Efficient Solar Steam Generation Research Articles

Full-spectrum-responsive Ti4O7-PVA nanocomposite hydrogel with ultrahigh evaporation rate for efficient solar steam generation

Solar steam generation (SSG) via interfacial photothermal conversion has emerged in sustainable seawater desalination and sewage purification. One of the grand challenges is that low light absorption generally limits photothermal materials on water evaporation rates and insufficient on-board performance for real practice. Herein, we propose a “molecular/phase dual-locking” strategy to homogeneously composite Magnéli phases like Ti4O7 nanoparticles and poly(vinyl alcohol) (PVA) by chemical-physical bi-crosslinking. As-obtained Ti4O7-PVA nanocomposite hydrogels (TPNHs) exhibit a narrow bandgap (~0.81 eV) for highly efficient sunlight absorption all through UV–vis–NIR full-spectrum wavelengths (up to ~99.56 %) and enable a record high evaporation rate of ∼4.45 kg m−2 h−1 with outstanding energy efficiency (~90.69 %) under one sun irradiation. A 20−day continuous test in real seawater manifests excellent long-term performance stability of TPNHs without salt accumulation. We further demonstrate the SSG efficacy of such hydrogels by applying them for efficient desalination/purification of varying seawater and sewage samples with low-to-high salinity, strong acids/bases, heavy metal ions, and organic dyes. This “molecular/phase dual-locking” design strategy and resultant Ti4O7-PVA nanocomposite hydrogels present a promising methodology to boost practical applications for seawater desalination and sewage purification.

Highly Efficient Solar Steam Generation and Desalination through Gourd‐Flesh Templated Polypyrrole Composite

Solar steam generation (SSG) is regarded as a promising technique due to its potential in seawater desalination. Photothermal conversion materials derived from biomass are good evaporators for SSG because of their sustainability and high efficiency. Herein, 3D‐cylindrical‐structured composite materials based on gourd flesh and polypyrrole (GPPY) are designed and used for high efficient SSG. The polypyrrole layer is deposited on the gourd flesh to provide broad optical absorption ability and high photothermal conversion efficiency. In addition, gourd flesh with porous structure can act as thermal insulators, confine the generated heat within the evaporative surface, and facilitate the efficient transport of water to the photothermally active area. Based on these characteristics of the composite, the evaporator made of GPPY can achieve a high evaporation rate of (1.63 kg m−2 h−1), and a superior photothermal conversion efficiency 95.8% under 1 solar irradiation (1 kW m−2). The GPPY can be expected to be a practical photothermal conversion material for commercial SSG based on its high efficiency and sustainability.

Multifunctional aerogel with antibiofouling properties for efficient solar steam generation and seawater desalination

Water purification through solar steam generation is an emerging renewable technology with a massive capacity for freshwater generation. However, designing a multifunctional evaporating system with efficient solar-driven steam conversion along with seawater desalination is still a challenge for large scale freshwater generation. Herein, we propose a design for multifunctional photothermal aerogel containing Ag3VO4 nanoparticles incorporated in reduced graphene oxide with prominent characteristics of large surface area, higher porosity, and surface roughness. The proposed aerogel is fabricated via a facile method and can be used as an all-in-one system for water decontamination via solar steam generation, photocatalytic degradation/disinfection of organic pollutants and desalination of seawater simultaneously. The photothermal aerogel simply floats on air-water interface, with a higher flux of localized heat at the surface that efficiently promotes water evaporation at a rate of 2.1 kg/(m2 h). Moreover, the aerogel can denaturalize microorganism and desalinate seawater even under saline conditions. We anticipate that such an efficient and stable photothermal aerogel will offer a sustainable strategy for water purification via desalination, decomposition, and solar steam generation allowing us to address the current clean water crisis on a large scale.

Harvesting solar energy with a Ni-MOF-based evaporator for efficient solar thermal storage and steam generation

A hybrid solar evaporator comprising a Ni-based metal–organic framework material and a phase change material composite was fabricated for high performance solar-thermal energy storage and continuous solar vapor generation.

Cuttlefish ink nanoparticles-integrated aerogel membranes for efficient solar steam generation

Cuttlefish inks offer nano-solar-absorbers for obtaining freshwater through interfacial evaporation.

Vertical porous aerogel based on polypyrrole and bimetallic modified β-cyclodextrin polymer-chitosan for efficient solar evaporation

Solar-driven interfacial evaporation (SDIE) stands out as a prospective technology for freshwater production, playing a significant role in mitigating global water scarcity. Herein, a cyclodextrin polymer/chitosan composite aerogel (PPy-La/Al@CDP-CS) with vertically aligned channels was prepared as a solar evaporator for efficient solar steam generation. The vertically aligned pore structure, achieved through directional freezing assisted by liquid nitrogen, not only improves water transport during evaporation but also enhances light absorption through multiple reflections of sunlight within the pores. The polypyrrole particles sprayed on the surface of the aerogel acted as a light-absorbing layer, resulting in an impressive absorbance of 98.15 % under wetting conditions. The aerogel has an evaporation rate of 1.85 kg m−2 h−1 under 1 kW m−2 irradiation. Notably, the vertical pore structure of the aerogel allows it to exhibit excellent evaporation performance and salt resistance even in highly concentrated salt solutions. Furthermore, this aerogel is an excellent solar-driven interfacial evaporator for purifying seawater and fluoride-containing wastewater. This photothermal aerogel has the advantages of excellent performance, low cost, and environmental friendliness, and thus this work provides a new approach to the design and fabrication of solar photothermal materials for water treatment.

Natural down fiber-reinforced and polypyrrole-modified silk fibroin composite aerogel for efficient solar steam generation toward seawater desalination and wastewater treatment

Poor mechanical properties and low photothermal efficiency of silk fibroin (SF)-based aerogels are current challenges that need to be addressed. Herein, SF composite aerogel was developed to enhance the mechanical properties through physical interpenetration of natural down fiber (Df) and hydrogen bonds formed among SF, Df, and polypyrrole (PPy) and to improve the evaporation performance via in-situ polymerization of PPy. The resultant Df/PPy@SF aerogel showed significant improvement of compressive stress (194.29 kPa), which was 6.96 times than that of SF aerogel (27.91 kPa), and also good compression resiliency. Furthermore, due to uniform distribution of PPy and high porosity of 95.27 %, Df/PPy@SF aerogel possessed high light absorbance of 99.87 % and low thermal conductivity (0.043 W·m−1·K−1). Thus, the Df/PPy@SF aerogel evaporator demonstrated high evaporation rates of 2.12 kg·m−2·h−1 for 3.5 wt% saline water, 2.04–2.15 kg·m−2·h−1 for various dye water, and 2.10 kg·m−2·h−1 for actual dye wastewater. Moreover, the developed aerogel exhibited evaporation stability and outstanding salt-resistance when treating seawater due to continuous water supply by superhydrophilic porous aerogel. Therefore, these findings demonstrate the excellent performance of Df/PPy@SF aerogel and will inspire further research on developing natural fiber-reinforced aerogels for use in the fields of solar water evaporation, energy, and other related applications.

A Fe-Ni-MOF-74@bamboo photothermal evaporator for efficient solar steam generation

Solar-driven interfacial steam generation is considered as a promising technology to solve the shortage of fresh water resources by using inexhaustible solar energy. In this field, the challenge comes from the design of an interfacial evaporator with high performance in photothermal conversion, water activation (low evaporation enthalpy) and water delivery ability. Herein, a composite evaporator was prepared by in-situ composition of bamboo and Fe-Ni-MOF-74 and subsequently simple carbonization. In this evaporator, bamboo ensures that water quickly reaches the evaporation interface, and rich hydrophilic groups have the function of activating water molecules. Fe-Ni-MOF-74 enhances photothermal effect due to bimetallic coordination. In addition, the hydrophilic feature and the pore structure strengthen the water activation and water absorption capacity. Meanwhile, carbonization under mild conditions compensates for the light absorption. As an outcome, the evaporator achieves high evaporation rate (3.61 kg m−2 h−1), high solar-vapor conversion efficiency (153 %), low evaporation enthalpy (1.517 kJ g−1), good stability in saline water and antibacterial function. Furthermore, both seawater and wastewater purified by the evaporator comply with drinking water standards. In the outdoor experiment, the evaporator can collect water of 4.01 kg m−2 during one daylight. The result highlights great potential of bamboo and MOF composite evaporator for producing fresh water using solar energy.

Peak-like three-dimensional CoFe2O4/carbon nanotube decorated bamboo fabrics for simultaneous solar-thermal evaporation of water and photocatalytic degradation of bisphenol A

Catalytic CoFe2O4 and solar-thermal carbon nanotube decorated bamboo fabrics (CCBF) are fabricated for integrating efficient solar steam generation from wastewater with catalytic degradation of its organic contaminants. Thanks to the numerous porous channels and polar groups of bamboo fabric and the efficient solar-thermal energy conversion of black carbon nanotubes, the porous and hydrophilic CCBF exhibits fast upward transport of water, efficient solar light absorption, and high solar-thermal energy conversion efficiency. The decorated CoFe2O4 not only enhances the solar-thermal energy conversion efficiency of CCBF but also activates potassium peroxymonosulfate to generate abundant highly active species for catalytic degradation of bisphenol A (BPA). Furthermore, folding the CCBF into a peak-like 3D evaporator can enhance solar energy utilization, and gain environmental energy for promoting solar-thermal water evaporation and catalytic degradation performances. The 3D CCBF evaporator achieves a water evaporation rate of 2.72 kg m–2 h–1 under 1-sun irradiation. Meanwhile, 100% of the BPA in the seawater can be degraded within 10 min. An exceptional high purification efficiency of 27.72 kg m–2 h–1 is achieved with the 3D evaporator during a long-term treatment of BPA-containing seawater under 1-sun irradiation. This work demonstrates efficient purification of seawater/wastewater with both metal ions and organic pollutants by simultaneous solar-thermal evaporation of water and catalytic degradation of organic pollutants.

Photothermal Ti2O3/polyurethane/polyacrylamide foam with high solar-evaporation efficiency

Photothermal material is indispensable for the fabrication of solar steam generation with easy-manufacture, cost-effective, and high-performance. Here, Ti2O3/polyacrylamide/polyurethane foams (Ti2O3/PU/PAM) were rationally designed, applying the synergetic effects from ball-milled Ti2O3, hydrophilic PAM, and heat-retaining structure of PU foam. With virtues of reduced evaporation enthalpy, abundant water transport pathways, and effective thermal insulation, the resulting Ti2O3/PU/PAM photothermal foam exhibits a high evaporation rate of 2.15 kg m−2 h−1 and a water evaporation efficiency of 140.42 % under 1 sun (1 kW m−2). In addition, the results of this study can serve as a reference for highly efficient, green, and recyclable seawater desalination. It is envisioned that the results of this study provided a strategy to fabricate novel photothermal materials for highly efficient, clean, and long-term solar steam generation.

Banana pseudostem-inspired fluidic photothermal structure towards efficient solar steam generation and continuous salt rejecting

Solar-driven steam generation (SSG) is emerging as a promising off-grid strategy to relieve freshwater shortage. In recent years, extensive research works have been conducted to develop full biomass-based SSGs due to their unique hierarchical structural features. However, the long-term durability of biomass-based SSGs remains a concern. Herein, the discarded banana pseudostems have been demonstrated as an excellent potential SSG through a simple surface flame treatment. Firstly, the well-developed pore structure, superior light absorbance, extremely low thermal conductivity and superhydrophilic properties of the surface carbonized banana pseudostem (SCBP) have been well revealed respectively. In addition, it is also demonstrated that the SCBP evaporator can achieve an impressive evaporation rate of up to 2.548 kg·m−2·h−1 with a 91.96 % solar-thermal conversion efficiency superior to most reported biomass based SSGs. Furthermore, a SCBP inspired one-way fluidic photothermal structure is dedicatedly constructed. It is found that the salinity on the top surface of the SCBP evaporator remains far below 26 wt% and the evaporation rate is maintained at 2.384 kg·m−2·h−1 in a 15 wt% NaCl solution even after 200 h. Finally, from a proof-of-concept demonstration, the SCBP evaporator also shows an excellent water purification and seawater desalination performance in a real ocean situation.

Configurations Manipulation of Electrospun Membranes Based on High‐Entropy Alloys–Enabled High‐Performance Solar Water Evaporation

Solar‐driven interfacial steam technology converts photons into heat energy directly and therefore realizes the effective removal of environmental pollutants, which presents huge potential in seawater desalination and freshwater production. To realize efficient and rapid solar‐driven water evaporation, developing and designing efficient photothermal conversion materials is of great significance. Herein, a high‐entropy alloy (HEA) fiber membrane with rapid heating and wide spectral response is synthesized via adjusting high‐entropy metals diffusion on the surface of carbon nanofibers by an electrospinning technology. Benefiting from the low equivalent evaporation enthalpy and high solar spectrum capacity of HEA fibers, the HEA (FeCoNiCuMn)‐carbon nanofiber‐5S2 achieves a rapid steam‐generation rate of 2.74 kg m−2 h−1 with a solar‐to‐vapor conversion efficiency of 99.4% under 1 sun illumination. In addition, the evaporator presented a stable seawater desalination and wastewater purification performance. Therefore, the HEA‐based solar evaporator can be an alternative photothermal material for efficient solar steam generation.

Carbon coated vermiculite aerogels by quick pyrolysis as cost-effective and scalable solar evaporators

Purification of seawater and wastewater by solar-driven interfacial evaporation is a promising way to alleviate water scarcity. However, the high cost, complex fabrication methods, and short service life of the materials limit their practical application. Herein, a novel three-dimensional (3D) photothermal aerogel composited of vermiculite nanosheets and polyvinyl alcohol (PVA) precursors have been prepared via freeze-drying and treated by quick pyrolysis for highly efficient solar-driven interfacial evaporation. The vermiculite nanosheets exfoliated from natural clay were used as the skeletal support of the composite aerogels, which are cheap and abundant natural materials. The introduced PVA improves the mechanical properties and produces carbon derivatives after pyrolysis, enhancing the light absorption capacity. The as-prepared aerogels have hierarchical porous structures, impressive mechanical properties, great light absorption capacity, and outstanding salt-rejection ability. The optimized aerogel not only exhibits a high evaporation rate of 2.64 kg m−2 h−1 (normalized to top and side surfaces) under 1.0 sun irradiation with excellent cost-effectiveness at 361.64 g h−1 $−1 but also shows superior performance in treating high-salt (15.0 wt%) brine water and organic dye-contained wastewater. The proposed method provides an attractive and effective way to prepare photothermal aerogels for efficient solar steam generation for mitigating water scarcity issues.

Pickering Emulsion Templated 3D Cylindrical Open Porous Aerogel for Highly Efficient Solar Steam Generation.

Porous-structured evaporators have been fabricated for achieving a high clean water throughput due to their maximized surface area. However, most of the evaporation surfaces in the porous structure are not active because of the trapped vapor in pores. Herein, a three-dimensional (3D) cylindrical aerogel-based photothermal evaporator with a disordered interconnected hierarchical porous structure is developed via a Pickering emulsion-involved polymerization method. The obtained cotton cellulose/aramid nanofibers/polypyrrole (CAP) aerogel-based evaporator achieved all-cold evaporation under 1.0 sun irradiation, which not only completely eliminated energy loss via radiation, convection, and conduction, but also harvested massive extra energy from the surrounding environment and bulk water, thus significantly increasing the total energy input for vapor generation to deliver an extremely high evaporation rate of 5.368kg m-2 h-1 . In addition, with the external convective flow, solar steam generation over the evaporator can be dramatically enhanced due to fast vapor diffusion out of its unique opened porous structure, realizing an ultrahigh evaporation rate of 18.539kg m-2 h-1 under 1.0 sun and 4.0 m s-1 . Moreover, this evaporator can continuously operate with concentrated salt solution (20 wt.% NaCl). This work advances rational design and construction of solar evaporator to promote the application of solar evaporation technology in freshwater production.

Sustainable sponge-like composite hydrogel evaporator for highly efficient solar steam generation

Solar steam generation (SSG) using a hydrogel-type solar evaporator has emerged as one of the most expedient approaches for producing clean water to address the issue of water scarcity at a global level. In this work, we developed a stable two-dimensional (2D) spongy hybrid hydrogel using partially hydrolyzed polyvinyl alcohol (PVA) and δ-MnO2 nanosheet (a solar absorber) in a simple and cost-effective method. Water-uptake capillaries in the 2D hydrogel have been effectively modified by optimizing the volume of the cross-linker, which in turn facilitates a balanced water transport speed and the heat localization ability of the solar absorber and hence the evaporation rate. Simultaneously, the 2D planar hydrogel is transformed into a three-dimensional (3D) spiral and cylinder-shaped evaporator, and its evaporation efficiency was tested employing a water contactless double-layer interfacial evaporating system. A prototype SSG system showed an evaporation rate of 1.56 kg/m2/h, 3.33 kg/m2/h, and 3.63 kg/m2/h corresponding to a solar to vapor conversion efficiency of 78%, 166%, and 181% respectively, for a 2D planar, 3D spiral and cylinder-shaped evaporator under 1 sun. The surface temperature was always below the environmental temperature during the illumination period, which helped the 3D systems absorb energy from the environment. This led to cold vaporization with zero energy loss and thus enhanced the efficiency of the 3D configurations compared to 2D. Furthermore, the designed double-layer evaporator maintained consistent long-term performance with antifouling and salt rejection properties and ensured clean water production from sewage and seawater.

Ethyl cellulose composite membranes containing a 2D material (MoS2) and helical carbon nanotubes for efficient solar steam generation and desalination

With the increasing water consumption, water evaporators have been investigated for clean water production. Herein, the fabrication of electrospun composite membrane evaporators based on ethyl cellulose (EC), with the incorporation of light-absorption enhancers 2D MoS2 and helical carbon nanotubes, for steam generation and solar desalination is described. Under natural sunlight, the maximum water evaporation rate was 2.02 kg m−2 h−1 with an evaporation efficiency of 93.2 % (1 sun) and reached 2.42 kg m−2 h−1 at 12:00 pm (1.35 sun). The composite membranes demonstrated self-floating on the air–water interface and minimal accumulation of superficial salt during the desalination process due to the hydrophobic character of EC. For concentrated saline water (21 wt% NaCl), the composite membranes maintained a relatively high evaporation rate of up to ~79 % compared to the freshwater evaporation rate. The composite membranes are robust due to the thermomechanical stability of the polymer even while operating under steam-generating conditions. Over repeated use, they exhibited excellent reusability with a relative water mass change of >90 % compared to the first evaporation cycle. Moreover, desalination of artificial seawater produced a lower cation concentration (~3–5 orders of magnitude) and thereby yielded potable water, indicating the potential for solar-driven freshwater generation.

Sustainable and low-cost cellulose aerogel-based absorber for solar steam generation

Solar steam generation is a promising technology for sustainable seawater desalination. However, its practical application is hindered by the low water evaporation rate and the high cost of materials. Carbon aerogels have demonstrated superior properties for clean water production through solar steam generation, but the complex and time-consuming preparation process inhibits their development and applications. In this study, high-performance solar steam absorbers based on cellulose-derived carbon aerogels were prepared from paper and waste paper using a simple green method. The fabricated carbon aerogels have a typical microporous structure (pore diameter: 20–250 µm), super-hydrophilic properties, good mechanical properties and efficient solar light absorption (∼96 %), which make them ideal for application in solar steam generation. Three different configurations based on cellulose and carbon aerogels were fabricated (bulk absorber, double-layer absorbers and ink-based absorber) to achieve the best design with high efficiency for steam generation. The surface temperature of the bulk absorber and dry double-layer absorbercan achieve 100 °C under 1 kWm−2irradiation. Among all configurations, the double-layer absorbers represented the highest efficiencies, 90.4 % for paper and 84.3 % for waste paper, under 1 kWm−2 irradiation, which are higher than most reported results. According to the results, the sustainable cellulose-based double-layer absorbers were promising materials for efficient solar steam generation due to their high hydrophilicity, high sunlight absorption, open porous structure, non-toxicity, biodegradability, availability and low cost.

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.

Synergistic effect of electrochemically fabricated polyaniline nanofibers and silver for efficient solar steam generation

Solar steam generation (SSG) has been recognized as a promising and green technology to resolve the scarcity of drinking water in the near future. On the other hand, there are still several challenges associated with SSG system to its practical utilization. Design of suitable photothermal materials with high solar absorption and conversion efficiency is one of the challenges associated with the SSG technology. Herein, we demonstrated a strategy for the fabrication of bilayer structure of porous polyaniline (PANI) nanofibers and conducting silver (Ag) on a carbon cloth (PANI/Ag@CC) substrate using a facile electrochemical deposition approach. As prepared binder-free PANI/Ag@CC showed an excellent steam generation rate of 2.21 kg/m2h with superior evaporation efficiency of 98.0 % under 1 sun illumination when used for the SSG application. Furthermore, the bilayered PANI/Ag@CC exhibited excellent durability, effective seawater desalination and wastewater purification. The superior SSG performance is associated with the synergistic effect of surface plasmon resonance of Ag and porous PANI nanofibers. Therefore, practically simple fabrication, outstanding evaporation rate and water purification properties convince that the PANI/Ag@CC structure can be a promising candidate for SSG applications.

3D wood-based evaporator for highly efficient solar steam generation

Abstract Interfacial solar-driven steam generation is one of the most promising techniques used to produce clean water. However, achieving rapid water evaporation using solar steam generation devices is challenging because of their two-dimensional (2D) planar structures and confined evaporation areas. The three-dimensional (3D) structural design of evaporation devices improves water evaporation rates, thereby enhancing solar-driven steam generation. This study developed a 3D wood-based evaporator through 3D structure shaping and the flexible treatment of wood that involved coating photothermal materials with tannic acid. Because of the ampliative evaporation area and outstanding absorption, the water evaporation rate of the prepared 3D wood-based evaporator was as high as 2.5 kg m−2 h−1, and the efficiency of energy transformation was up to 101 % under simulated 1-sun irradiation; the evaporation rate and efficiency of energy transformation were considerably higher than those of 2D planar wood evaporators. Furthermore, the effective seawater desalination performance and good durability of the 3D wood-based evaporator were demonstrated. This study provides different insights into the fabrication of high-efficiency wood-based solar steam generators with high prospects for application in seawater desalination.