstrates a new direction for development of high performance water evaporation system with the ability of dynamic reconfiguration and reassembly.

Magnetic nanostructure and biomolecule synergistically promoted Suaeda-inspired self-healing hydrogel composite for seawater evaporation

Multifunctional hydrogels with excellent comprehensive performance are essential prerequisite for the implementation of effective water resources technology with high efficiency and low energy consumption. Inspired by the water purification and self-healing properties of natural plants, and based on the synergy of photothermal and biological effects, high photothermal Fe₃O₄ nanoparticles and natural polyhydroxy oligomeric proanthocyanidin (OPC) are introduced into a water-active polyvinyl alcohol (PVA) hydrogel. Two new bio-hydrogels of PVA/Fe₃O₄/graphite and PVA/OPC with self-healing and stretchable properties are proposed and designed. The obtained hydrogels exhibit reversible covalent cross-linked water-promoted healing (chemically) and photothermal melting/recrystallization healing (physically). The double-layered hydrogel composite demonstrates a dual response function (sunlight and near-infrared light), along with water purification properties. It is prepared through a water spray triggered self-healing process. The ultimate fracture strain of the photothermal layer and purification layer hydrogel was more than 1000% and 400% respectively after self-healing.After 48 h of hydrogel composite adsorption, the color of a methylene blue solution faded, and the absorption peak at 664 nm decreased. In addition, this research adopts a phased evaporation method to concentrate local energy and provide power for seawater evaporation. The evaporation efficiency of seawater induced by near-infrared (NIR) light was up to 3.15 kg m^-2 h^-1, whereas that under sunlight was 1.25 kg m^-2 h^-1. Selection of the evaporation excitation light source allowed control of the evaporation efficiency. The proposed technology is expected to be widely applicable to the staged evaporation of seawater as well as water purification.

Marangoni Effect Drives Salt Crystallization Away from the Distillation Zone for Large-Scale Continuous Solar Passive Desalination

Solar desalination shows great potential in dealing with global water scarcity. A multistage passive solar distiller with thermal localization is especially attractive for its high-water yield. However, achieving long-term stability in large-scale devices remains a challenge because of the easy accumulation of crystallized salt inside the distiller. Here, we reported that the Marangoni effect can drive crystallized salt away along a long distance in a capillary wick, which endow the multistage passive solar distiller with the ability of salt-rejecting. In a 36 h continuous testing, the salinity of the distillation zone is limited below 12 wt % and crystallized salt only accumulates outside the device. The water yield is about 1.7 kg m^-2 h^-1 in a three-stage device, with a solar-to-vapor conversion efficiency of 114% under one sun. This novel design proves a new principle for high efficiency and long-term stable solar desalination.

Sunlight Recovering the Superhydrophobicity of a Femtosecond Laser-Structured Shape-Memory Polymer

Superhydrophobic surfaces have aroused increasing attentions in the fields of self-cleaning, anti-fouling, heat transfer, etc. However, one of the major problems of the artificial superhydrophobic surface in practical applications is the poor durability. Inspired by the self-healing property of nature organism, we developed a sunlight-driven recoverable superhydrophobic surface by femtosecond laser constructing micropillar array on the surface of the photo-responsive shape-memory polymer (SMP). The photo-responsive SMP composite was prepared by adding reduced graphene oxide (RGO) into thermal-responsive SMP matrix. Due to the excellent sunlight-to-heat transformation property of RGO, the temperature of the as-fabricated RGO-SMP composite could be rapidly increased above the shape transformation temperature of the RGO-SMP under one sunlight irradiation. Once the micropillar array of the RGO-SMP composite was deformed by pressing or stretching treatments, the surface would lose superhydrophobicity. Upon sunlight irradiation, the surface morphology and the wettability of the RGO-SMP micropillars could completely recover to the original states. Meanwhile, this reversible morphology and wettability transformation process could be repeated multiple times. We envision that such a sunlight-recoverable superhydrophobic surface will have great applications in the future.

A Simple Polypyrrole/Polyvinylidene Fluoride Membrane with Hydrophobic and Self-Floating Ability for Solar Water Evaporation

The traditional hydrophobic solarevaporator is generally obtained through the modification of alkyl or fluoroalkyl on the photothermal membrane. However, the modified groups can easily be oxidized in the long-term use process, resulting in the poor salt resistance and stability of photothermal membrane. In order to solve this problem, a simple polypyrrole/polyvinylidene fluoride membrane, consisting of an intrinsic hydrophobic support (polyvinylidene fluoride) and a photothermal material (polypyrrole), was fabricated by ultrasonically mixing and immersed precipitation. This photothermal membrane showed good self-floating ability in the process of water evaporation. In order to further improve the photothermal conversion efficiency, a micropyramid structure with antireflective ability was formed on the surface of membrane by template method. The micropyramids can enhance the absorption efficiency of incident light. The water evaporation rate reached 1.42 kg m⁻² h⁻¹ under 1 sun irradiation, and the photothermal conversion efficiency was 88.7%. The hydrophobic polyvinylidene fluoride ensures that NaCl cannot enter into membrane during the evaporation process of the brine, thus realizing the stability and salt resistance of polypyrrole/polyvinylidene fluoride in 3.5%wt and 10%wt NaCl solution.

Tailoring the Salt Transport Flux of Solar Evaporators for a Highly Effective Salt-Resistant Desalination with High Productivity

Developing highly effective salt-resistant solar evaporators for a long-term desalination with a high evaporation rate and water production rate remains a great challenge. Herein, we fabricated a three-dimensional printed hierarchical porous reduced graphene oxide/carbon black (3DP-HP rGO/CB) solar evaporator constructed with a thin layer of porous photothermal interface and a grid of hierarchical porous transport channel possessing a large-sized porous microstructure. The 3DP-HP rGO/CB solar evaporator demonstrates a tailored high-salt transport flux of up to 4.3 kg·m^-2·h^-1, which displays a highly effective salt-resistant performance at a high evaporation rate of 10.5 kg·m^-2·h^-1 during a desalination of 10 wt % NaCl brine under 8 kW·m^-2 illumination. Experiments and theoretical calculations prove that the large porous microstructure with abundant and low-resistance salt ion channels endows solar evaporators with a high salt transport flux, therefore boosting salt resistance compared to traditional solar evaporators. A 10 d desalination experiment shows the long-term salt resistance of a 3DP-HP rGO/CB solar evaporator for a high-rate and stable evaporation and water production. Furthermore, the 3DP-HP rGO/CB evaporator can purify 10 wt % NaCl brine at an ultrafast water production rate of up to 5.6 L·m^-2·h^-1 under natural sunlight. This work demonstrates great potential for the practical implementation of solar desalination with high productivity.

Carbon Materials for Solar Water Evaporation and Desalination

Seawater desalination is viewed as a promising solution to world freshwater scarcity. Solar assisted desalination is proposed to overcome the high energy consumption in current desalination technologies, as it uses abundant and sustainable solar energy as the only energy input. Interfacial solar vapor generation (SVG) has attracted considerable research interest due to its high energy conversion efficiency, simple implementation, and cost-effectiveness. Among all the candidate materials for solar evaporators, carbon-based materials stand out due to their intrinsic high solar absorption, highly tunable structure, easy preparation, low cost, and earth-abundancy. In this review, the recent progress on carbon-based materials for the development of interfacial SVG is summarized. First, a brief introduction to the basic design principles of the interfacial SVG system is presented. Then, recent efforts in carbon-based solar evaporators, from artificial structures to bioinspired configurations, focusing on their structure-function relationship are highlighted. Strategies for designing antisalt-fouling desalination systems are also summarized. Last, the challenges and opportunities of carbon-based materials for solar evaporation technology are elaborated.

Programmable Asymmetric Nanofluidic Photothermal Textile Umbrella for Concurrent Salt Management and In Situ Power Generation During Long-Time Solar Steam Generation

Although solar-driven seawater desalination affords a highly promising strategy for freshwater-electricity harvesting by employing abundant solar energy and ocean resources, the inevitable salt crystallization on the surface of evaporators causes a sharp decline in evaporation performance and the poor electricity output of most coupled inflexible evaporation-power generation devices limits the scalability and durability in long-time practical applications. Herein, we report a simple programmable nanofluidic photothermal textile umbrella by asymmetrically depositing MoS₂ nanosheets on cotton textiles, which allows for controllable gravity-assisted edge-preferential salt crystallization/harvesting via self-manipulated saline solution transportation in the wet umbrella and simultaneous drenching-induced electrokinetic voltage generation (0.535 V)/storage (charging a capacitor to 12.2 V) in over 120 h of the nonstop solar desalination process (with 7.5 wt % saline solution). Notably, the morphology and salt crystallization areas can be managed via the programmed umbrellas. Moreover, the asymmetric textile umbrellas possess admirable sewable features for large-scale integration to enhance the evaporation and voltage output efficiency. Importantly, this textile umbrella evaporator shows excellent output stability and durability even after 40 times of washing. This work may pave a scalable way to design programmable solar evaporators for sustainable seawater desalination with scalabilities of zero-waste discharge, valuable resource recovery, and energy harvesting.

Conformal Microfluidic-Blow-Spun 3D Photothermal Catalytic Spherical Evaporator for Omnidirectional Enhanced Solar Steam Generation and CO2 Reduction

Solar-driven water evaporation and valuable fuel generation is an environmentally friendly and sustainable way for clean water and energy production. However, a few bottlenecks for practical applications are high-cost, low productivity, and severe sunlight angle dependence. Herein, solar evaporation with enhanced photocatalytic capacity that is light direction insensitive and of efficiency breakthrough by virtue of a three-dimensional (3D) photothermal catalytic spherical isotopic evaporator is demonstrated. A homogeneous layer of microfluidic blow spun polyamide nanofibers loaded with efficient light absorber of polypyrrole nanoparticles conformally wraps onto a lightweight, thermal insulating plastic sphere, featuring favorable interfacial solar heating and efficient water transportation. The 3D spherical geometry not only guarantees the omnidirectional solar absorbance by the light-facing hemisphere, but also keeps the other hemisphere under shadow to harvest energy from the warmer environment. As a result, the light-to-vapor efficiency exceeds the theoretical limit, reaching 217% and 156% under 1 and 2 sun, respectively. Simultaneously, CO2 photoreduction with generated steam reveals a favorable clean fuels production rate using photocatalytic spherical evaporator by secondary growth of Cu2 O nanoparticles. Finally, an outdoor demonstration manifests a high evaporation rate and easy-to-perform construction on-site, providing a promising opportunity for efficient and decentralized water and clean fuel production.

Hierarchical Photothermal Fabrics with Low Evaporation Enthalpy as Heliotropic Evaporators for Efficient, Continuous, Salt-Free Desalination

Solar-driven seawater evaporation is usually achieved on floating evaporators, but the performances are substantially limited by high evaporation enthalpy, solid salt crystallization, and reduced evaporation due to inclined sunlight. To solve these problems, we fabricated hierarchical polyacrylonitrile@copper sulfide (PAN@CuS) fabrics and proposed a prototype of heliotropic evaporator. Hierarchical PAN@CuS fabrics show significantly decreased water-evaporation enthalpy (1956.32 kJ kg^-1, 40 °C), compared with that of pure water (2406.17 kJ kg^-1, 40 °C), because of the disorganization of the hydrogen bonds at the CuS interfaces. Based on this fabric, a heliotropic evaporation model was developed, where seawater slowly flows from high to low in the fabric. Under solar irradiation (1.0 kW m^-2), this model exhibits a high-rate evaporation (∼2.27 kg m^-2 h^-1) and saturated brine production without solid salt crystallization. In particular, under inclined sunlight (angle range: from -90° to +90°), the heliotropic model retains an almost unchanged solar evaporation rate, whereas the floating model shows severe evaporation reduction (83.9%). Therefore, our study provides a strategy for reducing the evaporation enthalpy, maximally utilizing solar energy and continuous salt-free desalination.

Solar-Powered Sustainable Water Production: State-of-the-Art Technologies for Sunlight-Energy-Water Nexus

Alternative water resources (seawater, brackish water, atmospheric water, sewage, etc.) can be converted into clean freshwater via high-efficiency, energy-saving, and cost-effective methods to cope with the global water crisis. Herein, we provide a comprehensive and systematic overview of various solar-powered technologies for alternative water utilization (i.e., "sunlight-energy-water nexus"), including solar-thermal interface desalination (STID), solar-thermal membrane desalination (STMD), solar-driven electrochemical desalination (SED), and solar-thermal atmospheric water harvesting (ST-AWH). Three strategies have been proposed for improving the evaporation rate of STID systems above the theoretical limit and designing all-weather or all-day operating STID systems by analyzing the energy transfer of the evaporation and condensation processes caused by solar-thermal conversion. This review also introduces the fundamental principles and current research hotspots of two other solar-driven seawater or brackish water desalination technologies (STMD and SED) in detail. In addition, we also cover ST-AWH and other solar-powered technologies in terms of technology design, materials evolution, device assembly, etc. Finally, we summarize the content of this comprehensive review and discuss the challenges and future outlook of different types of solar-powered alternative water utilization technologies.

Unidirectionally Driving Nanofluidic Transportation via an Asymmetric Textile Pump for Simultaneous Salt-Resistant Solar Desalination and Drenching-Induced Power Generation

Solar-driven seawater desalination provides a promising technology for sustainable water energy harvesting. Although tremendous efforts have been dedicated to developing efficient evaporators, the challenge of preventing salt accumulation while simultaneously realizing high-performance steam-electricity cogeneration remains to be addressed. In this work, inspired by the water and solute transportation in plants via the wicking mechanism, a one-way asymmetric nanofluidic photothermal evaporator fabricated by disproportionately depositing photothermal MXene nanosheets on a hydrophilic cotton textile is reported for simultaneous freshwater and power production. By unidirectionally driving dynamic saline transportation via this photothermal cotton textile pump, this evaporator not only enables self-operating salt rejection for stable steam generation but also affords continuous electric power generation induced by the formation of an asymmetric double electrode layer within MXene nanochannels under the drenching state. Specifically, the solar-driven evaporation rate and voltage generation reach 1.38 kg/m²/h (with a conversion efficiency of 83.1%) and 363 mV under 1 sun irradiation, respectively. Notably, this designed nanofluidic system suffers negligible performance depreciation after 30 h of operation and washing 15 times, which indicates its outstanding stability and reusability. This facile design of the asymmetric nanofluidic photothermal system may provide prospective opportunities for scaling up sustainable freshwater and electric power production.

Impact of PEGDA photopolymerization in micro-stereolithography on 3D printed hydrogel structure and swelling

3D printing complex architectures of responsive-hydratable polymers are enabled by stereolithography via photopolymerization. Yet, insufficient crosslinking leads to compromised structural integrity of the photopolymerized samples, which affects the functionality and reliability of hydrogel devices significantly. Here we investigate how curing parameters and ink formulation affect 3D printed PEGDA samples by using a combination of microfabrication, structural characterization, and reactive coarse-grained molecular dynamics simulation. Our findings show that the degree of curing exhibits a graded profile from confocal Raman spectroscopy and submicron pores from atomic force microscopy, both of which are also observed in our molecular simulations. Moreover, with environmental scanning electron microscopy, we probe the microscopic swelling and bending dynamics of 3D printed hydratable PEGDA structures as well as their structural integrity. Our in-depth characterization results reveal how hydrogel elasticity and irreversible densification due to pore formation highly depends on the exposure time, light intensity and the associated degree of crosslinking. This work provides new molecular insights into processing-structure relation in stereolithography 3D printing.

Reed Leaves Inspired Silica Nanofibrous Aerogels with Parallel-Arranged Vessels for Salt-Resistant Solar Desalination

Sufficient and clean freshwater is still out of reach for billions of people around the world. Solar desalination from brine is regarded as one of the most promising proposals to solve this severe crisis. However, most of the reported evaporators to date still suffer from the decreasing evaporation rate caused by salt crystallization accumulated on their surface. Here, inspired by the vascular tissue structure, transpiration, and antifouling function of reed leaves, we design biomimetic hierarchical nanofibrous aerogels with parallel-arranged vessels and hydrophobic surfaces for highly efficient and salt-resistant solar desalination. Foldable vessel walls and flexible silica nanofibers give the reed leaf-inspired nanofiber aerogels (R-NFAs) excellent mechanical properties and enable them to withstand repeated compression. Besides, the R-NFAs can efficiently absorb sunlight (light absorption efficiency: 94.8%) and evaporate the brine to vapor, similar to reed leaves (evaporation rate: 1.25 kg m^-2 h^-1 under 1 sun). More importantly, enabled by the hydrophobic surfaces and parallel-arranged vessels, the R-NFAs can work stably in high-concentration brine (saturated, 26.3 wt %) under high-intensity light (up to 6 sun), demonstrating potent salt resistance. It is expected that R-NFAs with combined antisalt pore and surface structures will provide a designed concept for salt-resistant solar desalination.

A Bioinspired Elastic Hydrogel for Solar-Driven Water Purification

The global demand for clean and safe water will continue to grow well into the 21st century. Moving forward, the lack of access to clean water, which threatens human health and strains precious energy resources, will worsen as the climate changes. Therefore, future innovations that produce potable water from contaminated sources must be sustainable. Inspired by nature, a solar absorber gel (SAG) is developed to purify water from contaminated sources using only natural sunlight. The SAG is composed of an elastic thermoresponsive poly(N-isopropylacrylamide) (PNIPAm) hydrogel, a photothermal polydopamine (PDA) layer, and a sodium alginate (SA) network. Production of the SAG is facile; all processing is aqueous-based and occurs at room temperature. Remarkably, the SAG can purify water from various harmful reservoirs containing small molecules, oils, metals, and pathogens, using only sunlight. The SAG relies on solar energy to drive a hydrophilic/hydrophobic phase transformation at the lower critical solution temperature. Since the purification mechanism does not require water evaporation, an energy-intensive process, the passive solar water-purification rate is the highest reported. This discovery can be transformative in the sustainable production of clean water to improve the quality of human life.

Photothermal Membrane Distillation toward Solar Water Production

Freshwater production is one of the biggest global challenges today. Though desalination can provide a climate-independent source of clean water, the process requires a high energy consumption. Emerging advancement of photothermal nanomaterials and the urgent demand for a green technology transition have reinvigorated the established solar distillation technology. The current development of photothermal vaporization focuses on material innovation and interfacial heating, which largely emphasizes vapor generation efficiency, without considering pragmatic water collection. Moreover, salt accumulation is another critical issue of seawater solar-driven vaporization. The incorporation of photothermal materials into a photothermal membrane distillation (PMD) solar evaporator design harmoniously resolves these issues through combination of renewable energy and efficient interfacial distillation, to achieve the ultimate goal of practical saline water into freshwater conversion. At this juncture, it is imperative to review the recent opportunities and progresses of the PMD system. Here, the fundamental photothermal processes, strategies for efficient evaporator design, evaluation of various criteria for photothermal material incorporation with desired properties, discussions on desalination, water treatment, and energy generation applications are covered. Guidelines in material and system designs to further advance the PMD system that is highly promising in delivering portable water for both large-scale and decentralized systems are provided.

Self-contained Janus Aerogel with Antifouling and Salt-Rejecting Properties for Stable Solar Evaporation

Janus structural interfacial vaporization by separating the solar absorber from the bulk working fluid has attracted tremendous attention due to its low heat losses and high solar conversion efficiency for desalination, water purification, energy generation, etc. However, a totally separated double-deck structure with a discontinuous interfacial transition and inefficient photothermic materials undermines its long-term use and large-scale practical exploitation. Herein, a low-cost Janus monolithic chitosan aerogel with continuous aligned run-through microchannels has been demonstrated to have a highly efficient photothermic effect on seawater desalination and wastewater purification. The top solar absorber layer enhances broadband light absorption and photothermal conversion efficiency via the multiple internal reflection of incident light in the aligned microchannels. Moreover, the insulating/hydrophilic bottom layer promotes water transportation and heat localization, and simultaneously prevents salt/fouling accumulation. As a result, a long-term solar vaporization rate of ∼1.76 kg m^-2 h^-1 is achieved, corresponding to a light-to-vapor efficiency of ∼91% under 1 sun irradiation. Notably, the large-vessel microchannels throughout the aerogel and favorable swelling property provide sufficient water replenishment and storage for completely isolating self-contained evaporation, illustrating an enhanced and time-extended self-contained solar steam generation. Such a low-cost bilayer aerogel with remarkable cycling stability in various fluids offers potential opportunities for freshwater production in remote rural areas.

Salt partitioning in ionized, thermo-responsive hydrogels: perspective to water desalination

Charged hydrogels are capable of swelling in aqueous salt solutions, whereby part of the salt ions is repelled due to the presence of fixed charged groups inside the hydrogel. This effect creates a concentration gradient between the absorbed solution and the surrounding fluid known as salt partitioning, offering a potential for these materials to be employed to desalinate saltwater. If the charged hydrogels are thermo-sensitive as well, then the purer, absorbed solution can be recovered by shrinking the hydrogels upon temperature change. To tailor that potential in water-purification and desalination applications, the main parameters influencing the salt partitioning, the deswelling of the hydrogels, and the recovery of water must be understood. In this paper, we analyze these factors based on equations derived from the Donnan theory. In addition, hydrogels composed of N-isopropyl acrylamide and acrylic acid are synthesized, and their salt rejection efficiency in a model desalination experiment is studied. A comparison of the experimental and the theoretical results demonstrates that the charge density of the hydrogels at their equilibrium swelling and the degree of water recovery are two parameters controlling the salt rejection efficiency. These parameters are individually controlled by the content of the ionic groups and the degree of cross-linking of the gel polymer network. In addition, the prediction of the theory and the experimental results demonstrate that the salt rejection efficiency can be significantly improved if a second water recovery step is performed by a secondary increase in the temperature in the deswelling process.

Nanocellulosics: Benign, Sustainable, and Ubiquitous Biomaterials for Water Remediation

Water is critical for all lives to thrive. Access to potable and safe water has been argued to rank top among the prerequisites for defining the standard of living of a nation. However, there is a global decline in water quality due to human activities and other factors that severely impact freshwater resources such as saltwater intrusion and natural disasters. It has been pointed out that the millions of liters of industrial and domestic wastewater generated globally have the potential to help mitigate water scarcity if it is appropriately captured and remediated. Among the many initiatives to increase access to clean water, the scientific community has focused on wastewater remediation through the utilization of bioderived materials, such as nanocellulosics. Nanocellulosics, derived from cellulose, have the advantages of being ubiquitous, nontoxic, and excellent adsorbents. Furthermore, the surface properties of nanocellulosic materials can easily be modified. These advantages make them promising materials for water remediation applications. This perspective highlights the most important new developments in the application of nanocellulosics in water treatment technologies, such as membrane, adsorption, sensors, and flocculants/coagulants. We also identify where further work is urgently required for the widespread industrial application of nanocellulosics in wastewater treatment.