Sun Irradiation Research Articles

Salt-resistant MXene-charge gradient hydrogel evaporator with boosted water transport for efficient photothermal desalination

Solar interfacial evaporation represents a highly promising approach for generating potable water from seawater utilizing clean, abundant, and sustainable solar energy. MXene-based materials exhibit outstanding photothermal conversion in desalination applications but face challenges in water transport and salt removal. Here, we introduce an effective MXene-charge gradient hydrogel (MCGH) evaporator that leverages the Donnan effect for salt rejection and internal osmotic pressure for water conveyance. The MCGH evaporator achieved 3.1 kg m−2 h−1 evaporation rate in 3.5 wt% NaCl under 1 sun irradiation. It also operates effectively in concentrated brines, reaching a notable 2.1 kg m−2 h−1 evaporation rate in 20 wt% NaCl solutions. This work introduces a new approach for salt-tolerant MXene photothermal evaporators, holding great promise for sustainable solar desalination applications.

When cellulose nanocrystals meet graphene oxide: Structurally enhanced aerogels for efficient solar steam generation and water purification

Pollution, population growth, and climate change are intensifying global freshwater shortages. Traditional methods of collecting freshwater, such as rainwater harvesting and sewage treatment, have high energy consumption, limiting their implementation in underdeveloped regions. On the other hand, solar-driven seawater evaporation offers a promising solution, purifying water using naturally abundant solar energy. Reduced graphene oxide (rGO) is considered as a strong candidate for this purpose due to its broad spectral absorption. However, its hydrophobicity hinders its direct use in solar steam generators. Here, we report the preparation of a series of cellulose nanocrystal (CNC)-rGO aerogels (CGAs) through a one-pot hydrothermal gelation process, followed by unidirectional freeze-drying. The introduction of CNCs enhances the hydrophilicity and structural stability of the resulting CGAs. The CGAs also feature uniform and unidirectional channels that promote efficient water transport, as confirmed by scanning electron microscopy (SEM) and X-ray microtomography (XMT). The CGAs have an optimized water evaporation rate of 1.80 kg m−2 h−1 under 1 sun irradiation, with 90 % solar-to-vapor energy efficiency. Moreover, durability and seawater desalination tests provide additional evidence for the practicality of CGAs in water purification. It is anticipated the implementation of CGAs will expedite the application of solar steam generators in practical scenarios.

Polypyrrole@TiO2 Composite Nanotube System with Enhanced Capillary Fluid and Charge Transfer for High‐Current Hydrovoltaic Energy Generation and Seawater Purification

AbstractHarnessing the energy generated from the evaporation of water has received considerable research attention in materials science; however, challenges such as poor conversion efficiency and low current output persist. Herein, an innovative synergistic material system based on titanium dioxide nanotubes coated with polypyrrole (PPy@TiO2NTs) is introduced for the simultaneous production of electricity and clean water from solar energy and seawater. The tubular structure of PPy@TiO2NT and the molecular interactions between TiO2 and PPy produce enhanced charge transfer, thereby providing the advantages of the hydrovoltaic effect, solar‐driven water evaporation (SWE), and photocatalysis. Consequently, PPy@TiO2NT‐loaded melamine foam can produce tens or more than a hundred microamperes of current in water of various salinities, which is an order of magnitude improvement over previously reported hydrovoltaic evaporation systems. In addition, under 1 sun irradiation, the system achieved an SWE rate of 2.13 kg m−2 h−1 and a methylene blue removal rate of more than 90% within 2 h. The proposed material system, featuring high electrical output and outstanding dual‐mechanism water treatment capabilities, shows high potential for synergistically harnessing solar energy and seawater, as well as for environmental management.

Novel and stable carbon black/polyvinyl acetal aerogels efficiently harvesting solar energy for seawater desalination

A novel interfacial solar steam generators (ISSG) was prepared by a porous carbon black/polyvinyl acetal aerogel (CPA) with high light-absorbing hydrophilic properties, to achieve efficient solar-driven water evaporation and seawater desalination. The polyvinyl acetal was produced by the aldol condensation reaction of polyvinyl alcohol(PVA) and glutaraldehyde(GA). It was freeze-dried to create a hydrophilic porous structure that constructs an efficient hydrophilic channel. Carbon black (CB) exhibits high light absorption capabilities. Incident light undergoes multiple scattering within its porous network structure, effectively reducing reflected light energy loss and enabling efficient thermal conversion of sunlight. Benefited from its highly light-absorbing porous hydrophilic structure, CPA-40-3 evaporation rate achieves an impressive 3.23 kg·m−2·h−1 and an evaporation efficiency of 94 % under 1 sun irradiation, without obvious decay even during long-term use. Furthermore, CPA-40-3 demonstrates remarkable salt tolerance, the evaporation rate remains at 2.55 kg·m−2·h−1 although in simulated Dead Sea salt water under 1 sun irradiation. Compared to traditional ISSG, the CPA has advantages such as superior mechanical properties, prevention of surface salt precipitation, faster water supply, and a larger light absorption area. This design had tremendous promise for efficient solar desalination due to its extraordinarily high evaporation performance in high-salinity brine.

Modulating intramolecular charge transfer via π-d conjugative effect in coordination polymers toward photo-thermo-electric conversion

The prospect of harnessing sunlight to generate cost-effective heat and electricity presents a captivating opportunity to address water scarcity and electricity shortages. Photothermal materials with a broad absorption spectrum are indispensable for effectively harnessing solar energy and converting it into heat/electricity. Herein, we developed an intramolecular charge transfer strategy via conjugated effect to regulate solar absorption and photothermal conversion ability of M-DABDT (M = Fe/Co/Ni/Cu/Zn, DABDT = 2,5-diaminobenzene-1,4-dithiol), overcoming a common limitation of narrow absorption and low photothermal efficiency in traditional metal-organic assemblies. The density functional theory calculations reveal that altering transition metal ions induces the structural torsion of organic linkers, resulting in a significant change in dihedral angle from 89.96° to 2.57°. The structural change significantly facilitates the charge transfer and electron relaxation, ultimately promoting the conversion of light to heat. Under one sun irradiation, the maximum temperature of Fe-DABDT can reach approximately 92.5 ℃. More significantly, the integration of M-DABDT CPs and thermoelectric devices under normal solar irradiation results in an extraordinary open circuit voltage (238 mV) and maximum power density (364.5 μW m−2), processing a peak output voltage density of 76.9 V m−2 at 11:00 a.m. in the presence of outdoor sunlight. This strategy presents an avenue for developing metal-organic solar absorbers for photo-thermo-electric conversion systems.

Biomimetic structural aerogel derived from green tide enteromorpha-prolifera: Multi-sided unidirectional freeze casting and solar-driven viscous oil spill remediation

The development of environmental remediation materials from renewable biowaste, especially for the cleanup of viscous oil spills in an eco-friendly manner, marks a substantial advancement in functional materials. This study proposes a biomass aerogel (M−MCEP) transformed from Enteromorpha prolifera (EP) in green tides for solar-driven recovery of high-viscosity oil spills. Inspired by the lamella-bridge architecture of Thalia dealbata stems, a biomimetic structure with multi-domain, long-range aligned lamella-bridge interconnections is constructed by a multi-sided unidirectional freeze-casting technique. Multi-scale interface optimization between rigid photothermal fillers and soft lamellar layers achieves multiple reinforcements, providing aerogel with a perfect balance of elasticity and strength. The multidomain low tortuosity channels and photothermal effects enhance M−MCEP’s photothermal conversion (95.2 %) and thermal conductivity (0.3517 W/m·K), reducing oil flow resistance and achieving high oil retention efficiency (>92 %). Under 1 sun irradiation, M−MCEP rapidly heats to 67.3 °C, effectively reducing the viscosity of crude oil in situ, with a crude oil adsorption rate of 1843 mL/m2 within 30 s. Moreover, M−MCEP captures emulsified oil in oil-in-water emulsions through high-speed repeated oscillations, achieving a separation efficiency of 96.42–99.21 %. Renewable resources and unique structural designs provided by nature drive the development of advanced biomimetic aerogels for efficiently remedying catastrophic oil spills.

Inclined interfacial solar evaporator using polypyrrole/polydopamine composites for efficient desalination and salinity-driven electricity generation

Water-electricity cogeneration using solar energy is an innovative technology to address global freshwater shortages and energy demands. Here, we designed an inclined evaporator based on polypyrrole/polydopamine photothermal materials for efficient water evaporation and electricity cogeneration. Due to the ingenious inclined structure of the evaporator, the water transport was highly promoted by gravity and siphon effect. This process not only improves the evaporation flux of water, but also create a salinity gradient that can be used for further electricity generation. The designed inclined PPy/PDA@MF evaporator exhibits an evaporation flux of 3.02 kg m−2 h−1 under one sun irradiance and achieves an open-circuit voltage of 56 mV during the electricity generation.

Interface Structure Strengthening of a Mesoporous Silicon/Expanded Perlite Microevaporator for Efficient Solar-Driven Interfacial Evaporation.

Solar-driven interfacial evaporation is one of the cutting-edge technologies for seawater desalination and wastewater purification. Herein, a floating carbon-coated silica microsphere/expanded perlite integrated interfacial microevaporator (HEPCL) is reported. The carbon nanolayer allows the HEPCL to have better broadband light absorption performance than natural graphite and graphene oxide. Through the low density of expanded perlite, HEPCL particles can self-float on the water surface and self-aggregate into an integrated whole under surface tension, which enhances the heat collection capacity. The hierarchical porous structure of the HEPCL has a continuous water absorption capacity. Notably, water molecules adsorbed in the HEPCL have a high desorption energy, which reduces the water evaporation enthalpy (1621 kJ/kg), making it easy to remove with external energy. Thanks to the design merits, the HEPCL achieves a water evaporation rate of 1.551 kg m-2 h-1 (efficiency of 94.85%) under 1 sun irradiation and may inspire a practicable solution of water scarcity.

Carbon nanodots-based interfacial nanofluid for high-performance solar-driven water evaporation

Solar steam generation through volumetric heating using nanofluids is a promising approach for wastewater treatment and desalination. However, low evaporation rate and slow response time to the change in solar intensity seriously affect their cumulative evaporation performance in practice. Here, we propose an interfacial nanofluid structure for high-performance solar-driven water evaporation using carbon nanodot (CDs) nanofluid and airlaid paper. CDs nanofluid transferred down through the paper from a source water tank to form an interfacial evaporation structure and ensure continuous water supply for evaporation. The solar conversion heat was only localized on a small amount of nanofluid on the paper resulting in low heat loss to the bulk nanofluid and a fast response time of within 2 min to reach a steady evaporation rate. In addition, the flowing nanofluid on the paper can absorb environmental energy to achieve high-rate evaporation of 1.93 kg m−2 h−1 under one sun irradiation. This study provides an effective strategy to improve the performance of volumetric heating systems for solar wastewater treatment and desalination.

Directional salt crystallization system for high-efficiency solar-driven evaporation to achieve zero-liquid discharge

Solar-driven interfacial evaporation is an efficient technology for water treatment, enabling the production of freshwater and the removal of impurities. However, achieving a high evaporation rate and a long-term stable operation is challenging due to the salt accumulation on the evaporation surface. In this study, a novel three-dimensional directional salt crystallization system is proposed. The melamine sponge modified with polydopamine and carbon black was used to transport brine, absorb sunlight, and generate steam. The non-photothermal evaporation regions were innovatively constructed by placing a thermally conductive aluminum structure with the deflector paper around the sponge, which increased the effective evaporation area of the system to accelerate the evaporation of brines from the overall system, resulting in an evaporation rate of 2.20 kg m−2 h−1 under one sun irradiation in a 15 wt% NaCl solution. Moreover, the non-photothermal evaporation regions were isolated from the evaporation interface as a salt crystallization region, which completely avoided salt accumulation at the evaporation interface and ensured the long-term stable operation of the system. Salt crystals can be easily collected by replacing the deflector paper regularly, and the salt collection efficiency is over 95 % to achieve zero-liquid discharge (ZLD) treatment. More importantly, the directional salt crystallization system achieves efficient purification of heavy metal ion wastewater and dye wastewater. Consequently, the system presents a highly efficient method for ZLD seawater treatment and wastewater purification.

Assembled Wood-Polyester Fabric-Hydrogel Janus Evaporator for Sustainable Seawater Desalination.

Solar-driven interfacial evaporation technology is a novel and efficient desalination process that helps alleviate the global shortage of freshwater resources. We developed a Janus evaporator assembled from cotton hydrogel, hydrophilic polyester fabric (PF), and Hydrophobic Wood (PW). By doping graphene oxide and TiO2 as light-absorbing materials within the hydrogel, we achieved a high absorptivity of over 90% across the entire solar spectrum. The hydrophilically modified PF, combined with the PW substrate, provided robust water transport and reduced thermal losses. Subsequent optical path simulations using TracePro74 software verified that the sawtooth light-trapping design of the wood substrate increased multiple light reflections and absorption (compared to a flat structure), enhancing light absorption capabilities. The sawtooth interface also enlarged the evaporation area, further boosting evaporation performance. The cleverly designed evaporator exhibited an evaporation rate of 1.722 kg m-2 h-1 and an efficiency of 83.1% under 1 sun irradiation. Additionally, after applying polydimethylsiloxane to the single surface of the photothermal hydrogel for low surface energy treatment, the resulting Janus structure demonstrated asymmetric wettability that prevented salt ions from accumulating on the irradiated interface. After 8 h of continuous evaporation in saline water (10 wt %), only slight salt crystallization occurred at the edges. The evaporator maintained long-term stability during a 15 day cyclic test, and the produced freshwater fully met the relevant drinking water standards. The components of the evaporator are characterized by simple fabrication, low cost, and eco-friendliness, offering significant application potential in the global context of energy conservation and emission reduction initiatives.

Full-spectrum plasmonic semiconductor with stabilized oxygen vacancies enables VOCs purification for durable clean water capture

To mitigate health risks associated with volatile organic compounds (VOCs) in solar-driven water evaporation, we developed Au/WO2.72 material with full-spectrum absorption capabilities and dual photothermal and photocatalytic properties. Injecting hot electrons from Au nanoparticles (NPs) into WO2.72 preserves oxygen vacancies, thus maintaining the plasmonic effect and significantly reducing hot electron relaxation. This leads to enhanced purification of VOCs. The MF-Au/WO2.72 water evaporator, constructed on a melamine–formaldehyde (MF) substrate, demonstrated a water evaporation rate of 1.36 kg m-2 h−1 and stability over 6 h daily for 12 days under one sun irradiation. Importantly, it achieved a 92.9 % removal efficiency for phenol VOCs. Outdoor experiments validated its effectiveness in organic wastewater purification and seawater desalination, highlighting its potential for efficient and clean water production by simultaneously removing VOCs during the evaporation process. This work provides valuable insights into utilizing plasmonic-coupling materials for solar water purification.

Cellulose aerogel evaporators with vertical channels inspired by lotus rods for highly efficient solar water evaporation

Designing and developing solar absorbers is essential for achieving high solar-to-vapor energy conversion efficiency and evaporation rate. Currently, evaporators with vertical channels have been developed to improve evaporation efficiency and salt tolerance, but high preparation and complex process limit their practical application. Herein, a cellulose aerogel evaporator with a vertical channel structure was fabricated using simple directional freezing technology. The evaporator exhibited outstanding light absorption capabilities across a spectrum of 250–2500 nm. Importantly, the exceptional hydrophilicity of cellulose and the synergistic effect of vertical channels facilitated water transport, thereby enhancing evaporation efficiency. When exposed to one sun irradiation (1 kW m−2), the cellulose aerogel evaporator achieved an evaporation rate of 1.80 kg m−2 h−1. Moreover, the evaporator can automatically discharge salt through convection and diffusion to ensure its long-term operation, and no salt accumulation is found on the surface of the evaporator during the evaporation cycles. This work introduces a straightforward, cost-effective, and easily deployable solar evaporator in which the presence of vertical channels provides technical support for the realization of efficient and sustainable solar seawater evaporation technology.

Carbonized coffee-based 3D polymeric xerogels for freshwater recovery by solar steam generation

Interfacial solar steam generation is a promising technology for freshwater recovery from seawater desalination and water purification. Herein, is presented an eco-friendly, three-dimensional (3D) porous composite system, made from materials recovered from waste, able to desalinate and purify water upon solar irradiation. The system that consists of carbonized spent coffee powder embedded in a polyglycerol polymer matrix, is developed upon thermal curing of a water-based solution and presents an interconnected porous network with super-hydrophilic properties. We explore the effect of the 3D shape of the composite on the solar steam generation, by varying the height over the radius (aspect ratio) of the structure, and we prove that biocomposites with higher aspect ratio give rise to a progressively higher solar steam generation rate reaching, under the current conditions, 2.72 kg·m−2·h−1 for an aspect ratio of 2.2 under 1 Sun irradiation. This is attributed to the enhancement of the total area of the water–air interface which in turn facilitates the steam escape from the porous structure while, at the same time, permits to the bulk water to be effectively entrapped in the whole porous structure. This, together with the fact that the developed material can be fully biodegradable at the end of its lifespan, opens up new prospective paths for sustainable and effective clean water production.

Capillary reinforcement strategy guided construction of robust oxygen functionalized carbon-based porous foam for highly efficient solar evaporation

Recent research on carbon-based porous foams has made great progress to alleviate global clean water scarcity. However, it is still a challenge to produce carbon-based porous foams with both high evaporation performance and good mechanical property because of weak interface interactions between carbon-based material and matrix. Herein, we report an effective capillary enhancement strategy to construct robust oxygen-functionalized 3D carbon-based porous foams (OCPF) with abundant hydrophilic oxygen-functional groups from oxidized carbon fiber (OCF) and graphite oxide (GO). Owing to capillary enhancement strategy, a robust foam can be obtained, such as compression stress increases by 6–70 times, and compression modulus reaches 0.56–8.01 MPa, and the obtained foam also contains abundant oxygen-functionalized carbon materials to modulate water state. As a result, the optimized OCPFs show a high evaporation rate of ∼ 3.08 kg·m−2·h−1 with an efficiency of ∼ 94 % under one sun irradiation, which can be further raised to 7.89 kg·m−2·h−1 (5 cm height with 3 m·s−1 wind speed). Besides, the OCPFs also exhibit satisfied desalination and purification performance in actual saline water, domestic and industrial sewage, corrosive and oily wastewater. The feasible fabrication process, excellent performances, and potential applications of OCPFs could provide a new insight into the future development of high-performance and durable carbon-based solar evaporators for large-scale practical applications.

Nature-inspired ultrathin wood-based interfacial solar steam generators for high-efficiency water purification

Here, inspired from butterfly wing, novel hierarchical biomimetic structures composed of tunable nano-structured surfaces, rich micro/nanopores and aligned grooves from polythiophene decorated fir wood veneer have been developed to solve it. Nanowire-shaped and button-like nanostructured polythiophenes as light absorption enhanced materials were in situ grown on wood surface by adjustable vapor deposition process (PFW and CPFW). Meanwhile, wood veneer with reversed-tree structure has a unique aligned grooves surface from split tracheids, serving as the substrate for the nanostructured polythiophenes. These ultrathin wood-based solar steam generators (0.6 mm) stand as one of the thinnest reported self-floating photothermal materials based on wood. Meanwhile, high evaporation flux (1.42 and 1.48 kg·m−2·h−1) and solar-to-vapor efficiencies (88.5 % and 92.4 %) for PFW and CPFW are acquired under 1 sun irradiation. Their structure superiority boosting photothermal conversion performance has been further verified by COMSOL simulated results. The synthesized solar steam generator exhibits exceptional capabilities in seawater desalination and wastewater treatment, demonstrating fantastic application potential in water purification.

MOF-801 enabled rapid-cycling atmospheric water harvester with vertically aligned photothermal channel

Sorption-based atmospheric water harvesting (SAWH) with metal–organic frameworks (MOFs) offer a promising solution to freshwater scarcity in arid regions. However, given the powder nature of MOFs, scaling-up such a concept with industrially favorable monolithic MOFs in bulky sizes remains challenging. In this study, a pore vertically aligned nanocomposite sorbent where MOF-801 is anchored at the polymeric structure surface was prepared via Fe3+-induced crosslinking and directional freezing methods. The continuous vertically aligned hierarchical pores not only offer sufficient sites for MOF-801 loading but also provide rapid moisture transport channels, as well as high solar-thermal conversion efficiency, resulting in a rapid ab/desorption duration of 2 h (including an absorption process for 1 h and a desorption process for 1 h under 1 sun irradiation) and multicycle daily water production of 1.40 L kg−1 at low RH of 20 % and 5.57 L kg−1 at higher RH of 80 %, respectively, which is outperformed most of the state-of-the-art MOFs based SAWH materials. This work provides a simple and effective way to shorten MOF-801 ab/desorption duration, which has great means for designing of high-performance solar-driven water harvesting materials.

Hydrogel-based 3D evaporator with cross-linked fixation by carbon dots for ultra-high and stable solar steam generation

Solar-driven water steam generation had been recognized as a promising strategy to address water scarcity in an environmentally friendly and cost-effective manner, and the development of an evaporator capable of efficient evaporation and stable long-term operation remains a huge challenge in the field. Herein, a three-dimensional (3D) hydrogel-based evaporator consisting of sodium alginate (SA), polyvinyl alcohol (PVA) and carbon dots (CDs) integrated into a melamine sponge (MS) structure was constructed, in which the CDs were firmly bonded to the SA/PVA double crosslinked network through hydrogen bonding, which improved the mechanical properties and load-bearing capacity of the evaporator. Crucially, as highly efficient light-absorbing carbon-based materials, the CDs were homogeneously dispersed in the hydrogel, significantly enhancing the photothermal conversion capability of the evaporator. The test results indicated that the evaporation rate of the 3D-CDs/SA/PVA-MS evaporator reached up to ultra-high solar steam generation rate of 4.79 kg m-2h−1 in 3.5 wt% NaCl solution at 1 sun irradiation, and exhibited the relatively excellent evaporation rate (4.13 kg m-2h−1) in high saline seawater (25 wt%). This study aimed to provide a simple and reliable modification method to enhance the evaporation performance and improve the hydrogel network of SA/PVA-based hydrogel evaporator and demonstrate their potential applications in seawater desalination and purification.

Enhanced photocatalytic performance of CuS/O,N-CNT composite for solar-driven organic contaminant degradation

Herein, a hydrothermal etching approach was used to generate an innovative CuS/O,N-CNT composite. The hydrothermal etching of g-C3N4 led to the creation of O,N-CNT, with ethanol as the oxygen source. The SEM and TEM characterizations confirmed the formation of CNT, whereas the XPS analysis proved the doping of oxygen and nitrogen in the CNT matrix along with the incorporation of CuS. Under sun irradiation, the produced CuS/O,N-CNT showed outstanding photocatalytic efficiency, eliminating methyl orange and methylene blue dyes with 97.21% and 98.11% efficacy, respectively. Adding hydrothermally etched O,N-CNT increased light absorption and charge migration kinetics, as can be studied from the UV-DRS and PL analysis; hence, the observed improvements in light absorption and charge transfer pathways contributed to the CuS/O,N-CNT composite's enhanced photocatalytic activity, indicating its potential for efficient elimination of organic contaminants under solar irradiation. The catalyst demonstrated high reusability performance up to six cycles and significantly degraded other dyes. Scavenger analysis, along with VB-XPS and UV-DRS analysis, aid in developing a photocatalytic mechanism that confirms the participation of hydroxyl and superoxide radicals in the degradation process.

MnO2-modified PEEK membrane for efficient oil-water separation and solar-assisted seawater desalination

Economic and efficient routes to achieve clean freshwater from oil-water mixtures and seawater have gained special attention to reduce the current water crisis, but still a challenge unsolved. Herein, poly (ether ether ketone) (PEEK) membrane, modified with MnO2 layer, has been prepared by facile hydrothermal method to address this issue aforementioned. Given the existence of PEEK and underwater superoleophobicity/underoil superhydrophilicity of MnO2, the composite membrane exhibits strong mechanic properties (tensile stress: 110.2 MPa) and high separation efficiencies (99.9 %) for different oil–water mixtures under gravity. Additionally, our membrane could also effectively separate immiscible oil mixtures according to the dipole–dipole interaction. Furthermore, firm chemical stability against dichloromethane, N, N-Dimethylformamide, 1 M NaOH, 1 M HCl, and 1 M NaCl has been achieved. Most importantly, our membrane displays durable evaporation efficiency (2.63 kg m-2h−1), high energy efficiency (85.9 %), and super salt tolerance under 1 sun irradiation, for solar-assisted seawater desalination.