A self-floating electrospun nanofiber mat for continuously high-efficiency solar desalination

Electrospun Nanofiber Materials for Photothermal Interfacial Evaporation

Photothermal interfacial evaporation with low cost and environmental friendliness has attracted much attention. However, there are still many problems with this technology, such as heat loss and salt accumulation. Due to their different structures and adjustable chemical composition, electrospun nanofiber materials generally exhibit some unique properties that provide new approaches to address the aforementioned issues. In this review, the rational design principles for improving the total efficiency of solar evaporation are described for thermal/water management systems and salt-resistance strategies. And we review the state-of-the-art advancements in photothermal evaporation based on nanofiber materials and discuss their derivative applications in desalination, water purification, and power generation. Finally, we highlight key challenges and opportunities in both fundamental research and practical applications to inform further developments in the field of interfacial evaporation.

A novel, flexible porous nanofibrous hydrogel interfacial solar evaporator for highly efficient seawater and wastewater purification

Solar desalination is recognized as one of the eco-friendly and sustainable ways to alleviate the global freshwater crisis but still requires further research, especially in developing high-performance evaporators. Herein, we prepared an efficient carbon nanotubes (CNTs)@polyvinyl alcohol (PVA) nanofibrous hydrogel evaporator by electrospinning and subsequently chemical cross-linking treatment. Due to CNTs with good light absorption capacity, the evaporator exhibited an excellent light absorption capacity (>90%) throughout the full spectrum range (250-2500 nm). Meanwhile, the interconnected pores from electrospinning, as well as the intermediate water in the hydrogel, ensured the prepared evaporator with a favorable evaporation rate of up to 2.16 kg m^-2 h^-1 and photothermal conversion efficiency of ∼88.13% under one solar light intensity. For long-term seawater desalination, the CNTs@PVA nanofibrous hydrogel evaporator also presented superior salt resistance, durability and good self-cleaning properties. Besides, various non-volatile pollutants can be completely removed by the prepared evaporator during the wastewater purification. As a result, this work is considered to provide a new direction for developing high-performance evaporators to provide freshwater through seawater desalination and wastewater purification.

Tri-functional aerogel photocatalyst with an S-scheme heterojunction for the efficient removal of dyes and antibiotic and hydrogen generation

A novel three-dimensional (3D) S-scheme S-gC₃N₄/TiO₂/SiO₂/PAN aerogel heterojunction photocatalyst (denoted as S-gTAHP) is rationally devised and manufactured by combining electrospinning, calcination, hydrothermal and freeze-drying techniques. The synthesized S-gC₃N₄ molecule is different from traditional g-C₃N₄, which has a small molecular structure similar to melamine. S-gC₃N₄ is embedded in the interwoven network structure of TiO₂/PAN short fibers, and the catalytic system of the S-scheme heterojunction is formed with SiO₂ as a crosslinking agent. S-gTAHP achieves perfect tri-functional photocatalytic capability, including remarkable hydrogen release capacity (806.7 μmol∙h^-1∙g^-1), efficient removal of three colored dyes with removal efficiencies up to 99.43% (MB, 15 min), 96.13% (RhB, 30 min) and 91.32% (MO, 40 min), and a degradation rate of the colorless antibiotic TCH reaching 84.20% in 40 min driven by simulated sunlight. Meanwhile, the effects of pH values and concentrations of contaminant solutions on the removal rates are explored, and the S-scheme mechanism of S-gTAHP strengthening photocatalytic activity is elucidated. The apparently heightened photocatalytic activities of S-gTAHP can be ascribed to the fact that the 3D hierarchical porous structure of the aerogel endows more active centers and enhanced light-harvesting capacity, and the S-scheme heterojunction supplies effective charge migrating channels, thereby affording the carriers with strong redox capability. Furthermore, S-gTAHP holds prominent reusability and is light weight. Hence, efficient and recyclable 3D aerogel photocatalysts with S-scheme heterojunctions have broad application prospects in practical sewage treatment and energy conversion fields.

Hydrophobic and porous carbon nanofiber membrane for high performance solar-driven interfacial evaporation with excellent salt resistance

Interfacial evaporation has recently received great interest from both academia and industry to harvest fresh water from seawater, due to its low cost, sustainability and high efficiency. However, state-of-the-art solar absorbers usually face several issues such as weak corrosion resistance, salt accumulation and hence poor long-term evaporation stability. Herein, a hydrophobic and porous carbon nanofiber (HPCNF) is prepared by combination of the porogen sublimation and fluorination. The HPCNF possessing a macro/meso porous structure exhibits large contact angles (as high as 145°), strong light absorption and outstanding photo-thermal conversion performance. When the HPCNF is used as the solar absorber, the evaporation rate and efficiency can reach up to 1.43 kg m^-2h^-1 and 87.5% under one sunlight irradiation, respectively. More importantly, the outstanding water proof endows the absorber with superior corrosion resistance and salt rejection performance, and hence the interfacial evaporation can maintain a long-term stability and proceed in a variety of complex conditions. The HPCNFs based interfacial evaporation provides a new avenue to the high efficiency solar steam generation.

A Simple Polypyrrole/Polyvinylidene Fluoride Membrane with Hydrophobic and Self-Floating Ability for Solar Water Evaporation

The traditional hydrophobic solarevaporator is generally obtained through the modification of alkyl or fluoroalkyl on the photothermal membrane. However, the modified groups can easily be oxidized in the long-term use process, resulting in the poor salt resistance and stability of photothermal membrane. In order to solve this problem, a simple polypyrrole/polyvinylidene fluoride membrane, consisting of an intrinsic hydrophobic support (polyvinylidene fluoride) and a photothermal material (polypyrrole), was fabricated by ultrasonically mixing and immersed precipitation. This photothermal membrane showed good self-floating ability in the process of water evaporation. In order to further improve the photothermal conversion efficiency, a micropyramid structure with antireflective ability was formed on the surface of membrane by template method. The micropyramids can enhance the absorption efficiency of incident light. The water evaporation rate reached 1.42 kg m⁻² h⁻¹ under 1 sun irradiation, and the photothermal conversion efficiency was 88.7%. The hydrophobic polyvinylidene fluoride ensures that NaCl cannot enter into membrane during the evaporation process of the brine, thus realizing the stability and salt resistance of polypyrrole/polyvinylidene fluoride in 3.5%wt and 10%wt NaCl solution.

Anchoring bismuth oxybromo-iodide solid solutions on flexible electrospun polyacrylonitrile nanofiber mats for floating photocatalysis

Constructing floating photocatalysts with highly efficient visible-light utilization is a promising approach for practical photocatalytic wastewater treatment. In this study, we anchored bismuth oxybromo-iodide (BiOBr_xI_1-x (0 ≤ x ≤ 1)) on flexible electrospun polyacrylonitrile (PAN) nanofiber mats to create BiOBr_xI_1-x@PAN nanofibers with tunable light absorption properties as floating photocatalysts at room temperature. As x increased, the photocatalytic activity of the BiOBr_xI_1-x@PAN nanofibers with similar loading content initially increased, and then decreased, for the degradation of bisphenol A (BPA) and methyl orange (MO) under visible-light irradiation (λ > 420 nm) conditions. The BiOBr_xI_1-x@PAN (0 < x < 1) nanofibers exhibited better photocatalytic performance compared to the BiOBr@PAN and BiOI@PAN nanofibers. Under visible-light irradiation, the BPA degradation rate of the BiOBr_0.5I_0.5@PAN nanofibers was 1.9 times higher than that of the BiOI@PAN nanofibers, while the BiOBr@PAN nanofibers had no noticeable degradation performance. The MO degradation rate of the BiOBr_0.5I_0.5@PAN nanofibers was 2.5 and 3.2 times higher than that of the BiOBr@PAN and BiOI@PAN nanofibers, respectively. The enhanced performance possibly originated from a balance between the light absorption and redox capabilities, along with efficient separation of electron-hole pairs in the BiOBr_0.5I_0.5@PAN nanofibers, as determined by ultraviolet-visible diffuse reflectance spectroscopy, X-ray photoelectron spectra analysis of the valence bands, and photocurrent response characterization. Compared to the powder structures, the BiOBr_xI_1-x@PAN nanofibers showed enhanced performance due to the excellent dispersion and immobilization of the BiOBr_xI_1-x solid solution, which provided more active sites during photocatalytic degradation. In addition, their flexible self-supporting structures allowed for floating photocatalysis near the water surface. They could be reused directly without separation and maximized the absorption of visible light during the photocatalytic reaction. Therefore, these solid-solution-based floatable nanofiber photocatalysts are good potential candidates for wastewater treatment applications.

Simultaneous Visual Detection and Removal of Cu2+ with Electrospun Self-Supporting Flexible Amidated Polyacrylonitrile/Branched Polyethyleneimine Nanofiber Membranes

Sensitive detection and effective removal of copper ions (Cu²⁺) from water are still arduous tasks required to protect public health and environmental safety because of the serious impacts of Cu²⁺ on humans and other organisms. Herein, we report the design and fabrication of self-supporting flexible amidated polyacrylonitrile/branched polyethyleneimine nanofiber membranes (abbreviated as aPAN/BPEI NMs) via facile electrospinning and a subsequent hydrothermal method, which are used not only as strips for the visual detection of Cu²⁺ but also as effective adsorbents for the removal of Cu²⁺ from water. Because aPAN/BPEI NMs are self-supporting, they can be easily removed from the solution to reduce secondary pollution to the environment. Based on the high Cu²⁺ binding capacity of BPEI, Cu²⁺ ions are adsorbed on the aPAN/BPEI NMs, which leads to the appearance of new absorbance bands at 280 and 636 nm and a color change from yellow to blue. aPAN/BPEI NMs are utilized for the visual detection of Cu²⁺ with a linear range of 50-700 μM and limits of detection of 11.5 and 4.8 μM (absorption peaks at 280 and 636 nm). More importantly, aPAN/BPEI NMs exhibit excellent selectivity and certain recovery with a simple treatment. Furthermore, by utilizing the adsorption characteristics of Cu²⁺ in aqueous media, it can be effectively removed by aPAN/BPEI NMs with a remarkable adsorption capacity of 209.53 mg·g^-1. Additionally, the removal of Cu²⁺ by aPAN/BPEI NMs does not exhibit interference by other foreign ions. The adsorption process conforms well to the pseudo-second order (PSO) kinetic model and Jovanovich model, proving that adsorption occurs via chemical and monolayer adsorption mechanisms. Accordingly, this work will provide theoretical and technical support for the design and fabrication of novel heavy metal ion detection-removal integrated materials exhibiting high sensitivity and strong adsorption.