Multifunctional Super-Hydrophilic MXene/Biomass Composite Aerogel Evaporator for Efficient Solar-Driven Desalination and Wastewater Treatment

Solar-driven interfacial evaporation is recognized as a sustainable and effective strategy for desalination to mitigate the freshwater scarcity issue. Nevertheless, the challenges of oil contamination, salt accumulation, and poor long-term stability of the solar desalination process limit its applications. Herein, a 3D biomass-based multifunctional solar aerogel evaporator is developed for water production with fabricated chitosan/lignin (CSL) aerogel as the skeleton, encapsulated with carbonized lignin (CL) particles and Ti3C2TiX (MXene) nanosheets as light-absorbing materials. Benefitting from its super-hydrophilic wettability, interconnected macropore structure, and high broadband light absorption (ca. 95.50%), the prepared CSL-C@MXene-20 mg evaporator exhibited a high and stable water evaporation flux of 2.351 kg m-2 h-1 with an energy conversion efficiency of 88.22% under 1 Sun (1 kW m-2) illumination. The CSL-C@MXene-20 mg evaporator performed excellent salt tolerance and long-term solar vapor generation in a 3.5 wt.% NaCl solution. Also, its super-hydrophilicity and oleophobicity resulted in superior salt resistance and anti-fouling performance in high salinity brine (20 wt.% NaCl) and oily wastewater. This work offers new insight into the manufacture of porous and eco-friendly biomass-based photothermal aerogels for advanced solar-powered seawater desalination and wastewater purification.

Dealloying-Derived Self-Supporting Nanoporous Zinc Film with Optimized Macro/Microstructure for High-Performance Solar Steam Generation

Solar steam generation (SSG) is a promising technology for the production of freshwater that can help alleviate global water scarcity. Nanostructured metals, known for their localized surface plasmon resonance effect, have generated significant interest, but low-cost metal films with excellent water evaporation properties are challenging. In this work, we present a one-step dealloying route for fabricating self-supporting black nanoporous zinc (NP-Zn) films with a bicontinuous ligament/channel structure, using Al-Zn solid solution alloys as the precursors. The influence of alloy composition on the formation and macro/microstructure of NP-Zn was investigated, and an optimal Al98Zn2 was selected. Additionally, in situ and ex situ characterizations were conducted to unveil the dealloying mechanism of Al98Zn2 and phase/microstructure evolution of NP-Zn during dealloying, including the phase transition of Al(Zn) → Zn, significant volume shrinkage (89.8%), and the development of high porosity (81.3%). The nanoscale ligament/channel structure and high porosity endow the NP-Zn films with good broadband absorption and superior hydrophilicity and, more importantly, give them excellent SSG performance. The NP-Zn2 film displays high evaporation efficiency, superior stability, and good seawater desalination performance. The efficient SSG performance, material abundance, and low cost suggest that NP-Zn films have promising applications in metal-based photothermal materials for SSG.

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 %.

A Solar Evaporator Based on Polypyrrole Coated 3D Carbon Nanotube Materials for Efficient Solar-Driven Vapor Generation

Highly porous light absorbers are fabricated based on polypyrrole (PPy)-coated carbon nanotube (CNT). Carbon nanotube sponge (CNTS) or carbon nanotube array (CNTA) with three-dimensional (3D) network structure is the framework of porous light absorbers. Both PPy@CNTS and PPy@CNTA composites exhibit excellent light absorption of the full solar spectrum. The CNTS and CNTA with porous structures have extremely large effective surface area for light absorption and for water evaporation that has great practical benefit to the solar-driven vapor generation. The PPy layer on CNT sidewalls significantly improves the hydrophilicity of porous CNTS and CNTA. The good wettability of water on CNT sidewalls makes water transport in porous CNT materials highly efficient. The PPy@CNTS and PPy@CNTA light absorbers achieve high water evaporation rates of 3.35 and 3.41 kg m-2 h-1 , respectively, under 1-sun radiation. The orientation of nano channels in CNTA-based light absorbers also plays an important role in the solar-driven vapor generation. The water transport and vapor escape are more efficient in CNTA-based light absorbers as compared to the CNTS-based light absorbers due to the relatively short path for the water transport and the vapor escape in CNTA-based light absorbers.

The Influence of Light-Generated Radicals for Highly Efficient Solar-Thermal Conversion in an Ultra-Stable 2D Metal-Organic Assembly

Solar-thermal water evaporation is a promising strategy for clean water production, which needs the development of solar-thermal conversion materials with both high efficiency and high stability. Herein, we reported an ultra-stable cobalt(II)-organic assembly NKU-123 with light-generated radicals, exhibiting superior photothermal conversion efficiency and high stability. Under the irradiation of 808 nm light, the temperature of NKU-123 rapidly increases from 25.5 to 215.1 °C in 6 seconds. The solar water evaporator based on NKU-123 achieves a high solar-thermal water evaporation rate of 1.442 and 1.299 kg m-2 h-1 under 1-sun irradiation with a water evaporation efficiency of 97.8 and 87.9 % for pure water and seawater, respectively. A detailed mechanism study revealed that the formation of light-generated radicals leads to an increase of spin density of NKU-123 for enhancing the photothermal effect, which provides insights into the design of highly efficient photothermal materials.

Anisotropic MXene/Poly(vinyl alcohol) Composite Hydrogels with Vertically Oriented Channels and Modulated Surface Topography for Efficient Solar-Driven Water Evaporation and Purification

Hierarchical structure and surface topography play pivotal roles in developing high-performance solar-driven evaporators for clean water production; however, there exists a notable gap in research addressing simultaneous modulation of internal microstructure and surface topography in hydrogels to enhance both solar steam generation performance and desalination efficiency. Herein, anisotropic poly(vinyl alcohol)/MXene composite hydrogels for efficient solar-driven water evaporation and wastewater purification are fabricated using a template-assisted directional freezing approach followed by precise surface wettability modulation. The resultant composite hydrogels exhibit vertically oriented channels that ensure fast water supply during evaporation, and their poly(vinyl alcohol) skeletons can reduce the vaporization enthalpy of the water in the hydrogels. The incorporation of MXene sheets enables efficient solar light absorption and solar-thermal conversion while providing structural reinforcement to the hydrogels. More importantly, the as-created undulating solar-thermal surface, featuring modulated hydrophilic troughs and hydrophobic crests, significantly enhances solar-thermal conversion efficiency, thereby boosting solar evaporation performances. As a result, the fabricated hydrogel-based evaporator exhibits an impressive evaporation rate of 2.55 kg m-2 h-1 under 1 sun irradiation, coupled with long-term durability and desalination stability. Notably, the outstanding mechanical robustness of the hydrogel further enables high portability through a readily achievable process of reversible dehydration/hydration.

Bioinspired Solar-Driven Osmosis for Stable High Flux Desalination

The growing global water crisis necessitates sustainable desalination solutions. Conventional desalination technologies predominantly confront environmental issues such as high emissions from fossil-fuel-driven processes and challenges in managing brine disposal during the operational stages, emphasizing the need for renewable and environmentally friendly alternatives. This study introduces and assesses a bioinspired, solar-driven osmosis desalination device emulating the natural processes of mangroves with effective contaminant rejection and notable productivity. The bioinspired solar-driven osmosis (BISO) device, integrating osmosis membranes, microporous absorbent paper, and nanoporous ceramic membranes, was evaluated under different conditions. We conducted experiments in both controlled and outdoor settings, simulating seawater with a 3.5 wt % NaCl solution. With a water yield of 1.51 kg m-2 h-1 under standard solar conditions (one sun), the BISO system maintained excellent salt removal and accumulation resistance after up to 8 h of experiments and demonstrated great cavitation resistance even at 58.14 °C. The outdoor test recorded a peak rate of 1.22 kg m-2 h-1 and collected 16.5 mL in 8 h, showing its practical application potential. These results highlight the BISO device's capability to address water scarcity using a sustainable approach, combining bioinspired design with solar power, presenting a viable pathway in renewable-energy-driven desalination technology.

Synergistic Effect of Ti3C2Tx MXene Nanosheets and Tannic Acid-Fe3+ Network in Constructing High-Performance Hydrogel Composite Membrane for Photothermal Membrane Distillation

Photothermal membrane distillation (PMD) has emerged as a promising and sustainable approach for seawater desalination and wastewater purification. However, the wide application of the technique is severely impeded by low freshwater production and membrane fouling/wetting issues. Herein, we developed an advanced hydrogel-engineered membrane with simultaneously enhanced photothermal conversion capacity and desired fouling and wetting resistance for PMD. By the synergies of photothermal Ti3C2Tx MXene nanosheets and the tannic acid-Fe3+ network in the hydrogel, the membrane was endowed with excellent surface self-heating ability, yielding the highest freshwater production rate (1.71 kg m-2 h-1) and photothermal efficiency among the fabricated hydrogel composite membranes under 1 sun irradiation. Meanwhile, the PMD membrane could robustly resist oil-induced fouling and surfactant-induced wetting, significantly extending the membrane lifespan in treating contaminated saline water. Furthermore, when desalinating real seawater, the membrane exhibited superior durability with a stable vapor flux and excellent ion rejection (e.g., 99.24% for boron) for 100 h.

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 Cu99 Ag0.75 Au0.25 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 Cu99 Ag0.75 Au0.25 , 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.

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.

Shape-Memory Three-Dimensional Evaporators with High Portability for Efficient Solar-Driven Freshwater Production

Solar-driven water evaporation can alleviate the severe water scarcity situation in a nonpolluting and sustainable manner. Although the design of integrated three-dimensional (3D) solar evaporators has been proven to be effective in achieving ultrahigh evaporation rates and energy efficiency, their scalable application is still hindered by complex manufacturing processes and poor portability. Herein, we report a highly portable shape-memory 3D solar evaporator by depositing MXene on low-cost lignin-cellulosic sponges for freshwater production. When not in use, the 3D evaporator can be compressed into a thin film with up to 89.3% volume reduction, ensuring minimal space occupation and high portability. When needed, due to the shape-memory effect, the 3D structure can be rapidly restored by swelling the compressed film in water, resulting in an efficient 3D solar evaporator. This 3D evaporator exhibits not only a high evaporation rate of 2.48 kg m-2 h-1 under 1 sun illumination but also excellent long-term stability and recyclability. In addition, the 3D evaporator itself can serve as a water reservoir without requiring a continuous water supply during evaporation, showing remarkable application flexibility. This work opens a new perspective for manufacturing highly portable and efficient 3D solar evaporators and may facilitate their progress from the laboratory to commercial applications.

Simultaneous Solar-Thermal Desalination and Catalytic Degradation of Wastewater Containing Both Salt Ions and Organic Contaminants

Although solar steam generation is promising in generating clean water by desalinating seawater, it is powerless to totally degrade organic contaminants in the seawater. Herein, solar steam generation and catalytic degradation are integrated to generate clean water by simultaneous solar-driven desalination and catalytic degradation of wastewater containing both salt ions and organic contaminants. Stepwise decoration of three-dimensional nickel foam with polypyrrole, reduced graphene oxide (RGO), and cobalt phosphate is realized to obtain polypyrrole/RGO/cobalt phosphate/nickel foam (PGCN) hybrids for solar-driven desalination and catalytic degradation of wastewater containing antibiotics and salt ions. The oxygen-containing groups of the RGO integrated with the porous nickel foam make the porous PGCN hybrid hydrophilic and ensure the upward transport of water to the evaporation surface, and the oxygen vacancies of the cobalt phosphate allow the PGCN to generate abundant highly active singlet oxygen that could still exhibit excellent catalytic degradation performances in the high salinity and highly alkaline environment of seawater. In addition to the high solar light absorbance and satisfactory solar-thermal conversion efficiency of polypyrrole and RGO, the thermally conductive nickel foam skeleton can effectively transfer the heat generated by the solar-thermal energy conversion to the adjacent cobalt phosphate catalyst and nearby wastewater, achieving a solar-thermal-promoted catalytic degradation of organic contaminants. Therefore, a high pure water evaporation rate of 2.08 kg m-2 h-1 under 1 sun irradiation and 100% catalytic degradation of Norfloxacin and dyes are achieved. The PGCN hybrid is highly efficient in purifying seawater containing 10 ppm Norfloxacin and simultaneously achieves a high purification efficiency of 100 kg m-2 h-1.

Overview of Solar Steam Devices from Materials and Structures

The global shortage of freshwater supply has become an imminent problem. The high energy consumption of traditional desalination technology cannot meet the demand for sustainable energy development. Therefore, exploring new energy sources to obtain pure water has become one of the effective ways to solve the freshwater resource crisis. In recent years, solar steam technology which utilizes solar energy as the sole input source for photothermal conversion has shown to be sustainable, low-cost, and environmentally friendly, providing a viable low-carbon solution for freshwater supply. This review summarizes the latest developments in solar steam generators. The working principle of steam technology and the types of heating systems are described. The photothermal conversion mechanisms of different materials are illustrated. Emphasis is placed on describing strategies to optimize light absorption and improve steam efficiency from material properties to structural design. Finally, challenges in the development of solar steam devices are pointed out, aiming to provide new ideas for the development of solar steam devices and alleviate the shortage of freshwater resources.

Hydrothermally Modified 3D Porous Loofah Sponges with MoS2 Sheets and Carbon Particles for Efficient Solar Steam Generation and Seawater Desalination

Although the emerging interfacial solar steam generation technology is sustainable and eco-friendly for generating clean water by desalinating seawater and purifying wastewaters, salt deposition on the evaporation surface during solar-driven evaporation severely degrades the purification performances and adversely affect the long-term performance stability of solar steam generation devices. Herein, to construct solar steam generators for efficient solar steam generation and seawater desalination, three-dimensional (3D) natural loofah sponges with both macropores of the sponge and microchannels of the loofah fibers are hydrothermally decorated with molybdenum disulfide (MoS₂) sheets and carbon particles. Benefiting from fast upward transport of water, rapid steam extraction, and effective salt-resistant capacity, the 3D hydrothermally decorated loofah sponge with MoS₂ sheets and carbon particles (HLMC) with an exposed height of 4 cm can not only obtain heat by its top surface under the downward solar light irradiation based on the solar-thermal energy conversion but also gain environmental energy by its porous sidewall surface, achieving a competitive water evaporation rate of 3.45 kg m^-2 h^-1 under 1 sun irradiation. Additionally, the 3D HLMC evaporator exhibits long-term desalination stability during the solar-driven desalination of an aqueous salt solution with 3.5 wt % NaCl for 120 h without apparent salt deposition because of its dual type of pores and uneven structure distribution.

Bioinspired Self-Standing, Self-Floating 3D Solar Evaporators Breaking the Trade-Off between Salt Cycle and Heat Localization for Continuous Seawater Desalination

Facing the global water shortage challenge, solar-driven desalination is considered a sustainable technology to obtain freshwater from seawater. However, the trade-off between the salt cycle and heat localization of existing solar evaporators (SE) hinders its further practical applications. Here, inspired by water hyacinth, a self-standing and self-floating 3D SE with adiabatic foam particles and aligned water channels is built through a continuous directional freeze-casting technique. With the help of the heat insulation effect of foam particles and the efficient water transport of aligned water channels, this new SE can cut off the heat transfer from the top photothermal area to the bulk water without affecting the water supply, breaking the long-standing trade-off between salt cycle and heat localization of traditional SEs. Additionally, its self-standing and self-floating features can reduce human maintenance. Its large exposure height can increase evaporation area and collect environmental energy, breaking the long-standing limitation of solar-to-vapor efficiency of conventional SEs. With the novel structure employed, an evaporation flux of 2.25 kg m^-2 h^-1 , and apparent solar-to-vapor efficiency of 136.7% are achieved under 1 sun illumination. This work demonstrates a new evaporator structure, and also provides a key insight into the structural design of next-generation salt-tolerant and high-efficiency SEs.

Tree-Inspired Aerogel with a Radial and Centrosymmetric Structure for Efficient Solar-Powered Water Purification

Solar-powered water purification is one of the promising choices for clean water production. However, it remains challenging to develop aerogel solar evaporators that simultaneously possess enhanced light-to-heat conversion, optimal thermal management, and salt crystal deposition inhibition. Herein, to address this challenge, we have developed a 3D chitosan-reduced graphene oxide/polypyrrole (CS-RGO/PPy) aerogel vaporizer with a vertical and radially aligned structure through a directional freezing process, inspired by the featured structure of conifers. The radially porous walls and vertically arranged channels within the 3D aerogel were able to facilitate high light absorption, localizing converted heat, rapid water transport, and self-salt discharge. Under 1 sun irradiation, the aerogel vaporizer displayed an improved light absorption characteristic of 95% and a high-rate evaporation (∼3.19 kg m^-2 h^-1) that achieved continuous freshwater from the saturated brine production without solid salt crystallization. Besides achieving seawater desalination, the obtained aerogel could purify organic wastewater and emulsions through solar distillation with high-rate continuous water production.

Bioinspired Aerogel with Vertically Ordered Channels and Low Water Evaporation Enthalpy for High-Efficiency Salt-Rejecting Solar Seawater Desalination and Wastewater Purification

Solar energy-driven water evaporation is a promising sustainable strategy to purify seawater and contaminated water. However, developing solar evaporators with high water evaporation rates and excellent salt resistance still faces a great challenge. Herein, inspired by the long-range ordered structure and water transportation capability of lotus stem, a biomimetic aerogel with vertically ordered channels and low water evaporation enthalpy for high-efficiency solar energy-driven salt-resistant seawater desalination and wastewater purification is developed. The biomimetic aerogel consists of ultralong hydroxyapatite nanowires as heat-insulating skeletons, polydopamine-modified MXene as a photothermal material with broadband sunlight absorption and high photothermal conversion efficiency, polyacrylamide, and polyvinyl alcohol as reagents to lower the water evaporation enthalpy and as glues to enhance the mechanical performance. The honeycomb porous structure, unidirectionally aligned microchannels, and nanowire/nanosheet/polymer pore wall endow the biomimetic aerogel with excellent mechanical properties, rapid water transportation, and excellent solar water evaporation performance. The biomimetic aerogel exhibits a high water evaporation rate (2.62 kg m^-2  h^-1 ) and energy efficiency (93.6%) under one sun irradiation. The superior salt-rejecting ability of the designed water evaporator enables stable and continuous seawater desalination, which is promising for application in water purification to mitigate the global water crisis.

Molecular Dynamics Simulations of High-Performance, Dissipationless Desalination across Self-Assembled Amyloid Beta Nanotubes

Climate change is causing droughts and water shortages. Membrane desalination is one of the most widely employed conventional methods of creating a source of clean water, but is a very energy-intensive process. Membrane separation requires high salt selectivity across nano-channels, yet traditional techniques remain inefficient in this regard. Herein, a bioinspired, chemically robust, amyloid-fibril-based nanotube is designed, exhibiting water permeability and salt rejection properties capable of providing highly efficient desalination. Molecular dynamics simulations show that nano-dewetting facilitates the unidirectional motion of water molecules on the surface of amyloid beta (Aβ) sheets owing to the ratchet structure of the underlying potential surface and the broken detailed balance. The water inside the self-assembled Aβ nanotube (ABNT) overflows, while the passage of salts can be blocked using amphiphilic peptides. The designed nanofilter ABNT shows 100% desalination efficiency with perfect NaCl rejection. The production of ≈2.5 tons of pure water per day without any energy input, which corresponds to a water flux up to 200 times higher than those of existing commercial methods, is assessed by this simulation method. These results provide a detailed fundamental understanding of potential high-performance nanotechnologies for water treatment.

A Fouling Comparison Study of Algal, Bacterial and Humic Organic Matters in Seawater Desalination Pretreatment Using Ceramic UF Membranes

This study investigates three types of organic matter, namely algal organic matter (AOM), bacterial organic matter (BOM), and humic organic matter (HOM). These organics are different in properties and chemical composition. AOM, BOM and HOM were compared in terms of organic content, fouling behavior, and removal efficiency in ceramic UF filtration. UF experiments were conducted at a constant flux mode using 5 kDa and 50 kDa ceramic membranes. Results showed that 5 kDa membrane removed more transparent exopolymer particles (TEP)/organics than 50 kDa membranes, but less fouling formation for all the three types of organic matters tested. Membranes exhibited the lowest trans-membrane pressure (TMP) during the filtration of HOM, most probably due to the high porosity of the HOM cake layer, contributed by big HOM aggregates under Ca bridging effect. AOM shows the highest MFI-UF (modified fouling index-ultrafiltration) and TMP (transmembrane pressure) values among the three organics and during all filtration cycles for both membranes. The AOM fouling layer is well known for having high fouling potential due to its compressibility and compactness which increase the TMP and eventually the MFI values. AOM and BOM organics exhibited a similar fouling behavior and mechanism. Furthermore, the divalent cations such as calcium showed a significant impact on membrane fouling. That is probably because calcium ions made the membranes and organic matter less negatively charged and easier to deposit on membranes, thus, enhancing the membrane fouling significantly.

Biochar-Based Photothermal Hydrogel for Efficient Solar Water Purification

The development of technology for solar interface evaporation has a significant meaning for the sustainable use of water resources in remote regions. However, establishing a solar evaporator with a high evaporation rate and favorable water treatment capabilities remains challenging. In this work, we reported a silver nanoparticle (AgNP)@carbonized cattail (CC)/polyvinyl alcohol (PVA) composite hydrogel (ACPH) membrane. Because of the successfully loaded AgNPs, which have a photothermal synergy with the CC, the ACPH-10 membrane obtained an excellent photothermal conversion performance. Additionally, the hydrophilicity of the ACPH-10 membrane ensures a sustainable water supply which is necessary for the improvement of the evaporation rate. Therefore, the ACPH-10 membrane achieves an evaporation rate of 1.66 kg m^-2 h^-1 and an efficiency of 88.0%, attributed to the remarkable photothermal conversion and water transmission. More importantly, the membrane exhibits superior purification ability in a variety of sewage. Pollutant removal rates in heavy metal and organic dye sewage have exceeded 99.8%. As a result, the ACPH membrane holds great promise for wastewater recovery and seawater desalination, which can aid in resolving the water crisis issue.

Electrosprayed CNTs on Electrospun PVDF-Co-HFP Membrane for Robust Membrane Distillation

In this investigation, the electrospraying of CNTs on an electrospun PVDF-Co-HFP membrane was carried out to fabricate robust membranes for the membrane distillation (MD) process. A CNT-modified PVDF-Co-HFP membrane was heat pressed and characterized for water contact angle, liquid entry pressure (LEP), pore size distribution, tensile strength, and surface morphology. A higher water contact angle, higher liquid entry pressure (LEP), and higher tensile strength were observed in the electrosprayed CNT-coated PVDF-Co-HFP membrane than in the pristine membrane. The MD process test was conducted at varying feed temperatures using a 3.5 wt. % simulated seawater feed solution. The CNT-modified membrane showed an enhancement in the temperature polarization coefficient (TPC) and water permeation flux up to 16% and 24.6%, respectively. Field-effect scanning electron microscopy (FESEM) images of the PVDF-Co-HFP and CNT-modified membranes were observed before and after the MD process. Energy dispersive spectroscopy (EDS) confirmed the presence of inorganic salt ions deposited on the membrane surface after the DCMD process. Permeate water quality and rejection of inorganic salt ions were quantitatively analyzed using ion chromatography (IC) and inductively coupled plasma-mass spectrometry (ICP-MS). The water permeation flux during the 24-h continuous DCMD operation remained constant with a >99.8% inorganic salt rejection.

Superelastic 3D Assembled Clay/Graphene Aerogels for Continuous Solar Desalination and Oil/Organic Solvent Absorption

Superelastic, arbitrary-shaped, and 3D assembled clay/graphene aerogels (CGAs) are fabricated using commercial foam as sacrificial skeleton. The CGAs possess superelasticity under compressive strain of 95% and compressive stress of 0.09-0.23 MPa. The use of clay as skeletal support significantly reduces the use of graphene by 50%. The hydrophobic CGAs show high solvent absorption capacity of 186-519 times its own weight. Moreover, both the compression and combustion methods can be adopted for reusing the CGAs. In particular, it is demonstrated a design of 3D assembled hydrophilic CGA equipped with salt collection system for continuous solar desalination. Due to energy recovery and brine transport management promoted by this design, the 3D assembled CGA system exhibits an extremely high evaporation rate of 4.11 kg m^-2  h^-1 and excellent salt-resistant property without salt precipitation even in 20 wt% brine for continuous 36 h illumination (1 kW m^-2 ), which is the best reported result from the solar desalination devices. More importantly, salts can be collected conveniently by squeezing and drying the solution out of the salt collection system. The work provides new insights into the design of 3D assembled CGAs and advances their applications in continuous solar desalination and efficient oil/organic solvent adsorption.

A Simple and Efficient Solar Interfacial Evaporation Device Based on Carbonized Cattail and Agarose Hydrogel for Water Evaporation and Purification

One of the main trends in the development of solar interface evaporation technology is the simple, efficient, and environmentally friendly bio-based evaporation device. However, the development of bio-based evaporators with high water evaporation rates and good pollution removal capability is a significant challenge. Here, we present a carbonized cattail-agarose hydrogel (CCAH) membrane with numerous microchannels resembling bamboo knots, exceptional hydrophilicity, outstanding light absorption capability, and potent adsorption. Under one solar irradiation, its evaporation rate and efficiency reached 1.93 kg m^-2 h^-1 and 95.8%, respectively. More importantly, the CCAH membrane produces steam water that is almost totally free of salts (Na⁺, K⁺, Mg²⁺, and Ca²⁺), heavy metal ions (Pb²⁺, Cd²⁺, and Cr²⁺), and organic dyes (Rhodamine B, methylene blue, and methyl orange). The CCAH membrane is highly promising for the use of saltwater desalination and wastewater recovery to help people in impoverished areas with water scarcity problems.

Opportunities of Reducing the Energy Consumption of Seawater Reverse Osmosis Desalination by Exploiting Salinity Gradients

This work presents a performance assessment of three seawater reverse osmosis-pressure-retarded osmosis (SWRO-PRO) hybrid schemes for energy consumption reduction in seawater desalination applications by using an external low salinity water source. For comparison purposes, another arrangement based on the conventional SWRO process combined with brackish water RO (BWRO) and desalination was analyzed. Reverse osmosis system analysis software environments were used to select the best SWRO configuration and operating conditions. A purposely developed model was used to evaluate the PRO system. Two different cases were assessed depending on the origin of the external low-salinity resource for the PRO process: industrial wastewater and urban treated wastewater. In the case of the industrial wastewater, due to regulations on wastewater reclamation, the best arrangement would be the first SWRO-PRO scheme which was analyzed with a specific energy consumption of 1.54 kWh/m³. If urban treated wastewater is available as an external resource, the results obtained show that this scheme, leading to the minimum specific energy consumption of 1.46 kWh/m³, is the conventional SWRO combined with BWRO. Therefore, hybrid SWRO-PRO systems are recommended to reduce the specific energy consumption of seawater desalination if an industrial wastewater source with low osmotic pressure is available.

Janus Carbon Nanotube@poly(butylene adipate-co-terephthalate) Fabric for Stable and Efficient Solar-Driven Interfacial Evaporation

Solar-driven seawater desalination is considered a promising method for alleviating the water crisis worldwide. In recent years, significant efforts have been undertaken to optimize heat management and minimize salt blockage during solar-driven seawater desalination. However, it remains challenging to achieve an efficient and stable seawater evaporator simply and practically. Here, we designed and prepared a novel three-dimensional (3D) water channel evaporator (3D WCE) equipped with a Janus CNT@PBAT fabric (JCPF). The as-prepared Janus CNT@PBAT fabric has broad-band light absorption (∼97.8%), excellent superhydrophobicity (∼162°), and photothermal properties. After optimizing the structure of the thermal insulator, our designed evaporator could realize the equilibrium between enhanced thermal management and sufficient water supply. As a result, the as-prepared evaporator achieved an excellent evaporation rate of 1.576 kg·m^-2·h^-1 and an energy efficiency of over 92.7% under 1 sun irradiation in 3.5 wt % saline water. Moreover, this evaporator also revealed good salt rejection performance compared to the traditional two-dimensional (2D) water channel evaporator (2D WCE) in high saline water, which could maintain stable evaporation rates under long-term evaporation of 8 h. Our study may develop a simple method for the design and fabrication of a low-cost, effective, and stable solar-driven evaporator for seawater desalination.

Biofouling control of membrane distillation for seawater desalination: Effect of air-backwash and chemical cleaning on biofouling formation

This study explored the applicability of chemical cleaning and air-backwash to alleviate biofouling on seawater membrane distillation (SWMD). Membrane performance and wettability properties maintained at optimum duration and frequency of the treatments, as indicated by low permeate conductivity throughout the tests. The cleaning of the membrane using 2% NaOH by immersing the membrane for 30 min after 240 min operation removed the biofouling layer, indicated by low permeate conductivity of 370 µScm^-1 after cleaning. However, more frequent membrane cleaning led to membrane damage, more severe wetting, and membrane hydrophobicity reduction. Ten-second air-backwash after 240 min of operation was also effective in controlling the biofouling, particularly when conducted at air pressure of 1 bar. More frequent air-backwash resulted in more aggravated inorganic fouling and accelerated biofouling formation due to the recurring introduction of air, leading to rapid membrane wetting.

Optimization of Evaporation and Condensation Architectures for Solar-Driven Interfacial Evaporation Desalination

Solar-driven interfacial evaporation is an ideal technology for seawater desalination, and the corresponding system is mainly composed of a solar evaporator and a condensing collector. The traditional scheme focuses on the evaporation efficiency of the evaporator. Still, it ignores the influence of condensing collection scheme on the overall efficiency, which is one of the obstacles to the practical use of solar seawater desalination. Here, we reported a new solar-driven interfacial evaporation seawater desalination system by studying the influence of the condensation architecture, i.e., vapor flow by a fan and an air pump, sidewall material, transparent cover shape and material, evaporation level, and transparent cover heating, on the apparent collection efficiency of the system. The apparent collection efficiency was up to over 90% after optimization. This study is expected to promote the practical application of solar evaporation desalination technology.

Exhausted Cr(VI) Sensing/Removal Aerogels Are Recycled for Water Purification and Solar-Thermal Energy Generation

Heavy metal pollution has resulted in numerous environmental challenges. However, classic approaches, involving the use of solid adsorbents are subject to limitations, including the high energy consumption required for processing before and after use. Accordingly, strategies that facilitate the use of metal capture media that extends beyond waste remediation are attractive. Herein, a porous fluorescent aerogel (CPC aerogel) is constructed by immersing amino-based carbon dots (CDs-NH₂ ) into a polyethyleneimine (PEI)/carboxymethylated cellulose (CMC) aerogel network for the simultaneous detection and adsorption of Cr(VI). Adsorption experiments confirm that the CMC/PEI containing CDs-NH₂ aerogel (CPC aerogel) exhibits good Cr(VI) extraction capacity, and can reach a level that conforms with industrial water safety standards. In addition, the CPC aerogel can continuously detect and remove Cr(VI) at high flux. Following Cr(VI) absorption, the CPC aerogel may be vulcanized (MS_x -CPC gel) and used for solar thermoelectric generation resulting in power generation. Additionally, the MS_x -CPC gel can be used for solar steam generation and exhibits excellent evaporation rates of ≈1.31 kg m^-2 h^-1 under one sun irradiation. The results serve to underscore how materials designed for metal ion recognition and adsorption once exhausted can be exploited to provide materials for solar thermoelectric power generation and seawater desalination.

Sustainable Self-Cleaning Evaporators for Highly Efficient Solar Desalination Using a Highly Elastic Sponge-like Hydrogel

Interfacial evaporation using light-absorbing hydrogels offers efficient solar evaporation performance under natural sunlight, ensuring an affordable clean water supply. However, achieving light-absorbing hydrogels with durable and efficient utilization is still a challenge due to inevitable salt accumulation, a difficult-to-control surface morphology, and poor mechanical properties on the surfaces of hydrogel-based evaporators. In this work, a photothermal sponge-like hydrogel with a 3D interconnected porous structure was constructed using low-cost activated carbon as a photothermal material, as well as a double-network polymer chain as the basic skeleton using a simple foaming polymerization strategy. The sponge-like hydrogel evaporator showed tailored surface topography, adequate water transport, excellent elasticity and toughness, good salt rejection, and thermal localization properties. Under the irradiation of simulated sunlight (1.0 kW/m²), a high evaporation rate of 2.33 kg·m^-2·h^-1 was achieved. Furthermore, efficient salt self-cleaning behavior was achieved due to the fast ion diffusion within the 3D interconnected porous structures. Even in highly concentrated brine of 15 wt %, continuous and efficient water evaporation was still achieved. The excellent evaporation and salt rejection properties of this photothermal sponge-like hydrogel indicated its promising long-term sustainable utilization in seawater desalination.

Environmentally Friendly Polyamide Nanofiber Membranes with Interconnective Amphiphobic Channels for Seawater Desalination

Seawater desalination is a promising and sustainable solution to alleviate freshwater scarcity; however, most existing desalination membranes suffer from poor channel interconnectivity and toxic solvent processing and encounter a tradeoff dilemma of salt rejection and water flux. Herein, we report a unique and facile one-step green solvent/nonsolvent spinning methodology to assemble environmentally friendly polyamide nanofiber membranes with a precisely designed interconnective/stable channel structure and surface anti-wettability for seawater desalination. Direct electrospinning without any post-treatments via in situ introduction of fluorinated chemicals enables highly interconnective amphiphobic channels within polyamide membranes, and the incorporation of nonsolvent (diacetone alcohol) into polyamide/solvent (ethanol) spinning solutions endows the green alcohol-based polyamide membranes with a stable bonding structure and small pore size. The resultant green solvent/nonsolvent-spun polyamide nanofiber membranes show impressive liquid entry pressure (120.5 kPa) and vapor permeation (12.5 kg m^-2 d^-1), achieving robust seawater desalination performance with a salt rejection of 99.97% and permeate flux of 47.4 kg m^-2 h^-1. The facile one-step solvent/nonsolvent spinning strategy, highly interconnective amphiphobic channels, and green solvent-based environmental friendliness in this work can open opportunities for future polyamide membranes for practical applications in water purification.

Portable Seawater Desalination System for Generating Drinkable Water in Remote Locations

A portable seawater desalination system would be highly desirable to solve water challenges in rural areas and disaster situations. While many reverse osmosis-based portable desalination systems are already available commercially, they are not adequate for providing reliable drinking water in remote locations due to the requirement of high-pressure pumping and repeated maintenance. We demonstrate a field-deployable desalination system with multistage electromembrane processes, composed of two-stage ion concentration polarization and one-stage electrodialysis, to convert brackish water and seawater to drinkable water. A data-driven predictive model is used to optimize the multistage configuration, and the model predictions show good agreement with the experimental results. The portable system desalinates brackish water and seawater (2.5-45 g/L) into drinkable water (defined by WHO guideline), with the energy consumptions of 0.4-4 (brackish water) and 15.6-26.6 W h/L (seawater), respectively. In addition, the process can also reduce suspended solids by at least a factor of 10 from the source water, resulting in crystal clear water (<1 NTU) even from the source water with turbidity higher than 30 NTU (i.e., cloudy seawater by the tide). We built a fully integrated prototype (controller, pumps, and battery) packaged into a portable unit (42 × 33.5 × 19 cm³, 9.25 kg, and 0.33 L/h production rate) controlled by a smartphone, tested for battery-powered field operation. The demonstrated portable desalination system is unprecedented in size, efficiency, and operational flexibility. Therefore, it could address unique water challenges in remote, resource-limited regions of the world.

Hierarchically Structured Black Gold Film with Ultrahigh Porosity for Solar Steam Generation

Plasmonic metals demonstrate significant potential for solar steam generation (SSG) because of their localized surface plasmon resonance effect. However, the inherently narrow absorption spectra of plasmonic metals significantly limit their applications. The fabrication of nanostructures is essential to achieve broadband solar absorption for high-efficiency vapor generation. Herein, a self-supporting black gold (Au) film with an ultrahigh porosity and a hierarchically porous structure is fabricated by formulating an extremely dilute Cu₉₉ Au₁ precursor and controlling the dealloying process. In situ and ex situ characterizations reveal the dealloying mechanism of Cu₉₉ Au₁ in a 1 m HNO₃ solution as that involving the phase transformation of Cu(Au) → Au(Cu) → Au, giant volume shrinkage (≈87%), structural evolution/coarsening of ligaments, and development of ultrahigh porosity (86.2%). The multiscale structure, consisting of ultrafine nanoporous nanowires, aligned nanogaps, and various microgaps, provide efficient broadband absorption over 300-2500 nm, excellent hydrophilicity, and continuous water transport. In particular, the nanoporous black Au film shows high SSG performance with an evaporation rate of 1.51 kg m^-2 h^-1 and a photothermal conversion efficiency of 94.5% under a light intensity of 1 kW m^-2 . These findings demonstrate that the nanoporous Au film has great potential for clean water production and seawater desalination.

Proteoliposome-Incorporated Seawater Reverse Osmosis Polyamide Membrane: Is the Aquaporin Water Channel Effect in Improving Membrane Performance Overestimated?

The water channel feature of the aquaporin (AQP) is considered to be the key in improving the permselectivity of AQP-based thin-film composite (TFC) polyamide (PA) membranes, yet much less attention has been paid to the physicochemical property changes of the PA layer induced by AQP-reconstituted proteoliposomes. This study systematically investigated the roles of proteoliposome constituents (liposome/detergent/AQP) in affecting the physicochemical properties and performance of the membranes. For the first time, we demonstrated that the constituents in the proteoliposome could facilitate the formation of a PA layer with enlarged protuberances and thinner crumples, resulting in a 79% increase in effective surface area and lowering of hydraulic resistance for filtration. These PA structural changes of the AQP-based membrane were found to contribute over 70% to the water permeability increase via comparing the separation performance of the membranes prepared with liposome, detergent, and proteoliposome, respectively, and one proteoliposome-ruptured membrane. The contribution from the AQP water channel feature was about 27% of water permeability increase in the current study, attributed to only ∼20% vesicle coverage in the PA matrix, and this contribution may be easily lost as a result of vesicle rupture during the real seawater reverse osmosis process. This study reveals that the changed morphology dominates the performance improvement of the AQP-based PA membrane and well explains why the actual AQP-based PA membranes cannot acquire the theoretical water/salt selectivity of a biomimetic AQP membrane, deepening our understanding of the AQP-based membranes.

Spontaneous Salt-Preventing Solar-Thermal Water Evaporator with a High Evaporation Efficiency through Dual-Mode Water Transfer

Benefiting from the abundant solar energy and the emergence of photothermal conversion equipment, solar-driven water evaporation has shown great potential in seawater desalination. One common problem for solar-thermal evaporation is that the salt crystallized on the surface of solar absorbers during the seawater evaporation process will significantly deteriorate the continuity and efficiency of the evaporation process. In most reports, efforts have been made to transfer the accumulated salts, while the studies on preventing salt crystallization, which leads to better continuity of the production, are limited. Herein, a spontaneous salt-preventing solar-thermal water evaporator was designed, utilizing a dual-mode water transfer structure consisting of in-plane diffusion and in-tube migration. The dual-mode structural system gave rise to uniform and continuous water transfer, efficiently suppressing the salt concentration in the evaporator. As a result, salt crystallization was scarcely found on the surface of the evaporator under 1 sun irradiation for an ultralong time (200 h), demonstrating its high efficiency in inhibiting salt crystallization. In addition, the small contact area between the water and the evaporator could reduce the heat loss during the solar-thermal evaporation process, which further improved the water evaporation rate (1.64 kg m^-2 h^-1).

Seawater Desalination by Modified Membrane Distillation: Effect of Hydrophilic Surface Modifying Macromolecules Addition into PVDF Hollow Fiber Membrane

Hollow fiber membranes of polyvinylidene fluoride (PVDF) were prepared by incorporating varying concentrations of hydrophilic surface-modifying macromolecules (LSMM) and a constant amount of polyethylene glycol (PEG) additives. The membranes were fabricated by the dry-wet spinning technique. The prepared hollow fiber membranes were dip-coated by hydrophobic surface-modifying macromolecules (BSMM) as the final step fabrication. The additives combination is aimed to produce hollow fiber membranes with high flux permeation and high salt rejection in the matter of seawater desalination application. This study prepares hollow fiber membranes from the formulation of 18 wt. % of PVDF mixed with 5 wt. % of PEG and 3, 4, and 5 wt. % of LSMM. The membranes are then dip-coated with 1 wt. % of BSMM. The effect of LSMM loading on hydrophobicity, morphology, average pore size, surface porosity, and membrane performance is investigated. Coating modification on LSMM membranes showed an increase in contact angle up to 57% of pure, unmodified PVDF/PEG membranes, which made the fabricated membranes at least passable when hydrophobicity was considered as one main characteristic. Furthermore, The PVDF/PEG/4LSMM-BSMM membrane exhibits 161 °C of melting point as characterized by the DSC. This value indicates an improvement of thermal behavior shows so as the fabricated membranes are desirable for membrane distillation operation conditions range. Based on the results, it can be concluded that PVDF/PEG membranes with the use of LSMM and BSMM combination could enhance the permeate flux up to 81.32 kg·m-2·h-1 at the maximum, with stable salt rejection around 99.9%, and these are found to be potential for seawater desalination application.

Janus Polypyrrole Nanobelt@Polyvinyl Alcohol Hydrogel Evaporator for Robust Solar-Thermal Seawater Desalination and Sewage Purification

The state-of-the-art solar-thermal evaporators demonstrating high energy utilization efficiency, a high evaporation rate, and salt rejection are highly desirable in solar-driven low-energy water purification/harvesting. Herein, a novel Janus solar evaporator is constructed by loading polypyrrole (PPy) nanobelts on the polyvinyl alcohol (PVA) hydrogel. The PPy nanobelts present a high solar absorption of 98.3%, leading to a localized solar-thermal efficiency of 82.5% when insulated from bulk water by the PVA hydrogel. The porous PVA hydrogel and the hydrophilic PPy nanobelts enable the efficient three-dimensional water transport. Taking advantages of the synergistic effect in the water-energy nexus, the Janus PPy nanobelt@PVA hydrogel evaporator evaporates water with a high rate of 2.26  kg  m^-2 h^-1 via 80.1% solar energy from 1 sun irradiance with a low PPy loading of ∼3 mg cm^-2 even at a rate of 2.64  kg  m^-2 h^-1 via 96.3% solar energy for a biomimetic conical evaporator. The Janus evaporator presents superior salt-resistant desalination and contaminant purification performance in seawater and sewage. Furthermore, a portable solar-thermal purifier equipped with the Janus evaporator desalts real seawater far above the drinking water standard with over a 99.9% salt rejection rate and eliminates 95.8% of chemical oxygen demand in real sewage, highlighting its potential for advanced clean water harvesting.

Hierarchical Photothermal Fabrics with Low Evaporation Enthalpy as Heliotropic Evaporators for Efficient, Continuous, Salt-Free Desalination

Solar-driven seawater evaporation is usually achieved on floating evaporators, but the performances are substantially limited by high evaporation enthalpy, solid salt crystallization, and reduced evaporation due to inclined sunlight. To solve these problems, we fabricated hierarchical polyacrylonitrile@copper sulfide (PAN@CuS) fabrics and proposed a prototype of heliotropic evaporator. Hierarchical PAN@CuS fabrics show significantly decreased water-evaporation enthalpy (1956.32 kJ kg^-1, 40 °C), compared with that of pure water (2406.17 kJ kg^-1, 40 °C), because of the disorganization of the hydrogen bonds at the CuS interfaces. Based on this fabric, a heliotropic evaporation model was developed, where seawater slowly flows from high to low in the fabric. Under solar irradiation (1.0 kW m^-2), this model exhibits a high-rate evaporation (∼2.27 kg m^-2 h^-1) and saturated brine production without solid salt crystallization. In particular, under inclined sunlight (angle range: from -90° to +90°), the heliotropic model retains an almost unchanged solar evaporation rate, whereas the floating model shows severe evaporation reduction (83.9%). Therefore, our study provides a strategy for reducing the evaporation enthalpy, maximally utilizing solar energy and continuous salt-free desalination.

Influence of Substitutional Defects in ZIF-8 Membranes on Reverse Osmosis Desalination: A Molecular Dynamics Study

In this study, molecular dynamics simulation is used to investigate the effects of water-based substitutional defects in zeolitic imidazolate frameworks (ZIF)-8 membranes on their reverse osmosis (RO) desalination performance. ZIF-8 unit cells containing up to three defect sites are used to construct the membranes. These substitutional defects can either be Zn defects or linker defects. The RO desalination performance of the membranes is assessed in terms of the water flux and ion rejection rate. The effects of defects on the interactions between the ZIF-8 membranes and NaCl are investigated and explained with respect to the radial distribution function (RDF) and ion density distribution. The results show that ion adsorption on the membranes occurs at either the nitrogen atoms or the defect sites. Complete NaCl rejection can be achieved by introducing defects to change the size of the pores. It has also been discovered that the presence of linker defects increases membrane hydrophilicity. Overall, molecular dynamics simulations have been used in this study to show that water-based substitutional defects in a ZIF-8 structure reduce the water flux and influence its hydrophilicity and ion adsorption performance, which is useful in predicting the type and number of defect sites per unit cell required for RO applications. Of the seven ZIF-8 structures tested, pristine ZIF-8 exhibits the best RO desalination performance.

Novel Magnetic Resonance Measurements of Fouling in Operating Spiral Wound Reverse Osmosis Membrane Modules

A novel magnetic resonance measurement (MRM) protocol for non-invasive monitoring of fouling in spiral wound reverse osmosis (SWRO) membrane modules is demonstrated. Sodium alginate was used to progressively foul a commercial SWRO membrane at industrially relevant operating conditions in a circulating flow loop. The MRM protocol showcased the following: (i) earlier, more sensitive detection and quantification of fouling in the membrane module compared to feed-channel pressure drop. This was achieved using appropriate detection of the total nuclear magnetic resonance (NMR) signal. (ii) 2D cross-sectional imaging of the location of the accumulated foulant material; this was preferentially located adjacent to the membrane spacer sheet nodes, which was subsequently confirmed by a module autopsy. This image contrast, which could also readily differentiate the membrane, feed spacer and permeate spacer regions, was realised based on differences in the NMR relaxation parameter, T_2,eff. (iii) High frequency acquisition of 2D cross-sectional velocity images of the module revealing very localised flow channelling in response to gradual foulant accumulation which impacted significantly on the flow pattern within the central permeate tube. Collectively this NMR/MRI measurement protocol provides a powerful analysis tool for the evolution of fouling in such complex modules, thus ultimately enabling more informed module design.

Cu3BiS3/MXenes with Excellent Solar-Thermal Conversion for Continuous and Efficient Seawater Desalination

Two-dimensional materials with unique physical and chemical properties have recently attracted widespread attention in the field of solar thermal conversion. However, affected by the Fresnel effect, traditional two-dimensional materials such as MXenes, graphene, transition metal disulfide often have relatively significant light reflection losses at the solid-liquid or gas interface. So how to improve the light absorption of the two-dimensional material performance has become a new challenge in photothermal conversion. Here, we use an improved thermal-injection method to uniformly grow Tricopper(I) Bismuth Sulfide (Cu₃BiS₃, CBS) on the surface of Ti₃C₂ nanosheets in a nonaqueous polar solvent environment. A three-dimensional nanoflower-nanosheet structure CBS-Ti₃C₂ for photothermal conversion has been constructed successfully. Owing to the excellent photothermal performance of Cu₃BiS₃ in the near-infrared region, the good thermal conductivity of Ti₃C₂, and the unique porous structure of the composite material, the composite achieves broadband absorption of light (more than 90% in the visible light region, more than 80% in the near-infrared region), which optical model and finite element simulation have theoretically verified. The composite material has obtained higher solar-to-heat conversion performance than similar material systems, and the steady-state temperature can reach 62.3 °C under 1 sun incident light intensity. CBS-Ti₃C₂ is expected to become a light-absorbing layer material for solar vapor generation devices due to its excellent light-to-heat conversion performance and good material flexibility. It still guarantees a reasonably high steam generation rate (1.32 kg·m^-2·h^-1) even with a thinner material thickness (0.48 mg·cm^-2) and a comprehensive conversion efficiency higher than 90%. Besides, CBS-Ti₃C₂ also exhibits the characteristics of resisting surface salt accumulation, which is conducive to maintaining the long-lasting photothermal seawater evaporation process. The material's electronic structure and the charge transfer process of the heterojunction interface have been studied with the first-principles calculation. The high light absorption performance and good thermal conductivity of the composite material are theoretically explained and supported.

Progress and Perspectives of Desalination in China

In recent decades, the ever-growing demands for clean water in households and industries have urged researchers to take every possible step to deal with the global water crisis. Seawater desalination has turned out to be the most promising and efficient way to provide clean water. Owing to the advancement of synthetic chemistries and technologies, great success has been achieved in the desalination and utilization of seawater worldwide. China, with the world’s largest population, has pushed the development of desalination and multipurpose utilization of seawater further in respect of materials, technologies and services, etc. This review reports recent progress of desalination technologies accomplished in China, from the viewpoints of facilities and equipment, collaborations, technologies, applications, research abilities, services, and standard systems. Inspired by the Fourteenth Five-year Plan, it also proposes future perspectives of desalination in China.

Cellulose Triacetate (CTA) Hollow-Fiber (HF) Membranes for Sustainable Seawater Desalination: A Review

Cellulose triacetate (CTA)-based hollow fiber (HF) membrane is one of the commercially successful semipermeable membranes that has had a long progress since the time the excellent semi-permeable feature of cellulose-based polymers was found in 1957. Because of the reliable and excellent performances, especially for drinking water production from seawater, CTA-HFs have been widely used as reverse osmosis (RO) membranes, especially in arid regions. In this review, recent developments and research trends on CTA-HF membranes for seawater reverse osmosis (SWRO) plants were presented. A flux analytical model, an optimization strategy for chlorine injection without losing salt rejection performance, and a module of current high performance CTA RO membranes along with its plant operation data were updated in this paper. Furthermore, a newly developed CTA-HF membrane for brine concentration (BC) application (called BC membrane) was also addressed. Finally, RO/BC hybrid operation was introduced as an effective SWRO desalination technique that enables minimizing the volume of brine disposal from the RO plant by increasing the recovery ratio and the subsequent amount of produced freshwater, without an additional energy input.

Comparative Analysis of Conventional and Emerging Technologies for Seawater Desalination: Northern Chile as A Case Study

The aim of this work was to study different desalination technologies as alternatives to conventional reverse osmosis (RO) through a systematic literature review. An expert panel evaluated thermal and membrane processes considering their possible implementation at a pilot plant scale (100 m³/d of purified water) starting from seawater at 20 °C with an average salinity of 34,000 ppm. The desalination plant would be located in the Atacama Region (Chile), where the high solar radiation level justifies an off-grid installation using photovoltaic panels. We classified the collected information about conventional and emerging technologies for seawater desalination, and then an expert panel evaluated these technologies considering five categories: (1) technical characteristics, (2) scale-up potential, (3) temperature effect, (4) electrical supply options, and (5) economic viability. Further, the potential inclusion of graphene oxide and aquaporin-based biomimetic membranes in the desalinization processes was analyzed. The comparative analysis lets us conclude that nanomembranes represent a technically and economically competitive alternative versus RO membranes. Therefore, a profitable desalination process should consider nanomembranes, use of an energy recovery system, and mixed energy supply (non-conventional renewable energy + electrical network). This document presents an up-to-date overview of the impact of emerging technologies on desalinated quality water, process costs, productivity, renewable energy use, and separation efficiency.

Advanced Technologies for Stabilization and High Performance of Seawater RO Membrane Desalination Plants

Seawater desalination plants that use reverse osmosis (RO) membranes have become a core part of social infrastructure, and should be designed to meet the needs of product water quality and production capacity, while considering various environmental factors such as the seawater quality, temperature and geographical features. Furthermore, stable operation while overcoming various problems should be achieved alongside the increasing demands for energy saving and cost reduction. As no universal plant apparatus and operation technology meets these various requirements, the plants need to be customized for individual solutions. This paper reviews and summarizes the proven technologies, including their advantages/disadvantages, and points to cutting-edge technologies related to the design and operation maintenance of seawater intake, pre-treatment and the RO desalination process.

Self-Assembled Hydrophobic/Hydrophilic Porphyrin-Ti3C2Tx MXene Janus Membrane for Dual-Functional Enabled Photothermal Desalination

Photothermal desalination is a promising approach for seawater purification by harvesting solar energy. Titanium carbide (Ti₃C₂T_x MXene) membranes have been regarded as potential materials for photothermal desalination by virtue of their excellent light-to-heat conversion. However, achieving a well-balanced synergy between high evaporation rate and good salt resistance remains a significant challenge due to their limited solar absorption and inferior stability. Herein, we report a self-assembled flexible porphyrin-Ti₃C₂T_x MXene Janus membrane (Janus PMX membrane) for dual-functional enabled photothermal desalination. The self-assembly of porphyrin on MXene not only effectively creates a favorable hydrophobic surface but also simultaneously enables efficient solar utilization. The significant interactions and charge redistribution between MXene and porphyrin lead to a stable hydrophobic/hydrophilic Janus structure with synergistically enhanced photothermal conversion. As a result, the Janus PMX membrane demonstrates highly efficient water pumping, heat localization, vapor generation, and salt resistance during photothermal desalination. This work presents an effective and facile strategy toward advancing a well-performing MXene membrane for efficient seawater desalination.

Tuning the Surface Structure of Polyamide Membranes Using Porous Carbon Nitride Nanoparticles for High-Performance Seawater Desalination

Enhancing the water flux while maintaining the high salt rejection of existing reverse osmosis membranes remains a considerable challenge. Herein, we report the use of a porous carbon nitride (C₃N₄) nanoparticle to potentially improve both the water flux and salt rejection of the state-of-the-art polyamide (PA) thin film composite (TFC) membranes. The organic–organic covalent bonds endowed C₃N₄ with great compatibility with the PA layer, which positively influenced the customization of interfacial polymerization (IP). Benefitting from the positive effects of C₃N₄, a more hydrophilic, more crumpled thin film nanocomposite (TFN) membrane with a larger surface area, and an increased cross-linking degree of PA layer was achieved. Moreover, the uniform porous structure of the C₃N₄ embedded in the ”ridge” sections of the PA layer potentially provided additional water channels. All these factors combined provided unprecedented performance for seawater desalination among all the PA-TFC membranes reported thus far. The water permeance of the optimized TFN membrane is 2.1-folds higher than that of the pristine PA-TFC membrane, while the NaCl rejection increased to 99.5% from 98.0%. Our method provided a promising way to improve the performance of the state-of-art PA-TFC membranes in seawater desalination.

Flexible Salt-Rejecting Photothermal Paper Based on Reduced Graphene Oxide and Hydroxyapatite Nanowires for High-Efficiency Solar Energy-Driven Vapor Generation and Stable Desalination

Vapor generation using solar energy is emerging as an efficient technology for wastewater purification and seawater desalination to relieve global water crisis. However, salt deposition on the evaporation surface seriously impairs the long-term steady water evaporation performance. Herein, the flexible salt-rejecting photothermal paper comprising reduced graphene oxide (rGO) and ultralong hydroxyapatite nanowires (HNs) has been developed for high-performance solar energy-driven water evaporation and stable desalination of seawater. The rGO/HN photothermal paper has advantages such as the hierarchical porous structure, interconnected channels, high mechanical strength, high efficiencies of solar light absorption and photothermal conversion, fast water transportation, and good heat insulation and salt-rejecting properties. Furthermore, the hydrophilicity and hydrophobicity of the rGO/HN photothermal paper can be adjusted by regulating the thermal treatment time. The water evaporation rate and energy efficiency of the hydrophilic rGO/HN photothermal paper are 1.48 kg m^-2 h^-1 and 89.2%, respectively, under 1 sun illumination (1 kW m^-2). The hydrophobic rGO/HN photothermal paper shows a long-time stable water evaporation and salt-rejecting performance in the process of seawater desalination. The flexible salt-rejecting rGO/HN photothermal paper can produce clean water from wastewater and seawater with high rejection rates of organic dyes, metal ions, and salt ions, and it is promising for applications in water purification and seawater desalination.

Enhanced Directional Seawater Desalination Using a Structure-Guided Wood Aerogel

Seawater desalination via solar energy has potential to alleviate freshwater scarcity. However, problems including insufficient air-water interface, large heat loss, and potential ecological impact have restricted its practical viability. Here, a novel wood-derived indirect-contact (hanging) photothermal evaporation system was designed. An evaporation rate of 1.351 kg·m^-2·h^-1 with efficiency up to 90.89% under one sun illumination (1 kW·m^-2) was achieved, which is the highest record to the best of our knowledge. More importantly, a series of simulations and numerical modeling were carried out to analyze the main factors affecting seawater collection and evaporation, and the synergetic mechanisms of oriented seawater collection, photothermal thermogenesis, and natural convection were elucidated. Taken together, this study provides a new wood-derived hanging seawater desalination system with superior mechanical strength, good repeatability, great ecological security, and excellent thermal stability. The corresponding mechanisms of the whole process are shown, and the seawater evaporation efficiency approaching the real demand is maximized.

Tandem Desalination/Salination Strategies Enabling the Use of Redox Couples for Efficient and Sustainable Electrochemical Desalination

As access to fresh water becomes an increasingly serious global issue, developing desalination methods that can reduce not only the cost but also the carbon footprint of desalination has become of utmost importance. In this study, we demonstrate the use of the oxidation and reduction of the same redox couple with fast redox kinetics as the anode and cathode reactions of an electrodialysis (ED) cell. This reduces the thermodynamic equilibrium cell potential to 0 V while also significantly reducing the kinetic overpotentials required for cell operation. As a result, the overall operating voltage of our ED cell is remarkably reduced, making it possible to use ED for seawater desalination and to operate the ED cell by using inexpensive portable power generators that provide a limited voltage. The sustainable use of the redox couple in the ED cell was enabled by a new strategy, where a desalination ED cell and a salination ED cell were operated in tandem. In this tandem system, the electrolytes in the anode and cathode compartments of the two cells were circulated such that the compositional changes of the electrolytes made in the desalination cell could be reversed in the salination cell. As a result, the feedwater (0.6 M NaCl) could be converted to 0 and 1.2 M NaCl solutions in the desalination cell and salination cell, respectively, without the accumulation of salt ions in the anode and cathode compartments. The operating principles and performance of a proof-of-concept tandem desalination/salination system are demonstrated.

Highly Efficient Solar Vapor Generator Enabled by a 3D Hierarchical Structure Constructed with Hydrophilic Carbon Felt for Desalination and Wastewater Treatment

Solar vapor generation holds great potential for seawater desalination and wastewater treatment. Although various efficient solar absorbers have been developed to enhance the performance of solar vapor generators in recent years, their efficiency is still limited by unnecessary heat loss. In this article, a novel 3D hierarchical solar vapor generator (3DHG) was constructed with hydrophilic carbon felt. Different from interfacial solar vapor generators reported before, the porous and hydrophilic channels of 3DHG were exposed to the air directly, which probably resulted in a lower saturated vapor pressure of 3DHG. Therefore, this structure was beneficial for vapor escaping and led to lower average temperature of 3DHG than that of the surroundings at the same time owing to negligible convection loss and radiation loss of 3DHG. The highest evaporation rate (ER) of 1.56 kg m^-2 h^-1 and efficiency of 98.1% were obtained under 1 sun. In addition, 3DHG was also used for industry dyeing wastewater treatment and exhibited a minimum ER of 1.45 kg m^-2 h^-1 even after 7 days. This study presents a novel approach not only to design a solar vapor generator with high efficiency but also widens its potential application in seawater desalination and practical wastewater treatment.