In Situ MXene Anchored Structure for Highly Durable Solar Steam Generation

As a promising fresh water harvesting technology, interfacial solar steam generation has attracted growing interest. Efficient solar absorption and long-term operational performance are critical requirements of this technology. However, developing robust evaporators to promote practical applications under extreme conditions is still a grand challenge. Herein, we propose a light-assisted strategy to in situ prepare a Ti3C2Tx MXene anchored structure (MXAS) for enhanced solar evaporation with superior mechanical properties (compressive strength of 78.47 MPa, which can withstand a pressure of 3.92 × 106 times its own weight). Light irradiation enlarges the interlayer spacing of MXene and improves the solar absorption capability. Under one sun, the three-dimensional MXAS evaporator exhibits a steam generation rate of 2.48 kg m-2 h-1and an evaporation efficiency of 89.3%, and it demonstrates long-term durability when testing in seawater. This strategy provides valuable insights into the potential application of a high-performance water evaporation system.

Self-Flipping Solar Seesaw Evaporators Leverage Scaling to De-Scale

Salt scaling poses a significant obstacle to the practical implementation of solar-driven evaporation for desalination. Attempts to mitigate scaling by enhancing mass transfer often lead to a compromise in evaporation efficiency due to associated heat loss. In the present work, a novel seesaw evaporator with a Janus structure to harness scaling for periodic self-descaling is reported. The seesaw evaporators are facilely fabricated by delignifying balsa wood and subsequently single-sided spray-coating it with soot and polydimethylsiloxane (PDMS). This unique Janus structure enables the evaporator to float on the brine while ensuring an ample supply of solution for evaporation. During evaporation, salt ions are transported directionally toward the cocked end of the evaporator to form scaling, triggering the seesaw evaporator to flip once a threshold is reached. The accumulated salts re-dissolve back into the solution. By adjusting the tilt angle, the evaporator can achieve an impressive evaporation rate of up to 2.65 kg m-2  h-1 when evaporating an 8 wt.% NaCl solution. Remarkably, these evaporators maintain a stable evaporation rate during prolonged 120 h operation and produce ≈3.93-6.35 L m⁻2 ·day⁻¹ of freshwater from simulated brines when assembled into an evaporation device.

Tailorable Lignocellulose-Based Aerogel to Achieve the Balance between Evaporation Enthalpy and Water Transport Rate for Efficient Solar Evaporation

Solar-driven interfacial evaporation technology has become an effective approach to alleviate freshwater shortage. To improve its evaporation efficiency, the pore-size dependence of the water transport rate and evaporation enthalpy in the evaporator should be further investigated. Based on the transportation of water and nutrients in natural wood, we facilely designed a lignocellulose aerogel-based evaporator using carboxymethyl nanocellulose (CMNC) cross-linking, bidirectional freezing, acetylation, and MXene-coating. The pore size of the aerogel was adjusted by controlling its CMNC content. When the channel diameter of the aerogel-based evaporator increased from 21.6 to 91.9 μm, the water transport rate of the proposed evaporator increased from 31.94 to 75.84 g min^-1, while its enthalpy increased from 1146.53 to 1791.60 kJ kg^-1. At a pore size of 73.4 μm, the evaporation enthalpy and water transport rate of the aerogel-based evaporator achieved a balance, leading to the best solar evaporation rate (2.86 kg m^-2 h^-1). The evaporator exhibited excellent photothermal conversion efficiency (93.36%) and salt resistance (no salt deposition after three cycles of 8 h). This study could guide the development of efficient solar-driven evaporators for seawater desalination.

Highly Effective Multifunctional Solar Evaporator with Scaffolding Structured Carbonized Wood and Biohydrogel

A solar evaporator that utilizes solar radiation energy can be a renewable approach to deal with energy crisis and fresh water shortage. In this study, a solar evaporator was prepared by assembling composite carbonized wood of Melaleuca Leucadendron L. and biobased hydrogel. The multilayer MXene (Ti₃C₂T_x) was embedded in the scaffolding structure of the wood to form composite carbonized wood, where the loose and ordered scaffolding structure of the carbonized wood significantly improves the efficiency of water transportation with increased capillary force. The MXene adsorbed in the carbonized wood has high binding energy with water molecules, leading to reduction of vaporization enthalpy and contact angle. Moreover, the addition of MXene can improve the light absorbance, especially for the infrared and ultraviolet light bands. The hydrogel was fabricated by crosslinking konjac glucomannan and sodium alginate polysaccharides with Ca²⁺, and it has a lower thermal conductivity than water and improves the evaporation efficiency by regulating the temperature distribution and concentrating the heat on the surface of the evaporator. This solar evaporator has an evaporation rate of 3.71 kg·m^-2·h^-1 and an evaporation efficiency of 129.64% under 2 sun illumination and is available to generate an open-circuit voltage of 1.8 mV after a 20 min hydrovoltaic, demonstrating a high performance and versatility. Also, experiments and numerical simulation were carried out to understand the mechanism and design principles of this solar evaporators.

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

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

Tailoring the Salt Transport Flux of Solar Evaporators for a Highly Effective Salt-Resistant Desalination with High Productivity

Developing highly effective salt-resistant solar evaporators for a long-term desalination with a high evaporation rate and water production rate remains a great challenge. Herein, we fabricated a three-dimensional printed hierarchical porous reduced graphene oxide/carbon black (3DP-HP rGO/CB) solar evaporator constructed with a thin layer of porous photothermal interface and a grid of hierarchical porous transport channel possessing a large-sized porous microstructure. The 3DP-HP rGO/CB solar evaporator demonstrates a tailored high-salt transport flux of up to 4.3 kg·m^-2·h^-1, which displays a highly effective salt-resistant performance at a high evaporation rate of 10.5 kg·m^-2·h^-1 during a desalination of 10 wt % NaCl brine under 8 kW·m^-2 illumination. Experiments and theoretical calculations prove that the large porous microstructure with abundant and low-resistance salt ion channels endows solar evaporators with a high salt transport flux, therefore boosting salt resistance compared to traditional solar evaporators. A 10 d desalination experiment shows the long-term salt resistance of a 3DP-HP rGO/CB solar evaporator for a high-rate and stable evaporation and water production. Furthermore, the 3DP-HP rGO/CB evaporator can purify 10 wt % NaCl brine at an ultrafast water production rate of up to 5.6 L·m^-2·h^-1 under natural sunlight. This work demonstrates great potential for the practical implementation of solar desalination with high productivity.

Fully Biomass-Based Hybrid Hydrogel for Efficient Solar Desalination with Salt Self-Cleaning Property

Solar-driven interfacial steam generation provides an opportunity for solar harvesting and freshwater yield as a promising and eco-friendly technology. Here, we demonstrate a sustainable, nontoxic, and highly efficient fully biomass-based GG/CI hydrogel evaporator consisting of gellan gum (GG) hydrogel as the matrix and cuttlefish ink (CI) as the photothermal material. Induced by the ice-template method and freeze-drying method, vertically aligned microchannels are generated along the ice crystal growth direction. Efficient photothermal conversion is enabled by the natural black cuttlefish ink powder and enhanced by the light trapping effect within vertical microchannels. The hydrophilic property of the gellan gum hydrogel and water capillary force in those microchannels boost water pumping to the top interfacial evaporation region. Effective rapid salt self-cleaning behavior is achieved due to the rapid ion diffusion within vertical microchannels. An evaporation rate of 3.1 kg m^-2 h^-1 under one sun irradiance is demonstrated by this fully biomass-based GG/CI hydrogel evaporator. This work offers a promising alternative for eco-friendly and sustainable freshwater generation with abundant natural biomasses.

Shape-Programmable Interfacial Solar Evaporator with Salt-Precipitation Monitoring Function

Interfacial solar evaporators (ISEs) for seawater desalination have garnered enormous attention in recent decades due to global water scarcity. Despite the progress in the energy conversion efficiency and production rate of ISE, the poor portability of large-area ISE during transportation as well as the clogging of water transport pathways by precipitated salts during operation remain grand challenges for its fielded applications. Here, we designed an ISE with high energy conversion efficiency and shape morphing capability by integrating carbon nanotube (CNT) fillers with a light-responsive shape memory polymer (SMP, cross-linked polycyclooctene (cPCO)). Utilizing the shape memory effect, our ISE can be folded to an origami with 1/9 of its original size to save space for transportation and allow for on-demand unfolding upon sunlight irradiation when deployed in service. In addition, the ISE is equipped with a real-time clogging monitoring function by measuring the capacitance of the electric double layer (EDL) formed at the evaporator/seawater nanointerface. Due to its good energy conversion efficiency, high portability, and clogging monitoring capability, we envisage our ISE as a promising selection in solar evaporation technologies.

Scalable High-Efficiency Bi-Facial Solar Evaporator with a Dendritic Copper Oxide Wick

Solar thermal distillation is a promising way to harvest clean water due to its sustainability. However, the energy density of solar irradiation inevitably demands scalability of the systems. To realize practical applications, it is highly desirable to fabricate meter-scale solar evaporator panels with high capillary performance as well as optical absorptance using scalable and high-throughput fabrication methods. Here, we demonstrate a truly scalable fabrication process for a bi-facial solar evaporator with copper oxide dendrites via the hydrogen bubble templated electrochemical deposition technique. Furthermore, we construct a theoretical model combining capillarity and evaporative mass transfer, which leads to optimal operation conditions and wick characteristics, including superhydrophilicity, extreme capillary performance, and omni-angular high optical absorptance. The fabricated porous surfaces with excellent capillary performance and productivity provide a pathway toward a highly efficient bi-facial solar evaporator panel with meter-level scalability.

Realization of Low Latent Heat of a Solar Evaporator via Regulating the Water State in Wood Channels

Solar-driven interfacial evaporation with heat localization is an efficient method for large-scale water purification. However, due to the high latent heat of water evaporation and dilute solar flux (1 kW m^-2), the solar steam productivity is low. Here, the latent heat of water evaporation was reduced because of the capillary water state in wood channels. We constructed a wood-based 3D solar evaporator via regulating the hydrophilicity of a surface of burnt wood and adjusting the height of the wood above a water surface. Capillary water was formed in the light absorption layer, resulting in the latent heat decrease from 2444 to 1769 J g^-1. A high evaporation rate of 1.93 kg m^-2 h^-1 under one sun irradiation (1 kW m^-2) was achieved. Together with the environmental energy-harvesting ability, the evaporation rate reached 3.91 kg m^-2 h^-1 (per occupied area), which is among the best values ever reported. More importantly, the 3D solar evaporator works efficiently in a water collection device, yielding 2.2 times more water than that of a common interfacial evaporator.