Surface Modification Of Carbon Nanotubes Research Articles

Biomimetic functionalization of carbon nanotubes with poly(ionic liquids) for highly efficient adsorption of organic dyes

The removal of environmental pollutants from wastewater through adsorption has regarded as one of the most efficient methods. A number of adsorbents based on nanomaterials and their composites have been examined for this purpose. Among them, carbon nanotubes (CNT) should be one of the promising candidates owing to their small size, large π conjugation system and high specific surface areas, however, the performance of CNT for adsorption is largely impeded by their poor dispersibility and lack of functional groups. Therefore, the development of simple and effective surface modification strategies to overcome the above drawbacks should be of great importance for their practical utilization in the environmental fields. In this study, a novel and simple biomimetic method was reported for the first time for surface modification of CNT with poly(ionic liquids) through the combination of mussel-inspired chemistry and subsequent surface-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization. An ionic liquid ([C16VIm+] [Br−]) was used as the monomer in this work because it is capable of introducing charged functional groups on the surface of CNT and thus boosts their adsorption performance towards environmental pollutants. As a model organic dye, Congo red (CR) was selected as the environmental pollutant and its adsorption behaviors of CR by CNT@IL composites were examined and analyzed in details. The results demonstrated that the adsorption capacity of CNT@IL intake CR (50 mg L−1) was obvious higher than that of unmodified CNT and the adsorption capacity reaches 178 mg g−1 with pH = 7 at 56 min. In addition, adsorption kinetic models and isotherm models were investigated to identify the adsorption kinetic rates and adsorption behavior, respectively. The adsorption principle that including electrostatic interaction, π-π interaction between imidazole rings on the surface of CNT@IL and CR, was proposed. This novel biomimetic surface modification could also be utilized for fabrication of many other functional materials with designable properties and improved performance. Therefore, this work will open up a new research avenue for the fabrication of multifunctional CNT based polymer composites.

Surface-Modified Carbon Nanotubes for Enhanced Ammonia Gas Sensitivity at Room Temperature.

By electron beam evaporation, noble metals (Au, Co, Pt, and Ag) with 2 and 4 nm nominal thicknesses were coated onto multi-walled carbon nanotube layers. The metals were in the form of nanoparticles mounted onto the side walls of carbon nanotubes (CNTs) to create a metal/CNT junction. The CNTs were directly grown on patterned Pt-electrode alumina substrates through chemical vapor deposition to produce a resistivity-based ammonia gas sensor. The metallic surface-modified CNT-based sensors were found sensitive to NH₃ gas at room temperature. Compared with pristine CNT sensor, the response of Au/CNTs sensor increased slightly, whereas the responses of the Pt/CNTs, Co/CNTs, and Ag/CNTs increased by two, three, and more than four times, respectively.

Tuning the composition and morphology of carbon nanotube-copper interface

Abstract Carbon nanotube (CNT)-copper nanocomposites are promising materials for light-weight high-ampacity conductors. The key issue in hybridization of CNT and metal is creating a strong bonding between them. This requires proper modification of the CNT surface. However, experimental works on determining the effect of interfacial functionalization on the properties of the metal/CNT system is scarce. In this paper, the effect of CNT surface modification on the morphology, interfacial interactions, and electrical properties Cu/CNT hybrid system is investigated. For this purpose, CNTs with carboxyl, thiol, and nitrogen doped surface groups were used as substrate for growth of Cu particles via a facile electrochemical process. It is observed that not only the morphology but also the chemical state of the Cu deposits are affected by the surface functional group on CNT. Thiol group significantly enhances copper wettability towards CNT, facilitating a uniform deposition of copper, and impedes oxidation. Also, Cu/CNT thin films fabricated via vacuum filtration that contain thiol-activated CNTs shows four and seven times higher electrical conductivity compared with systems that contain carboxyl and N-doped surface groups, respectively.

Preparation and Characterization of Polydopamine-Modified Ni/Carbon Nanotubes Friction Composite Coating

In this paper, dopamine (DA) was used for the surface modification of carbon nanotubes (CNTs) to solve the agglomeration problem. High resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) were utilized to understand the morphology and presence of different elements in the modified CNTs. The treated CNT surfaces were wrapped by a pDA layer and the layer thickness was controlled by reaction time. The dispersion test showed that the treated CNTs remained uniformly dispersed in solution for more than 30 days. The Ni/CNTs@pDA composite coating on the mild steel specimen was obtained by the electrodeposition technique. Ball-on-disc friction-wear equipment and an electrochemical workstation were used to test the friction-wear and corrosion resistance of the composite coating. The results indicated that the Ni/CNTs@pDA coating showed excellent tribological performance and were superior to the pure Ni coating.

Facile fabrication of glycosylated and PEGylated carbon nanotubes through the combination of mussel inspired chemistry and surface-initiated ATRP.

Surface modification of carbon nanotubes (CNTs) through controlled living polymerization has demonstrated to be a useful route for preparation of CNTs based polymer composites. However, surface oxidation of CNTs is often required to generate functional groups, which can be further utilized for immobilization of polymerization initiator and grafting polymers. The surface oxidation procedure is rather complex, high energy cost, low efficient and will destroy the structure of CNTs. Therefore, the development of simple and efficient strategies for preparation of CNTs based composites should be of great research interest and raised much attention recently. In this work, a novel mussel inspired strategy that combination of ATRP and ring-opening reaction has been developed for simultaneous preparation of glycosylated and PEGylated CNTs for the first time. CNTs were first coated with polydopamine (PDA) through self-polymerization of dopamine under alkaline aqueous solution. Then polymerization initiator was immobilized on CNT-PDA through simple esterification and amidation reaction to obtain CNT-PDA-Br. The PEGylated CNTs were synthesized through ATRP using CNT-PDA-Br as initiator and polyethylene glycol monoester acrylate and itaconic anhydride (IA) as the monomers. Finally, glucosamine was conjugated with IA via ring-opening reaction. The successful preparation of glycosylated and PEGylated CNTs (CNT-PDA-Poly(PEGMA-co-IA)-Glu) was confirmed by a number of characterization techniques in details. The obtained CNTs based composites showed improved aqueous dispersibility and desirable cytocompatibility, implying their biomedical application potential. As compared with the conventional covalent strategies, the mussel inspired method described in this work will not destroy the structure for introduction functional groups on the surface of CNTs, that can occur under rather mild experimental conditions, including room temperature, short reaction time and aqueous solution. On the other hand, the mussel inspired chemistry can also be used for surface modification of almost any materials regardless of their size, morphology and compositions. Therefore, we believe that the mussel inspired strategy should be a general method for fabrication of various polymer composites for different applications.

Potential-Driven Electron Transfer Lowers the Dissociation Energy of the C-F Bond and Facilitates Reductive Defluorination of Perfluorooctane Sulfonate (PFOS).

The widespread environmental occurrence of per- and polyfluoroalkyl substances (PFAS) has attracted significant regulatory, research, and media attention because of their toxicity, recalcitrance, and ability to bioaccumulate. Perfluorooctane sulfonate (PFOS) is a particularly troublesome member of the PFAS family due to its immunity to biological remediation and radical-based oxidation. In the present study, we present a heterogeneous reductive degradation process that couples direct electron transfer (ET) from surface-modified carbon nanotube electrodes (under low potential conditions) to sorbed PFOS molecules using UV-generated hydrated electrons without any further chemical addition. We demonstrate that the ET process dramatically increases the PFOS defluorination rate while yielding shorter chain (C3-C7) perfluorinated acids and present both experimental and ab initio evidence of the synergistic relationship between electron addition to sorbed molecules and their ability to react with reductive hydrated electrons. Because of the low energy consumption associated with the ET process, the use of standard medium-pressure UV lamps and no further chemical addition, this reductive degradation process is a promising method for the destruction of persistent organic pollutants, including PFAS and other recalcitrant halogenated organic compounds.

Rheological and electrical properties of polystyrene nanocomposites via incorporation of polymer-wrapped carbon nanotubes

Carbon nanotubes (CNTs) are used as nanofillers in polymer nanocomposites to improve the properties of a matrix polymer because of their excellent properties. However, CNTs tend to aggregate due to the strong van der Waals force between CNTs. To solve the problem, surface-modified CNTs with hydrophilic polymers, such as polyvinyl pyrrolidone (PVP) and polystyrene sulfonate (PSS), were employed. Polystyrene (PS)/CNT nanocomposites were fabricated by latex technology, which is a suitable method for dispersing nanofillers in aqueous particle suspension. The effect of the incorporation of the modified CNT was significant, thereby resulting in increased modulus at lower frequencies when compared to that of neat PS. Electrical percolation thresholds of PS/PSS-wrapped CNT and PS/PVP-wrapped CNT nanocomposites corresponded to 0.39 and 0.52 wt.%, respectively. The PS/PSS-CNT nanocomposites exhibited higher rheological and electrical properties than the PS/PVP-CNT counterparts due to the hydrophilic nature of PSS with strong negative charge groups.

Effect of rare earth surface modification of carbon nanotubes on enhancement of interfacial bonding of carbon nanotubes reinforced epoxy matrix composites

Rare earth (RE) lanthanum chloride was used to modify carbon nanotubes (CNTs) to obtain rare earth modified carbon nanotubes (RECNTs). The modified CNTs were characterized by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The results show that RE has a significant effect on improving the surface activity of carbon nanotubes. Through the chemical function of RE, the CNTs were successfully grafted with functional groups such as amino groups and carboxyl groups. This method can be used to connect any oxygen- or nitrogen-containing functional groups to the CNTs according to actual needs. Then, the modified CNTs were incorporated into epoxy resin (EP) to prepare composite (REACNTs/EP). The mechanical properties of the composites were tested by Zwick/Roell Z100 and Zwick/Roell Z20 test machine, and the tensile fractural sections were analyzed by scanning electron microscopy, and compared to the composites prepared with untreated CNTs (CNTs/EP), acidified carbon nanotubes (ACNTs/EP), acidification and RE synergistic modification of carbon nanotubes (REACNTs/EP). The results show that the ultimate tensile strength and tensile modulus of RECNTs/EP were increased by 33.9%, 73.7%, respectively, compared with pure EP, while the properties of REACNTs/EP were increased by 50.7%, 90.9%, indicating that RE has excellent effect on improving the mechanical properties of carbon nanotube-reinforced composites.

A study on the effect of carbon nanotube surface modification on mechanical and thermal properties of CNT/HDPE nanocomposite

In this article, the effect of carbon nanotube’s (CNT) surface modification on mechanical, thermal, and morphological properties of nanocomposite with different content of CNTs was studied. CNT/high-density polyethylene (HDPE) nanocomposites were prepared by a mini twin-screw extruder. To modify the dispersion of MWCNTs in HDPE, the surface of CNTs was functionalized by HNO3 and stearic acid (SA). The tensile tests results show that addition of 5% of acid-treated CNT in HDPE cause to increase in Young’s modulus and yield strength up to 4% and 6%, respectively; as compared to unmodified CNT/HDPE nanocomposite. The presence of the SA on CNTs can lead to slight decrease of the CNT-SA/HDPE strength properties; when compared to pure CNT/PE nanocomposite. However, there is a fracture toughness enhancement in CNT-SA/HDPE up to 10% compare to unmodified CNT/PE nanocomposite. Furthermore, the calculation of the stress whitening zone of all samples verifies the fracture toughness data of CNT/HDPE nanocomposites. Scanning electron microscopic images showed that the best dispersion of CNTs in the HDPE matrix was seen in CNT-SA/HDPE nanocomposite.

2+1] Additions of (n,0)(n=6−10) single-walled carbon nanotubes with di-vacancies based on defect curvature: A first-principles study

Binding energies ([Formula: see text], geometric and electronic structures for [[Formula: see text]](O/[[Formula: see text]]) additions of O atom on ([Formula: see text])([Formula: see text] − 10) single-walled carbon nanotubes with di-vacancies are studied using a GGA-PBE method, and defect curvature ([Formula: see text]) is used to predict reactivities of different C—C bonds at defect area. Calculated results show that the C—C bonds can be divided into two types: broken C—C bonds corresponding to adducts with a C—O—C configuration structure and unbroken C—C bonds corresponding to adducts with a closed-3MR structure. [Formula: see text] of O/[[Formula: see text]] additions for the adduct with the C—O—C configuration structure monotonously increases with the increase of [Formula: see text] in any ([Formula: see text],0)([Formula: see text]) tube and decreases with the increase of [Formula: see text] in ([Formula: see text],0)([Formula: see text], 7, 10) tubes. Besides the fact that [Formula: see text] value is mainly determined by the defect curvature, it is also affected by band gaps, bonding characteristic of C—C bonds in the highest occupied molecular orbital (HOMO) and geometric structures. The study would provide a theoretical basis for surface modifications of carbon nanotubes with atomic vacancy defects.

Electrochemical fabrication and evaluation of a self-standing carbon nanotube/carbon fiber composite electrode for lithium-ion batteries.

A binder-free self-standing carbon nanotube (CNT)/carbon fiber (CF) composite electrode, which has been developed using an electrophoretic deposition approach, was utilized as a lithium-ion battery anode. The morphology of the CNT/CF composite has been examined using scanning electron microscopy, and the results indicated that a CNT layer uniformly deposited on the CFs. The thickness and density of the CNT layer increased as the electrodeposition time increased, while overdeposition caused the CNT layer to exfoliate. Electrochemical evaluation revealed that the specific capacity, cycling stability, and rate capability of the CNT/CF anode were superior to those of the CF anode. The electrochemical impedance analysis results further revealed that the solid/electrolyte interface resistance and interface resistance induced by the oxygen-containing surface functional groups of CFs dominated the impedance of the anode. However, these resistance values could be potentially reduced via CNT surface modification, which could lead to the enhanced electrochemical performance of the CNT/CF anode. Our findings should open new avenues for the potential use of the CNT/CF composite as a self-standing anode for lithium-ion battery applications.

Highly flexible strain sensors based on polydimethylsiloxane/carbon nanotubes (CNTs) prepared by a swelling/permeating method and enhanced sensitivity by CNTs surface modification

Flexible sensors for large strain detection have recently been attracted the attention of researchers. This investigation reports a stretchable strain sensor in which carbon nanotubes (CNTs) were diffused into polydimethylsiloxane (PDMS) using a facile swelling/permeating method. The CNTs were further modified by using a silane coupling agent (SCA) to improve dispersion and the interaction between CNTs and PDMS. The CNTs permeated the skin layer of the PDMS composite and the inner core of PDMS contained few CNTs, forming a sandwich-like structure. The low CNTs content (0.48 wt%) and sandwich-like structure resulted in excellent composite flexibility which allowed work strains to exceed 350% and Young's modulus to increase from 0.25 MPa to 0.40 MPa. Surface modification of the CNTs improved their permeation depth and dispersion, which was shown to enhance composite sensitivity. The relative resistance change reached 4850% with a gauge factor of 20 by 1.0 wt% SCA modification. Cycled electromechanical properties showed a stable resistance response and sensitivity against strain. Therefore, the PDMS/CNTs nanocomposites prepared by swelling/permeating and CNTs surface modification in this study have various application potentials in the flexible sensor field.

"Electron-Sharing" Mechanism Promotes Co@Co3O4/CNTs Composite as the High-Capacity Anode Material of Lithium-Ion Battery.

Hybridization of nanostructured cobalt oxides with carbon nanotubes (CNTs) is considered to be an operative approach to harvest high-performance anode material for lithium-ion batteries (LIBs). On the other hand, there are numerous related works, most of which adopted a "post-combination" strategy, which is not only complicated but also ecologically unpromising for using toxic acid for surface modification of CNTs. Herein, we productively fabricate Co@Co3O4/CNTs nanocomposite with excellent conductivity through arc discharge following low-temperature oxidation in air. As the anode material for LIBs, this nanocomposite shows an exceedingly high reversible capacity of 820 mA h g-1 at a current density of 0.2 A g-1 after 250 cycles, much higher than its theoretical capacity. The rate performance of the material is also outstanding, with a capacity of 760 mA h g-1 after 350 cycles at 1 A g-1 (103% of the initial capacity) and 529 mA h g-1 after 600 cycles at 2 A g-1. X-ray photoelectron spectroscopy tests are accomplished to disclose the true cause of extra capacity. And for the first time, we propose an "electron-sharing" storage mode, where extra electrons and Li+ can separate and be stored at the interface of cobalt metal/Li2O. This not only gives a reasonable revelation for this unusual capacity exceeding the theoretical value but also directs the capacitor-like electrochemical behavior extra capacity.

Grafting Carbon Nanotube for Dye-Sensitized Solar Cell Improvement

Carbon nanotubes (CNTs) were modified by grafting polymerization with copolymer of polyaniline and poly (vinyl acetate) for improving their electrical conductivity and water dispersion. After surface modification of CNTs, they were used to fabricate as the photoelectrode or working electrode for the dye-sensitized solar cell (DSSC). The characterizations of the modified CNTs were done by FTIR, TEM and SEM. Lastly, the efficiency of DSSC prepared from the modified CNT was evaluated by photovoltaic test. The results showed the high performance of the grafting CNTs-added working electrode.

Characterization of Surface Interaction between Chitosan-modified Liposomes and Mucin Layer by Using CNT Probe AFM Method

In order to characterize the adhesion and deformation behavior between chitosan-modified liposomes and the mucin layer of the small intestine, mucin was coated on hydrophobic surface-modified carbon nanotube (CNT) probe of an atomic force microscope. The interaction between this mucin layer and the liposomes with or without chitosan modification in phosphoric acid buffer solution was determined by atomic force microscopy. The pH of the buffer solution was controlled at 2.8 and 7.0. The chitosan modification increased the attractive force between the liposomes and mucin layer during the separation process under both pH conditions. This result corresponded with that from a previous study about the liposome adhesion behavior on the surface of the small intestine of rats. By using the mucin-coated CNT probe, the long range and different types of attractive forces between the chitosan-modified liposomes and mucin layer was observed. Furthermore, the small-scaled deformation behavior change on the liposomal surfaces due to chitosan modification was also observed by the CNT probe. The detail deformation and adhesion behavior of the liposomes with or without chitosan modification was detected.

Surface Modification of Carbon Nanotubes as a Key Factor on Rheological Characteristics of Water-Based Drilling Muds

This study investigates the effect of functionalized Multi-Walled Carbon NanoTube (f-MWCNT) on rheological properties of water-based drilling muds. Functionalization of multi-walled carbon nanotube was performed by introducing a hydrophilic functional group onto the surface of nanotubes via acid treatment. In order to guarantee the results, X-ray fluorescence, transmission electron microscopy, and thermogravimetric analysis were performed on samples. Temperature and mud density variations were also considered along with the effect of f-MWCNT addition. Furthermore, a novel study was performed on the influence of the degree of functionalization on plastic viscosity and yield stress of drilling mud samples. The results obtained from this study revealed that the addition of f-MWCNT greatly affects the rheological characteristics of water-based drilling muds like plastic viscosity, apparent viscosity, yield stress, and thixotropic properties. Moreover, test results indicated that the shear stress versus shear rate diagram fitted well the Herschel-Bulkley rather than the Bingham plastic model.

Assembly of mesoporous SnO2 spheres and carbon nanotubes network as a high-performance anode for lithium-ion batteries

We report a facile and effective aerosol-spray strategy toward high-performance anodes for lithium-ion batteries by incorporating mesoporous SnO2 spheres of high-capacity materials with surface-modified carbon nanotubes (MCNTs). SnO2 nanocrystals are self-assembled into mesoporous spheres, and MCNTs with abundant carboxylic groups serve as a conductive scaffold. Driven by the strong interaction between the surface of metal oxide and the carboxylic groups on CNTs, a robust nanocomposite architecture is in situ formed. Such nanocomposite architecture possesses several advantages as an anode for lithium-ion batteries. First, mesoporous SnO2 spheres inherit the advantageous features of conventional nanoparticles, such as the capability to accommodate volume expansion and reduce Li+ diffusion distance. Second, the robust interface between nanocrystals in the SnO2 spheres provides the high structural stability that would prolong the life span of the electrode. Third, MCNTs that strongly bind to SnO2 spheres serve as a three-dimensional network, offering both improved electronic transport and mechanical strength of the electrode. Therefore, as-prepared nanocomposite delivers high capacity of 963 mAh g−1 at 0.1 C and 701 mAh g−1 at 5 C, respectively. Significantly improved cycling performance is achieved over the bare SnO2 spheres counterpart.

Enhanced mechanical properties of aluminum based composites reinforced by chemically oxidized carbon nanotubes

Uniform dispersion and suitable interface are two critical issues to realize the high strengthening potential of carbon nanotubes (CNTs) in metal based composites. In this work, surface modification of CNTs was applied to simultaneously overcome these two challenges in Al matrix composites by a chemical oxidization method. It was found that the functional groups, such as hydroxyl and carboxyl groups, can be successfully decorated on the surface of CNTs by chemical oxidization, thus improving the dispersion of CNTs in ethanol. Concurrently, the morphology of oxidized CNTs and the Al-CNTs interface depend strongly on the activity of the applied oxidants. The mixture of sulphuric acid and hydrogen peroxide can slightly etch the outer walls of CNTs, which benefits the anchoring bonding between the CNTs inner walls and Al matrix, and improves the interface stability, hence exploits the load bearing capacity of the CNTs inner walls and eventually leads to the effective load transfer between Al and CNTs. The outstanding reinforcing effect of surface-modified CNTs was investigated and discussed by the strengthening models. This work provides a new approach to uniformly disperse CNTs and improve interfacial bonding for CNTs reinforced composites simultaneously.

Covalent functionalization of carbon nanotubes with hydroxyl-terminated polydimethylsiloxane to enhance filler dispersion, interfacial adhesion and performance of poly(methylphenylsiloxane) composites

Surface modification of carbon nanotubes (CNTs) were performed by grafting of hydroxyl-terminated polydimethylsiloxane (HPDMS) covalently. The results of dissolution experiments revealed that long-time stable dispersions of HPDMS-functionalized CNTs (CNTs-HPDMS) were achieved in a range of solvents including ethanol, ethyl acetate, dimethylbenzene and cyclohexane, even after being placed for 3 months. Subsequently, CNTs-HPDMS were incorporated into poly(methylphenylsiloxane) (PMPS) matrix to prepare composites. Scanning electron microscopy analysis showed that CNTs-HPDMS had homogeneous dispersion and strong interfacial adhesion in PMPS, which led to much better mechanical properties of composites compared to those filled with untreated CNTs. Furthermore, the incorporation of CNTs-HPDMS significantly enhanced the thermal stability of PMPS composites both under nitrogen and air. The improved barrier effect of CNTs-HPDMS resulted from the better filler dispersion was considered to play a crucial role, which on the one hand suppressed the depolymerization of PMPS under nitrogen and on the other hand inhibited the oxygen diffusion in matrix under air. Besides, the hydroxyl groups of HPDMS could react with PMPS to form additional crosslinking during heating, and thus delayed the degradation of PMPS to some extent.

Fabrication and characterization of hyperbranched polyglycerol modified carbon nanotubes through the host-guest interactions

Carbon nanotubes (CNTs) are novel carbon composites that have received extensive research attention for biomedical applications thanks to their excellent cell membrane penetration capability and large specific surface areas. Nevertheless, the poor dispersibility in aqueous solution still perplexes the biomedical applications of CNTs. Although, there are many researched about that modify hydrophilic polymers to the surface of CNTs, facile and efficient strategies are still highly desirable to be developed. In this produce, an efficient and facile strategy for surface modification of CNTs with excellent water dispersibility was developed via supramolecular chemistry. On the one hand, we synthesize the β-CD-HPG via anionic polymerization. On the other hand, adamantane chloride was first reacted with the hydroxyl group of radiant CNTs through esterification to obtain CNT-Ad. Finally, it only need mild reaction conditions and fast reaction time (30 min) that β-CD-HPG form an exact 1:1 inclusion complex with CNT-Ad via host-guest interaction. The successful preparation of CNT-β-CD-HPG composites could be confirmed via a series of characterization techniques. Then, we further verify that CNT-β-CD-HPG composites possess the remarkable water dispersibility and enormous potential for controlled drug delivery systems. Therefore the facile strategy for the preparation of CNT-β-CD-HPG composites with excellent water dispersibility via supramolecular chemistry would possess rosy prospects in biomedical applications.