Three-Dimensional Mirror-Assisted and Concave Pyramid-Shaped Solar-Thermal Steam Generator for Highly Efficient and Stable Water Evaporation and Brine Desalination

Effect of Folded Structures on Interfacial Solar-Driven Seawater Desalination

Currently, solar-driven interface evaporation for seawater desalination is believed to be an effective way to overcome freshwater shortage. To improve the efficiency of solar-driven interfacial evaporators, designing the evaporator's structure is essential. In this study, we proposed a folded structure solar-driven interfacial evaporator with electrospun recycled PET/carbon nanotube fibrous membranes. The as-spun membranes were folded into 4, 8, and 16 petals. The results suggested that F@8 (fold with eight petals) had the best solar-driven evaporation performance, with a photothermal conversion efficiency of 90.59% and an evaporation rate of 1.31 kg·m-2·h-1, due to its lower light projection area and greater light absorption. The evaporation performance remained stable after 10 cycles. In addition, the concentration of ions in the freshwater collected after desalination was 2~3 orders of magnitude lower than that before desalination. These results indicate that a properly designed folded structure can effectively enhance evaporators through changing the light projection area and absorption. This approach might provide an effective way to optimize the structure of interfacial solar-driven evaporators.

Preparation of Calcium Alginate-Based Hydrogels with Precisely Designed Centrosymmetric Geometries for Efficient Water Evaporation in Response to Different Solar Incidence Angles

Hydrogels are popular materials for desalination and can significantly reduce the vaporization enthalpy of water; however, there are few reports on hydrogels with a controllable multilevel structural design for water evaporation. Herein, a calcium alginate and traditional Chinese ink-based evaporator (CIE) are proposed and fabricated using directed freezing technology to construct radial channels, followed by freeze-drying and physical cross-linking. Because of the squeezing of ice crystals and the shaping effect of the PDMS template, the prepared evaporator exhibits a sea-urchin-shaped highly geometrical centrosymmetric structure with numerous multilevel pore channels, which promotes the rapid transport of water under different solar incidence angles as the sun rotates as well as overcomes the structural shrinkage of the hydrogel caused by insufficient water supply. Additionally, the radial channels in the spherical hydrogel overcome the traditional limitation of saltwater being continuously concentrated in the same area where the evaporation rate is the highest. As a result, the urchin-structured CIE exhibits a water evaporation rate of 3.52 kg m-2 h-1 at 1 sun irradiation, which is 45.5% higher than that of the unpatterned CIE. This multilevel structural design provides a strategy for the fabrication of an all-day water hydrogel-based evaporator without structural shrinkage under solar irradiation.

Recent innovations in 3D solar evaporators and their functionalities

Interfacial solar evaporation (ISE) has emerged as a promising technology to alleviate global water scarcity via energy-efficient purification of both wastewater and seawater. While ISE was originally identified and developed during studies of simple double-layered two-dimensional (2D) evaporators, observed limitations in evaporation rate and functionality soon led to the development of three-dimensional (3D) evaporators, which is now recognized as one of the most pivotal milestones in the research field. 3D evaporators significantly enhance the evaporation rates beyond the theoretical limits of 2D evaporators. Furthermore, 3D evaporators could have multifaceted functionalities originating from various functional evaporation surfaces and 3D structures. This review summarizes recent advances in 3D evaporators, focusing on rational design, fabrication and energy nexus of 3D evaporators, and the derivative functions for improving solar evaporation performance and exploring novel applications. Future research prospects are also proposed based on the in-depth understanding of the fundamental aspects of 3D evaporators and the requirements for practical applications.

Fully Integrated Biosensing System for Dynamic Monitoring of Sweat Glucose and Real-Time pH Adjustment Based on 3D Graphene MXene Aerogel

The development of noninvasive glucose sensors capable of continuous monitoring without restricting user mobility is crucial, particularly for managing diabetes, which demands consistent and long-term observation. Traditional sensors often face challenges with accuracy and stability that curtail their practical applications. To address these issues, we have innovatively applied a three-dimensional porous aerogel composed of Ti3C2Tx MXene and reduced graphene oxide (MX-rGO) in electrochemical sensing. It significantly reduces the electron-transfer distance between the enzyme's redox center and the electrode surface while firmly anchoring the enzyme layer to effectively prevent any leakage. Another pivotal advancement in our study is the integration of the sensor with a real-time adaptive calibration mechanism tailored specifically for analyzing sweat glucose. This sensor not only measures glucose levels but also dynamically monitors and adjusts to pH fluctuations in sweat. Such capabilities ensure the precise delivery of physiological data during physical activities, providing strong support for personalized health management.

Salt-rejecting 3D cone flowing evaporator based on bilayer photothermal paper for high-performance solar seawater desalination

Solar energy-driven water evaporation technology is a promising, low-cost and sustainable approach to alleviate the global clean water shortage, but usually suffers from low water evaporation rate and severe salt deposition on the water evaporation surface. In this work, a hydrophilic bilayer photothermal paper-based three-dimensional (3D) cone flowing evaporator was designed and prepared for stable high-performance seawater desalination with excellent salt-rejecting ability. The as-prepared bilayer photothermal paper consisted of MXene (Ti3C2Tx) and HAA (ultralong hydroxyapatite nanowires, poly(acrylic acid), and poly(acrylic acid-2-hydroxyethyl ester)). The accordion-like multilayered MXene acted as the efficient solar light absorber, and ultralong hydroxyapatite (HAP) nanowires served as the thermally insulating and supporting skeleton with a porous networked structure. A siphon effect-driven unidirectional fluid transportation unit in the 3D cone flowing evaporator could guide the concentrated saline flowing away from the evaporating surface to prevent salt deposition on the evaporation surface, avoiding severe deterioration of the performance in solar water evaporation. Furthermore, combining high solar light absorption and high photothermal conversion efficiencies, low water evaporation enthalpy (1838 ± 11 J g-1), and additional energy taken from the ambient environment, the as-prepared cone flowing evaporator exhibited a high water evaporation rate of 3.22 ± 0.20 kg m-2 h-1 for real seawater under one sun illumination (1 kW m-2), which was significantly higher than many values reported in the literature. This study provides an effective approach for designing high-performance solar energy-driven water evaporators for sustainable seawater desalination and wastewater purification.

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

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