Removal Of Oxygen-containing Groups Research Articles

Reduction of graphene oxide on polyethylene terephthalate surface by using transmission femtosecond laser

Graphene has great application prospects in electronic chips and sensors due to its excellent electrical and thermal conductivity. Many methods have been reported to generate graphene, among which the use of a laser to irradiate graphene oxide (GO) surface is capable of reducing and patterning GO simultaneously. To date, the sheet resistance of laser reduced graphene oxide (LRGO) in the air is somewhat high. In this paper, we report a new method for GO reduction by femtosecond laser transmitting from the GO-free side of polyethylene terephthalate (PET). Under this technique, the sheet resistance of 75 Ω/sq, one of the lowest in the air, is obtained. The mechanism of sheet resistance evolution is examined. In a low laser power range, removing oxygen-containing groups by breaking C-O bonds plays a major role in sheet resistance dropping. When laser power rises to a high range, the removal of oxygen-containing groups and the conversion of sp3 to sp2 hybridized carbon work simultaneously. Meanwhile, the influence of PET substrate has been taken into consideration. More interestingly, LRGO could expand up to 610% in height. In addition, the adhesion between LRGO and PET reaches the 5B level, further proving its essential bonding property for flexible electronics.

Optimization of Reducing Agents for Selective Bandgap Manipulation in Visible Region of Graphene Oxide and Its Work Function Estimation

In the present study, we report an effective way for reduction of graphene oxide (GO) as well as tuning of bandgap using various reducing agents. It is found that sodium borohydride (NaBH4) can be a promising reducing agent, as it can reduce the bandgap to 2.30 eV and has a higher capacity to restore the carbon–carbon bonds compared with other reducing agents. Further bandgap tuning has been obtained by hydrogenation of GO as well as NaBH4-reduced GO (NGO). It was observed that after hydrogenation, the bandgap of GO was reduced from 2.48 to 1.95 eV, whereas it reduced from 2.45 to 1.87 eV in NGO. Hydrogenation of GO results in rearranging of C=O functionalities and removal of oxygen-containing groups. Furthermore, transmission electron microscopy observations corroborate the observation that after reduction with NaBH4, GO shows a more uniform nature than GO. The intensity ratio (I{1,100}/I{1,200}) of the {1,200} and {1,100} planes is found to be 1. After reduction with NaBH4, the ID/IG ratio decreased from 1.05 to 0.92, suggesting a decrease in defect density and better reduction. The intrinsic work function of GO and hydrogenated NGO is determined using electrostatic force microscopy and found to be 5.19 ± 0.1 eV and 4.39 ± 0.1 eV, respectively.

Microwave-constructed honeycomb architectures of h-BN/rGO nano-hybrids for efficient microwave conversion

Honeycomb architectures of h-BN/rGO nano-hybrids were built from the self-assemblies of hexagonal boron nitride (h-BN) and graphene oxide (GO) through microwave heating for a few seconds. Incorporation of h-BN nanosheets into 3D reduced graphene oxide (rGO) foams was accompanied by the removal of oxygen-containing groups during the rapid “bread baking” process. TEM and SEM images revealed the layer-stacked structure of the samples. XPS, Raman and XRD spectra showed the presence of h-BN layers that were interlaced into the honeycomb architectures of rGO frameworks. The microwave absorption properties and the complex permittivity could be adjusted by varying the microstructure and the content of h-BN. For the wax composite filled with 6.25 wt% h-BN/rGO nano-hybrid with thickness of 1.8 mm, the reflection loss value reached −35.63 dB at 17.2 GHz, and the effective frequency bandwidth reached 6.96 GHz at 2.6 mm with a low surface density. The honeycomb architecture of the hybrid provided multiple electromagnetic transmission paths and consumed significant amount of microwave energy due to the multiple interfaces. Embedding h-BN in the architecture enables excellent impedance matching, and provides highly efficient dielectric material that can be used for microwave absorption. This work demonstrates that microwave treatment is a facile approach to obtaining optimal microwave absorbing properties of h-BN/rGO nano-hybrids.

Thermal Evolution of the Structure and Activity of Non-Doped Graphene as Metal-Free Oxygen Reduction Electrocatalysts

Herein, graphene oxide (GO) is directly heat-treated in N2 atmosphere at different temperatures to investigate thermal evolution of the structure and activity as a non-doped metal-free oxygen reduction reaction (ORR) electrocatalyst. Heat-treatment temperature plays a crucial effect on improving the ORR electrocatalytic performance in alkaline electrolyte: the higher the heat-treatment temperature the better the electrocatalytic performance. Generation of defects arising from the removal of oxygen-containing group as a consequence of heat-treatment plays an essential role. Both XRD and Raman indicate that the higher heat-treatment temperature the greater defective nature of graphene, indicating the significant contribution of carbon intrinsic defects to its ORR activity. XPS of GO-800 distinctly shows the only presences of C1s and O1s without any other element, especially metal signal, namely the dopant-free graphene. This work confirms graphene without interruption by any other dopants can be applied as an efficient ORR electrocatalyst.

One-Pot Green Synthesis of Highly Reduced Graphene Oxide Decorated with Silver Nanoparticles

A one-pot green sonochemical process assisted by ascorbic acid as the reducing agent to produce highly reduced graphene oxide (rGO) decorated with silver nanoparticles (AgNPs) is demonstrated. A complete removal of oxygen-containing group in the GO sheets was confirmed by no observation of the peak corresponds to C-O, C=O and -OH bond. The unexpected decrease of peak intensity corresponds to sp2 hybridized C=C group is explained by a so-called bond polarity effect. The peak observed at ~400 nm seems to show the presence of AgNPs and the red shifting of C=C peak to ~270 nm after the introduction of ascorbic acid indicates the formation of highly reduced GO. The increase of AgNPs size and the crumpled silk-like morphology after the introduction of ascorbic acid also indicate the aggressive reduction of both AgNPs and GO. The increase of ID/IG ratio after the introduction of ascorbic acid seems to indicate the increase of the number of small sp2 domains, the presence of unrepaired defects and the restoration of the sp2 network. This work provides the promising green sonochemical approach by utilizing non-toxic and environmental-friendly reducing agent to produce highly reduced GO decorated with AgNPs for various applications.

Green approach for preparation of reduced graphene oxide decorated with gold nanoparticles and its optical and catalytic properties

Graphene oxide (GO) was reduced and modified by gold nanoparticles using aqueous leaf extract of green tea. Successful formation of gold nanoparticles (AuNPs) on graphene oxide surface was determined by scanning electron microscopy (SEM). Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared analyses (FT-IR) have been used to demonstrate the behavior of complex of reduced graphene oxide with gold nanoparticles (rGO-AuNPs), the removal of oxygen-containing groups from the graphene, and subsequent formation of reduced graphene oxide (rGO). We also demonstrated the change of optical properties of GO after the reduction and formation of gold nanoparticles on its surface by UV–vis spectroscopy and fluorescence spectroscopy. The positive impact of rGO-AuNPs composite on safranin T reduction in the presence of NaBH4 without light irradiation was examined, as well. The dye decolorization was observed within 60 min which highlights the exceptional catalytic potential of the rGO-AuNPs.

Changes of oxygen-containing groups during thermal treatment and their influences on moisture readsorption of lignite

ABSTRACTThe changes in oxygen-containing groups in the thermal treatment process of lignite were analyzed and the moisture readsorption amounts of upgraded coals were related in this study. A chemical titration method was applied to determine the types and contents of oxygen-containing groups in raw lignite and upgraded coals obtained in the temperature range of 353–633 K under atmospheres of argon, air, and carbon dioxide. Experimental results showed that the oxygen-containing groups mainly involved carbonyl, phenolic hydroxyl, and carboxylic groups (including carboxyl and carboxylate), among which phenolic groups were dominant. These different oxygen-containing groups decomposed discriminatingly with temperature according to thermal stability. The removal of oxygen-containing groups proceeded more easily in a CO2 atmosphere compared to in Ar. The oxidation reaction occurring on the surface of lignite exposed to air led to an increase in oxygen-containing groups. The different types of oxygen-containing groups possessed various combining abilities with water, among which carboxyl was considered the most important group for the moisture readsorption. Decomposition of oxygen-containing groups in the thermal treatment process of lignite mainly caused a reduction in monolayer water adsorption and further decreased the multilayer water.

Ultraviolet-assisted reduction of BBL/graphene nanocomposite

Graphene oxide (GO) and GO/poly(benzimidazobenzophenanthroline) (BBL) films were reduced by ultraviolet (UV) irradiation. UV-assisted reduction, by the removal of oxygen-containing groups from the GO and the GO/BBL nanocomposite films, was confirmed with Raman and X-ray photoelectron spectroscopies. The UV reduction of the GO film in selective regions was successfully demonstrated with patterning of the letters KNU. The sheet resistance of the BBL/GO film (GO content=80 wt%) on the glass substrate was ∼106 Ω/□ after UV irradia-tion (25 mW/cm2) for ∼2 h. Furthermore, the electrically insulating GO in the BBL/GO nanocomposite film on the glass substrate became electrically conductive after UV reduction.

Annealing Effect on As-Synthesized Pd/MWNTs Catalyst for Ethanol Oxidation

The annealing effect on the catalytic performances of multi-walled decorated palladium nanocatalyst (Pd/MWNTs) for ethanol was investigated. The as-synthesized and annealed nanocatalysts were characterized by X-ray diffraction (XRD), which implied similar crystal structure but different average particle sizes. Transmission electron microscope (TEM) revealed different Pd particle sizes, suggesting varying steps: diffusing, contacting and coercing of Pd nanoparticles (NPs) on MWNTs surface with increasing the annealing temperatures. The removal of oxygen-containing groups on the tube wall surface during the annealing process was confirmed by the increased ID/IG ratio in raman spectroscopy and thermogravimetric analysis (TGA). Cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) displayed enhanced peak current, increased stability and decreased charge transfer resistance for Pd/MWNTs annealed at 100 °C (Pd/MWNTs-100). The reason might be due to the smallest Pd particle size, increased electrochemically active surface area (ECSA) and decreased oxygen content. Agglomeration of Pd NPs is responsible for the decreased catalytic performance for nanocatalysts annealed at high temperatures. Meantime, it's also found that the electric-catalytic activity towards ethanol oxidation was determined by a delicate cover balance between ethanol and OHadspecies. Significant fast kinetics at higher temperatures indicates that increasing temperature can greatly activate the ethanol oxidation process, ensuring greater tolerance towards ethanolic residues at higher temperatures. Experimental 100.0 mg carboxylic groups functionalized MWNTs (MWNTs-COOH) and 304.0 mg palladium acetylacetonate (Pd(acac)2) were uniformly dispersed in 80 mL xylene using a 250-mL 3-neck flask and kept refluxing for 3 hrs. Pd/MWNTs powder was obtained from filtering the reacted solution. The synthesized Pd/MWNTs was annealed at different temperatures, 100, 300, and 500 °C under hydrogen gas (5 % H2balanced with 95 % Ar) flow in a quartz tube situated in a tubular furnace. The annealing temperature was increased to a desired temperature at a heating rate of 2 °C/min and was maintained for 2 hrs at the set temperature. Results and Discussions Pd NPs with same Pd crystalline planes but different Pd NPs sizes are confirmed in Transmission electron microscope (TEM) and X-ray diffraction (XRD), the Pd NPs of as-synthesized/annealed Pd/MWNTs nanocatalyts varied according to steps as diffusing, contacting and coercing with the increase of annealing temperature. The clean particle surface, the smallest Pd particle size and increased ECSA are responsible for the best electro-catalytic performance of Pd/MWNTs-100, however, agglomeration of Pd NPs at higher annealing temperatures is the main reason causing the decrease of electro-catalytic activity. Conclusions In this work, different annealing temperature effect on as-synthesized Pd/MWNTs was investigated, Pd NPs followed steps as diffusing, contacting and coercing on MWNTs surface with the increase of annealing temperature, the particle size was observed to decrease first due to the partially segregated small Pd NPs from agglomerated ones and further aggregated forming size-increased Pd NPs. The smallest Pd NPs size, decreased oxygen content and increased ECSA were responsible for the best performance of Pd/MWNTs-100 ºC demonstrated in CV, CA, and EIS tests, The best electro-catalytic performance of Pd/MWNTs-100 was achieved in 2.0 M KOH containing 4.0 M ethanol which provided balance coverages of OHadsand ethanol. A pronounced influence of temperature on the reaction kinetics was manifested implying greater tolerance of the catalyst towards ethanol residues at higher temperatures. Acknowledgments The financial supports from Seeded Research Enhanced Grant (REG) and College of Engineering at Lamar University are kindly acknowledged. Figure 1(a-c) areTEM images of Pd/MWNTs, Pd/MWNTs-100 and Pd/MWNTs-300, respectively, inset TEMs are corresponding histograms of particle size distribution. Figure (d) is the CVs in 1.0 M KOH containing 1.0 M ethanol at a scan rate of 50 mV s-1. a, Pd/MWNTs, b, Pd/MWNTs-100, c, Pd/MWNTs-300 and d, Pd/MWNTs-500.

Renewal of sp2 bonds in graphene oxides via dehydrobromination

Graphene-based materials are emerging to become one of the most exciting candidates for various applications. There has been a keen interest in developing methods that will not only result in their bulk production, but could also generate graphene-based materials that possess good electrical and physical properties. The most convenient method towards bulk production of graphene-based materials is often via the reduction of graphene oxide. In this context, numerous reduction techniques have been previously applied based on standard organic chemistry reagents. Although most standard reducing agents work well in the removal of oxygen-containing groups from the graphene oxide surfaces, they do not theoretically result in the important restoration of the defective sp2 carbon network. Particularly in this work, we focused on the restoration of the defective sp2 carbon network of graphene oxide via a dehydrohalogenation method. This was achieved through a prior substitution of hydroxyl to bromine groups, followed by a dehydrobromination step. This strategy offers a great potential for the production of chemically reduced graphene of high conductivity.