Core-shell-embedded Mesoporous Silica Capsules for Atmospheric Water Harvesting

A one-step ultrasonic mechanical method was used to synthesize a kind of atmospheric water harvesting material with high water harvesting performance in a wide relative humidity(RH)range,especially at low RH(RH<40%),namely,mesoporous silica capsule(MSC)with core-shell structure.Transmission electron microscopy(TEM),nitrogen adsorption and other characterization techniques were used to study the formation process of nano-microspheres.A new mechanism of self-adaptive concentration gradient regulation of silicon migration and recombination core-shell structure was proposed to explain the formation of a cavity in the MSC system.The core-shell design can enhance the specific surface area and pore volume while maintaining the monodispersity and mesoporous size.To study the water harvesting performance of MSC,solid silica nanoparticles(SSN)and mesoporous silica nanoparticles(MSN)were prepared.In a small atmospheric water collection test(25℃,40%RH),the water vapour adsorption and desorption kinetics of MSC,SSN,MSN and a commercial silica gel(CSG)were compared and analyzed.The results show that the MSC with mesoporous channels and core-shell structure can provide about 0.324 gwater/gadsorbent,79%higher than the CSG(0.181 gwater/gadsorbent).It is 25.1%higher than that of 0.259 gwater/gadsorbentof un-hollowed MSN and 980%higher than that of0.03 gwater/gadsorbentof un-hollowed SSN.The material has a large specific surface area and pore volume,simple preparation method and low cost,which provides a feasible idea for realising atmospheric water collection in arid and semi-arid regions.

Multivariate MOF for optimizing atmospheric water harvesting

Atmospheric water harvesting offers a powerful and promising solution to address the problem of global freshwater scarcity.In the past decade,significant progress has been achieved in utilizing hydrolytically stable metal-organic frameworks as recyclable water-sorbent materials under low relative humidity,especially in those arid areas.Recently,Yaghi's group has employed a combined crystallographic and theoretical technique to decipher the water filling mechanism in MOF-303,where the polar organic linkers rather than the inorganic units of MOF are demonstrated as the key factor.Hence,the hydrophilic strength of the water-binding pocket in MOFs can be optimized through the approach of multivariate modulations,resulting in enhanced water harvesting properties.

An atmospheric water harvester with fast and energy-saving water removal and recovery

Moisture removal and water recovery from the air are vital for regulating indoor humidity and mitigating water scarcity.Most atmospheric water harvesters(AWH)focus primarily on increasing the moisture capture rate,but for it to be economical and sustainable,it is essential to consider the energy required to recover and harvest the captured water.Here,a mechanically flexible,biphilic sorption-based AWH made of green,environmentally friendly material is presented.It consists of a hygroscopic chitosan polymer embedded within a flexible,hydrophobic silica xerogel that can harvest 86.3 g water/g chitosan at 97%relative humidity and 25℃reaching saturation after 30 days(i.e.2.88 g water/g chitosan/day).Roughly 88%of the sorbed moisture was recovered by mechanical squeezing(ca.0.020 MPa)within 150 s.Repeated water harvesting experiments and uniaxial compression tests demonstrate that chitosan-silica xerogel is durable for longterm operations,providing a fast,reliable,and sustainable moisture removal and water harvesting tool.

Recent Progress of Atmospheric Water Harvesting Using Metal-Organic Frameworks

Atmospheric water harvesting based on vapor adsorption is a newly emerged and potential technology to supply portable water for arid areas.To efficiently harvest vapor from the air,sorbents are required to have conside-rable adsorption capacity,easy regeneration and high stability.With the advantages of porous structure,tunable pore size and tailorable hydrophilicity,metal-organic frameworks(MOFs)have demonstrated excellent performance in vapor adsorption and water generation.In this review,we first discuss the degradation mechanisms of MOFs exposed to water and summarize the structure-stability relationship;by centering on the adsorption isotherms,the connection between the structure of MOFs and the water adsorption property is illuminated;finally,some prospects are suggested in order to push forward the progress of this technology.

Round-the-clock water harvesting from dry air using a metal-organic framework

Harvesting water from the atmosphere is an important process to solve the extreme lack of water resources in arid regions. Adsorption-based atmospheric water harvesting(AWH) takes advantage of solar thermal energy to harvest water from air. This technique is particularly suitable for arid regions characterized by low humidity and an abundance of sunshine. Nonetheless, under low humidity conditions, AWH is highly dependent on water-adsorbing materials exhibiting excellent performance. In this work, a metal–organic framework(MOF), namely [Zn_(2)(bpy)(btec)(H_(2)O)_(2)]·2H_(2)O, also denoted as MWH-1, was investigated for application in water harvesting under low humidity conditions(<20%). Notably,MWH-1 displayed outstanding water and thermal stability. At temperatures of 293–333 K and low pressure, activated MWH-1a exhibited competitive water uptake(relative humidity(RH) = 5%,uptake>200 cm^(3)·cm^(-3);RH = 10%, uptake >250 cm^(3)·cm^(-3)). This ensured effective water harvesting at high temperatures during the day. In situ powder X-ray diffraction and Fourier-transform infrared analyses confirmed the sensitive water adsorption process of MWH-1a. The X-ray single-crystal study further demonstrated that single-crystal structures could be completely restored following water harvesting.MWH-1 showed good structural stability and enabled water harvesting under low humidity and high temperature conditions. Thus, it has the potential for application in round-the-clock water harvesting in extremely arid regions.

Carbon-based functional materials for atmospheric water utilization

Atmospheric water,as one of the most abundant natural resources on Earth,has attracted huge research interest in the field of water harvesting and energy harvesting and conversion owing its environmental friendliness and easy access.The developments of new materials have seen advanced technologies that can extract water and energy out of this long-neglected resource,suggesting a promising and sustainable approach to address the water and energy crises over the world.Carbon-based functional materials have been considered to be indispensable materials for atmospheric water utilization due to their large surface area,excellent adsorption performance,and higher surface activity.In this review,first,we analyze the interaction between carbon-based functional materials and atmospheric water molecular.Then,technologies developed in recent years for atmospheric water utilization based on carbon-based functional materials are reviewed,mainly focusing on atmospheric water harvesting,moisture-enabled electricity generation,and moisture-responsive actuation.Finally,the remaining challenges and some tentative suggestions possibly guiding developments are proposed,which may pave a way for a bright future of carbon-based functional material in the utilization of atmospheric water.

Photothermal hygroscopic hydrogel for simultaneous generation of clean water and electricity

Harvesting water from the air using adsorbents and obtaining fresh water by solar-driven desorption is considered as one of the most effective ways to solve the freshwater crisis in arid and desert regions.Based on a simple and low-cost photothermal hygroscopic hydrogel,a new strategy is proposed to boost solar energy efficiency by coupling solar-driven atmospheric water harvesting technology with thermoelectric power generation technology in this paper.Photothermal hygroscopic hydrogel ink PAM-CaCl_(2)is prepared by in situ polymerization using Acrylamide as monomer,Ammonium persulfate as thermal initiator and CaCl_(2)as hygroscopic component.During the day,the photothermal hygroscopic hydrogel absorbs solar energy and evaporates its own internal water to obtain fresh water.Simultaneously,the residual waste heat is utilized to power the thermoelectric panel,which produces electricity based on Seebeck effect.At night,the hydrogel harvests water molecules in the air to achieve regeneration.This hybrid system can achieve a water production rate of 0.33 kg m^(-2)h^(-1)and an additional electrical energy gain of 124 mW m^(-2)at 1 kW m^(-2)solar intensity.Theoretical model of the hybrid system is developed to understand the heat flow and thermoelectric generation process.The results provide new insights into energy and freshwater replenishment options in arid or desert areas with abundant solar energy.

面向可持续淡水供应的吸附式空气取水技术的研究进展与展望:材料、装置和系统

Establishing alternative methods for freshwater production is imperative to effectively alleviate global water scarcity,particularly in land-locked arid regions.In this context,extracting water from the ubiquitous atmospheric moisture is an ingenious strategy for decentralized freshwater production.Sorption-based atmospheric water harvesting(SAWH)shows strong potential for supplying liquid water in a portable and sustainable way even in desert environments.Herein,the latest progress in SAWH technology in terms of materials,devices,and systems is reviewed.Recent advances in sorbent materials with improved water uptake capacity and accelerated sorption–desorption kinetics,including physical sorbents,polymeric hydrogels,composite sorbents,and ionic solutions,are discussed.The thermal designs of SAWH devices for improving energy utilization efficiency,heat transfer,and mass transport are evaluated,and the development of representative SAWH prototypes is clarified in a chronological order.Thereafter,state-of-the-art operation patterns of SAWH systems,incorporating intermittent,daytime continuous and 24-hour continuous patterns,are examined.Furthermore,current challenges and future research goals of this cutting-edge field are outlined.This review highlights the irreplaceable role of heat and mass transfer enhancement and facile structural improvement for constructing high-yield water harvesters.

一种基于“最优捕集窗口”设计的全球化空气取水系统

Atmospheric water harvesting(AWH)is a promising solution to the water shortage problem.Current sorption-based AWH(SAWH)systems seldom obtain both wide climatic adaptability and high energy efficiency due to the lack of thermodynamic optimization.To achieve the ideal harvesting circulation in SAWH systems,the“optimal harvesting window”(OHW)design based on thermodynamic analysis was first proposed and validated by our prototype.The“OHW”theory indicates the water production rate and energy efficiency could be improved by properly reducing the adsorption temperature.As the humidity increases,the optimal adsorption temperature should be closer to the dew point of the environment.Experimental results revealed that,loaded with 3 kg widely adopted silica gel,the daily water production could reach 5.76-17.64 L/d with ultrahigh energy efficiency of 0.46-1.5 L/kWh.This prototype could also achieve optimal performance in wide climatic conditions in terms of 13-35℃and 18%-72%RH.Lastly,the performance of photovoltaic(PV)-driven SAWH was evaluated.Results showed that a 1 m^(2)PV panel could generate 0.66-2 L water per day in Shanghai throughout the year,the highest in opening literature.Notably,this work introduces a promising concept that can help achieve large-scale,ultra-fast,energyefficient AWH worldwide.