Preparation and tribological properties of graphene/TiO2 ceramic films

Single and multiple-layer TiO₂ (GT) ceramic films with graphene nanoplatelets were obtained by sol-gel method. X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), UV–vis diffuse reflection spectroscope and atomic force microscope (AFM) were used to investigate the structure. Interestingly, the GT ceramic films were decorated by graphene nanoplatelets on surface and at interlayer. After heat treatment, graphene kept non-oxidized. The tribological properties of GT ceramic films were investigated using a reciprocating ball-on-plate configuration. The GT ceramic films show excellent antifriction and abrasion resistant properties that the minimum frictional coefficient approximates to 0.1. With more graphene quantity, less frictional coefficient and larger abrasive resistance were observed. When the graphene quantity keeps equally, the frictional coefficient decreases with layers of ceramic film. At high temperature, the frictional coefficient shows a decrease tendency, which reaches the minimum at 100 °C.     

Synthesis of graphene foams and their sorption properties of n-hexane

Journal of Porous Materials - The influence of preparation conditions of the graphene foams on their physicochemical properties is shown. Different graphene aerogels were obtained from various...     

Low temperature elastic properties of chemically reduced and CVD-grown graphene thin films

We have measured internal friction and shear modulus of both reduced graphene oxide and chemical-vapor deposited graphene films measuring as thin as 5 nm. Graphene oxide films were deposited from solutions by spin-coating, and graphene films were synthesized by chemical-vapor deposition (CVD) on Ni thin films. In both cases, these films were transferred from their host substrate into a water bath, then re-deposited onto to a high-Q single crystal silicon mechanical double-paddle oscillator. A minimal thickness dependence of both internal friction and shear modulus was found within the experimental uncertainty for reduced graphene oxide films varying thickness from 5 to 90 nm. The internal friction of all films exhibits a temperature independent plateau below 10 K. The values of the plateaus are similar for both the reduced graphene oxide films and CVD graphene films, and they are as high as the universal “glassy range” where the tunneling states dominated internal friction of amorphous solids lies. This result shows that from a mechanical loss point of view, both graphene oxide and CVD graphene films have high and similar level of disorder. Raman measurements performed on the same samples show higher structure order in CVD graphene films than in graphene oxide films. Our results suggest that internal friction probes different sources of disorder from those by Raman, and the disorder is not directly related to the existence of C–O binding in the graphene oxide films. The shear modulus averages 53 GPa after subtracting Young's modulus component from the vibration mode used in experiments.     

原位聚合法制备GO/PAN复合膜及其性能的研究（英文）

通过原位聚合法制备了氧化石墨烯/聚丙烯腈(GO/PAN)聚合物,采用水相成膜法制得GO/PAN复合膜,探讨了聚合过程中GO用量对PAN的单体转化率(Y)和增比黏度(ηsp)的影响,研究了GO/PAN复合膜的结构和性能。结果表明:GO的加入使PAN的ηsp和Y都有所提高;当加入GO质量分数为2%时,相对于PAN,其Y提高了13.4%,ηsp提高了77.3%;GO片层均匀地分布在GO/PAN复合膜基体当中,并且GO与PAN之间存在一定的作用力;与纯PAN相比,GO/PAN复合膜的结晶度、热稳定性和力学性能都得到一定程度提高,当GO质量分数为2%时,所制得的GO/PAN复合膜的结晶度为47.9%,最大分解温度304℃,600℃时质量保持率为49.8%,强度为6.0 MPa。     

氧化石墨烯复合TiO2-B薄膜的制备及其电致变色性能

目前具有一维纳米结构的TiO₂薄膜在电致变色领域应用主要受限于材料光调制幅度小、响应时间长、循环稳定性差等缺点。为了解决上述问题,本文采用沉积法将B型二氧化钛纳米管（TiO₂-B）与氧化石墨烯复合,以TiO₂粉末为原料,采用水热法得到钛酸纳米管后,利用沉积法在氟掺杂的氧化锡玻璃（FTO）基底上制备了高透明度、大光调制范围以及优良循环性能的氧化石墨烯复合B型二氧化钛纳米管电致变色薄膜（GO/TiO₂）。借助XRD、XPS、Raman、FESEM、HR-TEM等分析手段研究了氧化石墨烯用量对GO/TiO₂复合薄膜电致变色性能的影响。研究结果表明,当GO与钛酸纳米管的质量比（GO/钛酸）为7％时,GO/TiO₂复合薄膜离子扩散系数为1.46×10^-8cm²/s,着色效率值为38.1cm²/C,具有良好的电致变色性能。在-1.6V、633nm处,GO/TiO₂电致变色薄膜的光调制幅度可达77％,GO/TiO₂薄膜的着色和漂白时间分别为28.6s和4.8s,100次循环后的光调制幅度保持率为96.1％。     

石墨烯量子点纳滤膜的仿生修饰及稳定性研究

亲水修饰是提高纳滤膜抗污染性能的重要方法。采用氯化胆碱（ChC）对石墨烯量子点（GQDs-TMC）纳滤膜进行后处理仿生修饰,模拟细胞膜上磷酰胆碱的两性离子抗污染表面。红外光谱（FTIR）和表面元素分析（EDS）表明ChC以共价键结合在纳滤膜分离层上。提高反应温度和氯化胆碱溶液浓度,可以增加纳滤膜的仿生修饰程度。ChC的季铵基团与GQDs-TMC纳滤膜分离层羧基基团形成两性离子结构,提高了仿生修饰（GQDs/ChC-TMC）纳滤膜的亲水性,降低了表面电势,提高了对染料分子和二价盐离子的截留率,并且显著增强了抗污染性能。经过酸、碱和氧化剂溶液浸泡处理及高温纳滤膜分离实验,GQDs/ChC-TMC纳滤膜的渗透率和截留率均未发生较大改变,表明仿生纳滤膜具有优异的化学稳定性和耐热稳定性。     

氧化石墨烯/水性聚氨酯复合薄膜的制备及性能研究

以自制的GO(氧化石墨烯)为填料,WPU(水性聚氨酯)为基体,采用溶液共混和流延成膜法制备了GO/WPU复合薄膜。着重考察了GO含量对GO/WPU复合薄膜力学性能和导热性能等影响。研究结果表明:随着GO含量的增加,复合薄膜的拉伸强度增强、导热系数增大;当w(GO)=4%(相对于复合薄膜质量而言)时,复合薄膜的拉伸强度(20.6 MPa)相对最大、导热系数[为0.208 W/(m·K)]相对最高[这是由于GO均匀分散在PU(聚氨酯)基体中,形成了连续褶皱状网络结构的缘故]。     

Influence of N-doping on the structural and photoluminescence properties of graphene oxide films

Nitrogen (N) was doped into graphene oxide (GO) films at temperatures of 600–900 °C under the flow of a mixture of NH₃ and Ar. The N (atomic) concentration was varied in the range of 3.63–7.45%. XPS and FTIR spectra show that there are mainly single C–N and double CN bonds in the GO sheet. Raman spectra indicate that the G band becomes closer to the position of the G band of graphite with increasing doping temperature, and thus reveal that N doping produces a blue-shift of the G-band. In room-temperature photoluminescence (PL) spectra, N-doping produces an increase not only in the overall PL intensity, but also in the wavelength of the peak maxima. The shift of the induced PL of N-doped graphene is attributed mainly to the increased number of graphitic (or quaternary) N.     

Conversion of pyrazoline to pyrazole in hydrazine treated N-substituted reduced graphene oxide films obtained by ion bombardment and their electrical properties

An efficient method for the conversion of pyrazoline to pyrazole in hydrazine treated N-substituted reduced graphene oxide (N-rGO) films at room temperature has been reported. This method comprises the Ar⁺ ion bombardment of the N-rGO films that are prepared by drop casting method. The X-ray photoelectron spectroscopy (XPS) data in association with the X-ray diffraction, Ultra-violet spectroscopy and Raman spectroscopy data reveal that the addition of hydrazine removes the epoxy and hydroxyl groups of graphite oxide largely, and the reaction of hydrazine with carbonyl groups at 1,3-position of GO yields the pyrazoline moiety at the edge of the exfoliated carbon network. Further, the XPS data of the bombarded N-rGO films at the threshold applied potential of ∼3 keV for 10 min show that the position of the N1s XPS peak shifts from 400.05 to 398.6 eV due to the bombardment, indicating a conversion occurs from non-aromatic pyrazoline to aromatic pyrazole moiety. The electrical results reveal that the conductivity of the N-rGO/pyrazole film (47,600 S/m) is higher than the N-rGO/pyrazoline film (25,000 S/m) by virtue of the enhancement in the length of the conjugation π bond. The conversion of pyrazoline to pyrazole is discussed based on the activation energy.     

Enzymatic degradability and release properties of graphene oxide/silk fibroin nanocomposite films

The structure evolution of silk fibroin (SF) in the nanocomposite films with graphene oxide (GO) was investigated and related to the enzymatic degradability and release property. The interaction with GO was found to induce conformation transition of SF from random coil to β-sheet. However, the surface binding constrained the rearrangement of the silk chains, leading to a decrease of β-sheet when GO content was more than 1.0%. The crystal structure of SF played a key role in the degradation of GO/SF composites. The preferential degradation of the hydrophilic blocks resulted in a faster degradation of SF films with higher β-sheet content. The addition of GO to SF matrix led to a slower release and a reduction of the burst release of RhB, the model compound. The release profile was well fitted to the Rigter–Peppas equation, from which the characteristic constant decreased and the diffusional exponent increased with increasing GO content but quickly leveled off when GO content was more than 1.0%. Degradation of the composites had little influence on the characteristic constant of RhB release, however, led to an increased diffusional exponent, which was more evident for the composites with higher β-sheet content.     

Layer-by-layer assembly of graphene/polyaniline multilayer films and their application for electrochromic devices

Graphene/polyaniline (PANI) multilayer films were prepared via alternate deposition of negatively charged graphene oxide (GO) and positively charged PANI upon electrostatic interaction, followed by the reduction of their GO components with hydroiodic acid. The thickness of the multilayer film increased linearly with the number of its bilayers and that of each bilayer was measured to be about 3 nm. Cyclic voltammetry studies indicated that these thin composite films were electroactive, and their redox reactions were related to the insertion-extraction of counter ions in PANI layers. Furthermore, the composite films were tested to be promising electrode materials for electrochromic devices even without using the conventional indium tin oxide (ITO) electrodes.     

Enhanced sound absorption properties of porous ceramics modified by graphene oxide films

Under the condition of constant thickness, improving the low-frequency sound absorption performance of conventional sound-absorbing materials is a challenging research topic. To address this issue, a new reduced graphene oxide/polyvinyl alcohol (RGO/PVA) porous composite ceramic was fabricated using freeze-drying and optimized by redesigning the internal connecting pores of porous ceramic matrixes with a reticular microstructure using RGO and PVA. The as-prepared porous structure showed significant enhancement in the low-frequency sound absorption band compared with pristine porous ceramics. In addition, the hybrid porous ceramics exhibited low thermal conductivity. These favorable properties indicate that the hybrid sound-absorbing ceramics have potential application prospects for noise reduction in the fields of construction and electrical and mechanical devices.     

Biomimetic mineralization and cytocompatibility of nanorod hydroxyapatite/graphene oxide composites

Nanorod hydroxyapatite (NRHA)/graphene oxide (GO) composites with weight ratios of 0.4, 1.5, and 5 have been fabricated by a facile ultrasonic-assisted method at room temperature and atmospheric pressure. The chemical structure properties and morphology of the composites were characterized by field emission source scanning electron microscope, X-ray diffraction, transmission electron microscopy, and high-resolution transmission electron microscopy. The results indicate that the NRHA/ GO composites have an irregular surface with different degree wrinkles and are stable, and NRHA are well combined with GO. In addition, the biomimetic mineralization mechanism of hydroxyapatite on the NRHA/GO composites in simulated body fluid (SBF) is presented. The presence of a bone-like apatite layer on the composite surface indicate that the NRHA/GO composites facilitate the nucleation and growth of hydroxyapatite crystals in SBF for biomimetic mineralization. Moreover, the NRHA- 1.5/GO composite and pure GO were cultured with MC3T3-E1 cells to investigate the proliferation and adhesion of cells. In vitro cytocompatibility evaluation demonstrated that the NRHA/GO composite can act as a good template for the growth and adhesion of cells. Therefore, the NRHA/GO composite could be applied as a GO-based, free-template, non-toxic, and bioactive composite to substitute for a damaged or defect bone.

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Preparation and properties of bacterial cellulose/graphene oxide composite films using dyeing method

In this study, bacterial cellulose (BC) hydrogels were cultured from a kombucha SCOBY starter. The scanning electron microscopy (SEM) results indicated that the dried BC exhibited an interpenetrating fibrous mat. The BC films harvested for 5, 10, and 15 days were 15–19, 14.4–24, and 30–31 μm thick, respectively. Then, BC/graphene oxide (GO) composite films were prepared via the exhaust dyeing method. GO sheets penetrated the BC matrix, resulting in the formation of a BC/GO composite, as revealed by the SEM analysis results. The mechanical properties of the composite films were investigated. Compared with virgin BC, the tensile strength of the composite films was higher, while the %E at break was lower, resulting in a significant increase in the Young's modulus. The X-ray diffraction results indicated that an increase in the dyeing time (0.5–2 h) gradually induced cellulose crystalline conformation, which in turn affected the swelling ability, mechanical properties, and electrical properties of the BC/GO composite films. After the reduction of GO to reduced GO (rGO), flexible conductive BC/rGO films were obtained, as confirmed by their resistivity values. Thus, flexible conductive composite films with excellent mechanical properties were successfully fabricated.     

Physicochemical and biological properties of electrodeposited graphene oxide/chitosan films with drug-eluting capacity

In this study, novel graphene oxide/chitosan nanocomposite coatings with long term drug-eluting potential are presented. The coatings are fabricated by the facile and reproducible electrophoretic deposition technique. Analysis of the prepared films shows that the graphene oxide nanosheets are exfoliated in the chitosan matrix. Fourier-transform infrared spectrometry reveals polymer attachment to the carboxylic bonds of graphene oxide, providing a strong interaction and exfoliation of the nanolayers. In vitro viability assay by human osteosarcoma cells (MG-63) demonstrates that the nanocomposite films are highly biocompatible up to 30 wt% graphene oxide, but at higher concentrations a slight cytotoxicity is noticed. Alkaline phosphates enzyme assay also reveals that the presence of graphene oxide nanosheets moderately hampers osteogenesis of the cultured cells. It is shown that vancomycin-loaded nanocomposite coatings gradually release the drug macromolecules for relatively long period of time (up to 4 weeks). The electrodeposited films also exhibit a high bactericidal potential against Gram-positive Staphylococcus aureus. Effects of graphene oxide nanosheets on the physicochemical, biological, antimicrobial and drug-eluting properties of electrodeposited chitosan films are presented and discussed. It is shown that the GO/CS films support the initial attachment, proliferation and growth of osteoblast-like cells.     

Theoretical study of strained porous graphene structures and their gas separation properties

The structural deformation of porous graphene (PG) under tensile stress and the diffusion properties of H₂, O₂ and CO₂ through PG under different strain conditions have been investigated using the first-principles density functional theory. It is found that the application of a tensile stress can effectively increase the diffusion rate of H₂, O₂, and CO₂ in PG by up to 7, 13, and 20 orders of magnitude, respectively. Therefore, we propose that applying tensile stress is an effective way to control the diffusion rate of gases through PG. By applying sufficiently large tensile stress, one might able to use PG for filtering larger gas molecules such as O₂ in addition to previously proposed H₂. The results open up an opportunity to utilize PG as a controllable gas separation membrane, leading to wide range of energy and environmental applications.     

Direct reduction of graphene oxide films into highly conductive and flexible graphene films by hydrohalic acids

We report a simple but highly-effective hydrohalic acid reducing method to reduce graphene oxide (GO) films into highly conductive graphene films without destroying their integrity and flexibility at low temperature based on the nucleophilic substitution reaction. GO films reduced for 1 h at 100 °C in 55% hydroiodic (HI) acid have an electrical conductivity as high as 298 S/cm and a C/O ratio above 12, both of which are much higher than films reduced by other chemical methods. The reduction maintains good integrity and flexibility, and even improves the strength and ductility, of the original GO films. Based on this reducing method, a flexible graphene-based transparent conductive film with a sheet resistance of 1.6 kΩ/sq and 85% transparency was obtained, further verifying the advantage of HI acid reduction.     

One-step scalable preparation of graphene nanosheets and high-thermal-conductivity flexible graphene films

It is well known that graphene nanosheets (GNSs) have many excellent properties. However, it has been a difficult thing to exfoliate graphite into GNSs in a controllable and scalable manner. In this research, a new strategy named xylitol-assisted ball milling exfoliation (XABME) was developed for the scalable preparation of GNSs. The experimental results characterized by a series of measurements showed that GNSs were successfully exfoliated by the XABME strategy. The structure of the prepared nanosheets was featured by large lateral size and ultra-small thickness. Furthermore, the prepared GNSs easily achieved high production yield (≈54%). Lastly, the as-obtained GNSs and cellulose nanofibers (CNF) were compounded to form some nanomaterial films. The prepared films exhibited excellent flexibility and higher thermal conductivity, with the in-plane thermal conductivity of 90 wt% GNS film (8.0 W/(m·K)) being 11.4 times higher than that of the film without GNSs. This shows that GNSs could effectively enhance the thermal conductivity of the CNF matrix and indicate that these prepared films have great potentials in the thermal management of portable mobile devices.     

Thin polymer films based on poly(vinyl alcohol) containing graphene oxide and reduced graphene oxide with functional properties

In this article, the effect of the addition of graphene oxide (GO) and reduced graphene oxide (rGO) on the mechanical properties, thermal stability, and electrical conductivity of polyvinyl alcohol (PVA) has been investigated. Different weight percentages of nanofillers ranging from 0.5 to 5 wt% have been combined with PVA. The ultrasonic technique has been applied to disperse nanofillers in the PVA solution. The nanocomposite films have been prepared via solution casting technique and the dispersion of nanofillers into the PVA has been studied through optical microscopy. The microstructure, crystallization behavior, and interfacial interaction were characterized through X-ray diffraction and Fourier transform infrared spectroscopy. Differential scanning calorimetry (DSC) and thermogravimetric analysis have been applied to study the thermal properties of the prepared nanocomposites. The DSC results revealed that the crystallization temperature and melting temperature were enhanced in the presence of GO nanofiller. Besides, the tensile strength at break was improved along with the addition of GO; however, elongation at break for PVA/GO and PVA/rGO was diminished. Moreover, all specimens showed insulating behavior and the only sample was electrically conducting, which contain a high amount of rGO (5 wt%).     

The effect of ambient humidity on the electrical properties of graphene oxide films

ABSTRACT: We investigate the effect of water adsorption on the electrical properties of graphene oxide (GO) films using the DC measurement and AC complex impedance spectroscopy. GO suspension synthesized by a modified Hummer's method is deposited on Au interdigitated electrodes. The strong electrical interaction of water molecules with GO films was observed through electrical characterizations. The DC measurement results show that the electrical properties of GO films are humidity- and applied voltage amplitude dependent. The AC complex impedance spectroscopy method is used to analyze the mechanism of electrical interaction between water molecules and GO films in detail. At low humidity, GO films exhibits poor conductivity and can be seen as an insulator. However, at high humidity, the conductivity of GO films increases due to the enhancement of ion conduction. Our systematic research on this effect provides the fundamental supports for the development of graphene devices originated from solution-processed graphene oxide.