Solar Water Purification Research Articles

An ecofriendly and efficient wood-based polyoxovanadate solar evaporation generator

Currently, freshwater scarcity is a global challenge, and developing low-cost methods for purifying, desalinating, and distilling seawater is crucial. Natural wood, owing to its advantages of high hydrophilicity, low density, microporous channels, and low thermal conductivity, is widely considered a vehicle for solar evaporation. However, the majority of the reported wood-based solar evaporation generators have been economically inefficient, with limited evaporation rates under low-power solar irradiation. Herein, we developed an ecofriendly and efficient wood-based solar evaporation generator comprising a material with excellent photothermal conversion efficiency, polyoxovanadate, loaded on the wood surface with a natural channel structure. The solar evaporation generator exhibited high light absorption capacity (∼98%) in the wide wavelength range of 200–1200 nm, rapid water transport through the wood channels, minimal heat dissipation due to the adiabaticity of the wood, and reduced evaporation enthalpy. Therefore, the overall evaporation efficiency was increased, and a high evaporation rate of 2.23 kg m−2 h−1 and solar-vapor efficiency of 90% under 1 Sun was observed. This environment-friendly, low-cost, and high-efficiency evaporation generator has enormous potential for practical applications in solar desalination and water purification.

Porous Hydrogel Photothermal Conversion Membrane to Facilitate Water Purification.

Solar water purification technology is one of the most potent methods to obtain freshwater due to its low cost and non-polluting characteristics. However, the purification efficiency is limited by the high ion concentration, organic pollution, and biological pollution during the actual water purification process. Here, we report a porous hydrogel membrane (Fe/TA-TPAM) for the purification of high ion concentration and contaminated water. The hydrogel membrane exhibits good light absorption and photothermal conversion ability, which shows high evaporation rates (1.4 kg m-2 h-1) and high solar efficiency for seawater. Furthermore, with the introduction of tannic acid (TA) and Ti3C2 MXenes, the Fe/TA-TPAM hydrogel membrane exhibits satisfied purification properties for organic-contaminated and biologically contaminated water. The excellent purification effect of Fe/TA-TPAM under light not only confirms the rationality of the hydrogel porous design and in situ generation of photosensitizer in improving the photothermal performance but also provides a novel strategy for designing advanced photothermal conversion membranes for water purification.

In Situ Latent Heat Transfer for Nearly 100% Condensation in Single-Stage Interfacial Solar Steam Generation

Interfacial solar steam generation is considered a promising alternative for freshwater production. Although efforts have been invested in enhancing the evaporation rate (ER), considerable discrepancies exist between the ER and the actual collection yield when used in practical devices. Here, we prepared a solar water purifier with a conical evaporator and a cylindrical condenser of the same diameter and achieved nearly 100% steam condensation efficiency by conducting the wastewater through the condenser surface via capillary action. A 2.5-fold increase in the water collection rate (CR) in a single-stage solar water purifier was achieved compared to conventional solar stills, irrespective of the absorber materials and illumination intensities. The high CR/ER ratio in this solar water purifier was attributed to the efficient in situ latent heat transfer from steam to the reservoir that maintained the condenser at a lower temperature, enhancing the steam condensation. A simple and cost-effective design technique with high water collection yield, this work provides a promising pathway toward portable and personalized freshwater generation in remote areas.

Bi-MOF-derived plasmonic Bi-C on carbon felt for efficient solar evaporation, water purification and salt-resistant desalination

Plasmonic nanostructures have been demonstrated to be an important class of photothermal absorbers, facilitating solar vapor generation by plasmonic heating. However, the high cost and sophisticated preparation of commonly used plasmonic noble metals pose significant obstacles to practical applications. Here, we report for the first time an affordable plasmonic evaporation system that combines the porous carbon frameworks encapsulated semimetal Bi nanoparticles (Bi-C) and carbon felt (CF). The hydrophilic Bi-C and porous network structure of CF favor effective light harvesting and fast water transmission, promoting photothermal conversion and mass transfer during solar evaporation. Under one sun irradiation, the designed Bi-C/CF exhibits the robust behavior for solar steam generation, achieving an expected high evaporation rate of 1.50 kg·m−2·h−1 and a comparable evaporation efficiency of 91.9 %. As a result, the excellent performance of Bi-C/CF not only benefits the sustainable freshwater production from saline water and seawater, but also enables efficient wastewater purification for energy-saving water source remediation.

A Lotus‐Petiole‐Inspired Hierarchical Design with Hydrophilic/Hydrophobic Management for Enhanced Solar Water Purification

AbstractSolar‐driven vapor generation offers an affordable and sustainable approach to solve global freshwater scarcity. Creating interfacial solar evaporators capable of increasing water production rates matching human water requirements is highly desirable but challenging due to the slow water transportation dynamics and unavoidable oil‐fouling. Herein, a bio‐inspired lotus‐petiole‐mimetic microstructured graphene/poly(N‐acryloyl glycinamide) solar evaporator with integrated hydrophilic and hydrophobic microregions is developed. Through accurate control of the supramolecular interactions, the optimized solar evaporator incorporating unique structural features and wettability shows high light harvesting, enhanced water activation, and reduced energy demand for water vaporization, enabling a groundbreaking comprehensive performance along evaporation rate up to 3.4 kg m−2 h−1 and energy conversion efficiency of ≈93% under one sun irradiation (1 kW m−2). Molecular dynamics simulations reveal that the abundant hydrogen bonding sites of the polymeric networks can thermodynamically modulate the escape behavior of water molecules. Notably, neither decrease in evaporation rate nor fouling on solar evaporators is observed during the prolonged purification process toward nano/submicrometer emulsions, oily brines, actual seawater, and domestic wastewater. This study provides distinctive insights into water evaporation behaviors at a molecular level and pioneers a rational strategy to design high‐yield freshwater‐generation systems for wastewater containing complex contaminants.

A magnetic nanostructure PAC@Fe3O4 driven design toward Janus hydrogel achieves highly efficient solar water evaporation

Solar water purification is a promising scheme to relieve the energy crisis and clean water shortages. In order to improve the efficiency of producing water, it is necessary to develop a novel photothermal conversion interface to manage heat loss and boost water evaporation efficiency. Herein, a Janus hydrogel evaporator of powder active carbon (PAC) and Fe3O4 in polyvinyl alcohol (PVA) and polystyrene sulfonate (PSS) cross-link hydrogel, called CFPS, is explored as the light absorber for broadband light absorption and formed a hydrogel network of the multi-hydrophilic group. Its hydrophilic/hydrophobic structure of CFPS is used to regulate heat loss and promote water transport, which can attain lower evaporation enthalpy and a higher evaporation rate. Specifically, the surface temperature of the CFPS can reach around 45 °C and 93.4% energy utilization efficiency under 1 sun illumination. In the comparison of the analogous Fe3O4-based evaporator, CFPS has the higher static evaporation rate with 3.43 kg m–2h−1. Besides, it has great mechanical properties, durability and anti-crystallization function, which can be adapted to the water purification scene of wastewater and hypersaline water desalination. This photosensitive magnetic hydrogel evaporator shows potential in the scenarios of wastewater purification and desalination.

All-weather photothermal-electrothermal integrated system for efficient solar steam generation

Interfacial solar-driven water evaporation is considered as an economic and efficient strategy to address the shortage of freshwater resources, which however suffers from severe salt pollution and poor long-term stable performance of seawater evaporation. Here, we design and construct a three-dimensional all-weather solar evaporator by zeolite-chitosan-TiO2@PPy aerogel (ZCTP), with an internally oriented pore arrangement structure by zeolite and chitosan assistance, which can efficiently enhance solar-driven water purification. Most importantly, long-term operation of the ZCTP aerogels using carbon fiber heating wires to fully utilize the solar energy that collected during the daytime to improve the efficiency of solar utilization and water purification. Benefiting from novel structural and functional design, the ZCTP aerogels exhibit high broadband light absorption (96 %), fast water transport (13 ms), and good thermal management properties (thermal conductivity of 0.1969 W m−1 K−1 in wet state). The obtained results show that the water evaporation rate of the ZCTP aerogel is 1.66 kg m-2h−1 under 1 sun illumination. The integrated system of photothermal and electrothermal energy conversion mechanisms obtains an ultra-high water evaporation rate of 11.70 kg m-2h−1 of 5 V voltage under 1 sun irradiation, achieving the purpose of continuous purification water around the clock. In addition, excellent salt resistance also enables perfect stability and reusability of ZCTP aerogel, even in the water with 20 % salt having minimal impact on the evaporation process and energy efficiency. Based on its excellent mechanical stability and highly ductility, simple and scalable manufacturing process, ZCTP aerogel may have great potential for all-weather efficient photothermal material for large-scale applications such as wastewater treatment, seawater desalination, and solar steam generation.

Performance evaluation of solar still integrated with thermoelectric heat pump system

<abstract> <p>This research presents a method for improving a conventional solar still to produce potable water during adverse conditions where there is low or no solar radiation. Summer and winter conditions in the Western Cape province of South Africa were considered. A comparative experimental study was conducted between a conventional solar still and the developed solar still. The developed solar still incorporated a photovoltaic powered thermoelectric heat pump. The purpose of the thermoelectric (TE) heat pump was to accelerate convection inside the developed solar still assembly. The coefficient of performance (COP) of the thermoelectric heat pump installed in the developed solar still ranged from 0.4 to 1.9 at an input current of 5 A. The results indicated that the developed solar still was able to produce 2300 mL per day of drinkable water during a good day in the winter, but the conventional solar still was only able to produce 650 mL per day. The developed solar still produced 2180 mL per day, whereas the ordinary solar still produced 1050 mL per day, during a mild summer day. The developed still had an accumulated water production of 1180 mL during a night with mild temperatures. This significant improvement in yield of the developed solar still system is due to the change in temperature difference between the glazing and the water surface within the developed solar still. This is a significant contribution to the technology of solar water purification.</p> </abstract>

High-Performance Janus Solar Evaporator for Water Purification with Broad Spectrum Absorption and Ultralow Heat Loss

Interfacial solar vapor generation offers a promising zero-CO2-consuming energy conversion technology for the production of renewable clean water. The key for boosting solar vapor efficiency relies on the rational design of materials composition and structure at the micro/nanoscale to improve light utilization. Here, we demonstrate a Janus evaporator based on a hydrophilic carbon-black-decorated copper oxide (C@CuO) membrane as the light-absorbing layer and an opposite hydrophobic polymer nanofibers as the thermal insulation layer, which enables efficient energy utilization and vapor generation through a synergistic light absorption and thermal confinement strategy. In addition, the hydrated C@CuO surface reduces vaporization enthalpy that accelerates the efficient evaporation of water. A high evaporation rate of 1.88 kg m–2 h–1 is achieved by the Janus evaporator under 1 sun irradiation. This high photothermal conversion rate and ultralow heat loss synergistic engineering offers a bright future for high-efficiency solar water purification applications.

Facile fabrication of Ni5P4-NiMoOx nanorod arrays with synergistic thermal management for efficient interfacial solar steam generation and water purification

Interfacial steam generation by harnessing renewable solar energy has been recognized as a sustainable solution to global freshwater crisis. A promising evaporator with key components of high spectral absorption, efficient thermal management and adequate water transport is highly desired. In the present study, an integrated design for three-in-one functionality is achieved by simply loading Ni5P4-NiMoOx (P-NMO) on a macroporous nickel foam (NF) carrier. In situ embedding broadband Ni5P4 absorber into insulating NiMoOx enables efficient photothermal conversion and heat localization. Benefiting from proper thermal management and abundant water transmission, P-NMO/NF exhibits the excellent performance for interfacial steam generation with a high evaporation rate of 1.49 kg m−2h−1 and evaporation efficiency of 93.0 % under one sun irradiation. Furthermore, the obtained P-NMO/NF is proven to be applicable for high-efficiency freshwater production in seawater desalination and wastewater purification, showing great potential for practical solar evaporator under natural environmental conditions.

Optical, Structural and Ethanol Sensing Properties of Spin-Coated ZnO Film

Among the various nanomaterials, Zinc Oxide (ZnO) has recently attracted the attention of researchers due to its potential application in various fields such as solar cells, bio-sensors, optoelectronic devices, gas sensors, water purification, piezoelectric devices, and liquid crystal displays. The accurate knowledge of the optical and structural properties of ZnO film is important for the fabrication of high-quality devices. In this work, 0.2M ZnO thin film was prepared by the economic spin coating technique. The Swanepoel method was employed to determine the average thickness and refractive index of the film with high accuracy in the spectral region of 200-1000 nm. The transmittance spectra were utilized to determine the absorption coefficient and extinction coefficients. The bandgap (Eg) was determined using Tauc’s formula and was found to be 3.22 eV. The real and imaginary parts of the dielectric decrease sharply with the wavelength. The single oscillator model was employed to discuss the dispersion parameters. The dispersion energy (Ed) and single-oscillator energy (Eo) were found to be 7.862 eV and 6.863 eV respectively with Eo≈ 2Eg proving the validity of the Swanepoel method for ZnO film. Structural analysis revealed that the film was polycrystalline in nature with a hexagonal wurtzite structure and an average crystallite size of ~31 nm with a Zn–O bond length of 1.9435 Å. The gas sensing properties in terms of the response of the ZnO sensor towards ethanol vapour were measured in the temperature range of 100–330 °C using DC electrical resistance. The ZnO film showed the maximum response of ~7 at temperature 260 °C for 800 ppm ethanol vapour exposure which may be due to the higher reaction rate at that temperature. The response of the sensor was increased on the exposure to a higher concentration of ethanol vapour. The sample showed a faster response on exposure to higher concentrations (400-800 ppm) of ethanol with a response time of ~13 s and a good response of 3.75 for 40 ppm of ethanol vapour exposure at 260 oC.

Architecting Janus hydrogel evaporator with polydopamine-TiO2 photocatalyst for high-efficient solar desalination and purification

Solar-powered water distillation is one of the effective and promising ways of water purification. However, new high-efficiency evaporators are especially needed to reduce the energy requirement and improve water yields under natural sunlight. In this study, a Janus structured hydrogel with an interpenetrating double network was formed by polyvinyl alcohol and natural polysaccharide to speed up solar water purification. Due to its unique pore structure, water molecules can quickly escape from the surface of Janus hydrogel by molecular dynamics simulations. The Janus evaporator worked stably and the evaporation rate was achieved to 3.53 kg·m−2·h−1 under 1 sun illumination, which was attributed to the outstanding water transport capacity and thermal localization capacity. Meanwhile, the Janus-based solar evaporator exhibited excellent durability in wide acid–base range (pH 1–13) and salinity range (0–350‰), and long term (30 days). The daily yield of the Janus hydrogel reached 24.5 kg·m−2·h−1 in outdoor tests. The Janus evaporator enables efficient desalination and purification of other unconventional water sources, and can degrade more than 95% of organic dyes (trypan blue and Congo red) as a result of the synergistic effect of Polydopamine (PDA) /TiO2 nanoparticles. This Janus structured hydrogel evaporator opens up potential applications in desalination and wastewater treatment.

Catalysis-involved 3D N-doped graphene aerogel achieves a superior solar water purification rate and efficiency

Solar-driven water evaporation is a promising technology to address the water scarcity concern. While in the past years this research direction has initiated sizable progress in water purification, its application remains challenging due to the low water evaporation rate and treatment efficiency. Herein, a 3D cylinder evaporator (SMNG) with superior evaporation rate and excellent water treatment efficiency is developed through a unique 3D structural design by incorporating catalytic Ag-MnO2 nanostructure with N-doped graphene aerogel. The SMNG evaporator possesses an evaporation rate as high as 6.46 kg m−2 h−1 under one sun irradiation, with a photothermal conversion efficiency of 90.25 %. In addition, the SMNG also exhibits a remarkable desalination ability, with an evaporation rate of 6.15 kg m−2 h−1 and an ions rejection rate up to 99.9 % on seawater. In an outdoor environment, the SMNG can attain a maximum seawater evaporation rate of 8.57 kg m−2 h−1, demonstrating its promising practical applications. The SMNG evaporator also shows over 99.9 % efficiencies in purifying wastewater that contains organic dyes, heavy ions, formaldehyde, and E. coli.

Antibacterial silver-loaded TiO2 ceramic photocatalyst for water purification

We developed an antibacterial photocatalytic material for purifying drinking water by immobilizing Ag nanoislands, which exhibit bactericidal activity even under dark conditions, on a robust TiO2 ceramic photocatalyst designed for underwater use. Hydrothermal synthesis was used to immobilize Ag nanoislands onto the TiO2 ceramic. This Ag/TiO2 ceramic was treated by ultrasonication for a total of 947 min in water, following which the unstably supported Ag nanoislands were removed from the TiO2 ceramic. The Ag elution remained below the provisional safety standard limit of 0.1 mg/L. This Ag-loaded TiO2 ceramic photocatalyst showed significant bactericidal effects even under dark conditions, despite the low Ag elution. This Ag-loaded TiO2 ceramic photocatalyst can probably be used for the photocatalytic sterilization during solar photocatalytic water purification under cloudy or rainy conditions.

Molecular engineering of a synergistic photocatalytic and photothermal membrane for highly efficient and durable solar water purification

In recent years, the solar-driven interfacial evaporation system (SIES) has obtained a lot of interest as a potential solution to freshwater scarcity. However, the organic pollutant residues affected the practical application of the distillate generated by SIES. Herein, a solar interfacial membrane (AuNPs@g-C3N4/CMF) (AMF) for desalination and removal of multiple water pollutants was prepared by generating Au-doped carbon nitride (AuNPs@g-C3N4) directly on the carbonized melamine (CMF) through a co-calcination process. The designed membrane features excellent light absorption, efficient water supply, and low thermal conductivity. All the above advantages of the AMF membrane contributed to an outstanding evaporation rate (1.675 kg m-2 h-1) and high photothermal conversion efficiency (94.03%) under 1 sun irradiation. For seawater desalination, the membrane performed well in removing ions from simulated seawater and demonstrated good stability during long-term desalination. Meanwhile, the membrane still exhibits a high evaporation rate (1.24 kg m-2 h-1) even in a 10% salt solution environment. Owing to the photocatalysis capability of AuNPs@g-C3N4, the AMF membrane also performs effectively in the removal of organic dyes and formaldehyde.

Molecular architecting of photothermal hydrogels reinforced by polar-porous C2NxO1-x for efficient solar water purification

Solar-powered interfacial evaporation provides a sustainable and effective means of harvesting green energy to relieve the global water scarcity issues. While hydrogel evaporators are effective for purifying the contaminated or saline water, the use of hydrophobic carbon-based light-absorbers that compromises the hydratability and local heat exchange poses an impediment to the evaporation rates. Herein, we propose a concept of using heteroatoms-rich and porous C2NxO1-x as the light absorber for molecular design of hydrogel-based evaporators for solar-powered water purification. The synergy of abundant polar groups within C2NxO1-x and hydratable skeleton (chitosan and polyvinyl alcohol) enables the decline of water evaporation enthalpy and thus facilitates vapor generation. The hydrophilic C2NxO1-x that penetrates hydrogel network enlarges the pore aperture with improved pore interconnectivity, which allows for rapid water transport and sufficient water supply. Importantly, the converted energy was localized to sufficiently power the evaporation of water molecules present in polar pores of C2NxO1-x due to adequate heat exchange. The resultant photothermal hydrogel attains a high evaporation rate of ca. 2.9 kg m−2 h−1 with an ultrahigh ion removal efficiency (99.9 %) in both simulated seawater and complex ionic contaminants under one sun irradiation. This study offers a useful guideline of utilizing hydrophilic porous light-absorber to develop high-performance hydrogel for efficient solar-powered water purification.

Biosafe Bi2O2Se ultrathin nanosheet for water disinfection via solar-induced photothermal synergistic effect

Solar-induced sterilization via photothermal synergy has attracted enormous attention due to its zero-energy consumption and the elimination of hazardous chemical disinfectant. Herein, we successfully synthesized a super biosafety Bi2O2Se with crossed nanosheet structure (Bi2O2Se-CN) for the sterilization of Escherichia coli (E. coli) via solar-induced photothermal synergistic effect. In comparison to bulk Bi2O2Se, the lower light reflection and more efficient photogenerated charge carrier separation under visible-infrared light irradiation resulted in the excellent sterilization effect of Bi2O2Se-CN, with a sterilization efficiency of 99.9% under the synergistic effect of light and heat. The crossed ultrathin nanosheet structure and suitable band gap width of Bi2O2Se-CN are fundamental reasons for its enhanced light absorption and charge carrier separation efficiency. Mechanistic studies showed that Bi2O2Se-CN can completely inactivate bacteria via generating a large amount of reactive oxygen species (•O2-, •OH, and 1O2) to attack the cell membrane, which further resulted in the reduced activity of intracellular enzymes and the leakage of intracellular contents. The biosafety property of Bi2O2Se-CN was confirmed by in vivo toxicological evaluation on the mice model. This work provided new ideas for the design of more efficient, energy-saving, biocompatible and environmental friendly solar water purification projects.

Hierarchical unidirectional fluidic solar-electro-thermal evaporator for all-day efficient water purification

Constructing a high-efficiency evaporation system with all-day operation capability remains a great challenge for the emerging solar water purification technologies due to the accompanied salt-fouling problem and uncertain natural sunlight conditions. Here, a hierarchical solar-electro-thermal evaporator with serpentine and unidirectional fluidic structure is developed by in situ assembling MoS2 nanosheet arrays on activated Ti mesh to integrate solar-thermal desalination and electro-thermal desalination for all-day efficient clean water production. The serpentine structure serves as controllable current channels for efficient Joule heating, whereas the unidirectional fluidic structure functions as water pathways for manipulating the salt migration. As a result, the fabricated device realizes continuous water extraction from 6.0% of concentrated brine under 3 sun for 8 h without salt accumulation, and the evaporator can achieve extremely high water evaporation rate of 7.88 kg/m2/h under solar-electro-thermal mode based on the critical synergistic effect (1 sun-2.0 A). As a proof-of-concept application, the 3D printing desalination system can achieve continuous clean water extraction from seawater and/or wastewater with high production rate of 7.4 kg/m2/d and salt ions concentration far below the drinking standards defined by the World Health Organization.

Single-shot production of Janus graphene thin film for solar steam generation with 94.5% efficiency

Interfacial solar-driven steam generation as a cost-effective green technology has shown a great potential in realizing water desalination and purification. To achieve high solar steam generation efficiency, it is important to simultaneously realize high solar absorption and effective water transportation. Among various solar absorbers, Janus structures composed of different layered materials for multiple functions have been demonstrated to be promising for high efficiency. However, the complex material composition and the corresponding multistep fabrication process become a barrier for high efficiency realization and large-scale applications. Developing a simple, low-cost, and fast fabrication process holds the key to producing Janus absorbers with high efficiency. Herein, we propose and demonstrate a monolithic Janus absorber fabricated by a single shot flash reduction of an ultrathin (370 nm) graphene oxide film within a millisecond time frame. By synchronising the advantages of a top three-dimensional (3D) porous graphene structure for high solar absorption (99%) and a bottom two-dimensional (2D) layered graphene oxide structure for efficient water transportation, the fabricated Janus absorber achieves high solar-to-vapour conversion efficiency of 94.5% under one sun illumination and steady water production (2.054 kg m−2 h−1). Such a large-scale high yield production method is orders of magnitude faster than the state-of-the-art Janus film fabrication method and offers a highly efficient and reliable approach for solar water desalination and purification.

Two-dimensional metamaterials as meta-foams for optimized surface-enhanced solar steam generation

We report on a new class of metamaterials, which consists of meta-foams, optimized for high performance in enhanced solar steam generation. The design of these meta-foams involves precise dimensional control of a periodic two-dimensional micro-pore array. Proof-of-concept of meta-foams efficiency is demonstrated using two fabrication technologies. The first one involves microscale plasma etching onto a nanostructured black silicon substrate. As an alternative low-cost technique, we also use 3D printing of a graphene-containing polymer material. The experimental validation shows that the best evaporation rate reaches 1.34 kg/(h·m2) under 1 sun illumination, in open-air conditions under normal temperature and relative humidity conditions of 20 °C and 58%, an unmatched value so far under similar conditions, while the theoretical limit is estimated at 1.5 kg/(h·m2). This corresponding to a 89% conversion efficiency. Experimental data concur well with the predicted performance obtained by numerical simulations. The proposed model simultaneously accounts for both heat and mass transfer, including photothermal conversion and water phase change, to guide the optimization towards the maximization of the evaporation rate, an important figure of merit in many applications, including solar heat harvesting and solar water purification.