Fluorinated Multi-walled Carbon Nanotubes Research Articles

One-step spraying preparation of omniphobic membrane with anti-wetting behavior for membrane distillation

Membrane distillation (MD) with the application of omniphobic membranes shows much promise for desalinating saline wastewater containing low surface tension contaminants. However, the complicated membrane production steps and the wetting of the membranes have hindered its industrial application. This study reported a simple and highly efficient air spraying strategy to fabricate an omniphobic membrane by spraying a coating solution comprising fluorinated multi-walled carbon nanotubes (F-MWCNTs) onto a commercial polytetrafluoroethylene (PTFE) membrane. The contact angles for water and hexadecane on the surface reached 173.0° and 161.2°, and the water flux remained stable for 12 h when tested in DCMD with low surface tension fluids (SDS and STAC). The omniphobic membrane showed higher wetting resistance in direct membrane distillation (DCMD) experiments than the PTFE membrane when feeding low surface tension feed solutions. During spraying, F-MWCNTs randomly accumulated, and solvent evaporation resulted in micron-level mounds and surface roughness. The presence of air gaps on the membrane surface prevented the surfactant molecules from directly contacting the membrane surface and enabled the membrane to operate generally in the liquid with surfactant for a long time. The membrane was not only resistant to wetting of liquids containing low surface tension but was also easy to prepare and was expected to be used for large-scale desalination of low surface tension wastewater.

Oil/water separation membranes with stable ultra-high flux based on the self-assembly of heterogeneous carbon nanotubes

Due to the problem of membrane fouling, the preparation of oil/water separation membranes with stable ultra-high flux is still a challenge. At present, ultra-hydrophilicity is the main antifouling strategy, which indeed renders ultra-high base flux and high flux recovery rate. However, the flux usually declines to a low level during the real oil/water separation. With the assist of low surface energy (LSE) strategy, the flux stability can be remarkably enhanced, but at the cost of the reduced base flux. In order to combine the advantages of hydrophilic and LSE strategies, and avoid the undesired side effects of the LSE strategy, the distribution of hydrophilic and LSE microdomains on membrane surfaces is rationally designed and accurately manipulated in this study. Membranes are prepared by the vacuum-assisted self-assembly of heterogeneous carbon nanotubes (HCNTs), which consist of fluorinated multi-walled carbon nanotubes (FMCNTs), amino multi-walled carbon nanotubes (AMCNTs) and carboxylic single-walled carbon nanotubes (CSCNTs). AMCNTs and CSCNTs form great-area continuous and high porous hydrophilic microdomains through membranes, providing high base flux. FMCNTs form discrete linear LSE microdomains, providing good flux stability via LSE antifouling strategy. Except for the ultra-hydrophilic strategy, this study provides a reasonably and accurately manipulated LSE strategy in the energy-efficient membrane water treatment.

Air nanobubbles (ANBs) incorporated sandwich-structured carbon nanotube membranes (CNM) for highly permeable and stable forward osmosis

The selective transport of water/ions through conventional forward osmosis (FO) membranes is largely impeded by solution-diffusion and internal concentration polarization (ICP). Herein, we report a novel air nanobubbles (ANBs) incorporated sandwich-structured carbon nanotube membrane (CNM) for highly permeable and stable FO desalination by taking advantage of the nanofluidic transport at the solid/liquid/vapor interface. Fluorinated multi-walled carbon nanotubes (F-MWCNTs) were assembled as the superhydrophobic interlayer between a hydrophilic cellulose acetate (CA) layer and a hydrophilic polyacrylonitrile (PAN) nanofibrous layer. The trapped ANBs in the superhydrophobic F-MWCNT layer crucially regulated the continuous water flow and effectively prevented salt diffusion. When tested with DI water as feed solution (FS) and 1 ​M NaCl as draw solution (DS), the ANBs incorporated sandwich-structured CNM achieved high water flux (158.0 ​L ​m−2 ​h−1) and ultralow reverse salt flux (0.4 ​g ​m−2 ​h−1) simultaneously, far beyond the state-of-the-art FO membranes. The PAN nanofibrous layer well protected the entrapped ANBs to allow a more durable FO performance. An ANBs-regulated nanofluidic flow model was proposed to elucidate selective water/salt transport mechanism. This work revealed the feasibility of ANBs incorporated membranes for osmosis-driven processes.

Robust Photothermal Coating Strategy for Efficient Ice Removal.

Preventing ice formation and ice swift removal from the solid surface are essential in numerous application fields. Superhydrophobic coating is an effective way to delay the icing phenomenon. However, the superhydrophobic coating was wetted easily after icing-deicing cycles that led to the failure of anti-icing. In this study, a robust, amphiphobic coating consisted of fluorinated multiwalled carbon nanotubes (FMWCNTs) and commercial polyurethane was constructed by a simply spray process. Because of the addition of FMWCNTs, the coating demonstrated a good amphiphobic feature and highly efficient photothermal conversion, which endowed the coating surface with excellent deicing and defrosting characteristics under sunlight irradiation. In addition, self-cleaning and self-healing properties of the coating under sunlight ensured its efficient photothermal conversion and long service life. To further improve the photothermal deicing effect, a coating system containing a photothermal layer (P), thermal-conductive layer (C), and thermal-protective layer (P) was constructed. The heat generating from the photothermal layer can transfer the whole coating surface by the conductive layer, but with limited transmission to substrate materials by a thermal-protective layer. The coating system can still deice and defrost rapidly on the whole surface and only a small portion of photothermal coating was irradiated under extremely low temperature. The outdoor experiment has confirmed that the coating melted and removed snow rapidly in a winter environment. The multifunctional photothermal deicing coating may have a wide application in outdoor surrounding.

Superamphiphobic surfaces with robust self-cleaning, abrasion resistance and anti-corrosion

Superamphiphobic surfaces, capable of repelling both water and low-surface-tension liquids, are important for many applications. Simple and efficient way to fabricate superamphiphobic surfaces and their robust self-cleaning and abrasion resistance are key requirements for superamphiphobic surfaces to realize their applications. Here, superamphiphobic surfaces with extremely high contact angles (CAs) and low contact angle hysteresis for both water and low-surface-tension liquids are fabricated by a facile spray method of fluorinated multi-walled carbon nanotubes (F-MWCNTs). The fluorine content of F-MWCNTs is as high as 47.4%. The random accumulation of F-MWCNTs and the evaporation of solvent during spraying process creates appropriate surface roughness and micro-hills-like re-entrant microstructures. So, the CA for water and hexadecane on the surface reach 172.4˚ and 163.0˚, and sliding angles (SAs) are 1.2˚ and 4.3˚ respectively. Meanwhile, water and hexadecane are bouncing on this surface. Whether immersed in oil or exposed to air, the surface still possesses robust self-cleaning property. In addition, the introduction of spray adhesive greatly promotes the robustness of the coating, and the whole surface region maintains great superamphiphobic property after 40 abrasion cycle. Moreover, after soaking in acid solution with pH of 2 or alkaline solution with pH of 12 for 48 h, the CA and SA of water and hexadecane on this surface changes slightly, and this surface still holds outstanding superamphiphobicity. Furthermore, the reagents and devices required for the entire method are readily available, so it will be a potential candidate for the industrial production.

Fluorinated MWCNTs for Preparation of High-Stability Li–SnO2 Batteries

The electrochemical performance of fluorinated multiwalled carbon nanotubes (F-MWCNTs) as a new type of conductive agent for Li–SnO2 batteries has been studied. Multiwalled carbon nanotubes (MWCNTs) were fluorinated to obtain F-MWCNTs with core–shell structure (fluorocarbon atomic ratio C/F = 1:1). The unique tubular structure of the F-MWCNTs allows more Li+ ions and electrons to enter the channel around the active material CF1, which increases the electrochemical reaction effect and reduces the polarization effect of the batteries, thereby improving the utilization of the active material, and the capacity as well as the stability of the discharge plateau of the resulting batteries. The F-MWCNTs are an excellent alternative to the traditional conductive graphite. The SnO2@F-MWCNTs battery showed high specific capacity (1588.71 mAh g−1 at 100 mA g−1), excellent cycle performance (962.92 mAh g−1 after 100 cycles), excellent coulombic efficiency (99.89%), and low internal resistance in repeated electrochemical tests.

Synergistic “Anchor” Effect of Carbon Nanotubes and Silica: A Facile and Efficient Double-Nanocomposite System To Reinforce High-Performance Polyimide Fibers

Double nanofillers are becoming an important and effective strategy to reinforce and functionalize polymeric materials, and maximizing the strength of nanofillers to compensate for their weaknesses remains of great interest in the field of nanocomposite. Herein, we report a facile and efficient double-nanofiller strategy to reinforce polyimide fibers. After grafting 3-aminopropyltriethoxysilane (APTES) onto fluorinated multiwalled carbon nanotubes (F-MWCNTs), the functionalized MWCNTs, APTES@F-MWCNTs, reacted with silica sol via the reactions of Si–OH groups. Because of the formation of chemical bonds, dispersibility of MWCNTs was improved by the assistance of a grafted silica sol; MWCNTs prevent the silica sol from diffusing into a coagulation bath and being lost of silica during wet-spinning. Synergistic “anchor” effect of carbon nanotubes and silica results in a considerable improvement of mechanical properties (44.4%) of polyimide fibers and an increase in the Tg value from 348 to 381 °C.

Improving electrocatalytic activity of fluorinated multi-walled carbon nanotubes modified with tetraaminophthalocyanines for lithium/thionyl chloride battery

A series of metal 1, 8, 15, 22-tetraaminophthalocyanines [1, 8, 15, 22-TAPcM, M = Mn(II), Fe(II), Ni(II), Cu(II), Zn(II)] are synthesized and used to chemically modify fluorinated multi-walled carbon nanotubes (F-MWCNTs) with the formation of certain chemical bonds on the surface of carbon nanotubes, and the corresponding composites 1, 8, 15, 22-TAPcM/MWCNTs are obtained. The electrocatalytic activities of the samples are studied by adding them into lithium/thionyl chloride (Li/SOCl2) batteries. The results indicate that the composites 1, 8, 15, 22-TAPcM/MWCNTs can improve the discharge voltage and lengthen the discharge time of the batteries much more than 1, 8, 15, 22-TAPcM, and the order of the electrocatalytic activities of 1, 8, 15, 22-TAPcM/MWCNTs and 1, 8, 15, 22-TAPcM with different metal ions in center is both Mn(II) > Ni(II) > Zn(II) > Fe(II) > Cu(II). It is also found that the discharge time and maximal discharge voltage and capacity for the battery contains 1, 8, 15, 22-TAPcMn/MWCNTs can be improved by 68.19%, 9.41%, and 82.6%, respectively.

Low temperature preparation of highly fluorinated multiwalled carbon nanotubes activated by Fe3O4 to enhance microwave absorbing property

Conventional approaches to preparing highly fluorinated multiwalled carbon nanotubes (MWCNTs) always require a high temperature. This paper presents a catalytic approach to realizing the effective fluorination of MWNCTs at room temperature (RT). Fe3O4/MWCNTs composites with Fe3O4 loaded on MWCNTs were first prepared using the solvothermal method, followed by fluorination treatment at RT. The attachment of Fe3O4 changes the charge distribution and dramatically improves the fluorination activity of MWCNTs. Consequently, the fluorine content of fluorinated Fe3O4/MWCNTs (F-Fe3O4/MWCNTs) can reach up to 17.13 at% (almost six times that of the unloaded sample) only after fluorination at room temperature, which leads to an obvious decrease in permittivity. Besides, the partial fluorination of Fe3O4 brings about abnormally enhanced permeability due to strengthened exchange resonance. Benefiting from the lower permittivity and higher permeability, F-Fe3O4/CNTs composite exhibits increased impedance matching and thus an enhanced microwave absorption property with a minimal reflection loss of −45 dB at 2.61 mm when the filler content is 13 wt%. The efficient absorption bandwidth (<−10 dB) reaches 4.1 GHz when the thickness is 2.5 mm. This work illustrates a novel catalytic approach to preparing highly fluorinated MWCNTs as promising microwave absorbers, and the design concept can also be extended to the fluorination of other carbon materials.

Bulk Oriented UHMWPE/FMWCNT Films for Tribological Applications.

Bulk oriented films based on ultrahigh molecular weight polyethylene (UHMWPE) with a drawing ratio of 35 were prepared by using a low solvent concentration. Bulk oriented films were filled with fluorinated multi-walled carbon nanotubes (FMWCNTs). The structure of bulk oriented films on UHMWPE, which were manufactured at different stages of orientation, was investigated by scanning electron microscope (SEM) and differential scanning calorimetry (DSC). The addition of FMWCNTs at a concentration of 0.05 wt % in bulk oriented UHMWPE films led to an increase in the tensile strength by 10% (up to 1020 ± 23 MPa) compared to unfilled oriented films. However, the addition of FMWCNTs at a concentration of more than 0.5 wt % led to a decrease in tensile strength due to excessive accumulation of nanotubes and hindering of self-diffusion of UHMWPE macromolecules. The multiple increase in tensile strength, doubling the hardness, the formation of fibrillar structure, and the presence of carbon nanotubes led to a significant increase in tribological properties in bulk oriented films. Bulk oriented UHMWPE/1% FMWCNT films can be operated at a maximum contact pressure that is 18 times higher and exhibit a specific wear rate more than an order of magnitude and less than the traditional UHMWPE of isotropic structure. Bulk oriented UHMWPE/1% FMWCNT films have an extremely low dry coefficient of friction (COF) of 0.075 at a contact pressure of 31 MPa. The developed bulk oriented films can be used for manufacturing frictional surfaces for sliding bearings, or for acetabular cups for knee and hip endoprostheses.

Mechanical, tribological and heat resistant properties of fluorinated multi-walled carbon nanotube/bismaleimide/cyanate resin nanocomposites

Bismaleimide containing cyanate resin (BMI/CE) pre-ploymer was used as resin matrix. Fluorinated multi-walled carbon nanotubes (F-MWCNTs) were used as fillers to prepare F-MWCNT/BMI/CE nanocomposites via a solution intercalation method. The influence of F-MWCNT content on the mechanical, tribological and heat resistant properties of the nanocomposites was investigated. The morphology of the fracture surface and the wear surface of nanocomposites were characterized by scanning electron microscopy. Results show that the addition of F-MWCNTs is beneficial to improving the mechanical and tribological properties of the nanocomposites. It’s worth noting that when the content of F-MWNTs was 0.6wt%, the performances of nanocomposite are optimized (i.e., highest impact strength, lowest frictional coefficient and wear rate). In addition, the nanocomposites exhibit good thermal stability in comparison with BMI/CE.

Electrocatalytic performances of multi-walled carbon nanotubes chemically modified by metal phthalocyanines in Li/SOCl2batteries

​A series of metal 2,9,16,23-tetraaminophthalocyanines have been prepared and used to chemically modify fluorinated multi-walled carbon nanotubes (F-MWCNTs). The modified F-MWCNTs can dramatically improve the capacity of the Li/SOCl2battery.

Effect of high-pressure fluorination on electrical properties of multi-walled carbon nanotubes sheet

High-pressure fluorination of multi-walled carbon nanotubes (MWNTs) sheet was performed at room temperature. This fluorine treatment increases the electrical conductivity of MWNTs sheet. In addition, low-temperature conductivity measurement data gives a good fit to variable-range hopping (VRH) model. Thus, VRH model was adopted to study and understand the increase in electrical conductivity. Estimation of the degree of disorder from the experimental data and VRH model indicate that degree of disorder of fluorinated multi-walled carbon nanotubes (FMWNTs) is higher than that of MWNTs. Higher degree of disorder of FMWNTs sheet substantiate the increase in electrical conductivity when compared to MWNTs. Scanning Electron Microscopy (SEM) and Raman analysis shows that change in structural disorder of FMWNTs network. Effect of fluorination on activation energy was also studied. The activation energy reduces with lower temperatures. The estimated values of temperature coefficient of resistance also show the increase in degree of disorder of FMWNTs. The change in electrical properties of FMWNTs is a much-needed requirement in the application of nano-electronics.

Enhanced electrochemical activity of rechargeable carbon fluorides–sodium battery with catalysts

In order to improve the electrochemical performance of Na/CFx cell, fluorinated multi-walled carbon nanotubes (F-MWCNTs) and a new composite consisting of CFx, graphene nanosheets (GNS) and FeF3 (labeled as CGF for short) were employed as cathode materials in rechargeable room-temperature sodium batteries for the first time. The polarizations of Na/F-MWCNTs and Na/CGF cell were found to be 1600 and 800mV, respectively. These values were much lower than that of Na/CFx cell (2000mV). MWCNTs formed after the discharge process with intrinsic high surface area, high catalytic activity and “cage” type structure enhance charge reaction activity. Analogically, the combination of GNS and FeF3 with CFx provides more active sites to facilitate the decomposition of NaF during charge process. Moreover, the CGF electrode may have specific channels to avoid the dissolution of fluorine into the electrolyte similarly as the structure function of the F-MWCNTs electrode, leading to much better cycling performance. Overall, our results have demonstrated that the electrochemical performance of Na/CFx cell can be greatly improved by using MWCNTs and FeF3–GNS as catalysts.

Multi-Walled Carbon Nanotubes Chemically Modified by Cobalt Tetraaminophthalocyanines with Excellent Electrocatalytic Activity to Li/SOCl2 Battery

Fluorinated Multi-walled carbon nanotubes (F-MWCNTs) are chemically modified successfully by cobalt 2, 9, 16, 23-tetraaminophthalocyanine and cobalt 1, 8, 15, 22-tetraaminophthalocyanine respectively. Their structures are characterized by IR, SEM, XPS and XRD. Important in this context is that the covalent linkages between F-MWCNTs and cobalt phthalocyanines are corroborated by monitoring the diagnostic signature of the nitrogen atoms as part of the formed -NH- bonds in them by XPS. The electrocatalytic activity of the two kinds of modified F-MWCNTs to Li/SOCl2 battery is evaluated by adding them into the electrolyte of the battery. It is found that the modified F-MWCNTs can dramatically improve the discharge voltage and lengthen the discharge time of the battery, and finally make the capacity of the battery increase by 97.5% and 103.3% than that of the battery in the absence of them. The excellent electrocatalytic performance of the modified F-MWCNTs may be owing to the fine synergistic effect between the cobalt phthalocyanines and the MWCNTs in them. A reasonable catalytic mechanism of the modified F-MWCNTs to the battery is proposed according to the CV results.

Characterization of Fluorinated Multi-Walled and Single-Walled Carbon Nanotubes Using High Resolution XPS and EDX

Pristine and fluorinated multi-walled carbon nanotubes (MWCNTs) and single-walled carbon nanotubes (SWCNTs) were characterized using energy dispersive X-ray spectra (EDX) and X-ray photoelectron spectroscopy (XPS), respectively. The fluorine percentages of fluorinated multi-walled carbon nanotubes (F-MWCNTs) and fluorinated single-walled carbon nanotubes (F-SWCNTs) were 10.42% and 9.67% respectively by EDX. The absorption and de-absorption of fluorine properties were studied using high resolution C 1s and F 1s core level XPS and valence band spectra. The fluorine can be completely dissociated from F-MWCNTs, but partially dissociated from SWCNTs. There was 5.79% fluorine in atomic percent remaining associated with the F-SWCNTs when annealing the nanotubes to 500 °C measured by EDX. The results of F 1s core level XPS indicated that the binding energy of fluorine associated on SWCNTs was shifted from 687.0 eV to 688.3 eV after annealing the nanotubes to 500 °C. The results of valence band spectra showed that the binding energy of F 2p and F 2s shifted from 7.5 eV and 31.0 eV to 8.8 eV and 32.5 eV respectively in SWCNTS. However, the two peaks disappeared in annealed MWCNTs.

Features of Resonant F KLL Auger Spectra from Fluorinated Multi-Walled Carbon Nanotubes

High-resolution resonant F KLL Auger spectra from solid TiF3 and F-MWCNTs have been measured using photon energies in the vicinity of the F K(1s) edge. The spectra obtained show considerable changes in intensities and energy positions of main bands when photon energy passing through first low-energy absorption peak. These findings are explained in terms of hybridized nature and space localization of free electron states near the bottom of conduction band which are responsible for the first absorption band. The conclusions on the hybridization character of low-energy free electron states agree well with results obtained previously for F-MWCNTs with x-ray absorption.

Electronic structure of fluorinated multiwalled carbon nanotubes studied using x-ray absorption and photoelectron spectroscopy

This paper presents the results of combined investigation of the chemical bond formation in fluorinated multiwalled carbon nanotubes (MWCNTs) with different fluorine contents (10-55 wt %) and reference compounds (highly oriented pyrolytic graphite crystals and white graphite fluoride) using x-ray absorption and photoelectron spectroscopy at C 1s and F 1s thresholds. Measurements were performed at BESSY II (Berlin, Germany) and MAX-laboratory (Lund, Sweden). The analysis of the soft x-ray absorption and photoelectron spectra points to the formation of covalent chemical bonding between fluorine and carbon atoms in the fluorinated nanotubes. It was established that within the probing depth (similar to 15 nm) of carbon nanotubes, the process of fluorination runs uniformly and does not depend on the fluorine concentration. In this case, fluorine atoms interact with MWCNTs through the covalent attachment of fluorine atoms to graphene layers of the graphite skeleton (phase 1) and this bonding is accompanied by a change in the hybridization of the 2s and 2p valence electron states of the carbon atom from the trigonal (sp(2)) to tetrahedral (sp(3)) hybridization and by a large electron transfer between carbon an fluorine atoms. In the MWCNT near-surface region the second fluorine-carbon phase with weak electron transfer is formed; it is located mainly within two or three upper graphene monolayers, and its contribution becomes much poorer as the probing depth of fluorinated multiwalled carbon nanotubes (F-MWCNTs) increases. The defluorination process of F-MWCNTs on thermal annealing has been investigated. The conclusion has been made that F-MWCNT defluorination without destruction of graphene layers is possible. (Less)

Electronic Structure of Fluorinated Carbon Nanotubes Studied by X‐ray Absorption and Photoelectron Spectroscopy

The results of the detailed investigation of the chemical bonding and electronic structure features for the series of fluorinated multi‐walled carbon nanotubes (F‐MWCNTs) with different fluorine concentrations (5–55%) using X‐ray absorption and photoelectron spectroscopy are outlined. All measurements were performed with the use of synchrotron radiation at the BESSY II. The C1s and F1s absorption and photoelectron spectra point to formation of covalent chemical bonding between the fluorine and carbon atoms in F‐MWCNTs.