Deoxygenation Efficiency Research Articles

X-ray absorption spectroscopy study on the thermal and hydrazine reduction of graphene oxide

X-ray absorption spectroscopy (XAS) was applied to systemically investigate the deoxygenation of graphene oxide (GO) via annealing and hydrazine treatment. Detailed evolution of the electronic structures and chemical bonding of GO was presented. The enhanced intensity of π* resonance and the appearance of splitting σ* resonance in C K-edge XAS spectra suggest high extents of recoveries of π-conjugation upon reduction using thermal annealing or hydrazine. Experimental results revealed that the carboxyl as well as epoxide and hydroxyl groups on the surface of GO were thermally reduced first, followed by the more difficult removal of carbonyl and cyclic ether groups at higher temperatures. The hydrazine reduction could remove epoxide, hydroxyl and carboxyl groups effectively, whereas the carbonyl groups were partially reduced with the incorporation of nitrogen species simultaneously. The residual oxygen functional groups on hydrazine-reduced GO could be further removed after modest thermal annealing. It was proposed that a combination of both types of reductions would give the best deoxygenation efficiency for the production of graphene.

Methyl oleate deoxygenation for production of diesel fuel aliphatic hydrocarbons over Pd/SBA-15 catalysts

BackgroundCatalytic deoxygenation is a prominent process for production of renewable fuels from vegetable oil. In this work, deoxygenation of technical grade methyl oleate to diesel fuel aliphatic hydrocarbons (C15 – C18) is evaluated with several parameters including temperature, hydrogen pressure and reaction time in a stirred batch reactor over Pd/SBA-15 catalysts.ResultsTwo different SBA-15 morphologies i.e. spherelike and necklacelike structures have been synthesize as supports for Pd active metal. It is found that Pd dispersion on necklacelike SBA-15 is higher than that of spherelike SBA-15. Notably, higher Pd dispersion on necklacelike SBA-15 provides significant deoxygenation efficiency as compared to Pd/SBA-15-spherelike. Results show that H2 pressures greatly determine the total ester conversion and selectivity to C15 – C18 aliphatic hydrocarbons. Total ester conversions with 55< selectivity to n-heptadecane are achieved using Pd/SBA-15-necklacelike at 270°C and 60 bar H2 pressure within 6 h reaction time. Gas phase study reveals that formation of C17 is generated via indirect decarbonylation when the reaction time is prolonged.ConclusionsPd/SBA-15-necklacelike catalyst exhibits good catalytic performance with high selectivity to diesellike aliphatic hydrocarbons (C15 – C18). The physicochemical properties of the Pd supported on different SBA-15 morphologies influence the deoxygenation activity of the catalysts. Furthermore, the reaction pathways are governed by the H2 pressure as well as reaction duration.

Catalytic pyrolysis of mannose as a model compound of hemicellulose over zeolites

Mannose was selected as a model compound of hemicellulose and its thermal behavior over zeolites has been investigated using a TG-FTIR analyzer. There was an initial study of the chemical structure of mannose and a characterization of the catalysts. All three catalysts, HZSM-5, H-β and USY, had a significant influence on the dehydration, cracking and deoxygenation reactions during the pyrolysis of mannose. The dehydration reaction in the initial stage was enhanced, resulting in two separate water release processes, while the char formation was suppressed. USY had the best effect on dehydration, and HZSM-5 obtained the highest deoxygenation efficiency. The presence of HZSM-5 and H-β catalyzed the formation of water and CO2, while suppressing the formation of oxygenated compounds and char residues.

Synthesis of Stable Colloidal Suspension of Graphene

In this article, graphite oxide was prepared via Hummers method, then reduced by L-ascorbic acid to obtain colloidal suspension of graphene. The resultant graphene was characterized by FT-IR, UV-vis, Raman, XRD, AFM, TEM in detail, and it was found that the the sp2 domain of graphene oxide is restored efficiently, the suspension is very stable and most of the graphene is single-layer. Compared to hydrazine hydrate, L-ascorbic acid has higher deoxygenation efficiency and inclines to gain few-layer graphene and its stable suspensions.

Melatonin as a powerful bio-antioxidant for reduction of graphene oxide

Graphene is usually synthesized through deoxygenation of graphene oxide (GO) by hydrazine as the most common and one of the strongest reducing agents. But, due to the high toxicity of hydrazine, it is not a promising reductant in large-scale production of graphene. Here, for the first time, we used melatonin (MLT), as a powerful antioxidant and a biocompatible competitor of hydrazine in reduction of GO suspension. X-ray photoelectron spectroscopy (XPS), current–voltage and optical characteristics of the sheets indicated that the deoxygenation efficiency of the GO suspensions by MLT and under heating in an alkaline condition for 3 h was comparable with the efficiency obtained by hydrazine in similar conditions for 30 min. Based on the XPS analysis, although the amount of nitrogen detected on the surface of the MLT-reduced GO sheets was higher than that of the hydrazine-reduced ones, smaller C–N bonds were formed on the surface of the former. The higher amount of nitrogen on the MLT-reduced GO sheets was assigned to the π–π adsorption of the oxidized MLT molecules on the reduced sheets, which resulted in more stability of the MLT-reduced GO suspension than the aggregation observed in the hydrazine-reduced one, as also confirmed by Raman spectroscopy. A mechanism describing the chemical reduction of the GO sheets by MLT was also proposed. Our results open up a promising outlook for substitution of hydrazine by a safe, biocompatible and powerful reductant for efficient deoxygenation of GO, especially in large-scale production and bio-applications.

Vitamin C Is an Ideal Substitute for Hydrazine in the Reduction of Graphene Oxide Suspensions

The preparation of solution-processable graphene from graphite oxide typically involves a hydrazine reduction step, but the use of such a reagent in the large-scale implementation of this approach is not desirable due to its high toxicity. Here, we compare the deoxygenation efficiency of graphene oxide suspensions by different reductants (sodium borohydride, pyrogallol, and vitamin C, in addition to hydrazine), as well as by heating the suspensions under alkaline conditions. In almost all cases, the degree of reduction attainable and the subsequent restoration of relevant properties (e.g., electrical conductivity) lag significantly behind those achieved with hydrazine. Only vitamin C is found to yield highly reduced suspensions in a way comparable to those provided by hydrazine. Stable suspensions of vitamin C-reduced graphene oxide can be prepared not only in water but also in common organic solvents, such as N,N-dimethylformamide (DMF) or N-methyl-2-pyrrolidone (NMP). These results open the perspective of replacing hydrazine in the reduction of graphene oxide suspensions by an innocuous and safe reductant of similar efficacy, thus facilitating the use of graphene-based materials for large-scale applications.

In-line deoxygenation for flow analysis with voltammetric detection

Voltammetric detection of metals in natural waters suffers from interference by dissolved oxygen. We describe here a deoxygenation method suitable for flow analysis with detection by cathodic stripping voltammetry (FIA-CSV). The apparatus is based on the permeation of oxygen through semi-permeable tubing (silicone, Poreflon and others) into an oxygen-free chamber. Two methods of oxygen removal are proposed: in the first oxygen is removed physically from the chamber by flushing with nitrogen at a rate of 50 ml min −1; in the second oxygen is removed chemically by filling the chamber with an aqueous solution of a reducing agent (Na 2SO 3 or other compounds). At a fixed sample flow rate of 1 ml min −1, the length of the tubing is the main parameter which affects the deoxygenation efficiency, as it determines the residence time of the sample. 98% oxygen removal is achieved using 3 m tubing (36 s residence time). A removal of 90% of oxygen (1 m tubing and 12 s residence time) is sufficient to obtain a background current similar to conventional (batch) voltammetric systems and reproducible metal (copper and cobalt) peak heights are obtained at low metal concentrations. This enables the determination of trace metals by flow analysis with voltammetric detection at concentration levels encountered in uncontaminated seawater.

Automated sample deoxygenation for improved luminescence measurements

Abstract : Quenching of luminescence by molecular oxygen is an inherent limitation in fluorescence and phosphorescence analysis. Consequently, greater analytical sensitivity, as well as lower detection limits, can be achieved by removal of oxygen from the sample prior to luminescence analysis. An automated system for rapid deoxygenation is described in this paper. This apparatus combines a multiple sampling valve and a membrane barrier to generate a concentration gradient for sample deoxygenation. this automatic, multisample, on-line deoxygenation technique reduces sample handling to a minimum because deoxygenation and luminescence analysis occur within a closed system. The usefulness of this procedure is discussed in terms of automation, reproducibility, detection limit, deoxygenation efficiency, and applications to a variety of compounds. In addition, potential application of this procedure to other analytical subdisciplines is also discussed. Keywords: Luminescence spectroscopy; Fluorescence analysis; Room temperature phosphorescence; Deoxygenation; Quenching.

Thermal decomposition of ammonium Y zeolite

This study presents a detailed analysis of the catalytic de-oxygenation of the liquid and gaseous pyrolytic products of two biomasses (beech wood and flax shives) using different catalysts (commercial HZSM-5 and H-Y, and lab-synthesised Fe-HZSM-5, Fe-H-Y, Pt/Al2O3 and CoMo/Al2O3). The experiments were all conducted in a semi-batch reactor under the same operating conditions for all feed materials. BET specific surface area, BJH pore size distribution and FT-IR technologies have been used to characterise the catalysts, while gas chromatography-mass spectrometry (GC-MS), flame ionisation detection (GC-FID) and thermal conductivity detection (GC-TCD) were used to examine the liquid and gaseous pyrolytic products. It was firstly seen that at higher catalyst-to-biomass ratios of 4:1, de-oxygenation efficiency did not experience any further significant improvement. Fe-HZSM-5 was deemed to be the most efficient of the catalysts utilised as it helped reach the lowest oxygen contents in the bio-oils samples and the second best was HZSM-5. It was also found that HZSM-5 and H-Y tended to privilege the decarbonylation route (production of CO), whilst their iron-modified counterparts favoured the decarboxylation one (production of CO2) for both biomasses studied. It was then seen that the major bio-oil components (carboxylic acids) underwent almost complete conversion under catalytic treatment to produce mostly unoxygenated aromatic compounds, phenols and gases like CO and CO2. Finally, phenols were seen to be the family most significantly formed from the actions of all catalysts.