Solar-driven Water Purification Research Articles

Spongy polyelectrolyte hydrogel with Janus porous for solar-driven interfacial evaporation and sustainable seawater desalination

Janus-structured hydrogels exhibit excellent advantages in interfacial solar desalination due to their hydrophilicity and low evaporative enthalpy of evaporation, as well as the better salt resistance and mechanical properties. In this research, a simple one-step self-stratification foaming technique is employed to transform hydrogels into Janus structured for seawater desalination. Polyvinyl alcohol (PVA), poly (diallyldimethylammonium chloride) (PDADMAC), and a photothermal material (carbon black, CB) are mechanically stirred with a foaming agent (sodium dodecyl sulfate, SDS), allowing for full mixing and air incorporation, ultimately forming a sponge-like polymeric electrolyte hydrogel with abundant Janus pore structures (PANS-J). The formation of Janus pores in the hydrogel is attributed to the flocculation and high density of hydrophilic PDADMAC, causing it to sink during gelation while hydrophobic PVA floats to the surface. The Janus structure produced by this method reduces heat loss and enhances evaporation performance, achieving a pure water evaporation rate of 3.35 kg m−2 h−1 under sunlight (1 kW m−2). Moreover, quaternary ammonium ions on PDADMAC effectively separate anions and cations in saltwater, reducing salt ion diffusion into the evaporator, preventing premature pore structure blockage, and thus improving long-term evaporator performance which can improve the salt resistance and mechanical properties. By combining these advantages, Janus evaporators hold significant promise for solar-driven water purification and other applications.

Spongy polyelectrolyte hydrogel with Janus porous for solar-driven interfacial evaporation and sustainable seawater desalination

Janus-structured hydrogels exhibit excellent advantages in interfacial solar desalination due to their hydrophilicity and low evaporative enthalpy of evaporation, as well as the better salt resistance and mechanical properties. In this research, a simple one-step self-stratification foaming technique is employed to transform hydrogels into Janus structured for seawater desalination. Polyvinyl alcohol (PVA), poly (diallyldimethylammonium chloride) (PDADMAC), and a photothermal material (carbon black, CB) are mechanically stirred with a foaming agent (sodium dodecyl sulfate, SDS), allowing for full mixing and air incorporation, ultimately forming a sponge-like polymeric electrolyte hydrogel with abundant Janus pore structures (PANS-J). The formation of Janus pores in the hydrogel is attributed to the flocculation and high density of hydrophilic PDADMAC, causing it to sink during gelation while hydrophobic PVA floats to the surface. The Janus structure produced by this method reduces heat loss and enhances evaporation performance, achieving a pure water evaporation rate of 3.35kgm-2 h-1 under sunlight (1kWm-2). Moreover, quaternary ammonium ions on PDADMAC effectively separate anions and cations in saltwater, reducing salt ion diffusion into the evaporator, preventing premature pore structure blockage, and thus improving long-term evaporator performance which can improve the salt resistance and mechanical properties. By combining these advantages, Janus evaporators hold significant promise for solar-driven water purification and other applications.

Robust Photocatalytic MICROSCAFS® with Interconnected Macropores for Sustainable Solar-Driven Water Purification.

Advanced oxidation processes, including photocatalysis, have been proven effective at organic dye degradation. Tailored porous materials with regulated pore size, shape, and morphology offer a sustainable solution to the water pollution problem by acting as support materials to grafted photocatalytic nanoparticles (NPs). This research investigated the influence of pore and particle sizes of photocatalytic MICROSCAFS® on the degradation of methyl orange (MO) in aqueous solution (10 mg/L). Photocatalytic MICROSCAFS® are made of binder-less supported P25 TiO2 NPs within MICROSCAFS®, which are silica-titania microspheres with a controlled size and interconnected macroporosity, synthesized by an adapted sol-gel method that involves a polymerization-induced phase separation process. Photocatalytic experiments were performed both in batch and flow reactors, with this latter one targeting a proof of concept for continuous transformation processes and real-life conditions. Photocatalytic degradation of 87% in 2 h (batch) was achieved, using a calibrated solar light simulator (1 sun) and a photocatalyst/pollutant mass ratio of 23. This study introduces a novel flow kinetic model which provides the modeling and simulation of the photocatalytic MICROSCAFS® performance. A scavenger study was performed, enabling an in-depth mechanistic understanding. Finally, the transformation products resulting from the MO photocatalytic degradation were elucidated by high-resolution mass spectrometry experiments and subjected to an in silico toxicity assessment.

3D macroporous MXene/sodium alginate aerogels with “brick-concrete” structures for highly efficient solar-driven water purification

Interfacial water evaporation, powered by solar energy, holds great promise to extract freshwater from seawater on a global scale. It has the potential to address the world's water scarcity challenges using renewable energy. While the ideal design of evaporator materials is critical to the interfacial vaporization desalination, tailoring the structures and compositions of solar evaporators and figuring out the structure/composition-performance relationship of evaporators remains unexplored. Herein, 3D macroporous “brick-concrete” MXene/sodium alginate aerogel (MSA) evaporators were designed and fabricated with constant MXene content and varying polymer loading. The as-made MSAs show sodium alginate-dependent evaporating performance with an optimum evaporation rate of 3.28 kg m−2 h−1 (1 sun). This exceptional rate is attributed to several factors, including enhanced light absorption, optimized pore sizes, reduced enthalpy of evaporation and improved water transport. The water molecule states and hydrogen bonding network in the aerogels can be tuned by their compositions, resulting in the reduced evaporation enthalpy, the monolithic structures with controlled thermal conductivity facilitate the exploitation of environmental energy, leading to the high evaporation rate. Our study not only establishes design principles for achieving superior evaporation performance, but also sheds light on the relationship between structures, compositions, and performance of solar evaporators.

Carboxymethylcellulose sodium-derived carbon aerogels for solar-driven water purification

Recycling polluted water via different techniques has become one of the most feasible ways to solve the freshwater crisis. We describe a novel method to prepare reusable and efficient photothermal energy conversion materials for water purification. Using crosslinked xerogels as precursor, the porous and interconnected carboxymethylcellulose sodium-derived carbon aerogels (abbreviated as CCAs) with good hydrophilic performance and strong light absorption capability are firstly fabricated through pyrolysis. Photothermal measurement results show that CCA15 exhibit excellent solar steam generation rate of 2.31 kg m−2 h−1 with high light-to-vapor conversion efficiency of 95.9% under 1 sun illumination. In addition, the feasible application of CCA15 for efficient water purification under 1 sun irradiation using a homemade water treatment device has been demonstrated successfully. The as-prepared CCAs shown in here can be a continuable solution to mitigate the global freshwater crisis.

A Tent-Inspired Portable Solar-Driven Water Purification Device for Wilderness Explorers.

Wilderness adventure favored by many enthusiasts often endanger lives due to lacking freshwater or drinking contaminated water. Therefore, compared to the inefficient methods of filtration, steaming, and direct solar heating, it is of great meaningfulness to develop a solar-driven water purification device with efficiency, lightweight, portability, and multi-water-quality purification by taking full advantage of solar-driven interfacial evaporation. Here, a tent-inspired portable solar-driven water purification device consisting of Janus-structured bacterial cellulose aerogel (JBCA) solar evaporator and tent-type condensation recovery device is reported. For the JBCA solar evaporator, it is prepared from biomass bacterial cellulose (BC) as raw material and hydroxylated carbon nanotubes (HCNT) as photothermal material, and the Janus property is achieved by the assistance of hydrophobic and hydrophilic chemical cross-linking. It exhibits lightweight, unibody, high photothermal conversion, efficient evaporation, and multi-water-quality purification capability for representative seawater, urine, and bacterial river water. For the tent-type condensation recovery device, it is based on the prototype of tent and uses flexible ultra-transparent polyvinyl chloride (PVC) film as raw material. Thanks to the rational prototype and material selection, it displays outstanding portability and lightweight through the folding/unfolding method. Therefore, the designed tent-inspired portable solar-driven water purification device demonstrates great potential application in wilderness exploration.

Well-designed lamellar reduced graphene oxide-based foam for high-performance solar-driven water purification

Although solar steam generation is promising for seawater desalination, it is less effective in purifying wastewater with both salt/heavy metal ions and organic contaminants. It is thus imperative to develop multifunctional integrated solar-driven water purification systems with high solar-thermal evaporation and photocatalytic degradation efficiencies. Herein, a lamellar reduced graphene oxide (L-RGO) foam with the vertical lamellar structure is fabricated by bidirectional-freezing, lyophilization, and slight chemical reduction for water purification. The unique vertical lamellar structure not only accelerates upward transport of water for facilitating water evaporation but also endows the L-RGO foam with superb high elasticity for tuning the interlayer distance and varying interactions between the oxygen-containing groups and water molecules to adjust water energy state. As a result, the L-RGO foam achieves a superb water evaporation rate of 2.40 kg m−2 h−1 along with an energy efficiency of 95.3 % under the compressive strain of 44.7 % under 1-sun irradiation. Equally importantly, the decoration of L-RGO foam with polypyrrole is capable of efficiently degrading organic pollutants while retaining high solar steam generation performances, exhibiting great potential in the comprehensive treatment of various water sources for relieving freshwater crisis.

High-efficiency solar-driven water purification enhanced by the in-plane temperature gradient and hydrated ions

Solar-driven water purification has become a promising way to overcome the freshwater crisis because of its environmentally-friendly features. Improving the evaporation rate and evaporation efficiency are eternal topics. In this work, we redesign the solar-driven vapor generation (SVG) device and a unique in-plane temperature gradient is established due to the oriented water transportation. The input energy is maximized and the superb evaporation rate of 6.40 kg m−2 h−1 with an efficiency of 243.8 % is achieved. By investigating the hydration state in NaCl solution and aqueous acid, the interaction mechanism between hydrated ions and non-woven fabrics is developed. Owing to the increased intermediate water proportion, the evaporation rate of the SVG device in 5 wt% NaCl solution can reach 6.38 kg m−2 h−1, which is almost the same as that in DI water. Moreover, the unique reversible doping properties make the non-woven fabrics a reusable and stable volatile acid purifier. The evaporation rate in pH = 4.0 aqueous acid can be enhanced to 6.75 kg m−2 h−1, while the generated water maintains a pH higher than 6.5. Our work provides a new perspective for designing high-efficiency and multifunctional SVG devices.

Super stable evaporators based on upcycled self-healing adsorbents for wastewater regeneration

Establishing a self-healing platform for the removal and resource recovery of heavy metals, enabling heavy metal-free drinking water.

A cationic radical metal–organic framework enabling low water evaporation enthalpy and high photothermal conversion efficiency for solar-driven water purification

An innovative solar evaporator, combining Cu foam with a cationic radical MOF (PFC-771) as the photothermal absorber, demonstrates rapid and efficient solar energy-driven water evaporation.

A bioinspired hydrogel with tailored nano-topography and desired mechanical performance for highly efficient solar-driven water purification

Solar-driven interfacial evaporation has emerged as a sustainable and innovative technology for efficient, clean water production.

Improved solar-driven water purification using an eco-friendly and cost-effective aerogel-based interfacial evaporator with exceptional photocatalytic capabilities

As a promising solution to address the global challenge of freshwater scarcity, solar-powered interfacial steam generation has undergone notable advancements. This study introduces a novel solar-driven interfacial evaporation membrane (ZnIn2S4@SiO2/ACSA, ZSAS) comprising a ZnIn2S4@SiO2 composite and a black sodium alginate aerogel infused with activated carbon. The ZSAS membrane demonstrates exceptional light absorption and thermal insulation, leading to elevated surface temperatures and reduced heat dissipation into the bulk water. Furthermore, the incorporation of AC reinforces the mechanical properties of the ZSAS membrane and enhances the water purification performance. These collective features result in an impressive evaporation rate of 1.485 kg m−2 h−1 and a high photothermal conversion efficiency of 91.2% under 1 sun irradiation for the optimal ZSAS membrane. Moreover, the optimal ZSAS membrane can effectively remove salts, heavy metal ions, and organic pollutants, benefitting from its superior evaporation separation effect and the photocatalytic properties of the ZnIn2S4@SiO2 composite.

Enhanced solar-driven thermoelectric power generation and water desalination via hydrothermally synthesized degenerately doped copper selenide nanocrystals composited with polydimethylsiloxane

In this study, we developed novel composites of degenerately doped copper selenide and polydimethylsiloxane (DDCS/PDMS) that efficiently harness a wide range of solar light for both electricity generation and water purification. The DDCS nanocrystals possess remarkable optical absorption capabilities across the near-infrared (NIR) solar spectrum, leading to enhanced photothermal effects. Within the DDCS/PDMS composite, this results in remarkable light-to-heat conversion, sustaining a consistent surface temperature of 51.5 °C in contrast to the 39.8 °C exhibited by bare PDMS when subjected to standard 1 sun intensity for 3 min, and leveraging its exceptional photothermal characteristics, the composite demonstrated noteworthy thermoelectric power generation, achieving 95 mV, while pristine PDMS only managed 49 mV under 1 sun conditions. Moreover, the DDCS/PDMS foam demonstrated outstanding solar-to-vapor performance, achieving a rate of 1.71 Kg m−2 h−1 with an efficiency of 91.5 % under equivalent sunlight exposure. Remarkably, the versatile DDCS/PDMS foam effectively demonstrated its capability in seawater desalination, achieving an efficiency exceeding 80 % even under the most challenging conditions. This study uncovers the compelling potential of solar-thermal energy utilization and introduces an innovative approach for solar-driven water purification and power generation. By addressing the challenges of sustainable energy and clean water provision, these findings offer a promising avenue forward.

A dual-functional lignin containing pulp foam for solar evaporation and contaminant adsorption

Recently, solar-driven evaporator has been widely investigated as an environmentally benign and sustainable method in water desalination and purification, but its evaporation efficiency is highly reliant on solar intensity, and the increased contamination in water can hinder the production of clean water. Herein, we designed a novel and scalable polydopamine-functionalized lignin containing pulp (LPNR@PDA) foam evaporator with the dual-purpose of high-efficiency desalination and multi-contaminant adsorption. With excellent light absorption (90 %), high water absorption ability (9.5 g g−1), low thermal conductivity (0.1 W mK−1) and chelation capabilities, the LPNR@PDA foam evaporator synergized solar evaporation and contaminant adsorption with one another, making the LPNR@PDA foam evaporator a desirable material with the capability of continuous clean water production in all-weather conditions. Additionally, the LPNR@PDA foam evaporator with unique porous structure presented potential applications in treatments of metal ion concentration and contaminated seawater, and also the LPNR foam exhibited excellent biodegradability in the natural environment compared to polystyrene foam. Therefore, this novel foam material will shine a new light for developing multifunctional photothermal system for solar-driven water purification.

The manipulation of the interfacial evaporation property of graphene porous membranes

Graphene membranes of excellent solar absorption and photothermal conversion efficiency have been used in solar-driven water evaporation (SDWE) systems as light-harvesting material. The interfacial evaporation property between graphene membranes and seawater is an important issue to further promote the development of SDWE. In this work, manipulation strategies are presented based on porous structures for tailoring the evaporation performance of graphene membranes. The non-equilibrium molecular dynamic (NEMD) simulation results show that the pore size, pore concentration, and distribution pattern are all key factors in enhancing the evaporation rate. The evaporation performance can achieve the best optimisation when the pore size is 3.1 Å and the pore concentration is the lowest. Moreover, the periodic distribution of porous structures can greatly increase the evaporation rate (about 100 water molecules per nanosecond) due to the improvement of adsorption and desorption balance compared with the random structure. The optimised configuration of the graphene porous used in SDWE systems is proposed, which could increase the evaporation rate to 357.1%. This study could provide some theoretical guidance on graphene membranes for application in both photothermal conversion and solar-driven water purification.

Facile fabrication of functionalized wood evaporator through deep eutectic solvent delignification for efficient solar-driven water purification

Solar-driven sewage purification was considered to be a promising technique for the alleviation of freshwater scarcity issues globally. However, most steam generation devices focused on ultrahigh photothermal conversion and also neglected to develop the potential functions of natural creatures. Here, a deep eutectic solvent (DES) functionalized wood was designed as the supported substrate decorated with black polypyrrole (PPy) to construct low-cost and efficient solar interfacial evaporator. DES modification selectively removed most of the lignin, which enhanced the hydrophilic wetness of wood for the efficient transportation of water from the bottom to the solar interface. The lignin selective removal lowered the thermal conductivity of the evaporator, facilitating the heat location on the gas-liquid interface for efficient steam generation. Most importantly, more cellulose hydroxyl was exposed on the wood surface by the DES process, which was conducive to the in-situ polymerization of pyrrole on the wood surface by hydrogen bond interaction. The prepared PPy-DES wood evaporator achieved a considerable water evaporation rate of about 1.94 kg m−2 h−1 with a corresponding photothermal conversion efficiency of about 83.4% in one sun, arising from the functionalized design of DES wood and efficient photothermal conversion. For seawater desalination and sewage purification, the prepared evaporator exhibited excellent salt self-cleaning ability and stable wastewater purification performance. It was envisioned that the strategy of functionalized design of natural evaporators would motivate a large-scale application of biomaterials for efficient wastewater purification.

Three-Dimensional Spiral Evaporator with Side Channels for Efficient Solar-Driven Water Purification.

Solar evaporators have the advantages of not consuming fossil fuels, being environmentally friendly, and nonpolluting, offering a promising sustainable method to obtain fresh water and alleviate the worldwide freshwater shortage crisis. In this work, we report that high-performance solar evaporators can be facilely fabricated by processing a cost-effective polypyrrole (PPy)-coated nonwoven fabric (PCNF) into a three-dimensional (3D) spiral structure and introducing side channels for vapor escape. The coated PPy layer ensures excellent photothermal properties and the chemical stability of the evaporator. Meanwhile, the as-created spiral structure of the evaporator can significantly increase the effective evaporation area and harvest energy from the environment, greatly stimulating the evaporation. The side opening channels can effectively facilitate the escape of vapor generated inside the 3D spiral structure, avoid the internal vapor accumulation, and ultimately promote the evaporation of the inner surface, leading to a boost of the evaporation performance. Combining these features, the resulting evaporator exhibits an ultrahigh evaporation rate of 3.26 kg m-2 h-1 and an energy efficiency of 138% under 1-sun irradiation. More importantly, we show that this evaporator can also be used to collect fresh water from soil and sand, demonstrating its great applicability for obtaining potable water in arid areas.

Clay-based aerogel combined with CuS for solar-driven interfacial steam generation and desalination

Solar-driven water purification is a promising technology that can effectively utilize solar energy for seawater desalination. However, poor materials are unable to meet the dense energy of solar steam generation in natural sunlight for real-time practical applications. Therefore, the demand for energy density can be increased by using improved semiconductor aerogel materials. Here, we report a simple chemical method to obtain a CuS@ATP/PS composite aerogel (named CuAP), which was made of attapulgite (ATP) and CuS loaded onto it using an N-template to give it good photothermal characteristics (CuS@ATP), and then cross-link it with potato starch (PS). The evaporation rate of CuAP-15 aerogel in pure water at 1 kW m−2 solar radiation is 1.57 kg m−2 h−1. Meanwhile, CuAP-15 aerogel showed excellent salt resistance with an evaporation rate of 1.35 kg m−2 h−1 in 20 wt% NaCl solution. And also exhibited excellent cycling durability in cycling stability tests. More importantly, the freshwater yield can reach 6.54 kg m−2 under natural light irradiation for 11 h. Therefore, CuAP aerogel has a great prospect of application in the field of seawater desalination in the future.

Photothermal-photocatalytic route of MOF-based membrane with nanosheet array structures for solar-driven water purification

Solar-driven interfacial evaporation technology is a promising sustainable approach to mitigate the global energy crisis and clean water scarcity. The advanced interfacial evaporation materials make a non-negligible contribution to the solar thermal utilization for water purification. In this work, a Cu-catecholate metal–organic framework-based photothermal membrane (Cu-CATM) is developed to generate freshwater from seawater and recover clean water from wastewater. Thanks to the unique photothermal effect and the three-dimensional nanosheet array structure of Cu-catecholate metal–organic framework (Cu-CAT MOF), the Cu-CATM enabled a promising evaporation rate of 2.43 kg m−2h−1 and a high solar-vapor conversion efficiency of 92% under solar irradiance of 1 sun. Further, the Cu-CATM could be applied to solar seawater desalination with durable evaporation rate and no salt accumulation. Also, the Cu-CATM enabled solar utilization for synchronous photothermal desalination and photocatalytic degradation, which highlighted the broader environmental application for water remediation or wastewater treatment via photothermal-photocatalytic route. This work presents a viable and effective route for the development of photothermal membranes toward future sustainable clean water production from non-conventional water resources.

Exploring perovskite oxide for advancing salt-resistant photothermal membranes and reliable thermoelectric generators

Solar-driven water purification is a promising technology that efficiently exploits solar energy for water purification, desalination, and energy generation. However, poor material compliance requires intensive energy to generate vapors under natural sunlight with real-time practical implications. Therefore, advanced functional nanomaterials are highly desirable for reducing energy demand for water evaporation. Herein, we report bifunctional La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) perovskite oxide for solar-driven steam and thermoelectric generation. The hydrophilic/hydrophobic structure endows excellent salt-rejection, thermal management, and hydrophilic water channels for an efficient solar evaporation rate (2.36 kg m−2 h−1) using seawater (3.5 wt%) under 1 kW m−2 irradiation. More importantly, the salt-resistant and thermally insulated evaporation structure drives brine through milli-drilled water channels and re-dissolves back into the water body without impeding evaporation efficiency (16.83 kg m−2 mass change during 8 h under 1 sun irradiation). Besides, the LSCF-based photo-thermoelectric generator harvests solar energy into an electric output (Vout ∼ 292.2 mV, and Iout ∼ 52.5 mA). The state-of-the-art investigations and heat transfer simulations portray the device's functionality and its optimization toward long-term durability, thermoelectricity, and a suitable option for remote sensing areas.