One-pot synthesized multi-functional graphene oxide as a water-tolerant and efficient metal-free heterogeneous catalyst for cycloaddition reaction

A series of functional graphene oxide (F-GO) materials were prepared by silylanization of graphene oxide (GO) with chlorine-terminal silanes and subsequent nucleophilic substitution reaction with tertiary amine in a one-pot approach. The quaternary ammonium salt was generated and immobilized simultaneously in situ, and the primary amine is beneficial to improve the number of surface functionalities on GO. This is the first time that a multi-functional GO material was designed, prepared and used for the synthesis of cyclic carbonates through the cycloaddition of carbon dioxide (CO₂) to epoxides. The F-GO catalyst can be easily separated and reused for at least five times without significant loss of activity (TOF = 46.4 h⁻¹). The excellent performance is attributed to the synergetic effect of silanol group and halide anion for ring opening of epoxide as well as the role of amine for CO₂ adsorption and activation. A possible mechanism is proposed for the cycloaddition reaction over F-GO.     

Effect of rhBMP-2 Immobilized Anorganic Bovine Bone Matrix on Bone Regeneration

Anorganic bovine bone matrix (Bio-Oss^®) has been used for a long time for bone graft regeneration, but has poor osteoinductive capability. The use of recombinant human bone morphogenetic protein-2 (rhBMP-2) has been suggested to overcome this limitation of Bio-Oss^®. In the present study, heparin-mediated rhBMP-2 was combined with Bio-Oss^® in animal experiments to investigate bone formation performance; heparin was used to control rhBMP-2 release. Two calvarial defects (8 mm diameter) were formed in a white rabbit model and then implanted or not (controls) with Bio-Oss^® or BMP-2/Bio-Oss^®. The Bio-Oss^® and BMP-2/Bio-Oss^® groups had significantly greater new bone areas (expressed as percentages of augmented areas) than the non-implanted controls at four and eight weeks after surgery, and the BMP-2/Bio-Oss^® group (16.50 ± 2.87 (n = 6)) had significantly greater new bone areas than the Bio-Oss^® group (9.43 ± 3.73 (n = 6)) at four weeks. These findings suggest that rhBMP-2 treated heparinized Bio-Oss^® markedly enhances bone regeneration.     

疏水改性氧化石墨烯/环氧复合涂料的制备及其防腐性能研究

以叔碳酸缩水甘油酯(E-10P)为疏水单体,通过环氧与羧酸的共价键合,在氧化石墨烯(GO)表面引入疏水性支化碳链,改性后的氧化石墨烯(F-GO)作为防锈填料加入环氧树脂中得到F-GO/环氧复合涂料。通过红外光谱、拉曼光谱、X-射线衍射、热重分析对F-GO的结构进行表征,通过场发射扫描电镜观察F-GO及复合涂料的微观形貌,并通过电化学阻抗、极化曲线和盐雾试验测试了复合涂料的防腐性能。结果表明:E-10P可利用其空间效应阻碍片层的团聚;疏水效应可提高F-GO的热稳定性和与环氧树脂的相容性;与空白环氧涂层相比,当复合涂料中F-GO质量分数为0.2%时,厚度为20~25 μm的防腐涂层的腐蚀电流可由2.358 6×10 ^-6 A/cm ²下降至2.000 2×10 ^-11 A/cm ²,阻抗值可由1.1×10 ⁷ Ω·cm ² 提升至6.9×10 ⁹ Ω·cm ²。     

Chitosan-gelatin/hydroxyapatite-based scaffold associated with mesenchymal stem cells differentiate into osteoblasts improves the surface of the bone lesion in mice C57BL/6J

Extensive injuries to bone tissue are still considered a significant clinical challenge; therefore, developing new bone tissue engineering (BTE) strategies is still necessary. This work aims to construct and characterize a chitosan-gelatin/hydroxyapatite-based (CG/H) scaffold to provide well-design support for mesenchymal stem cell (MSC) growth and differentiation to osteoblasts. First, the CG/H scaffolds are construct by freeze-drying. Then, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy, x-ray diffraction, water uptake, and degradation profiles evaluate the material's surface. In addition, the CG/H morphological, biochemical, and MSC adhesion processes and growth behavior are also assess, indicating reasonable adhesion rates to the surface, low material cytotoxicity, and excellent alkaline phosphatase activity compared to control on the cellular framework. Based on these results, we obtain a highly biocompatible scaffold and that can support osteoblast differentiation. Finally, the in vivo studies demonstrate the CG/H scaffold with MSC adhere is capable of differentiating into osteoblasts, and the application of this scaffold is able to significantly enhance the closure of the bone lesion. Therefore, the CG/H scaffold has potential clinical application for bone regeneration.     

Versatile photoluminescence from graphene and its derivatives

Graphene and its derivatives exhibit many interesting photoluminescence (PL) properties because of their unique electronic structures. In spite of the absence of the bandgap, graphene shows PL due to hot electrons. Graphene oxide (GO) fluorescence is different from that of a single organic fluorophore, for which the spectral properties and emission lifetime are independent of wavelength. Single-layered GO sheets are made of a large number of covalently connected independent fluorophores of varying sizes. These fluorophores are aromatic π-conjugated sp²-hybridized subsystems of carbon atoms surrounded by sp³ regions. The PL of GO is pH dependent because of the presence of many oxygen-containing groups in GO sheets. Reduced graphene oxide (rGO) PL is somewhat different from GO because the number and size of sp² fragments are increased in rGO due to the elimination of the functional groups containing oxygen via reduction. Nanosized graphene/GO possesses a strong quantum confinement effect and hence emits intense excitation wavelength-dependent PL. Moreover, graphene quantum dots show upconversion PL due to anti-Stokes transition. The diverse PL properties including the effect of reduction, pH, and solvent have been reported in many recent studies. Here, the versatile PL features of graphene derivatives are reviewed to elucidate the mechanism of PL.     

Electronic properties and atomic structure of graphene oxide membranes

We have performed a near-edge X-ray absorption fine-structure (NEXAFS) and a transmission electron microscopy (TEM) investigation of freely suspended graphene oxide (GO) sheets. We utilized a photoemission electron microscope to identify GO membranes and to acquire C K and O K absorption spectra. The overall line shape of C K-edge spectra demonstrates that the honeycomb carbon network of graphene is the scaffold of GO. However, the intensity ratio of π^∗ and σ^∗ resonances, and a broad feature at about 20 eV from the edge, indicate the presence of new carbon bonds. The O K-edge spectra show that oxidized regions are made of carbonyl, epoxide, and hydroxyl groups attached to the plane of graphene, while carboxyl groups might also be present at the edges. Further, our study indicates the presence of ordered arrangements of oxygen atoms in GO sheets. Our investigation provides a new and efficient route to study the electronic structure of suspended membranes.     

Preparation and properties of dopamine reduced graphene oxide and its composites of epoxy

To improve the thermal and mechanical properties and further to expand its applications of epoxy in electronic packaging, reduced graphene oxide/epoxy composites have been successfully prepared, in which dopamine (DA) was used as reducing agent and modifier for graphene oxide (GO) to avoid the environmentally harmful reducing agents and address the problem of aggregation of graphene in composites. Further studies revealed that DA could effectively eliminate the labile oxygen functionality of GO and generate polydopamine functionalized graphene oxide (PDA‐GO) because DA would be oxidated and undergo the rearrangement and intermolecular cross‐linking reaction to produce polydopamine (PDA), which would improve the interfacial adhesion between GO and epoxy, and further be beneficial for the homogenous dispersion of GO in epoxy matrix. The effect of PDA‐GO on the thermal and mechanical properties of PDA‐GO/epoxy composites was also investigated, and the incorporation of PDA‐GO could increase the thermal conductivity, storage modulus, glass transition (T_g), and dielectric constant of epoxy. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39754.     

Biomimetic Polycaprolactone-Graphene Oxide Composites for 3D Printing Bone Scaffolds

Bone shows a radial gradient architecture with the exterior densified cortical bone and the interior porous cancellous bone. However, previous studies presented uniform designs for bone scaffolds that do not mimic natural bone's gradient structure. Hence, mimicking native bone structures is still challenging in bone tissue engineering. In this study, a novel biomimetic bone scaffold with Haversian channels is designed, which approximates mimicking the native bone structure. Also, the influence of adding graphene oxide (GO) to polycaprolactone (PCL)-based scaffolds are investigated by preparing PCL/GO composite ink containing 0.25% and 0.75% GO and then 3D printing scaffolds by an extrusion-based machine. Scanning electron microscopy (SEM) is used for morphological analysis. SEM reveals good printability and interconnected pore structure. The contact angle test shows that wettability reinforces with the increase of GO content. The mechanical behavior of the scaffolds under compression is examined numerically and experimentally. The results indicate that incorporation of GO can affect bone scaffolds' Young's modulus and von Mises stress distribution. Moreover, the biodegradation rates accelerate in the PCL/GO scaffolds. Biological characterizations, such as cell growth, viability, and attachment, are performed utilizing osteoblast cells. Compared to pure PCL, an enhancement is observed in cell viability in the PCL/GO scaffolds.     

Polymer-derived ceramic/graphene oxide architected composite with high electrical conductivity and enhanced thermal resistance

A low temperature method for the fabrication of architected ceramic composites contining graphene is developed based on the infiltration of lightweight graphene oxide (GO) micro-lattices with a preceramic polymer. Self-supported highly porous three-dimensional (3D) GO structures fabricated by direct ink writing are infiltrated with a liquid organic-polysilazane (a compound of Si, C, H, N), and subsequently pyrolyzed at temperatures of 800–1000?ºC to activate the ceramic conversion. These ceramic composites replicate the patterned GO skeleton and, whereas the graphene network provides the conductive path for the composite (electrical conductivity in the range 0.2–4?S?cm^?1), the ceramic wrapping serves as a protective barrier against atmosphere, temperature (up to 900?°C in air) and even direct flame. These structured composites also show hydrophobicity (wetting angle above 120°) and better load bearing capacity than the corresponding 3D GO lattice. The process is very versatile, being applicable to different liquid precursors.     

Microwave assisted ultrafast synthesis of graphene oxide based magnetic nano composite for environmental remediation

We have successfully synthesized multi-layer graphene oxide and graphene oxide based magnetic nanocomposite (M/GO) by microwave-assisted modified Hummers’ method for removal of toxic lead (Pb²⁺) and cadmium (Cd²⁺) ions from aqueous solution. The X-ray diffraction spectra of synthesized graphene oxide and M/GO confirm increased interlayer spacing along c-axis. Raman spectra revealed the good quality of synthesized GO and M/GO. The wrinkles were seen in the SEM images of synthesized graphene oxide. The presence of conjugated double bond (CC) and carbonyl (CO) were confirmed by using the UV–Vis spectroscopic spectra. Brunauer–Emmett–Teller (BET) analysis showed high (126 m²/g) surface area M/GO composite which accounts for large number of active binding sites for the adsorption of heavy metal ions. The adsorption studies revealed that Pb²⁺ ions were efficiently adsorbed on GO sheets. Interestingly, M/GO showed better adsorption for cadmium ions.     

Characterization and performance of dodecyl amine functionalized graphene oxide and dodecyl amine functionalized graphene/high‐density polyethylene nanocomposites: A comparative study

Dodecyl amine (DA) functionalized graphene oxide(DA‐GO) and dodecyl amine functionalized reduced graphene oxide (DA‐RGO) were produced by using amidation reaction and chemical reduction, then two kinds of well dispersed DA‐GO/high‐density polyethylene (HDPE) and DA‐RGO/HDPE nanocomposites were prepared by solution mixing method and hot‐pressing process. Thermogravimetric, X‐ray photoelectron spectroscopy, Fourier transforms infrared spectroscopy, X‐ray diffractions, and Raman spectroscopy analyses showed that DA was successfully grafted onto the graphene oxide surface by uncleophilic substitution and the amidation reaction, which increased the intragallery spacing of graphite oxide, resulting in the uniform dispersion of DA‐GO and DA‐RGO in the nonpolar xylene solvent. Morphological analysis of nanocomposites showed that both DA‐GO and DA‐RGO were homogeneously dispersed in HDPE matrix and formed strong interfacial interaction. Although the crystallinity, dynamic mechanical, gas barrier, and thermal stability properties of HDPE were significantly improved by addition of small amount of DA‐GO or DA‐RGO, the performance comparison of DA‐GO/HDPE and DA‐RGO/HDPE nanocomposites indicated that the reduction of DA‐GO was not necessary because the interfacial adhesion and aspect ratio of graphene sheets had hardly changed after reduction, which resulting in almost the same properties between DA‐GO/HDPE and DA‐RGO/HDPE nanocomposites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39803.     

Fabrication of ZrO2/rGO nanocomposites by flash sintering under AC electric fields

Ceramic matrix nanocomposites containing graphene possess superior mechanical properties. However, these nanocomposites are very difficult to be prepared using the conventional methods due to severe grain growth and simultaneous degradation of the graphene at high sintering temperatures and long dwell time. Herein, the dense ZrO₂/rGO (reduced graphene oxide) nanocomposites are successfully fabricated by flash sintering of the green compacts consisting of ZrO₂ nanoparticles and graphene oxide (GO) at 893–951℃ in merely 5 seconds under the alternating current (AC) electric fields of 130–150 V cm⁻¹. The GO can be in situ thermal reduced during the flash sintering. The as-prepared ZrO₂/rGO nanocomposites exhibit excellent mechanical properties. This study presents a green and simple approach to fabricate the dense ceramic matrix nanocomposites reinforced with graphene at low temperatures in a short time.     

金刚烷胺/氧化石墨烯复合材料的制备及其吸附性能

以氧化石墨烯和金刚烷为原料，通过水相合成法制备了金刚烷胺功能化氧化石墨烯复合材料A/GO，以FT-IR、XRD和XPS对A/GO进行了结构表征，并考察了A/GO对有机染料的吸附性能。结果表明，与氧化石墨烯相比，A/GO对甲基蓝（AB93）表现出高效吸附性，其吸附动力学和吸附等温模型分别符合拟二级动力学和Langmuir模型，理论最大吸附容量（qm）为1250.0 mg/g。热力学分析表明，A/GO吸附AB93是自发的放热过程。A/GO吸附AB93对盐（NaCl和KCl）表现出良好的耐盐性，而CaCl2能有效地促进A/GO吸附AB93。对于刚果红和AB93等的混合染料体系，A/GO能选择性吸附AB93。     

Graphene oxide-anchored reactive sulfonated copolymer via simple one pot condensation polymerization: proton-conducting solid electrolytes

A rapid and efficient post-polymerization functionalization of poly(urea-co-urethane) (PUU) onto the graphene oxide (GO) nanosheets has been developed to produce super-acidic polymer/GO hybrid nanosheets. Thus, the surface of GO nanosheets were functionalized with 3-(triethoxysilyl)propyl isocyanate (TESPIC) from hydroxyl groups to yield isocyanate functionalized graphene oxide nanosheets. Then, sulfonated polymer/GO hybrid nanosheets were prepared by condensation polymerization of isocyanate-terminated pre-polyurea onto isocyanate functionalized graphene oxide nanosheets through the formation of carbamate bonds. FTIR and TGA results indicated that TESPIC modifier agent and poly(urea-co-urethane) were successfully grafted onto the GO nanosheets. The grafting efficiency of poly(urea-co-urethane) polymer onto the GO nanosheets was estimated from TGA thermograms to be 205.9%. Also, sulfonated polymer/GO hybrid nanosheets showed a proton conductivity as high as 3.7 mS cm^?1. Modification and morphology of GO nanosheets before and after modification processes were studied by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD).     

Conversion of pencil graphite to graphene/polypyrrole nanofiber composite electrodes and its doping effect on the supercapacitive properties

Graphene platelets were synthesized from pencil flake graphite and commercial graphite by chemical method. The chemical method involved modified Hummer's method to synthesize graphene oxide (GO) and the use of hydrazine monohydrate to reduce GO to reduced graphene oxide (rGO). rGO were further reduced using rapid microwave treatment in presence of little amount of hydrazine monohydrate to graphene platelets. Chemically modified graphene/polypyrrole (PPy) nanofiber composites were prepared by in situ anodic electropolymerization of pyrrole monomer in the presence of graphene on stainless steel substrate. The morphology, composition, and electronic structure of the composites together with PPy fibers, graphene oxide (GO), rGO, and graphene were characterized using X‐ray diffraction (XRD), laser‐Raman, and scanning electron microscopic (SEM) methods. From SEM, it was observed that chemically modified graphene formed as a uniform nanocomposite with the PPy fibers absorbed on the graphene surface and/or filled between the graphene sheets. Such uniform structure together with the observed high conductivities afforded high specific capacitance and good cycling stability during the charge–discharge process when used as supercapacitor electrodes. A specific capacitance of supercapacitor was as high as 304 F g^?1 at a current density of 2 mA cm^?1 was achieved over a PPy‐doped graphene composite. POLYM. ENG. SCI., 55:2118–2126, 2015. © 2014 Society of Plastics Engineers     

Surface amorphization and deoxygenation of graphene oxide paper by Ti ion implantation

Ti ion implantation with different doses was used to modify the surface and deoxygenate graphene oxide (GO) papers. The morphologies, microstructures and surface chemical states of the modified GO papers were investigated. Based on the results, the surface amorphization of GO papers is realized by Ti ion implantation. In addition, the whole GO paper is reduced or deoxygenated, which can be attributed to the annealing effect. However, at a low implantation dose of 5 × 10¹⁶ cm⁻², the deoxygenation of GO paper is found to be incomplete. With a high implantation dose of 3 × 10¹⁷ cm⁻², a surface composed of whirlpool-like structures is generated, while the layer-by-layer stacking structure of the as-prepared GO paper is retained.     

纳米氧化石墨烯改性PVDF微滤膜在MBR中的抗污染性能

利用强亲水性氧化石墨烯（GO）作为添加剂,自制了PVDF/GO复合微滤膜,并将其应用于MBR系统中,进行长期应用研究。研究发现,共混膜的表面性质得到改善,其表面含氧基团达到29.33%（GO=3%）;共混膜与PVDF膜对污染物的去除效果相近,但共混膜（GO=3%）仅进行了一次清洗,清洗周期是PVDF的4倍;PVDF/GO共混膜的膜阻力要低于PVDF膜,并且共混膜的不可逆污染阻力显著下降,其数值仅仅是PVDF膜的9.0%（GO=3%）;EPS分析发现,共混膜表面的EPS浓度明显减少,其降幅分别达到59.98%（GO=1%）和69.57%（GO=3%）,抗污染性能显著提高;通过SEM与CLSM分析发现,随着氧化石墨烯加入量的提高,共混膜表面形成了滤饼层变得疏松,厚度也变薄,甚至露出了部分膜表面（GO=3%）,保证了共混膜稳定的渗透率。     

Hydrous-ferric oxide nanorods grown on PEGylated graphene oxide with superior capacity for selective adsorption of albumin

A ferrate functionalized graphene-based composite is prepared by growth of hydrous ferric oxide (FeOOH) on the polyethylene glycol (PEG) modified graphene oxide (GO) sheets. The obtained GO–PEG–FeOOH composite is characterized by ATR-FTIR, TEM, AFM, XPS and ICP-MS. The PEGylation significantly changes the surface property of the bare graphene oxide, which not only generates a nano-bio-interface for protein interaction but also reduces the non-specific adsorption of proteins. The PEGylation and growth of FeOOH nanorods on GO sheets obviously enhanced the selectivity toward the adsorption of albumin through strong hydrogen bonding interaction, exhibiting an ultra-high adsorption capacity of 1377.4 mg g⁻¹ for bovine serum albumin (BSA). It is obviously higher than those achieved by any hitherto reported graphene based materials and other carbon nanomaterials. Albumin retained by the composite could be effectively recovered with a 4.0 mM B–R buffer through the affinity of boronic acid toward protein, giving rise to a recovery of 70%. Circular dichroism (CD) spectra indicate no conformational change for BSA during the process of adsorption/desorption. The practical applicability of the GO nanocomposite is further demonstrated by the selective adsorption/isolation of albumin from complex biological samples matrixes, e.g., human whole blood.     

In situ synthesis of ultrathin 2-D TiO2 with high energy facets on graphene oxide for enhancing photocatalytic activity

Two kinds of TiO₂ with novel structures, interpenetrating anatase TiO₂ tablets (IP-TiO₂), and overlapping anatase TiO₂ nanosheets (OL-TiO₂) with exposed {0 0 1} facets, are synthesized. The graphene oxide (GO) supported ultrathin TiO₂ nanosheets (OL-TiO₂/GO) is also prepared by one-pot hydrothermal method. The microscopic feature, morphology, phase, and nitrogen adsorption–desorption isotherms are characterized. The performance of photocatalytic degradation of methyl blue is also measured. Compared with IP-TiO₂, the OL-TiO₂ with GO possess higher photocatalytic efficiency. The GO can improve the photocatalytic property by increasing specific surface area, accelerating the separation of electron–hole pairs, as well as extending the electron life. The growth process of TiO₂ nanosheets on graphene oxide layers probably follows a step-growth mechanism with F⁻ as morphology controlling agent. The steps on the surface can improve the photocatalytic activity further due to the increase of dangling bonds of 5-coordinated Ti (Ti_5c) which are considered to be the active sites in the photocatalytic reaction.     

Graphene‐based composite with microwave absorption property prepared by in situ reduction

Binary composite of graphene/poly(ethylene oxide) (PEO) with microwave absorption property is prepared by in situ reduction process. Graphite oxide (GO) is prepared from flake graphite by modified Hummers' method and further dispersed in distilled water to get GO solution. Then, PEO powder is slowly added into GO solution to get GO/PEO solution, and graphene/PEO composites is prepared via a facile and quick reduction process in GO/PEO solution. PEO and graphene/PEO composites are characterized by scanning electron microscopy, atomic force microscopy, thermo gravimetric analysis, and vector network analyzer. The results show that graphene is uniformly dispersed in PEO matrix because GO and PEO can be uniformly dispersed at molecular level due to their water‐solubility and the agglomeration of graphene can be prevented by PEO macromolecular chains during in situ reduction process. Graphene/PEO composite has better thermal stability than PEO, which can be explained by the graphene restoration of sp² bonded carbon structure. Meanwhile, graphene/PEO composite shows excellent microwave absorption property at low grapheme content. The minimum reflection loss of graphene/PEO composite is up to −20.0 dB when the content of graphene is only 1 wt%. POLYM. COMPOS., 35:461–467, 2014. © 2013 Society of Plastics Engineers