Interfacial Solar Heating Research Articles

Twisted integration of high-efficiency photothermal/water-transported yarns for boosting solar-powered fabric evaporator

Positioned as high-efficiency low-cost desalination technology, solar interfacial vapor generation still remains challenging in precisely managing interfacial photothermal behaviors. Here, an integral solar-heating yarn twisted by both carbon nanotube (CNT) fibers and cotton yarns processed via carbon black slurry is developed for architecting high-efficiency fabric evaporators, where modified CNT and cotton serve as the solar-heating unit and water-supply unit, respectively. The unique structure of hybrid yarns features pronounced gradient photothermal difference of 5 °C between CNT and cotton regions in dry state, and meanwhile enables robust Marangoni vapor flows and weak hydration state. As a result, the crafted fabric evaporator has a superior evaporation rate of 2.83 kg m−2 h−1, which is the highest value reported among 2D fabric evaporators. This work introduces an innovative strategy for high-efficiency interfacial solar heating, significantly boosting evaporation performance of flexible and portable evaporators.

Generation of H2O2 and halogenated by-products at the evaporator surface during seawater desalination based on air-water interfacial solar heating

Seawater desalination based on air-water interfacial solar heating has attracted significant attention in recent years. However, the “high temperature, high salinity, sunlight irradiation and enrichment of photosensitive substances” environment formed at the evaporator surface unavoidably enhances the photochemical reaction, which in the next step may lead to the production of active species and by-products. In this work, H2O2, as an important reactive oxygen species and a transit substance for reactive oxygen species such as ·OH, 1O2, and ·O2−, was monitored during solar evaporation. The average H2O2 concentration at the evaporator surface was 2.24 mg·L−1 with a maximum concentration of 5.0 mg·L−1, which is significantly higher than the average H2O2 concentration in the ocean. The effects of the nitrate ions, halogen ions, iron ions, dissolved organic matter, and solar intensity on the generation of H2O2 concentrations were explored. Finally, halogenated by-products were detected at the evaporator surface when phenol, a model pollutant, was present in the feedwater. This work fills the knowledge gap in understanding the generation of H2O2 and the formation of halogenated by-products at the evaporator surface during solar evaporation.

Solventless autothermic production of energy-intensive furanic biofuels expedited by photothermal effect

Driving C-C coupling reactions to produce biofuels is usually energy-consuming and requires well-tailored catalysts. Herein, a novel photothermal catalytic strategy was developed to be highly efficient for cascade hydroxyalkylation-alkylation (HAA) of various biomass-derived aldehydes/ketones with 2-methylfuran or acetalization of different bioalcohols with furfural to exclusively afford furanic biofuel molecules (up to 94.8 % yield). The developed bio-based SO3H-functionalized graphene-like catalyst (GLB-SO3H-700) could complete the HAA and acetalization reactions in 10 min under solvent-free and room-temperature conditions. Infrared thermal imaging revealed that the local photothermal effect of interfacial solar heating could in-situ remove water co-product, thereby improving the reaction selectivity and rate as evidenced by kinetic study. Moreover, the GLB-SO3H-700 catalyst exhibited good stability and recyclability. The developed SO3H-functionalized graphene-like photothermal materials hold great potential for catalytic upgrading of biomass into high-quality biofuels under mild conditions.

Photothermal technique-enabled ambient production of microalgae biodiesel: Mechanism and life cycle assessment

Thermocatalytic (trans)esterification of oils/lipids to produce biodiesel is generally energy-consuming, reversible, and controlled by the equilibrium law. Herein, a light-induced photothermal process was illustrated to be highly efficient for biodiesel production (96.8 % yield) from microalgae lipids at room temperature enabled by a biomass-based SO3H-functionalized graphene-like heterogeneous catalyst (S-NGL-600), as optimized by response surface methodology. Infrared thermal imaging indicated that interfacial solar heating led to forming a local photothermal catalytic system, reaching 72.2 °C in 2 min. The local light heating was conducive to evaporation and removal of water from acid sites, resulting in local excess of microalgae lipids to facilitate the forward reaction. Notably, the photothermal catalyst was highly recyclable and exhibited a significantly higher conversion rate of microalgae lipids than industrially used catalyst H2SO4. Life cycle assessment suggested energy-saving advantage (0.87 MJ/MJ) and environmental protection (-89.42 CO2eq/MJ) of the photothermal-driven protocol for microalgae biodiesel production.

Inhibition of phenolic compounds from entering condensed freshwater by surfactant-modified evaporators during solar-driven seawater desalination

Seawater desalination based on air–water interfacial solar heating is considered to be one of the effective methods to solve the freshwater shortage crisis in islands. However, the high temperature of the air–water interface unavoidably makes volatile organic compounds (VOCs) such as phenolic compounds volatilize into the condensed freshwater, resulting in freshwater pollution. In this work, solar evaporators with different photothermal materials such as carbon black, MoS2 and carbon nanotubes were modified with cetyl trimethyl ammonium bromide (CTAB) and were applied for both solar evaporation and inhibition of phenolic compounds from entering condensed freshwater. The distillation rates (RD) of 10 phenolic compounds could be significantly reduced. For example, the RD value of phenol was reduced from 77% to 4.6%, which was mainly due to the electrostatic force between the quaternary ammonium group of CTAB and phenol, the binding effect of CTAB micelle on phenol, as well as the hydrogen bond between phenol and air-laid cloth in the evaporator. In addition, the phenolic compounds with the boiling point above 230 °C have RD values all below 10%, while the RD values of phenolic compounds with the boiling point below 230 °C are significantly correlated with n-octanol/water partition coefficient (logKow) values with a correlation coefficient R2 of 0.915. This work demonstrates that the CTAB-modified solar evaporators can be used for clean condensed freshwater production during solar-driven seawater desalination.

Removal of Typical Volatile Organic Compounds in Condensed Freshwater by Activated Persulfate during Interfacial Solar Distillation

Recently, seawater desalination based on interfacial solar heating has attracted attention because of its environmental protection and high photothermal conversion efficiency. However, the high air–water interface temperature may cause freshwater quality safety risks because the volatile organic compounds (VOCs) in seawater are more likely to evaporate and condense into freshwater. In this work, typical VOCs (phenol) were prevented from entering into the condensed freshwater by using activated persulfate to take full advantage of interfacial solar distillation. The results showed that the addition of both peroxodisulfate (PDS) and peroxymonosulfate (PMS) could effectively reduce the concentration of phenol in condensed freshwater. The phenol’s distillation concentration rate (RD) was reduced from 74.4% to 14.3% with PMS and 20.5% with PDS. The Cl– was the main factor for activation of PMS, while carbon black, light, and heat were the main factors for activation of PDS. Meanwhile, PMS is better suited for removing VOCs due to its lower oxidant dosage and chlorinated disinfection byproducts compared with PDS. Finally, when real seawater samples were used as the source water for solar distillation, the water quality of typical indicators was lower than the limits set by Drinking Water Quality in China, US EPA, and WHO.

Water harvesting from desert soil via interfacial solar heating under natural sunlight

Freshwater crisis seriously challenges human survival and development, especially in arid regions. Solar-driven interfacial evaporation has recently received tremendous interest for collecting clean water, yet is only feasible in regions with available surface water. Atmospheric water harvesting is independent of surface water but requires high RH, additional energy input and complex equipment. Here, we demonstrate efficient water harvesting from desert soil in very dry regions (air RH < 10%, soil moisture content < 3%) via interfacial solar heating under natural sunlight. The water harvesting device, composed of merely a thin layer of activated carbon (for interfacial solar heating on soil surface), a commercially available polyethylene film (for vapor condensation and water transport) and a water container, could collect 1.13 kg of clean water per square meter of desert soil per day (8 h), i.e., 0.53 kg of clean water per kilogram of activated carbon per hour, under a solar flux of 0.26–0.55 kW m−2. Besides, the soil water harvesting system is very portable, low-cost and scalable. This work opens up a new sustainable approach for solving the freshwater crisis in arid and impoverished regions.

Low-Cost, Unsinkable, and Highly Efficient Solar Evaporators Based on Coating MWCNTs on Nonwovens with Unidirectional Water-Transfer.

Solar vapor generation technology is promising in seawater desalination, sewage purification, and other fields. However, wide application of this technology is still largely confined due to its high cost and difficulties for scalable production. In this study, an ever‐floating solar evaporator is fabricated by coating multiwall carbon nanotubes on a bicomponent nonwoven composed of polypropylene/polyethylene core–sheath fibers. This all‐fiber structure is highly porous and ultralight, with large specific area (for efficient water evaporation), interconnected channels (for easy vapor escape), and low thermal conductivity (to avoid heat loss). The unique unidirectional water‐transfer behavior of the nonwoven enables it to spontaneously pump an adjustable amount of water for interfacial solar heating and a delicate balance between water supply and loss may accelerate the evaporation speed of water. These distinct benefits endow the solar evaporator with excellent evaporation rates of 1.44 kg m–2 h–1 under the simulated irradiation of 1 sun and 12.81 kg m–2 d–1 under natural sunlight. Moreover, the evaporator can be fabricated by using low‐cost materials and industrialized methods (overall cost ≈2.4 USD m−2), making one believe its practical significance for commercial solar steam evaporation.

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

Solar‐driven water evaporation and valuable fuel generation is an environmentally friendly and sustainable way for clean water and energy production. However, a few bottlenecks for practical applications are high‐cost, low productivity, and severe sunlight angle dependence. Herein, solar evaporation with enhanced photocatalytic capacity that is light direction insensitive and of efficiency breakthrough by virtue of a three‐dimensional (3D) photothermal catalytic spherical isotopic evaporator is demonstrated. A homogeneous layer of microfluidic blow spun polyamide nanofibers loaded with efficient light absorber of polypyrrole nanoparticles conformally wraps onto a lightweight, thermal insulating plastic sphere, featuring favorable interfacial solar heating and efficient water transportation. The 3D spherical geometry not only guarantees the omnidirectional solar absorbance by the light‐facing hemisphere, but also keeps the other hemisphere under shadow to harvest energy from the warmer environment. As a result, the light‐to‐vapor efficiency exceeds the theoretical limit, reaching 217% and 156% under 1 and 2 sun, respectively. Simultaneously, CO2 photoreduction with generated steam reveals a favorable clean fuels production rate using photocatalytic spherical evaporator by secondary growth of Cu2O nanoparticles. Finally, an outdoor demonstration manifests a high evaporation rate and easy‐to‐perform construction on‐site, providing a promising opportunity for efficient and decentralized water and clean fuel production.

Ti3C2/PVDF membrane for efficient seawater desalination based on interfacial solar heating

Abstract The photothermal material of Ti3C2 was synthesized by etching Ti3AlC2 with hydrofluoric acid. The as-prepared Ti3C2 was deposited on a polyvinylidene fluoride (PVDF) membrane via vacuum filtration to form a Ti3C2/PVDF membrane, which was used for seawater desalination in the next step based on interfacial solar heating. The water evaporation rate of the Ti3C2/PVDF membrane could be enhanced to 0.98 kg/m2·h under 2 sun irradiance, which was 2.8 times and 5.4 times higher than that of pure water (0.35 kg/m2·h) and PVDF (0.18 kg/m2·h) respectively. The temperature difference between the two air–water interfaces with and without the Ti3C2/PVDF membrane was as high as 11.8 °C, confirming the interfacial heating behavior. The water evaporation rate under 2 sun irradiance kept mostly in the range of 0.96–0.86 kg/m2·h over 30 days under continuous operation, indicating the high stability of the Ti3C2/PVDF membrane. Finally, it was demonstrated that the typical water-quality indexes of the condensed fresh water were below the limit values of the Standards for Drinking Water Quality in China, WHO, and US EPA.

Water Delivery Channel Design in Solar Evaporator for Efficient and Durable Water Evaporation with Salt Rejection

Recently, solar evaporators composed of photothermal materials and their carriers have been designed and produced to enhance the solar evaporation rates based on interfacial solar heating. However,...

Photothermal Catalytic Gel Featuring Spectral and Thermal Management for Parallel Freshwater and Hydrogen Production

AbstractDesalination processes often require large amounts of energy to create clean water, and vice versa for the generation of energy. This interdependence creates a tension between the two essential resources. Current research focuses on one or the other, which exacerbates water‐energy stress, while few tackle both issues jointly. Herein, a low‐carbon technology, H2O–H2 co‐generation system that enables concurrent steady freshwater and clean energy output is reported. The water‐energy coupled technology features a spectrally and thermally managed solar harvesting gel for photoredox and photoheating effects. This photothermal catalytic gel exploits interfacial solar heating for heat confinement, and localized plasmonic heating at the catalyst active sites to remarkably improve water and hydrogen production, thus maximizing energy value per area. To this end, a stand‐alone renewable solar desalination system is successfully demonstrated for parallel production of freshwater and hydrogen under natural sunlight. By doing so, the water–energy nexus is transformed into a synergistic bond that offers opportunities to better meet expected demand rather than acting in competition.

Ultrahigh-efficiency desalination via a thermally-localized multistage solar still

Passive vapor generation systems combining interfacial solar heating and vaporization enthalpy recycling enable high-efficient low-cost desalination.

Hydrophobic lithiated titania floating film for efficient solar-driven water evaporation

Abstract Recently, the development of new photothermal materials for seawater desalination based on air–water interfacial solar heating has become a new research hotspot. In this paper, hydrophobic lithiated titania was synthesized by lithium reaction with amorphous titania followed by surface modification with a thin 1H,1H,2H,2H-perfluorooctyltrichlorosilane (PFOTS) monolayer. The hydrophobic lithiated titania was used as a photothermal material for seawater evaporation based on this new process. A thin lithiated titania floating film was assembled under simulated solar light irradiance due to the combined actions of water surface tension and the water molecules' thermal motion. The formation of the thin floating film significantly promoted water evaporation. The water evaporation rate by the lithiated titania floating film was 0.87 kg·m−2·h−1 under 2.0 sun solar irradiance, which was 2.4 times higher than that of pure water. Parameters affecting the solar evaporation process such as lithiated titania dose, solar light intensity, and storage time were investigated. Finally, the quality of the condensed fresh water was tested to evaluate the potential application of the lithiated titania floating film in practical settings of seawater desalinization.

Collective behaviors mediated multifunctional black sand aggregate towards environmentally adaptive solar-to-thermal purified water harvesting

As a renewable and efficient technology, interfacial solar heating has emerged as a new and promising avenue for treating undrinkable water to clean one via a variety of well-designed solar absorbers. However, it is still urgent to develop an accessible material system in a simple, low-cost and effective way to easily tackle water shortage. Inspired by natural sand with highly important role in purifying water during the natural recycling, in this work, we demonstrate a concept of an all-round black sand aggregate with specific collective behaviors for environmentally adaptable clean water collection from seawater, polluted water and even atmospheric moisture. To endow the raw sand desirable photo-thermal features, polydopamine and Cl−-doped polypyyrole are successively modified onto the sand surface for a stable structure. Owing to the specific aggregative structure of the black sands, a self-channelled device combined adjustable 2D/3D solar-driven evaporation can be readily achieved, and yield a high evaporation performance (1.43 kg m−2 h−1) in comparison with other reported naturally derived materials. Notably, the black sand aggregate could handle with oil-contained polluted water (P-WA) to guarantee high-efficient and sustainable water purification. Furthermore, even if in some draughty areas or deserts, the collective black sands could also extract water from air by absorbing atmospheric moisture and sequentially realizing an in situ water evaporation by heat location. The successful demonstration of multifunctional black sand aggregate may provide a new avenue for purified water collection under changeable environments.

An Interfacial Solar Heating Assisted Liquid Sorbent Atmospheric Water Generator.

Harvesting water from air is a promising strategy for fresh-water production, and it is particularly desirable for areas that lack direct access to clean water. While high-concentration liquid sorbent is well-known for high sorption, it has not been widely used for atmospheric water collection, being primarily limited by the difficulty in desorption. Interfacial solar heating based on a salt-resistant GO-based aerogel is now shown to enable a high-concentration liquid sorbent (CaCl2 50 wt % solution) based atmospheric water generator. Fresh water (2.89 kg m-2 day-1 ) can be produced at about 70 % relative humidity, with only solar energy input and energy efficiency of desorption as high as 66.9 %. This low-cost and effective approach provides an attractive pathway to extract water from air, to relieve the thirst of arid, land-locked, and other areas where fresh water is scarce.

An Interfacial Solar Heating Assisted Liquid Sorbent Atmospheric Water Generator

AbstractHarvesting water from air is a promising strategy for fresh‐water production, and it is particularly desirable for areas that lack direct access to clean water. While high‐concentration liquid sorbent is well‐known for high sorption, it has not been widely used for atmospheric water collection, being primarily limited by the difficulty in desorption. Interfacial solar heating based on a salt‐resistant GO‐based aerogel is now shown to enable a high‐concentration liquid sorbent (CaCl2 50 wt % solution) based atmospheric water generator. Fresh water (2.89 kg m−2 day−1) can be produced at about 70 % relative humidity, with only solar energy input and energy efficiency of desorption as high as 66.9 %. This low‐cost and effective approach provides an attractive pathway to extract water from air, to relieve the thirst of arid, land‐locked, and other areas where fresh water is scarce.

A carbon black floating film for seawater desalination based on interfacial solar heating

Abstract Superhydrophobic carbon black (CB) nanoparticles were prepared by deposition of a monolayer of 1H,1H,2H,2H-perfluorooctyltrichlorosilane (PFOTS) on their surfaces. A thin CB floating film was assembled under solar light irradiance with the assistance of the water's surface tension and the water molecules' thermal motion. The formation of a thin floating film with suitable CB dose significantly enhanced the water evaporation rate, which was 1.9, 3.0, and 7.2 times higher than that without formation of a CB film, CB nanoparticles uniformly dispersed in water, and pure water, respectively. The temperature difference between the two air–water interfaces with and without the CB floating film was as high as 20.1 °C, which strongly confirms the interfacial heating behavior. There was no decrease of water evaporation rate over the whole measured period of 30 days, which undoubtedly reveals the excellent stability and durability of the CB floating film. Finally, a real seawater sample was used for solar distillation and the typical water-quality indexes before and after solar distillation were compared.

Ultra-low cost cotton based solar evaporation device for seawater desalination and waste water purification to produce drinkable water

Steam generation using solar energy has been impractical for years ascribable to its low efficiency. In recent years, interfacial heating of water has been touted as the practical solution to harvest large scale steam generation. In this paper, we present an extremely low cost candle soot coated cotton as an ideal floating absorber to generate highly efficient steam using the concept of interfacial solar heating. The floating absorber was synthesized from traditional household materials and a photothermal efficiency of 80% was achieved under 1 sun illumination. In addition, the novel floating absorber is easy to fabricate as it requires no sophisticated laboratory instruments or expertise. The floating absorber was tested for solar desalination of actual sea water using a homemade solar still where the purified water had salinity levels comparable to other drinking water levels like tap water, packaged drinking water and so on. In addition to the salinity levels of water, the purified water obtained from water purification of sewage was tested for bacteria colonies and no colony forming units (CFU) were present which again suggests the obtained purified water being drinkable. The results of this work should motivate further research in simplistic, low cost photothermal materials and its application in the production of clean drinkable water.

Simple, Low-Dose, Durable, and Carbon-Nanotube-Based Floating Solar Still for Efficient Desalination and Purification

A simple, low-dose, durable, and carbon nanotube-based floating solar still (CNTs-FSS) has been prepared for seawater desalination based on interfacial solar heating. The CNTs-FSS is composed of a ...