Interfacial Solar Vapor Generation Research Articles

Solar-Driven Multistage Device Integrating Dropwise Condensation and Guided Water Transport for Efficient Freshwater and Salt Collection.

Interfacial solar vapor generation (ISVG) is an emerging technology to alleviate the global freshwater crisis. However, high-cost, low freshwater collection rate, and salt-blockage issues significantly hinder the practical application of solar-driven desalination devices based on ISVG. Herein, with a low-cost copper plate (CP), nonwoven fabric (NWF), and insulating ethylene-vinyl acetate foam (EVA foam), a multistage device is elaborately fabricated for highly efficient simultaneous freshwater and salt collection. In the designed solar-driven device, a superhydrophobic copper plate (SH-CP) serves as the condensation layer, facilitating rapid mass and heat transfer through dropwise condensation. Moreover, the hydrophilic NWF is designed with rational hydrophobic zones and specific high-salinity solution outlets (Design-NWF) to act as the water evaporation layer and facilitate directional salt collection. As a result, the multistage evaporator with eight stages exhibits a high water collection rate of 2.25 kg m-2 h-1 under 1 sun irradiation. In addition, the desalination device based on the eight-stage evaporator obtains a water collection rate of 13.44 kg m-2 and a salt collection rate of 1.77 kg m-2 per day under natural irradiation. More importantly, it can maintain a steady production for 15 days without obvious performance decay. This bifunctional multistage device provides a feasible and efficient approach for simultaneous desalination and solute collection.

Effect of far-field ambient conditions on interfacial solar vapor generation using a two-phase closed thermosyphon

Effect of far-field ambient conditions on interfacial solar vapor generation using a two-phase closed thermosyphon

Can the Interfacial Solar Vapor Generation Performance Be Really “Beyond” Theoretical Limit?

AbstractThe interfacial solar vapor generation (ISVG) process is an environmentally friendly approach that utilizes solar to produce steam, which can solve the water shortage. Despite many previous research studies, claims beyond the theoretical limit have risen due to limitations in the efficiency of converting solar to vapor and the rate of solar evaporation, which are still being debated. Energy losses remain even under ideal conditions, which means that the efficiency of the system will never be ≥100%. This review primarily analyzes the theoretical values of evaporation rate and energy efficiency in the ISVG process. Utilizing a theoretical formula for energy distribution, the factors contributing to the current exceedance of conversion efficiency and evaporation rate are scrutinized. By examining various strategies, such as the reduction of vaporization enthalpy for photothermal materials and the utilization of environmental energy for evaporation, these studies seek to enhance evaporation efficiencies, but they ignore the problem of the theoretical limit of evaporation. Therefore, this review emphasizes misconceptions about efficiencies beyond theoretical limits and aims to guide researchers to provide plausible explanations for such breakthroughs under specific conditions, alongside established reference conditions. Ultimately, this study lays a solid theoretical foundation for practical solar water purification.

Rational Design of a Hydrophilic Core-Hydrophobic Shell Yarn-Based Solar Evaporator with an Underwater Aerophilic Surface for Self-Floating and High-Performance Dynamic Water Purification.

Interfacial solar vapor generation holds great promise for alleviating the global freshwater crisis, but its real-world application is limited by the efficiently choppy water evaporation and industrial production capability. Herein, a self-floating solar evaporator with an underwater aerophilic surface is innovatively fabricated by weaving core-shell yarns via mature weaving techniques. The core-shell yarns possess capillary water channels in the hydrophilic cotton core and can trap air in the hydrophobic electrospinning nanofiber shell when submerged underwater, simultaneously realizing controllable water supplies, stable self-flotation, and great thermal insulation. Consequently, the self-floating solar evaporator achieves an evaporation rate of 2.26 kg m-2 h-1 under 1 sun irradiation, with a reduced heat conduction of 70.18 W m-2. Additionally, for the first time, a solar evaporator can operate continuously in water with varying waveforms and intensities over 24 h, exhibiting an outdoor cumulative evaporation rate of 14.17 kg m-2 day-1.

Distribution-according-to-work: Enhancing solar vapor generation of photothermal sponge by using cellulose-based water storage platform

Interfacial solar vapor generation (ISVG) has shown extraordinary promise in achieving high-efficiency water purification. However, the rapid water supply often leads to excessive water in the solar absorber, resulting in undesired heat loss and a decrease in evaporation rate. To tackle this issue, we developed a bio-based solar evaporator comprising cellulose-based water retention resin (CRR) and straw-derived photothermal sponge. CRR serves as an effective water storage platform with a high binding capacity for water molecules, preventing water from entering the absorber and reducing the water evaporation enthalpy. The water management of CRR confines the solar-to-vapor conversion to the interface between CRR and the photothermal sponge, thereby eliminating the adverse effects of excess water. Additionally, the ISVG process operates based on the principle of Distribution-according-to-work, meaning that the quantity of generated vapor depends on the evolution of the sponge structure. Optimal sponge configuration enables evaporation rates of 2.28 and 1.53 kg/m2/h under solar irradiation of 1.0 and 0.5 kW/m2, respectively. Additionally, the obtained evaporator is capable of producing 7.1 kg/m2/day of freshwater in outdoor experiment. This report proposes a novel approach to designing an ISVG device that incorporates effective water management strategy for achieving high-efficiency water purification in real-world scenarios.

Multi-Functional Janus Hollow Solar Evaporator Based on Copper Foam for Non-Contact High-Efficiency Solar Interfacial Distillation.

As a sustainable, clean, and friendly technology with a minimal carbon footprint when treating seawater or wastewater, interfacial solar vapor generation (ISVG) technology is a great alternative to traditional desalination and water purification methods (e.g., reverse osmosis and ultrafiltration). So far, it presents tremendous potential for applications in realizing desalination of seawater or brine, wastewater treatment, and so forth. However, the precipitated salt particles during conventional ISVG inevitably block the evaporator surface, resulting in the degradation of photothermal conversion and decrease of evaporation rate. Herein, a multi-functional non-contact Janus hollow evaporator based on copper foam was prepared, which was assembled by a hydrophobic light-to-heat conversion layer and a hydrophilic interfacial water evaporation layer as two separate parts. Accordingly, the precipitated salt in the ISVG system does not block the photothermal interface, increasing the stability of solar capture and reusability of the evaporator. Notably, the hollow structure of the evaporator has a local interfacial heating effect, endowing the evaporation system with a high seawater evaporation rate of 2.249 kg m-2 h-1. The evaporator is capable of stable operation for 10 h under 1 sun illumination even when evaporating concentrated brine (15 wt %). Moreover, the evaporation rate of water under one sun irradiation reached 2.284 kg m-2 h-1 and the solar-to-vapor efficiency reached 96.6%. Not only that, the evaporator was able to successfully purify wastewater containing dyes and heavy metal ions. The multi-functional Janus hollow interfacial solar evaporator will provide inspiration for upcoming research on the production of safety water.

Robust direct solar water production by integrating interfacial evaporation and membrane distillation

Interfacial solar vapor generation (ISVG) is an important technique for producing water with a minimal carbon footprint. For customers who need a lot of water, the state-of-the-art ISVG devices are unbearable and unacceptable because of their low condensation capacity. This paper introduces a novel configuration that integrates ISVG and direct contact membrane distillation (DCMD) devices to increase the water yield. A carbon nanoparticle-based solar absorber that can collect 94.6 % of incident sunlight and has a substantial water supply capacity is employed for ISVG. For high vapor permeability, moreover, a hydrophobic polyvinylidene fluoride membrane with a moderate pore structure is adopted. The result shows that the ISVG-DCMD device has a water productivity of up to 2.71 kg m−2h−1 under 2 sun illumination. More importantly, the system has a sustainable water productivity of 2.08 kg m−2h−1 when operating in NaCl solution with a concentration of 3.5 % (w/w). This work effectively solves the problem of vapor condensation of the interfacial photothermal evaporator, offering a novel concept for scalable and robust direct solar water production.

Biomimetically Assembled Sponge‐Like Hydrogels for Efficient Solar Water Purification

AbstractHydrogel‐based evaporators for interfacial solar vapor generation (SVG) have emerged as a promising and sustainable strategy for freshwater production. Nevertheless, developing a green and simple approach in the fabrication of porous hydrogel‐based evaporators with tunable porous structures and superior mechanical properties continues to be a challenge. Herein, cryo‐assembled templating and polymerization (CTP) is proposed as an ecological, simple yet effective approach to synthesizing sponge‐like hydrogels (SPHs) with outstanding mechanical properties. Moreover, inspired by the structural geometry of conifer plants of radially aligned microchannels and vertical vessels granting impressive water transportation abilities, the polyzwitterionic SPH evaporators with biomimetically assembled structure (B‐SPH) raise the water transport rate by up to nearly 2 orders of magnitude compared to bulk hydrogels. The B‐SPH also enables an SVG rate up to ≈ 3.45 kg m−2 h−1 under one sun irradiation and an energy efficiency of ≈ 95%. In addition, the as‐prepared materials feature stable mechanical properties and SVG performance even after being rolled, folded, and twisted over hundred times. It is anticipated that the B‐SPH prepared by CTP method provides insights into scalable hydrogel‐based evaporators with elaborate porous structures and durable mechanical properties in an energy‐efficient manner.

Formation, evolution, and enhancement mechanisms of mixed temperature gradient during interfacial solar vapor generation

The solar evaporator, which generates a mixed temperature gradient (MTG) in the process of solar-driven interfacial water evaporation (SIWE), has shown great application potential in clean water production. It is also expected to provide a more comprehensive understanding to shed light on the formation, evolution, and enhancement mechanisms of the MTG. Herein, the space-time evolution of the solar absorber temperature and the evaporation performance in the column solar absorber are studied through a three-dimensional and multi-physical model coupling heat transfer and water transport. The results will demonstrate not only the temperature distribution during the SIWE process but the interface between positive temperature gradient (PTG) and negative temperature gradient (NTG). Moreover, the relationship between evaporation rate and light intensity, bulk water temperature, and environment humidity will be investigated. Importantly, the contributions of solar heating, PTG, NTG, and environment heating to the total evaporation rate will be quantitatively analyzed. Finally, based on the above results, the formation conditions, evolution characteristics, and enhancement mechanisms of MTG will be revealed. This paper will provide theoretical guidance for the successful construction and operation of an MTG evaporator for SIWE acceleration.

Demand for off-grid desalination technology in small-island communities — Can interfacial solar vapor generation be the answer?

The demand for an off-grid desalination technology and the feasibility of using interfacial solar vapor generation (ISVG) to address the problem were evaluated within the context of Bungin Island. Bungin Island is a small-island community in Indonesia facing water scarcity. By conducting interviews with households there, we found that households located on the exterior portion of the island faced the greatest challenges to water access. For example, only 17 % of exterior households had piped water access, whereas 67 % central households had piped water access. Similar inequities for exterior households were also found with respect to the cost of getting additional water. Thus, we determined that an off-grid desalination technology is best suited for solving the water access problems for the most vulnerable communities in small islands. ISVG technologies that draw on the radiative energy in sunlight to achieve desalination are promising in increasing water access by offering a floating off-grid devices on water near exterior households, passive operation, low capital investment, and simple maintenance. These findings stress the importance of understanding how contextual factors shape barriers to water access and provide a road map on how to begin incorporating these factors into the development of a more sustainable desalination technology.

Round-the-clock interfacial solar vapor generator enabled by form-stable phase change materials with enhanced photothermal conversion capacity

Owing to the intermittent nature of solar energy, the water generation yield of interfacial solar vapor generation during the nighttime is limited. Herein, we propose a phase change material (PCM)-integrated solar vapor generator to address this limitation. Specifically, three types of polyethylene glycol (PEG800, PEG1500, PEG2000)/expanded graphite (EG) form-stable PCMs (FSPCMs) with different thermophysical properties were fabricated. Upon comparing the performances of the three FSPCMs, PEG1500/EG was found to be the optimal specimen and the associated mechanism was discussed in detail. Further, a proof-of-concept evaporator was assembled to find that the all-day mass change of the FSPCM-integrated solar vapor generator was 1.5 times that of the conventional evaporator and 3.0 times that of pure water. Moreover, the mass change of the FSPCM-integrated solar vapor generator during the night was 3.6 times that of the conventional evaporator. Benefiting from the thermal energy storage capacity of the prepared FSPCMs, the FSPCM-integrated solar vapor generator can store the extra energy of the sun in the daytime and achieve continuous vapor generation in both daytime and nighttime. Furthermore, COMSOL simulations indicate that the overall performance of the FSPCM-integrated solar vapor generator can be further improved because the FSPCM module has good scalability. In a word, this study provides a novel strategy to effectively improve the all-day vapor generation yield of interfacial solar vapor generation and inspires further research aimed at the use of thermal storage technology to enable round-the-clock solar vapor generation.

Recent advances in interfacial solar vapor generation: clean water production and beyond

This review summarizes the recent progress in interfacial solar vapor generation, which was first proposed in 2014. The technique shows great potential for decentralized desalination applications using ubiquitous and renewable solar energy.

Achieving fast interfacial solar vapor generation and aqueous acid purification using Ti3C2Tx MXene/PANI non-woven fabrics.

Acid rain is a worldwide problem because of the emission of acidic gases into the atmosphere, leading to the acidification of first-order streams and aggravation of fresh water shortage. Therefore, it is of great importance to develop an environmentally friendly method for removing acid from water. Herein, an advanced technology that can achieve aqueous acid purification using solar energy is realized with Ti3C2Tx MXene/polyaniline (PANI) hybrid non-woven fabrics (MPs) through interfacial solar vapor generation, with PANI acting as an acid absorber through the doping process. Benefiting from the porous structure and crumpled micro-surface of MPs, a high evaporation rate of 2.65 kg m-2 h-1 with an efficiency of 93.7% can be achieved under one-sun illumination. Moreover, MPs present an even higher evaporation rate of 2.83 kg m-2 h-1 in high concentration aqueous acid and can generate clean water with a pH higher than 6.5. More importantly, thanks to the unique reversible doping process of PANI, when used as an aqueous acid purifier, MPs show good stability and reusability after dedoping. Our work sheds light on an efficient strategy for dealing with aqueous acid and acid rain.

High-Performance Janus Solar Evaporator for Water Purification with Broad Spectrum Absorption and Ultralow Heat Loss

Interfacial solar vapor generation offers a promising zero-CO2-consuming energy conversion technology for the production of renewable clean water. The key for boosting solar vapor efficiency relies on the rational design of materials composition and structure at the micro/nanoscale to improve light utilization. Here, we demonstrate a Janus evaporator based on a hydrophilic carbon-black-decorated copper oxide (C@CuO) membrane as the light-absorbing layer and an opposite hydrophobic polymer nanofibers as the thermal insulation layer, which enables efficient energy utilization and vapor generation through a synergistic light absorption and thermal confinement strategy. In addition, the hydrated C@CuO surface reduces vaporization enthalpy that accelerates the efficient evaporation of water. A high evaporation rate of 1.88 kg m–2 h–1 is achieved by the Janus evaporator under 1 sun irradiation. This high photothermal conversion rate and ultralow heat loss synergistic engineering offers a bright future for high-efficiency solar water purification applications.

Polyzwitterionic Hydrogels for Highly Efficient High Salinity Solar Desalination

Interfacial solar vapor generation (SVG) is regarded as a promising and sustainable strategy for clean water production. While many materials have demonstrated excellent evaporation rates under one sun, it remains challenging to design solar evaporators without compromising SVG performance in high-salinity brines (≥10 wt %). Herein, polyzwitterionic hydrogels (PZHs) are proposed as a novel platform for high-salinity solar desalination. Taking advantage of the unique anti-polyelectrolyte effects, PZHs can trap salt ions from the brine water to form a more hydrated polymer network, leading to enhanced SVG performance. PZHs exhibit an exceptional solar evaporation rate of 4.14 kg m-2 h-1 in 10 wt % brine, which is ≈20 % higher than that in pure water. It is anticipated that salt-responsive PZHs may provide insights for the design of next-generation solar desalination systems.

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.

All-cellulose-based freestanding porous carbon nanocomposites and their versatile applications

Porous carbons are key functional materials in a range of industrial processes such as gas adsorption and separation, water treatment, and energy conversion and storage. It is, however, important from a sustainability perspective for porous carbons to be synthesized from naturally abundant biopolymers. Nanoengineering of porous carbons using facile binder-free techniques presents significant challenges, but is deemed beneficial for broadening their field of use and improving their application performance. This paper discusses the processing of cellulose-based porous carbons interwoven with cellulose nanofibers to fabricate freestanding nanopapers and aerogels, aiming at developing processable, fully sustainable, and all-cellulose-based carbon nanocomposites. The aerogels, which have cellular networks, low density and high mechanical strength, were investigated as sorbents for CO 2 capture and removal of various organics. The presence of rich ultramicropores allows the aerogels to adsorb relatively high amounts of CO 2 , with high selectivity of CO 2 -over-N 2 (up to 111). More importantly, the sorbents have high CO 2 working capacities and excellent recyclability under temperature swing adsorption conditions. In addition, the aerogels can adsorb various organic solvents remarkably well, corresponding to 100–217 times their own weight. The nanopapers are active photothermal materials that can be applied as solar absorbers for interfacial solar vapor generation, providing a high evaporation rate (1.74 kg m −2 h −1 under one sun illumination). The nanopapers were also employed as electrodes in flexible, foldable supercapacitors with high areal capacitances. This study may provide a basis for further development of and new application areas for all-cellulose-based nanocomposites. • All-cellulose-based freestanding porous carbon aerogels and nanopapers were designed. • The elastic aerogels were efficient sorbents for CO 2 separation and removal of VOCs. • The freestanding nanopapers was applied for interfacial solar vapor generation. • The freestanding nanopaper electrodes were assembled into flexible supercapacitors.

Vapor generation via porous nanochannel wicks

Vapor generation rate in nano/microstructured-based interfacial vapor generation devices is limited by water supply. Here, we report an innovative design for enhancement in vapor generation using porous nanochannel wicks. Vapor generation rate of 1.18 kg m − 2 h -1 is achieved in a dark environment (without heat input) and of 17.12 kg m − 2 h -1 is achieved with a heat input of 5.08 W at low temperature of 62°C, significantly higher than a typical vapor generation rate reported for interfacial solar vapor generation systems. We also demonstrate our wick’s performance under solar heat flux of 1.25 sun and attain a vapor generation rate of 4.87 kg m − 2 h -1 at surface temperature below 35°C. Thus, we present an unconventional approach of separating surfaces of vapor generation and heat supply that would provide additional flexibility in the choice of energy source, such as solar energy and waste heat from exhaust gases. This approach can be consequential in low-grade waste heat recovery. • Wick made of cross-connected buried nanochannels with micropores at intersections • Capillary-induced passive water supply with simultaneous evaporation at micropores • Thin film evaporation causes high vapor generation rate at low surface temperature Vapor generation rates are limited in passive nano/microstructure-based interfacial vapor generation devices. Ranjan et al. report the performance of a porous nanochannel wick design that can achieve high vapor generation rate with solar heat flux, with waste heat, and even in the absence of heat supply.

Polymeric materials for solar water purification

AbstractSolar‐based desalination or water purification is regarded as one of the promising solutions to global water scarcity as the only energy input is abundant and sustainable solar light. Interfacial solar vapor generation (SVG), which converts natural sunlight into clean water vapor, has attracted extensive research interests due to its high‐energy utilization efficiency and simple implementation. With tunable molecular structures and tailorable physical properties, polymers have demonstrated great potential as candidate materials for solar evaporators. In this review, we summarize the recent progress on polymer materials for solar‐powered water purification. First, we present functional polymers with highly tunable molecular composition and morphology as high‐efficiency solar absorbers. Next, the recent development of various polymeric materials and structural engineering strategies for adequate water supply and efficient thermal management are discussed, along with their excellent desalination and purification performance. Last, we outline the challenges and future directions on the further development of polymer materials for solar water purification technologies.

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.