Tuning the curing behavior of fluoroelastomer (FKM) by incorporation of nitrogen doped graphene nanoribbons (CNx-GNRs)

Graphene nanoribbons (GNRs), obtained by different methods from carbon nanotubes (CNTs) or graphene, are attractive materials for polymer nanocomposites due to their considerably high interfacial area, as compared to CNTs. Consequently, a better adhesion with a polymer matrix is anticipated for GNRs. Also, surface modification of these nanofillers, such as nitrogen doping, is known to be an efficient method to improve their properties. In this work, fluoroelastomers (FKM) were used as the polymer matrix to host GNRs. Undoped and nitrogen doped GNRs were synthesized from the parent multiwall carbon nanotubes (MWCNTs). MWCNT/FKM and GNR/FKM nanocomposites were prepared via a solution mixing/melt mixing protocol.     

Boron doped graphene cathode for capacitor via a new one-step method

The graphene cathode was doped with boron via a new and fast method of plasma enhanced chemical vapor deposition (PECVD) at room temperature. Various plasma species of BH_x (x?=?0–3) with high reactivity reacted with graphene electrode via surface re-reactions and gas-interface intersection. The cathode made of boron doping into graphene (BG) exhibited excellent electrochemical performances in Li-ion capacitors, including a large discharge capacity of 140?mAh?g^?1 (voltage range: 1.5–4.2?V vs. Li/Li⁺, current density: 100?mA?g^?1) and the coulombic efficiency of more than 99.6% within 1000 circles. The capacity, coulombic efficiency and circle performance of the BG electrode were more superior to the undoped graphene electrode owing to the uniform doping of boron plasma species. The PECVD method has the advantages of being simple, is conducted at room-temperature, is time efficient and uniform, thus making it a fast and effective way for doping hetero-atoms into the electrode.     

氧化石墨烯的制备及其掺杂的炭/炭复合材料导热性能研究

设定两种不同配比强酸氧化剂,以鳞片石墨为原料,采用Hummers法,制备了氧化石墨烯,再经过高温炭化得到热处理氧化石墨烯。并分别以中间相沥青为基体炭前驱体,炭纤维为增强相,氧化石墨烯及其热处理物为热疏导功能体,制备出掺杂氧化石墨烯的炭/炭复合材料。TEM、SEM等表征表明,选用强酸氧化剂组合配比用量较少的制备出的氧化石墨烯,其形貌整体上要优于用量较多的,具有独特的褶皱结构;相比于氧化石墨烯,掺杂其热处理物的复合材料界面覆盖均匀平滑且结合更优良,且其导热系数可达到60 W.m-1.K-1,是无掺杂的纯复合材料两倍多,导热系数得到了较大幅度提高。     

Investigation of bismuth doped bioglass/graphene oxide nanocomposites for bone tissue engineering

In this study, bismuth doped 45S5 nanobioactive bioglass (nBG) and graphene oxide (GO) nanocomposites were developed and characterized in terms of microstructural, mechanical, bioactivity and biological properties. Bismuth (Bi) - doped nBG was synthesized by sol-gel method and sintered at 600 °C for 2 h. Nanosized GO was homogeneously mixed with Bi doped bioglass at various ratios to prepare nanocomposites. Addition of Bi increased the density of nBG samples while a considerable decrease in density was observed for nanocomposites with GO incorporation. Bi improved the diametral tensile strength of nBG and addition of 2.5% GO to the composite also increased the diametral tensile strength of the nanocomposites. However, addition of more than 2.5% GO had negative effect on the diametral tensile strength of the composites. Bi doping to bioglass and its composite with GO increased the biocompatibility of 45S5 nBG in which 96.5BG1Bi2.5GO (containing 96.5% BG 1% Bi 2.5% GO in weight ratio) showed highest cell viability. Overall, it can be concluded that composites of Bi doped 45S5 nBG with GO hold promise as biomaterial for biomedical applications.     

Piezoelectric Anisotropy and Polarization Sublattice Coupling in Perovskite Crystals

Anisotropic piezoelectricity has been intensively investigated in PbZrO₃- or PbTiO₃-based perovskite ceramics, in comparison with the isotropic characteristic in the intermediate composition of the solid-solution Pb(Zr, Ti)O₃ system. In order to explain the piezoelectric anisotropy, a phenomenological treatment is proposed for a perovskite sublattice system, including electromechanical coupling terms. Electrostrictive couplings, especially between the two sublattices, provide significant contribution to the piezoelectric anisotropy.     

Conductance recovery and spin polarization in boron and nitrogen co-doped graphene nanoribbons

We present an ab initio study of the structural, electronic, and quantum transport properties of B–N-complex edge-doped graphene nanoribbons (GNRs). We find that the B–N edge codoping is energetically a very favorable process and furthermore can achieve novel doping effects that are absent for the single B or N doping. The compensation effect between B and N is predicted to generally recover the excellent electronic transport properties of pristine GNRs. For the zigzag GNRs, however, the spatially localized B–N defect states selectively destroy the doped-side spin-polarized GNR edge currents at the valence and conduction band edges. We show that the energetically and spatially spin-polarized currents survive even in the fully ferromagnetic metallic state and heterojunction configurations. This suggests a simple yet efficient scheme to achieve effectively smooth GNR edges and graphene-based spintronic devices.     

Designed nitrogen doping of few-layer graphene functionalized by selective oxygenic groups

Few-layer nitrogen doped graphene was synthesized originating from graphene oxide functionalized by selective oxygenic functional groups (hydroxyl, carbonyl, carboxyl etc.) under hydrothermal conditions, respectively. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) observation evidenced few-layer feature of the graphene oxide. X-ray diffraction (XRD) pattern confirmed phase structure of the graphene oxide and reduced graphene oxide. Nitrogen doping content and bonding configuration of the graphene was determined by X-ray photoelectron spectroscopy (XPS), which indicated that different oxygenic functional groups were evidently different in affecting the nitrogen doping process. Compared with other oxygenic groups, carboxyl group played a crucial role in the initial stage of nitrogen doping while hydroxyls exhibited more evident contribution to the doping process in the late stage of the reaction. Formation of graphitic-like nitrogen species was controlled by a synergistic effect of the involved oxygenic groups (e.g., -COOH, -OH, C-O-C, etc.). The doping mechanism of nitrogen in the graphene was scrutinized. The research in this work may not only contribute to the fundamental understandings of nitrogen doping within graphene but promote the development of producing novel graphene-based devices with designed surface functionalization.     

Hydrogen adsorption in nitrogen enriched ordered mesoporous carbons doped with nickel nanoparticles

Ordered mesoporous carbons were enriched with nitrogen, then loaded with nickel nanoparticles and the effects on hydrogen storage were investigated. Firstly, a comparative characterization was carried out using transmission electronic microscopy, X-ray diffraction, nitrogen adsorption isotherm and thermogravimetric analysis. It was shown that the nickel was interacting with the nitrogen functional groups on the surface of the carbon support and even led to the formation of particles of different sizes. Secondly, hydrogen storage was studied. Hydrogen adsorption by volumetric method at 77, 298 and 373 K and high pressures (3 MPa) exhibited two distinct behaviors. At 77 K, the textural properties are critical and the adsorption capacities decreased with the nickel loading. On the contrary, at ambient and higher temperatures, the contribution of nickel nanoparticles was positive and marked by increased amounts of hydrogen reversibly adsorbed. Furthermore, the electrosorption of hydrogen was examined. It consists of the electrolysis of water that causes the formation and the diffusion of hydrogen on the adsorbent surface. In that particular application, the combination of nickel doping and nitrogen enrichment was detrimental to the adsorption capacities. However, nickel doped on pure carbons enhanced the amount of hydrogen electrosorbed.     

Synthesis and characterization of phosphorus–nitrogen doped multiwalled carbon nanotubes

Phosphorus–nitrogen doped multiwalled carbon nanotubes (CN_xP_y) were prepared using a floating catalyst chemical vapor deposition method. Triphenylphosphine (TPP), as phosphorus (P) precursor, was used to control the structure of the CN_xP_y. Transmission electron microscope (TEM) observation indicated that with the increase of TPP amount, the outer diameter and wall thickness of the CN_xP_y gradually increased, while their inner diameter decreased. TEM and backscattered electron imaging revealed that structural changes of the nanotubes could be attributed to the shape change of the catalyst particles, from conical for nitrogen-doped carbon nanotubes (CN_x) to elongated for CN_xP_y, with the addition of TPP. X-ray photoelectron spectroscopy analysis demonstrated that the P content in CN_xP_y can reach as high as 1.9 at.%. Raman analysis indicated that CN_xP_y had a lower crystallinity than CN_x.     

Preparation of silica glass doped with nitrogen by modified chemical vapor deposition

A thermodynamic analysis of the doping of silica glass with nitrogen by the chemical vapor deposition methods has been carried out. The fundamental differences are revealed between the plasma chemical vapor deposition and modified chemical vapor deposition methods. The basic parameters of nitrogen introduction into silica glass are determined by thermodynamic calculations. It is found that the main factor that ensures doping of silica glass with nitrogen by the modified chemical vapor deposition is an extremely low partial oxygen pressure in the reaction zone. The results of theoretical analysis are used in practice for nitrogenizing silica glass by modified chemical vapor deposition. The increment in the refractive index is equal to 0.0015.     

HPHT synthesis of large single crystal diamond doped with high nitrogen concentration

Large green single crystal diamond with high nitrogen concentration is firstly synthesized by temperature gradient method under high pressure and high temperature (HPHT). Sodium azide (NaN₃) is added as the source of nitrogen to the synthesis system of high pure graphite and kovar alloy (Fe₅₉Co₂₅Ni₁₇). The HPHT synthesis condition is 5.4 GPa and 1480 K. The maximum crystal size is 3.2 mm. The infrared absorption spectra indicate that the nitrogen concentration in the green large single crystal diamond reaches 1520 ppm in the form of single substitution, which is close to that in nature diamond, and several times higher than that in the man-made Ib large single crystal diamond previously.     

Preparation of silica glass doped with nitrogen by modified chemical vapor deposition

A thermodynamic analysis of the doping of silica glass with nitrogen by the chemical vapor deposition methods has been carried out. The fundamental differences are revealed between the plasma chemical vapor deposition and modified chemical vapor deposition methods. The basic parameters of nitrogen introduction into silica glass are determined by thermodynamic calculations. It is found that the main factor that ensures doping of silica glass with nitrogen by the modified chemical vapor deposition is an extremely low partial oxygen pressure in the reaction zone. The results of theoretical analysis are used in practice for nitrogenizing silica glass by modified chemical vapor deposition. The increment in the refractive index is equal to 0.0015.     

Study on a novel composite coating based on PDMS doped with modified graphene oxide

The low surface activity of graphene oxide (GO) stemming from its large conjugated electronic structure can easily affect the dispersion behavior of GO-based polymer matrices. This significantly undermines the properties of the resulting composite materials. Therefore, in order to increase the GO surface activity for use in polymer-based composites, GO was modified using silane coupling agent which was then doped into polydimethylsiloxane (PDMS) polymer to prepare novel paints by sol–gel reaction strategy. The subsequent novel composite coatings based on PDMS/modified GO (mGO) were finally cured with tetraethoxysilane as the hardening agent in the presence of dibutyltin dilaurate catalyst. The effect of doping mGO into PDMS polymer was systematically studied using infrared spectroscopy, micro-Raman spectroscopy, TEM, SEM, XRD, TGA, mechanical test, thermal conductivity test, and the erosion resistance test. It was concluded that the phase compatibility between GO and PDMS was enhanced due to the new interconnecting chemical bonds brought about by the mGO in the composite.     

Anodic chlorine/nitrogen co-doping of reduced graphene oxide films at room temperature

Room temperature simultaneous doping of reduced graphene oxide films with oxygen, nitrogen and chlorine was performed through anodic polarization in a neutral nitrogen-deaerated KCl electrolyte. The thermodynamic electrochemical windows of water, dissolved nitrogen and chlorine anions were analyzed on the basis of the Pourbaix diagram. Anode polarization demonstrated that the nitrogen, water and chlorine anions can be oxidized at an applied potential of 1.7 V vs. NHE. The oxidative products, i.e. oxygen, nitrate anion and hypochlorous acid, can react with the reduced graphene oxide surface. X-ray photoelectron spectroscopy proved the chlorine–nitrogen co-doping of the treated film, along with an increase of oxygen groups. Surface structure evolution was also confirmed by Raman and Fourier-transform infrared spectroscopies. The anodic doping can be hindered by covering the reduced graphene oxide surface with sulfate anions or forming stable carbon–nitrogen bonds. Incorporation of oxygen, nitrogen and chlorine also helps to enhance the supercapacitance of the doped film.     

S，N耦合掺杂TiO2柱撑蒙脱石催化剂制备

以Na基蒙脱石为吸附剂,二氧化钛（TiO2）水解溶胶、L-半胱氨酸为双组分吸附质,采用双组分竞争吸附的方法,制备了S,N耦合掺杂TiO2柱撑蒙脱石光催化剂。探讨了蒙脱石的吸附特点,修正了Langmuir双组分竞争吸附公式,利用二元回归方法,求出了修正因子Y1=1．00011,Y2=0．99938。吸附实验表明,双组分吸附体系中,吸附质之间的相互作用不容忽视;XRD分析：表明,催化剂中TiO2全部为锐钛矿相晶体;XPS光电子能谱分析表明,S^4＋替换Ti^4＋进入TiO2晶格,S^2-、N^2-替换晶格氧而进入TiO2晶格;光催化降解实验表明,可见光照射下,催化剂有较高的光催化活性,3h内亚甲基蓝脱色率达65％左右。     

S,N耦合掺杂TiO_2柱撑蒙脱石催化剂制备

以Na基蒙脱石为吸附剂,二氧化钛(TiO2)水解溶胶、L-半胱氨酸为双组分吸附质,采用双组分竞争吸附的方法,制备了S,N耦合掺杂TiO2柱撑蒙脱石光催化剂。探讨了蒙脱石的吸附特点,修正了Langmuir双组分竞争吸附公式,利用二元回归方法,求出了修正因子Y1=1.000 11,Y2=0.999 38。吸附实验表明,双组分吸附体系中,吸附质之间的相互作用不容忽视;XRD分析表明,催化剂中TiO2全部为锐钛矿相晶体;XPS光电子能谱分析表明,S4+替换Ti4+进入TiO2晶格,S2-、N2-替换晶格氧而进入TiO2晶格;光催化降解实验表明,可见光照射下,催化剂有较高的光催化活性3,h内亚甲基蓝脱色率达65%左右。     

First‐Principles Molecular Dynamics Studies of Oxygen Sublattice Melting in Thoria

We apply first‐principles molecular dynamics to investigate the order–disorder transition in the oxygen sublattice, observed experimentally in thoria. The mean‐square displacements were calculated at high temperatures (2700 K–3660 K) and we demonstrate that oxygen atoms become mobile at 3000 K, while they stay confined at 2700 K. The rate of diffusion of oxygen atoms was calculated while for thorium atoms the mean‐square amplitudes of vibrations were evaluated. Thoria is predicted to exhibit a higher increase in thermal expansion with temperatures in the premelting region, similar to urania.     

Adsorptive removal kinetics of anionic dye onto chitosan films doped with graphene oxide: An in situ fluorescence monitoring

The aqueous adsorption of a fluorescent dye (pyranine) onto crosslinked chitosan-graphene oxide composite films was studied. In situ fluorescence monitoring technique is introduced as easy and fast experimental technique to select optimal adsorbent conditions. The effect of ionic crosslinker on adsorption was studied with sodium tripolyphosphate, trisodium citrate, and sodium sulfate, respectively. Among the crosslinkers, it was realized that sodium sulfate crosslinked films showed a greater adsorption rate for pyranine than the other two types of crosslinked films. Recently, graphene oxide is of interest as a filler compound for many biopolymer applications due to its favorable thermal, mechanical and surficial properties. In the present study, graphene oxide incorporation increased adsorption rate of the dye and the mechanical strength of ionically crosslinked chitosan films. The adsorption behavior of the adsorbent was explained by a kinetic model. Samples were characterized using scanning electron microscopy, thermogravimetric analysis, swelling experiments and tensile testing method.     

Substrate temperature effects on the electron field emission properties of nitrogen doped ultra-nanocrystalline diamond

For the purpose of improving the electron field emission properties of ultra-nanocrystalline diamond (UNCD) films, nitrogen species were doped into UNCD films by microwave plasma chemical vapor deposition (MPCVD) process at high substrate temperature ranging from 600° to 830 °C, using 10% N₂ in Ar/CH₄ plasma. Secondary ion mass spectrometer (SIMS) analysis indicates that the specimens contain almost the same amount of nitrogen, regardless of the substrate temperature. But the electrical conductivity increased nearly 2 orders of magnitude, from 1 to 90 cm^− 1 Ω^− 1, when the substrate temperature increased from 600° to 830 °C. The electron field emission properties of the films were also pronouncedly improved, that is, the turn-on field decreased from 20 V/μm to 10 V/μm and the electron field emission current density increased from less than 0.05 mA/cm² to 15 mA/cm². The possible mechanism is presumed to be that the nitrogen incorporated in UNCD films are residing at grain boundary regions, converting sp³-bonded carbons into sp²-bonded ones. The nitrogen ions inject electrons into the grain boundary carbons, increasing the electrical conductivity of the grain boundary regions, which improves the efficiency for electron transport from the substrate to the emission sites, the diamond grains.