Aqueous Sulphuric Acid Research Articles

Degradation of indigo carmine dye with peroxydisulphate ion in aqueous sulphuric acid phase: Kinetic study

AbstractThe quest for cleaner environments is a global concern. Hence, the investigation of degradation of the indigo carmine dye (IC) with peroxydisulphate ion in an aqueous sulphuric acid system with a view to understanding its kinetic degradation and mechanism. The degradation depicts first‐order kinetics in [S2O82−] and [IC], and the degradation mole ratio of IC: S2O82− is 1:1. The degradation rate is dependent on the change in ionic strength and medium permittivity of the system. Also, added ions (NH4+ and NO3−) influence the degradation rate of the dye which further supported the outcome of the change in ionic strength. Free radical participation is ruled out. The experimental rate law is given as (Kk3[H+])[IC][S2O82−]. Owing to the absence of detectable intermediates in the degradation process, an outer‐sphere mechanism is proposed. The study is significant in textile industries and medical settings for making environments less toxic with a well‐understood degradation rate pathway.

Spectrophotometric Determination of Phosphates in Detergent Samples Available in Tansen, Palpa

Phosphate is primarily used as a builder in detergents, which helps soften hard water, thereby increasing the cleansing power of detergents. Extensive discharge of phosphate from detergents leads to eutrophication of surface water bodies. This work aims to assess the amount of phosphate present in detergent samples available in Tansen, Palpa, and compare its concentration between local and foreign detergents. Phosphate in detergent samples can be determined by the molybdenum blue phosphorus method using a spectrophotometer. The experimental process relies on forming a phosphomolybdate blue complex with ammonium molybdate and the subsequent reduction of the complex by hydrazine hydrate in an aqueous sulphuric acid medium. The system obeys Beer-Lambert’s law at 830 nm in the concentration range of 2-16 ppm. In this study, the phosphate concentration in local detergents (Dhoni, Light, V-Series, Nirma, Upahar, Patanjali, Rin Shakti and Dr Jhatka) varied from 15.54-33.03 ppm, and that of foreign detergents (Wheel, Super Check, Surf Excel, Tide and Ariel) ranged from 23.81- 32.65 ppm. The amount of phosphate was compared between local and foreign detergent samples using the student's t-test, which revealed no significant difference between them. The results obtained from the study disclosed that the detergents under investigation are within the permissible limits of phosphate. However, non- phosphate-based builders can be used to discourage the use of phosphate in detergents.

Effect of Cetyltrimethylammonium Bromide and Sodium Dodecyl Sulphate on Oxidation of Indigo Carmine with Potassium Peroxy Diphosphate: A Kinetic and Mechanistic Study

The oxidative kinetic study of Indigo carmine (IC) with potassium peroxydiphosphate (PDP) in absence and presence of cationic cetyl-trimethylammonium bromide (CTAB) and anionic sodium dodecyl sulphate (SDS) micelles was studied in an aqueous sulphuric acid medium by maintaining the ionic strength at 3.0 mol dm-3 using sodium sulphate. The pseudo-zero-order constant was determined from the linear plots of absorbance versus time under the conditions [IC] < [PDP]. The reaction obeys zero-order kinetics with respect to varying [IC], first order kinetics with respect to varying [H+] and [PDP] in the absence and in presence of micelles. The reaction rate was accelerated with varying [CTAB] and [SDS] and reached a limiting value. The [surfactant] rate profile has limited nature since the reaction is unimolecular on the micelle surface. The binding constant of peroxy diphosphate was also determined with CTAB and SDS micelles by applying Berezin equation for the kinetic pattern.

MnO2/CoO electrode for supercapacitor: Synthesis and electrochemical performance

In this work, Cobalt Oxide (CoO) was prepared by co-precipitation method by taking 1:3M of Co (NO3)2·6H2O and NaOH. Synthesis of Manganese dioxide (MnO2) was done by reduction of potassium permanganate (KMnO4) with aqueous sulphuric acid (H2SO4) by hydrothermal process. For making the coin cell capacitor CoO and MnO2 were spin-coated on the thin copper sheet which was used as the current collector, PEDOT: PSS poly (3,4 – ethylene dioxythiophene) as electrolyte and cellulose paper as a separator. Scanning electron microscopy (SEM) analysis has been employed to study surface morphology and to confirm the formation of nanoparticles. An image analysis approach using ImageJ has been used to measure the percentage of porosity from the SEM micrographs. The parameters like specific capacitance, energy density, and power density were calculated from the CV measurements and were compared. When both electrodes are MnO2, it has a specific capacitance of 33.57F/g, the energy density of 16.84 J/g, and power density of 4.21 W/g and when both electrodes are CoO it has a specific capacitance of 29.19F/g, the energy density of 14.59 J/g and power density of 3.65 W/g. But one side with MnO2 and the other side with CoO electrode shows a specific capacitance of 44.92F/g, an energy density of 22.46 J/g, and a power density of 5.62 W/g.

Corrosion inhibition activity of Cefixime on mild steel surface in aqueous sulphuric acid

Interaction of pharmaceutically active drug Cefixime on mild steel surface in 0.5M sulphuric acid solution was studied using gravimetric analysis techniques, Polarization techniques i.e. Polarization resistance, tafel polarization and Electrochemical Impedance Spectroscopy (EIS) techniques. It shows more than 96% of corrosion inhibition efficiency at ambient temperature of 308oK on mild steel surface with the 4.0×10-4 M inhibitor concentration. Gravimetric studies were also conducted at various temperature and concentration range of the testing solution to justify their range of applicability at various practical conditions. And It is found very much suitable for their workings at the normal temperature and lower acid concentration ranges. Adsorption parameters and thermodynamic parameters were calculated from gravimetric analysis data obtained at different temperature and concentration range and reveals that the inhibitor follows the physical adsorption mechanism. Adsorption of Cefixime molecule is governed by Langmuir's adsorption isotherm. Inhibition of Cefixime on surface of mild steel is supplemented by atomic force microscopy, which reveals that the inhibited surface has less roughness than the uninhibited surface.

Solution Electrochemical Approach to Synthesis of Low Stage Graphite Bisulphate

Since their discovery in 1841, Graphite Intercalation Compounds (GICs) have found tremendous applications in various industrial and research fields such as supercapacitors, superconductors, heterogeneous catalysts, anode materials, hydrogen and lithium-ion storage and notably in graphene synthesis. GICs are a type of graphitic compounds formed by the insertion of a different atomic, ionic or molecular species, known as intercalants between the layers of graphite host. Intercalation occurs in stages, and the phenomenon of staging is characterised by stage index n, which is the number of carbon layers present between two successive intercalate layers. The concentration of intercalant in graphite increases as the stage index decreases.Oxyacids readily intercalate in graphite. Researchers have studied intercalation of graphite in a wide variety of such acids such as H2SO4, HNO3, H2SeO4, HClO4 and H3PO4, and concluded that sulphuric acid is the best intercalant for graphite owing to higher efficiency and lesser reaction times. Intercalation in sulphuric acid gives Graphite Bisulphate (GB). Conventional GB chemical synthesis methods, pose an environmental and safety hazard due to the usage of hazardous and explosive oxidants. Moreover, chemical methods such as Hummers’ are primarily oxidation routes for the synthesis of Graphene Oxide (GO) wherein GB is believed to be the process intermediate, which is difficult to isolate.Electrochemical synthesis of GB is inexpensive, scalable and provides an easy defect-free transfer to the application substrate due to its ability to deliver the product in a suspension. Furthermore, the electrochemical approach provides an environment- friendly solution to the synthesis of GB because it replaces harsh chemical oxidants with an external polarisation potential. The quantity of electricity passed can also be controlled by changing the applied potential to obtain desired stages of GB.However, the synthesis of low stage GB by the electrochemical process in aqueous sulphuric acid solutions is an arduous task as a result of the excess water present in the system. Water molecules react with surface C atoms to form bulky surface groups which hinder the process of intercalation. Furthermore, undissociated water molecules may also co-intercalate with the bisulphate ions from aqueous sulphuric acid. Electrochemical oxidation of this intercalated water causes reduction of bisulphate ions and ultimately results in the vigorous evolution of oxygen and sulphur dioxide, which exfoliates graphite. Thus, GB formed before exfoliation is disintegrated and lost.On the other hand, water also facilitates intercalation by opening up graphitic grain boundaries for intercalation by carrying out a nucleophilic attack on the edge sites. Thus an optimal concentration of water in aqueous sulphuric acid along with an optimal positive polarisation potential is required for the synthesis and stability of GB. The present study aims at the electrochemical synthesis and characterisation of low stage GB and determination of optimal reaction conditions for the process. A pure stage GB synthesised and isolated this way can be particularly useful for the synthesis of layer-specific graphene flakes. Intercalation reduces the force of attraction between layers of graphite and hence makes selective cleaving possible by sonication. The stage index is strongly correlated with the number of graphene layers produced upon electrochemical exfoliation and is thus a key parameter to tune the electrochemical exfoliation of graphite.

MnO₂/rGO Nanocomposites as a Supercapacitor Electrode Material.

MnO₂ nanoparticles were incorporated in reduced graphene oxide (rGO) sheets employing an in-situ, one-step and eco-friendly method. The X-ray diffraction result shows that MnO₂ nanoparticles encapsulation increases the interlayer spacing of rGO. The UV-Vis, FTIR, X-ray photoelectron and Raman spectroscopic studies show that MnO₂ nanoparticles are well intercalated within reduced graphene oxide sheets. The electrochemical studies were executed in 0.5 M aqueous sulphuric acid. The maximum 'specific capacitance' value for MnO₂/reduced graphene oxide nanocomposite was 152.5 F/g at 0.05 V/s. The MnO₂/reduced graphene oxide (MnO₂/rGO) nanocomposite sample displayed an excellent charge retention capacity of 92% after 1000 cycles.

Recovery of zinc as zinc phosphate and by-products from hydrometallurgical treatment of hot-dip galvanizing (Zn-Al) dross

Zinc dross is the waste product generated during the hot-dip galvanizing, wherein around 11% of the total zinc is arrested by the dross leading to huge zinc losses. Though, there exist several pyro-metallurgical approaches to recover zinc but these are highly energy and cost intensive process; where hydrometallurgical processes take an edge. In this regard, this study holistically focusses on the hydrometallurgical recovery of zinc as zinc phosphate and other impurities like Al as alumina from zinc dross (Zn-Al) obtained from in-house hot-dip galvanizing unit at our laboratory. Zinc dross is leached as received in aqueous sulphuric acid medium without pulverization and stirring requirements, followed by separation of aluminium using NaOH based precipitation. Aluminium hydroxide precipitate is calcined to obtain alumina, whereas the supernatant solution is subsequently treated with disodium hydrogen phosphate to obtain products like zinc phosphate and sodium sulphate. The proposed process is simple, facile and scalable for recovery of zinc and other valuables from dross.

Electrochemical evaluation of cr-mn austenitic stainless steel in aqueous sulphuric acid and influence of thiocyanate ions

PurposeLow nickel austenitic stainless steel (ASS) has attracted much attention worldwide because of its economical price. This study aims to investigate the effect of different corrosive environments on the corrosion behavior of chrome-manganese (Cr-Mn) ASS. The tests were carried out as a function of H2SO4 concentrations, temperature and addition of ammonium thiocyanate (NH4SCN) (0.01 M). Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques were used to study the corrosion behavior of Cr-Mn ASS. It was observed that with increasing H2SO4 concentration, temperature and with the addition of NH4SCN solution, icorr, icrit and ipassive values increased. EIS data show decreasing charge transfer resistance value with increasing concentration and temperature. Higher corrosion rate with increasing temperature and concentration of H2SO4 is related to the anions (SO42−), which is responsible for reducing the stability of passive films. With the presence of 0.01 M NH4SCN thiocyanate (SCN− anion), there is a higher dilution of the passive film resulting in a higher corrosion rate. Energy-dispersive spectroscopy (EDS) analysis reveals the adsorption of sulfur on the surface in NH4SCN containing a solution. The significant presence of counter ions and the adsorbed sulfur species on the steel surface play a vital role in corrosion behavior.Design/methodology/approachAll the experiments were performed on a 3 mm thick sheet of Cr-Mn ASS (202 ASS) in hot rolled condition. The samples were then annealed at 1,050°C for 1 h, followed by water quenching. For microstructural examination, they were electrochemically etched in 10 Wt.% oxalic acid solution at 1 amp for 90 s. A computer-controlled Potentiostat (Biologic VMP-300) was used. After the cell was set up, the working electrode (WE) was electrostatically cleaned at −1 V vs saturated calomel electrode (SCE) for 30 s to remove the air-formed film. Then, WE were allowed to attain stable open circuit potential (OCP) for 1 h, following by the EIS test and potentiodynamic polarization test. The polarization test was started from a cathodic potential (−1.2 V vs SCE) and continued up to an anodic potential (1.6 V vs SCE) a scan rate of 0.1667 mV/s. EIS experiment was conducted on the same instrument by using a sinusoidal AC signal of 10 mV in a frequency range of 1,000,000 to 0.01 Hz at OCP.FindingsPotentiodynamic polarization graph shows that with the increase in sulphuric acid concentration. Increasing temperature from 20°C to 80°C in 0.5 M H2SO4 solution increases the corrosion rate (icorr) of Cr-Mn ASS. On the addition of 0.01 M NH4SCN to the sulfuric acid solution (0.1, 0.5 and 1 M) the corrosion rate increases drastically almost four to five times. EDS and XRD analysis shows the presence of sulfur over the oxide film and preferential site for dissolution of Cr and Mn at the steel surface when NH4SCN is added to the sulfuric acid solution.Originality/valueA study on the corrosion behavior of Cr-Mn ASS is scanty according to the author’s knowledge. Therefore, the present study will investigate the corrosion behavior of Cr-Mn ASS on SO4−2 anions, temperature and the addition of SCN− ion in sulfuric acid.

Titanium dissolution from decomposed Ilmenite using NaOH into the aqueous sulphuric acid solutions

At present work, the experiment to dissolve titanium from the Indonesian Ilmenite into the aqueous sulphuric acid solutions has been done through the following process: Ilmenite decomposition using NaOH at temperature 800°C for 5 hours to produced decomposed Ilmenite, followed with titanium dissolution from the decomposed Ilmenite into the aqueous sulphuric acid solutions in the glass reactor. The variables used for dissolution process were covering: dissolution temperature from 30°C to 70°C, sulphuric acid concentrations from 5% to 15%, and dissolution time from 30 minutes up to 180 minutes. The influence of those all variables were observed on the titanium dissolution from the decomposed Ilmenite. Result of the dissolution experiment show that the dissolved titanium in the aqueous sulphuric acid solutions increased when the dissolution temperature was increased from 30°C to 60°C, sulphuric acid concentration were increased from 5% to 15% and dissolution time were extended from 30 minutes to 180 minutes.

Spectrophotometer Aided Kinetic, Mechanistic and Thermodynamic Study of Ruthenium(III) Catalysed Oxidation of Esmolol by Sulphate of Cerium(IV) in Aqueous Sulphuric Acid Medium

Spectrophotometer Aided Kinetic, Mechanistic and Thermodynamic Study of Ruthenium(III) Catalysed Oxidation of Esmolol by Sulphate of Cerium(IV) in Aqueous Sulphuric Acid Medium

Electrochemical oxidation of formic acid at carbon supported Pt coated rotating disk electrodes

The effect of electrode rotation on the oxidation of formic acid in aqueous sulphuric acid has been investigated at a glassy carbon electrode coated with a carbon supported Pt catalyst. Substantial mass transport effects were observed in cyclic voltammetry, steady-state measurements at constant potential, and chronoamperometry. However, a purely mass transport limited current was not observed under any conditions because of a decrease in the kinetic current at high potentials due to Pt oxide formation. Steady-state measurements, and currents from the cathodic scans in cyclic voltammetry, gave linear Koutecky–Levich plots with slopes in agreement with the literature diffusion coefficient. However, non-linearity and inaccurate slopes were observed for anodic scans and chronoamperometry. This has been shown to be due to small increases in the kinetic current with increasing rotation rate. Accurate kinetic currents can be obtained by applying the Koutecky–Levich equation at each rotation rate and use of the known mass transport limited current.

Retrieval of Venus' cloud parameters from VIRTIS nightside spectra in the latitude band 25°-55°N

Two years of data from the M-channel of the Visible and InfraRed Thermal Imaging Spectrometer (VIRTIS), on board the European Space Agency mission Venus Express operating around the planet Venus, are analysed. Nocturnal data from a nadir viewpoint in the latitude band 25°N-55°N are selected for their configuration advantages and maximisation of the scene homogeneity. A reference model, and radiance spectrum, is defined based on average accepted values of the Venus main atmospheric and cloud parameters found in the literature. Extensive radiative transfer simulations are performed to provide a synthetic database of more than 10 000 VIRTIS radiances representing the natural variability of the system parameters (atmospheric temperature profile, cloud H2OH2SO4 solution concentration and vertical distribution, particle size distribution density and modal radius). A simulated-observed fitting algorithm of spectral radiances in window channels, based on a weighting procedure accounting for the latitudinal observed radiance variations, is used to derive the best atmosphere-cloud configuration for each observation.Results show that the reference Venus model does not adequately reproduce the observed VIRTIS spectra. In particular, the model accounting for a constant sulphuric acid concentration along the vertical extent of the clouds is never selected as a best fit. The 75%/96% and 84%/96% concentrations (the first values refer to the upper cloud layers and the second values to the lower ones) are the most commonly retrieved models representing more than 85% of the retrieved cases for any latitudinal band considered. It is shown that the assumption of stratified concentration of aqueous sulphuric acid allows to adequately fit the observed radiance, in particular the peak at 1.74 μm and around 4 μm.The analysis of the results concerning the microphysics suggests larger radii for the upper cloud layers in conjunction with a large reduction of their number density with respect to the reference standard. Considerable variation of the particle concentration in the Venus' atmosphere is retrieved for altitudes between 60 and 70 km. The retrieved models also suggest that lower cloud layers have smaller particle radii and larger number density than expected from the reference model. Latitudinal variations of microphysical and chemical parameters are also analysed.

Quantifying charge transfer to nanostructures: Polyaniline nanotubes

The nano-impact method is used to quantify electrolytic doping levels of single polyaniline nanotubes in aqueous sulphuric acid solution. Even at extreme potentials only partial (≤18%) doping of the tubes is observed. Comparisons are made with the doping of ensembles of tubes where the levels of charge transfer appears even less. The implications for practical applications are assessed.

Phenformin Effect on the Anodic Dissolution of Nickel in Acid Media

Nickel electrodes are used in different interesting technological applications, as well as example of not-inert electrodes. Their electrochemical behaviour depends on the production methods and particularly on their surface morphology. The polycrystalline nickel electrode has been the subject of extensive studies in acid aqueous media, where dissolution and passivation processes are observed. Those processes were postulated through reactive schemes which begin with two common electrochemical steps, where an intermediate specie of Ni(II) is produced and then it leads to two competitive reactions, to yield Ni2+ in solution or/and the formation of a non-conductive passive layer containing Ni(OH)2 in different hydration degrees [1,2]. Depending on the pH-solution, the phenformin cation can be found in the neutral, monoprotonated or diprotonated form. The values of the pKa determined by UV-spectroscopy are pKa1= 2.7 and pKa2 =10.7 [3]. The monoprotonated cation is a planar Π-electronic system with an electronic dislocation around the overall biguanide group, stabilized by the hydrogen bonding between the nitrogen atoms: In this work, the effect of phenformin hydrochloride on the polycrystalline nickel electrode in aqueous sulphuric acid media was studied. The results indicate that phenformin plays an active role in the anodic dissolution of nickel electrode. The experimental results are explained from a kinetic model where the electrical elements measured by means electrochemical impedance are related with the kinetic constants of the electrochemical mechanism. This biguanide adsorbs on the nickel surface and also reacts with the corrosion products, being able to inhibit the nickel electro-dissolution, while at low concentrations of phenformin the Ni dissolution process is enhanced. From the obtained results, it could be concluded that biguanides such as phenformin show interesting properties for different surface treatments as are electro-polishing and corrosion inhibition of nickel materials. Because its chelating action on Ni(II) ions, its overall positive charge, the located pair of electrons located on nitrogen atoms, its adsorption on the metallic surfaces, and pH effects, phenformin could be used with different promising objectives in technological processes. The kinetic model proposed allows to be correlated the kinetic parameters with the electrical magnitudes of the equivalent circuit. Therefore the electrochemical impedance is useful in order of characterise the double layer and also how depends the rate of the steps of the electrochemical dissolution of nickel on the media composition. The impedance Z was fitted to the equation Z = Ru + ZT, where: Table 1. Impedance parameters obtained by fitting the impedance experimental data at h = 25 mV In 0.245 M K2SO4 + x M H2SO4 (pH=3.0) + (0.1-z) KCl + CF M phenformin hydrochloride aqueous solution. T = 298 K. h = + 0.25 V. Ru is the uncompensated resistance. Cdl is the double layer capacity. Rct is the charge transfer resistance. a2 is the CPE exponent. CF / M 105Cdl/ mF.cm-2 Rct/ W.cm2 L/ Henry.cm2 a2 0 1.5 1389 304 0.78 1·10-4 2.5 965 1284 0.72 1·10-2 1.9 866 631 0.70 3·10-2 1.6 1321 770 0.84 6·10-2 1.8 1538 1027 0.83 In spite of the observed inhibition of the nickel corrosion caused for the phenethyl biguanide cation across the formation of chelate compounds, the chloride anion plays an important role in the overall process due their aggressive character [4]. Another important factor in the overall process is the increase of the pH when increases the amount of phenformin, which enhances the formation of the passive layer. REFERENCES [1] S.G. Real, J.R. Vilche and A.J. Arvia, Corros. Sci., 20, 563 (1980). [2] M.R. Barbosa, S.G. Real, J.R. Vilche and A.J. Arvia. J. Electrochem. Soc. 135, 1077 (1988). [3] F. Vicente, J. Trijueque, F. Tomás, Química e Industría, 28, 307 (1982). [4]J. Gregori, J. J. García-Jareño, D. Giménez-Romero, F. Vicente. J. Electrochem. Soc.:153 B206-B212 (2006).. ACKNOWLEDGEMENTS Part of this work was supported by FEDER-CICyT CTQ2015-71794-R

Phase Behaviour of Cellulose Nanocrystal Dispersion in Aqueous Sulphuric Acid and Development of an Energy Efficient Separation Technique for the Acid-Cellulose Nanocrystal System

In this paper, the phase behaviour of a cellulose nanocrystal (CNCs) dispersion in sulphuric acid solutions was investigated, aimed at the development of an energy efficient separation method for this mixture. The system in consideration was a mixture of 30 wt% aqueous sulphuric acid (ρl = 1219 kg/m3) containing 12.6 mg/ml of cellulose nanocrystals (CNCs) (ρs = 1590 kg/m3, volume fraction of CNCs less than 1%). This volume filling mixture was obtained directly from a CNC extraction process, as obtained after the hydrolysis of cotton using 64 wt% sulphuric acid at ca. 45 ̊C for 45 minutes (this condition was required for the extraction of CNCs from cotton) followed by quenching the hydrolysis with water. The CNCs form the desired product and need to be separated from the acid that can then be recycled. Conventionally this separation has been difficult and requires a large input of energy. This work addresses this problem by investigating into the phase behaviour and physicochemical and hydrodynamic character of this mixture. This understanding led to the development of a very energy efficient separation mechanism for this mixture, which is 5 orders of magnitude more energy efficient than the most widely used centrifugation systems.

Ethylenediaminetetraacetic acid catalyzed oxidative conversion of N-(2-hydroxyethyl)phthalimide to n-methylphthalimide by cerium(IV) in aqueous sulphuric acid medium : A kinetic and mechanistic approach

Ethylenediaminetetraacetic acid catalyzed oxidative conversion of N-(2-hydroxyethyl)phthalimide to n-methylphthalimide by cerium(IV) in aqueous sulphuric acid medium : A kinetic and mechanistic approach

A spectroscopic investigation of kinetics and mechanism of ruthenium(III)-catalyzed oxidation of N-(2-hydroxyethyl)phthalimide by cerium(IV) in aqueous sulphuric acid and sulphate media

AbstractThe oxidation of N-(2-hydroxyethyl)phthalimide with cerium(IV) with a small amount of ruthenium(III) present as a catalyst has been studied by spectrophotometric means. The spectroscopic study has been carried out in aqueous H2SO4 and SO42- media at constant ionic strength of I = 1.60 mol dm−3. Stoichiometric analysis shows that one mole of NHEP reacts with two moles of cerium(IV). The oxidation products were identified by IR and GC–MS. Orders with respect to substrate, oxidant, ruthenium(III) and acid concentrations were determined. Increase in sulphuric acid concentration increases the rate. Effect of ionic strength and solvent polarity of the medium on the rate of the reaction was studied. The added product, cerium(III), has no significant effect on the rate of reaction. The active species of oxidant in sulphate medium and catalyst are CeSO42+ and [Ru(H2O)6]3+. Based on the experimental results a suitable mechanism is proposed. The activation parameters and the thermodynamic quantities are also...

Influence of thermal treatments on the stability of Pd nanoparticles supported on graphitised ordered mesoporous carbons

The graphitisation of ordered mesoporous carbons (CMK-3) was carried out by thermal treatments under different conditions of temperature and heating rate. The electrochemical characterization in acidic medium of the graphitised CMK-3 showed that such a thermal treatment is effective to decrease the carbon oxidation rate (corrosion) while preserving a good porosity in terms of capacitance. Besides, the graphitisation degree and, in consequence the electrochemical corrosion resistance, can be modulated by an appropriate choice of thermal treatment conditions, where the heating rate and temperature appear as critical parameters. Under certain graphitisation conditions, the carbon corrosion of CMK-3 can be minimized showing lower rates compared to a commercial carbon black (Vulcan XC-72R). Palladium nanoparticles were supported on the most promising graphitised CMK-3 and Vulcan using a method based on impregnation and reduction with borohydride, resulting in suitable metal crystallite sizes. The electrocatalytic activity towards the oxidation of carbon monoxide and formic acid were assessed in aqueous sulphuric acid electrolyte for application at the anode of direct formic acid fuel cells (DFAFCs). The best activity results were obtained for the Pd catalyst supported on a graphitised CMK-3.

High yield and facile microwave-assisted synthesis of conductive H2SO4 doped polyanilines

The microwave-assisted synthesis of polyaniline (PANI) was performed using ammonium persulphate (APS) as oxidizing agent in 0.5 M–2.5 M concentration range of aqueous sulphuric acid (H2SO4) at 93 W applied microwave power of 10 min duration. The microwave (MW) synthesized PANIs had 3 times higher yield in comparison to PANI samples prepared using a classical method, CS (0 W MW power) at the same temperature for 10 min synthesis duration period. Fourier Transform Infrared (FTIR) and UV–Vis spectroscopies confirmed the formation of PANI structure in all products. The influence of H2SO4 acid dopant on the spin concentration of MW and CS H2SO4 doped PANI samples were examined by EPR spectroscopy, while the morphological characteristics were investigated by using scanning electron microscopy (SEM). XRD results showed amorphous phases in both MW and CS H2SO4 doped PANI samples. Conductivity measurements revealed ∼1.5 times higher conductivity values for MW H2SO4 doped PANI samples in comparison with PANI samples prepared by the CS method under same condition. The influence of sulfate anion in comparison to chloride anion as a dopant on morphological, dopant levels and conductivity properties of MW PANI samples were also investigated.