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

Natural Fiber@MXene-Engineered Chitosan Aerogels: Thermodynamic-Transport Synergy for Solar-Driven Hypersaline Interfacial Evaporation

Enhancing interfacial evaporation rates and optimizing energy utilization remain critical challenges in solar-driven steam generation. Natural fiber@MXene-engineered chitosan aerogels with hierarchically oriented channels to achieve high-efficiency solar-driven steam generation are developed. The kapok fiber@MXene core-shell units (MKFs) construct photon-entrapping topological networks that enhance light absorption while simultaneously reinforcing the aerogel's structural integrity and durability for practical applications. The aerogel's oriented microchannels establish thermodynamic potential gradients, facilitating spontaneous capillary-driven water replenishment and environmental thermal harvesting. Both experimental results and COMSOL multiphysics simulations systematically demonstrate that hierarchical pore channels enhance water transport, improve solar-thermal/environmental energy synergy, and promote the downward diffusion of concentrated ions from the evaporation surface, achieving an evaporation rate up to 4.40 kg m-2 h-1 with efficient salt rejection. Long-term outdoor tests with various corrosive wastewater solutions further validate the aerogel's durability in solar-driven interfacial evaporation. This study provides a theoretical foundation for understanding the interrelation between solar energy absorption, water transport, and salt diffusion in aerogel evaporators with hierarchical fiber-pore architectures.

Janus-structured MXene-PA/MS with an ultrathin intermediate layer for high-salinity water desalination and wastewater purification

Solar-driven interfacial evaporation presents significant potential for seawater desalination and wastewater purification. However, prolonged operation in marine environments often results in salt accumulation, which adversely impacts the performance and lifetime of system. Despite the progress in material design, achieving efficient evaporation while mitigating salt crystallization remains challenging in high-salinity water. In this study, we synthesized a hierarchically structured C18H37-MXene/PA/MS evaporator employing a simple yet effective methodology specifically designed for applications in high-salinity water environments. The evaporator features a dual-region configuration, with an upper hydrophobic light-absorbing layer comprising modified MXene and polyamide (PA) membranes and a hydrophilic lower layer consists of hydrophilic melamine sponge (MS). This innovative design, incorporating an ultra-thin polyamide interlayer, significantly enhances interfacial stability, thereby mitigating the interfacial separation typically observed in conventional Janus materials during prolonged usage. Furthermore, the meticulous control over the thickness of the hydrophobic layer (5.54 μm) ensures optimal thermal insulation properties of the material. Consequently, the C18H37-MXene/PA/MS evaporator demonstrates an impressive evaporation rate of 1.49 kg m-2 h-1 under 1 sun illumination, with a high energy efficiency of 92.8 %. Furthermore, the Janus architecture ensures steady performance in high salinity conditions, sustaining a high evaporation rate of 1.46 kg m-2 h-1 even in a 20 wt% NaCl solution. Furthermore, under natural sunlight, the daily freshwater yield reaches 8.91 kg m-2. The exceptional evaporation efficiency and robust salt resistance highlight its strong potential for water desalination and wastewater treatment, contributing to the advancement of sustainable water resource management.

Polyanionic Electrolyte Ionization Desalination Empowers Continuous Solar Evaporation Performance

Solar evaporation contributes to sustainable and environmentally friendly production of fresh water from seawater and wastewater. However, poor salt resistance and high degree of corrosion of traditional evaporators in brine make their implementation in real applications scarce. To overcome such deficiency, a polyanionic electrolyte functionalization strategy empowering excellent uniform desalination performance over extended periods of time is exploited. This 3D superhydrophilic graphene oxide solar evaporator design ensures stable water supply by the enhanced self-driving liquid capillarity and absorption at the evaporation interface as well as efficient vapor diffusion. Meanwhile, the polyanionic electrolyte functionalization implemented via layer-by-layer static deposition of polystyrene sodium sulfonate effectively regulates/minimizes the flux of salt ions by exploiting the Donnan equilibrium effect, which eventually hinders local salt crystallization during long-term operation. Stable evaporation rates in line with the literature of up to 1.68 kg m-2 h-1 are achieved for up to 10 days in brine (15‰ salinity) and for up to 3 days in seawater from Hangzhou Bay in the East China Sea (9‰ salinity); while, maintaining evaporation efficiencies of ≈90%. This work demonstrates the excellent benefits of polyanionic electrolyte functionalization as salt resistance strategy for the development of high-performance solar powered seawater desalination technology and others.

Dual-Sided Superhydrophobic Laser-Induced Graphene Evaporator for Efficient Desalination and Brine Treatment under High Salinity

The immense energy footprint of desalination and brine treatment is a barrier to a green economy. Interfacial evaporation (IE) offers a sustainable approach to water purification by efficient energy conversion. However, conventional evaporators are susceptible to fluctuations in solar radiation and the salinity of handling liquid. The present research is an innovative step toward the fabrication of superhydrophobic laser-induced graphene (LIG) interfacial evaporators for desalination and brine treatment. The fabricated dual-sided superhydrophobic laser-induced graphene (DSLIG) exhibits self-cleaning ability on both sides, enhancing salt rejection capabilities through a lotus effect. This multilayered evaporator comprises a top layer of MPES LIG and a bottom layer of PVDF AR 972 LIG, resulting in superior localized heat generation ability. The engineered surface has undergone performance analysis with DI water and NaCl solutions with concentrations of 3.5-24 wt %. The dual-stacked configuration with coupled solar (one sun)-joule heating (5 V) attained evaporation rates of ∼5 kg m-2 h-1 for distilled water and ∼2.2 kg m-2 h-1 for a 24 wt % NaCl solution. The remarkable outcome resulted from substantial thermophysical property changes with LIG formation. The DSLIG's bottom concentration gradient promoted salt back diffusion and ceased salt penetration to the top surface. The work can be further extended to treat the desalination brine for sustainable desalination and zero liquid discharge.

Superhydrophobic, Multifunctional, and Mechanically Durable Carbon Aerogel Composites for High-Performance Underwater Piezoresistive Sensing

Carbon aerogel piezoresistive sensors (CAPSs), owing to their good thermal stability, self-constructed conductive network, and fast response to pressure, have attracted extensive attention in the field of flexible and wearable electronics in recent years. However, it is still a great challenge for CAPSs to monitor subtle deformations and achieve high-performance underwater piezoresistive sensing. Herein, a superhydrophobic and electrically conductive carbon aerogel composite (CAC) was fabricated by the combination of fluorination of carbon aerogels and decoration of fluorinated halloysite nanotubes (HNTs). Due to the exceptional light absorption and excellent photothermal conversion performance, CAC has a fast and accurate response to temperature with a high-temperature coefficient of resistance (TCR) of -1.06%/°C. The resistance of CAC exhibits a linear response toward compressive strain up to 80% with a high gauge factor of -1.24. Significantly, the CAC sensor can effectively detect tiny deformations, thanks to its excellent waterproof performance, and it enables stable output of sensing signals in an underwater environment. This work provides new insights into the development of superhydrophobic, multifunctional, and mechanically durable piezoresistive sensors with potential applications in underwater flexible electronics.

Salt-resistant continuous solar evaporation composites based on nonwovens with synergistic photothermal effect of graphene oxide/copper sulphide

Solar interfacial evaporation is an innovative and environmentally friendly technology for producing freshwater from seawater. However, current interfacial evaporators are costly to manufacture, have poor tolerance to environmental conditions, exhibit instability in evaporation efficiency in highly saline solutions, and fail to prevent salt crystallization. The production of user-friendly, durable and salt-resistant interfacial evaporators remains a significant challenge. By spraying graphene oxide on a nonwoven material using PVA as a binder and adding biphasic Cu x S by an in situ growth method, we designed 2D/3D micro- and nanostructured graphene oxide nanosheets/copper sulfide nanowires (GO/Cu x S) with synergistic photo-thermal effects in the full spectral range. The evaporation efficiency in pure water was 94.61% with an evaporation rate of 1.5622 kg m-2 h-1. In addition, we enhanced convection by employing a vertically aligned water-guide rod structure design, where the concentration difference drives salt dissolution thereby reducing the formation of salt crystals. The evaporation efficiency in 20% salt water was 80.41% with an evaporation rate of 1.3228 kg m-2 h-1 and long-term stability of brine evaporation was demonstrated under continuous sunlight. This solar steam generator expands the potential application areas of desalination and wastewater purification.

A Zero-Gap Gas Phase Photoelectrolyzer for CO2 Reduction with Porous Carbon Supported Photocathodes

A modified Metal-Organic Framework UiO-66-NH2-based photocathode in a zero-gap gas phase photoelectrolyzer was applied for CO2 reduction. Four types of porous carbon fiber layers with different wettability were employed to tailor the local environment of the cathodic surface reactions, optimizing activity and selectivity towards formate, methanol, and ethanol. Results are explained by mass transport through the different type and arrangement of carbon fiber support layers in the photocathodes and the resulting local environment at the UiO-66-NH2 catalyst. The highest energy-to-fuel conversion efficiency of 1.06 % towards hydrocarbons was achieved with the most hydrophobic carbon fiber (H23C2). The results are a step further in understanding how the design and composition of the photoelectrodes in photoelectrochemical electrolyzers can impact the CO2 reduction efficiency and selectivity.

Adsorptive removal of organophosphate pesticides from aqueous solution using electrospun carbon nanofibers

Organophosphate pesticides (OPPs) are widely prevalent in the environment primarily due to their low cost and extensive use in agricultural lands. However, it is estimated that only about 5% of these applied pesticides reach their intended target organisms. The remaining 95% residue linger in the environment as contaminants, posing significant ecological and health risks. This underscores the need for materials capable of effectively removing, recovering, and recycling these contaminants through adsorption processes. In this research, adsorbent materials composed of electro-spun carbon nanofibers (ECNFs) derived from polyacrylonitrile was developed. The materials were characterized through several techniques, including scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier Transform Infrared Spectroscopy (FTIR), Brunauer-Emmett-Teller (BET) analysis, and contact angle measurements. SEM analysis revealed details of the structural properties and inter-fiber spacing variations of the carbon nanofibers. The results revealed that ECNFs possess remarkable uniformity, active surface areas, and high efficiency for adsorption processes. The adsorption studies were conducted using batch experiments with ethion pesticide in aqueous solution. High-Performance Liquid Chromatography-Diode Array Detector (HPLC-DAD) was utilized to quantify the concentrations of the OPP. Various parameters, including adsorbent dosage, pH, contact time, and initial ethion concentration, were investigated to understand their impact on the adsorption process. The adsorption isotherm was best described by the Freundlich model, while the kinetics of adsorption followed a non-integer-order kinetics model. The adsorption capacity of the ECNFs for OPP removal highlights a significant advancement in materials designed for environmental remediation applications. This study demonstrates the potential of ECNFs to serve as effective adsorbents, contributing to the mitigation of pesticide contamination in agricultural environments.

Scalable Superhydrophilic Solar Evaporators for Long-Term Stable Desalination, Fresh Water Collection and Salt Collection by Vertical Salt Deposition

Solar-driven interfacial evaporation (SIE) is very promising to solve the issue of fresh water shortage, however, poor salt resistance severely hinders long-term stable SIE and fresh water collection. Here, we report design of superhydrophilic solar evaporators for long-term stable desalination, fresh water collection and salt collection by vertical salt deposition. The evaporators are prepared by sequentially deposition of silicone nanofilaments, polypyrrole and Au nanoparticles on a polyester fabric composed of microfibers. The evaporators feature excellent photothermal effect and ultrafast water transport, due to their unique micro-/nanostructure and superhydrophilicity. As a result, during SIE the salt gradually deposits vertically rather than occupies larger area on the evaporators. Consequently, long-term stable SIE with high evaporation rates of 2.4-2.1 kg m-2 h-1 for 3.5-20 wt % brine in continuous 10 h is achieved under 1 sun illumination. Meanwhile, the loosely deposited salt can be easily collected, realizing zero brine discharge. Moreover, scalable preparation of the evaporator is achieved, which exhibits efficient collection of high quality fresh water (10.08 kg m-2 in 8 h) via SIE desalination under weak natural sunlight (0.46~0.66 sun). This strategy sheds a new light on the design of high-performance solar evaporators and their real-world fresh water collection.

Investigating Permselectivity in PVDF Mixed Matrix Membranes Using Experimental Optimization, Machine Learning Segmentation, and Statistical Forecasting

This research examines the correlation between interfacial characteristics and membrane distillation (MD) performance of copper oxide (Cu) nanoparticle-decorated electrospun carbon nanofibers (CNFs) polyvinylidene fluoride (PVDF) mixed matrix membranes. The membranes were fabricated by a bottom-up phase inversion method to incorporate a range of concentrations of CNF and Cu + CNF particles in the polymer matrix to tune the porosity, crystallinity, and wettability of the membranes. The resultant membranes were tested for their application in desalination by comparing the water vapor transport and salt rejection rates in the presence of Cu and CNF. Our results demonstrated a 64% increase in water vapor flux and a salt rejection rate of over 99.8% with just 1 wt % loading of Cu + CNF in the PVDF matrix. This was attributed to enhanced chemical heterogeneity, porosity, hydrophobicity, and crystallinity that was confirmed by electron microscopy, tensiometry, and scattering techniques. A machine learning segmentation model was trained on electron microscopy images to obtain the spatial distribution of pores in the membrane. An Autoregressive Integrated Moving Average with Explanatory Variable (ARIMAX) statistical time series model was trained on MD experimental data obtained for various membranes to forecast the membrane performance over an extended duration.

Natural lignocellulosic kapok fiber/MXene constructed hydrogel evaporators for high efficiency solar steam generation

Solar-driven interfacial evaporation (SDIE) is a green and sustainable technique for desalination. Hydrogel composite evaporators have been widely used for SDIE, but it is still challenging for the hydrogel evaporators to achieve uniform distribution of the light absorbing nanomaterials and at the same time possess satisfactory evaporation rate, durability and environmental applicability. We developed a 3D hydrogel evaporator with an asymmetric structure for high-efficiency SDIE. Natural kapok fibers, an important lignocellulosic plant fiber with a hollow structure, are decorated with MXene nanosheets for construction of one-dimensional photothermal conversion network. The top composite hydrogel serves as the light-absorption layer where MXene-modified kapok fibers are evenly dispersed in PVA hydrogel, while the bottom PVA hydrogel with an oriented structure acts as water delivery path. The evaporator exhibits a high solar evaporation rate and efficiency (2.49 kg·m-2·h-1 and 91.5 %, respectively) under one sun irradiation (1 kW·m-2). Even in a high salinity brine, emulsion and corrosive solutions, the evaporator can work normally with a slightly decreased evaporation rate. The 3D hydrogel evaporator with long-term stability and durability shows promising applications in purification of seawater and different waste water.

Carbon nanofiber reinforced carbon aerogels for steam generation: Synergy of solar driven interface evaporation and side wall induced natural evaporation

Solar-based interface evaporation (SIE) is a green, efficient and cost-effective technique to harvest fresh water. 3D solar evaporators show their unique advantages in gaining energy from environment and hence possess a higher evaporation rate than 2D evaporators. However, much effort is still required to develop mechanically robust and superhydrophilic 3D evaporators with strong water transportation capability and salt-rejection performance, and at the same time reveal how they gain energy from environment via the natural evaporation. In this work, a novel carbon nanofiber reinforced carbon aerogel (CNFA) is prepared for the SIE. The CNFA has a high light absorption up to 97.2% and outstanding photothermal conversion performance. The heteroatom doping and hierarchically porous structure endow the CNFA with superhydrophilicity and thus powerful water transportation capability and salt rejection performance. Benefiting from synergy of the SIE and side wall induced natural evaporation, the CNFA evaporator exhibits a high evaporation rate and efficiency (as high as 3.82 kg m^-2h^-1 and 95.5%, respectively) with long-term stability and durability. The CNFA can also work normally in high-salinity and corrosive seawater. This study demonstrates a new method to fabricate all-carbon aerogel solar evaporators and provides insights for the effective thermal management during the interface evaporation.

One-step synthesis of Enteromorpha graphene aerogel modified by hydrophilic polyethylene glycol achieving high evaporation efficiency and pollutant tolerance

Photothermal evaporation using solar energy is a sustainable way to produce fresh water from seawater. Aiming to explore functional materials as a solar-energized evaporator with enhanced evaporation rate and pollutant tolerance, this study was to synthesize a self-floating composite graphene aerogel (GA) doped with Enteromorpha and modified polyethylene glycol (PEG), named as PEGA using solar energy for desalination. Physio-chemical properties and evaporative mechanism of PEGA were experimentally investigated and analyzed with respect to molecular weight, PEG dosage, and ratio of Enteromorpha and graphene oxide. Experimental data revealed that the modification of PEG improved hydrophilic functional ability of PEGA, resulting in increasing the evaporation rate and photothermal conversion efficiency up to 2.55 kg/(m²·h) and 105.71 %, respectively. The ion removal rate of seawater exceeds 99.99 % via the PEGA conducted solar evaporation. Furthermore, PEGA possessed an excellent property of salinity emulsion pollution tolerance. Particularly, the evaporation rate of the PEG-modified biomass-based aerogel was 2.84 kg/(m²·h) in a 15 wt% NaCl solution (1 sun, 6 h) and 2.50 kg/(m²·h) at 1 h. The formation of hydrogen bonds between -OH of PEG and water molecules assist to conduct water along the graphene matrix to improve water evaporation. The cost of the graphene aerogel modified by Enteromorpha was reduced by 38.88 % less than the original graphene aerogel. The results from this study will greatly promote the application of graphene aerogel for desalination via solar evaporation.