Reduced Graphene Oxide Substrate Research Articles

Tuning photoluminescence quenching efficiency of reduced graphene oxide substrates using silver nanoparticles

In this paper we report the synthesis of reduced graphene oxide doped with silver nanoparticles using aqueous extract of Psidium guajava. The dependence of photoluminescence (PL) quenching efficiency of reduced graphene oxide with variable dosage of silver nanoparticles using methylene blue as a model dye is investigated. The effect of excitation energies on the PL quenching efficiency of as-synthesized samples is also systematically studied. At 420 nm excitation, the plasmonic field of silver nanoparticles accelerates charge transfer from methylene blue to reduced graphene oxide resulting in efficient PL quenching as compared to pristine reduced graphene oxide. However at 650 nm excitation, the PL quenching efficiency of reduced graphene oxide surpasses silver nanoparticles doped reduced graphene oxide. This is attributed to strong interaction between reduced graphene oxide and methylene blue in absence of plasmonic fields at lower excitation energies. In order to enhance the quenching efficiency of silver nanoparticle doped reduced graphene oxide at 650 nm excitation, the concentration of silver nanoparticles over graphene surface is increased. This leads to increase in inhomogeneously sized and shaped nanoparticles over graphene surface which not only broadens the plasmonic absorption band but also improves the quenching efficiency at 650 nm. The schematics of charge transfer states via which the PL quenching occurs at different excitation energies are also presented.

Carbon‐Encapsulated SnO2 Core–Shell Nanowires Directly Grown on Reduced Graphene Oxide Sheets for High‐Performance Li‐Ion Battery Electrodes

AbstractA designed electrode material of carbon‐encapsulated tin dioxide core–shell nanowires that are synthesized directly on reduced graphene oxide substrates is reported, and its application as a positive electrode material for lithium‐ion battery is shown. Each of the individual tin dioxide nanowires is wrapped with carbon shell layers and grown on a reduced graphene oxide substrate, which gives rise to structural benefits for electrochemical performance of the lithium‐ion battery. Such carbon structures allow the electrode materials to withstand the mechanical stress during repeated charge/discharge processes and facilitate the reaction kinetics for the lithiation/delithiation processes. In the electrochemical cell tests, the synergetic effect of the proposed electrode design is explicitly verified by presenting highly enhanced rate capability and cycle durability on full‐cell batteries as well as half‐cell tests.

Improving the glial differentiation of human Schwann-like adipose-derived stem cells with graphene oxide substrates.

There is urgent need to improve the clinical outcome of peripheral nerve injury. Many efforts are directed towards the fabrication of bioengineered conduits, which could deliver stem cells to the site of injury to promote and guide peripheral nerve regeneration. The aim of this study is to assess whether graphene and related nanomaterials can be useful in the fabrication of such conduits. A comparison is made between graphene oxide (GO) and reduced GO substrates. Our results show that the graphene substrates are highly biocompatible, and the reduced GO substrates are more effective in increasing the gene expression of the biomolecules involved in the regeneration process compared to the other substrates studied.

In-situ growth of ultrathin cobalt monoxide nanocrystals on reduced graphene oxide substrates: an efficient electrocatalyst for aprotic Li–O2 batteries

Large over-potentials during battery operation remain a big obstacle for aprotic Li–O2 batteries. Herein, a nanocomposite of about 4 nm cobalt monoxide nanocrystals grown in situ on reduced graphene oxide substrates (CoO/RGO) has been synthesized via a thermal decomposition method. The CoO/RGO cathode delivers a high initial capacity of 14 450 mAh g−1 at a current density of 200 mA g−1. Simultaneously it displays little capacity fading after 32 cycles with a capacity restriction of 1000 mAh g−1. Additionally, compared with Ketjenblack and general CoO nanoparticles, ultrathin CoO nanoparticle-decorated RGO electrode materials with a delaminated structure display an observable reduction of over-potential in Li–O2 batteries. These results demonstrate that the introduction of RGO improves the performance of CoO, which is a promising strategy for optimizing the design of electrocatalysts for aprotic rechargeable Li–O2 batteries.

Stem Cell Substrates: Pulsed‐Electromagnetic‐Field‐Assisted Reduced Graphene Oxide Substrates for Multidifferentiation of Human Mesenchymal Stem Cells (Adv. Healthcare Mater. 16/2016)

Stem Cell Substrates: Pulsed‐Electromagnetic‐Field‐Assisted Reduced Graphene Oxide Substrates for Multidifferentiation of Human Mesenchymal Stem Cells (Adv. Healthcare Mater. 16/2016)

Calixarene Assisted Rapid Synthesis of Silver-Graphene Nanocomposites with Enhanced Antibacterial Activity.

Demonstrated herein is a single rapid approach employed for synthesis of Ag-graphene nanocomposites, with excellent antibacterial properties and low cytotoxicity, by utilizing a continuous hydrothermal flow synthesis (CHFS) process in combination with p-hexasulfonic acid calix[6]arene (SCX6) as an effective particle stabilizer. The nanocomposites showed high activity against E. coli (Gram-negative) and S. aureus (Gram-positive) bacteria. The materials were characterized using a range of techniques including transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, UV-vis spectrophotometry, FT-IR, and X-ray powder diffraction (XRD). This rapid, single step synthetic approach not only provides a facile means of enabling and controlling graphene reduction (under alkaline conditions) but also offers an optimal route for homogeneously producing and depositing highly crystalline Ag nanostructures into reduced graphene oxide substrate.

Pulsed-Electromagnetic-Field-Assisted Reduced Graphene Oxide Substrates for Multidifferentiation of Human Mesenchymal Stem Cells.

Electromagnetic fields (EMFs) can modulate cell proliferation, DNA replication, wound healing, cytokine expression, and the differentiation of mesenchymal stem cells (MSCs). Graphene, a 2D crystal of sp(2) -hybridized carbon atoms, has entered the spotlight in cell and tissue engineering research. However, a combination of graphene and EMFs has never been applied in tissue engineering. This study combines reduced graphene oxide (RGO) and pulsed EMFs (PEMFs) on the osteogenesis and neurogenesis of MSCs. First, the chemical properties of RGO are measured. After evaluation, the RGO is adsorbed onto glass, and its morphological and electrical properties are investigated. Next, an in vitro study is conducted using human alveolar bone marrow stem cells (hABMSCs). Their cell viability, cell adhesion, and extracellular matrix (ECM) formation are increased by RGO and PEMFs. The combination of RGO and PEMFs enhances osteogenic differentiation. Together, RGO and PEMFs enhance the neurogenic and adipogenic differentiation of hABMSCs. Moreover, in a DNA microarray analysis, the combination of RGO and PEMFs synergically increases ECM formation, membrane proteins, and metabolism. The combination of RGO and PEMFs is expected to be an efficient platform for stem cell and tissue engineering.

Rational Design of a Unique Ternary Structure for Highly Photocatalytic Nitrobenzene Reduction

The rational design and controllable synthesis of TiO2 and noble metal composite photocatalysts represent an unprecedented challenge for developing the solar-driven reduction of nitrobenzene (NB) to aminobenzene (AB), owing to the recombination over the interface between the noble metals and TiO2, which is harmful to the conversion efficiency of NB to AB. Here, we design a unique ternary structure (the high separation of TiO2 and Pt nanoparticles on the surface of reduced graphene oxide (RGO)) through the sol–gel and microwave-assisted strategies. The substrate of RGO can be used as an “electric wire” to effectively transfer the photogenerated electrons from the isolated TiO2 nanocrystals to the isolated Pt nanoparticles, which greatly decreases the interface recombination between TiO2 and Pt and further improves the conversion efficiency of NB to AB under the solar light irradiation. We anticipate our research provides a new way to overcome the interface recombination on the binary photocatalysts in the ...

Pt-Au bimetallic nanoparticles decorated on reduced graphene oxide as an excellent electrocatalysts for methanol oxidation

In this study, we report a general and simple strategy for the synthesis of platinum nanoparticles (PtNPs), highly dispersed on reduced graphene oxide (RGO) substrate with Au nanoparticles. The electrochemically active surface area (ECSA) of the Pt-Au-RGO electrocatalyst is found to be higher than the Pt-RGO electrocatalyst, which is more comparable to a commercial Pt/C catalyst. The obtained ratio of the voltammetric forward peak current to the reverse peak current for the Pt-Au-RGO electrocatalyst (If/Ib=2.33) is much higher than that of the Pt-RGO electrocatalyst (If/Ib=1.16). This phenomenon is attributed to the synergistic effects of the Au and the RGO substrate, which help to enhance the electrochemical activity of Pt nanoparticles for methanol oxidation and carbonaceous poisoning resistance. The reported methanol oxidation is found to exhibit excellent electrocatalytic performance, reliability, and stability, surpassing that of several reported modified electrodes that can also be used for platinum-based catalysts in fuel cell applications.

Self-assembly of mildly reduced graphene oxide monolayer for enhanced Raman scattering

Graphene-enhanced Raman scattering (GERS) has attracted much attention recently. In present study, monolayer of chemically reduced graphene oxide (RGO) nanosheets was chemically bonded on Si substrates and their possible applications in Raman scattering were investigated. In comparison with the mechanically exfoliated graphene, mildly reduced graphene oxide (MR-GO) monolayer is a better substrate to quench the fluorescence (FL) signals and simultaneously enhance the Raman signals of adsorbed Rhodamin 6G (R6G) molecules. Raman and X-ray photoelectron spectra indicate that π–π stacking and the residual polarized oxygen groups on MRGO surface, which can produce a strong local electric field under laser excitation, are mainly responsible for the excellent GERS effect of MR-GO substrate, while the charge transfer between R6G and MR-GO has a relatively low contribution for GERS effect. Our results not only provide a new approach to realize sensitive GERS substrate, but also are helpful for improving the fundamental understanding of GERS effect on RGO substrate.

Superhydrophobic SERS Substrates Based on Silver-Coated Reduced Graphene Oxide Gratings Prepared by Two-Beam Laser Interference

Reported here is the fabrication of reduced graphene oxide (RGO) grating structures by two-beam laser interference (TBLI) for the development of highly efficient SERS substrates via simple physical vapor deposition (PVD) coating of silver. TBLI has been utilized to make hierarchical RGO grating structures with microscale gratings and nanoscale folders through a laser treatment induced ablation and photoreduction process. The hierarchical structures contribute to the formation of plasmonic structures after silver coating, giving rise to the formation of plenty of SERS "hot spots", while the RGO substrate would provide chemical enhancement of Raman signal through interaction with analytes molecules. The significantly increased roughness with respect to the hierarchical structures in combination with the removal of hydrophilic oxygen-containing groups endow the resultant substrates with unique superhydrophobicity, which leads to the enrichment of analytes and further lowers the detection limit. The synergistic effects make the silver coated RGO gratings a highly efficient SERS substrate; in the detection of Rhodamine B, our SERS substrates showed high SERS enhancement and good reproducibility, a detection limit of 10(-10) M has been achieved.

Facile fabrication of PtCuAu nanoparticles modified reduced graphene oxide with high electrocatalytic activity toward formic acid oxidation

A facile electrochemical approach to synthesize reduced graphene oxide (RGO) modified glassy carbon (GC) electrode as an excellent support for anchoring PtCuAu nanoparticles is reported. The as-prepared PtCuAu/RGO catalyst has been characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and electrochemical methods. It is found that the PtCuAu nanoparticles formed alloy structures and are evenly distributed on the RGO substrate. Compared with Pt/RGO, PtCu/RGO, PtAu/RGO and CuAu/RGO electrodes, the PtCuAu/RGO catalyst exhibits distinctly enhanced current density and nice stability toward formic acid electrooxidation. The experimental results indicate that the prepared PtCuAu/RGO catalyst has enormous potential applications in direct formic acid fuel cells (DFAFC).

Superior electrochemical performance of ultrasmall SnS2 nanocrystals decorated on flexible RGO in lithium-ion batteries

A hybrid structure involving efficient plentiful ultrasmall SnS2 nanocrystals decorated on flexible reduced graphene oxide (RGO) has been successfully realized via a simple refluxing method. Compared to previous studies, the ultrasmall SnS2 nanocrystals can compactly and orderly cover the RGO nanosheets, increasing the loading number of SnS2 per unit area of the RGO substrates. The ultrasmall SnS2 nanocrystals@RGO nanocomposites were investigated as electrode materials for lithium-ion batteries. In this hybrid structure, RGO was not only used as a solid support to uniformly distribute the SnS2 nanocrystals, but also as a carrier to accelerate electron transport. In addition, the uniform size and homogeneous SnS2 nanocrystals on the RGO nanosheets reduced electrode polarization, resulting in excellent electrochemical performance for lithium-ion batteries. A specific capacity up to 1034 mA h g−1 was realized from an ultrasmall SnS2 nanocrystals@RGO electrode even after 200 cycles at 0.1 C. Importantly, the ultrasmall SnS2 nanocrystals@RGO electrode showed excellent capacity retention for up to 450 cycles even at a high rate of 5 C. The cost-effective synthesis of SnS2 nanocrystals@RGO and excellent electrochemical performance indicates the great potential for this type of nanocomposites as an active electrode for lithium-ion batteries.

Tribology Study of Reduced Graphene Oxide Sheets on Silicon Substrate Synthesized via Covalent Assembly

Reduced graphene oxide (RGO) sheets were covalently assembled onto silicon wafers via a multistep route based on the chemical adsorption and thermal reduction of graphene oxide (GO). The formation and microstructure of RGO were analyzed by X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, Raman spectroscopy, and water contact angle (WCA) measurements. Characterization by atomic force microscopy (AFM) was performed to evaluate the morphology and microtribological behaviors of the samples. Macrotribological performance was tested on a ball-on-plate tribometer. Results show that the assembled RGO possesses good friction reduction and antiwear ability, properties ascribed to its intrinsic structure, that is, the covalent bonding to the substrate and self-lubricating property of RGO.