Enhanced Fluorescence of Graphene Oxide by Well-Controlled Au@SiO2 Core-Shell Nanoparticles

Graphene and graphene derivatives, including graphene oxide (GO) and reduced GO (rGO), have attracted remarkable attention in different fields due to their unique electronic, thermal, and mechanical properties, whereas the fluorescence property is rarely been studied. This paper reports on metal-enhanced fluorescence Au@SiO₂ composite nanoparticles adsorbed graphene oxide nanosheets, where the silica-shell is used to control the distance between gold-core and fluorophore GO, and a positively charged polyelectrolyte poly(allylamine hydrochloride) (PAH) is used to adsorb the negatively charged silica-shell and GO by layer-by-layer assembly (LbL) approach. The silica-shell around the 80 nm gold-core can be well-controlled by ending the reaction at different times. Various analytical techniques were applied to characterize the morphology and optical characters of the as-prepared particles. A more than three-fold increase of the fluorescence intensity of GO was obtained.     

Laser and ion beams graphene oxide reduction for microelectronic devices

Reduced graphene oxide (rGO) is a two-dimensional material, which is attracting increasing attention due to its special properties. It can be obtained by laser or ion beam irradiations of pristine graphene oxide (GO). It shows high mechanical resistance, considerable electric and thermal conductivity. All these rGO characteristics together with the high number of molecular species that can be embedded between its layers, make graphene oxide a potential material for electronic sensors or efficient support on which conductive strips, condensers, and micrometric electronic devices can be designed. In particular, as it is described in this paper, it is possible to carry out high spatial resolution lithography in GO by using a focused laser or micro ion beam in order to design macro, micro, and submicron geometrical structures. The use of the reduced graphene oxide for the laser and ion beam fabrication of electrical resistances and capacitances is presented.     

Functionalization of Graphene Oxide and its Biomedical Applications

Graphene oxide (GO) offers interesting physicochemical and biological properties for biomedicine due to its versatility, biocompatibility, small size, large surface area, and its ability to interact with biological cells and tissues. GO is a two-dimensional material of exceptional strength, unique optical, physical, mechanical, and electronic properties. Ease of functionalization and high antibacterial activity are two major properties identified with GO. Due to its excellent aqueous processability, amphiphilicity, surface functionalization capability, surface enhanced Raman scattering (SERS), and fluorescence quenching ability, GO chemically exfoliated from oxidized graphite is considered a promising material for biological applications. In addition, due to π-π* transitions, a low energy is required for electron movement, a property important in Biosensor and Bioimaging applications of GO. In this article, we present an overview of current advances in GO applications in biomedicine and discuss future perspectives. We conclude that GO is going to play a vital role in Biomedical applications in the near future.     

Tuning of electronic properties and dynamical stability of graphene oxide with different functional groups

The structural, electronic and vibrational properties of graphene oxide (GO) with varying proportion of epoxy and hydroxyl functional groups have been studied using density functional theory. The functional groups and oxygen density have an obvious influence on the electronic and vibrational properties. The dependence of band gap on associated functional groups and oxygen density shows a possibility of tuning the band gap of graphene by varying the functional groups as well as oxidation level. The absorption of high oxygen content in graphene leads to the gap opening and resulting in a transition from semimetal to semiconductor. Phonon dispersion curves show no imaginary frequency or no softening of any phonon mode throughout the Brillouin zone which confirms the dynamical stability of all considered GO models. Different groups and different oxygen density result into the varying characteristics of phonon modes. The computed results show good agreement with the experimental observations. Our results present interesting possibilities for engineering the electronic properties of graphene and GO and impact the fabrication of new electronics.     

Fabrication and characterization of graphene oxide/zinc oxide nanorods hybrid

This work presented a hybrid architecture of graphene oxide (GO)/ZnO nanorods (ZNs) with ZNs attached parallel onto GO sheets. ZNs were synthesized by refluxing zinc acetate dehydrate in methanol solution under basic conditions followed by surface modification of 3-aminopropyl triethoxysilane (ATS), and then the preformed ZNs were attached onto GO sheets by reaction of the amino groups on the outer wall of ZNs with the carboxyl groups on the GO surface. Transmission electron microscopy (TEM) image of the as-prepared hybrid reveals the morphology of the architecture of GO/ZNs hybrid. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA) ultraviolet-visible (UV-vis) and fluorescence spectroscopy were also performed to characterize the structure and properties of the GO/ZNs hybrid. It was shown that ZNs maintained their initial morphology and crystallinity in the hybrid and the luminescence quenching of yellow-green emission of ZNs confirmed the electron transfer from excited ZnO to GO sheets.     

First-principles insight into Li and Na ion storage in graphene oxide

The structural, electronic, and adsorption properties of Li/Na ions on graphene decorated by epoxy groups are investigated by first-principles calculations based on density functional theory.Our results show that the concentration of epoxy groups remarkably affects the structural and electronic properties of graphene.The bandgaps change monotonically from0.16 eV to 3.35 eV when the O coverage increases from 12.5% to 50%(O/C ratio).Furthermore, the highest lithiation potential of 2.714 V is obtained for the case of graphene oxide(GO) with 37.5 % O coverage, while the highest sodiation potential is 1.503 V for GO with 12.5% O coverage.This clearly demonstrates that the concentration of epoxy groups has different effects on Li and Na storage in GO.Our results provide a new insight into enhancing the Li and Na storage by tuning the concentration of epoxy groups on GO.     

A simple approach to synthesize nanosized sulfur/graphene oxide materials for high-performance lithium/sulfur batteries

We report on a simple and facile synthesis route for the sulfur/graphene oxide composite via ultrasonic mixing of the nano-sulfur and graphene oxide aqueous suspensions followed by a low-temperature heat treatment. High-resolution transmission and scanning electronic microscopy observations revealed the formation of a highly porous structure consisting of sulfur with uniform graphene oxide coating on its surface. The resulting sulfur/graphene oxide (S/GO) composite exhibited high and stable specific discharge capacities of 591 mAh g^?1 after 100 cycles at 0.1 C and good rate capability. This enhanced electrochemical performance could be attributed to the effective confining the polysulfides dissolution and accommodation of the volume changes during the Li-S electrochemical reaction by the functional groups on the graphene oxide coating layer. Furthermore, the highly developed porous structure of S/GO composite favors the enhanced ion transport and electrolyte diffusion.     

通过光致还原调制氧化石墨烯寿命并用于微纳图形制备

氧化石墨烯因其宽带可调谐的荧光发射特性已被广泛应用于荧光成像、金属离子高灵敏检测和光电器件的制备.相比于荧光强度,氧化石墨烯荧光寿命不受材料厚度和激发功率的影响,具有更为稳定和均一的特性.本文研究了在激光还原过程中氧化石墨烯荧光寿命逐渐减小的变化行为,发现了长寿命sp~3杂化结构向短寿命sp~2杂化结构的转变.通过精确控制还原时间,结合激光直写技术,在单层氧化石墨烯薄膜上实现了二维码、条形码、图形和数字等微纳图形的制备,还在多层氧化石墨烯薄膜结构上获得了多寿命多层微纳图形.这种微纳图形的制备具有灵活无掩膜、高对比和多模式的特点,可用于高密度光学存储、信息显示和光电器件制备等诸多领域.     

氧化石墨烯猝灭罗丹明6G荧光的机理研究

The fluorescence quenching of Rhodamine 6G (R6G) by graphene oxide (GO) was interrogated by R6G fluorescence measurements using a set of controlled GO samples with varied C/O ratios as the quencher.The carbonyl groups on the GO nanosheet turned to play a dominant role in quenching the R6G fluorescence.The quenching in the static regime can be described by the "sphere of action" model.The significant absorption of the R6G fluorescence by the ground-state complex formed between R6G and GO was identified to be responsible for the static quenching.This work offers helpful insights into the fluorescence quenching mechanisms in the R6G/GO system.     

Science and Engineering of Graphene Oxide

Functional and synthesis diversity of graphene oxide (GO) has led to various fundamental and applied scientific explorations. GO can be viewed as an in‐plane, hybrid 2D lattice consisting of sp2 and sp3 carbon regions. Engineering the type and distribution of sp3 regions can tune the physical properties of resultant GO. This article reviews the development in the field of GO since the 19th century, with a thorough discussion on its status after the discovery of graphene in last decade. Detailed structure, optical properties, electrochemical behavior, and its viability for biological applications are discussed from both a scientific and technological perspective and a future outlook for GO research is presented.     

Graphene grown on transition metal substrates: Versatile templates for organic molecules with new properties and structures

The interest in graphene (a carbon monolayer) adsorbed on metal surfaces goes back to the 60's, long before isolated graphene was produced in the laboratory. Owing to the carbon-metal interaction and the lattice mismatch between the carbon monolayer and the metal surface, graphene usually adopts a rippled structure, known as moiré, that confers it interesting electronic properties not present in isolated graphene. These moiré structures can be used as versatile templates where to adsorb, isolate and assemble organic-molecule structures with some desired geometric and electronic properties. In this review, we first describe the main experimental techniques and the theoretical methods currently available to produce and characterize these complex systems. Then, we review the diversity of moiré structures that have been reported in the literature and the consequences for the electronic properties of graphene, attending to the magnitude of the lattice mismatch and the type of interaction, chemical or physical, between graphene and the metal surface. Subsequently, we address the problem of the adsorption of single organic molecules and then of several ones, from dimers to complete monolayers, describing both the different arrangements that these molecules can adopt as well as their physical and chemical properties. We pay a special attention to graphene/Ru(0001) due to its exceptional electronic properties, which have been used to induce long-range magnetic order in tetracyanoquinodimethane (TCNQ) monolayers, to catalyze the (reversible) reaction between acetonitrile and TCNQ molecules and to efficiently photogenerate large acenes.     

Silane coupling agent grafted graphene oxide and its modification on polybenzoxazine resin

Graphene oxide (GO), as a two-dimensional carbon material with excellent properties including strong mechanical properties and good thermal resistance, can be used to modify the polybenzoxazine (PBZ) resins. Unfortunately, the poor dispersity of GO is still the main obstacle restricting the effects of GO in PBZ resin. Silane coupling agent, 3-aminopropyltriethoxy-silane (APTS), is a good choice to modify the surface of GO to improve the dispersity and the bridging action between GO and PBZ resin. In this way, not only the poor dispersion of GO in benzoxazine can be overcome, but also the potential of GO, such as good thermal resistance and strong mechanical properties, can be explored during the modification of PBZ resin.     

Frictional behavior of oxide graphene nanosheets as water-base lubricant additive

Oxide graphene (GO) nanosheets were prepared by modified Hummers and Offeman methods. The products were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectrometry (FTIR), and thermogravimetric analysis (TGA). The tribological properties of GO nanosheets as water-base lubricant additive were investigated using a UMT-2 ball-plate tribotester. By the addition of GO nanosheets in pure water, the antiwear ability was improved and the friction coefficient was decreased. The water with GO nanosheets showed better tribological properties than the water with oxide multiwall carbon nanotubes (CNTs-COOH). It is concluded that the formation of a thin physical tribofilms on the substrate can explain the good friction and wear properties of GO nanosheets.     

Elucidating synthesis of noble metal nanoparticles/graphene oxide in free-scavenger γ-irradiation

Three representative noble metal (Ag, Au and Pt) nanoparticles decorated graphene oxide (NMNPs/GO) composites were fabricated via γ-irradiation without scavenger. The NMNPs/GO composites exhibited the pure and well-dispersed particles structure, which directly illustrated that the GO could be acted as scavenger to benefit reduction and growth of NMNPs. Compared with irradiated GO (IGO), the GO substrate of composites had the lower relative content of hydroxyl groups, meanwhile, the relative contents of carbonyl groups (Pt > Au > Ag) were increased with increasing valence of noble metal. Such results illustrated that the abundant hydroxyl groups could convert the hydrated electrons, hydroxyl and hydrogen radicals to promote the growth of NMNPs on the surface of GO. In addition, the Raman signals of Ag NPs/GO composites were significantly enhanced (6.18 fold more than pristine GO, respectively), exhibiting obvious surface-enhanced Raman scattering activity. Therefore, this paper revealed that the GO could convert the hydrated electrons and radicals to synthetizing NMNPs/GO composites during γ-ray irradiation.     

氧化石墨烯/壳聚糖复合薄膜材料的制备及其非线性光限幅效应的研究

石墨烯及其衍生物作为新型碳纳米结构,由于其优异的光限幅性能而受到广泛关注,但现有的工作多侧重于其在液相体系中光限幅效应及其起因研究.本文以壳聚糖为成膜基质,将氧化石墨烯(GO)与壳聚糖(CS)在液相中均匀共混后成膜,对比研究GO溶液和GO-CS复合膜的光限幅效应及其起因.结果表明在线性透过率相同的情况下,GO在固相基质中表现出比液相基质更强的光限幅效应和更弱的非线性散射.这说明不同于碳纳米管简单的非线性散射,在GO中可能存在多种非线性光学效应.     

Molecular responses of cells to 2-mercapto-1-methylimidazole gold nanoparticles (AuNPs)-mmi: investigations of histone methylation changes

Reduced graphene oxide (RGO) sheet was functionalized with nanocrystalline cellulose (NCC) via click coupling between azide-functionalized graphene oxide (GO-N₃) and terminal propargyl-functionalized nanocrystalline cellulose (PG-NCC). First, the reactive azide groups were introduced on the surface of GO with azidation of 2-chloroethyl isocyanate-treated graphene oxide (GO-Cl). Then, the resulted compounds were reacted with PG-NCC utilizing copper-catalyzed azide-alkyne cycloaddition. During the click reaction, GO was simultaneously reduced to graphene. The coupling was confirmed by Fourier transform infrared, Raman, DEPT135, and ¹³C NMR spectroscopy, and the complete exfoliation of graphene in the NCC matrix was confirmed with X-ray diffraction measurement. The degree of functionalization from the gradual mass loss of RGO-NCC suggests that around 23 mass % has been functionalized covalently. The size of both NCC and GO was found to be in nanometric range, which decreased after click reaction.     

Synthesis and characterization of nanocomposites films with graphene oxide and reduced graphene oxide nanosheets

Graphene oxide (GO) and reduced graphene oxide (CRGO), as a graphene derivatives, possess unique properties and a high aspect ratio, indicating great potential in nanocomposite fields. The present work reports the fabrication of the nanocomposite films by a simple and environmentally friendly process using aqueous solution and optimized time sonication for better exfoliation of the graphene sheets within Poly(Vinyl alcohol) (PVA) as matrix. The films were characterized using high-resolution TEM (HRTEM), X-ray diffraction (XRD), Microtensile testing, Differential scanning calorimetry (DSC) and Thermogravimetric analysis (TGA). The TEM images revealed a successfully exfoliation of the GO/CRGO nanosheets. XRD combined with TGA and DSC measurements showed an improvement in the thermal stability and tunable thermal properties. In addition, the Young's modulus and tensile yield strength of the composite films containing 1 wt% GO were obtained to be 4.92 GPa and 66 MPa respectively. These excellent reinforcement effects were achieved by the strong interaction between the components.     

Grafting of polymers onto graphene oxide by cationic and anionic polymerization initiated by the surface-initiating groups

The grafting of polymers onto graphene oxide (GO) was achieved by two process: (1) cationic polymerization initiated by carboxyl (COOH) groups on GO and (2) anionic alternating copolymerization of epoxides with cyclic acid anhydrides initiated by potassium carboxylate (COOK) groups on GO. The cationic polymerizations of isobutyl vinyl ether and N-vinylcarbazole were successfully initiated by COOH groups on GO to give the corresponding polymer-grafted GO. The cationic polymerization was considered to be initiated by proton addition from COOH groups to monomer and propagation of polymer cation proceeds with carboxylate anion as a counter ion. It was found that the corresponding polymer was successfully grafted onto GO based on the termination reaction of growing polymer cation and surface counter carboxylate anion. On the other hand, the anionic ring-opening alternating copolymerization of epoxide and cyclic acid anhydrides were also initiated by COOK groups on GO, which were previously introduced onto GO by the neutralization of COOH groups with KOH. During the anionic ring-opening copolymerization of styrene oxide (SO) with phthalic anhydride (PAn) and maleic anhydride (MAn), the corresponding polyesters, poly(SO-alt-PAn) and poly(SO-alt-MAn), were successfully grafted onto GO, based on the propagation of the polyesters from COOK groups. The grafting of polymers onto GO during the above cationic and anionic polymerizations was confirmed by thermal decomposition gas chromatogram/mass spectrum. The untreated GO in THF was immediately precipitated within 15 min. On the contrary, these polymer-grafted GOs gave stable dispersions in THF and no precipitation of polymer-grafted GOs was observed even after one week.     

A simple approach to synthesize novel sulfur/graphene oxide/multiwalled carbon nanotube composite cathode for high performance lithium/sulfur batteries

A sulfur/graphene oxide/multiwalled carbon nanotube (S/GO/MWNT) composite was synthesized via a simple ultrasonic mixing method followed by heat treatment. By taking advantage of this solution-based self-assembly synthesis route, poisonous and noxious reagents and complicated fabrication processes are rendered unnecessary, thereby simplifying its manufacturing and decreasing the cost of the final product. Transmission and scanning electronic microscopy observations indicated the formation of the three-dimensional interconnected S/GO/MWNT composite through the environmentally friendly process. The GO layers and long MWNTs synergistically constructed hierarchical electron/ion pathways, favoring the ion transport and electrolyte diffusion. The interlaced network can serve as sponges to physically absorb polysulfides to their wrinkled surface and porous structure. In addition, GO could confine the polysulfides’ dissolution through chemical absorption by the functional groups on GO layers. Therefore, the resulting S/GO/MWNT composite exhibits good rate capability and highly stable specific discharge capacity of 773 mA h g^?1 after 100 cycles at 0.1 C.     

水热法快速制备荧光氧化石墨烯量子点及其在细胞成像中的应用

作为一种新型荧光纳米材料,氧化石墨烯量子点(GO QDs)凭借其良好的水溶性和生物相容性得到广泛的关注。以氧化石墨烯为原料,过氧化氢为氧化剂,一步水热法在90 min内快速制备氧化石墨烯量子点,实现了快速、高效及绿色制备氧化石墨烯量子点。所制备得到的氧化石墨烯量子点分布均匀,透射电镜(TEM)图片表明氧化石墨烯量子点粒径分布在2.25～5.25 nm,傅里叶红外光谱(FTIR)和X射线电子能谱(XPS)显示氧化石墨烯量子点表面含有大量的羟基、羧基、羰基等含氧功能团,表明氧化石墨烯量子点具有很好的水溶性。荧光发射光谱(PL)表明氧化石墨烯量子点具有激发波长依赖性。基于其独特的纳米结构,良好的光学性能和生物相容性,氧化石墨烯量子点可替代传统荧光纳米材料应用于细胞成像。