N-Graphene Nanowalls via Plasma Nitrogen Incorporation and Substitution: The Experimental Evidence

Incorporating nitrogen(N)atom in graphene is considered a key technique for tuning its electrical properties.However,this is still a great challenge,and it is unclear how to build N-graphene with desired nitrogen configurations.There is a lack of experimental evidence to explain the influence and mechanism of structural defects for nitrogen incorporation into graphene compared to the derived DFT theories.Herein,this gap is bridged through a systematic study of different nitrogen-containing gaseous plasma post-treatments on graphene nanowalls(CNWs)to produce N-CNWs with incorporated and substituted nitrogen.The structural and morphological analyses describe a remarkable difference in the plasma–surface interaction,nitrogen concentration and nitrogen incorporation mechanism in CNWs by using different nitrogen-containing plasma.Electrical conductivity measurements revealed that the conductivity of the N-graphene is strongly influenced by the position and concentration of C–N bonding configurations.These findings open up a new pathway for the synthesis of N-graphene using plasma post-treatment to control the concentration and configuration of incorporated nitrogen for application-specific properties.

Synthesis of vertical graphene nanowalls by cracking n-dodecane using RF inductively-coupled plasma-enhanced chemical vapor deposition

A facile and controllable one-step method to treat liquid hydrocarbons and synthesize vertical graphene nanowalls has been developed by using the technique of inductively-coupled plasma-enhanced chemical vapor deposition for plasma cracking of n-dodecane.Herein,the morphology and microstructure of solid carbon material and graphene nanowalls are characterized in terms of different operating conditions,i.e.input power,H2/Ar ratio,injection rate and reaction temperature.The results reveal that the optimal operating conditions were 500 W,5:10,30μl min^-1 and 800℃ for the input power,H2/Ar ratio,injection rate and reaction temperature,respectively.In addition,the degree of graphitization and the gaseous product are analyzed by Raman spectroscopy and gas chromatography detection.It can be calculated from the Raman spectrum that the relative intensity of ID/IG is approximately 1.55,and I2D/IG is approximately 0.48,indicating that the graphene prepared from n-dodecane has a rich defect structure and a high degree of graphitization.By calculating the mass loading and detecting the outlet gas,we find that the cracking rate of n-dodecane is only 6%-7%and that the gaseous products below C2 mainly include CH4,C2H2,C2H4,C2H6 and H2.Among them,the proportion of hydrogen in the outlet gas of n-dodecane cracking ranges from 1.3%-15.1%under different hydrogen flows.Based on our research,we propose a brand new perspective for both liquid hydrocarbon treatment and other value-added product syntheses.

Quantum Chemistry Modeling of Formation of Graphene and Graphene Nanowalls for Emission Electronics

The system ＂substrate--graphene island on its surface＂ was modeled with using semi-empirical quantum chemistry methods for various substrates. Such system imitates the graphene nucleation and growth when using CVD （chemical vapor deposition） technique. Herewith the carbon atoms can enter the island from both the substrate and the bulk of the CVD reactor. The authors show that for a wide island size range the carbon nanowalls placed perpendicularly as to the substrate is the most favorable configuration. But a transfer to this configuration is only possible providing two conditions are realized： the CVD technique is stimulated by plasma, when a strong electrical field exists near the substrate surface and preliminary decomposition of carbon carrier is realized in the bulk of the CVD-reactor.

Manipulation of Crawling Growth for the Formation of Sub-millimeter Long ZnO Nanowalls

Vapor-phase growth of ZnO nanowires based on gold catalyst is usually accompanied with lateral crawling growth on the substrate surface. We present results from our systematic experiments where the growth temperature and catalyst size are controlled. The data corroborate that it is possible to obtain clean vertical nanowire arrays while avoiding the crawling growth. 0% the other hand, crawling growth can be manipulated to obtain root-interconnected nanowire arrays, which could be useful for certain applications. Our results also imply that the previously suggested growth mechanism for the wire-on-wall hybridstructure might be incorrect. Finally, we show the formation of sub-millimeter long, straight ZnO nanowalls by combining a gold-catalyzed epitaxial growth of vertical nanowires and their mergence due to a confined crawling growth. These unconventional nanostructures might have unique electric or optical transport properties.

Porous NiCoP nanowalls as promising electrode with high-area and mass capacitance for supercapacitors

The design of the electrode with high-area and mass capacitance is important for the practical application of supercapacitors. Here, we fabricated the porous NiCoP nanowalls supported by Ni foam(NiCo-P/NF) for supercapacitors with win-win high-area and mass capacitance. The NiCoOH nanowall precursor was prepared by controlling the deposition rate of Ni^2+ and Co^2+ on NF through a sodium acetate-assisted(floride-free) process. After the phosphorization, the NiCo-P nanowalls formed with high loading about8.6 mg cm-2 on NF. The electrode combined several advantages favorable for energy storage: the plentiful pores beneficial for ion transport, the nanowalls for easy accommodation of electrolyte, good conductivity of NiCo-P for easy transport of electrons. As expected, the NiCo-P/NF exhibited a high specific mass capacitance(1,861 F g^-1 at 1 A g^-1,1,070 F g^-1 at 10 A g^-1 and high area capacitance(17.31 F cm-2 at 5 mA cm-2 and 10 F cm^-2 at 100 mA cm^-2.The asymmetric supercapacitor(ASC) composed of NiCo-P/NF positive electrode coupled with commercial active carbon negative electrode exhibited a high energy density of44.9 W h kg^-1 at a power density of 750 W kg^-1. The ASC can easily drive fans, electronic watch and LED lamps, implying their potential for the practical application.

CVD preparation of vertical graphene nanowalls/VO_(2)(B)composite films with superior thermal sensitivity in uncooled infrared detector

Vanadium dioxide with superior thermal sensitivity is one of the most preferred materials used in microbolometer,and the B phase of VO_(2) is particularly prominent.However,conventional VO_(2)(B)undergoes low temperature-coefficient of resistance(TCR)values and large resistances.In this paper,simple controllable composite films of vertical graphene nanowalls/VO_(2)(B)(i.e.,VGNWs/VO_(2)(B))with a suitable square resistance(12.98 kU)and a better temperature-coefficient of resistance(TCR)(-3.2%/K)were prepared via low pressure chemical vapor deposition.The VGNWs can provide a fast channel for electron transport and enhance the conductivity of VO_(2)(B).This preparation method can provide a low cost,facile and simple pathway for the design and fabrication of high performance VO_(2)(B)thin films with superior electrical properties for its application in uncooled infrared detectors.

Architecting Pyrenyl-graphdiyne Nanowalls for High Capacity and Long-life Lithium Storage

Graphdiyne,as the novel carbon allotrope,which is composed of sp^(2)-and sp-hybridized carbon,has exhibited excellent catalytic activity and conductivity.It has been applied in series of fields,such as Li-battery,catalyst and energy conversion.Expanding well-defined structures and useful applications of graphdiyne is still full of challenges in material chemistry.Herein,we optimized the synthesis condition of pyrenylgraphdiyne to obtain the nanowall structure.Compared with the typical nanosheet structure,the pyrenyl-graphdiyne nanowalls(Pyr-GDY-NWs)have more area for lithium insertion.Lithium-ion battery featuring Pyr-GDY-NWs-based electrode exhibits a high reversible specific capacity up to 1464 mA·h/g,which is triple than that of the commercial graphite.We also used the theoretical calculation to investigate the mechanism of Li storage in Pyr-GDY-NWs.The experiment and theoretical data showed that Pyr-GDY-NWs had the potential application in lithium batteries.Therefore,Pyr-GDY with a defined structure would be applied in energy storage and energy conversion.

Nanostructured Graphene Surfaces Promote Different Stages of Bone Cell Differentiation

Nanostructured graphene films were used as platforms for the differentiation of Saos-2 cells into bonelike cells. The films were grown using the plasma-enhanced chemical vapor deposition method, which allowed the production of both vertically and horizontally aligned carbon nanowalls(CNWs). Modifications of the techniqueallowed control of the density of the CNWs and their orientation after the transfer process. The influence of two different topographies on cell attachment, proliferation,and differentiation was investigated. First, the transferred graphene surfaces were shown to be noncytotoxic and were able to support cell adhesion and growth for over 7 days.Second, early cell differentiation(identified by cellular alkaline phosphatase release) was found to be enhanced on the horizontally aligned CNW surfaces, whereas mineralization(identified by cellular calcium production), a later stage of bone cell differentiation, was stimulated by the presence of the vertical CNWs on the surfaces. These results show that the graphene coatings, grown using the presented method, are biocompatible. And their topographies have an impact on cell behavior, which can be useful in tissue engineering applications.

Synthesis of Zinc Oxide Nanostructures on Graphene/Glass Substrate via Electrochemical Deposition: Effects of Potassium Chloride and Hexamethylenetetramine as Supporting Reagents

The effects of the supporting reagents hexamethylenetetramine(HMTA)and potassium chloride(KCl)mixed in zinc nitrate hexahydrate(Zn(NO3)2 6H2O)on the morphological,structural,and optical properties of the resulting Zn O nanostructures electrodeposited on graphene/glass substrates were investigated.The supporting reagent HMTA does not increase the density of nanorods,but it does remarkably improve the smoothness of the top edge surfaces and the hexagonal shape of the nanorods even at a low temperature of 75°C.Hydroxyl(OH-)ions from the HMTA suppress the sidewall growth of non-polar planes and promote the growth of Zn O on the polar plane to produce vertically aligned nanorods along the c axis.By contrast,the highly electronegative chlorine(Cl-)ions from the supporting reagent KCl suppress the growth of Zn O on the polar plane and promote the growth on non-polar planes to produce vertical stacking nanowall structures.HMTA was found to be able to significantly improve the crystallinity of the grown Zn O structures,as indicated by the observation of much lower FWHM values and a higher intensity ratio of the emission in the UV region to the emission in the visible region.Equimolar mixtures of Zn(NO3)2 6H2O and the supporting reagents HMTA and KCl seem to provide the optimum ratio of concentrations for the growth of high-density,uniform Zn O nanostructures.The corresponding transmittances for such molar ranges are approximately 55–58%(HMTA)and 63–70%(KCl),which are acceptable for solar cell and optoelectronic devices.

Near-infrared absorbing 2D/3D ZnIn2S4/N-doped graphene photocatalyst for highly efficient CO2 capture and photocatalytic reduction

Hierarchical heterostructure photocatalysts with broad spectrum solar light utilization,particularly in the nearinfrared(NIR)region,are emerging classes of advanced photocatalytic materials for solar-driven CO2 conversion into value-added chemical feedstocks.Herein,a novel two-demensional/three-demensional(2 D/3 D)hierarchical composite is hydrothermally synthesized by assembling vertically-aligned ZnIn2 S4(ZIS)nanowall arrays on nitrogen-doped graphene foams(NGF).The prepared ZIS/NGF composite shows enhancement in photothermal conversion ability and selective CO2 capture as well as solar-driven CO2 photoreduction.At273 K and 1 atm,the ZIS/NGF composite with 1.0 wt%NGF achieves a comparably high CO2-to-N2 selectivity of 30.1,with an isosteric heat of CO2 adsorption of 48.2 kJ mol^-1.And in the absence of cocatalysts and sacrificial agents,the ZIS/NGF composite with cyclability converts CO2 into CH4,CO and CH3 OH under simulated solar light illumination,with the respective evolution rates about 9.1,3.5,and 5.9 times higher than that of the pristine ZIS.In-depth analysis using in-situ irradiated X-ray photoelectron spectroscopy(ISI-XPS)in conjunction with Kelvin probe measurements reveals the underlying charge transfer pathway and process from ZIS to NGF.

Orientation-controlled,low-temperature plasma growth and applications of h-BN nanosheets

Dimensionality and orientation of hexagonal boron nitride(h-BN)nanosheets are promising to create and control their unique properties for diverse applications.However,low-temperature deposition of vertically oriented h-BN nanosheets is a significant challenge.Here we report on the low-temperature plasma synthesis of maze-like h-BN nanowalls(BNNWs)from a mixture of triethylamine borane(TEAB)and ammonia at temperatures as low as 400℃.The maze-like BNNWs contained vertically aligned stacks of h-BN nanosheets.Wavy h-BN nanowalls with randomly oriented nanocrystalline structure are also fabricated.Simple and effective control of morphological type of BNNWs by the deposition-mperature is demonstrated.Despite the lower synthesis temperature,thermal stability and oxidation resistivity of the maze-like BNNWs are higher than for the wavy nanowalls.The structure and oxidation of the nanowalls was found to be the critical factor for their thermal stability and con trolled luminescence properties.Cytotoxic study dem on strated sign ificant antibacterial effect of both maze-like and wavy h-BN nanowalls against E.coli.The reported results reveal a significant potential of h-BN nanowalls for a broad range of applications from electronics to biomedicine.

Defect-rich MoS2 nanowall catalyst for efficient hydrogen evolution reaction

Designing efficient electrocatalysts for the hydrogen evolution reaction （HER） has attracted substantial attention owing to the urgent demand for clean energy to face the energy crisis and subsequent environmental issues in the near future. Among the large variety of HER catalysts, molybdenum disulfide （MoS2） has been regarded as the most famous catalyst owing to its abundance, low price, high efficiency, and definite catalytic mechanism. In this study, defect-engineered MoS2 nanowall （NW） catalysts with controllable thickness were fabricated and exhibited a significantly enhanced HER performance. Benefiting from the highly exposed active edge sites and the rough surface accompanied by the robust NW structure, the defect-rich MoS2 NW catalyst with an optimized thickness showed an ultralow onset overpotential of 85 mV, a high current density of 310.6 mA·cm^-2 at η = 300 mV, and a low potential of 95 mV to drive a 10 mA·cm^-2 cathodic current. Additionally, excellent electrochemical stability was realized, making this freestanding NW catalyst a promising candidate for practical water splitting and hydrogen production.

Morphology-controlled growth of large-area PtSe_(2) films for enhanced hydrogen evolution reaction

Transition metal dichalcogenides(TMDs)have emerged as a promising electrocatalyst for hydrogen evo-lution reaction(HER)due to its excellent conductivity and abundant electrocatalytic active sites of its edges.TMDs nanowall can expose abundant of edges so that they tend to show better catalytic performance for hydrogen evolution reaction.Herein,PtSe_(2) nanowall films with morphology controlled at centimeters level are synthesized by selenizing Pt film.The dynamic and thermodynamics of selenation reaction are investigated.The nanowall structure can be obtained by controlling the growth temperature,and the thickness of nanowall can be tuned by the original thickness of Pt film.The Pt atoms can be rearranged into ordered distribution at 550℃ and can be induced to well-ordered PtSe_(2) nanowalls finally.The well-ordered PtSe_(2) nanowall films show excellent HER performance,with an overpotential of 0.3 V at-10 mA·cm^(-2) and a Tafel slope of~52 mV·dec^(-1).This work demonstrates the great potential of activated 2D PtSe_(2) as an ultrathin film catalyst for the HER,which is valuable to provide instruction and afford experience for further application at industrial level.