Selective glycerol oxidation using platinum nanoparticles supported on multi-walled carbon nanotubes and nitrogen-doped graphene hybrid

Selective oxidation of glycerol is a hot topic.Increased biodiesel production has led to glycerol oxidation over Au- and Pt-based catalysts being widely studied.However,Pt catalysts suffer from deactivation because of weak metal-support interactions.In this study,multi-walled carbon nanotube（MWCNTs）-pillared nitrogen-doped graphene（NG） was prepared by direct pyrolysis of melamine on MWCNTs,and the synthesized NG-MWCNT composite was used as the support for Pt.Characterization results showed that the surface area（173 m^2/g） and pore volume of the NG-MWCNT composite were greater than those of bare MWCNTs and the separated melamine pyrolysis product（CH_x）.Pt（1.4±0.4 nm） dispersion on the NG-MWCNTs was favorable and the Pt/NG-MWCNT catalyst was highly active and selective in the oxidation of glycerol to glyceric acid（GLYA） in base-free aqueous solution.For example,the conversion of glycerol reached 64.4% with a GLYA selectivity of 81.0%,whereas the conversions of glycerol over Pt/MWCNTs and Pt/CN_x were 29.0% and 31.6%,respectively.The unique catalytic activity of the Pt/NG-MWCNTs is attributed to well-dispersed Pt clusters on the NG-MWCNTs and the electron-donating effect of the nitrogen dopant in the NG-MWCNTs.

N-doped graphene quantum dot-decorated N-TiO2/P-doped porous hollow g-C_(3)N_(4) nanotube composite photocatalysts for antibiotic photodegradation and H2 production

Exclusive responsiveness to ultraviolet light (~3.2 eV) and high photogenerated charge recombination rate are the two primary drawbacks of pure TiO_(2). We combined N-doped graphene quantum dots (N-GQDs), morphology regulation, and heterojunction construction strategies to synthesize N-GQD/N-doped TiO_(2)/P-doped porous hollow g-C_(3)N_(4) nanotube (PCN) composite photocatalysts (denoted as G-TPCN). The optimal sample (G-TPCN doped with 0.1wt% N-GQD, denoted as 0.1% G-TPCN) exhibits significantly enhanced photoabsorption, which is attributed to the change in bandgap caused by elemental doping (P and N), the improved light-harvesting resulting from the tube structure, and the upconversion effect of N-GQDs. In addition, the internal charge separation and transfer capability of0.1% G-TPCN are dramatically boosted, and its carrier concentration is 3.7, 2.3, and 1.9 times that of N-TiO_(2), PCN, and N-TiO_(2)/PCN(TPCN-1), respectively. This phenomenon is attributed to the formation of Z-scheme heterojunction between N-TiO_(2) and PCNs, the excellent electron conduction ability of N-GQDs, and the short transfer distance caused by the porous nanotube structure. Compared with those of N-TiO_(2), PCNs, and TPCN-1, the H2 production activity of 0.1%G-TPCN under visible light is enhanced by 12.4, 2.3, and 1.4times, respectively, and its ciprofloxacin (CIP) degradation rate is increased by 7.9, 5.7, and 2.9 times, respectively. The optimized performance benefits from excellent photoresponsiveness and improved carrier separation and migration efficiencies. Finally, the photocatalytic mechanism of 0.1% G-TPCN and five possible degradation pathways of CIP are proposed. This study clarifies the mechanism of multiple modification strategies to synergistically improve the photocatalytic performance of 0.1% G-TPCN and provides a potential strategy for rationally designing novel photocatalysts for environmental remediation and solar energy conversion.

Flexible piezoresistive pressure sensor based on a graphene-carbon nanotube-polydimethylsiloxane composite

Flexible sensors are used widely in wearable devices, specifically flexible piezoresistive sensors, which are common and easy to manipulate.However, fabricating such sensors is expensive and complex, so proposed here is a simple fabrication approach involving a sensor containing microstructures replicated from a sandpaper template onto which polydimethylsiloxane containing a mixture of graphene and carbon nanotubes is spin coated. The surface morphologies of three versions of the sensor made using different grades of sandpaper are observed, and the corresponding pressure sensitivities and linearity and hysteresis characteristics are assessed and analyzed. The results show that the sensor made using 80-mesh sandpaper has the best sensing performance. Its sensitivity is 0.341 kPa-1in the loading range of 0–1.6 kPa, it responds to small external loading of 100 Pa with a resistance change of 10%, its loading and unloading response times are 0.126 and 0.2 s, respectively,and its hysteresis characteristic is ~7%, indicating that the sensor has high sensitivity, fast response, and good stability. Thus, the presented piezoresistive sensor is promising for practical applications in flexible wearable electronics.

Nitrogen⁃doped 3D graphene⁃carbon nanotube network for efficient lithium storage

A 3D nitrogen⁃doped graphene/multi⁃walled carbon nanotube(CS⁃GO⁃NCNT)crosslinked network mate⁃rial was successfully synthesized utilizing chitosan and melamine as carbon and nitrogen sources,concomitant with the incorporation of multi⁃wall carbon nanotubes and employing freeze drying technology.The material amalgamates the merits of 1D/2D hybrid carbon materials,wherein 1D carbon nanotubes confer robustness and expedited elec⁃tron transport pathways,while 2D graphene sheets facilitate rapid ion migration.Furthermore,the introduction of nitrogen heteroatoms serves to furnish additional active sites for lithium storage.When served as an anode material for lithium⁃ion batteries,the CS⁃GO⁃NCNT electrode delivered a reversible capacity surpassing 500 mAh·g^(-1),mark⁃edly outperforming commercial graphite anodes.Even after 300 cycles at a high current density of 1 A·g^(-1),it remained a reversible capacity of up to 268 mAh·g^(-1).

Toxicity of Multi-Walled Carbon Nanotubes,Graphene Oxide,and Reduced Graphene Oxide to Zebrafish Embryos

Objective This study was aimed to investigate the toxic effects of 3 nanomaterials, i.e. multi-walled carbon nanotubes （MWCNTs）, graphene oxide （GO）, and reduced graphene oxide （RGO）, on zebrafish embryos. Methods The 2-h post-fertilization （hpf） zebrafish embryos were exposed to MWCNTs, GO, and RGO at different concentrations （1, 5, 10, 50, 100 mg/L） for 96 h. Afterwards, the effects of the 3 nanomateria on spontaneous movement, heart rate, hatching rate, length of larvae, mortality, and malformations Is were evaluated. Results Statistical analysis indicated that RGO significantly inhibited the hatching of zebrafish embryos. Furthermore, RGO and MWCNTs decreased the length of the hatched larvae at 96 hpf. No obvious morphological malformation or mortality was observed in the zebrafish embryos after exposure to the three nanomaterials. Conclusion MWCNTs, GO, and RGO were all toxic to zebrafish embryos to influence embryos hatching and larvae length. Although no obvious morphological malformation and mortality were observed in exposed zebrafish embryos, further studies on the toxicity of the three nanomaterials are still needed.

An Overview of Carbon Nanotubes and Graphene for Biosensing Applications

With the development of carbon nanomaterials in recent years, there has been an explosion of interests in using carbon nanotubes(CNTs) and graphene for developing new biosensors. It is believed that employing CNTs and graphene as sensor components can make sensors more reliable, accurate, and fast due to their remarkable properties. Depending on the types of target molecular, different strategies can be applied to design sensor device. This review article summarized the important progress in developing CNT-and graphene-based electrochemical biosensors, field-effect transistor biosensors, and optical biosensors. Although CNTs and graphene have led to some groundbreaking discoveries, challenges are still remained and the state-of-the-art sensors are far from a practical application. As a conclusion, future effort has to be made through an interdisciplinary platform, including materials science, biology, and electric engineering.

Applications of carbon nanotubes and graphene for third-generation solar cells and fuel cells

Carbon nanotubes (CNTs) and graphene have attracted great attention since decades ago because of their interesting structure and properties and important application in many areas. They can have high conductivity, high specific surface area, high transparency in the visible range and high mechanical flexibility. They have important application in energy conversion systems including solar cells and fuel cells. They have been extensively studied as the transparent electrode and interfacial materials of organic solar cells (OSCs) and perovskite solar cells (PSCs). They are also used as the catalytic counter electrode of dye-sensitized solar cells (DSSCs). In addition, graphene oxide (GO) is exploited as an auxiliary binder of TiO2 paste for the mesoporous TiO2 layer of DSSCs, and GO and functionalized CNTs are adopted as gelators of gel electrolyte for quasi-solid state DSSCs. CNTs and graphene also have important application in fuel cells. They can be used as catalyst support for the oxidation of fuels or oxygen reduction reaction (ORR). CNTs and graphene, particularly when doped with nitrogen, can be directly used metal-free catalysts. This article provides a brief review on the application of CNTs and graphene in OSCs, PSCs, DSSCs and fuel cells.

An experimental study on thermal characteristics of nanofluid with graphene and multi-wall carbon nanotubes

High-thermal conductivity enhancement of nanofluid is one of the promising topics of the nanoscience research field. This work reports the experimental study on the preparation of graphene(GN) and multi-walled carbon nanotubes(MWCNTs) based nanofluids with the assistance of sodium dodecyl benzene sulfonate(SDBS) and sodium dodecyl sulfate(SDS) surfactants, and their thermal behaviors. The present work suggests not a solution, but a solution approach and deduces a new conclusion by trying to resolve the agglomeration problem and improve the dispersibility of nanoparticles in the base fluid. The analysis results of FESEM, thermal conductivity, diffusivity, effusivity and heat transfer coefficient enhancement ratio of nanofluid with surfactants SDS and SDBS expose strong evidence of the dispersing effect of surfactant on the making of nanofluid.

EBSD characterization of Al7075/graphene nanoplates/carbon nanotubes composites processed through post-deformation annealing

The effects of the post-deformation annealing on the microstructural evolution of hot rolled Al7075 matrix composites reinforced with CNTs and GNPs were investigated.The multi-pass hot rolling was applied on the stir cast samples.Annealing was then applied to the composites at 450℃ for 4 h.Microstructural evolution was examined by SEM,EDS,and EBSD techniques.EBSD data showed that the addition of 0.87 vol.%(GNPs+CNTs)significantly inhibited the occurrence of recrystallization.Also,in the composite with 0.96 vol.%CNTs,recrystallization was partially inhibited.Whereas,in composites with 0.92 vol.%of GNPs,the occurrence of recrystallization through particle stimulated nucleation(PSN)mechanism was significantly accelerated.The volume fraction of recrystallized grains depends significantly on the occurrence of PSN in the presence of reinforcements.The intensity and type of the main components of the texture as well as the FCC fibers depend on the type of reinforcement.

Review of Electrochemical Capacitors Based on Carbon Nanotubes and Graphene

Electrochemical capacitors, which can store large amount of electrical energy with the capacitance of thousands of Farads, have recently been attracting enormous interest and attention. Carbon nanostructures such as carbon nanotubes and graphene are considered as the potentially revolutionary energy storage materials due to their excellent properties. This paper is focused on the application of carbon nanostructures in electrochemical capacitors, giving an overview regarding the basic mechanism, design, fabrication and achievement of latest research progresses for electrochemical capacitors based on carbon nanotubes, graphene and their composites. Their current challenges and future prospects are also discussed.

Acetylcholinesterase Biosensor Based on Poly(diallyldimethylammonium chloride)-multi-walled Carbon Nanotubes-graphene Hybrid Film

In this paper, an amperometric acetylcholinesterase(ACh E) biosensor for quantitative determination of carbaryl was developed. Firstly, the poly(diallyldimethy-lammonium chloride)-multi-walled carbon nanotubes-graphene hybrid film was modified onto the glassy carbon electrode(GCE) surface, then ACh E was immobilized onto the modified GCE to fabricate the ACh E biosensor. The morphologies and electrochemistry properties of the prepared ACh E biosensor were investigated by using scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. All variables involved in the preparation process and analytical performance of the biosensor were optimized. Based on the inhibition of pesticides on the ACh E activity, using carbaryl as model compounds, the biosensor exhibited low detection limit, good reproducibility and high stability in a wide range. Moreover, the biosensor can also be used for direct analysis of practical samples, which would provide a new promising tool for pesticide residues analysis.

A comparative study of polymer nanocomposites containing multi-walled carbon nanotubes and graphene nanoplatelets

Featuring exceptional mechanical and functional performance, MWCNTs and graphene(nano)platelets(GNPs or Gn Ps;each platelet below 10 nm in thickness) have been increasingly used for the development of polymer nanocomposites. Since MWCNTs are now cost-effective at US$30 per kg for industrial applications, this work starts by briefly reviewing the disentanglement and surface modification of MWCNTs as well as the properties of the resulting polymer nanocomposites. GNPs can be made through the thermal treatment of graphite intercalation compounds followed by ultrasonication;GNPs would have lower cost yet higher electrical conductivity over 1,400 S cmthan MWCNTs. Through proper surface modification and compounding techniques, both types of fillers can reinforce or toughen polymers and simultaneously add anti-static performance. A high ratio of MWCNTs to GNPs would increase the synergy for polymers. Green, solvent-free systhesis methods are desired for polymer nanocomposites. Perspectives on the limitations, current challenges and future prospects are provided.

sp^(3)-like defect structure of hetero graphene-carbon nanotubes for promoting carrier transfer and stability

Three-dimensional(3 D) hybrid of nanocarbons is a very promising way to the high-performance design of electrocatalysis materials.However,sp^(3)-like defect structure,a combination of high strength and conduction of graphene and carbon nanotubes(CNTs) is rarely reported.Herein,3 D neural-like hybrids of graphene(from reduced graphene oxide) and carbon nanotubes(CNTs) have been integrated via sp^(3)-like defect structure by a hydrothermal approach.The sp^(3)-like defect structure endows 3 D nanocarbon hybrids with an enhanced carrier transfer,high structural stability,and electrocatalytic durability.The neural-like structure is shown to demonstrate a cascade effect of charges and significant performances regarding bio-electrocatalysis and lithium-sulfur energy storage.The concept and mechanism of "sp^(3)-like defect structure" are proposed at an atomic/nanoscale to clarify the generation of rational structure as well as the cascade electron transfer.

Preparation of Multi-Wall Carbon Nanotubes/Graphene Composites with Cadmium Sulfide in Dye-Sensitized Solar Cells (DSSCs)

In the present work, Dye Sensitized Solar Cells (DSSCs) have been fabricated by utilizing a dense layer of photoelctrode cadmium sulfide thin film (CdS) as n-type, which prepared by spray coating, while p-type electrode was multi-wall carbon nanotubes/graphene (MWNT-G) composites. The experimental results showed the higher energy conversion efficiency for CdS/MWNT-G was 0.056% in comparison with the others, which were CdS/MWNT with 0.044% and CdS/G with 0.037% respectively, which referred to improvement in the conductivity by using MWNT-G. The microstructure and nanostructure of CdS, MWNT, G, and MWNT-G nanocomposite were carried out by employing Scanning Electron Microscopy (SEM). X-Ray Diffraction (XRD) has been used to get crystal size of CdS, Raman scattering, and optical absorption also used for characterizations the samples. This study promised to increase and enhance the conversion efficiency of photovoltaic devices.

Functionalization of carbon nanotubes/graphene by polyoxometalates and their enhanced photo-electrical catalysis

Carbon nanotubes and graphene are carbon-based materials, which possess not only unique structure but also prop- erties such as high surface area, extraordinary mechanical properties, high electronic conductivity, and chemical stability. Thus, they have been regarded as an important material, especially for exploring a variety of complex catalysts. Considerable efforts have been made to functionalize and fabricate carbon-based composites with metal nanoparticles. In this review, we summarize the recent progress of our research on the decoration of carbon nanotubes/graphene with metal nanoparticles by using polyoxometalates as key agents, and their enhanced photo-electrical catalytic activities in various catalytic reactions. The polyoxometalates play a key role in constructing the nanohybrids and contributing to their photo-electrical catalytic properties.

Enhanced Removal of Tetracycline from Aqueous Solution by Graphene Oxide Hydrogel Doped with TiO_2 Nanotubes

The detection on tetracycline( TC) in drinking water poses an environmental issue since TC has been widely used to prevent animal disease and promote their growth. In addition,TC was difficult to remove or biodegrade,which posed a challenge to the conventional techniques. In this work,the batch experiments on TC adsorption in aqueous solution of hydrogel( HG) consisting of graphene oxide( GO) and TiO_2 nanotubes( TN) were successfully conducted. HG composite( HG-TN-GO) was prepared with TN and GO with self-assembly method during the oxidation-reduction reaction,and criogel( CG) with TN and GO was characterized by pH at point of zero charge( pH_(pzc)), transmission electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy( XPS). The adsorption capacity of HG-TN-GO on TC was evaluated by analyzing its isotherms. The maximum adsorption capacity reached 751. 3 mg/g. Besides,the adsorption isotherms were well fitted by the Langmuir model, with the theoretical maximum( q_m) of 797. 0 mg/g. The adsorption process was systematically studied by varying pH during the whole adsorption process. The adsorption occurred probably via π-π interaction and cation-π bonding between TC and the HG-TN-GO surface. The composite could be regenerated in 50% ethanol aqueous solution,without significant capacity loss. After 6 recycles,the decrease of adsorption capacity was less than 10%.

Development of a reversed dispersive based graphene functionalized with multiwalled carbon nanotubes for detection ofβ2-agonists in pork by high-performance liquid chromatography

A reliable and inexpensive pretreatment procedure in the determination ofβ2-agonists in pork was developped.The procedure used a nanocomposite of multiwalled carbon nanotubes(CNTs)functionalized with graphene(rGO)as the reversed dispersive sorbent.It was analyzed after purification by highperformance liquid chromatography,the extraction time and the properties of the nanocomposite were optimized.Under optimized conditions,present method has linear response over concentration range of 0.5–50 ng/mL in pork samples with a satisfactory detection limit close to 0.1 ng/mL.The precisions of the current method(coefficient of variation)are lower than 5%,while recoveries are more than 98.3%.The nanocomposite exhibited high adsorptivity,long-term storage stability,satisfactory anti-interfering activity and high selectivity toward2-agonists compared with those of rGO and CNTs.

Different Charging-Induced Modulations of Highest Occupied Molecular Orbital Energies in Fullerenes in Comparison with Carbon Nanotubes and Graphene Sheets

The highest occupied molecular orbital（HOMO） energies of fullerenes are found by quantitative first-principles calculations to be raised by negative charging, and the rising rate rank of the fullerenes is C60 >C70 >C80 >C90>C100 >C180. Then we compare fullerenes with carbon nanotubes（CNTs） and graphene sheets（GSs） and find that the increase of the HOMO energy of a fullerene is much faster than that of CNTs and graphene sheets with the same number of C atoms. The rising rate rank is fullerene>CNT>GS, which holds no matter what the number of C atoms is or which structure the fullerene isomer is. This work paves a new path for developing all-carbon devices with low-dimensional carbon nanomaterials as different functional elements.

A Self-supported Graphene/Carbon Nanotube Hollow Fiber for Integrated Energy Conversion and Storage

Wearable fiber-shaped integrated energy conversion and storage devices have attracted increasing attention,but it remains a big challenge to achieve a common fiber electrode for both energy conversion and storage with high performance.Here,we grow aligned carbon nanotubes(CNTs)array on continuous graphene(G)tube,and their seamlessly connected structure provides the obtained G/CNTs composite fiber with a unique self-supported hollow structure.Taking advantage of the hollow structure,other active materials(e.g.,polyaniline,PANI)could be easily functionalized on both inner and outer surfaces of the tube,and the obtained G/CNTs/PANI composite hollow fibers achieve a high mass loading(90%)of PANI.The G/CNTs/PANI composite hollow fibers can not only be used for high-performance fiber-shaped supercapacitor with large specific capacitance of 472 mF cm^-2,but also can replace platinum wire to build fiber-shaped dye-sensitized solar cell(DSSC)with a high power conversion efficiency of 4.20%.As desired,the integrated device of DSSC and supercapacitor with the G/CNTs/PANI composite hollow fiber used as the common electrode exhibits a total power conversion and storage efficiency as high as 2.1%.Furthermore,the self-supported G/CNTs hollow fiber could be further functionalized with other active materials for building other flexible and wearable electronics.

Carbon nanotube and graphene reinforced magnesium matrix composites:A state-of-the-art review

Magnesium(Mg)composites reinforced with carbon-based nanomaterial(CBN)often exhibit low density,enhanced strength,good conductivity,improved wear resistance,and excellent biocompatibility when compared to current industry Mg alloys.This review aims to critically evaluate recent developments in Mg-CBN composites and is divided into five sections:First,a brief introduction to Mg-CBN composites is provided,followed by a discussion of different fabrication techniques for these composites,including powder metallurgy,casting,friction stir processing,and selective laser melting.A particular focus is on the current processing challenges,including dispersion strategies to create homogeneous Mg-CBN composites.The effect of processing on the quantifying disorder in CBNs and distinguishing different sp2carbon materials is also highlighted.Then,the effect of CBN on various properties of Mg-CBN composites is thoroughly analyzed,and the strengthening efficiency of CNTs and graphene in the Mg matrix is examined.Finally,the potential applications of Mg-CBN composites in various industries are proposed,followed by a summary and suggestions for future research directions in the field of Mg-CBN composites.