Intercalation Of Sulfuric Acid Research Articles

Synthesis of graphene oxide: Effect of sonication during oxidation

The oxidation of graphite to graphene oxide (GO) is a widely used approach to exfoliate graphite. Nevertheless, achieving precise control over the degree of oxidation and the resulting properties of GO has considerable challenges. In this study, we demonstrate that using sonication during the oxidation of graphite by Hummers' method alters the chemistry and properties of the GO. Contrary to our expectations, we found that sonication slows the oxidation of graphite by impeding the intercalation of sulfuric acid. This results in fewer oxygen-containing functional groups on the GO and minimizes functionalization of the basal plane of the graphene oxide sheets, leading to superior electrochemical and mechanical properties of GO-based composites compared to GO synthesized without sonication. In this study, we use X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier Transform Infrared spectroscopy (FTIR), cyclic voltammetry, and compression testing to quantify the effects of sonication during oxidation and propose the mechanism leading to those effects.

Fluorescence enhancement induced by sulfuric acid intercalation on melem-based polymer

Fluorescent materials have achieved a great success in the fields of biomedicine, photonic devices, light-emitting diodes and others; however, millions of fluorescent materials lose their emission properties owing to aggregation-caused quenching (ACQ) effect, especially in solid state. Herein, we report the enhanced fluorescence of Melem-based polymer film via sulfuric acid modification. We propose a new strategy for maintaining fluorescence in the aggregated state by sulfuric acid intercalation, which separate the fluorophores and avoid the self-quenching. The Melem-based polymer is synthesized through a simple liquid phase reaction, and exhibits excellent fluorescence in the aggregated state after treatment with concentrated acid. This anion intercalation represents a general strategy to avert ACQ effect for existing intrinsic fluorescent materials.

High-efficiency extraction of aluminum from low-grade kaolin via a novel low-temperature activation method for the preparation of poly-aluminum-ferric-sulfate coagulant

A facile hydrometallurgical method was proposed for high-efficiency extraction of aluminum at low activation temperature from low-grade kaolin involving sulfuric acid assisted activation followed by water leaching. After the slurry mixture of low-grade kaolin and sulfuric acid solution was stirred at 25 °C for 3 h and further heated at 150 °C for 2 h, the optimal extraction efficiencies of Al (98.8%) and Fe (98.1%) were achieved via water leaching at room temperature. The activation mechanism was proposed via investigating the intermediates during the activation process. It was found that the low activation temperature and the high extraction efficiencies result from the intercalation of sulfuric acid. The poly-aluminum-ferric-sulfate (PAFS) coagulant was further obtained from the leachate, and its coagulation performance was evaluated by jar tests. It was found that the PAFS is highly effective under acid conditions, and shows the highest removal efficiency of 93.7% for Direct Blue 2B with a dosage of 140 mg/L. Furthermore, the leaching residue was also utilized to prepare silica for rubber compounding ingredients to make full use of the silicon in low-grade kaolin, and simultaneously reduce the discharge of waste. Moreover, the corresponding scale-up experiments and the extended experiments showed that the Al extraction efficiencies of the diasporic bauxite and the spent fluid catalytic cracking catalyst reach 95.4% and 97.2%, respectively via the proposed method. This work provides a new highly efficient Al extraction strategy from low-grade kaolin and other similar ores and wastes containing rich Al element to prepare Al–Fe coagulant.

Investigation of sulfuric acid intercalation into thermally expanded graphite in order to optimize the synthesis of electrochemical graphene oxide

This paper is devoted to a detailed study of the electrochemical intercalation of sulfuric acid into the foil structure based on thermally expanded graphite, as the decisive stage in the process of producing electrochemical graphene oxide. In the work, the potentials of individual areas of anodic polarization were determined, passing without destroying the carbon electrode. The diffusion control characteristic of the entire range of intercalation potentials is shown. The effective capacities, characteristic times, and acid consumption for the electrochemical intercalation process are evaluated. The minimum termination potential of the intercalation process is found. It is shown that limiting the anodic polarization of thermally expanded graphite at the minimum potential for the termination of intercalation can significantly reduce the energy consumption of the entire method for producing electrochemical graphene oxide. A comparison is made of electrochemical graphene oxide with graphene oxide, obtained by a modified Hammers method, by a number of physicochemical methods.

Effect of friction on oxidative graphite intercalation and high-quality graphene formation

Oxidative wet-chemical delamination of graphene from graphite is expected to become a scalable production method. However, the formation process of the intermediate stage-1 graphite sulfate by sulfuric acid intercalation and its subsequent oxidation are poorly understood and lattice defect formation must be avoided. Here, we demonstrate film formation of micrometer-sized graphene flakes with lattice defects down to 0.02% and visualize the carbon lattice by transmission electron microscopy at atomic resolution. Interestingly, we find that only well-ordered, highly crystalline graphite delaminates into oxo-functionalized graphene, whereas other graphite grades do not form a proper stage-1 intercalate and revert back to graphite upon hydrolysis. Ab initio molecular dynamics simulations show that ideal stacking and electronic oxidation of the graphite layers significantly reduce the friction of the moving sulfuric acid molecules, thereby facilitating intercalation. Furthermore, the evaluation of the stability of oxo-species in graphite sulfate supports an oxidation mechanism that obviates intercalation of the oxidant.

Magnetic graphite suspensions with reversible thermal conductivity

Magnetic graphite nanoflake (GN) suspensions with reversible thermal conductivity (TC) are reported. A process of sulfuric acid intercalation, microwave expansion magnetization, and ultrasonic dispersion is followed to make magnetic GN Poly-Alpha-Olefin (PAO) suspensions. Magnetic field was observed to increase the TC of the suspensions dramatically, up to 325% with 0.8% (w/w) of magnetic GNs. After removing the magnetic field, the TC trends to decrease reversibly. The maximal TC contrast ratio reaches 3 times before and after the effects of magnetic field. Such materials with magnetically reversible TC have great potential in next generation “smart” cooling devices.

Supercapacitor carbon electrodes with high capacitance

Electrochemical behavior of electrodes on the basis of CH900-20 activated carbon (AC) cloth has been studied in concentrated sulfuric acid solution. Cyclic voltammetric curves have been studied in the reversibility range (from 0.1 to 0.9 V RHE) and in the deep cathodic charging potential range (from –0.8 to 1 V RHE). It has been shown that electric double layer (EDL) charging occurs in the reversibility range, while faradaic processes of hydrogen intercalation into AC carbon take place in the range of negative potentials (←0.1 V). The intercalation process is governed by slow solid-phase hydrogen diffusion. The specific charge value grows at an increase in concentrated sulfuric acid solution. The mechanism of double intercalation of sulfuric acid and hydrogen into the AC material is suggested. On the basis of the reached specific discharge capacitance of 1,560 C/g (or 1,110 F/g) and Faraday's law, it has been concluded that the compound of C6H is formed in the limiting case of deepest cathodic charging. The obtained data have been used in a mathematical charge–discharge model for an AC electrode taking into account the EDL charging and the hydrogen intercalation. The galvanostatic recharge curves have been calculated in the diapason of currents by the developed model.

Carbon electrodes with high pseudocapacitance for supercapacitors

Electrochemical properties of electrodes on the basis of CH900-20 activated carbon (AC) cloth were studied in concentrated H2SO4 solutions in a wide range of potentials from −0.8 to +1 V RHE. Cyclic voltammetric curves measured in two ranges of potentials were analyzed: in the reversibility range (from 0.1 to 0.9 V) and in the deep cathodic charging range (from −0.8 to 1 V). Electric double layer (EDL) charging occurs in the reversibility range, while faradaic processes of hydrogen chemisorption and its intercalation into carbon take place in the range of negative potentials (<−0.1 V). The intercalation process is controlled by slow solid-phase hydrogen diffusion. For the first time, the maximum value of specific discharge capacity of 1560 C/g was obtained, which is much higher than the values known from the literature for carbon electrodes. On the basis of this value and Faraday’s law, it was assumed that the compound of C6H is formed in the limiting case of AC deep cathodic charging. The specific charge value grows at an increase in the concentration of H2SO4. The mechanism of double intercalation of sulfuric acid and hydrogen into the AC is suggested. The data obtained are used to develop a mathematical charging-discharge model for an AC electrode taking into account the EDL charging, chemisorption, and hydrogen intercalation.

Sulfuric Acid Intercalation of Whole Wood Block Char Encapsulated with Cone-Shaped Graphitic Whiskers in its Cell Lumen

Sulfuric Acid Intercalation of Whole Wood Block Char Encapsulated with Cone-Shaped Graphitic Whiskers in its Cell Lumen

Sulfuric Acid Intercalation and Exfoliation of Nano Shell Carbon from Ni-catalyzed Wood Char

Sulfuric Acid Intercalation and Exfoliation of Nano Shell Carbon from Ni-catalyzed Wood Char

HTR Fuel Waste Management: TRISO separation and acid-graphite intercalation compounds preparation

Considering the need to reduce waste production and greenhouse emissions and still keeping high energy efficiency, various 4th generation nuclear energy systems have been proposed. As far as graphite-moderated reactors are concerned (future high temperature fast or thermal reactors), one of the key issues is the large volumes of irradiated graphite encountered. With the objective to reduce volume of waste in the HTR concept, it is very important to be able to separate the fuel from low level activity graphite representing a large volume. The separated TRISO particles can then be reprocessed for waste separation or disposed off in geological repository. In addition, preparation of acid-GICs from the separated graphite may constitute a way to recycle this waste. We used HTR-type compact fuel with ZrO 2 TRISO particles to test two separation methods: low (H 2SO 4 + H 2O 2) and high (H 2SO 4 + HNO 3) temperature acid treatments. In both cases the TRISO separation was complete but some TRISO layers oxidized at high temperature. At low temperature, the desegregation of graphite grains is facilitated by intercalation of sulfuric acid between the graphene layers. The acid-GIC obtained consists of pure phases of high quality suggesting their potential industrial recycling.

납축전지 전류집전체로서 그라파이트 시트의 전기화학적 안정성과 방전성능 평가

납축전지 전류 집전체로서의 가능성을 보기위해 납 도금된 그라파이트 시트를 적용하여 평가하였다. 전기화학적 특성을 평가하기 위해 순환 전압전류법을 실시하였다. 납 도금된 그라파이트 시트는 납축전지의 음극으로 운용되는 전압범위에서 전기화학적으로 안정하였으나, 양극으로 운용되는 전압범위에서는 산소발생과 황산의 인터칼레이션으로 인해 전기화학적으로 불안정하였다. 납 도금된 그라파이트와 주조된 납 기판을 음극 전류집전체로 사용하여 전지를 제작하고, 방전 성능을 평가하였다. 납 도금된 그라파이트 시트를 적용한 납축전지가 금속 납 전류 집전체를 적용한 전지보다 더 높은 용량을 나타내었고, 에너지밀도 또한 더 높았다. Graphite sheet electro-deposited with lead was evaluated as a possible candidate for current collectors of lead acid batteries. Cyclic voltammetry was performed on the materials to evaluate the electrochemical properties. The graphite sheet electro-deposited with lead is electrochemically stable in the cathodic potential sweep. However, in the anodic potential sweep, the graphite sheet electro-deposited with lead is electrochemically unstable due to the oxygen evolution and the intercalation of sulfuric acid. Lead acid batteries were prepared by using a graphite sheet and a cast grid as current collectors for anode and performance test using those batteries was carried out. A lead acid battery with graphite sheets showed higher capacity and energy density than a conventional lead acid battery with cast grid.

Evaluation of the electrochemical stability of graphite foams as current collectors for lead acid batteries

Graphite foams with high electrical and thermal conductivities, good mechanical strength, and low mass have been synthesized and evaluated as possible current collector materials to replace lead alloys for the development of lightweight lead acid batteries. Cyclic voltammetry and galvanostatic charge–discharge tests were performed on these foams prior to and after graphitization to evaluate their electrochemical properties. In the voltage range where the negative electrode of lead acid batteries operates, the graphite foam is electrochemically stable. However, in the voltage range of the positive electrode, the graphite foam is not electrochemically stable due to intercalation of sulfuric acid into graphite. For the positive electrode, the non-graphitized foam shows better electrochemical stability and warrants further study for use as a current collector. Preliminary charge/discharge characterization of these graphite and non-graphitized foams coated with a lead oxide battery paste supports these conclusions, although the paste formulation and coating process need to be improved for cycle life evaluation.

Potential change during intercalation of sulfuric acid in host carbons with different textures

From the electric potential changes, the intercalation reaction of sulfuric acid in graphite was divided into two elemental processes: the charging process of the interface between graphite layer and intercalated sulfuric acid in pure stages, which corresponded to a steep increase in potential, and the stage transformation process caused by further intercalation, which showed a plateau on the potential change due to equilibrium between two stage structures. On the assumption that a part of the electric quantity applied to further intercalation during the stage transformation process was consumed on extra-charging of graphite layers, the potential curve against electric quantity could be simulated. The simulated potential curves were compared with experimental ones observed by galvanostatic and chemical intercalations in three host carbon materials with different nanotextures, natural graphite flakes, mesophase-pitch-based carbon fiber and vapor-grown carbon fiber. The host with high crystallinity as natural graphite flakes showed distinct plateaux in potential, suggesting a lower degree of overlapping of extracharging of graphite layers into the stage transformation process. On the other two hosts, a higher degree of overlapping was observed. The effect produced by host carbon texture on the intercalation was discussed by mutual comparison.

Discussion on the structural criteria for the intercalation of sulfuric acid into carbon materials

Structural criteria for the formation of the stage-2 structure of intercalation compounds with sulfuric acid are discussed using different carbon materials. The formation of intercalation compounds is confirmed to be governed by crystallite thickness L c , rather than by degree of graphitization P 1 or crystallite diameter L a .

Criteria for the Intercalation of Sulfuric Acid

Abstract The criteria for the intercalation of sulfuric acid were studied. The intercalation reaction was found to be governed by the relation between the onset potential values for each stage structure and the upper limit of the saturated potential. It was also shown clearly that the intercalation of sulfuric acid was possible on the hosts with the crystallite thickness along the c-axis above 20 nm and also with positive magnetoresistance at room temperature.

Positive electrode for galvanic cells prepared by anodization of CrO 3-graphite intercalation compounds in aqueous sulfuric acid

Cathode materials have been prepared in 12 M H 2SO 4 by electrochemical oxidation of CrO 3-graphite intercalation compounds (CrO 3-GICs). Striking effects appearing on cyclic potentiodynamic curves of CrO 3-GICs because of intercalation of sulfuric acid are discussed in relation to the formation of the CrO 3-graphite oxide system. Charge/discharge characteristics of these cathodes are compared with those of graphite oxide prepared from pure graphite.

Spontaneous Intercalation of Sulfuric Acid into Graphite and Synthesis of a New Graphite-Uranyl Sulfate Compound

Spontaneous Intercalation of Sulfuric Acid into Graphite and Synthesis of a New Graphite-Uranyl Sulfate Compound

Chemical synthesis of graphite hydrogenosulfate: Calorimetry and potentiometry studies

In the present work dynamics of sulfuric acid intercalation into graphite by chemical oxidation were investigated by means of the calorimeter and potentiometer techniques. Phase composition of intermediate and end-products of the reaction was investigated by X-ray diffraction.

Anodic oxidation of CrO 3-graphite intercalation compounds in sulfuric acid

Anodic intercalation-deintercalation of 18 M sulfuric acid into chromium trioxide-graphite intercalation compounds (CrO 3-GICs) is examined in comparison with the process occurring for pure graphite. Distinct differences in the influence of the CrO 3 dissolved in acid and intercalated into graphite on the intercalation process of H 2SO 4 are demonstrated by means of galvanostatic and cyclic potentiodynamic methods. The proposed model of intercalation of H 2SO 4 into CrO 3-GICs concerns both electrochemical process and chemical reactions involving the CrO 3 intercalant. To account for surprising effects found in the curves recorded for CrO 3-GICs the changes proceeding from the structural and chemical properties of these compounds because of intercalation of sulfuric acid are considered.