Superhydrophobic Carbon Nanotube Research Articles

Super high flux oil/water separation and efficient separation of water-in-oil emulsions by a versatile superhydrophobic multi-walled carbon nanotubes coating

This study presents a fabrication method of superhydrophobic coating for efficient oil/water separation application from modified multi-walled carbon nanotubes (MWCNTs) and epoxy resin. Exceptional superhydrophobic (CA = 155.5°, SA = 4.6°) and superoleophilic (CA ≈ 0°) behaviors were demonstrated by spraying the superhydrophobic MWCNTs coating onto 250# stainless steel mesh (SSM). Their separation efficiencies were as high as 98.5 % for CCl4/water mixtures, 97.2 % for chloroform/water mixtures, 98.6 % for gasoline/water mixtures, 99 % for xylene/water mixtures, and 92.5 % for petroleum ether/water mixtures, respectively. Gravity-driven separation of CCl4/water and chloroform/water mixtures achieved high oil fluxes at 77023.6 L⋅m−2⋅h−1 and 55267.2 L⋅m−2⋅h−1, respectively. Additionally, water-in-oil emulsions were effectively separated with efficiencies exceeding 99.5 %. The superhydrophobic MWCNTs coating in this study offers a versatile solution for high flux oil/water separation and efficient separation of water-in-oil emulsions.

Superhydrophobic composite membranes for membrane distillation based on CNTs networks: Overcoming the trade-off between water vapor permeability and wetting resistance

Enhancing the wetting resistance of the membrane is crucial for consolidating the stability of the membrane distillation (MD) process, but this generally leads to the decline of water vapor flux. Herein, we developed a superhydrophobic composite membrane composed of a highly hydrophobic polyvinylidene fluoride (PVDF) porous support layer and a functional superhydrophobic carbon nanotubes (CNTs) network. The CNTs network with high thermal conductivity not only reduces the temperature polarization effect, but also increases the effective evaporation area, thereby enhancing the mass transfer driving force of the MD process. Additionally, the CNTs network significantly reduces the maximum pore radius of the composite membrane, and the perfluorination treatment also reduces the surface energy of the CNTs network, thereby synergistically increasing the liquid entry pressure. The results showed that when treating high salinity water containing 3.5 wt% NaCl, the water vapor flux of the composite membrane increased from 20.0 LMH of the original PVDF membrane to 24.4 LMH, an increase of 22 %. Furthermore, the performance of the original PVDF membrane deteriorates rapidly when the concentration of surfactant in the feed exceeds 1.0 mM, while the composite membrane still maintains a stable water vapor permeability and salt rejection. More importantly, the composite membrane exhibits excellent resistance to wetting induced by gypsum scaling when using gypsum solution as the feed, which is attributed to its small surface pore size and high hydrophobicity. This research supplies new insights into the design of membrane structures used in MD processes to overcome the trade-off between water vapor permeability and wetting resistance.

A Robust Bridge‐Type Airflow Sensor Based on Flexible Superhydrophobic Carbon Nanotube Fiber Thin Films

AbstractDespite a great deal of research about airflow sensors by far, it is still hard to maintain ultra‐low limit of detection, short response, and recovery time under humid and rainy environment, which compromises its practical applications. Herein, a robust bridge‐type airflow sensor base on flexible superhydrophobic carbon nanotube fiber thin films is developed, which can not only own remarkable sensitive properties with ultra‐low limit of detection, fast response, and rapid recovery, but also exclude the influence of moisture or water drops in real applications. Both response time and recovery time are reduced compared with that of the previously reported flexible carbon‐based airflow sensors. Particularly, recovery time is reduced by ≈2/3. Meanwhile, the superhydrophobic structure renders normal functioning of the sensor in severe environment of high humidity or even in the rain, so that the influence of moisture and raindrops can be excluded, a property deficient in the previously reported airflow sensors. Not only can the sensor detect ambient airflow sensitively, but it also exhibits outstanding performance in respiratory health monitoring. Hence, the novel sensor designed in this work realizes operation in the environment of high humidity and rain, which tremendously uplifts the applicability of flexible sensors.

Superhydrophobic and Stretchable Carbon Nanotube/Thermoplastic Urethane-Based Strain Sensor for Human Motion Detection

Challenges to developing new types of stretchable and flexible strain sensors with high sensitivity, good stability, and high antifouling properties still exist. Here, through a layer-by-layer self-assembly method, we successfully prepared a superhydrophobic carbon nanotube (CNT)/thermoplastic urethane (TPU) nanocomposite fibrous mat. CNT was used to construct the conductive layer, and polyhedral oligomeric silsesquioxane (POSS) and 1H,1H,2H,2H-perfluorooctyltrimethoxysilane (FAS) were used to form the hydrophobic layer. The obtained CNT/F-TPU mat possessed good hydrophobicity and mechanical stability; meanwhile, it exhibited a remarkable tensile property up to 550% strain. The CNT/F-TPU-based strain sensor showed an excellent sensing performance, including stable sensitivity, fast responsivity, and excellent repeatability. It can successfully detect not only large deformation movements of the human body, such as the bending of fingers, wrists, elbows, and knees, but also output stable signals for small deformation, such as smiling, blinking, swallowing, and vocalizing. This superhydrophobic CNT/F-TPU nanocomposite fibrous mat shows great potential for developing high-performance strain sensors suitable for monitoring human health and designing wearable devices.

Facile fabrication of SWCNT film-based superhydrophobic cotton fabrics for oil/water separation and self-cleaning

With the increase of oily waste, oil-water separation has become an urgent and difficult task. However, the current challenge is to fabricate such efficient membrane materials for oil-water separation. Herein, superhydrophobic single-walled carbon nanotubes (SWCNTs)/cotton fabric (CF) was prepared via a dry process. In which the ultrathin SWCNT films with a low content of hydrophilic groups were prepared by a facile floating catalyst chemical vapor deposition method and directly deposited on CF without solvent dispersion. The obtained SWCNT@CF was further treated by 1 H,1 H,2 H,2 H-perfluorooctyltriethoxysilane (POTS). Due to the synergistic effect of SWCNTs and POTS, the POTS-modified SWCNT@CF displayed excellent superhydrophobicity with a water contact angle（WCA）of ∼163.3°, and consequently can be further used as a membrane for oil-water separation. These superhydrophobic fabrics have high oil/water separation efficiency (99.2% for dichloromethane/water) and high oil flux (28.71 ×103 L·m−2·h−1 for dichloromethane/water). Even after 25 separation cycles, oil/water separation efficiency and oil flux maintain 98.8% and 25.15 × 103 L·m−2·h−1, respectively. In addition, it exhibits high separation efficiency (∼99%) for water-in-oil emulsion. Moreover, under extreme environmental conditions, the contact angle of the obtained POTS-modified SWCNT/CF was maintained at ∼155°, keeping stable superhydrophobicity. This reported preparation strategy of superhydrophobic fabrics is environmentally friendly, low cost, sustainable, and easy to scale up, thereby exhibiting great potential in practical applications.

Robust superhydrophobic TiO2@carbon nanotubes inhibitor with bombax structure for strengthening wellbore in water-based drilling fluid

Shale gas has become one of the most promising energies to cope with the ever-increasing energy demand, while wellbore instability incidents frequently occur due to the hydration and subsequent swelling of shale during the long horizontal drilling process. In this paper, a novel superhydrophobic carbon nanotube composite for high-efficiency water-based drilling fluid was prepared by the combination of the chemical vapor deposition method and the in-situ precipitation method. The prepared composite can form a superhydrophobic adsorption layer with high roughness and low surface free energy on the rock surface, achieving hydration inhibition by wettability alteration. The functional groups, surface morphology, electrical properties, and element valence of the synthesized composite were characterized by FTIR, SEM, zeta potentiometer, and XPS technique, result evidenced that the product was prepared as expected design. The effect of superhydrophobic carbon nanotube composites on the rheology and filtration properties of drilling fluid was studied, the drilling fluid can maintain favorable viscosity and shear force after adding the composite; the linear expansion rate test, the contact angle measurement, and lubrication experiments were performed to evaluate the inhibition and lubrication performance, the linear expansion rate of core decreased from 59.1 % to 21.9 % after treated with 1 % composite solution for 16 h, the wettability of rock surface can be altered from liquid-wetting to strong hydrophobicity, the reduction rate of extreme pressure lubrication coefficient was 46.9 %, and the zeta potential of shale decreased with the increasing concentration of composite. The possible explanation for its excellent performance could be that the superhydrophobic carbon nanotube composite can form a dense hydrophobic adsorption layer on the shale surface through electrostatic attraction, and an anchoring structure between the neighboring crystal lattices can be preferentially formed by the amino groups in the non-polar end of the molecule, which can alleviate the intrusion of drilling fluid, achieving the inhibition of the hydration and expansion of shale.

A superhydrophobic carbon nanotube hollow fiber membrane for electrically self-heating membrane distillation

Self-heating membrane distillation has been considered as an alternative technology to alleviate water crisis, while the unsatisfactory energy efficiency and distillate flux limit the practical application. Herein, an all-in-one conductive hollow fiber membrane without supporting layer was fabricated, in which carbon nanotube (CNT) guaranteed the rapid electro-thermal conversion and polydimethylsiloxane (PDMS) endowed the composite membrane with superhydrophobicity to enhance membrane stability. The narrow channel of the hollow fiber membrane encircled the feed solution in a localized space to achieve efficient vaporization, which was benefit for both high higher distillate flux and low energy requirement. As a result, the CNT/PDMS hollow fiber membrane obtained a high distillate flux of 24.27 ± 0.89 kg m−2 h−1 and salt rejection rate > 99.9 % under 2.5 W input power with a flow rate of 12.81 mm s−1. Meanwhile, this membrane displayed a superior salt-resistance with increasing of the feed solution concentration from 10 g L−1 to 100 g L−1. For actual seawater desalination, the concentration of representative ions in collected water met the requirement standard of soft drinking water, indicating a great feasibility in practical application. Thus, this energy-efficient hollow fiber membrane provides a promising avenue to fabricate high-performance self-heating membrane for membrane distillation.

Natural rubber reinforced with super-hydrophobic multiwalled carbon nanotubes: obvious improved abrasive resistance and enhanced thermal conductivity

Abstract Polyurethane chain was successfully grafted onto carbon nanotubes, affording polyurethane-functionalized multiwalled carbon nanotubes (P-MWCNTs) with super-hydrophobic property, which shows improved abrasive resistance obviously and enhanced thermal conductivity for natural rubber (NR) vulcanizate. Under the optimized conditions, the akron abrasion loss of NR vulcanizate combined with 5 parts per hundred rubber (5 phr) P-MWCNTs is 0.9 cm3/1.61 km compared to 2.96 cm3/1.61 km of pristine NR vulcanizate. The thermal conductivity of NR vulcanizate combined with 5 phr P-MWCNTs has been improved by 40.3% compared to that of pristine NR vulcanizate. The decreased height of the maximum tan δ peak shows that P-MWCNTs can reduce the heat buildup and damping capability of NR/P-MWCNTs composites. The good dispersion of P-MWCNTs with a continuous network, particularly at high loading (5 phr) in the NR composites, was evidenced from transmission electron microscopy (TEM).

Ultrasensitive and Recyclable Multifunctional Superhydrophobic Sensor Membrane for Underwater Applications, Weather Monitoring, and Wastewater Treatment.

Although flexible sensors have attracted considerable attention in emerging fields, including wearable electronics and soft robotics, their stability must be considered in practical applications, especially the effects of external factors on the sensing performance. Herein, a recyclable flexible sensor with superhydrophobicity and a highly sensitive strain response was developed by combining electrospinning and ultrasonication anchoring techniques. The constructed hierarchical network structure is composed of the fluorine-free superhydrophobic multiwalled carbon nanotubes and a porous elastomer membrane substrate reinforced by nanoparticles. The obtained sensor exhibited exceptional strain-sensing performance in terms of ultrahigh sensitivity (maximum gauge factor of 12 172.46), a fast response time of 80 ms, and excellent durability (10 000 cycles). Based on these outstanding merits, the strain sensor can detect various human motions without being interfered with by harsh environments. Moreover, superhydrophobic membranes can be combined with electronic devices for weather monitoring and underwater sensing. Noteworthily, damaged sensors can be quickly dissolved by a small amount of cyclohexane, enabling material recovery. The recyclable multifunctional membranes could reduce the potential pollution to the environment and show highly promising applications in complex environments.

Superhydrophobic Carbon Nanotube Network Membranes for Membrane Distillation: High-Throughput Performance and Transport Mechanism.

Despite increasing sustainable water purification, current desalination membranes still suffer from insufficient permeability and treatment efficiency, greatly hindering extensive practical applications. In this work, we provide a new membrane design protocol and molecule-level mechanistic understanding of vapor transport for the treatment of hypersaline waters via a membrane distillation process by rationally fabricating more robust metal-based carbon nanotube (CNT) network membranes, featuring a superhydrophobic superporous surface (80.0 ± 2.3% surface porosity). With highly permeable ductile metal hollow fibers as substrates, the construction of a superhydrophobic (water contact angle ∼170°) CNT network layer endows the membranes with not only almost perfect salt rejection (over 99.9%) but a promising water flux (43.6 L·m-2·h-1), which outperforms most existing inorganic distillation membranes. Both experimental and molecular dynamics simulation results indicate that such an enhanced water flux can be ascribed to an ultra-low liquid-solid contact interface (∼3.23%), allowing water vapor to rapidly transport across the membrane structure via a combined mechanism of Knudsen diffusion (more dominant) and viscous flow while efficiently repelling high-salinity feed via forming a Cassie-Baxter state. A more hydrophobic surface is more in favor of not only water desorption from the CNT outer surface but superfast and frictionless water vapor transport. By constructing a new superhydrophobic triple-phase interface, the conceptional design strategy proposed in this work can be expected to be extended to other membrane material systems as well as more water treatment applications.

A general tape-coating strategy to construct multifunctional superhydrophobic surfaces with self-adhesion, self-healing, and conductivity on various substrates

Recently, integrating multifunctionality into superhydrophobic surfaces is becoming a tendency to meet the complexity of substrates and practical applications. However, the types of multifunctional superhydrophobic surfaces are limited and effectively constructing superhydrophobic surfaces on random substrates especially with special materials, environments, or shape is still a challenge. Herein, a tape-strategy to obtain superhydrophobic surfaces with special properties just by a simple pasting process is reported. In detail, multifunctional superhydrophobic tape is achieved through the method of spraying the superhydrophobic conductive carbon nanotubes on polyurethane (PU) coating, which could conveniently manufacture the superhydrophobic surfaces on various solid substrates (Al, CF/EP, polyimide, and glass). Depending on the proper crosslinking density of PU, existing of disulfide-bond, and uniform distribution carbon nanotubes, the obtained tape endows the solid surfaces with the multifunctional performance of superhydrophobicity, desirable self-adhesive/self-healing properties as well as conductivity. Moreover, the tap could fabricate arbitrary patterns by a simple pasting and heating process, which is adaptable for various shapes or substrates. Generally, this work provides new sights for fabricating multifunctional superhydrophobic surfaces, and the tap would have promising potential in electromagnetic stealth cloth, various multifunctional sensors, the motion monitoring, or other applications in future.

Superhydrophobic Carbon Nanotube–Metal Rubber Composites for Emulsion Separation

Superhydrophobic Carbon Nanotube–Metal Rubber Composites for Emulsion Separation

Near Superhydrophobic Carbon Nanotube Coatings Obtained via Electrophoretic Deposition on Low‐Alloy Steels

Sucker rods are a key element in certain oil‐extraction processes as they link the motor group on the surface with the pumps located downhole. During the transport from the production site toward the extraction well, these components are prone to corrosion. A hydrophobic carbon nanotube (CNT) coating, deposited via electrophoretic deposition (EPD), is proposed as a protective layer, shielding the rods from harsh environmental conditions. Three different coating systems are considered and thoroughly characterized (depending on the additive that is used to deposit the CNT), namely, magnesium nitrate hexahydrate (Mg–Nit), triethylamine (TEA), and a duplex coating (DD). The latter presents an approach which combines the advantages of each additive, mechanical stability from Mg–Nit and strong hydrophobicity from TEA (near superhydrophobic). The former coatings are further processed to overcome their individual shortcomings, resulting in an increase in the coating's stability for TEA coating, as well as transforming the hydrophilic Mg–Nit surface into a hydrophobic surface.

Improved wettability and enhanced ionic transport in highly porous CNT sponge

We investigated the effect of an electric treatment on the wettability of aqueous solution on carbon nanotubes (CNT) and ion transport behaviors in superhydrophobic porous carbon nanotube sponges (CNTS). This electric activation treatment where an electric voltage was applied across highly porous CNT sponge induced an electrowetting effect. This effect significantly reduced interfacial tensions between CNT sidewalls and aqueous liquids. Meanwhile, polar functional groups were also introduced on CNTs. Both electrowetting effect and polar functional groups greatly improved the wettability of aqueous solutions on CNT sidewalls. After the electric treatment, we observed a dramatic increase in the overall rate of ion flow across porous CNT sponges. The formation of solution channels during the electric treatment is responsible for the enhanced ionic transport in porous CNT sponges. The overall rate of ion flow increased with the increases in electric treatment time and voltage. The crucial role of electric treatment parameters in the ion transport provides a new strategy for precisely controlling the ion transport across CNT sponges by tuning electric treatment time or voltage. Importantly, the good wettability of aqueous solution on CNT sidewalls greatly increased the effective surface area of CNT sponges and thus significantly improved the performance of CNTS-based supercapacitors after the electric treatment.

Flexible Superhydrophobic Metal-Based Carbon Nanotube Membrane for Electrochemically Enhanced Water Treatment.

Treatment of highly saline wastewaters via conventional technology is a key challenging issue, which calls for efficient desalination membranes featuring high flux and rejection, low fouling, and excellent stability. Herein, we report a high-strength and flexible electro-conductive stainless steel-carbon nanotube (SS-CNT) membrane, exhibiting significantly enhanced anticorrosion and antifouling ability via a microelectrical field-coupling strategy during membrane distillation. The membrane substrates exhibited excellent mechanical strength (244.2 ± 9.8 MPa) and ductility, thereby overcoming the critical bottleneck of brittleness of traditional inorganic membranes. By employing a simple surface activation followed by self-catalyzed chemical vapor deposition, CNT was grown in situ on SS substrates via a tip-growth mechanism to finally form robust superhydrophobic SS-CNT membrane. To address the challenging issues of significant corrosion and fouling, using a negative polarization microelectrical field-coupling strategy, simultaneously enhanced antifouling and anticorrosion performance was realized for treatment of organic high salinity waters while exhibiting stable high flux and rejection via an electrostatic repulsion and electron supply mechanism. This application-oriented rational design protocol can be potentially used to extend toward high performance composite membranes derived from other electro-conductive metal substrates functionally decorated with CNT network and to other applications in water treatment.

MWCNTs polyurethane sponges with enhanced super-hydrophobicity for selective oil–water separation

ABSTRACTIn this work, long-chain hexadecyl siloxane groups were introduced into hydroxylated multi-walled carbon nanotubes (MWCNTs-OH) to obtain modified carbon nanotubes (CNTs) with super-hydrophobic characteristics. A novel super-hydrophobic/super-oleophilic polyurethane sponge (SH-MWCNTs@PU sponges) was achieved by performing further surface-modification with the super-hydrophobic CNTs via the immersion-coating process. The results showed that SH-MWCNTs@PU sponges exhibited excellent super-hydrophobic properties, with a water contact angle of 157.4 ± 1.1°, and water droplets roll-off angle of only 6.7°. In addition, its mechanical strength was greatly improved by the introduction of CNTs. Significantly, it exhibits excellent adsorption capability for different oils and organic solvents. The initial oil adsorption capacity is still maintained with a contact angle of 152.2° after 10 oil adsorption cycles, demonstrating good reusability of the SH-MWCNTs@PU sponges. The low-cost (the used MWCNTs-OH are industrial-grade), durable, and super-hydrophobic sponge is a promising material for oil–water separation with high efficiency and selectivity.

Highly conductive, washable and super-hydrophobic wearable carbon nanotubes e-textile for vacuum pressure sensors

Electronic textiles (e-textiles) have shown promise applications in wearable electronics and multifunctional smart clothes due to the combination of the advanced electronic functions, ultra-lightweight and flexibility. In this work, we report the functionalized conductive, sensitive, wearable and washable vacuum pressure sensor based on carbon nanotubes (CNTs) e-textile with unique nanostructures growth on the non-woven fabric (NWF) by using the novel and facile nano-soldering method. The electronic resistance of the CNTs e-textile sensor is sensitive to vacuum pressure and show the good linearity, the high sensitivity with a maximum sensitivity of 3.06, the wide measurement ranges from 7.3×10−5 to 1.0 ×103 mbar, and low power consumption of 0.21 mW. And the pressure sensitive mechanism is discussed, and the oxygen chemisorption and energy band were used to reasonably explained it. Moreover, the conductive CNTs e-textile sensors show good repeatability, washability, durability and super-hydrophobic performance, and it can be used for smart clothes, flexible sensors by monitoring vacuum pressures in real time.

Facile Single-Step Fabrication of Robust Superhydrophobic Carbon Nanotube Films on Different Porous Supports

Superhydrophobic carbon nanotube (CNT) films have attracted extensive research attention because of the superior CNT properties that have a significant impact on the mass/energy transfer at the CNT/liquid interface. Until now, most reported methods for producing superhydrophobic CNT films require multiple steps, making the fabrication process very complicated and time-consuming, and may deteriorate the CNT intrinsic properties. In this study, superhydrophobic CNT films composed of short CNT strands were fabricated through a single-step chemical vapor deposition method on various types of supports, including hollow fiber and disc supports. Attributed to its firm structure, this durable superhydrophobic film could withstand water invasion and show promising stability and renewability during a 4-week wettability test. Benefiting from the preservation of CNT properties without post modifications, the film exhibited excellent chemical robustness to corrosive liquids from pH = 0–14. In addition, the application...

Strong and super-hydrophobic hybrid carbon nanotube films with superior loading capacity

Superhydrophobic surface has attracted enormous interests due to its attractive potential applications. Here, we prepare all carbon nanotube hybrid films simply by depositing multi-walled carbon nanotubes on strong single-walled carbon nanotube films through vacuum filtration. The hybrid films behave some exciting superhydrophobic properties of a large water contact angle of 152° and an ultra-low sliding angle of only 2°. The rebounding height of a water droplet dipping from 5 cm above the hybrid film reaches 9.4 mm, which is 3 times that of on the natural lotus leaf. The superhydrophobic hybrid film also have high specific loading capacity of 627 g/g, more than 12 times that of the natural lotus leaf. The hybrid films can mimic lotus leaf in water repelling, self-cleaning, and carrying heavy things quite well.

Super high-rate fabrication of high-purity carbon nanotube aerogels from floating catalyst method for oil spill cleaning

In this study, we apply an advanced floating catalyst method to fabricate carbon nanotube (CNT) aerogels at super high deposition rate for oil spill cleaning. The aerogels consist of 3D porous network of stacking double-walled CNT bundles with low catalyst impurity (9%) and high thermal stability (650 °C). With high porosity, surface areas, and water contact angles, the CNT aerogels exhibit a high oil adsorption of up to 107 g/g and good reusability of up to four adsorption-burning cycles. This work suggests that the lightweight, porous, and super hydrophobic CNT aerogels can be promising sorbent materials for environmental applications.