Nanotube Aerogels Research Articles

Enhancing mechanical performances of polystyrene composites via constructing carbon nanotube/graphene oxide aerogel and hot pressing

Mixture of styrene and initiator polymerized in situ in three-dimensional graphene oxide (GO)/carbon nanotube (CNT) aerogel (GOCA) obtained via modified Hummers' method and freeze-drying method to form GOCA/polystyrene (GOCA/PS) nanocomposites. After heating processing, the prepared GOCA/PS nanocomposite sheets exhibited excellent mechanical properties. Results revealed that GOCA was well dispersed and embedded into the PS matrix. When the mass ratio of GO to CNT was 7:3 and the total loading of GOCA was 1.02 wt%, tensile, flexural, compressive, and impact strengths were greatly improved (increased by 64.05%, 54.7%, 107.38%, and 66.5%, respectively, compared with neat PS). Meanwhile, the prepared GOCA/PS nanocomposites presented great microhardness of ~265 MPa and compressive modulus of ~689 MPa. We believe that these effective methods may provide good idea for designing and investigating reinforced composites.

Direct synthesis of carbon nanotube aerogel using floating catalyst chemical vapor deposition: effect of gas flow rate

Carbon nanotube aerogel (CNT aerogel) was synthesized through the catalytic decomposition of toluene in the mixture of ferrocene and thiophene through floating catalyst chemical vapor deposition method. This study described the effect of (Ar and H2) carrier gas flow rate on the quality and yield of CNT aerogel. Results indicated that the flow rate of the gas was an important parameter which helped in determining the yield and quality of the CNTs. The CNTs are multiwalled with its diameter decreased when the H2 flow rate was increased. Scanning electron microscopy indicated the average diameter of ≈ 31, 30, 27, 26, 18, and 15 nm when the H2 flow rate was increased from 400, 450, 500, 550, 600, 650 sccm, respectively. Furthermore, elemental analysis with energy dispersion spectrum for CNT aerogel produced at 600 sccm resulted in a 96.22 wt% carbons along with 3.78 wt% iron in the CNT aerogel sample. Results indicated that a hydrogen flow rate of 600 sccm produced high yield and good CNTs morphology.

Free-standing flexible graphene-based aerogel film with high energy density as an electrode for supercapacitors

Abstract Two-dimensional graphene film exhibits sluggish ion diffusivity while three-dimensional (3D) graphene aerogel has low packing density and poor mechanical flexibility. Consequently, there is an urgent need for graphene-based film with both mechanical robustness and high specific capacitance. Here, we present an easy and scalable strategy for fabricating a free-standing flexible graphene-based aerogel film electrode with a two-layered structure, in which the top layer is an interconnected macroporous reduced graphene oxide/carbon nanotube (RGO/CNT) aerogel, and the bottom layer is a flexible electrospun polyacrylonitrile (PAN) nanofiber membrane. The porous 3D structure of the aerogel provides fast transport of electrolyte ions and electrons, while the nanofiber membrane provides both strong support for the aerogel and mechanical flexibility. Polypyrrole (PPy) can be uniformly loaded on RGO/CNT/PAN (RCP) composite aerogel film to provide pseudocapacitance, and nitrogen-doped RGO/CNT/carbon nanofiber (NRCC) aerogel film can be obtained by further pyrolysis. The resultant RCP@PPy-0.05//NRCC based asymmetric supercapacitor can have a maximum voltage of 1.7 V and a maximum energy density of 60.6 W h kg−1 at 850.2 W kg−1. This indicates that free-standing graphene-based aerogel film can be used in flexible supercapacitors.

Utilization of waste engine oil for carbon nanotube aerogel production using floating catalyst chemical vapor deposition

The floating catalyst chemical vapor deposition (FCCVD) approach has been successfully employed in offering a continuous single-step process to the synthesis of carbon nanotubes aerogel (CNT aerogel) in terms of the industrial scale. Industrial applications require selecting a carbon source that is abundant, cost-effective and environment-friendly. Thus, waste engine oil (WEO) is preferably employed as a carbon source involving the production of CNT aerogel. In this research study, the catalytic decomposition of the WEO was employed to synthesize CNT aerogel. First, fractional distillation of WEO was achieved resulted in five (5) fractions. As per analysis is performed via GC-MS, low molecular weight hydrocarbons could be efficiently separated, which is required for catalyst dissolving. As per CNS analysis, each fraction was found to contain >69% carbon, <0.1% sulfur and <0.3% nitrogen. The FCCVD method was employed to synthesize CNT aerogel via a WEO fraction 1 mixed along with ferrocene catalyst at a temperature of 1150 °C. It was found that the product’s MWCNTs were associated with 86.74% purity and 496% carbon deposition yield. The aerogel was found to possess a mesopore distribution of 142.9 m2 g−1 as its specific surface area, 39.079 nm as average pore diameter and 1.3964 cm3 g−1 as total pore volume. The CNTs tend to assemble randomly as well as get entangled to form a 3-D structure.

Graphene-carbon nanotube hybrid aerogel/polyethylene glycol phase change composite for thermal management

A simple graphene-carbon nanotube aerogel composite was prepared. In this paper, we studied the three-dimensional (3 D) thermally conductive frameworks with different ratios of graphene oxide (GO) and carbon nanotubes (CNTs). The effects of 3 D thermal conductive frameworks with different ratios of GO and CNT on the morphology, structure and thermal conductivity of phase change composites were also studied. The results show that the 3 D thermally conductive framework has the advantages of managing the thermal conductivity of phase change composites. The obtained phase change composite with only 1 wt% of graphene-carbon nanotube aerogels showed top-quality thermal conductivity of 0.76 W/m·K. The preparation process was simple and has the advantage of environmental protection, so which was suitable for practical applications using polyethylene glycol/graphene-carbon nanotube aerogel phase change composite as energy materials, and has manageable energy conversion, storage and thermal conductivity properties.

Synthesis and characterization of mercapto-modified graphene/multi-walled carbon nanotube aerogels and their adsorption of Au(III) from environmental samples

In this study, mercapto-modified graphene/multi-walled carbon nanotube aerogels were facilely constructed by using L-cysteine as a cross-linking agent and modifier. The effective adsorption behaviors of Au(III) from environmental samples by the aerogels were investigated. The aerogels were characterized, and many influencing factors, such as pH value, adsorbent dosage, and contact time, were optimized. The kinetic data followed the pseudo-second-order model, and the equilibrium data fitted well to the Freundlich isotherm model. The maximum adsorption capacity for Au(III) reached approximately 47 mg g−1. Moreover, the Au(III) could be desorbed with 1 M HCl containing 4% thiourea and detected by inductively coupled plasma atomic emission spectroscopy. Finally, the aerogels were used in lake water, seawater, and soil samples for Au(III) adsorption with recovery rates from 87.0% to 102.8%. The results indicate that the developed aerogel is an excellent adsorbent for removing Au(III) from samples and has significant application prospects in environmental research.

The preparation of novel polyvinyl alcohol (PVA)-based nanoparticle/carbon nanotubes (PNP/CNTs) aerogel for solvents adsorption application

In this paper, a novel PVA-based polymer nanoparticles/carbon nanotubes (PNP/CNTs) aerogel was successfully developed. Firstly, certain amount water-dispersed carbon nanotubes were introduced into PVA solution and undergo hydrothermal process in the presence of ferric iron to obtain novel PNP/CNTs solution. Then, the PNP/CNTs aerogels were fabricated by the “freeze-thaw” cycle and freeze-drying methods, followed by the vapor deposition of trimethylchlorosilane to obtain hydrophobic aerogel. The morphology and structure of polymer nanoparticles were characterized by SEM, TEM, FT-IR, Raman, UV–vis and XRD. The density, structure and thermal stability of PNP/CNTs aerogel were also investigated. The compressive performance of PNP/CNTs aerogels were better than PVA aerogel and showed small difference before and after hydrophobic treatment. In addition, the adsorption measurements of different aerogels were also studied. The results showed that hydrophobic PNP/CNTs-6 aerogel exhibited better adsorption capacities and reusability than others. These outstanding properties can make PNP/CNTs aerogels considered as a promising candidate to remove organic solvents from aqueous solution.

Alkylated Nanofibrillated Cellulose/Carbon Nanotubes Aerogels Supported Form-Stable Phase Change Composites with Improved n-Alkanes Loading Capacity and Thermal Conductivity.

The exploitation of phase change materials (PCMs) with excellent shape stability, considerable latent heat storage capacity, and superior thermal conductivity is essential for their applications in heat storage and thermal regulation. Here, form-stable composite PCMs based on n-octacosane, nanofibrillated cellulose (NFC), and carbon nanotubes (CNTs) were successfully obtained by impregnating n-octacosane into the alkylated NFC/CNTs hybrid aerogels. The three-dimensional interconnected porous aerogels could adequately support the melted n-octacosane and prevent the leakage problem due to strong capillary force and surface tension. After treatment with alkylated modification, the affinity between NFC/CNTs aerogels and n-alkanes was significantly improved, resulting in excellent shape stability, improved thermal reliability, and high n-alkanes loading capacity for the as-prepared composite PCMs. The differential scanning calorimetry analysis showed that composite PCMs based on the alkylated NFC/CNTs aerogels exhibited an extremely high phase change enthalpy ranging from 250.9 to 252.9 J/g. Furthermore, the thermal conductivity and photothermal conversion and storage efficiency of the synthesized PCMs were effectively enhanced by the introduction of CNTs. Thus, the synthesized composite PCMs exhibit considerable potential for practical application in heat storage and thermal regulation.

Three-Dimensional Monolithic Organic Battery Electrodes.

Design of freestanding electrodes incorporated with redox-active organic materials has been limited by the poor intrinsic electrical conductivity and lack of methodology driving the feasible integration of conductive substrate and the organic molecules. Single-walled carbon nanotube (SWCNT) aerogels, which possess continuous network structure and high surface area, offer a three-dimensional electrically conducting scaffold. Here, we fabricate monolithic organic electrodes by coating a nanometer-scale imide-based network (IBN) that possesses abundant redox-active sites on the 3D SWCNT scaffold. The substantially integrated 3D monolithic organic electrodes sustain high electrical conductance through a 3D electronic pathway in their compressed form (∼21 μm). A thin and controllable layer (<8 nm) of IBN organic materials has a strong adhesion onto the ultra-lightweight and conductive substrate and facilitates multielectron redox reactions to deliver a specific capacity of up to 1550 mA h g-1 (corresponding to the areal capacity of ∼2.8 mA h cm-2). The redox-active IBN in synergy with the 3D SWCNT scaffold can enable superior electrochemical performances compared to the previously reported organic-based electrode architectures and inorganic-based electrodes.

Piezoresistive effect of superelastic graphene aerogel spheres

Abstract Graphene aerogels have recently become one of the most attractive carbon metamaterials due to their unique properties such as ultralight weight, large specific surface area, high electrical conductivity and excellent compressibility. However, there still remain some challenges to efficiently fabricate superelastic graphene aerogels through the facile and cost-effective processes and assemble them into a well-designed unity for wider applications. Here we show superelastic grouped graphene/carbon nanotube (CNT) aerogel spheres (GCSs) for intelligent piezoresistive sensors by wet-spinning technique. With the synergistic effect of graphene and CNTs, such grouped GCSs with core-shell structure annealed at 1000 °C show excellent elasticity and fatigue resistance, which are comparable to those of graphene spheres annealed at 2500 °C. The grouped GCSs can fully recover after compression at 95% strain, and still retain 70% of maximum stress with negligible plastic deformation and structural damage even after 1000 cycles at 70% strain. Significantly, the robust, superelastic and conductive GCSs are suitable for pressure sensors, exhibiting extraordinary cycling stability and long working life. Due to intact and tough shells, the small-scale GCSs with high sensitivity can be easily assembled into stretchable piezoresistive sensors with pixel arrays for spatial pressure distribution measurement and object shape recognition.

Three‐dimensional Polypyrrole Derived N‐doped Carbon Nanotube Aerogel as a High‐performance Metal‐free Catalyst for Oxygen Reduction Reaction

AbstractA novel N‐doped carbon nanotube aerogel has been synthesized by pyrolysis of the three‐dimensional tubular polypyrrole networks and evaluated as a metal‐free electrocatalyst for the oxygen reduction reaction. The carbon aerogel catalysts are pyrolyzed at 500 °C (PPy/C‐500), 700 °C (PPy/C‐700), 900 °C (PPy/C‐900) and 1050 °C (PPy/C‐1050), and display the pyrolyzed temperature‐dependent activity and stability. The catalytic activity is increased with the increase of pyrolysis temperature from 500 °C to 1050 °C, ascribed to the high electronically conductive graphitic phases, the thin wall of the three‐dimensional tubular carbon aerogel framework and the increased effective active sites. The nitrogen content is reduced with the increase of pyrolysis temperature, and which plays an important role in the stability of the pyrolyzed catalyst. After 1500 cycles, the PPy/C‐1050 catalyst shows more positive half‐wave potential than the commercial Pt/C catalyst, and displays a quasi‐four‐electron pathway toward the oxygen reduction reaction in the acid solution. This work provides an effective strategy for preparing the low cost and metal‐free N‐doped carbon aerogel catalyst from the conjugated conducting polymer, to achieve high activity and stability.

The Synergistic Effect of a Bimetallic Catalyst for the Synthesis of Carbon Nanotube Aerogels and their Predominant Chirality.

Synthesis of continuous spinnable carbon nanotube (CNT) fibers is the most promising method for producing CNT fibers for commercial applications. The floating-catalyst chemical vapor deposition (FC-CVD) method is a rapid process that achieves catalyst formation, CNT nucleation and growth, and aerogel-like sock formation within a few seconds. However, the formation mechanism is unknown. Herein, the progress of CNT fiber formation with bimetallic catalysts was studied, and the effect of catalyst composition to CNT fiber synthesis and their structural properties was investigated. In the case of bimetallic catalysts, the carbon source rapidly decomposes and generates various secondary hydrocarbon species, such as CH4 , C2 H4 , C2 H2 , C3 H6 , and C4 H10 whereas monometallic catalysts generate only CH4 and C2 H4 on decomposition. CNT fiber formation with Fe1 Ni0 begins about 400 mm from the reactor entrance, whereas CNT formation with Fe0.8 Ni0.2 and Fe0.5 Ni0.5 begins at about 500 and 300 mm, respectively. The formed CNT bundles and individual CNTs are oriented along the gas flow at these locations. The enhanced rate of fiber formation and lowering of growth temperature associated with bimetallic catalysts is explained by the synergistic effects between the two metals. The synthesized CNTs become predominantly semiconducting with increasing Ni contents.

Silver Nanowires on Carbon Nanotube Aerogel Sheets for Flexible, Transparent Electrodes.

Flexible, free-standing transparent conducting electrodes (TCEs) with simultaneously tunable transmittances up to 98% and sheet resistances down to 11 Ω/sq were prepared by a facile spray-coating method of silver nanowires (AgNWs) onto dry-spun multiwall carbon nanotube (MWNT) aerogels. Counterintuitively, the transmittance of the hybrid electrodes can be increased as the mass density of AgNWs within the MWNT aerogels increases; however, the final achievable transmittance depends on the initial transparency of the MWNT aerogels. Simultaneously, a strong decrease in sheet resistance is obtained when AgNWs form a percolated network along the MWNT aerogel. Additionally, anisotropic reduction in sheet resistance and polarized transmittance of AgNW/MWNT aerogels is achieved with this method. The final AgNW/MWNT hybrid TCEs transmittance and sheet resistance can be fine-tuned by spray-coating mechanisms or by choosing initial MWNT aerogel density. Thus, a wide range of AgNW/MWNT hybrid TCEs with optimized optoelectronic properties can be achieved depending of the requirements needed. Finally, the free-standing AgNW/MWNT hybrid TCEs can be laminated onto a wide range of substrates without the need of a bonding aid.

Synthesis and mechanism perspectives of a carbon nanotube aerogel via a floating catalyst chemical vapour deposition method

An effective and cost-effective approach to synthesize new materials can be determined via research on a carbon nanotube (CNT) aerogel. This review paper gives an overview of the current synthetic methodologies and routes to enhance understanding. It also investigates the appropriate issues on the development of CNT-based three-dimensional (3-D) porous materials in an attempt to fill the knowledge gap regarding viability. First, an elaborate description on CNTs is provided, followed by a focus on CNT macrostructure fabrication, showcasing their key features, disadvantages, advantages and other aspects that were considered as related. Then, the methods for synthesis pertaining to the CNT aerogel are discussed with a focus on a floating catalyst chemical vapour deposition method as well as the growth mechanism pertaining to CNTs employing the method. Key parameters, including catalyst, reaction time, carbon source, carrier gas and reaction temperature, which could cast an impact on the efficiency of the process are discussed subsequently.

Highly Compressive Boron Nitride Nanotube Aerogels Reinforced with Reduced Graphene Oxide.

Boron nitride nanotubes (BNNTs), structural analogues of carbon nanotubes, have attracted significant attention due to their superb thermal conductivity, wide bandgap, excellent hydrogen storage capacity, and thermal and chemical stability. Despite considerable progress in the preparation and surface functionalization of BNNTs, it remains a challenge to assemble one-dimensional BNNTs into three-dimensional (3D) architectures (such as aerogels) for practical applications. Here, we report a highly compressive BNNT aerogel reinforced with reduced graphene oxide (rGO) fabricated using a freeze-drying method. The reinforcement effect of rGO and 3D honeycomb-like framework offer the BNNTs/rGO aerogel with a high compression resilience. The BNNTs/rGO aerogels were then infiltrated with polyethylene glycol to prepare a kind of phase change materials. The prepared phase change material composites show zero leakage even at 100 °C and enhanced thermal conductivity, due to the 3D porous structure of the BNNTs/rGO aerogel. This work provides a simple method for the preparation of 3D BNNTs/rGO aerogels for many potential applications, such as high-performance polymer composites.

Interplay of topologically interconnected mesoporous network and defects number density in improving electroactivity of graphene-single-walled carbon nanotube aerogels

Electroactivity of graphene-family nanomaterials and three-dimensional porous architectures is key for various applications at the grand challenges of “energy-water-sensing nexus.” It requires well-controlled morphology, manipulation of surface chemistry, interconnected topologic network, as well as electronic properties. Here, we demonstrate by taking advantage of hierarchical mesoporosity, optimized defects number density, nD (edges-plane and pore sites, oxygenated and nitrogenated functionalities), further invoked by synergistic coupling between one-dimensional single-walled carbon nanotube (SWCNT) as “nano” spacers and polymer linker with two-dimensional reduced graphene oxide derived three-dimensional scaffolds (known as aerogels) under hydrothermal conditions, and improved electrochemical (re)activity by enhancing the heterogeneous electron transfer rate (kET). We determined the correlation among nD, in-plane sp2C cluster, La and interdefect distance, LD (all via Raman spectroscopy), and kET (via scanning electrochemical microscopy) to establish “structure–property–functionality–electroactivity” relationships. The prominent Raman bands were also analyzed to determine the sp2-bonded C cluster size (La) for graphene- and nanotube-rich phases. The interplay of (1) rich surface redox chemistry due to carbonyl—C=O, carboxyl—COOH, pryridinic—N and pyrrolic—N functional groups, and geometric defects; (2) protruded edge plane and nanopores sites; (3) topological network; and (4) finite density of states with increased vacancy sites is emphasized and signifies the inherently activated electronic states in functionalized nanoporous composite carbon aerogels, for improved physicochemical processes (following graphene &amp;lt; N-graphene &amp;lt; graphene-SWCNT &amp;lt; N-graphene-SWCNT aerogels) relevant for electrocatalysis, thermo-electrochemical energy harvesting, desalination, and biosensing.

Free-standing integrated cathode derived from 3D graphene/carbon nanotube aerogels serving as binder-free sulfur host and interlayer for ultrahigh volumetric-energy-density lithium[sbnd]sulfur batteries

The actual applications of lithium sulfur (LiS) batteries are significantly obstructed by limited cyclability and low volumetric-energy-density due to the shuttling effect of polysulfides and low mass density of sulfur cathode. Herein, we report a free-standing, compact, conductive and integrated cathode (G/CNT-S//G/CNT), constructed by compressing graphene/carbon nanotubes (G/CNT) aerogels, simultaneously serving as bi-functionalities of binder- and metal-current-collector-free sulfur host (G/CNT-S) and interlayer (G/CNT), for high volumetric-energy-density LiS batteries. The G/CNT aerogels display three-dimensional interconnected porous network, large surface area (363 m2 g−1) and high electrical conductivity (67 S m−1), which can endow the cathode with ultrahigh volumetric mass density (1.64 g cm−3) and superior electron-ion transport network. Meanwhile, the compressed ultralight G/CNT film can act as flexible interlayer for synergistically suppressing the polysulfide shuttling via both chemical interaction and physical restriction. Consequently, the compact cathodes, achieve high capacity of 1286 mAh g−1 at 0.2 C and long-term cyclability with an extremely low decay rate of 0.06% over 500 cycles at 2 C. Most importantly, our compact cathodes represent unprecedented volumetric capacity of 1841 Ah L−1 and volumetric-energy-density of 2482 Wh L−1, both of which are the highest values of LiS batteries reported to date. Therefore, this proposed strategy will open a new avenue for developing high volumetric-energy-density LiS batteries.

Three dimensional nylon66@carbon nanotube aerogel: A platform for high-performance electromagnetic wave absorbing composites

Carbon nanotube aerogels are highly desirable for application in the field of the energy conversion and energy storage due to their superior electrical conductivity. Herein, three-dimensional carbon nanotube/nylon 66 (3D CNT/PA66) aerogels have been fabricated for the first time by freeze-drying, where CNTs are coated with the PA66. Meanwhile, CNT/PA66 aerogels can form a continuous conductive network at low CNTs loading. Therefore, CNT/PA66 aerogels have good electromagnetic wave (EM) absorption properties with a maximum reflection loss of −44.3 dB at 13.9 GHz, a reflection loss of less than −10 dB in the frequency range of 12.2–15.7 GHz, and a bandwidth of 3.5 GHz. Our results indicate that the CNT/PA66 aerogel is a promising platform for the preparation of high-performance EM absorbing composites.

A Directional Strain Sensor Based on Anisotropic Microhoneycomb Cellulose Nanofiber-Carbon Nanotube Hybrid Aerogels Prepared by Unidirectional Freeze Drying.

Aerogels are one of the most popular composite reinforcement materials because of their high porosity and their continuous and homogeneous network. Most aerogels are isotropic, thus leading to isotropic composites when they are used as fillers. This fundamentally limits their applications in areas where anisotropy is needed. Here, an anisotropic microhoneycomb cellulose nanofiber- (CellF)-carbon nanotube (CNT) aerogel (denoted MCCA) is reported that contains unidirectionally aligned penetrating microchannels, which is prepared by a unidirectional freeze-drying method, using the structure-directing function of the CellFs. Due to its anisotropic nature, MCCA-reinforced polydimethylsilexane (denoted MCCA/PDMS) shows distinct anisotropic behavior, with the electrical conductivity and Young's modulus along the direction of penetrating microchannels being approximately twice those in the orthogonal direction. MCCA/PDMS is used to make "directional" strain sensors with electrical resistance as the output signal. They demonstrate a 92% sensitivity difference between the microchannel direction and its orthogonal direction. This approach can be used to prepare anisotropic MCCA-based composites with other polymers for different applications.

A novel graphene oxide-carbon nanotubes anchored α-FeOOH hybrid activated persulfate system for enhanced degradation of Orange II

Persulfate activation has been applied as one of the efficient advanced oxidation processes (AOPs) to remediate polluted environments. In this study, a novel α-FeOOH anchored by graphene oxide (GO)-carbon nanotubes (CNTs) aerogel (α-FeOOH@GCA) nanocomposite activated persulfate system (α-FeOOH@GCA + K2S2O8) was applied for decolorization of Orange II (OII). The decolorization of OII was remarkably enhanced to a level of ~99% in this system compared with that of pristine α-FeOOH (~44%) or GO-CNTs (~18%). The enhanced catalytic activity of α-FeOOH@GCA was due to the formation of a heterojunction by α-FeOOH and GO-CNTs as confirmed by the presence of Fe–O–C chemical bonds. The degradation intermediates of OII were comprehensively identified. The proposed degradation pathway of OII begins with the destruction of the conjugated structures of OII by the dominant reactive oxygen species, surface-bound SO4•−. The decolorization efficiency of OII by the α-FeOOH@GCA activated persulfate system decreased from the first to third cycle of recycling. Ultraviolet (UV) irradiation or introduction of a small amount of Fe2+ could restore the activation of this system. The results show that the α-FeOOH@GCA persulfate activation system promises to be a highly efficient environmental remediation method for organic pollutants.