Polydopamine-coated Carbon Nanotubes Research Articles

Carbon nanotube incorporated quaternized lignin-based loose nanofiltration membrane toward dye/salt separation

Lignin is a promising raw material for membrane fabrication due to its abundant oxygen-containing functional groups, branched molecular structure, and high abundance in the botanic field. In this report, polydopamine (PDA) coated carbon nanotubes (PCNTs) are synthesized. Then, a PCNT-incorporated lignin-based loose nanofiltration membrane is fabricated using quaternized lignin (QL) as a raw material, triphosgene (TP) as a crosslinker, and PCNTs as nanoadditive by interfacial polymerization. The results show that the PCNTs uniformly distribute in the QL-based separation layer providing quick diffusion paths for water molecules and salt ions. The coated PDA layer improves the chemical compatibility between the PCNTs and the separation layer. The incorporated PCNTs optimize the membrane microstructure and elevate the pure water permeance to 45.5 LMH bar−1. The membrane exhibits high rejections to various dyes (> 90%) and high salt permeation (> 90%), demonstrating an excellent dye/salt separation performance. Moreover, it has satisfactory capabilities for resisting dye adsorption and fouling, and its separation capability also has good tolerances to the acid, alkali, and active chlorine treatments. The quaternary ammonium ions and hydrophilic surface endow the membrane with favorable bactericidal property (99.3%) and bacteria-adhesion resistance. Besides, TP is a better crosslinker than trimesoyl chloride for optimizing the membrane microstructure and crosslinking degree in terms of dye/salt separation.

Highly sensitive and extremely durable wearable e-textiles of graphene/carbon nanotube hybrid for cardiorespiratory monitoring

Electroconductive textile yarns are of particular interest for their use as flexible and wearable sensors without compromising the properties and comfort of usual textiles. However, the detection of fine actions of the human body is quite challenging since it requires both the relatively higher sensitivity and stability of the sensor. Herein, highly sensitive, ultra-stable, and extremely durable piezoresistive wearable sensors were prepared by loading N-doped rGO and polydopamine-coated carbon nanotubes into silicon rubber tube. The wearable sensors thus produced show an excellent ability to sense subtle movement or stimuli with good sensitivity and repeatability. Furthermore, by bending the straight conductive silicon rubber tube (CSRT) into three different patterns, its sensitivity was then dramatically increased. Finally, the CSRT was found capable of sensing cardiorespiratory signals, indicating that the sensor would be an important step toward realizing bio-signal sensing for next-generation personalized health care applications.

Poly (vinylidene fluoride)-based microcellular dielectrics filled with polydopamine coated carbon nanotubes for achieving high permittivity and ultralow dielectric loss

Poly (vinylidene fluoride) (PVDF)-based microcellular dielectrics with polydopamine (PDA) coated carbon nanotubes (CNTs) were fabricated through scCO2 foaming technologies. Compared with pristine CNT/PVDF foam composites, the dielectric permittivity and loss factor of coated composites were much lower due to the significantly reduced polarizability within particle/polymer interfaces. Besides, these two parameters were also reduced with increasing expansion ratio, which was ascribed to the disaggregation of conductive particles and the increased air in the cells. Furthermore, it was demonstrated that more nucleation points initiated by the enlarged saturation pressure yielded the increased number of cells and the space restriction led to a mild growth of the cell size, which benefited for minimizing the increase of inter-particle spacing and the disentanglement between particles. Accordingly, the PDA@CNT/PVDF composites foamed to a high ER achieved a relatively large permittivity and an ultralow dielectric loss, which paved a new way to fabricate microcellular dielectrics.

Thermal insulation performance and ablation resistance of ethylene propylene diene monomer insulation materials reinforced with polydopamine-coated carbon nanotubes

Filler reinforced ethylene propylene diene monomer (EPDM) rubber was widely used as insulation material for solid rocket motors (SRMs). Carbon nanotubes (CNTs) were employed fillers owing to their excellent physicochemical properties. However, the addition of CNTs to EPDM reduces its thermal insulation performance. To solve this problem, polydopamine-coated CNTs (CNTs @ PDA) were prepared by in-situ polymerization and mixed with EPDM through mechanical compounding. The effects of CNTs @ PDA on the thermal properties and ablation resistance of the resulting CNTs @ PDA/EPDM were investigated. The results indicate that the addition of CNTs @ PDA can reduce the thermal conductivity of the insulation material and the maximum back temperature during oxyacetylene ablation test. The ablation rate of the insulation material decreased as the amount of PDA used to coat on the CNTs increased, compared with the uncoated CNTs (10-CNTs) formulation, the PDA-2 formulation reduced the linear ablation rate by 62 % to 0.01 mm/s. Furthermore, the micro-morphology of the char layer was observed by SEM, combined with the compression resistance of the char layer to explain the effect on the ablation performance of the insulation material. The mechanical performance test results also reveal that the CNTs @ PDA formulation has higher tensile strength.

Improved Biomedical Properties of Polydopamine-Coated Carbon Nanotubes.

Carbon nanotubes (CNTs) due to their outstanding mechanical, thermal, chemical, and optical properties were utilized as a base material and were coated with polydopamine (PDA) (PDA@CNT) via the simple self-polymerization of dopamine (DA). Then, PDA@CNT coatings of up to five layers were examined for potential biomedical applications. The success of multiple coating of CNTs with PDA was confirmed via increased weight loss values with the increased number of PDA coatings of CNTs at 500 °C by thermogravimetric analysis. The surface area of bare CNTs was measured as 263.9 m2/g and decreased to 197.0 m2/g after a 5th coating with PDA. Furthermore, the antioxidant activities of CNT and PDA@CNTs were determined via total flavonoid content (TFC), total phenol content (TPC), and Fe(III)-reducing antioxidant power (FRAP) tests, revealing the increased antioxidant ability of PDA@CNTs with the increasing numbers of PDA coatings. Moreover, a higher inhibition percentage of the activity of the alpha-glucosidase enzyme with 95.1 ± 2.9% inhibition at 6 mg/mL PDA-1st@CNTs concentration was found. The CNT and PDA@CNTs exhibited blood compatibility, less than a 2.5% hemolysis ratio, and more than 85% blood clotting indexes. The minimum inhibition concentration (MIC) of PDA-5th@CNTs against E. coli and S. aureus bacteria was determined as 10 mg/mL.

Biomimetic 3D aligned conductive tubular cryogel scaffolds with mechanical anisotropy for 3D cell alignment, differentiation and in vivo skeletal muscle regeneration

Developing 3D conductive aligned cryogels has great potential for skeletal muscle trauma treatment because they can mimic anisotropic structure, conductivity, and recoverable cyclic compression of the microenvironment of native skeletal muscle. In this work, a series of cryogels possessing 3D aligned morphology, conductivity, and excellent anisotropic mechanical compression property based on gelatin (GT) and polydopamine coated carbon nanotubes (PCNTs) were fabricated as skeletal muscle tissue scaffolds by using unidirectional freeze casting technology. The aligned microstructure of cryogels depended on gelatin concentration, and GT7.5 (with the gelatin content of 7.5% w/v) showed excellent aligned structure. Interestingly, the mechanical property of the aligned cryogels was similar to that of native skeletal muscle in terms of the dynamic contraction behavior and the anisotropic compression property due to the internal anisotropy structure. The aligned cryogel GT7.5 with good biocompatibility significantly promoted the alignment and elongation of C2C12 myoblasts. Moreover, the introduction of PCNTs enhanced the mechanical properties of cryogel GT7.5 and had a positive effect on myogenic differentiation of C2C12 cells. The aligned conductive GT7.5C2 cryogel significantly promoted new born muscle tissue generation compared to non-aligned group (GT7.5C2N) and non-conductive group (GT7.5) in a rat tibialis anterior muscle defect model. These data suggested that the 3D aligned conductive cryogel with conductivity and anisotropic compression property is a promising scaffold candidate for skeletal muscle tissue engineering.

Hybrid proton exchange membrane of sulfonated poly(ether ether ketone) containing polydopamine-coated carbon nanotubes loaded phosphotungstic acid for vanadium redox flow battery

A hybrid membrane of sulfonated poly(ether ether ketone)/polydopamine-coated carbon nanotubes loaded phosphotungstic acid (S/DCNTs-HPW) is proposed for vanadium redox flow battery (VRFB). With the DCNTs-HPW nanofillers as the proton donor and acceptor, a high proton conductivity and low vanadium ions permeability of the S/DCNTs-HPW hybrid membranes is demonstrated owing to the formed acid-base interaction. Specifically, S/DCNTs-HPW-1 gives higher ion selectivity (25.4 × 103 S min cm−3) than that of pristine SPEEK (4.3 × 103 S min cm−3) and Nafion 117 (4.0 × 103 S min cm−3). Cell utilizing S/DCNTs-HPW-1 reveals excellent coulombic efficiency (98.2–99.4%) and energy efficiency (89.5–69.0%) under the current density of 50–160 mA cm−2, and a 34.5% charge capacity retention under 100 cycles is achieved based on the excellent membrane structure and chemical stability. The S/DCNTs-HPW-1 membrane shows a self-discharge time of 576 h, which is longer than that of the Nafion 117 membrane (23 h). Thus, the S/DCNTs-HPW hybrid membranes are suggested for potential use as alternative PEMs in the VRFB system.

Mussel-inspired, antibacterial, conductive, antioxidant, injectable composite hydrogel wound dressing to promote the regeneration of infected skin

Infection is a major obstacle to wound healing. To enhance the healing of infected wounds, dressings with antibacterial activities and multifunctional properties to promote wound healing are highly desirable. Herein, gelatin-grafted-dopamine (GT-DA) and polydopamine-coated carbon nanotubes (CNT-PDA) were used to engineer antibacterial, adhesive, antioxidant and conductive GT-DA/chitosan/CNT composite hydrogels through the oxidative coupling of catechol groups using a H2O2/HRP (horseradish peroxidase) catalytic system. The addition of the antibiotic doxycycline endowed the hydrogels with antimicrobial activity to treat infected full-thickness defect wounds. Additionally, CNT-PDA endowed these hydrogels with an excellent photothermal effect, leading to good in vitro and in vivo antibacterial activities against Gram-positive and Gram-negative bacteria. The catechol group and polydopamine imparted tissue adhesiveness, and the hemostatic and antioxidant abilities of these hydrogels were also investigated. The porosity, degradability, swelling, rheological, mechanical, and conductive behaviors of these hydrogels were finely regulated by changing the concentration of CNT-PDA. Hemolysis and cytocompatibility tests using L929 fibroblast cells confirmed the good biocompatibility of these hydrogels. The wound closure, collagen deposition, histomorphological examination and immunofluorescence staining results demonstrated the excellent effects of these hydrogels in an infected full-thickness mouse skin defect wound. In summary, the adhesive antibacterial and conductive GT-DA/chitosan/CNT hydrogels showed great potential as multifunctional bioactive dressings for the treatment of infected wounds.

Conductive poly(high internal phase emulsion) foams incorporated with polydopamine-coated carbon nanotubes

Electrically conductive poly(high internal phase emulsion) (polyHIPE) nanocomposite foams based on poly(styrene-co-divinylbenzene) were prepared by incorporating polydopamine-coated carbon nanotubes (PDA-CNTs). Conductive yet amphiphobic CNTs were modified to PDA-CNTs by coating with PDA on the surface of CNTs to provide hydrophilicity. As a result, it was possible to prepare highly stable HIPEs having PDA-CNT content >10 wt% and resultant polyHIPE foams having enhanced conductivity due to the good dispersion of PDA-CNTs in aqueous phase. The foams made with a water-to-monomer ratio of 10:1 showed well-developed interconnected microcellular structure. With increasing PDA-CNT content, the yield stress and storage modulus of HIPE increased and the cell size of the polyHIPE foam decreased. The electrical percolation threshold was determined to be less than PDA-CNT 1 wt% and the conductivity at PDA-CNT content of 8 wt% was increased to as high as 10−2 Sm−1. Surface modification of CNTs by PDA was very effective in providing electrical conductivity due to their stable dispersion in aqueous phase while keeping the intrinsic properties of CNTs intact.

Epoxy resin reinforced with nanothin polydopamine-coated carbon nanotubes: a study of the interfacial polymer layer thickness

Carbon nanotubes (CNTs) functionalized by a nanothin poly(dopamine) (PDA) layer were produced by a one-pot, nondestructive approach, with direct polymerization of dopamine on the CNT surface.

New strategy toward enhanced air electrode for Li–air batteries: apply a polydopamine coating and dissolved catalyst

In this article, we report a new strategy for enhancing the electrochemical performance of Li–air batteries through the combined use of polydopamine-coated carbon nanotubes (CNTs) and a dissolved LiI catalyst. The polydopamine layer modified the CNT surface from hydrophobic to hydrophilic, improving the wettability of the CNT-based electrode. This, in turn, increased the area of the electrode that actively participates in the reaction between the lithium ions and the dissolved oxygen in the electrolyte. LiI contained in the electrolyte effectively decreases the overpotential of the Li–air cell, by freely accessing the whole surface of the wetted electrode. We introduced the polydopamine-coated CNTs and LiI-doped electrolyte as an alternative to electrodes composed of carbon and solid catalysts. The electrochemical properties of this new system, including its capacity, overpotential, and cyclic performance, were characterized.

High loading of uniformly dispersed Pt nanoparticles on polydopamine coated carbon nanotubes and its application in simultaneous determination of dopamine and uric acid

Multiwalled carbon nanotubes (MWCNT) were homogeneously covered with a bio-functional polydopamine (PDOP) by a simple dip-coating approach in mild basic solution. Then, uniformly dispersed and highly loaded platinum nanoparticles (PtNPs) were deposited on MWCNT@PDOP by a mild reductant, and were characterized by transmission electron microscopy and x-ray photoelectron spectroscopy. Afterwards, this nanocomposite was modified on the glass carbon electrode and applied to simultaneously determine dopamine (DA) and uric acid (UA) by differential pulse voltammetry (DPV). Results showed that a linear electro-oxidation response was found for DA and UA in the range of 0.25–20 μM and 0.3–13 μM with the detection limit (S/N = 3) of 0.08 μM and 0.12 μM, respectively. In addition, the detection sensitivities for DA and UA by DPV were 1.03 μA μM−1 and 2.09 μA μM−1, respectively, which were much higher than those from a cyclic voltammogram. Finally, the reproducibility and stability of the nanocomposite were also evaluated, demonstrating that such MWCNT@PDOP@PtNPs can be a promising candidate for advanced electrode material in electrochemical sensing and other electrocatalytic applications.

A label-free cytosensor for the enhanced electrochemical detection of cancer cells using polydopamine-coated carbon nanotubes

An electrochemical, label-free method was developed to detect folate receptor positive tumor cells by specific recognition of a polydopamine-coated carbon nanotubes-folate nanoprobe to cell-surface folate receptors. This strategy offers great promise to extend its application in studying the interaction of ligand and cell-surface receptor.

The in vitro biomineralization and cytocompatibility of polydopamine coated carbon nanotubes

In this work, polydopamine coated carbon nanotubes were firstly prepared by a simple and feasible route. Then, for comparison, the in vitro bioactivity and cytocompatibility of the carbon nanotubes and the polydopamine coated carbon nanotubes were assessed by immersion study in simulated body fluids and 3-(4,5-dimethyldiazol-2-yl)-2,5-diphenyl tetrazolium bromide test using osteoblast cells (MC3T3-E1), respectively. As a result, it has been demonstrated that the introduction of polydopamine coating can greatly enhance the bioactivity and promote cell proliferation of the carbon nanotubes. The improvement of bioactive behavior is attributed to the good combination of catecholamines structure of the polydopamine and the structural advantages of carbon nanotubes as a framework material. It is anticipated that the polydopamine coated carbon nanotubes would find potential applications in bone tissue engineering and other biomedical areas.