Rapid Water Transport Research Articles

Graphene Oxide and its Composites: Advanced Membranes for Selective Water Permeation.

Graphene oxide (GO) membranes have gained significant attention as a promising material for separation by selective permeation processes due to their advantageous structural and chemical properties, including high water permeability, chemical resistance, and mechanical strength. In this study, we explore the potential applications of GO membranes in pervaporation to separate liquid mixtures. The layered structure and hydrophilic nature of GO membrane facilitate rapid and selective water transport through angstrom-scale interlayer spacings, resulting in superior performance over conventional polymeric and inorganic membranes. The unique mass transport mechanisms - slip flow and molecular alignment - enable GO membranes to selectively permeate water over organic solvents. For chemical dehydration, GO membranes are the most potential candidates. Furthermore, advancements in composite GO membranes and cross-linking techniques that improve their stability and separation performance are discussed. This study highlights the advantages of GO membranes and their potential to replace or complement existing technologies, by emphasizing their role in advancing membrane-based separation and promoting environmental sustainability. Future research is expected to optimize the fabrication techniques for GO membranes and expand their application scope.

Horizontal Transport in Ti3C2Tx MXene for Highly Efficient Osmotic Energy Conversion from Saline‐Alkali Environments

AbstractOsmotic energy from the ocean has been thoroughly studied, but that from saline‐alkali lakes is constrained by the ion‐exchange membranes due to the trade‐off between permeability and selectivity, stemming from the unfavorable structure of nanoconfined channels, pH tolerance, and chemical stability of the membranes. Inspired by the rapid water transport in xylem conduit structures, we propose a horizontal transport MXene (H‐MXene) with ionic sequential transport nanochannels, designed to endure extreme saline‐alkali conditions while enhancing ion selectivity and permeability. The H‐MXene demonstrates superior ion conductivity of 20.67 S m−1 in 1 M NaCl solution and a diffusion current density of 308 A m−2 at a 10‐fold salinity gradient of NaCl solution, significantly outperforming the conventional vertical transport MXene (V‐MXene). Both experimental and simulation studies have confirmed that H‐MXene represents a novel approach to circumventing the permeability‐selectivity trade‐off. Moreover, it exhibits efficient ion transport capabilities, addressing the gap in saline‐alkali osmotic power generation.

Horizontal Transport in Ti3C2Tx MXene for Highly Efficient Osmotic Energy Conversion from Saline-Alkali Environments.

Osmotic energy from the ocean has been thoroughly studied, but that from saline-alkali lakes is constrained by the ion-exchange membranes due to the trade-off between permeability and selectivity, stemming from the unfavorable structure of nanoconfined channels, pH tolerance, and chemical stability of the membranes. Inspired by the rapid water transport in xylem conduit structures, we propose a horizontal transport MXene (H-MXene) with ionic sequential transport nanochannels, designed to endure extreme saline-alkali conditions while enhancing ion selectivity and permeability. The H-MXene demonstrates superior ion conductivity of 20.67 S m-1 in 1 M NaCl solution and a diffusion current density of 308 A m-2 at a 10-fold salinity gradient of NaCl solution, significantly outperforming the conventional vertical transport MXene (V-MXene). Both experimental and simulation studies have confirmed that H-MXene represents a novel approach to circumventing the permeability-selectivity trade-off. Moreover, it exhibits efficient ion transport capabilities, addressing the gap in saline-alkali osmotic power generation.

Tree-Inspired Aerogel Comprising Nonoxidized Graphene Flakes and Cellulose as Solar Absorber for Efficient Water Generation.

As global freshwater shortages worsen, solar steam generation (SSG) emerges as a promising, eco-friendly, and cost-effective solution for water purification. However, widespread SSG implementation requires efficient photothermal materials and solar evaporators that integrate enhanced light-to-heat conversion, rapid water transportation, and optimal thermal management. This study investigates using nonoxidized graphene flakes (NOGF) with negligible defects as photothermal materials capable of absorbing over 98% of sunlight. By combining NOGF with cellulose nanofibers (CNF) through bidirectional freeze casting, we created a vertically and radially aligned solar evaporator. The hybrid aerogel exhibited exceptional solar absorption, efficient solar-to-thermal conversion, and improved surface wettability. Inspired by tree structures, our design ensures rapid water supply while minimizing heat loss. With low NOGF content (∼10.0%), the NOGF/CNF aerogel achieves a solar steam generation rate of 2.39 kg m-2 h-1 with an energy conversion efficiency of 93.7% under 1-sun illumination, promising applications in seawater desalination and wastewater purification.

Simultaneous efficient evaporation and stable electricity generation enabled by a wooden evaporator based on composite photothermal effect

The current solar interfacial evaporators have limited evaporation performance due to their single photothermal mechanism, insufficient light utilization, and improper heat management. Therefore, a novel approach involving polypyrrole (PPy) and Ag nanoparticles (AgNPs) modified wooden evaporator (AgPW) using an in-situ polymerization and growth method was proposed for efficient and sustainable freshwater purification. The composite photothermal effect of PPy and AgNPs led to a significantly enhanced light absorption capacity and superior photothermal conversion efficiency in a wide spectrum range, which coupled with the rapid water transport capacity conferred by the regular vertical channels and superior hydrophilicity of the delignified wood, resulted in remarkable evaporation performance through the coordinated regulation of thermal and water management. The optimized AgPW50 achieved an evaporation rate of up to 2.04 kg m−2 h−1 and an evaporation efficiency of 90.7 % under 1 kW m−2 irradiation. Importantly, this evaporator was highly salt resistant and long-term desalination stability, and can also be extended to the purification of various types of wastewaters while converting the released waste heat into stable electricity generation. The innovative Ag/PPy wooden evaporator integrates biomass resources with solar energy utilization, demonstrating an environmentally friendly, efficient and cost-effective strategy for seawater desalination and energy production, providing a new sustainable development pathway to solve the challenge of balancing water security and energy consumption.

Turning trash into treasure: Integrating waste MXene sediment with bagasse into photothermal composite aerogel for efficient solar-driven interfacial evaporation

Solar-driven interfacial evaporation (SDIE) technique holds significant potential in addressing the global freshwater scarcity issue. Using waste resources to construct an evaporator is the promising choice for SDIE with low energy consumption, low cost, and sustainability. Herein, an aerogel photothermal evaporator composed of waste MXene sediment (WM) and bagasse-derived cellulose was demonstrated. WM was a mixture of outstanding light absorption and photothermal conversion. Cellulose served as the skeleton. Besides, the ordered vertical microchannel array within the aerogel evaporator (WM/BCA) was successfully fabricated using a super-frozen ice crystal as a template during the directional freeze process. The excellent photothermal characteristic of WM and the unique microstructure of aerogel endowed the high light absorption, superior hydrophilicity, rapid water transport, and salt reflux of composite evaporator. Benefiting from the above advantages, the optimal sample (WM/BCA-3) demonstrated excellent water evaporation, desalination ability, and long-term stability. Furthermore, the effect of aerogel evaporator size on evaporation was investigated. The evaporation rate was enhanced to 2.03 kg·m−2·h−1 (deionized water as source) with 94.5 % solar efficiency through the reduction in diameter of the aerogel evaporator, while an increase in the number of aerogels facilitated an improvement in vapor yield. Finally, an outdoor test exhibited the practical application potential of composite aerogel in freshwater production. This work presents a promising approach to constructing and optimizing an efficient solar-driven interfacial evaporator using waste materials.

Tree-inspired coir fiber-based array evaporator with rapid water transportation and effective solar water evaporation

Coconut husk as a raw material for the production of solar water evaporators has received considerable attention due to its abundance and availability. However, common treatment methods such as carbonization applied to capacitate the coconut husks for photothermal conversion were not favor for realizing rapid evaporation, as they failed to exploit the original structure of coconut husks. Herein, coir fibers extracted from the coconut husks were directly supplied to the production of functionalized evaporators with carbon nanoparticle coating, which preserved the pristine structure of coir fibers and allowed them to rapidly transport water in multiple directions like trees. These fibers were further assembled into array evaporators to maximize their exposed surface area for efficient evaporation. As a result, the carbon-coated coir fiber array evaporator prepared in the present work showed the highest evaporation rate of 4.19 kg m-2h−1 during solar water evaporation experiments under 1.0 sun illumination. Our work presents an approach for achieving effective solar water evaporation based on carbon-coated coir fiber array evaporator with large exposed surface area and tree-inspired multidirectional fast water transportation.

Glycine-Modified Co-MOF Pervaporation Membrane to Enhance Water Transporting.

Cobalt-based metal-organic frameworks (Co-MOFs) with a two-dimensional layered morphology have received increasing attention for pervaporation due to their stability and hydrophilic properties. Using amino glycine (Gly) as a cross-linking agent, the Co-MOF ultrathin two-dimensional membrane doped with organic filler sodium alginate (SA) with the "brick-mixed-sand" structure was proposed. Polyacrylonitrile (PAN) was selected as the support layer of the hybrid membrane. The introduction of Gly efficiently solved the nanomaterial stacking problem and controllably adjusted the interlayer spacing between the nanosheets, which demonstrated good performance for ethanol dehydration. The results of this experimental research showed that the total flux of alcohol/water (9:1) separation by Gly-Co-MOF-SA/PAN hybrid membranes reached 1902 g m-2 h-1, which was 67% higher than that of the pure SA membranes. The "brick-mixed-sand" lamellar dense morphology of Gly-Co-MOF not only enhances membrane hydrophilicity but also provides effective channels for the rapid transport of water, which is expected to be used for the dehydration of organic solvents.

(Ca0.25La0.5Dy0.25)CrO3 Ceramic Fiber@Biomass-Derived Carbon Aerogel with Enhanced Solute Transport Channels for Highly Efficient Solar Interface Evaporation.

The use of solar interface evaporation for seawater desalination or sewage treatment is an environmentally friendly and sustainable approach; however, achieving efficient solar energy utilization and ensuring the long-term stability of the evaporation devices are two major challenges for practical application. To address these issues, we developed a novel ceramic fiber@bioderived carbon composite aerogel with a continuous through-hole structure via electrospinning and freeze-casting methods. Specifically, an aerogel was prepared by incorporating perovskite oxide (Ca0.25La0.5Dy0.25)CrO3 ceramic fibers (CCFs) and amylopectin-derived carbon (ADC). The CCFs exhibited remarkable photothermal conversion efficiencies, and the ADC served as a connecting agent and imparted hydrophilicity to the aerogel due to its abundant oxygen-containing functional groups. After optimizing the composition and microstructure, the (Ca0.25La0.5Dy0.25)CrO3 ceramic fiber@biomass-derived carbon aerogel demonstrated remarkable properties, including efficient light absorption and rapid transport of water and solutes. Under 1 kW m-2 light intensity irradiation, this novel material exhibited a high temperature (48.3 °C), high evaporation rate (1.68 kg m-2 h-1), and impressive solar vapor conversion efficiency (91.6%). Moreover, it exhibited long-term stability in water evaporation even with highly concentrated salt solutions (25 wt%). Therefore, the (Ca0.25La0.5Dy0.25)CrO3 ceramic fiber@biomass-derived carbon aerogel holds great promise for various applications of solar interface evaporation.

Novel cellulose-based films with highly efficient photothermal performance for sustainable solar evaporation and solar-thermal power generation

Solar-driven interfacial evaporation has received substantial attention in a variety of applications, including water purification, seawater desalination, and energy production. However, creating a straightforward, adaptable, and scalable method for correctly integrating hybrid solar-thermal systems continues to be a challenging task. Herein, we propose an economical, scalable, and environmentally friendly approach for achieving synergistic coupling of interfacial solar energy conversion for evaporation and low-grade thermal energy conversion to electricity by incorporating zinc oxide (ZnO) nanoparticle-modified MXene (ZNM- MXene) into cellulose nanofiber (CNF) films. The vacuum filtering approach produces CNF@ZNM-MXene composite films with enhanced photothermal conversion efficiency, capillary hydrophilicity, and thermal localization. Because of its rapid water transport capability, excellent sunlight absorption, and efficient solar-thermal conversion under 1 kW m−2 irradiance, the CNF@ZNM-MXene solar evaporator's evaporation rate reaches 1.27 kg m−2 h−1, and the solar-vapor conversion efficiency is as high as 82.15%, outperforming most previously reported solar evaporators. Moreover, when compared to a standalone thermoelectric (TE) module, the output power of the solar thermal conversion system coupled with a CNF@ZNM-MXene composite films and a TE module is boosted by 15.32 times. This work offers a practical and effective method for simultaneously capturing solar energy and desalinating saltwater.

Is there a fast track (“Darmstrasse”) for fluids in the small intestine? Evidence from magnetic resonance imaging

BackgroundThe transit and distribution pattern of fluids in the small intestine is a key parameter for the dissolution and absorption of drugs. Although some information is known about the small intestinal water content after administration of fluid volumes and meals, the intestinal transit of orally ingested fluids and solutions has been barely investigated. The aim of this three-arm, cross-over, 9-subject human study was to investigate the transit of orally ingested water in the small intestine under fasting and postprandial conditions using MRI. To identify the ingested water, manganese gluconate, which can be identified with T1-weighted MRI sequences, was added as a marker. Using Horos (DICOM software), quantification of the distribution of Mn2+ ions in the gastrointestinal tract in fasted versus fed state (standard meal by FDA guidance and a light meal) was possible. The distribution and approximate wetted intestinal length was very similar in the fasting and postprandial states, suggesting rapid transport of water ingested after a meal through the chyme-filled small intestine in continuation of the “Magenstrasse” (stomach road). In some subjects, manganese gluconate reached deeper parts of the small intestine even more quickly in the postprandial state than in the fasting arm of the study. A deeper understanding of the behaviour of solutes in the gastrointestinal tract is fundamental to a mechanistic explanation for the kinetic interaction between food and drug intake (food effects).

Chinese yam-derived aerogel as a versatile platform for efficient freshwater production and pollution remediation

Water scarcity and pollution have become major obstacles to sustainable global development. The development of a versatile platform that can simultaneously produce clean water and remediate pollutants from water is highly desirable but still difficult to realize. Herein, to address this challenge, we have developed a CY@PPy@Ag aerogel with excellent photothermal and photocatalytic capabilities through a freeze-drying process, followed by polypyrrole coating and Ag deposition. The excellent characteristics, including broad-spectrum light absorption (97.2%), localization of converted heat, rapid water transport, and porous open microchannels, enabled it to act as an advanced solar evaporator for efficient and continuous steam generation without salt crystallization. Moreover, the high evaporation rate (1.51 kg m−2 h−1) was maintained even in high concentrations of brine and real seawater. Taking advantage of its enhanced photocatalytic performance, organic dyes in water could be rapidly and completely decomposed by the CY@PPy@Ag aerogel under solar irradiation, and this photodegradation process was significantly accelerated with the help of NaBH4. This work is expected to provide a one-stone-two-birds strategy to simultaneously achieve clean water harvesting and pollution remediation, which holds great promise in the fields of solar energy harvesting, wastewater treatment, and seawater desalination.

Role of Carbon Nanotube Wetting Transparency in Rapid Water Transport for a Nanopore Membrane.

A carbon nanotube (CNT) may facilitate near-frictionless water transport within it. In this work, we elucidate the slip flow characteristics for a CNT embedded in a silicon nitride matrix using the molecular dynamics (MD) method. We reveal that the wetting transparency of a CNT, the transmission of the membrane matrix wetting property over a CNT, cannot be ignored. Due to the effect of CNT wetting transparency, the orientation flip behavior of water molecules should be the primary cause of the entrance and exit losses, which is a dominant factor influencing the interfacial friction coefficient for the thin CNT membrane. The relationship between the friction coefficient and pore size follows a logarithmic function, which agrees well with the reported experimental data. Our findings bridge the gap between the MD prediction and experimental observation for water transport in a CNT membrane and provide a clear understanding of the mechanism behind its ultrafast flow performance.

JUJUNCAO-Stem-Based Interfacial Solar-Driven Evaporator with Natural Two-Phase Composite Structures of Functional Partition and Inherent Ultralow Vaporization Enthalpy of Water for Stable and Efficient Steam Production.

The interfacial solar-driven evaporation has been deemed as an environmentally friendly approach for freshwater generation. Nevertheless, there is still a challenge to obtain solar evaporators with efficient vapor production from low-cost and renewable biomass through a simple preparation process. Herein, the JUJUNCAO stem was selected as the substrate material, and a kind of interfacial solar-driven evaporator with natural two-phase composite structures and inherent ultralow water vaporization enthalpy was constructed by a dip-coating process. The natural two-phase composite structures were utilized as independent functional partition: the low-tortuosity and hydrophilic vascular bundles served as hierarchical channels for rapid water transportation and continuous steam escape, and the honeycomb-like parenchyma cells were considered natural heat insulators for effective thermal management. Furthermore, the JUJUNCAO stem exhibited inherent ultralow water vaporization enthalpy which was only 1.15 kJ g-1. Benefiting from the natural two-phase composite structures of functional partition and inherent ultralow water vaporization enthalpy, the C-Js evaporator could achieve an evaporation rate of 2.77 kg m-2 h-1 with an efficiency of 85.6% under 1 sun illumination. Meanwhile, the C-Js exhibited a stable and ideal evaporation performance and metal ion rejection behavior in the actual brine desalination process. Owing to the cost-effective and simple pretreatment process, the C-Js evaporator has the potential for freshwater generation in undeveloped areas.

Constructing hydrophobic microenvironment in the separation layer by a small molecule for improving reverse osmosis membrane performance

The development of reverse osmosis (RO) membranes with both high permeability and selectivity is a key goal for RO technology, the leading water treatment technology. This work presents a simple and cost-effective method for improving RO membrane performance obviously via introducing a hydrophobic small molecule, benzoic acid (BA), in the polyamide (PA) separation layer. The introduction of BA is achieved by adding it in the oil phase of the interfacial polymerization technology because of its oil solubility, which is pretty simple. The hydrophobicity and self-assembly characteristic of BA could establish hydrophobic microenvironments within the PA separation layer. The hydrophobicity of this microenvironment can reduce the number of hydrogen bonds between water molecules, accelerating the rapid transport of water and thereby enhancing membrane performance. Concurrently, BA as a small molecule could moderately increase the space between PA chains and thus enlarge the free volume of hydrophobic microenvironment region, which is also in favour of the improvement of membrane flux. The as-developed RO membrane possessed both high rejection rate (with a NaCl rejection rate of 98.9 %) and high flux (91.7 L m−2 h−1) under the brackish water testing condition, surpassing the performance of many previously reported membranes, and noticeably, a flux increase of 113 % was achieved by utilizing BA. Besides, the performance showed a good long-term stability. It is worth mentioning that small molecules are generally purchasable and cheap, which is beneficial to the large-scale production. This work showcased the great potential of hydrophobic small molecules in improving PA water treatment membrane performance, paving the way for diverse small molecules to develop PA water treatment membrane with both high permeability and selectivity.

High-performance desalination through tortuous pathways in multilayer ABC-stacked large-pore covalent organic frameworks: a theoretical study

The optimal integration of stacking pattern, skeleton width and pore size enhances desalination performance by facilitating rapid water transport via tortuous pathways while effectively hindering ion transmission due to the presence of the skeleton.

A durable hydrophobic photothermal membrane based on a honeycomb structure MXene for stable and efficient solar desalination.

Solar powered water evaporation is a green and environmentally friendly water treatment technology, which is a hot research topic for water purification at present. Advanced structural design and hydrophilic photothermal materials have achieved efficient solar evaporation of pure water, but the long-term stability of high salinity desalination has become a problem that cannot be ignored in practical applications. In order to solve this problem, a hydrophobic honeycomb structure MXene/AuNFs composite membrane was proposed in this paper, which used the three-dimensional highly porous microstructure of MXene and multibranched structure of gold nanoflowers particles to improve the light absorption and photothermal conversion efficiency of MXene/AuNFs. At the same time, the surface of the composite membrane was modified with hydrophobic fluorosilane 1H,1H,2H,2H-perfluorodecyltriethoxysilane (PFTE). The hydrophobic layer can prevent the accumulation of salt particles on the surface of the membrane, so that the composite film can continue to produce water vapor in a high salt environment. With high utilization rate of light energy, multiple-level geometrical structures of MXene for rapid water transport on the filter membrane and salt barrier on the membrane good stability, the hydrophobic MXene/AuNFs achieves solar evaporation rate of 1.59 kg m-2 h-1 and solar conversion efficiency is 97.8%, and stable operation under simulated sea water conditions under one sun irradiation over more than 10 cycles. The hydrophobic MXene/AuNFs membrane proved to be an efficient and stable photothermal material for solar desalination.

Developing a highly efficient, environmentally friendly and cost-effective copper sulfide semiconductor sponge for nuclear wastewater treatment under one sun

Solar-driven interfacial evaporation technology, as a green and low-energy water treatment method, finds widespread applications in desalination, power generation, and wastewater treatment systems. In this study, a three-dimensional sponge solar evaporator was prepared using hydrophilic compounds (konjac glucomannan, KGM) and a solar absorber (copper sulfide, CuS). In a single instance of solar irradiation, the sponge demonstrated swift evaporation rates at 1.58 kg m−2 h−1, coupled with an impressive interfacial water evaporation efficiency of 94.30%. Due to the characteristics of CuS and KGM, the sponge demonstrated photothermal properties, insulation, and rapid water transport. Even under radiation (1 kW/m2) and a wide range of pH conditions (pH∼2–12), the concentration of elements in radioactive wastewater could be reduced by a million times (from 1 g/L to 0.253 μg/L). Notably, during 20 cycles of testing, the sponge's evaporation efficiency only decreased by 1.13%. Furthermore, over an extended 5-hour evaporation period, it consistently sustained a steady evaporation rate of 1.577 kg m−2 h−1, showcasing its exceptional reproducibility and enduring resilience. Therefore, solar-driven interfacial evaporation technology exhibits significant potential for efficient treatment of radioactive wastewater.

Three-dimensional X-ray imaging of macropore flow

Macropores are known to be important pathways for the rapid transport of water, solutes and colloids in soil. Nevertheless, we still know very little about how the topology and geometry of macropore networks govern water flow configurations and velocities in natural soil. In this study, we aimed at gaining more insight into macropore flow by using X-ray tomography to quantify air–water distributions in the macropore networks of undisturbed topsoil and subsoil columns of a clay soil at varying steady-state flow rates. We observed that while large fractions of the macropore network remained air-filled, the air phase only became entrapped when the irrigation rate was very close to the saturated hydraulic conductivity of the soil. The data enabled us to parameterize a kinematic wave model for water flow following the approach proposed in Jarvis et al. (2017a). Follow-up experiments would be required to evaluate whether these kinematic wave parameters derived by X-ray imaging match with those obtained from outflow measurements. We found that quantitative X-ray imaging of macropore flow through soils still remains a challenging task. We recommend that future experiments are conducted on smaller soil samples to improve image resolution and minimize experimental time spans as well as X-ray image noise and illumination bias. Such experiments could also include 3-D tracer imaging to identify the imaged macropore networks transporting most of the water (i.e. the backbone) at varying steady irrigation rates.

In situ polymerization of three-dimensional polypyrrole aerogel for efficient solar-driven interfacial evaporation and desalination

Solar-driven interfacial evaporation (SIE) and desalination is a promising approach to mitigate the scarcity of freshwater resources. Here, a three-dimensional polypyrrole (3D PPy) aerogel was prepared by in situ polymerization of pyrrole to serve as an independent evaporator. The interconnected pore structure and super-hydrophilicity enabled PPy evaporators with rapid water transport to the top interface (< 5 s). The hydrogen interaction between polymer chains and water molecules induced large amount of intermediate water, thereby reducing the evaporation enthalpy of water in PPy aerogels. As a result, the optimized PPy aerogel attained an evaporation rate of 2.90 kg m−2 h−1 and an energy conversion efficiency of 114% under 1 sun irradiation. Moreover, the generated steam can be accelerated by the convection and an evaporation rate as high as 6.10 kg m−2 h−1 was realized at 2.5 m s−1. The rapid water transport also enabled PPy aerogel with high-efficiency of self-salt-discharge and efficient desalination for 3.5 wt% brine under 2.5 m s−1. In the outdoor SIE experiment, the excellent evaporation performance was achieved at 12:40 (7.04 kg m−2 h−1 under 74.2 mW cm−2 of solar intensity and 2.5 m s−1 of convective flow), and the cumulative evaporation of 41.50 kg m−2 for successive 9 h was obtained. After the evaporation of simulated seawater and heavy metal wastewater, the concentration of collected fresh water could be reduced about 2–3 orders of magnitude. This 3D PPy evaporation platform with high light absorption, porous structure, super-hydrophilic property, effective steam diffusion, and excellent salt resistance provides an effective way to develop advanced solar-driven water treatment technology.