Masked Reactivity of Hydrated Clusters of Monovalent Manganese Ions: Water Insertion versus Nitrous Oxide Activation-A Density Functional Theory Investigation

Previous mass spectrometric (MS) studies demonstrated that singly charged hydration clusters of manganese ions [Mn(H2O)n]+ were, on one hand, highly reactive toward intracluster water insertion but, on the other hand, inert toward nitrous oxide activation. This contrast in reactivity has been rationalized by our present theoretical investigation for the interconversion between the pristine Mn(I) monovalent form as a monatomic ion in [MnI(H2O)n]+ and the oxidized Mn(III) trivalent form as a hydride-hydroxide in [HMnIIIOH(H2O)n-1], as well as their reactivity toward nitrous oxide activation. Our theoretical interpretations are supported with quantum chemical calculations based on density functional theory (DFT), performed systematically for the cluster-size range of n = 1 - 12. Our DFT results show that water insertion is kinetically and thermodynamically favorable for n ≥ 8, suggesting [HMnIIIOH(H2O)n-1]+ is the predominant form, as observed in previous MS experiments. While [MnI(H2O)n]+ is capable of N2O reduction, the process of which is highly exothermic, similar reactions are unfavorable with [HMnIIIOH(H2O)n-1]+, which can only form weakly bound adducts with N2O. This work demonstrates the masking effect of water molecules over the high reactivity of the hydrated Mn(I) center and sheds light on the potential roles of water in transition metal systems.

Self-Assembly Morphology Manipulation by Side-chain Engineering of Quinoxaline-Substituted Organic Photothermal Molecules for Efficient Solar-Thermal Conversion and Application

Organic photothermal materials have attracted more and more attention due to the structural diversity, flexibility, and compatibility. However, the energy conversion efficiency is limited due to the narrow absorption spectrum, strong reflection/transmittance and insufficient non-radiative decay. Herein, we synthesized two quinoxaline-based D-A-D-A-D type molecules with ethyl (BQE) or carboxylate (BQC) substitutes. The strong intramolecular charge transfer endow both molecules broad absorption ranging from 350-1000 nm. Besides, the high reorganization energy and weak molecular packing of BQE yield efficient non-radiative decay. More importantly, the self-assembly of BQE leads to textured surface and enhances the light-trapping efficiency with dramatically reduced light reflection/transmittance. Consequently, BQE achieved impressive solar-thermal conversion efficiency of 18.16% under 1.0 kW m-2 irradiation with good photobleaching resistance. Inspired by this, the water evaporation rate attained to 1.2 kg m-2 h-1 with efficiency of 83% for BQE based interfacial evaporation device under 1.0 kW m-2 simulated sunlight. Eventually, synergetic integration of solar-steam and thermoelectric co-generation device based on BQE is realized without sacrificing solar-steam efficiency significantly, highlighting the practical application toward impactful photothermal exploitation. This work provides new insights of molecular design for enhancing light-trapping management by molecular self-assembly, which paves the way of photothermal-driven application of organic photothermal materials.

Efficient Solar-Driven Interfacial Water Evaporator using Hydrogel Modified Carbon-Based Biomass with Abundant Microchannels

The conventional sea water desalination technologies are not yet adopted worldwide, especially in the third world countries due to their high capital cost as well as large energy requirement. To solve this issue in a sustainable way an interfacial solar water evaporation device is designed and proposed in this article using the branches of Prunus serrulata (PB). The PB has abundant microchannels and shows excellent photothermal conversion capability after carbonization. Moreover, the easy access to raw materials and the facile fabrication process makes the solar water evaporating device very cost effective for seawater desalination application. Experiments show that in the presence of the fabricated evaporator the evaporation rate of water can reach 3.5 kg m-2  h-1 under 1 sun, which is superior to many similar experimental devices. In addition, its advantages, such as effective sewage purification capability, low cost, and environmental friendliness, make this evaporator highly competitive in the extensive promotion of this technology and can be considered as a new sustainable solution for seawater desalination with great application potential and prospects.

Harvesting Energy from Atmospheric Water: Grand Challenges in Continuous Electricity Generation

Atmospheric water is ubiquitous on earth and extensively participates in the natural water cycle through evaporation and condensation. This process involves tremendous energy exchange with the environment, but very little of the energy has so far been harnessed. The recently emerged hydrovoltaic technology, especially moisture-induced electricity, shows great potential in harvesting energy from atmospheric water and gives birth to moisture energy harvesting devices. The device performance, especially the long-term operational capacity, has been significantly enhanced over the past few years. Further development; however, requires in-depth understanding of mechanisms, innovative materials, and ingenious system designs. In this review, beginning with describing the basic properties of water, the key aspects of the water-hygroscopic material interactions and mechanisms of power generation are discussed. The current material systems and advances in promising material development are then summarized. Aiming at the chief bottlenecks of limited operational time, advanced system designs that are helpful to improve device performance are listed. Especially, the synergistic effect of moisture adsorption and water evaporation on material and system levels to accomplish sustained electricity generation is discussed. Last, the remaining challenges are analyzed and future directions for developing this promising technology are suggested.

Nanofluid-Guided Janus Membrane for High-Efficiency Electricity Generation from Water Evaporation

Harvesting electricity from widespread water evaporation provides an alternative route to cleaner power generation technology. However, current evaporation power generation (EPG) mainly depends on the dissociation process of certain functional groups (e.g., SO3 H) in water, which suffers from low power density and short-term output. Herein, the Janus membrane is prepared by combining nanofluid and water-grabbing material for EPG, where the nanoconfined ionic liquids (NCILs) serve as ion sources instead of the functional groups. Benefiting from the selective and fast transport of anions in NCILs, such EPG demonstrates excellent power performance with a voltage of 0.63 V, a short-circuit current of 140 µA, and a maximum power density of 16.55 µW cm-2 while operating for at least 180 h consistently. Molecular dynamics (MD) simulation and surface potential analysis reveal the molecular mechanism, that is, the diffusion of Cl- anions during evaporation is much faster than that of cations, generating the voltage and current across the membrane. Furthermore, the device performs well in varying environmental conditions, including different water temperatures and sources of evaporating water, showcasing its adaptability and integrability. Overall, the nanofluid-guided Janus membrane can efficiently transform low-grade thermal energy in evaporation into electricity, showing a competitive advantage over other sustainable applied approaches.

An Azulene-Based Crystalline Porous Covalent Organic Framework for Efficient Photothermal Conversion

The designed synthesis of a crystalline azulene-based covalent organic framework (COF-Azu-TP) is presented and its photothermal property is investigated. Azulene, a distinctive 5-7 fused ring non-benzenoid aromatic compound with a large intramolecular dipole moment and unique photophysical characteristics, is introduced as the key feature in COF-Azu-TP. The incorporation of azulene moiety imparts COF-Azu-TP with broad-spectrum light absorption capability and interlayer dipole interactions, which makes COF-Azu-TP a highly efficient photothermal conversion material. Its polyurethane (PU) composite exhibits a solar-to-vapor conversion efficiency (97.2%) and displays a water evaporation rate (1.43 kg m-2 h-1 ) under one sun irradiation, even at a very low dosage of COF-Azu-TP (2.2 wt%). Furthermore, COF-Azu-TP is utilized as a filler in a polylactic acid (PLA)/polycaprolactone (PCL) composited shape memory material, enabling rapid shape recovery under laser stimulation. A comparison study with a naphthalene-based COF isomer further emphasizes the crucial role of azulene in enhancing photothermal conversion efficiency. This study demonstrates the significance of incorporating specific building blocks into COFs for the development of functional porous materials with enhanced properties, paving the way for future applications in diverse fields.

Conductive Metal-Organic Framework Nanosheets Constructed Hierarchical Water Transport Biological Channel for High-Performance Interfacial Seawater Evaporation

Solar interfacial water evaporation shows great potential to address the global freshwater scarcity. Water evaporation being inherently energy intensive, Joule-heating assisted solar evaporation for addressing insufficient vapor under natural conditions is an ideal strategy. However, the simultaneous optimization of low evaporation enthalpy, high photothermal conversion, and excellent Joule-heating steam generation within a single material remain a rare achievement. Herein, inspired by the biological channel structures, a large-area film with hierarchical macro/microporous structures is elaborately designed by stacking the nanosheet of a conductive metal-organic framework (MOF), Ni3 (HITP)2 , on a paper substrate. By combining the above three features in one material, the water evaporation enthalpy reduces from 2455 J g-1 to 1676 J g-1 , and the photothermal conversion efficiency increases from 13.75% to 96.25%. Benefiting from the synergistic photothermal and Joule-heating effects, the evaporation rate achieves 2.60 kg m-2 h-1 under one sun plus input electrical power of 4 W, surpassing the thermodynamic limit and marking the highest reported value in MOF-based evaporators. Moreover, Ni3 (HITP)2 -paper exhibits excellent long-term stability in simulated seawater, where no salt crystallization and evaporation rate degradation are observed. This design strategy for nanosheet films with hierarchical macro/microporous channels provides inspiration for electronics, biological devices, and energy applications.

PDI-Based Organic Small Molecule Regulated by Inter/Intramolecular Interactions for Efficient Solar Vapor Generation

Organic small molecules with processing feasibility, structural diversity, and fine-tuned properties have the potential applications in solar vapor generation. However, the common defects of narrow solar absorption, low photothermal conversion efficiency, and photobleaching result in limited materials available and unsatisfactory evaporation performance. Herein, the perylene diimide (PDI) derivatives are exploited as stable sunlight absorbers for solar vapor generation. Particularly, the N,N'-bis(3,4,5-trimethoxyphenyl)-3,4,9,10-perylenetetracarboxylic diimide (PDI-DTMA) is well-designed with donor-acceptor-donor configuration based on plane rigid PDI core. The efficient photothermal conversion is enabled through strong intermolecular π-π stacking and intramolecular charge transfer, as revealed by experimental demonstration and theoretical calculation. The PDI-DTMA with a narrow band gap of 1.17 eV exhibits expanded absorption spectrum and enhanced nonradiative transition capability. The 3D hybrid hydrogels (PPHs) combining PDI-DTMA and polyvinyl alcohol are constructed. With the synergistic effect of solar-to-heat conversion, thermal localization management, water activation, and unobstructed water transmission of PPHs, the high water evaporation rates can reach 3.61-10.07 kg m-2 h-1 under one sun. The hydrogels also possess great potential in seawater desalination and sewage treatment. Overall, this work provides valuable insights into the design of photothermal organic small molecules and demonstrates their potentials in solar water evaporation.

A Flexible Tough Hydrovoltaic Coating for Wearable Sensing Electronics

The lack of a strong binding mechanism between nanomaterials severely restricts the advantages of the evaporation-driven hydrovoltaic effect in wearable sensing electronics. It is a challenging task to observably improve the mechanical toughness and flexibility of hydrovoltaic devices to match the wearable demand without abandoning the nanostructures and surface function. Here, a flexible tough polyacrylonitrile/alumina (PAN/Al2 O3 ) hydrovoltaic coating with both good electricity generation (open-circuit voltage, Voc  ≈ 3.18 V) and sensitive ion sensing (2285 V M-1 for NaCl solutions in 10-4 to 10-3  m) capabilities is developed. The porous nanostructure composed of Al2 O3 nanoparticles is firmly locked by the strong binding effect of PAN, giving a critical binding force 4 times that of Al2 O3 film to easily deal with 9.92 m s-1 strong water-flow impact. Finally, skin-tight and non-contact device structures are proposed to achieve wearable multifunctional self-powered sensing directly using sweat. The flexible tough PAN/Al2 O3 hydrovoltaic coating breaks through the mechanical brittleness limitation and broadens the applications of the evaporation-induced hydrovoltaic effect in self-powered wearable sensing electronics.

Customized Microenvironments Spontaneously Facilitate Coupled Engineering of Real-Life Large-Scale Clean Water Capture and Pollution Remediation

Harnessing abundant renewable resources and pollutants on a large scale to address environmental challenges, while providing sustainable freshwater, is a significant endeavour. This study presents the design of fully functional solar vaporization devices (SVD) based on organic-inorganic hybrid nanocomposites (CCMs-x). These devices exhibit efficient photothermal properties that facilitate multitargeted interfacial reactions, enabling simultaneous catalysis of sewage and desalination. The localized interfacial heating generated by the photothermal effect of CCMs-x triggers surface-dominated catalysis and steam generation. The CCMs-x SVD achieves a solar water-vapor generation rate of 1.41 kg m-2 h-1 (90.8%), and it achieves over 95% removal of pollutants within 60 min under one-sun for practical application. The exceptional photothermal conversion rate of wastewater for environmental remediation and water capture is attributed to customized microenvironments within the system. The integrated parallel reaction system in SVD ensures it is a real-life application in multiple scenarios such as municipal/medical wastewater and brine containing high concentrations. Additionally, the SVD exhibits long-term durability, antifouling functionality toward complex ionic contaminants. This study not only demonstrates a one-stone-two-birds strategy for large-scale direct production of potable water from polluted seawater, but also opens up exciting possibilities for parallel production of energy and water resources.

Phonon-Engineered Hard-Carbon Nanoflorets Achieving Rapid and Efficient Solar-Thermal Based Water Evaporation and Space-Heating

Generation and utilization of green heat produced from solar energy demand broadband absorbers with the elusive combination of strong phonon-driven photon thermalization and, contrastingly, weak phonon-lattice thermal conductivity. Here, we report a new class of porous, nanostructured hard-carbon florets (NCFs) consisting of isotropically assembled conical microcavities for greater light entrapment and efficient broad-band absorption (95% over 250-2500 nm). Resembling marigolds, the NCF exhibits short-range graphitic order that promotes instantaneous and efficient solar-thermal conversion (ηSTC = 87%) while exhibiting long-range intrinsic disorder providing low thermal conductivity (1.5 W m-1 K-1) to minimize thermal loss (13%). Solution processable NCF coatings on arbitrarily substrates (filter paper, terracotta, Cu and Al tubes) generate surface temperature of 400 ± 2 K and exhibit high thermal effusance (519 W s0.5 m-2 K-1) to achieve highest combination of (a) rate of solar-driven interfacial water evaporation (Rw = 5.4 kg m-2 h-1, 2 sun), (b) solar-vapor conversion efficiency (ηSVC = 186%), and (c) ηSTC (87%) among known materials. Such robust performance is retained for beyond 30 days of continuous operation and under different solar power (1 sun to 5 sun). Furthermore, active space heating (outlet air temperature = 346 ± 3 K) using NCF coatings is demonstrated.

Boosting Water Evaporation by Construction of Photothermal Materials with a Biomimetic Black Soil Aggregate Structure

Solar-driven interfacial evaporation is considered an efficient way to get fresh water from seawater. However, the low evaporation rate, surface salt crystallization, and low energy collection of the photothermal evaporation layer limit its further application in an outdoor freshwater field. And the aggregate structure design of the material itself is often ignored in solar-driven water evaporation. Black soil (BS), with a unique soil aggregate structure, is rich in tubular pores, which can be used for multilevel sunlight utilization and good capillary water transport. Based on the extraordinary photothermal properties and pumping capacity of BS, a reasonable unidirectional salt-collecting device is designed, which can realize long-term collection of mineral salts and continuous evaporation of seawater and generate electric energy in the continuous evaporation. Inspired by the unique aggregate structure, the photothermal material doping of halloysite and nigrosin will simulate the generation of this aggregate structure and retain a good water transport effect while obtaining multistage utilization of sunlight. The solar-driven evaporation rate of a nigrosin-halloysite solar steam generator is 1.75 kg m-2 h-1 under 1 kW m-2 mimic solar radiation; it can achieve stable salt leaching-induced voltage generation of 240 mV. This work demonstrates not only a solar evaporator that can continuously achieve desalination but also the design strategy of BS-like aggregate photothermal materials, which promotes the development of low-cost resource recovery and energy generation for practical outdoor seawater desalination.

Microfluidic-Assisted Self-Assembly of 2D Nanosheets toward in situ Generation of Robust Nanofiber Film

Methods allow the enhancement of nanofibers via self-assembly are potentially important for new disciplines with many advantages, including multi-anchor interaction, intrinsic mechanical properties and versatility. Herein, a microfluidic-assisted self-assembly process to construct hydroxyl functionalized boron nitride nanosheets (OH-BNNS)/graphene oxide (GO)/thermoplastic polyurethane (TPU) composite nanofiber film, in which stable and precisely controlled self-assembly is fulfilled by the confined ultra-small-volume chip is demonstrated. Multiple fine structural analyses alongside with the density-functional theory (DFT) calculations are implemented to confirm the synergistic effect of noncovalent interactions (hydrogen bonding interaction, π - π stacking interaction, and van der Waals attraction) plays a critical role in the robust micro-structure and a massive 700% enhancement of mechanical strength via adding only 0.3 wt% OH-BNNS and GO. Importantly, profiled from broadband optical absorption ability, robust mechanical properties and outstanding flexibility, the self-assembled 3D OH-BNNS/GO/TPU nanofiber film reveals an adorable evaporation rate of 4.04 kg m-2  h-1 under one sun illumination with stable energy transfer efficiency (93.2%) by accompanying hydrogen bonding interaction. This microfluidic-assisted self-assembly strategy will provide a constructive entry point for the rational design of nanofibers and beyond.

Gradience Free Nanoinsertion of Fe3O4 into Wood for Enhanced Hydrovoltaic Energy Harvesting

Hydrovoltaic energy harvesting offers the potential to utilize enormous water energy for sustainable energy systems. Here, we report the utilization and tailoring of an intrinsic anisotropic 3D continuous microchannel structure from native wood for efficient hydrovoltaic energy harvesting by Fe3O4 nanoparticle insertion. Acetone-assisted precursor infiltration ensures the homogenous distribution of Fe ions for gradience-free Fe3O4 nanoparticle formation in wood. The Fe3O4/wood nanocomposites result in an open-circuit voltage of 63 mV and a power density of ∼52 μW/m2 (∼165 times higher than the original wood) under ambient conditions. The output voltage and power density are further increased to 1 V and ∼743 μW/m2 under 3 suns solar irradiation. The enhancement could be attributed to the increase of surface charge, nanoporosity, and photothermal effect from Fe3O4. The device exhibits a stable voltage of ∼1 V for 30 h (3 cycles of 10 h) showing good long-term stability. The methodology offers the potential for hierarchical organic-inorganic nanocomposite design for scalable and efficient ambient energy harvesting.

Borophene Embedded Cellulose Paper for Enhanced Photothermal Water Evaporation and Prompt Bacterial Killing

Solar-driven photothermal water evaporation is considered an elegant and sustainable technology for freshwater production. The existing systems, however, often suffer from poor stability and biofouling issues, which severely hamper their prospects in practical applications. Conventionally, photothermal materials are deposited on the membrane supports via vacuum-assisted filtration or dip-coating methods. Nevertheless, the weak inherent material-membrane interactions frequently lead to poor durability, and the photothermal material layer can be easily peeled off from the hosting substrates or partially dissolved when immersed in water. In the present article, the discovery of the incorporation of borophene into cellulose nanofibers (CNF), enabling excellent environmental stability with a high light-to-heat conversion efficiency of 91.5% and water evaporation rate of 1.45 kg m^-2 h^-1 under simulated sunlight is reported. It is also demonstrated that borophene papers can be employed as an excellent active photothermal material for eliminating almost 100% of both gram-positive and gram-negative bacteria within 20 min under three sun irradiations. The result opens a new direction for the design of borophene-based papers with unique photothermal properties which can be used for the effective treatment of a wide range of wastewaters.

Effect of Model Tear Film Lipid Layer on Water Evaporation

Purpose

A majority of in vitro models were incapable of reproducing the evaporation resistance of tear film lipid layer (TFLL) in vivo. The purpose of this research is to develop a novel in vitro model to study the effect of TFLL on water evaporation.

Methods

A ventilated, closed-chamber, droplet evaporimeter with a constant surface area has been invented to study the evaporation resistance of TFLL. This evaporimeter ensures a rigorous control of environmental conditions, including the temperature, relative humidity, airflow rate, surface area, and surface pressure, thus allowing for reproducible water evaporation measurements over a time period of only 5 minutes. The volumetric evaporation rate of this droplet evaporimeter is less than 2.7 µL/min, comparable to the basal tear production of healthy adults. Together with direct film imaging using atomic force microscopy (AFM), we have studied the effect of a model TFLL on water evaporation, as a function of the lipid composition and surface pressure.

Results

A model TFLL composed of 40% wax esters, 40% cholesteryl esters, and 20% polar lipids was capable of reducing the water evaporation rate by 11% at surface pressure 47 mN/m. AFM revealed that the model TFLL at high surface pressures consists of discrete droplets/aggregates of the nonpolar lipids residing atop a polar lipid monolayer with phase separation.

Conclusions

The TFLL may resist water evaporation with a combined mechanism by increasing film compactness of the polar lipid film at the air-water surface, and, to a lesser extent, by increasing film thickness of the nonpolar lipid film.

Enhanced Water Evaporation from Å-Scale Graphene Nanopores

Enhancing the kinetics of liquid-vapor transition from nanoscale confinements is an attractive strategy for developing evaporation and separation applications. The ultimate limit of confinement for evaporation is an atom thick interface hosting angstrom-scale nanopores. Herein, using a combined experimental/computational approach, we report highly enhanced water evaporation rates when angstrom sized oxygen-functionalized graphene nanopores are placed at the liquid-vapor interface. The evaporation flux increases for the smaller nanopores with an enhancement up to 35-fold with respect to the bare liquid-vapor interface. Molecular dynamics simulations reveal that oxygen-functionalized nanopores render rapid rotational and translational dynamics to the water molecules due to a reduced and short-lived water-water hydrogen bonding. The potential of mean force (PMF) reveals that the free energy barrier for water evaporation decreases in the presence of nanopores at the atomically thin interface, which further explains the enhancement in evaporation flux. These findings can enable the development of energy-efficient technologies relying on water evaporation.

Nanocomposite-Enhanced Efficient Evaporation System for Solar-Driven Seawater Desalination-An Optimized Design for Clean Water Production

Solar-driven evaporation is a promising technology for desalinating seawater and wastewater without mechanical or electrical energy. The approaches to obtaining fresh water with higher evaporation efficiency are essential to address the water-scarcity issue in remote sensing areas. Herein, we report a highly efficient solar evaporator derived from the nanocomposite of anatase TiO₂/activated carbon (TiO₂/AC), which was coated on washable cotton fabric using the dip-dry technique for solar water evaporation. The ultra-black fabric offers enhanced solar absorption (93.03%), hydrophilic water transport, and an efficient evaporation rate of 1.65 kg/m²h under 1 kW m^-2 or one sun solar intensity. More importantly, the sideways water channels and centralized thermal insulation of the designed TiO₂/AC solar evaporator accumulated photothermal heat at the liquid and air interface along with an enhanced surface temperature of 40.98 °C under one sun. The fabricated solar evaporator desalinated seawater (3.5 wt%) without affecting the evaporation rates, and the collected condensed water met the standard of drinking water set by the World Health Organization (WHO). This approach eventually enabled the engineering design groups to develop the technology pathways as well as optimum conditions for low-cost, scalable, efficient, and sustainable solar-driven steam generators to cope with global water scarcity.

Carbon Nanotubes Grown on the Carbon Fibers to Enhance the Photothermal Conversion toward Solar-Driven Applications

Photothermal conversion is a directly, sustainable, and green path to use solar energy and the one of the most important keys is the photothermal conversion material. How to obtain the durable and effective material for photothermal conversion with low cost and facile preparation is still a great challenge. In this work, the carbon nanotubes (CNTs) are grown on the carbon fibers (CFs) via the catalysis of trapped Fe and Co. The absorption of the as-prepared CFs/CNTs illustrate the enhancement from the visible light to the near-infrared light range. The photothermal conversion characterization shows the grown CNTs promoting the higher surface temperature and the highest temperature reaches to about 325 °C under 10 sun irradiations. The water evaporation on the CFs/CNTs is measured 1.40 ± 0.03 kg·cm^-2·h^-1 under 1 sun irradiation and the water evaporation rate is also found depending on the irradiation density. The photothermal conversion applications and the water evaporation under natural irradiation also reveal the suitable candidate of the CFs/CNTs for photothermal conversion application. This work provides a facile path to obtain effective carbon-based materials for photothermal application.

In Situ Small-Angle Neutron Scattering Analysis of Water Evaporation from Porous Exhaust-Gas-Catalyst Supports

Porous media as catalyst supports are key to developing automotive exhaust purification systems. In particular, the water content of these porous media is attracting research attention because catalyst supports containing condensed water vapor at the early stage of cold start require a longer warm-up period. In this regard, water isotherms and evaporation in porous Al₂O₃ were investigated in this study using in situ small-angle neutron scattering (SANS) experiments. Unlike conventional evaluation methods, such as weighing and X-ray tomography, SANS distinguishes water in the primary and secondary pores using a contrast-matching method. Time-resolved measurements showed that water started to evaporate from the secondary pores in tens of seconds and subsequently from the primary pores in a hundred seconds. Exhaustive experiments conducted using nine alumina-based samples revealed that the drying rate depended on the secondary pore size of the porous Al₂O₃. The proposed approach can enable the evaluation of controlling factors to additionally optimize the performance of automotive exhaust gas catalysts, especially during cold start.

Highly Efficient Photothermal Conversion and Water Transport during Solar Evaporation Enabled by Amorphous Hollow Multishelled Nanocomposites

Solar evaporation, which enables water purification without consuming fossil fuels, has been considered the most promising strategy to address global scarcity of drinkable water. However, the suboptimal structure and composition designs still result in a trade-off between photothermal conversion, water transport, and tolerance to harsh environments. Here, an ultrastable amorphous Ta₂ O₅ /C nanocomposite is designed with a hollow multishelled structure (HoMS) for solar evaporation. This HoMS results in highly efficient photoabsorption and photothermal conversion, as well as a decrease of the actual water evaporation enthalpy. A superfast evaporation speed of 4.02 kg m^-2 h^-1 is achieved. More importantly, a World Health Organization standard drinkable water can be achieved from seawater, heavy-metal- and bacteria-containing water, and even from extremely acidic/alkaline or radioactive water sources. Notably, the concentration of pseudovirus SC2-P can be decreased by 6 orders of magnitude after evaporation.

Considerations of Thermodynamics and Kinetics for the Effects of Relative Humidity on the Electrolyte in Electrochemical Toxic Gas Sensors

In this paper, the physical chemistry of the absorption and desorption of water vapor for electrochemical gas sensors with commonly used sulfuric acid as the electrolyte is investigated. Electrochemical gas sensors are being increasingly used for monitoring toxic gases in the environment, and they are, in principle, simple devices, but in practice, their operation is complex. In particular, changes in atmospheric humidity and temperature can have significant effects on the sensor output. A model has been developed for the calculation of sensor weight changes as humidity varies, which are in good agreement with the analysis of experimental results. This then allows for the calculation of the rather more important electrolyte volume variations. Changes in acid molarity and physical characteristics of the electrolyte have also been determined. The effects on working electrode (WE) electrocatalytic activity are discussed, and potential problems with sensors for environmental monitoring are highlighted. In particular, changes in the electroactive area of the WE and, consequently, of the sensor output, and flooding of the WE catalyst aggregates which can lead to problems with electrolyte leakage from sensors are considered.

Design of Persistent and Stable Porous Radical Polymers by Electronic Isolation Strategy

Conjugated organic radical polymers with stable radical features are difficult to design because the π conjugation in the polymer backbones makes the radicals readily delocalize and tend to undergo covalent bonding processes. In this work, we report an electronic isolation strategy to design stable porous radical polymers by homocoupling reaction from a meta-position active monomer. The meta linkage ensures less conjugation in the polymer skeletons, localizes the resonant radicals, and prevents them from recombination. The resulting porous radical polymer exhibits exceptional radical characters with ultralow band gap of 0.68 eV, strong yet extended UV/Vis-NIR absorption up to 1800 nm, and high spin density. The above features make the polymer very promising in the photothermal conversion with record-high photothermal temperature increment of ≈∼240 °C and striking solar-driven water evaporation efficiency of 96.8 %. Our results demonstrate the feasibility of electronic isolation of radicals for producing outstanding photothermal materials.

Conjugated Organic Photothermal Films for Spatiotemporal Thermal Engineering

With the growth of photoenergy harvesting and thermal engineering, photothermal materials (PTMs) have attracted substantial interest due to their unique functions such as localized heat generation, spatiotemporal thermal controllability, invisibility, and light harvesting capabilities. In particular, π-conjugated organic PTMs show advantages over inorganic or metallic PTMs in thin film applications due to their large light absorptivity, ease of synthesis and tunability of molecular structures for realizing high NIR absorption, flexibility, and solution processability. This review is intended to provide an overview of organic PTMs, including both molecular and polymeric PTMs. A description of the photothermal (PT) effect and conversion efficiency (η_PT ) for organic films is provided. After that, the chemical structure and optical properties of organic PTMs are discussed. Finally, emerging applications of organic PT films from the perspective of spatiotemporal thermal engineering principles are illustrated.

High-Entropy-Alloy Nanoparticles with Enhanced Interband Transitions for Efficient Photothermal Conversion

Photothermal materials with broadband optical absorption and high conversion efficiency are intensively pursued to date. Here, proposing by the d-d interband transitions, we report an unprecedented high-entropy alloy FeCoNiTiVCrCu nanoparticles that the energy regions below and above the Fermi level (±4 eV) have been fully filled by the 3d transition metals, which realizes an average absorbance greater than 96 % in the entire solar spectrum (wavelength of 250 to 2500 nm). Furthermore, we also calculated the photothermal conversion efficiency and the evaporation rate towards the steam generation. Due to its pronounced full light capture and ultrafast local heating, our high-entropy-alloy nanoparticle-based solar steam generator has over 98 % efficiency under one sun irradiation, meanwhile enabling a high evaporation rate of 2.26 kg m^-2  h^-1 .

Synthesis of a Co-Sn Alloy-Deposited PTFE Film for Enhanced Solar-Driven Water Evaporation via a Super-Absorbent Polymer-Based "Water Pump" Design

Solar-driven water evaporation is a promising solution to water pollution, the energy crisis, and water shortages. However, the approach in which the photothermal film is in direct contact with bulk water for water evaporation may lead to a large amount of heat loss, thereby reducing the light-to-heat conversion efficiency (η) of the photothermal film. Here, a highly efficient solar-driven water evaporation system was developed using a Co-Sn alloy-deposited Teflon (PTFE) film (Co-Sn alloy@PTFE) and super-absorbent polymers (SAPs) supported with a floating foam substrate. The Co-Sn alloy with full-spectrum (200-2500 nm) absorption characteristics is devoted to high light-to-heat conversion, while the porous PTFE with high mechanical performance can support the Co-Sn alloy. We used density functional theory to prove that the Co-Sn alloy had a strong adhesive force with PTFE without surfactants due to the high adsorption energy between the (101) crystal plane of the Co-Sn alloy and the hydroxyl group on the PTFE film. Importantly, via the SAP-based "water pump" design, we improved the η of the Co-Sn alloy@PTFE film to 89%, mainly because the SAP not only effectively performed water transportation but also markedly reduced the heat loss of the Co-Sn alloy@PTFE film. Our work highlights the strong potential of Co-Sn alloy@PTFE-based light-to-heat conversion systems for realizing highly effective solar energy-driven water evaporation.

Coating of Wood with Fe2O3-Decorated Carbon Nanotubes by One-Step Combustion for Efficient Solar Steam Generation

As the global water shortage becomes increasingly serious, it is highly imperative to develop efficient, renewable, and large-scale water purification devices. Herein, an efficient solar-driven water purification device of wood coated with Fe₂O₃ nanoparticle-decorated carbon nanotubes (Fe₂O₃/CNT) is fabricated in only a few seconds by one-step combustion of ferric acetylacetonate in an ambient environment. The thin layer of the Fe₂O₃/CNT hybrid coated on the upper surface of the wood serves as a solar-light absorber for converting solar energy to thermal energy, while the thermally insulating wood layer with vertically aligned channels endows the device with rapid water upward transport and localizes the generated heat inside the Fe₂O₃/CNT layer for solar-driven water evaporation. As a result, the wood/Fe₂O₃/CNT device achieves a high water steam generation capability of 1.42 kg m^-2 h^-1 along with an excellent evaporation efficiency of 87.2% under 1 sun irradiation, higher than most of the wood-based solar-driven water evaporation device reported. This device is also efficient in the purification of seawaters and wastewaters. This work demonstrates a rapid and facile methodology for large-scale fabrication of wood/Fe₂O₃/CNT devices for efficient solar-driven water purification.

Bioinspired Hierarchical Nanofabric Electrode for Silicon Hydrovoltaic Device with Record Power Output

Direct electricity generation from water flow/evaporation, coined hydrovoltaic effect, has recently attracted intense interest as a facile approach to harvest green energy from ubiquitous capillary water flow or evaporation. However, the current hydrovoltaic device is inferior in output power efficiency compared to other renewable energy devices. Slow water evaporation rate and inefficient charge collection at device electrodes are two fundamental drawbacks limiting energy output efficiency. Here, we report a bioinspired hierarchical porous fabric electrode that enables high water evaporation rate, efficient charge collection, and rapid charge transport in nanostructured silicon-based hydrovoltaic devices. Such an electrode can efficiently collect charges generated in nanostructured silicon as well as induce a prompt water evaporation rate. At room temperature, the device can generate an open-circuit voltage (V_oc) of 550 mV and a short-current density (J_sc) of 22 μA·cm^-2. It can output a power density over 10 μW·cm^-2, which is 3 orders of magnitude larger than all those reported for analogous hydrovoltaic devices. Our results could supply an effective strategy for the development of high-performance hydrovoltaic devices through optimizing electrode structures.

Direct Observation of the Light-Induced Exfoliation of Molybdenum Disulfide Sheets in Water Medium

Single and a few atomic-layer molybdenum disulfide (MoS₂) is a promising material in the fields of hydrogen generation, battery, supercapacitor, and environmental protection, owing to the outstanding electronic, optical, and catalytic properties. Although many approaches have been developed for exfoliation of MoS₂ sheets, it is still essential to develop simple, convenient, and environmental friendly exfoliation methods. More importantly, the microscopic exfoliation process and the mechanism are still not clear, limiting a deeper understanding of the exfoliation. Herein, we develop a convenient and clean method for exfoliation of the 2H phase MoS₂ (2H-MoS₂) deposited on an indium tin oxide (ITO) surface. Importantly, the exfoliation process is observed directly and continuously under an optical microscope to reveal the detailed exfoliation process and mechanism. As illustrated, the light illumination triggers the exfoliation of the 2H-MoS₂ sheets, and the presence of water is essential in this exfoliation process. The light intensity and wavelength, humidity, and bias all affect the exfoliation process obviously. The exfoliation is caused by the vaporization of the water molecules intercalated in 2H-MoS₂ interlayers. By using this method, 2H-MoS₂ nanosheets with different thicknesses are prepared on the ITO substrate, and microscopic catalysis mapping of the exfoliated sheets is demonstrated with single-molecule fluorescence microscopy, revealing that the prepared thin-layer 2H-MoS₂ nanosheets show improved electrocatalysis activity (roughly 20 times). Our work will not only help deepen the understanding of exfoliation process of two-dimensional nanosheets but also provide an effective tool for the in situ study of various properties of the exfoliated sheets.

Titanium Nitride Nanodonuts Synthesized from Natural Ilmenite Ore as a Novel and Efficient Thermoplasmonic Material

Nanostructures of titanium nitride (TiN) have recently been considered as a new class of plasmonic materials that have been utilized in many solar energy applications. This work presents the synthesis of a novel nanostructure of TiN that has a nanodonut shape from natural ilmenite ore using a low-cost and bulk method. The TiN nanodonuts exhibit strong and spectrally broad localized surface plasmon resonance absorption in the visible region centered at 560 nm, which is well suited for thermoplasmonic applications as a nanoscale heat source. The heat generation is investigated by water evaporation experiments under simulated solar light, demonstrating excellent solar light harvesting performance of the nanodonut structure.

Rational Design of MOF-Based Hybrid Nanomaterials for Directly Harvesting Electric Energy from Water Evaporation

The continuous exploration of clean-energy technology is critical for the sustainable development of society. The recent work on the electric energy harvesting from water evaporation has made a significant contribution to the utilization of clean energy for self-powering systems. Here, a novel metal-organic-framework-based hybrid nanomaterial is delicately designed and synthesized by the growth of UIO-66 nanoparticles on 2D AlOOH nanoflakes. Due to the combined merits from the 2D morphology, which is inherited from the AlOOH nanoflakes, and the high surface potential, which originates from the UIO-66 nanoparticles, the device made of the AlOOH/UIO-66 hybrid nanomaterials can harvest electric energy from natural water evaporation. An open-circuit voltage of 1.63 ± 0.10 V can be achieved on the prototype devices made of the hybrid nanomaterial. As a proof-of-concept application, a small electric appliance, e.g., a digital calculator, is powered up by a 3 × 3 device array connected in a combined series-parallel configuration.

High Efficiency Solar Membranes Structurally Designed with 3D Core-2D Shell SiO2@Amino-Carbon Hybrid Advanced Composite for Facile Steam Generation

Steam generation through efficient utilization of solar energy is a promising technology in addressing the challenge of global freshwater shortage and water pollution. One of the biggest hurdles for traditional photothermal membranes to function continuously in a high temperature, high salt, and corrosive environment has been attributed to their rapid decline of mechanical properties. In this work, a highly efficient solar-driven interfacial water evaporation system has been developed via a polydopamine/carbon/silicon (PCS) composite membrane supported by a floating insulation foam substrate. A 3.1 fold increase in the water vaporization rate was recorded compared with the pure water system. The 2D-carbon nanolayer on the surface was successfully prepared by carbonizing low-cost linear polyethylene with a glass fiber (GF) membrane as the substrate, and then the carbon membrane was modified with dopamine to control water transport on the carbon coating and within the glass fiber. The PCS membrane has a high efficiency for solar steam generation owing to high optical absorption and has excellent solar thermal conversion capability. The evaporation rate and solar thermal conversion efficiency of the PCS membrane under simulated sunlight irradiation with 1 sun (1 kW·m^-2) are 1.39 kg·m^-2·h^-1 and 80.4% respectively, which are significantly higher compared to GF membrane, carbon/silicon (CS) membrane, and pure water without a photothermal membrane. The water evaporation system retained high efficiency after 20 cycles under simulated sunlight irradiation of 1 sun. This study provides critical insight on the design and fabrication of a highly efficient and durable evaporation system.

Flexible Pt3Ni-S-Deposited Teflon Membrane with High Surface Mechanical Properties for Efficient Solar-Driven Strong Acidic/Alkaline Water Evaporation

Solar-driven water evaporation provides a promising solution to the energy crisis and environmental issues. Capitalizing on the high photothermal conversion efficiency and excellent resistance to strong acids or strong alkalis of Pt₃Ni-S nanowires, we strategically design and prepare a flexible Pt₃Ni-S-deposited Teflon (PTFE) membrane for achieving efficient strong acid/alkaline water evaporation under simulated sunlight irradiation (1 sun). By comparing the surface morphology, mechanical properties, and water evaporation performance of the as-prepared three different membranes, we have screened out a high-performance photothermal membrane that has good hydrophobicity (water contact angle = 106°), strong mechanical properties, high light-to-heat conversion efficiency (η = 80%), and excellent durability (10 cycles in a range of pH = 1.2-12). In particular, we explore the mechanism of high surface mechanical properties of the as-prepared membrane using density functional theory. The results demonstrate that the related mechanism can be ascribed to two main reasons: (1) hydrogen bonds can be formed between the 2-pyrrolidone ring and PTFE-3 and (2) the O atom in PTFE-3 carries more negative charge (-0.19 |e|) than PTFE-1 (-0.16 |e|) and PTFE-2 (-0.15 |e|). Our work highlights the great potentials of a Pt₃Ni-S-deposited PTFE membrane as a device for implementing solar energy-driven evaporation of industrial wastewater with strong acidity or alkalinity and provides a new strategy for improving the surface mechanical properties of a photothermal membrane.

Graphene and Rice-Straw-Fiber-Based 3D Photothermal Aerogels for Highly Efficient Solar Evaporation

Solar-steam generation is one of the most promising technologies to mitigate the issue of clean water shortage using sustainable solar energy. Photothermal aerogels, especially the three-dimensional (3D) graphene-based aerogels, have shown unique merits for solar-steam generation, such as lightweight, high flexibility, and superior evaporation rate and energy efficiency. However, 3D aerogels require much more raw materials of graphene, which limits their large-scale applications. In this study, 3D photothermal aerogels composed of reduced graphene oxide (RGO) nanosheets, rice-straw-derived cellulose fibers, and sodium alginate (SA) are prepared for solar-steam generation. The use of rice straw fibers as skeletal support significantly reduces the need for the more expensive RGO by 43.5%, turning the rice straw biomass waste into value-added materials. The integration of rice straw fibers and RGO significantly enhances the flexibility and mechanical stability of the obtained photothermal RGO-SA-cellulose aerogel. The photothermal aerogel shows a strong broad-band light absorption of 96-97%. During solar-steam generation, the 3D photothermal aerogel effectively decreases the radiation and convection energy loss while enhancing energy harvesting from the environment, leading to an extremely high evaporation rate of 2.25 kg m^-2 h^-1, corresponding to an energy conversion efficiency of 88.9% under 1.0 sun irradiation. The salinity of clean water collected during the evaporation of real seawater is only 0.37 ppm. The materials are environmentally friendly and cost-effective, showing great potential for real-world desalination applications.

Ultrafast Diameter-Dependent Water Evaporation from Nanopores

Evaporation from nanopores plays an important role in various natural and industrial processes that require efficient heat and mass transfer. The ultimate performance of nanopore-evaporation-based processes is dictated by evaporation kinetics at the liquid-vapor interface, which has yet to be experimentally studied down to the single nanopore level. Here we report unambiguous measurements of kinetically limited intense evaporation from individual hydrophilic nanopores with both hydrophilic and hydrophobic top outer surfaces at 22 °C using nanochannel-connected nanopore devices. Our results show that the evaporation fluxes of nanopores with hydrophilic outer surfaces show a strong diameter dependence with an exponent of nearly -1.5, reaching up to 11-fold of the maximum theoretical predication provided by the classical Hertz-Knudsen relation at a pore diameter of 27 nm. Differently, the evaporation fluxes of nanopores with hydrophobic outer surfaces show a different diameter dependence with an exponent of -0.66, achieving 66% of the maximum theoretical predication at a pore diameter of 28 nm. We discover that the ultrafast diameter-dependent evaporation from nanopores with hydrophilic outer surfaces mainly stems from evaporating water thin films outside of the nanopores. In contrast, the diameter-dependent evaporation from nanopores with hydrophobic outer surfaces is governed by evaporation kinetics inside the nanopores, which indicates that the evaporation coefficient varies in different nanoscale confinements, possibly due to surface-charge-induced concentration changes of hydronium ions. This study enhances our understanding of evaporation at the nanoscale and demonstrates great potential of evaporation from nanopores.

A Microstructured Graphene/Poly(N-isopropylacrylamide) Membrane for Intelligent Solar Water Evaporation

Intelligent solar water evaporation (iSWE) was achieved with a thermally responsive and microstructured graphene/poly(N-isopropylacrylamide) (mG/PNIPAm) membrane. As the solar intensity varies, the water evaporation is tuned through reversible transformations of microstructures reminiscent of the stomatal opening and closing of leaves. Consequently, this mG/PNIPAm membrane displays a high water evaporation rate change (ΔWER) of 1.66 kg m^-2  h^-1 under weak sunlight (intensity<1 sun) and a low ΔWER of 0.24 kg m^-2  h^-1 under intense sunlight (1 sun<intensity<2 sun). Because of the double-layer structure with predictable shape and dynamics, the leaf-like membrane can further autonomously modulate the water evaporation by self-curling under intense solar irradiation in accordance with simulation results. This mG/PNIPAm membrane provides a smart material platform with self-adaptability in response to changing environments.

Melt Electrospun Reduced Tungsten Oxide /Polylactic Acid Fiber Membranes as a Photothermal Material for Light-Driven Interfacial Water Evaporation

The development of efficient photothermal materials is the most important issue in solar water evaporation. In this work, melt electrospun reduced tungsten oxide/polylactic acid (WO_2.72/PLA) fiber membranes were successfully prepared with improved near-infrared (NIR) photothermal conversion properties owing to strong NIR photoabsorption by the metal oxide. WO_2.72 powder nanoparticles were incorporated into PLA matrix by melt processing, following which the composites were extruded into wires using a single screw extruder. Subsequently, fiber membranes were prepared from the extruded wire of the WO_2.72/PLA composite by melt electrospinning, which is a cost-effective technique that can produce fiber membranes without the addition of environmentally unfriendly chemicals. The melt electrospun WO_2.72/PLA fiber membranes, floatable on water due to surface hydrophobicity, were systematically designed for, and applied to, vapor generation based on the interfacial concept of solar heating. With the photothermal WO_2.72/PLA fiber membrane containing 7 wt % WO_2.72 nanoparticles, the water evaporation efficiency was reached 81.39%, which is higher than that for the pure PLA fiber membrane and bulk water. Thus, this work contributes to the development of novel photothermal fiber membranes in order to enhance light-driven water evaporation performance for potential applications in the fields of water treatment and desalination.

MXene Ti3C2: An Effective 2D Light-to-Heat Conversion Material

MXene, a new series of 2D material, has been steadily advancing its applications to a variety of fields, such as catalysis, supercapacitor, molecular separation, electromagnetic wave interference shielding. This work reports a carefully designed aqueous droplet light heating system along with a thorough mathematical procedure, which combined leads to a precise determination of internal light-to-heat conversion efficiency of a variety of nanomaterials. The internal light-to-heat conversion efficiency of MXene, more specifically Ti₃C₂, was measured to be 100%, indicating a perfect energy conversion. Furthermore, a self-floating MXene thin membrane was prepared by simple vacuum filtration and the membrane, in the presence of a rationally chosen heat barrier, produced a light-to-water-evaporation efficiency of 84% under one sun irradiation, which is among the state of art energy efficiency for similar photothermal evaporation system. The outstanding internal light-to-heat conversion efficiency and great light-to-water evaporation efficiency reported in this work suggest that MXene is a very promising light-to-heat conversion material and thus deserves more research attention toward practical applications.