Hydroxyl-functionalized Carbon Research Articles

Thermal properties and mechanical behavior of functionalized carbon nanotube-filled polypropylene composites using molecular dynamics simulation

Polypropylene (PP) is widely recognized as an environmentally friendly material for cable insulation due to its good insulation performance and environmental friendliness. One common method for enhancing the overall performance of PP is the addition of nanoparticles. To analyze the influence of different functionalized multi-walled carbon nanotubes (MWCNT) fillers on the properties of PP/MWCNT composite materials from a microscale perspective, molecular dynamics is used to construct pure PP models and models filled with untreated carbon nanotubes (UFCNT), amino-functionalized carbon nanotubes (AFCNT), carboxyl-functionalized carbon nanotubes (CFCNT), and hydroxyl-functionalized carbon nanotubes (HFCNT) (functionalized MWCNT with 4 or 8 functional groups grafted onto them). The simulation results indicate that the doping of nanotubes can effectively enhance the thermodynamic properties of PP. Among them, PP/CFCNT-8 exhibits the most significant improvement in melting temperature and mechanical properties, with an increase in melting temperature of 88.85 K and a 184.52 % increase in Young's modulus. The melting temperature of PP/HFCNT-8 is second only to PP/CFCNT-8, with an increase of 82.59 K. The results indicate that the thermodynamic properties of PP nanocomposites filled with functionalized MWCNT are improved with the grafting rate. The filling of functionalized MWCNT alters the microscale properties of PP composites, with a significant decrease in root mean square displacement (RMSD), and improvement in free volume fraction (FFV) as well as interfacial binding energy, which can better maintain the electrical properties of PP insulation materials. Applying functionalized carbon nanotubes to filled PP can significantly increase the electrical insulation properties of PP cable materials, which provides meaningful guidance for adopting polypropylene cable insulation materials.

Intrinsically Nonswellable Multifunctional Hydrogel with Dynamic Nanoconfinement Networks for Robust Tissue-Adaptable Bioelectronics.

Developing bioelectronics that retains their long-term functionalities in the human body during daily activities is a current critical issue. To accomplish this, robust tissue adaptability and biointerfacing of bioelectronics should be achieved. Hydrogels have emerged as promising materials for bioelectronics that can softly adapt to and interface with tissues. However, hydrogels lack toughness, requisite electrical properties, and fabrication methodologies. Additionally, the water-swellable property of hydrogels weakens their mechanical properties. In this work, an intrinsically nonswellable multifunctional hydrogel exhibiting tissue-like moduli ranging from 10 to 100kPa, toughness (400-873 J m-3 ), stretchability (≈1000% strain), and rapid self-healing ability (within 5min), is developed. The incorporation of carboxyl- and hydroxyl-functionalized carbon nanotubes (fCNTs) ensures high conductivity of the hydrogel (≈40Sm-1 ), which can be maintained and recovered even after stretching or rupture. After a simple chemical modification, the hydrogel shows tissue-adhesive properties (≈50kPa) against the target tissues. Moreover, the hydrogel can be 3D printed with a high resolution (≈100µm) through heat treatment owing to its shear-thinning capacity, endowing it with fabrication versatility. The hydrogel is successfully applied to underwater electromyography (EMG) detection and ex vivo bladder expansion monitoring, demonstrating its potential for practical bioelectronics.

Molecular dynamics investigation of the mechanical properties and fracture behaviour of hydroxyl-functionalised carbon and silicon carbide nanotubes-reinforced polymer nanocomposites

ABSTRACT The tensile properties and fracture mechanism of hydroxyl-functionalized silicon carbide nanotubes (O-fSiCNTs) inserted into polymer matrices are explored and the outcomes are compared to results for the hydroxyl-functionalized carbon nanotubes (O-fCNTs) incorporated in similar matrices. The molecular dynamics (MD) method is used and the simulations are based on the notion of representative volume elements (RVEs). The incorporation of chemisorbed nanotubes in polymers has a profound effect on the enhancement of their mechanical properties. The O-fSiCNTs inside the polyethylene (PE) and polypropylene (PP) (O-fSiCNTs/PE and O-fSiCNTs/PP) possess lower Young’s modulus, maximum stress, and strain energy as compared to the O-fCNTs/PE and O-fCNTs/PP. The zigzag O-fSiCNTs/polymer experiences lower bearable maximum strains in response to imposed loads in comparison with the O-fCNTs/polymer which is opposite to what occurs in the armchair O-fSiCNTs and O-fCNTs/polymer. The more the functionalization degree is, the weaker the structure is and its stiffness, tensile strength, tolerable strain before fracture, and ability to absorption of internal energy decline. Not only are the zigzag O-fSiCNTs/polymer stiffer than the armchair O-fSiCNTs/polymer in every percent of functionalization, but also as compared to the armchair ones, they show a lower decrease in the variation of Young’s modulus with increasing the functionalization percentage.

Proton conduction and electrochemical enzyme-free glucose sensitive sensing based on a newly constructed Co-MOF and its composite with hydroxyl carbon nanotubes

It is a great challenge to construct MOFs-based materials with low activation energy for potential applications in proton exchange membrane fuel cells (PEMFCs) as well as fine electrocatalytic glucose sensing performance. Herein, we report a novel 2D Co-MOF {[Co(iip)(bbbm)(H2O)2]·2DMF·2H2O}n obtained through the assembly between Co(II) and 5-iodoisophthalic acid (H2iip) in the presence of the hydrophobic ligand 1,1-(1,4-butanediyl)bis-1H-benzimidazole (bbbm). Its composite with hydroxyl-functionalized carbon nanotubes (Co-MOF@CNTs) was fabricated under ambient conditions. The (8) hydrogen-bonded ring exists in Co-MOF. Both the composite membranes of Co-MOF and Co-MOF@CNTs with nafion exhibit interesting proton-conductive behavior, which are even superior to that of nafion in aqueous medium with the same pH values. Among them, the proton conductivity of the composite Co-MOF@CNTs/nafion membrane is expectedly superior to that of the composite Co-MOF/nafion membrane. Remarkably, the composite Co-MOF@CNTs/nafion membrane exhibited an exceptionally low activation energy (Ea = 0.082 eV, pH = 3), which is among one of the lowest Ea values for the reported novel proton-conducting polymeric materials/composites, resulting in almost unchanged conductivity over the measured temperature range, revealing its potential application in PEMFCs. Moreover, both the pristine Co-MOF and its composite Co-MOF@CNTs could serve as electrocatalytic materials toward glucose oxidation. The Co-MOF@CNTs electrode exhibits expectedly more rapid and sensitive electrochemical glucose sensing with relatively lower determination limit (LOD = 3 μM) and larger detection range (0.01–5 mM) in comparison with that of the pristine Co-MOF (LOD = 0.021 mM, 0.01–2.40 mM).

Tuning of water distribution in the membrane electrode assembly of anion exchange membrane fuel cells using functionalized carbon additives

Water management of membrane electrode assemblies (MEAs) has a significant impact on both the power performance and durability of anion exchange membrane fuel cells (AEMFCs). In this work, the hydrophobicity of catalyst layers (CLs) was systematically tuned using hydroxyl-functionalized and fluoroalkyl-functionalized carbon additives to improve water management. The inclusion of the fluorinated carbon in the anode CL effectively suppresses anode water flooding, whereas the hydroxyl-functionalized carbon additive in the cathode prevents cathode drying. The pairing of the hydrophobic anode CL and the hydrophilic cathode CL increases the maximum current density by 1.7 times compared with the carbon-additive-free MEA and ensures stable constant current operation for more than 1000 h due to the mitigation of water imbalance between the cathode and anode. This work highlights the importance of water management and provides simple and diversified means to tune the water distribution of an AEMFC.

On the adsorption of volatile organic compounds on hydroxyl-functionalized carbon nanotubes in aqueous solution

Volatile organic compounds (VOCs) are among the primary concerns due to their practical threatening on living environment and human health. This work aims at examining the physical adsorption behavior of four representative VOC species on hydroxyl-functionalized CNTs in terms of molecular dynamics simulations. Simulation results indicate that the adsorption affinities of these four VOC species follow the order of toluene > ether > acetone > methanol for both the unfunctionalized and hydroxyl-functionalized CNTs. This adsorption preference is endorsed by the binding energy calculations based on the umbrella sampling algorithm. The surface modifications due to the introduction of hydroxyl groups affect both the adsorption mechanism and equilibrium configuration. The hydrogen-bond network near the adsorption region is rebuilt for stabilizing the adsorption kinetics. Compared to the dominant van der Waals interaction, the electrostatic interaction between the charged hydroxyl groups and the VOC molecules are found to be much less significant. With the increase of hydroxyl concentration, the adsorption affinity decays for all four VOC species. This conclusion is confirmed by both the binding free energies and the number of successfully adsorbed VOC molecules. The fundamental mechanism is due to the reduction of the originally hydrophobic area of CNTs surface and the additional bonding competition from water molecules. This work presents a molecular insight on the interaction between VOC molecules and hydroxyl-functionalized CNTs in aqueous solution. It can also benefit the development and design of smart filtration devices of VOC molecules for their early removal in aqueous solutions.

Atomistic Insights on the Adsorption of Long-Chain Undecane Molecules on Hydroxyl-Functionalized Carbon Nanotubes

Atomistic Insights on the Adsorption of Long-Chain Undecane Molecules on Hydroxyl-Functionalized Carbon Nanotubes

On the Adsorption of Volatile Organic Compounds on Hydroxyl-Functionalized Carbon Nanotubes in Aqueous Solution

On the Adsorption of Volatile Organic Compounds on Hydroxyl-Functionalized Carbon Nanotubes in Aqueous Solution

Effect of hydroxylated carbon nanotubes on the thermal and electrical properties of derived epoxy composite materials

Carbon nanotubes are efficient thermal conductors and exhibit unique electrical properties. What is not entirely clear, however, is how to effectively transfer the carbon nanotube's unique attributes exhibited at the nanoscale to the macroscale. The primary focus of this study was upon identifying the main causes that can lead to improvements in thermal and electrical conductivity for polymers with the use of the reinforcement material. The effects of carbon nanotube type and structure on the physical properties of derived epoxy composite materials were investigated experimentally to better understand the applied physics of thermal and electrical transport at the nanoscale. The thermal and electrical properties of the composite materials were also investigated theoretically with various models. The results indicated that the hydroxyl functionalization of carbon nanotubes can be an effective means to enhance the thermal and electrical properties of the derived composite materials. Hydroxyl-functionalized carbon nanotubes exhibit considerably improved thermal and electrical conductivity in applications including polymer composites. Hydroxylated carbon nanotubes can achieve at least one or more of the following objectives: improves the solubility and dispersibility of the carbon nanotubes in polymer materials into which the carbon nanotubes are to be mixed, reduces contact resistance between carbon nanotubes incorporated into the polymer material by drawing the carbon nanotubes closer together, and provides a conductive bridge between carbon nanotubes to reduce the electrical contact resistance there between. Multi-walled carbon nanotubes can reduce the probability of inelastic phonon scattering due to grain boundaries, thereby yielding a higher effective thermal conductivity for derived polymer composite materials.

Effective Trapping of Lithium Polysulfides Using a Functionalized Carbon Nanotube-Coated Separator for Lithium-Sulfur Cells with Enhanced Cycling Stability.

The critical issues that hinder the practical applications of lithium-sulfur batteries, such as dissolution and migration of lithium polysulfides, poor electronic conductivity of sulfur and its discharge products, and low loading of sulfur, have been addressed by designing a functional separator modified using hydroxyl-functionalized carbon nanotubes (CNTOH). Density functional theory calculations and experimental results demonstrate that the hydroxyl groups in the CNTOH provoked strong interaction with lithium polysulfides and resulted in effective trapping of lithium polysulfides within the sulfur cathode side. The reduction in migration of lithium polysulfides to the lithium anode resulted in enhanced stability of the lithium electrode. The conductive nature of CNTOH also aided to efficiently reutilize the adsorbed reaction intermediates for subsequent cycling. As a result, the lithium-sulfur cell assembled with a functional separator exhibited a high initial discharge capacity of 1056 mAh g-1 (corresponding to an areal capacity of 3.2 mAh cm-2) with a capacity fading rate of 0.11% per cycle over 400 cycles at 0.5 C rate.

One-step microwave synthesis of N-doped hydroxyl-functionalized carbon dots with ultra-high fluorescence quantum yields.

A one-step microwave synthesis of N-doped hydroxyl-functionalized carbon dots (CDs) with ultra-high fluorescence quantum yields (QYs) of 99% is reported. These ultra-high QY CDs were synthesized using citric acid and amino compound-containing hydroxyls like ethanolamine and tris(hydroxylmethyl)aminomethane. Amino and carboxyl moieties can form amides through dehydration condensation reactions, and these amides act as bridges between carboxyl and hydroxyl groups, and modify hydroxyl groups on the surface of the CDs. The entire reaction can be carried out within 5 min. When the molar ratio of reactants is 1 : 1, the hydroxyl and graphitic nitrogen content is the highest, and the synergy leads to a high ratio between the radiative transition rate and nonradiative transition rate as well as a high QY. The developed pathway to N-doped hydroxyl-functionalized CDs can provide unambiguous and remarkable insights into the design of highly luminescent functionalized carbon dots, and expedite the applications of CDs.

In situ synthesis of zeolitic imidazolate frameworks/carbon nanotube composites with enhanced CO2 adsorption

A series of ZIF-8 and hydroxyl-functionalized carbon nanotube (CNT) composites were successfully synthesized by the solvothermal method. The obtained ZIF-8/CNT composites were characterized by XRD, SEM, TGA and N2 adsorption at 77 K. The contents of ZIF-8 and CNTs in the composites were calculated from thermal analysis data. CO2 and N2 adsorption at 273 K on the composites was also investigated and compared. The ZIF-8 particles in the composites exhibit similar crystal structures and morphology to those of pure ZIF-8, but display enhanced thermal stability. The surface areas and pore volumes of the ZIF-8/CNT composites are higher than the values calculated for hypothetical physical mixtures, and the synergetic effect between ZIF-8 and CNTs can be proposed. This phenomenon demonstrates that the incorporation of CNTs into ZIF-8 can facilitate the nucleation and crystallization of ZIF-8. As a result, the composites with an optimal CNT content (3.63 wt%) show improved CO2 adsorption capacity and higher relative selectivity for CO2/N2 compared with pure ZIF-8.

Interfacial improvement of carbon fiber/epoxy composites using a simple process for depositing commercially functionalized carbon nanotubes on the fibers

An aqueous suspension deposition method was used to coat the sized carbon fibers T700SC and T300B with commercially carboxylic acid-functionalized and hydroxyl-functionalized carbon nanotubes (CNTs). The CNTs on the fiber surfaces were expected to improve the interfacial strength between the fibers and the epoxy. The factors affecting the deposition, especially the fiber sizing, were studied. According to single fiber-composite fragmentation tests, the deposition process results in improved fiber/matrix interfacial adhesion. Using carboxylic acid-functionalized CNTs, the interfacial shear strength was increased 43% for the T700SC composite and 12% for the T300B composite. The relationship between surface functional groups of the CNTs and the interfacial improvement was discussed. The interfacial reinforcing mechanism was explored by analyzing the surface morphology of the carbon fibers, the wettability between the carbon fibers and the epoxy resin, the chemical bonding between the fiber sizing and the CNTs, and fractographic observation of cross-sections of the composites. Results indicate that interfacial friction, chemical bonding and resin toughening are responsible for the interfacial improvement of nanostructured carbon fiber/epoxy composites. The mechanical properties of the CNT-deposited composite laminate were further measured to confirm the effectiveness of this strategy.

A temperature-responsive carbon black nanoparticle prepared by surface-induced reversible addition–fragmentation chain transfer polymerization

A reversible addition–fragmentation chain transfer (RAFT) agent, 2-{[(dodecylsulfanyl)carbonothioyl]sulfanyl}propanoic acid (DSCTSP), was immobilized on the hydroxyl-functionalized carbon black (CB) surface via a direct condensation reaction, producing CB–DSCTSP. Then, RAFT polymerizations were carried out on carbon black surface using the CB–DSCTSP as a chain transfer agent. Poly( N-isopropylacrylamide) (PNIPAAm) chains were grown from the carbon black surface by a surface-induced reversible addition–fragmentation chain transfer (SI-RAFT) polymerization. FT-IR, 1H NMR, TGA, TEM, and dynamic light scattering were used to characterize the carbon black grafted with poly( N-isopropylacrylamide) (CB- g-PNIPAAm). Dispersion experiment showed that CB- g-PNIPAAm had a good solubility in water. 1H NMR, AFM and dynamic light scattering measurements showed that CB- g-PNIPAAm behaved a reversible temperature-responsive property in water.