Interfacial Solar Evaporation by a 3D Graphene Oxide Stalk for Highly Concentrated Brine Treatment

Surface Roughness Engineering for High-Salt-Tolerant Solar Evaporator with Enhanced Efficiency in Sustainable Desalination

The accumulation of dense crystal layers on solar evaporators compromises the performances by reducing light absorption efficiency and obstructing water transport channels, ultimately diminishing evaporation rate. To mitigate this issue, spatially separated crystallization sites can be engineered on the evaporator surface to disrupt salt adhesion and prevent dense layers formation. In this study, a 3D column-shaped wood evaporator (KOH-activated carbon- delignified wood (KAC-DW)) is developed by coating DW with KAC. The KAC coating creates microstructured surface featuring abundant protrusions (≈144 mm-2, each 20 μm in height), which effectively inhibit salt crystal adhesion. Under 1 kW m-2 solar radiation with a 15 wt% NaCl solution, the KAC-DW evaporator achieves an impressive water evaporation rate of 8.18 kg m-2 h-1 over 96 h (0 m s-1 wind speed)-more than double the performance of uncoated DW (3.91 kg m-2 h-1). This enhancement stems from two key mechanisms: 1) the KAC protrusions prevent dense crystal layer formation, preserving open surface channels for evaporation, and 2) they promote the growth of loose salt crystals, thereby expanding the effective evaporation area and further boosting the evaporation rate.

Optimization of Delignified Wood Rods for Interfacial Solar Evaporation

Interfacial solar evaporation using three-dimensional evaporator materials has shown promise to achieve high evaporation rates exceeding the photothermal limit for water treatment and resource recovery processes. However, challenges remain in optimizing the material geometry to balance the vertical capillary uptake of water and the rate of evaporation to achieve both stable and high evaporation rates. Delignified wood can serve as a highly porous and hydrophilic substrate material to achieve high evaporation rates. In this work, we designed a suspended biochar-coated delignified wood rod evaporator and investigated the influence of its geometric parameters on its evaporation performance. The height of the evaporator exposed to air for evaporation was observed to be an important parameter in governing the evaporation rate, as shorter evaporators limited the available surface area for evaporation, but taller evaporators could not achieve sufficient rates of capillary uptake to maintain stable evaporation rates over 24 h under 1-sun illumination (1 kW m-2). The exposed height of the evaporator was optimized to achieve an average hourly evaporation rate of 3.05 ± 0.23 kg m-2 h-1, which could be maintained in saline solutions containing up to 5 wt % NaCl.

High-Performance Roller Tube-Shaped Copper Foam Solar Evaporators with Copper Foil Integration for Enhanced Thermal Control

The growing global freshwater shortage and climate crisis are increasing the dependence on water desalination technologies. To meet this pressing demand, innovative solutions that utilize renewable energy sources like solar power, with an emphasis on improving evaporation processes, are essential. Although considerable research has been conducted on a variety of materials and structural designs, the development of highly efficient solar steam generators for large-scale use remains a challenge. Here, we introduce a novel design: a two-layer vertical evaporation cylinder in a roll format that integrates a small, inverted cone-shaped pure copper (ICPC) foam and etched copper foil to enhance thermal management. The primary objective is to advance direct solar desalination and interfacial evaporation by effectively capturing both direct and reflected light while preventing salt accumulation through self-cleaning. This design leverages the optical properties of the three materials─absorption, reflection, and transmission─while providing deeper insights into seawater behavior within the foam's interconnected pores. It also addresses common challenges encountered by traditional solar evaporators, such as salt buildup, uncontrolled water flow, and poor thermal management. This cutting-edge solar evaporation system exhibits exceptional performance, remarkable adaptability to diverse configurations, and represents a breakthrough in sustainable chemistry, featuring an advanced engineering design that achieves an outstanding evaporation rate of 17.15 kg·m-2·h-1 under 1 sun irradiation.

Solar evaporator coupled with strong/weak convection and its cascade utilization

Modulating the macro/nanoarchitecture of evaporators to effectively harness diverse renewable energy sources is of paramount importance for optimizing the performance of solar-driven interfacial evaporation. Inspired by the geometric structure of a windmill, we designed an innovative solar evaporator that expertly harnesses both strong and weak convection. During the purification of heavy metal wastewater, the maximum evaporation rate can reach 4.95 kg m-2 h-1 under one sun irradiation by introducing an ultralow wind flow (0.1 m s-1), yielding an evaporation rate that is twice that of traditional evaporators. However, the gradual deposition of inorganic salt sediments on the evaporator surface is clearly observable. To address this issue, we present several innovative proof-of-concept cascade treatments that significantly extend the evaporator's operational lifespan. The innovative design and exceptional performance of this solar evaporator open avenues for advancements in sustainable water treatment, energy generation, and environmental remediation.

A heterogeneous nanocomposite architecture with contrasting thermal conductivity and hydrophilicity for synergistic solar-thermal storage and evaporation

Solar-driven evaporation is an eco-friendly and cost-effective freshwater production technique. It is essential to maintain continuous evaporation under intermittent sunlight for practical application. Integrating solar-thermal storage with evaporation is a promising solution. However, existing designs struggle to balance high evaporation rates with effective thermal energy storage in a single device due to conflicting thermal conductivity and hydrophilicity requirements for the two functions. Here, we develop a heterogeneous 3D graphene architecture featuring a hydrophilic gradient hydrogel evaporator (GHE) encircled by a hydrophobic thermal storage composite (TSC). The thermally conductive and hydrophobic TSC made from 3D graphene and paraffin wax enhances solar-thermal conversion and storage, while the thermally insulative and hydrophilic GHE featuring radiating channels with gradient pores facilitates efficient heat localization and water transport. This structurally and compositionally separated design leverages contrasting thermal and hydrophilic properties, achieving a high evaporation rate of 3.6 kg m-2 h-1 under direct sunlight and extending the evaporation at a rate of 2.7 kg m-2 h-1 for 30 minutes even when sunlight dims. The integrated device produces twice as much water as the hydrogel evaporator alone under intermittent lighting. This work presents an effective strategy for extending water generation capabilities under intermittent sunlight.

Forward Osmosis Desalination Using Thermoresponsive Ionic Liquids: Bench-Scale Demonstration and Cost Analysis

Forward osmosis (FO) desalination using thermoresponsive ionic liquid (IL)-water mixtures is a promising technology for treating nontraditional water sources. However, its demonstration has primarily been at the lab-scale, with water flux and recovery values that are not representative of realistic applications. In this work, the performance of tetrabutyl-phosphonium trifluoroacetate (P4444TFA), as well as a new dual draw of P4444TFA with tetrabutyl-ammonium trifluoroacetate (N4444TFA) is characterized. The dual draw combines the higher osmolality of one IL with the lower critical solution temperature (LCST) of the second IL to outperform its constituents at the same total concentration of IL in water (70 wt %). Experiments were first performed in a lab-scale coupon tester to understand the effects of draw osmotic pressure and viscosity on water flux through the membrane. Bench-scale experiments were then performed in an element tester with a 1 m2 membrane area to evaluate the performance of IL-based FO for the desalination of produced water feed from oil and gas. Specifically, 10 kg of IL-water draw solution was used with 3 kg of real produced water feed, resulting in water recoveries of 60% with initial and final water fluxes of 14 LMH and 3 LMH, respectively. The bench-scale experimental results were used as inputs for a cost analysis, yielding a levelized cost of water (LCOW) of $1.18 per m3. This reveals the potential of IL-based draw solutions for cost-effective desalination of challenging feedwaters using FO.

Surface Oxygen Vacancy Engineering for Enhanced Volatile Organic Compounds Removal in Solar-Interfacial Water Evaporation

Solar-interfacial water-vapor conversion has emerged as a promising method for clean water production, particularly in water-scarce regions, but a major challenge is the volatile organic compounds (VOCs) along with water vapor, leading to polluted condensed water. This study introduces a novel design strategy that leverages surface oxygen vacancies (OVs) in photocatalysts to maximize both oxygen (O2) utilization from the air and photocarrier efficiency at the air-water interface, building upon previous research that demonstrated that oxygen concentration at the interface can be significantly higher than that in bulk water. By enhancing oxygen adsorption and facilitating charge carrier separation, OVs significantly improve reactive oxygen species (ROS, including ·O2- and ·OH) generation and overall photocatalytic activity. As a demonstration, the surface OVs-engineered BiOCl-based photocatalytic solar interfacial evaporator demonstrated a 3.41-fold increase in VOC (phenol) removal efficiency compared to a conventional system, achieving over 99.6% VOC removal in condensed water and maintaining a high water vapor generation flux of 1.90 kg/m2/h. This innovative design was further validated using ZnO-based photocatalysts, demonstrating the broad applicability of OV-engineering in interfacial systems. By fully utilizing both the high oxygen content at the air-water interface and improving photocarrier dynamics, this approach represents a significant advancement in photocatalytic water treatment technologies, offering a scalable and highly efficient solution for VOC removal and clean water production.

High-performance and scalable contactless solar evaporation with 3D structure

Solar evaporation is a sustainable pathway for diverse water treatment technologies. The contactless evaporation stands out for its superior anti-contamination property. However, the evaporation performance is significantly limited by the non-contact heat transport, which is more pronounced in scalable applications with suppressed vapor escaping and tilted solar irradiation. Here, we propose a high-performance contactless solar evaporation design with three-dimensional (3D) solar-heating and vapor-escaping structure. Our theoretical analysis reveals that mass transport is the true bottleneck of contactless solar evaporation in scalable application, and can be significantly improved by our 3D design. A laboratory solar evaporation rate of 1.03 kg m-2 h-1 was demonstrated with our 3D design, which was 110% higher than the conventional design. Owing to the enhanced solar harvesting and transport, an average evaporation rate of 1.21 kg m-2 h-1 was demonstrated in outdoor field test with dilute solar flux of 589.98 W m-2. The scalability of 3D design was proved by the minimal difference (3%) in natural seawater evaporation performance between the small and large 3D devices. This work provides a robust, high-performance, and scalable solution for solar evaporation, especially for those scenarios with limited tolerance for contamination.

Mineral Scaling in 3D Interfacial Solar Evaporators─A Challenge for Brine Treatment and Lithium Recovery

In this work, we analyzed the effects of mineral scaling on the performance of a 3D interfacial solar evaporator, with a focus on the cations relevant to lithium recovery from brackish water. The field has been rapidly moving toward resource recovery applications from brines with higher cation concentrations. However, the potential complications caused by common minerals in these brines other than NaCl have been largely overlooked. Therefore, in this study, we thoroughly examined the effects of two common cations (calcium and magnesium) on the long-term solar evaporation performance of a 3D graphene oxide stalk. The 3D stalk can achieve an evaporation flux as high as 17.8 kg m-2 h-1 under one-sun illumination, and accumulation of NaCl on the stalk surface has no impact. However, the presence of CaCl2 and MgCl2 significantly reduces the evaporative flux even in solutions lacking scale-forming anions. A close examination of scale formation during long-term evaporation experiments revealed that CaCl2 and MgCl2 tend to precipitate out within the stalk, thus blocking water transport through the stalk and significantly dropping the evaporation rates. These findings imply that research attention is needed to modify and optimize the internal water transport channels for 3D evaporators. Additionally, we emphasize the importance of testing realistic mixtures─including prominent divalent cations─ and testing long-term operations in interfacial solar evaporation research and investigating approaches to mitigate the negative impacts of divalent cations.

Welding Pollen-Based Solar Evaporator for Clean Water Production

The world faces a trade-off between water availability and food supply, as agricultural irrigation consumes the largest freshwater globally. Inspired by inherent water transport channels in plants, a cost-effective welding pollen-based solar evaporator (PSE) is developed to obtain clean water from seawater desalination. Based on the convex and folded surface structure of natural pollen (Helianthus annuus) and the porous structure of welding pollen evaporator interconnection, the PSE reveals an efficient evaporation rate of 1.86 kg m-2 h-1 under one-sun illumination and further exhibits excellent cycling performance for 10 cycles tested in 7.0 wt.% saline water without salt accumulation. In addition, PSE has superior mechanical stability (3.44 MPa) and remains stable after being immersed in pH 1 and 14 solutions for 24 h without sacrificing mechanical properties. Importantly, the work has demonstrated the success of the freshwater collected from the evaporation process, which can effectively facilitate the cultivation of lettuce, rice, and wheat. These findings highlight the practical application of pollen as a low-cost, eco-friendly natural resource in interfacial solar evaporation. Furthermore, they inspire addressing current global water scarcity and promoting sustainable agriculture.

Refractory plasmonic material based floating solar still for simultaneous desalination and electricity generation

Floating interfacial solar evaporation offers a land-saving, eco-friendly, and low-infrastructure alternative for freshwater production. However, challenges include maximizing heat localization, preventing salt accumulation, and operating under harsh environmental conditions. This work demonstrates a plasmonic titanium carbide (TiC) nanoparticle (NP)-based floating solar desalination system that produces clean water using sunlight on saline water sources. The components of the floating still were carefully chosen to optimize freshwater output, with TiC produced by upcycling tire waste. Outdoor experiments in Halifax, Canada, where solar insolation reached around 6 kW m-2 day-1, resulted in daily water yields of up to 3.67 L m-2, corresponding to a solar-to-vapor conversion efficiency of 40%. Water can be produced at a cost of $0.0086 L-1, and the still can be modified to generate thermoelectricity, enabling small onboard devices to test water quality without external electricity. This study contributes to the development of scalable floating solar desalination systems, providing potable water for water-stressed communities.

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.

Carbon Ink Enhanced Calcium Alginate-Based Hydrogel with Response Surface Methodology Optimized for Solar-Driven Salt-Tolerant Desalination

The global shortage of freshwater resources is becoming more and more serious; therefore, it is necessary to obtain freshwater by desalinating seawater resources. Solar-driven interfacial photothermal evaporation, which is an environmentally friendly and energy-efficient technology, has been used to desalinate seawater for water purification and production. Herein, the IPCA hydrogel with abundant pores consisting of carbon ink as a photothermal conversion material and PU sponge loaded with calcium alginate as a water transport medium was successfully prepared and used to obtain portable water. The parameters of the synthesized IPCA are optimized by Response Surface Methodology analysis, and it was found that the IPCA exhibits a high evaporation efficiency of 3.779 kg m-2 h-1 and up to 95.98% of photothermal conversion capacity under one solar intensity. It maintains a high evaporation efficiency and salt resistance after 10 cycles of evaporation in actual seawater. Moreover, IPCA shows a high removal of various organic dye pollutants in wastewater. The results suggest a new approach for the preparation of simple, efficient, and green solar evaporators in practical application.

A 3D self-floating solar vapor generator based on a novel self-healing aero-hydrogel containing peach gum polysaccharide with durability and continuous operation

Solar energy interfacial evaporation represents a promising and sustainable approach with considerable potential for seawater desalination and wastewater treatment. Nonetheless, creating durable evaporators for continuous operation presents a challenge. Motivated by natural self-healing mechanisms, this study developed a novel 3D hybrid aero-hydrogel, which exhibited a self-healing efficiency of 89.4 % and an elongation at break post-healing of 637.7 %, featuring self-healing capabilities and continuous operation potential. Especially, the incorporation of hyperbranched water-soluble polymers (peach gum polysaccharide) endow the final solar water evaporators with a lower evaporation enthalpy of water, resulting in that the refined SVG3, with a notable water surface architecture and an expanded evaporation area, achieved a steam generation rate of 2.13 kg m-2 h-1 under 1 Sun. Notably, SVG2 achieved a high evaporation rate of 2.43 kg m-2 h-1 with the combined energy input of 1 Sun and 6 V, significantly surpassing the rate of 1.96 kg m-2 h-1 without voltage input. The results indicate that electrical energy significantly enhances and synergizes with SVG, facilitating continuous operation both day and night through the combined use of solar energy and electrical input. This study offers insightful perspectives for the strategic design of multifunctional hydrogels for solar water evaporation.

An in-depth study of integrating cascaded photocatalytic H2O2 generation and activation with solar-driven interfacial evaporation for in-situ organic contaminant remediation

Integrating cascaded photocatalytic H2O2 generation and subsequent activation of H2O2 (into ·OH radicals) with solar-driven interfacial evaporation techniques offers an effective and sustainable approach for in-situ treating water contaminated with organic substances. Unlike traditional water-dispersed catalysts, the interfacial evaporation approach presents unique challenges in photocatalytic reactions. We explored these dynamics using an AgI/PPy/MF interfacial photothermal set, achieving H2O2 production efficiency (approximately 1.53 mM/g/h) - three times higher than submerged counterparts. This efficiency is attributed to exceptional solar light absorption (about 95 %), a significant surface photothermal effect (raising temperatures by approximately 36 °C), and enhanced oxygen availability (38 times more than in water), all characteristic of the interfacial system. The in-situ activation of H2O2 into ·OH notably improves the degradation of organic pollutants, achieving up to 99 % removal efficiency. This comprehensive analysis highlights the potential of combining photocatalytic H2O2 processes with interfacial evaporation for efficiently purifying organically polluted water.

Electrified Solar Zero Liquid Discharge: Exploring the Potential of PV-ZLD in the US

Current brine management strategies are based on the disposal of brine in nearby aquifers, representing a loss in potential water and mineral resources. Zero liquid discharge (ZLD) is a possible strategy to reduce brine rejection while increasing the resource recovery from desalination plants. However, ZLD substantially increases the energy consumption and carbon footprint of a desalination plant. The predominant strategy to reduce the energy consumption and carbon footprint of ZLD is through the use of a hybrid desalination technology that integrates renewable energy. Here, we built a computational thermodynamic model of the most mature electrified hybrid technology for ZLD powered by photovoltaic (PV). We examine the potential size and cost of ZLD plants in the US. This work explores the variables (geospatial and design) that most influence the levelized cost of water and the second law efficiency. There is a negative correlation between minimizing the LCOW and maximizing the second-law. And maximizing the second-law, the states that more brine produces, Texas is the location where the studied system achieves the lowest LCOW and high second-law efficiency, while California is the state where the studied system is less favorable. A multiobjective optimization study assesses the impact of considering a carbon tax in the cost of produced water and determines the best potential size for the studied plant.

High Performance Solar-Driven Power-Water Cogeneration for Practical Application: From Micro/Nano Materials to Beyond

Solar-driven water-electricity cogeneration is a promising strategy for tackling water scarcity and power shortages. However, comprehensive reviews on performance, scalability, commercialization, and power density are lacking. This Perspective presents an overview of recent developments and insights into the challenges and future outlooks for practical applications in this area. We summarize recent advances in high-efficiency water production, focusing on rapid evaporation and condensation. Then we categorize power-water cogeneration systems by power generation mechanisms like steam, evaporation, salinity gradient, photovoltaics, and temperature gradient, providing a comprehensive summary of the performance and applicability of these systems in different scenarios. Finally, we highlight challenges in current systems, considering nanoscale mechanisms and large-scale manufacturing, while also exploring potential trends for future practical applications.

Natural-inspired hierarchic double-Janus solar evaporator for stable clean water production from high-salinity emulsions

Interfacial solar evaporation shows great potential in clean water production, emulsions separation, and high-salinity brine treatment. However, it remains challenging for the evaporators to maintain a high evaporation rate in the high-salinity emulsions due to the co-pollution of salt and oil. Herein, we first proposed a hierarchic double-Janus solar evaporator (HDJE) with a hydrophobic salt-rejecting top layer and oil-rejecting bottom layer. Compared to the traditional one, HDJE could treat industrial high-salinity oil-in-water emulsions stably for over 70 h, with a stable average evaporation rate of 1.73 kg m-2 h-1 and a high purification efficiency of up to 99.8 % for oil and ions. It was also verified that HDJE could be used for high-efficiency purification of oily concentrated seawater outdoor. An average water production rate of 3.59 kg m-2 d-1 and a TOC removal ratio of over 98 % was obtained. In conclusion, this study provides a novel way to effectively dispose of high-salinity oily wastewater.

KOH Activated Carbon Coated 3D Wood Solar Evaporator with Highest Water Transport Height and Evaporation Rate for Clean Water Production

The water evaporation rate of 3D solar evaporator heavily relies on the water transport height of the evaporator. In this work, a 3D solar evaporator featuring a soil capillary-like structure is designed by surface coating native balsa wood using potassium hydroxide activated carbon (KAC). This KAC-coated wood evaporator can transport water up to 32 cm, surpassing that of native wood by ≈8 times. Moreover, under 1 kW m-2 solar radiation without wind, the KAC-coated wood evaporator exhibits a remarkable water evaporation rate of 25.3 kg m-2 h-1, ranking among the highest compared with other reported evaporators. The exceptional water transport capabilities of the KAC-coated wood should be attributed to the black and hydrophilic KAC film, which creates a porous network resembling a soil capillary structure to facilitate efficient water transport. In the porous network of coated KAC film, the small internal pores play a pivotal role in achieving rapid capillary condensation, while the larger interstitial channels store condensed water, further promoting water transport up more and micropore capillary condensation. Moreover, this innovative design demonstrates efficacy in retarding phenol from wastewater through absorption onto the coated KAC film, thus presenting a new avenue for high-efficiency clean water production.

Exploring Recent Developments in Graphene-Based Cathode Materials for Fuel Cell Applications: A Comprehensive Overview

Fuel cells are at the forefront of modern energy research, with graphene-based materials emerging as key enhancers of performance. This overview explores recent advancements in graphene-based cathode materials for fuel cell applications. Graphene's large surface area and excellent electrical conductivity and mechanical strength make it ideal for use in different solid oxide fuel cells (SOFCs) as well as proton exchange membrane fuel cells (PEMFCs). This review covers various forms of graphene, including graphene oxide (GO), reduced graphene oxide (rGO), and doped graphene, highlighting their unique attributes and catalytic contributions. It also examines the effects of structural modifications, doping, and functional group integrations on the electrochemical properties and durability of graphene-based cathodes. Additionally, we address the thermal stability challenges of graphene derivatives at high SOFC operating temperatures, suggesting potential solutions and future research directions. This analysis underscores the transformative potential of graphene-based materials in advancing fuel cell technology, aiming for more efficient, cost-effective, and durable energy systems.

Developing Salt-Rejecting Evaporators for Solar Desalination: A Critical Review

Solar desalination, a green, low-cost, and sustainable technology, offers a promising way to get clean water from seawater without relying on electricity and complex infrastructures. However, the main challenge faced in solar desalination is salt accumulation, either on the surface of or inside the solar evaporator, which can impair solar-to-vapor efficiency and even lead to the failure of the evaporator itself. While many ideas have been tried to address this ″salt accumulation″, scientists have not had a clear system for understanding what works best for the enhancement of salt-rejecting ability. Therein, for the first time, we classified the state-of-the-art salt-rejecting designs into isolation strategy (isolating the solar evaporator from brine), dilution strategy (diluting the concentrated brine), and crystallization strategy (regulating the crystallization site into a tiny area). Through the specific equations presented, we have identified key parameters for each strategy and highlighted the corresponding improvements in the solar desalination performance. This Review provides a semiquantitative perspective on salt-rejecting designs and critical parameters for enhancing the salt-rejecting ability of dilution-based, isolation-based, and crystallization-based solar evaporators. Ultimately, this knowledge can help us create reliable solar desalination solutions to provide clean water from even the saltiest sources.

Identifying the Stripping of Oxide Debris from Graphene Oxide: Evidence from Experimental Analysis and Molecular Simulation

In this study, characteristics of oxidation debris (OD) and its stripping mechanism from graphene oxide (GO) were explored. The results demonstrated that OD contains three components, namely, protein-, fulvic acid-, and humic acid-like substances; among these, protein-like substances with lower molecular weight and higher hydrophilicity were most liable to be stripped from GO and were the primary components stripped from GO at pH < 10, whereas humic acid- and fulvic acid-like substances were stripped from GO at pH > 10. During the stripping of OD, hydrogen bonds from carboxyl and carbonyl were the first to break, followed by hydrogen bonds from epoxy. Subsequently, π-π interactions were broken, and hydrogen bond interactions induced by hydroxyl groups were the hardest to break. After the stripping of OD, the recombination of OD on GO was observed, and regions containing relatively fewer oxygen-containing functional groups were favorable binding sites for the readsorbed OD. The stripping and recombination of OD on GO resulted in an uneven GO surface, which should be considered during the development of GO-based environmental materials and the evaluation of their environmental behavior.

Engineering High-Tortuosity 3D Gradient Structure and CFD-Assisted Multifield Analysis for Solar Interfacial Evaporation

Solar interfacial evaporation is a promising method for solving the global shortage of fresh water. While 2D evaporators can efficiently localize solar-converted heat at the thin layer of the water-air interface, 3D solar evaporators can maximize energy reutilization while maintaining effective mass transport ability, few studies are conducted to explore the effect of gradient porosity on evaporation performance. In this study, a multifield assisted strategy based on a gradient 3D structure with high tortuosity is proposed, which creates a thermal field environment for efficient evaporation through high absorption of sunlight and excellent photothermal conversion and uses the gradient structure to optimize the internal pressure field to enhance water evaporation and transport. This hierarchically nanostructured solar absorber, with porosity inhomogeneity-induced pressure gradient and optimized temperature management, is a valuable design idea for manufacturing a more efficient 3D solar evaporator in the field of seawater desalination. Owing to the understanding of optimizing the dimension by various simulation parameters, the evaporation efficiencies of such structures are found to be 165.7%, suppressing the most evaporator. Moreover, it can provide new ideas and references for the fields of mass transfer and thermal management.

The Future of Municipal Wastewater Reuse Concentrate Management: Drivers, Challenges, and Opportunities

Water reuse is rapidly becoming an integral feature of resilient water systems, where municipal wastewater undergoes advanced treatment, typically involving a sequence of ultrafiltration (UF), reverse osmosis (RO), and an advanced oxidation process (AOP). When RO is used, a concentrated waste stream is produced that is elevated in not only total dissolved solids but also metals, nutrients, and micropollutants that have passed through conventional wastewater treatment. Management of this RO concentrate─dubbed municipal wastewater reuse concentrate (MWRC)─will be critical to address, especially as water reuse practices become more widespread. Building on existing brine management practices, this review explores MWRC management options by identifying infrastructural needs and opportunities for multi-beneficial disposal. To safeguard environmental systems from the potential hazards of MWRC, disposal, monitoring, and regulatory techniques are discussed to promote the safety and affordability of implementing MWRC management. Furthermore, opportunities for resource recovery and valorization are differentiated, while economic techniques to revamp cost-benefit analysis for MWRC management are examined. The goal of this critical review is to create a common foundation for researchers, practitioners, and regulators by providing an interdisciplinary set of tools and frameworks to address the impending challenges and emerging opportunities of MWRC management.

A Self-Adaptive and Regenerable Hydrogel Interfacial Evaporator with Adjustable Evaporation Area for Solar Water Purification

Solar-driven interfacial evaporation is a potential water purification solution. Here, a novel regenerable hydrogel interfacial evaporator is designed with tunable water production. Such an evaporator is fabricated by readily mixing hydroxypropyl chitosan (HPCS) and dibenzaldehyde-functional poly(ethylene glycol) (DF-PEG) at ambient conditions. Dynamic Schiff base bonds bestow on the HPCS/DF-PEG hydrogel (HDH) evaporator self-adaptivity and pH responsiveness. The as-prepared HDH is enabled to spontaneously change shape to adapt to different molds, endowing the evaporator with adjustable evaporation area. The water production performance of the intelligent evaporator is first evaluated using tunable evaporation index (TEI, the tunable evaporated water mass per hour), which can be altered from 0 kg h-1 to 3.21 kg h-1 under one sun. Besides, the large-scale evaporator can be expediently fabricated by virtue of the self-adaptivity. Benefiting from the pH responsiveness, the HDH evaporator is successfully regenerated with the removal of organic dye by the liquefaction-dialysis-regeneration operations. Meanwhile, the re-created evaporator maintains the self-adaptive characteristic and almost constant water evaporation rate compared to that of the initial evaporator. Therefore, this distinctive concept provides a facile strategy to develop smart and recyclable solar-driven interfacial evaporators for flexible water purification.

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.

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.

Prioritizing the Best Potential Regions for Brine Concentration Systems in the USA Using GIS and Multicriteria Decision Analysis

We propose a methodology for identifying and prioritizing the best potential locations for brine concentration facilities in the contiguous United States. The methodology uses a geographic information system and multicriteria decision analysis (GIS-MCDA) to prioritize the potential locations for brine concentration facilities based on thermodynamic, economic, environmental, and social criteria. By integrating geospatial data with a computational simulation of a real brine concentration system, an objective weighting method identifies the weights for 13 subcriteria associated with the main criteria. When considering multiple dimensions for decision making, brine concentration facilities centered in Florida were consistently selected as the best location, due to the high second-law efficiency, low transportation cost, and high capacity for supplying municipal water needs to nearby populations. For inland locations, Southeast Texas outperforms all other locations for thermodynamic, economic, and environmental priority cases. A sensitivity analysis evaluates the consistency of the results as the priority of a main criterion varies relative to other decision-making criteria. Focusing on a single subcriterion misleads decision making when identifying the best location for brine concentration systems, identifying the importance of the multicriteria methodology.

Pickering Emulsion Templated 3D Cylindrical Open Porous Aerogel for Highly Efficient Solar Steam Generation

Porous-structured evaporators have been fabricated for achieving a high clean water throughput due to their maximized surface area. However, most of the evaporation surfaces in the porous structure are not active because of the trapped vapor in pores. Herein, a three-dimensional (3D) cylindrical aerogel-based photothermal evaporator with a disordered interconnected hierarchical porous structure is developed via a Pickering emulsion-involved polymerization method. The obtained cotton cellulose/aramid nanofibers/polypyrrole (CAP) aerogel-based evaporator achieved all-cold evaporation under 1.0 sun irradiation, which not only completely eliminated energy loss via radiation, convection, and conduction, but also harvested massive extra energy from the surrounding environment and bulk water, thus significantly increasing the total energy input for vapor generation to deliver an extremely high evaporation rate of 5.368 kg m-2 h-1 . In addition, with the external convective flow, solar steam generation over the evaporator can be dramatically enhanced due to fast vapor diffusion out of its unique opened porous structure, realizing an ultrahigh evaporation rate of 18.539 kg m-2 h-1 under 1.0 sun and 4.0 m s-1 . Moreover, this evaporator can continuously operate with concentrated salt solution (20 wt.% NaCl). This work advances rational design and construction of solar evaporator to promote the application of solar evaporation technology in freshwater production.

Environmental energy enhanced solar-driven evaporator with spontaneous internal convection for highly efficient water purification

Solar-driven interfacial evaporation for water purification is limited by the structural design of the solar evaporator and, more importantly, by the inability to separate the water from volatile organic compounds (VOCs) present in the water source. Here, we report a three-dimensional (3D) bifunctional evaporator based on N-doped carbon (CoNC/CF), which enables the separation of fresh water from VOCs by activating PMS during the evaporation process with a VOC removal rate of 99%. There is abundant van der Waals interaction between peroxymonosulfate (PMS) and CoNC/CF, and pyrrolic N is confirmed as the active site for binding phenol, thus contributing to the separation of phenol from water. With the advantageous features of sufficient light absorption, adequate water storage capacity, and spontaneous internal convection flow on its top surface, the 3D evaporator achieves a high evaporation rate under one sun (1 kW/m2) at 3.16 kg/m2/h. More notably, through careful structural design, additional energy from the environment and water can be utilized. With such a high evaporation rate and satisfactory purification performance, this work is expected to provide a promising platform for wastewater treatment.

Optimized Water Supply in a Solar Evaporator for Simultaneous Freshwater Production and Salt Recycle

Solar desalination has shown great potential in alleviating global water scarcity. However, the trade-off between energy efficiency and salt rejection remains a challenge, restricting its practical applications. In this study, we report a three-dimensional nitrocellulose membrane-based evaporator featuring a high evaporation rate (1.5 kg m-2 h-1) and efficient salt precipitation at the edges. Additionally, the salt is isolated from the photothermal area of the evaporator and falls automatically with a salt recovery rate of 97 g m-2 h-1 in brine with 10 wt % salt content. The distinctive performance is attributed to the precise water supply control, which was adjusted by changing the resistance force and driven force in the evaporator. With a high evaporation rate, stable performance, and specific salt recovery ability, this solar evaporation structure holds great potential in water desalination and resource recovery.

Enhancing Freshwater Production via Customizable and Highly Efficient Solar-Driven Seawater Desalination

Solar-powered water generation is an appealing strategy for cost-effective and energy-sustainable seawater purification/desalination, where rational material selection and device design is crucial. Nevertheless, prevailing carbon-based photothermal materials in such systems still suffer from mediocre steam-to-water efficiency, failing to satisfy an adequate freshwater supply. Herein, we demonstrate a biomimetic corrugated evaporator (CE) affording carbon nanotube (CNT) encapsulated Fe nanocluster-decoration in the pursuit of high-efficiency seawater purification. The thus-customized CE demonstrates a maximum evaporation rate of 4.2 kg m-2 h-1 with a refraction angle of 60° and a water-lifting height of 5.5 cm, outperforming most state-of-the-art carbon-based counterparts. By employing a tailored architectural design and optimized condensing volume, the steam-to-water efficiency increases from 65.8 to 88.2% as the volume enlarges from 0.8 to 5.3 L, further harvesting a peak value of 91% under negative pressure. Light intensity simulation and experimental mechanistic investigation disclose the dual property-performance relationships between evaporator microstructure and evaporation rate, as well as between condensing device volume and steam-to-water efficiency. The universality of the theoretical guidance of this work will offer insight into the development of solar-driven evaporator construction toward simultaneous seawater desalination and clean water generation.

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.

Carbon nanofiber reinforced carbon aerogels for steam generation: Synergy of solar driven interface evaporation and side wall induced natural evaporation

Solar-based interface evaporation (SIE) is a green, efficient and cost-effective technique to harvest fresh water. 3D solar evaporators show their unique advantages in gaining energy from environment and hence possess a higher evaporation rate than 2D evaporators. However, much effort is still required to develop mechanically robust and superhydrophilic 3D evaporators with strong water transportation capability and salt-rejection performance, and at the same time reveal how they gain energy from environment via the natural evaporation. In this work, a novel carbon nanofiber reinforced carbon aerogel (CNFA) is prepared for the SIE. The CNFA has a high light absorption up to 97.2% and outstanding photothermal conversion performance. The heteroatom doping and hierarchically porous structure endow the CNFA with superhydrophilicity and thus powerful water transportation capability and salt rejection performance. Benefiting from synergy of the SIE and side wall induced natural evaporation, the CNFA evaporator exhibits a high evaporation rate and efficiency (as high as 3.82 kg m^-2h^-1 and 95.5%, respectively) with long-term stability and durability. The CNFA can also work normally in high-salinity and corrosive seawater. This study demonstrates a new method to fabricate all-carbon aerogel solar evaporators and provides insights for the effective thermal management during the interface evaporation.

R S, Lim HW, Lee SJ. Conversion of Hazardous Diesel Soot Particles into a Novel Highly Efficient 3D Hydrogel for Solar Desalination and Wastewater Purification

Diesel particulate matter (DPM) generated as vehicular exhaust is one of the main sources of atmospheric soot. These soot particles have been known to cause adverse health problems in humans and cause acute environmental problems. Despite great efforts for minimizing soot production, research on the disposal and recycling of inevitable diesel soot is scarce. However, DPM consists mainly of carbonaceous soot (DS) that can be easily utilized as a photothermal material for solar desalination. Recently, interfacial solar steam generation using three-dimensional (3D) structures has gained extensive attention. 3D-structured hydrogels have exhibited incredible performance in solar desalination owing to their tunable physicochemical properties, hydrophilicity, intrinsic heat localization, and excellent water transport capability. Herein, a novel DS-incorporated 3D polyvinyl alcohol (PVA)-based hydrogel is proposed for highly efficient solar desalination. The polymer network incorporated with purified DS (DSH) achieved an excellent evaporation rate of 3.01 kg m-2 h-1 under 1 sun illumination due to its vertically aligned water channels, hydrophilicity, and intrinsic porous structure. In addition, the DSH-PVA hydrogel could generate desalinated water efficiently (2.5 kg m-2 h-1) with anti-salt fouling properties. The present results would motivate the utilization and recycling of waste materials like DS as photothermal materials for efficient, low-cost, and sustainable solar desalination.

Membranes prepared from graphene-based nanomaterials for water purification: a mini-review

Graphene-based nanomaterials (GBnMs) are currently regarded as a critical building block for the fabrication of membranes for water purification due to their advantageous properties such as easy surface modification of functional groups, adjustable interlayer pore channels for solvent transportation, robust mechanical properties, and superior photothermal capabilities. By combining graphene derivatives with other emerging materials, heteroatom doping and rational design of a three-dimensional network can enhance water transportation and evaporation rates through channels of GBnM laminates and such layered structures have been applied in various water purification technologies. Herein, this mini-review summarizes recent progress in the synthesis of GBnMs and their applications in water treatment technologies, specifically, nanofiltration (NF) and solar desalination (SD). Finally, personal perspectives on the challenges and future directions of this promising nanomaterial are also provided.

Critical aspects to enable viable solar-driven evaporative technologies for water treatment

While passive solar-driven evaporative systems promise higher economic and environmental sustainability in water treatment, many challenges remain for their effective adoption. Here, the author identifies three main pillars and corresponding issues which future research should focus on to bring these technologies to the next maturity level.

Mechanically robust biomass-derived carbonaceous foam for efficient solar water evaporation

The biomass-derived carbonaceous foam with excellent mechanical strength and evaporation efficiency has promising potential for practical interfacial solar water treatment.