Tree-Inspired Aerogel Comprising Nonoxidized Graphene Flakes and Cellulose as Solar Absorber for Efficient Water Generation.

As global freshwater shortages worsen, solar steam generation (SSG) emerges as a promising, eco-friendly, and cost-effective solution for water purification. However, widespread SSG implementation requires efficient photothermal materials and solar evaporators that integrate enhanced light-to-heat conversion, rapid water transportation, and optimal thermal management. This study investigates using nonoxidized graphene flakes (NOGF) with negligible defects as photothermal materials capable of absorbing over 98% of sunlight. By combining NOGF with cellulose nanofibers (CNF) through bidirectional freeze casting, we created a vertically and radially aligned solar evaporator. The hybrid aerogel exhibited exceptional solar absorption, efficient solar-to-thermal conversion, and improved surface wettability. Inspired by tree structures, our design ensures rapid water supply while minimizing heat loss. With low NOGF content (∼10.0%), the NOGF/CNF aerogel achieves a solar steam generation rate of 2.39 kg m-2 h-1 with an energy conversion efficiency of 93.7% under 1-sun illumination, promising applications in seawater desalination and wastewater purification.

Crystal Plane Engineering to Boost Water Cluster Evaporation for Enhanced Solar Steam Generation.

Polymer based low evaporation enthalpy materials have become a universal selection for improving the efficiency of solar steam generation. Although water cluster and intermediate water mechanisms have been proposed to explain the low evaporation enthalpy, the production process and microstructure of activated water are still unclear. Here, crystal plane engineering is used to investigate the intermediate water state and the water cluster activation mechanism. The unique open-closed coordination structure on the optimized crystal surface promotes the generation of firm water clusters by optimizing the intermediate water state. Under the similar solar energy absorption of all materials, crystal plane engineering increased the solar steam generation rate of the evaporator by 31.2% and increased the energy efficiency to 94.8%. Exploring the micro-evaporation process and activated water structure is expected to stimulate the development of the next generation low evaporation enthalpy materials.

Biomimetic Design of 3D Fe3O4/V-EVOH Fiber-Based Self-Floating Composite Aerogel to Enhance Solar Steam Generation Performance.

An interfacial solar steam generation evaporator for seawater desalination has attracted extensive interest in recent years. Nevertheless, challenges still remain in relatively low evaporation rate, unsatisfactory energy conversion efficiency, and salt accumulation. Herein, we have demonstrated a biomimetic bilayer composite aerogel consisting of bottom hydrophilic and vertically aligned EVOH channels and an upper hydrophobic conical Fe3O4 array. Thanks to the design merits, the 3D Fe3O4/V-EVOH evaporator exhibits a high evaporation rate of ∼2.446 kg m-2 h-1 and an impressive solar energy conversion efficiency of ∼165.5% under 1 sun illumination, which is superior to those of state-of-the-art evaporators reported so far. Moreover, the asymmetrical wettability not only allows the evaporator to self-float on the water but also facilitates the salt ion diffusion in the channels; thus, the evaporator shows no salt crystals on its surface and only a 6% decrease in evaporation performance even after the salt concentration increases from 0 to 10.0 wt %.

Structure/Composition/Phase Regulations of Dealloying-Derived Nanoporous Metals and Their Solar Steam Generation Performances.

Structural regulation is of primary importance in structure-property/application studies of dealloyed nanoporous metals. Three aspects are mainly considered to affect the microstructure of nanoporous metals: design of precursor alloy, choosing of dealloying parameter, and annealing treatment. Herein, through the combination of the above three strategies, the regulation of structure, composition and phase in nanoporous metals are simultaneously achieved. With a dilute Cu99Ag0.75Au0.25 as the precursor, three kinds of nanoporous films are fabricated, including bi-phase nanoporous Cu-Ag-Au (B-NP-CuAgAu), hierarchically nanoporous Au (H-NPG) and single-phase homogeneously nanoporous Au (S-NPG). In situ X-ray diffraction and ex situ characterizations are utilized to reveal the structure/composition/phase evolutions during dealloying of Cu99Ag0.75Au0.25, as well as the macroscopic changes of the dealloyed samples. Notably, the ultrafine ligaments/channels of B-NP-CuAgAu and the two-level nanoporous structure of H-NPG endow them with good broadband light absorption and excellent hydrophilicity, which contribute to their outstanding solar steam generation (SSG) performances. Specially, the B-NP-CuAgAu film shows a more efficient SSG performance with water evaporation rate of 1.49 kg m-2 h-1 and photothermal efficiency of 93.6% at 1 kW m-2, and good seawater desalination ability.

Hofmeister Effect-Assisted Facile Fabrication of Self-Assembled Poly(Vinyl Alcohol)/Graphite Composite Sponge-Like Hydrogel for Solar Steam Generation.

The use of hydrogel-based interfacial solar evaporators for desalination is a green, sustainable, and extremely concerned freshwater acquisition strategy. However, developing evaporators that are easy to manufacture, cheap, and have excellent porous structures still remains a considerable challenge. This work proposes a novel strategy for preparing a self-assembling sponge-like poly(vinyl alcohol)/graphite composite hydrogel based on the Hofmeister effect for the first time. The sponge-like hydrogel interfacial solar evaporator (PGCNG) is successfully obtained after combining with graphite. The whole process is environmental-friendly and of low-carbon free of freezing process. The PGCNG can be conventionally dried and stored. PGCNG shows impressive water storage performance and water transmission capacity, excellent steam generation performance and salt resistance. PGCNG has a high evaporation rate of 3.5 kg m-2 h-1 under 1 kW m-2 h-1 solar irradiation and PGCNG demonstrates stable evaporation performance over both 10 h of continuous brine evaporation and 30 cycles of brine evaporation. Its excellent performance and simple, scalable preparation strategy make it a valuable material for practical interface solar seawater desalination devices.

Fabrication of Oriented MOF-Based Mixed Matrix Membrane via Ion-Induced Synchronous Synthesis.

Developing a facile strategy for constructing oriented mixed matrix membranes (MMMs) with uniformly dispersed and high-loading metal-organic frameworks (MOFs) is a crucial scientific challenge in probing the enhanced capability and potential applications of MOF-polymer MMMs. Herein, a novel synchronous synthetic method for constructing oriented CuBDC/poly(m-phenylenediamine) (CuBDC/PmPD) MMM with uniform MOF dispersion at high loading at the air-solution interface via the dual function of metal ions is reported. The resulting MMM exhibits excellent separation performance in ion sieving and seawater desalination due to the structural integrity of the proposed membrane and the highly interconnected channels created through the oriented distribution of MOF in a polymer matrix. Such a cutting-edge approach may provide promising insights into the development of advanced MMMs with optimized structure and superior performances.

A Magneto-Heated Silk Fibroin Scaffold for Anti-Biofouling Solar Steam Generation.

Macroscopic 3D porous materials are ideal solar evaporators for water purification. However, the limited sunlight intensity and penetrating depth during solar-driven evaporation cannot prevent the biofouling formation by photothermal effect, thus leading to the deterioration of evaporation rate. Herein, a magnetic heating strategy is reported for anti-biofouling solar steam generation based on a magnetic silk fibroin (SF) scaffold with bi-heating property. Under one sun, the solar-heated top surface of magnetic SF scaffolds accelerates water evaporation at 2.03 kg m-2 h-1 , while the unheated inner channels suffer from the formation of biofilm. When exposed to alternating magnetic field (AMF), the magnetic SF scaffold can be integrally heated, leading to an efficient inner temperature to prevent biofouling in channels for water transportation. Accordingly, magneto-heated scaffolds show steady water evaporation rates after exposure to S. aureus and E. coli, which maintained 93.6-94.6% of original performance. In contrast, the evaporation rates of the scaffolds without AMF treatment are reduced to 1.31 (S. aureus) and 1.32 (E. coli) kg m-2 h-1 , decreased by 35.5% and 35.0%, respectively. In addition, the magneto-heated scaffold inhibits biofouling formation in natural lake water, maintaining 99.5% original performance.

Synergistic Solar-Driven Freshwater Generation and Electricity Output Empowered by Wafer-Scale Nanostructured Silicon.

Electricity generation triggered by the ubiquitous water evaporation process provides an intriguing way to harvest energy from water. Meanwhile, natural water evaporation is also a fundamental way to obtain fresh water for human beings. Here, a wafer-scale nanostructured silicon-based device that takes advantage of its well-aligned configuration that simultaneously realizes solar steam generation (SSG) for freshwater collection and hydrovoltaic effect generation for electricity output is developed. An ingenious porous, black carbon nanotube fabric (CNF) electrode endows the device with sustainable water self-pumping capability, excellent durable conductivity, and intense solar spectrum harvesting. A combined device based on the CNF electrode integrated with nanostructured silicon nanowire arrays (SiNWs) provided an aligned numerous surface-to-volume water evaporation interface that enables a recorded continuous short-circuit current 8.65 mA and a water evaporation rate of 1.31 kg m-2 h-1 under one sun illumination. Such wafer-scale SiNWs-based SSG and hydrovoltaic integration devices would unchain the bottleneck of the weak and discontinuous electrical output of hydrovoltaic devices, which inspires other sorts of semiconductor-based hydrovoltaic device designs to target superior performance.

A Lotus Seedpods-Inspired Interfacial Solar Steam Generator with Outstanding Salt Tolerance and Mechanical Properties for Efficient and Stable Seawater Desalination.

Interfacial solar steam generators (ISSGs) can capture solar energy and concentrate the heat at the gas-liquid interface, resulting in efficient water evaporation. However, traditional ISSGs have limitations in long-term seawater desalination processes, such as limited light absorption area, slow water transport speed, severe surface salt accumulation, and weak mechanical performance. Inspired by lotus seedpods, a novel ISSG (rGO-SA-PSF) is developed by treating a 3D warp-knitted spacer fabric with plasma (PSF) and combining it with sodium alginate (SA) and reduces graphene oxide (rGO). The rGO-SA-PSF utilizes a core-suction effect to achieve rapid water pumping and employs aerogel to encapsulate the plasma-treated spacer yarns to create the lotus seedpod-inspired hydrophilic stems, innovatively constructing multiple directional water transport channels. Simultaneously, the large holes of rGO-SA-PSF on the upper layer form lotus seedpod-inspired head concave holes, enabling efficient light capture. Under 1 kW m-2 illumination, rGO-SA-PSF exhibits a rapid evaporation rate of 1.85 kg m-2  h-1 , with an efficiency of 96.4%. Additionally, it shows superior salt tolerance (with no salt accumulation during continuous evaporation for 10 h in 10% brine) and self-desalination performance during long-term seawater desalination processes. This biomimetic ISSG offers a promising solution for efficient and stable seawater desalination and wastewater purification.

A Multifunctional Asymmetric Fabric for Sustained Electricity Generation from Multiple Sources and Simultaneous Solar Steam Generation.

Harvesting electrical energy from water and moisture has emerged as a novel ecofriendly energy conversion technology. Herein, a multifunctional asymmetric polyaniline/carbon nanotubes/poly(vinyl alcohol) (APCP) that can produce electric energy from both saline water and moisture and generate fresh water simultaneously is developed. The constructed APCP possesses a negatively charged porous structure that allows continuous generation of protons and ion diffusion through the material, and a hydrophilicity-hydrophobic interface which results in a constant potential difference and sustainable output. A single APCP can maintain stable output for over 130 h and preserve a high voltage of 0.61 V, current of 81 µA, and power density of 82.4 µW cm-3 with 0.15 cm3 unit size in the water-induced electricity generation process. When harvesting moisture energy, the APCP creates dry-wet asymmetries and triggers the spontaneous development of electrical double layer with a current density of 1.25 mA cm-3 , sufficient to power small electronics. A device consisting of four APCP can generate stable electricity of 3.35 V and produce clean water with an evaporation rate of 2.06 kg m-2  h-1 simultaneously. This work provides insights into the fabrication of multifunctional fabrics for multisource energy harvesting and simultaneous solar steam generation.

Improved Photo-Excited Carriers Transportation of WS2 -O-Doped-Graphene Heterostructures for Solar Steam Generation.

Two-dimensional (2D) transition metal dichalcogenides and graphene have revealed promising applications in optoelectronic and energy storage and conversion. However, there are rare reports of modifying the light-to-heat transformation via preparing their heterostructures for solar steam generation. In this work, commercial WS2 and sucrose are utilized as precursors to produce 2D WS2 -O-doped-graphene heterostructures (WS2 -O-graphene) for solar water evaporation. The WS2 -O-graphene evaporators demonstrate excellent average water evaporation rate (2.11 kg m-2  h-1 ) and energy efficiency (82.2%), which are 1.3- and 1.2-fold higher than WS2 and O-doped graphene-based evaporators, respectively. Furthermore, for the real seawater with different pH values (pH 1 and 12) and rhodamine B pollutants, the WS2 -O-graphene evaporators show great average evaporation rates (≈2.08 and 2.09 kg m-2  h-1 , respectively) for producing freshwater with an extremely low-grade of dye residual and nearly neutral pH values. More interestingly, due to the self-storage water ability of WS2 -O-graphene evaporators, water evaporation can be implemented without the presence of bulk water. As a result, the evaporation rate reaches 3.23 kg m-2  h-1 , which is ≈1.5 times higher than the regular solar water evaporation system. This work provides a new approach for preparing 2D transition metal dichalcogenides and graphene heterostructures for efficient solar water evaporation.

MoS2 Nanosheets Decorated with Fe3O4 Nanoparticles for Highly Efficient Solar Steam Generation and Water Treatment.

The shortage of water resources has always been one of the most difficult problems that perplexes humanity. Solar steam generation (SSG) has been a new non-polluting and low-cost water purification method in recent years. However, the high cost of traditional photothermal conversion materials and the low efficiency of photothermal conversion has restricted the large-scale application of SSG technology. In this work, composite materials with Fe3O4 nanospheres attached to MoS2 nanosheets were synthesized, which increased the absorbance and specific surface area of the composite materials, reduced the sunlight reflection, and increased the photothermal conversion efficiency. During the experiment, the composite material was evenly coated on cotton. The strong water absorption of cotton ensured that the water could be transported sufficiently to the surface for evaporation. Under one sun irradiation intensity, the evaporation rate of the sample synthesized in this work reached 1.42 kg m-2 h-1; the evaporation efficiency is 89.18%. In addition, the surface temperature of the sample can reach 41.6 °C, which has far exceeded most photothermal conversion materials. Furthermore, the use of this composite material as an SSG device for seawater desalination and sewage purification can remove more than 98% of salt ions in seawater, and the removal rate of heavy metal ions in sewage is close to 100%, with a good seawater desalination capacity and sewage purification capacity. This work provides a new idea for the application of composite materials in the field of seawater desalination and sewage purification.

Multivariate Synthetic Strategy for Improving Crystallinity of Zwitterionic Squaraine-Linked Covalent Organic Frameworks with Enhanced Photothermal Performance.

Two-dimensional covalent organic frameworks (2D COFs) offer a designable platform to explore porous polyelectrolyte frameworks with periodic ionic skeletons and uniform pore channels. However, the crystallinity of ionized 2D COF is often far from satisfactory as the electrostatic assembly of structures impedes the ordered layered arrangement. Here, a multivariate synthetic strategy to synthesize a highly crystalline squaraine (SQ)-linked zwitterionic 2D COF is proved. A neutral aldehyde monomer copolymerizes with squaric acid (SA) and amines in a controlled manner, resulting in the ionized COF with linkage heterogeneity in one tetragonal framework. Thus, the zwitterions of SQ are spatially isolated to minimize the electrostatic interaction and maintain the highly ordered layered stacking. With the addition of 85%-90% SA (relative to a total of aldehydes and SA), a fully SQ-linked zwitterionic 2D COF is achieved by the in-situ conversion of imine to SQ linkages. Such a highly crystalline SQ-linked COF promotes absorptivity in a full spectrum and photothermal conversion performances, and in turn, it exhibits enhanced solar-to-vapor generation with an efficiency of as high as 92.19%. These results suggest that synthetically regulating charge distribution is desirable to constitute a family of new crystalline polyelectrolyte frameworks.

2D Higher-Metal Nitride Nanosheets for Solar Steam Generation.

Higher-metal (HM) nitrides are a fascinating family of materials being increasingly researched due to their unique physical and chemical properties. However, few focus on investigating their application in a solar steam generation because the controllable and large-scale synthesis of these materials remains a significant challenge. Herein, it is reported that higher-metal molybdenum nitride nanosheets (HM-Mo5 N6 ) can be produced at the gram-scale using amine-functionalized MoS2 as precursor. The first-principles calculation confirms amine-functionalized MoS2 nanosheet effectively lengthens the bonds of MoS leading to a lower bond binding energy, promoting the formation of MoN bonds and production of HM-Mo5 N6 . Using this strategy, other HM nitride nanosheets, such as W2 N3 , Ta3 N5 , and Nb4 N5 , can also be synthesized. Specifically, under one simulated sunlight irradiation (1 kW m-2 ), the HM-Mo5 N6 nanosheets are heated to 80 °C within only ≈24 s (0.4 min), which is around 78 s faster than the MoS2 samples (102 s/1.7 min). More importantly, HM-Mo5 N6 nanosheets exhibit excellent solar evaporation rate (2.48 kg m-2  h-1 ) and efficiency (114.6%), which are 1.5 times higher than the solar devices of MoS2 /MF.

Developing Flexible Quinacridone-Derivatives-Based Photothermal Evaporaters for Solar Steam and Thermoelectric Power Generation.

Solar-driven interfacial vaporization by localizing solar-thermal energy conversion to the air-water interface has attracted tremendous attention. In the process of converting solar energy into heat energy, photothermal materials play an essential role. Herein, a flexible solar-thermal material di-cyan substituted 5,12-dibutylquinacridone (DCN-4CQA)@Paper was developed by coating photothermal quinacridone derivatives on the cellulose paper. The DCN-4CQA@Paper combines desired chemical and physical properties, broadband light-absorbing, and shape-conforming abilities that render efficient photothermic vaporization. Notably, synergetic coupling of solar-steam and solar-electricity technologies by integrating DCN-4CQA@Paper and the thermoelectric devices is realized without trade-offs, highlighting the practical consideration toward more impactful solar heat exploitation. Such solar distillation and low-grade heat-to-electricity generation functions can provide potential opportunities for fresh water and electricity supply in off-grid or remote areas.

Reclaimable MoS2 Sponge Absorbent for Drinking Water Purification Driven by Solar Energy.

With the fast development of modern industries, scarcity of freshwater resources caused by heavy metal pollution (i.e., Hg2+) has become a severe issue for human beings. Herein, a 3D-MoS2 sponge as an excellent absorbent is fabricated for mercury removal due to its multidimensional adsorption pathways, which decreases the biomagnification effect of methylmercury in water bodies. Furthermore, a secondary water purification strategy is employed to harvest drinkable water with the exhausted adsorbents, thus alleviating the crisis of drinking water shortage. Compared to the conventional landfill treatment, the exhausted MoS2 sponge absorbents are further functionalized with a poly(ethylene glycol) (PEG) layer to prevent the heavy metals from leaking and enhance the hydrophilicity for photothermal conversion. The fabricated evaporator displays excellent evaporation rates of ∼1.45 kg m-2 h-1 under sunlight irradiation and produces freshwater with Hg2+ under the WHO drinking water standard at 0.001 mg L-1. These results not only assist in avoiding the biodeposition effect of mercury in water but also provide an environment-friendly strategy to recycle hazardous adsorbents for water purification.

Janus Biopolymer Sponge with Porous Structure Based on Water Hyacinth Petiole for Efficient Solar Steam Generation.

Solar-driven steam generation for desalination is a facile, sustainable, and energy-saving approach to produce clean freshwater. However, the complicated fabrication process, high cost, potential environmental impact, and salt crystallization of conventional evaporators limit their large-scale application. Herein, we present a sustainable Janus evaporator based on a biopolymer sponge from the water hyacinth petiole (WHP) for high-performance solar steam generation. The freeze-dried WHP maintained its original porous structure and aligned channels well, and therefore holds the capability for rapid water transport due to strong capillary action. The WHP coated with carbon nanotubes/ethyl cellulose paste on its surface (WHP-C) gains a good photothermal property, thus achieving an efficient solar steam generation with a rate of 1.50 kg m-2 h-1 under 1 sun irradiation. Moreover, the WHP-C after hydrophobic modification by fluorocarbon (WHP-CH) is endowed with high water repellency and exhibits good salt resistance during long-term solar desalination. Additionally, we demonstrate that a stable wet surface that enables efficient water supply and vapor escape is also significant to the successive desalination of a solar evaporator. Our work provides new insights into the high-value utilization of biomass waste, i.e., water hyacinth, and the development of sustainable interfacial solar evaporators for the environmentally friendly production of freshwater.

Enhanced Solar Evaporation Using a Scalable MoS2 -Based Hydrogel for Highly Efficient Solar Desalination.

Interfacial photo-vapor conversion has been suggested as a cost-effective and sustainable technology for seawater desalination. However, the conversion performance was still limited by some drawbacks, like salt accumulation and poor mechanical stability. Herein, a scalable MoS2 -based porous hydrogel (SMoS2 -PH) with good mechanical stability and salt resistance was successfully constructed through a crosslinking foaming polymerization method. With the high porosity (92.63 %), the SMoS2 -PH performed an impressive evaporation rate of 3.297 kg m-2 h-1 and photothermal conversion efficiency of 93.4 % under 1-sun illumination. Most importantly, the SMoS2 -PH could maintain high and stable photothermal properties for 15 days on the surface of seawater. We believe that the excellent salt resistance, the high photothermal conversion efficiency, the ease of scale preparation method and the available commercial MoS2 make the SMoS2 -PH a promising device for full-scale seawater desalination.

Superhydrophilic 2D Covalent Organic Frameworks as Broadband Absorbers for Efficient Solar Steam Generation.

The intrinsic hydrophobicity and limited light absorption especially in the near-infrared (NIR) region of porous organic polymers are two bottlenecks impeding their applications in solar steam generation (SSG). Herein, we develop a 1,4,5,8-tetrakis(phenylamino)anthracene-9,10-dione (TPAD)-based covalent organic framework (COF) (TPAD-COF) featuring both superhydrophilicity and broad light absorption covering from the entire UV/Vis to NIR regions for SSG. TPAD-COF serving as a highly efficient photothermal conversion material without any additives displays an excellent water evaporation of 1.42 kg m-2 h-1 and achieves a high energy conversion efficiency of 94 % under 1 sun irradiation. Further extension of the light absorption range of the TPAD-based COF is realized through post-synthetic modification by chelating BF2 moieties. Systematic control experiments and analysis confirm that the hydrophilicity of photothermal conversion materials plays a more dominant role in the current TPAD-based COFs for SSG.

Aligned Millineedle Arrays for Solar Power Seawater Desalination with Site-Specific Salt Formation.

As a sustainable and clean water production technology, solar thermal water evaporation has been extensively studied in the past few years. One challenge is that upon operation, salt would form on surface of the solar absorbers leading to inefficient water supply and light absorption and thus much reduced water vaporization rate. To address this problem, a simple solar evaporator based on an array of aligned millineedles for efficient solar water evaporation and controlled site-specific salt formation is demonstrated. The maximum solar evaporation rate achieved is 2.94 kg m-2 h-1 under one Sun irradiation in brine of high salinity (25 wt% NaCl), achieving energy conversion efficiency of 94.5% simultaneously. More importantly, the spontaneously site-specific salt formation on the tips of millineedles endows this solar evaporator with salt harvesting capacity. Rationally separating the clean water and salt from brine by condensation and gravity assistance, this tip-preferential crystallization solar evaporator is not affected by the salt clogging compared with conventional 2D solar evaporators. This study provides new insights on the design of solar evaporators and advances their applications in sustainable seawater desalination and wastewater management.