Efficient synthesis of graphene sheets using pyrrole as a reducing agent

The efficient synthesis of graphene sheets using pyrrole as a reducing agent was explored. The obtained graphene sheets were dispersible in organic solvents such as ethanol, isopropanol, N,N-dimethylformamide, N-methylpyrrolidone, dimethylsulfoxide, tetrahydrofuran, and acetone. During this reduction reaction, pyrrole was oxidized, forming oxidation product of pyrrole and adsorbed on the graphene sheets surface by π–π interaction. The oxidation product of pyrrole acted as a capping agent for graphene sheets by preventing re-stacking and formed organically dispersible graphene. The formation of graphene and its crystalline nature was indicated by the transmission electron microscopy and the atomic force microscopy analysis. Raman, X-ray photoelectron spectroscopy and X-ray diffraction provided the evidence for graphene formation from graphene oxide precursor. Furthermore, the reduced oxygen content and N 1s peak observed by the X-ray photoelectron spectroscopy analysis of graphene sheets confirmed the reduction reaction and presence of adsorbed oxidation product on the surface of graphene sheets. The resulting graphene sheets were readily dispersible in solvents and easily to process.     

Process optimization for aqueous extraction of reducing sugar from cashew apple bagasse: A potential, low cost substrate

The present investigation deals with optimization of aqueous extraction of reducing sugar from cashew apple bagaase, a potential low cost substrate. Response Surface Methodology (RSM) based Box Behnken Design (BBD) was employed to obtain the best possible combination of liquid: solid, pH, extraction time and extraction temperature for maximum reducing sugar extraction. The optimum extraction conditions were as follows: liquid: solid 3.26 (mL/g), pH 6.42, extraction time 6.30 h and temperature 52.27 °C. Under these conditions, the experimental yield was 56.89 (g/100 g dry substrate), which was well matched with the predictive yield 57.64 (g/100 g dry substrate). Further analysis of sugar was done by HPLC which revealed glucose (34.28 g/100 g dry substrate), fructose (18.57 g/100 g dry substrate) and arabinose (3.42 g/100 g dry substrate).     

Chemical functionalization of graphene and its applications

Functionalization and dispersion of graphene sheets are of crucial importance for their end applications. Chemical functionalization of graphene enables this material to be processed by solvent-assisted techniques, such as layer-by-layer assembly, spin-coating, and filtration. It also prevents the agglomeration of single layer graphene during reduction and maintains the inherent properties of graphene. Therefore, a detailed review on the advances of chemical functionalization of graphene is presented. Synthesis and characterization of graphene have also been reviewed in the current article. The functionalization of graphene can be performed by covalent and noncovalent modification techniques. In both cases, surface modification of graphene oxide followed by reduction has been carried out to obtain functionalized graphene. It has been found that both the covalent and noncovalent modification techniques are very effective in the preparation of processable graphene. However, the electrical conductivity of the functionalized graphene has been observed to decrease significantly compared to pure graphene. Moreover, the surface area of the functionalized graphene prepared by covalent and non-covalent techniques decreases significantly due to the destructive chemical oxidation of flake graphite followed by sonication, functionalization and chemical reduction. In order to overcome these problems, several studies have been reported on the preparation of functionalized graphene directly from graphite (one-step process). In all these cases, surface modification of graphene can prevent agglomeration and facilitates the formation of stable dispersions. Surface modified graphene can be used for the fabrication of polymer nanocomposites, super-capacitor devices, drug delivery system, solar cells, memory devices, transistor device, biosensor, etc.     

Preparation of non-covalently functionalized graphene using 9-anthracene carboxylic acid

A simple way of achieving stable aqueous dispersion of graphene by non-covalent functionalization using 9-anthracene carboxylic acid has been successfully accomplished. Unlike in chemically reduced graphene, the C-sp(2) network of the graphene remains undistorted and therefore of superior quality. The non-covalent functionalization facilitates the exfoliation of graphite layers in a polarity controlled combination of media. A detailed exfoliation mechanism is proposed based on the controlled experiment and is supported by the data from UV-vis spectroscopy, transmission electron microscopy, and x-ray diffraction studies. Formation of monolayer graphene has been confirmed from Raman spectroscopy. The graphene based ultracapacitor shows a high value of specific capacitance (148 F g(-1)).     

ECG signal classification and arrhythmia detection using ELM-RNN

Arrhythmia is a unique type of heart disease which produces inefficient and irregular heartbeat. This is a cardiac disease which is diagnosed through electrocardiogram (ECG) procedure. Several studies have been focused on the speed and accuracy on the learning algorithm by applying pattern recognition, artificial intelligence in the classification algorithm. In this work a novel classification algorithm is planned based on ELM (Extreme Learning Machine) with Recurrent Neural Network (RNN) by using morphological filtering. The popular publicly available ECG arrhythmia database (MIT-BIH arrhythmia DB) is used to express the performance of the proposed algorithm where the level of accuracy is compared with the existing similar types of work. The comparative study shows that performance of our proposed model is much faster than the models working with RBFN (radial basis function network), BPBB(back propagation neural network) and Support Vector Machine. The experimental result with the MIT BIH database with hidden neurons of ELM with RNN, the accuracy is 96.41%, sensitivity 93.62% and specificity 92.66%. The classification methodology follows main four steps the heart beat detection, the ECG feature extraction, feature selection and the construction of the proposed classifier.

     

A novel scheduling with multi-criteria for high-performance computing systems: an improved genetic algorithm-based approach

Engineering with Computers - Scheduling in high-performance computing systems is experiencing potential challenges in modern computing applications due to different application sizes, computational...     

Synthesis and characterization of non-noble nanocatalysts for hydrogen production in microreactors

Nanoscale Co and Ni catalysts in silica were synthesized using sol–gel method for hydrogen production from steam reforming of methanol (SRM) in silicon microreactors with 50 μm channels. Silica sol–gel support with porous structure gives specific surface area of 452.35 m² g⁻¹ for Ni/SiO₂ and 337.72 m² g⁻¹ for Co/SiO₂. TEM images show the particles size of Ni and Co catalysts to be <10 nm. The EDX results indicate Co and Ni loadings of 5–6 wt.% in silica which is lower than the intended loading of 12 wt.%. The DTA and XRD data suggest that 450 °C is an optimum temperature for catalyst calcination when most of the metal hydroxides are converted to metal oxides without significant particle aggregation to form larger crystallites. SRM reactions show 53% methanol conversion with 74% hydrogen selectivity at 5 μL min⁻¹ and 200 °C for Ni/SiO₂ catalyst, which is higher than that for Co/SiO₂. The activity of the metal catalysts decrease significantly after SRM reactions over 10 h, and it is consistent with the magnetization (VSM) results indicating that ∼90% of Co and ∼85% of Ni become non-ferromagnetic after 10 h.     

Separation of toluene–methanol mixtures by pervaporation using crosslink IPN membranes

Polyvinyl alcohol (PVOH) has been chemically modified by crosslink copolymerization of acrylic acid (AA) and hydroxyethylmethacrylate (HEMA) in aqueous solution of PVOH and finally crosslinking PVOH to produce a full interpenetrating network (IPN) membrane termed as PVAH. Accordingly, three such full crosslink IPNs membranes, i.e. PVAHI, PVAHII and PVAHIII containing varied weight ratio of PVOH and copolymer have been synthesized and used for pervaporative separation of methanol from its mixtures with toluene. For comparison, a conventional PVOH membrane crosslinked with glutaraldehyde has also been used for the same pervaporation study. The flux and selectivity of these IPN membranes were found to be much higher than the conventional glutaraldehyde crosslinked PVOH membrane. Among the three membranes, PVAHII with 50 wt% polyAH incorporation showed optimum performance in terms of flux and methanol selectivity.