Effect of light intensity on solar-driven interfacial steam generation

Heat-Localized and Salt-Resistant 3D Hierarchical Porous Ceramic Platform for Efficient Solar-Driven Interfacial Evaporation

Solar-driven interfacial evaporation (SDIE) is a highly promising approach to achieve sustainable desalination and tackle the global freshwater crisis. Despite advancements in this field, achieving balanced thermal localization and salt resistance remains a challenge. Herein, the study presents a 3D hierarchical porous ceramic platform for SDIE applications. The utilized alumina foam ceramics (AFCs) exhibit remarkable corrosion resistance and chemical stability, ensuring a prolonged operational lifespan in seawater or brines. The millimeter-scale air-filled pores in AFCs prevent thermal losses through conduction with bulk water, resulting in heat-localized interfaces. The hydrophilic nature of macroporous AFC skeletons facilitates rapid water replenishment on the evaporating surface for effective salt-resistant desalination. Benefiting from its self-radiation adsorption and side-assisted evaporation capabilities, the AFC-based evaporators exhibit high indoor evaporation rates of 2.99 and 3.54 kg m-2 h-1 under one-sided and three-sided illumination under 1.0 sun, respectively. The AFC-based evaporator maintains a high evaporation rate of ≈2.77 kg m-2 h-1 throughout the 21-day long-term test. Furthermore, it achieves a daily water productivity of ≈10.44 kg m-2 in outdoor operations. This work demonstrates the potential of 3D hierarchical porous ceramics in addressing the trade-off between heat localization and salt resistance, and contributes to the development of durable solar steam generators.

Superspreading Surface with Hierarchical Porous Structure for Highly Efficient Vapor-Liquid Phase Change Heat Dissipation

Superspreading surfaces with excellent water transport efficiency are highly desirable for addressing thermal failures through the liquid-vapor phase change of water in electronics thermal management applications. However, the trade-off between capillary pressure and viscous resistance in traditional superspreading surfaces with micro/ nanostructures poses a longstanding challenge in the development of superspreading surfaces with high cooling efficiency in confined spaces. Herein, a heat-treated hierarchical porous enhanced superspreading surface (HTHP) for highly efficient electronic cooling is proposed. Compared with the single porous structures in nanograss, nanosheets, and copper foam, HTHP with hierarchical honeycomb pores effectively resolves the trade-off effect by introducing large vertical through-pores to reduce viscous resistance, and connected small pores to provide sufficient capillary pressure synergistically. HTHP exhibits excellent capillary performance in both horizontal spreading and vertical rising. Despite a thickness of only 0.33 mm, the as-prepared ultrathin vapor chamber (UTVC) fabricated to exploit the superior capillary performance of HTHP achieved effective heat dissipation with outstanding thermal conductivity (12 121 Wm-1K-1), and low thermal resistance (0.1 KW-1) at a power of 5 W. This regulation strategy based on hierarchical honeycomb porous structures is expected to promote the development of high-performance superspreading surfaces with a wide range of applications in thermal management.

Bird's Nest-Shaped Sb2 WO6 /D-Fru Composite for Multi-Stage Evaporator and Tandem Solar Light-Heat-Electricity Generators

Herein, an integrated solar-thermal-power protocol is presented at a micro-nanoscopic level to maximize the energy utilization efficiency involving utilization period and utilization patterns, and the nexus of freshwater production and nanogeneration is realized. This sophisticated vaporization device is constructed with the merits of thermally confined evaporation space in favor of recycling latent heat of condensation and optimizing light absorption based on the local sunlight angle of incidence. Inspired by a bird's nest, Sb2 WO6 /D-Fructose composites are prepared as photothermal absorbers to achieve a superior water evaporation rate of 2.78 kg m-2  h-1 in the Multi-stage evaporator. In addition, a synergistic tandem photo thermal-electric device with a combination of solar-driven water evaporation and further waterflow-driven hydrovoltaic generation, which can output a stable voltage of up to 360.8 mV with effective utilization of steam energy and a limited water source, is exploited. Such integrated configurations pave a pathway for clean water production and renewable power generation simultaneously toward energy issues.

JUJUNCAO-Stem-Based Interfacial Solar-Driven Evaporator with Natural Two-Phase Composite Structures of Functional Partition and Inherent Ultralow Vaporization Enthalpy of Water for Stable and Efficient Steam Production

The interfacial solar-driven evaporation has been deemed as an environmentally friendly approach for freshwater generation. Nevertheless, there is still a challenge to obtain solar evaporators with efficient vapor production from low-cost and renewable biomass through a simple preparation process. Herein, the JUJUNCAO stem was selected as the substrate material, and a kind of interfacial solar-driven evaporator with natural two-phase composite structures and inherent ultralow water vaporization enthalpy was constructed by a dip-coating process. The natural two-phase composite structures were utilized as independent functional partition: the low-tortuosity and hydrophilic vascular bundles served as hierarchical channels for rapid water transportation and continuous steam escape, and the honeycomb-like parenchyma cells were considered natural heat insulators for effective thermal management. Furthermore, the JUJUNCAO stem exhibited inherent ultralow water vaporization enthalpy which was only 1.15 kJ g-1. Benefiting from the natural two-phase composite structures of functional partition and inherent ultralow water vaporization enthalpy, the C-Js evaporator could achieve an evaporation rate of 2.77 kg m-2 h-1 with an efficiency of 85.6% under 1 sun illumination. Meanwhile, the C-Js exhibited a stable and ideal evaporation performance and metal ion rejection behavior in the actual brine desalination process. Owing to the cost-effective and simple pretreatment process, the C-Js evaporator has the potential for freshwater generation in undeveloped areas.

Waterwheel-inspired rotating evaporator for efficient and stable solar desalination even in saturated brine

Solar desalination is one of the most promising technologies to address global freshwater shortages. However, traditional evaporators encounter the bottleneck of reduced evaporation rate or even failure due to salt accumulation in high-salinity water. Inspired by ancient waterwheels, we have developed an adaptively rotating evaporator that enables long-term and efficient solar desalination in brines of any concentration. The evaporator is a sulphide-loaded drum-type biochar. Our experiments and numerical simulations show that this evaporator, thanks to its low density and unique hydrophilic property, rotates periodically under the center-of-gravity shift generated by salt accumulation, achieving self-removal of salt. This allows it to maintain a high evaporation rate of 2.80 kg m-2 h-1 within 24 h even in saturated brine (26.47%), which was not achieved previously. This proof-of-concept work therefore demonstrates a concentration- and time-independent, self-rotation-induced solar evaporator.

A highly efficient and sustainable photoabsorber in solar-driven seawater desalination and wastewater purification

Producing freshwater from seawater and wastewater is of great importance through interfacial solar steam generation (ISSG). Herein, the three-dimensional (3D) carbonized pine cone, CPC1, was fabricated via a one-step carbonization process as a low-cost, robust, efficient, and scalable photoabsorber for the ISSG of seawater as well as a sorbent/photocatalyst for use in wastewater purification. Taking advantage of the large solar-light-harvesting ability of CPC1 due to the presence of carbon black layers on the 3D structure, its inherent porosity, rapid water transportation, large water/air interface, and low thermal conductivity, a conversion efficiency of 99.8% and evaporation flux of 1.65 kg m-2 h-1 under 1 sun (kW m-2) illumination were achieved. After carbonization of the pine cone, its surface becomes black and rough, which leads to an increase in its light absorption in the UV-Vis-NIR region. The photothermal conversion efficiency and evaporation flux of CPC1 did not change significantly during 10 evaporation-condensation cycles. CPC1 exhibited good stability under corrosive conditions without significant change in its evaporation flux. More importantly, CPC1 can be used to purify seawater or wastewater by the removal of organic dyes as well as by the reduction of polluting ions, like nitrate ions in sewage.

Ion-Transfer Engineering via Janus Hydrogels Enables Ultrahigh Performance and Salt-Resistant Solar Desalination

Emerging solar interfacial evaporation offers the most promising response to the severe freshwater crisis. However, the most challenging bottleneck is the conflict between resisting salt accumulation and maintaining high evaporation performance since conventional salt-resistant evaporators enhance water flow to remove salt, leading to tremendous heat loss. Herein, an ion-transfer engineering is proposed via a Janus ion-selective hydrogel that enables ion-electromigration salt removal, breaking the historical dependence on water convection, and significantly lowering the heat loss. The hydrogels drive cations downward and anions upward, away from the evaporation surfaces. An electrical potential is thus established inside the evaporator and salt in 15 wt% brine is removed stably for seven days. A record-high evaporation rate of 6.86 kg m^-2  h^-1 in 15 wt% brine, 2.5 times the previously reported works, is achieved. With the from-scratch salt-resistant route, comprehensive water-thermal analysis, and record-high performance, this work holds great potential for the future salt-resistant evaporators.

Three-Dimensional Coffee-Ring Effect Induced Deposition on Foam Surface for Enhanced Photothermal Conversion

Uniformly depositing a thin layer of functional constituents on porous foam is attractive to realize their concentrated interfacial application. Here, a simple but robust polyvinyl alcohol (PVA)-mediated evaporation drying strategy to achieve uniform surface deposition on melamine foam (MF) is introduced. Solutes can be accumulated homogeneously to the surface periphery of MF due to the enhanced coffee-ring effect of PVA and its stabilizing effect on various functional constituents, including molecules and colloidal particles. The deposition thickness is positively correlated with the feeding amounts of PVA but seems to be independent of drying temperature. 3D outward capillary flow driven by the combination of contact surface pinning and continual interfacial evaporation induces the forming of core-shell foams. The enhanced interfacial photothermal effect and solar desalination performance using PVA/polypyrrole-coated MF as a Janus solar evaporator are demonstrated.

Interface Engineering of a Ti4O7 Nanofibrous Membrane for Efficient Solar-Driven Evaporation

Solar-driven interfacial evaporation provides a feasible and sustainable way to solve the fresh water shortage using abundant solar energy and has recently attracted considerable attention. However, it has been limited by the evaporation rate and solar-heat conversion efficiency of the current materials. Herein, a novel Ti₄O₇ membrane with synergetic photothermal and electrothermal effects was developed using a straightforward in situ approach. Based on interface engineering, the interface between the surface of the membrane and water was hydrophobically modified, and a thermal insulation layer was added to the bottom of the membrane. The optimized self-floating membrane with excellent sunlight absorbability and conductivity achieved a remarkably high evaporation rate of 7.51 kg m^-2 h^-1 with a voltage of 3 V as compensation under one-sun irradiation (1 kW m^-2). Moreover, the bilayered membrane displayed efficient salt ion rejection, and the collected water can meet the World Health Organization (WHO) standard required for potable water.

Recent Development of Carbon-Nanotube-Based Solar Heat Absorption Devices and Their Application

Population growth and the current global weather patterns have heightened the need to optimize solar energy harvesting. Solar-powered water filtration, electricity generation, and water heating have gradually multiplied as viable sources of fresh water and power generation, especially for isolated places without access to water and energy. The unique thermal and optical characteristics of carbon nanotubes (CNTs) enable their use as efficient solar absorbers with enhanced overall photothermal conversion efficiency under varying solar light intensities. Due to their exceptional optical absorption efficiency, low cost, environmental friendliness, and natural carbon availability, CNTs have attracted intense scientific interest in the production of solar thermal systems. In this review study, we evaluated CNT-based water purification, thermoelectric generation, and water heating systems under varying solar levels of illumination, ranging from domestic applications to industrial usage. The use of CNT composites or multilayered structures is also reviewed in relation to solar heat absorber applications. An aerogel containing CNTs was able to ameliorate water filtering performance at low solar intensities. CNTs with a Fresnel lens improved thermoelectric output power at high solar intensity. Solar water heating devices utilizing a nanofluid composed of CNTs proved to be the most effective. In this review, we also aimed to identify the most relevant challenges and promising opportunities in relation to CNT-based solar thermal devices.

Janus Carbon Nanotube@poly(butylene adipate-co-terephthalate) Fabric for Stable and Efficient Solar-Driven Interfacial Evaporation

Solar-driven seawater desalination is considered a promising method for alleviating the water crisis worldwide. In recent years, significant efforts have been undertaken to optimize heat management and minimize salt blockage during solar-driven seawater desalination. However, it remains challenging to achieve an efficient and stable seawater evaporator simply and practically. Here, we designed and prepared a novel three-dimensional (3D) water channel evaporator (3D WCE) equipped with a Janus CNT@PBAT fabric (JCPF). The as-prepared Janus CNT@PBAT fabric has broad-band light absorption (∼97.8%), excellent superhydrophobicity (∼162°), and photothermal properties. After optimizing the structure of the thermal insulator, our designed evaporator could realize the equilibrium between enhanced thermal management and sufficient water supply. As a result, the as-prepared evaporator achieved an excellent evaporation rate of 1.576 kg·m^-2·h^-1 and an energy efficiency of over 92.7% under 1 sun irradiation in 3.5 wt % saline water. Moreover, this evaporator also revealed good salt rejection performance compared to the traditional two-dimensional (2D) water channel evaporator (2D WCE) in high saline water, which could maintain stable evaporation rates under long-term evaporation of 8 h. Our study may develop a simple method for the design and fabrication of a low-cost, effective, and stable solar-driven evaporator for seawater desalination.

Robust and multifunctional natural polyphenolic composites for water remediation

The scarcity of clean water has become a global environmental problem which constrains the development of public health, economy, and sustainability. In recent years, natural polyphenols have drawn increasing interests as promising platforms towards diverse water remediation composites and devices, owing to their abundant and renewable resource in nature, highly active surface chemistry, and multifunctionality. This review aims to summarize the most recent advances and highlights of natural polyphenol-based composite materials (e.g., nanofibers, membranes, particles, and hydrogels) for water remediation, by focusing on their structural and functional features, as well as their diversified applications including membrane filtration, solar distillation, adsorption, advanced oxidation processes, and disinfection. Finally, the future challenges in this field are also prospected. It is anticipated that this review will provide new opportunities towards the future development of natural polyphenols and other kinds of naturally occurring molecules in water purification applications.

Double-Sided Suspending Evaporator with Top Water Supply for Concurrent Solar Evaporation and Salt Harvesting

Solar evaporation of seawater is promising to mitigate the fresh water scarcity problem in a green and sustainable way. However, salt accumulation on the photothermal material prevents the system continuous operation, and the water supply driven by capillary force severely limits the scale-up of the evaporators. Here, we demonstrate a double-sided suspending evaporator with top water supply and a surface water distributor for high-efficient concurrent solar evaporation and salt harvesting for large area applications. Both sides of the evaporator can evaporate water with automatic salt harvesting from the edge concurrently. Top water supply gets away from the limitation of capillary force for a larger area application and completely cuts off the heat leak to the bulk water below for higher efficiency. The energy conversion efficiency reaches 95.7% at 1.40 kg·m^-2·h^-1 with deionized water under 1 sun with a remarkable low surface average temperature (28.2 °C). Based on the simulation and experiment, a novel radial arterial water distribution system is developed to efficiently distribute water on a larger evaporation surface. The water distribution system alters the water transport path in the evaporation surface, leading to salt accumulation on the surface body, where salt is unable to be harvested by gravity automatically. This problem is further resolved by cutting out the salt accumulation area (16.4%) on the surface to create a floriform evaporator, which forcedly exposes the salt at the edge for harvesting. Up to70 h continuous solar evaporation from salt water at a rate of 1.04 kg·m^-2·h^-1 with concurrent salt collection on this floriform evaporator is achieved. This work resolves water supply and salt accumulation problems in scaling up the solar evaporators and advances the structural design of evaporators for high-efficient large area applications.

All-Day Freshwater Harvesting by Selective Solar Absorption and Radiative Cooling

Solar interfacial evaporation for freshwater harvesting has received attention recently due to its high evaporation rate and environmental friendliness. Traditional interfacial evaporation mostly uses black porous polymers to absorb solar radiation and transport water which involve high thermal radiation loss to the environment and heat conduction loss to the bulk water. In addition, the freshwater collection ratio is usually lower than the solar evaporation ratio due to the high temperature of the condensation surface under solar irradiation, and no freshwater can be harvested at night due to the absence of sunlight. Here, we design an all-day freshwater-harvesting device using a solar-selective absorber (SSA) and sky radiative cooling. The prepared SSA with a high solar absorptance of 0.92 and a mid-infrared thermal emittance of 0.11 provides a great solar-thermal conversion performance (87.1% vs 51.4% for the black porous polymer at 25 °C) by minimizing the thermal radiation loss, and a hollow structure is also used to reduce the conductive heat loss, resulting in a high solar evaporation rate (1.23 vs 0.79 kg m^-2 h^-1 for the black porous polymer). In addition, a transparent radiative cooling polymer after plasma treatment is used for freshwater collection by enhancing the solar transmittance (0.92) and mid-infrared thermal emittance (0.91 at 25 °C). A theoretical freshwater collection rate of 0.044 kg m^-2 h^-1 is achieved at night-time. Outdoor results show that the all-day water harvesting is 0.87 kg m^-2. This strategy to achieve all-day water collection by coupling with the SSA and transparent radiative cooling has potential application in the field of desalination and freshwater harvesting in tropical desert areas.

A bioinspired solar evaporator with a horizontal channel-like framework for efficient and stable high-salinity brine desalination

In recent years, solar steam generation has been one of the most promising and sustainable techniques for water desalination. However, the heat loss to bulk water dramatically decreases the evaporation rate. Besides, salt deposition on the evaporation surface during brine treatment limits the long-term operation of evaporators. Herein, solar evaporators with a horizontal channel-like framework are reported and high efficiency and outstanding salt resistance are achieved. Firstly, eggplants with a hollow fiber alignment structure were carbonized as CEP evaporators. The CEP-H evaporator with a horizontal fiber growth direction shows a high evaporation efficiency of 90.6% and excellent salt resistance when treating high-salinity brine (20 wt%). The low thermal conductivity perpendicular to the fiber growth direction impedes the conductive heat transfer into bulk water, and fast water transport along the fiber growth direction is beneficial for salt resistance. In addition, a proof-of-concept evaporator polypyrrole-coated polypropylene hollow fiber membrane with a horizontal channel-like framework (PPy/PP-H) has also been developed. This hollow fiber membrane shows a high evaporation rate of 1.64 kg m^-2 h^-1 due to multiangle evaporation and also demonstrates excellent salt-resisting performance for high-salinity brine treatment (20 wt%). The study demonstrates the effect of the horizontal channel-like framework for high evaporation performance and salt resistance, providing new insights into the solar evaporator design for seawater desalination and wastewater treatment.