Manganese Dioxide Graphite Composite Electrodes Formed via a Low Temperature Method: Detection of Hydrogen Peroxide,Ascorbic Acid and Nitrite

Manganese dioxide modified carbon powder was prepared via a wet impregnation method from the solution of permanganate salt. After heating at 120 °C over night in air, the formation of manganese oxide was confirmed by cathodic stripping voltammetry. The synthesized material was used for fabrication of composite electrodes and their potential application in the field of electroanalysis investigated. The composite electrodes based on the manganese dioxide modified carbon powder proved to be useful as electrodes for detection of hydrogen peroxide, ascorbic acid and nitrite ions.     

Effect of phosphate complexation on Cd2+ sorption by manganese dioxide (beta-MnO2)

Sorption of metal ions on oxide/hydroxide surfaces mediates the fate and transport of these ions in many natural systems. These metallic ions often exist in bulk in the aqueous phase as complexes with inorganic and organic ligands. In the present study, we investigated the sorption properties of manganese dioxide in the presence of phosphate which is thought to be one of the most important complex forming species. The surface area, point of zero charge and structural morphology of the solid manganese dioxide were determined. Cd(2+) sorption studies were carried out on manganese dioxide as a function of pH, temperature and phosphate concentration. Cd(2+) sorption increased with increasing pH, temperature and phosphate concentration. It was found that phosphate formed both outer and inner sphere complexes via metal and ligand-like adsorption. The Langmuir equation was applied to describe the data and from the constants of this equation different thermodynamic parameters such as DeltaH(0), DeltaS(0) and DeltaG(0) were evaluated.     

Manganese dioxide graphite composite electrodes: application to the electroanalysis of hydrogen peroxide, ascorbic acid and nitrite.

The modification of carbon powder with manganese dioxide using a wet impregnation procedure with electrochemical characterisation of the modified powder is described. The process involves saturation of the carbon powder with manganese(II) nitrate followed by thermal treatment at ca. 773 K leading to formation of manganese(IV) oxide on the surface of the carbon powder. The construction of composite electrodes based on manganese dioxide modified carbon powder and epoxy resin is also described, including optimisation of the percentage of the modified carbon powder. Composite electrodes showed attractive performances for electroanalytical applications, proving to be suitable for the electrochemical detection of hydrogen peroxide, ascorbic acid and nitrite ions with limits of detection comparable to the detection limits achieved by other analytical techniques. The results obtained for detection of these analytes, together with composite electrodes flexible design and low cost offers potential application of composite electrodes in biosensors.     

A kinetic study of the permanganate oxidation of triethylamine. Catalysis by soluble colloids

The kinetics of the reaction between permanganate ion and triethylamine in aqueous phosphate buffers (pH 6–8) has been studied. The reaction is autocatalytic, a soluble form of colloidal manganese dioxide temporarily stabilized in solution by adsorption of phosphate ions on its surface having been identified as the autocatalyst. The reaction is also catalyzed by gum arabic. Mechanisms in agreement with the kinetic data are proposed for the reaction pathways taking place in the bulk solution (for both triethylamine and triethylammonium ion as reductants) and on both the gum arabic and manganese dioxide colloidal particles.     

Kinetics and mechanisms of the oxidation by permanganate of L-Phenylalanine

The oxidation of L-Phenylalanine by permanganate ion in aqueous phosphate buffers is autocatalized by the inorganic reaction product, which is stabilized in solution by adsorption of phosphate ions on its surface. This product is a soluble form of colloidal manganese dioxide. The rate of the noncatalytic reaction pathway is first-order in both the oxidizing and reducing agent. It is not affected by potassium chloride addition to the solution, but by phosphate addition. The rate increases with the pH of the medium. The autocatalytic pathway is first-order in both permanganate ion and colloidal manganese dioxide, (the permanganate ion according to the Langmuir isotherm). The autocatalytic rate increases with reductant concentration (follows the Langmuir adsorption isotherm). It is not affected by potassium chloride addition to the solution, whereas an increase in the phosphate concentration results in an increase in the rate with the same pH of the medium. Mechanisms consistent with the experimental data are proposed.     

Kinetics of anodic formation and cathodic reduction of MnO2 in the sulfate electrolyte solutions

The anodic formation of manganese dioxide is studied voltammetrically in a wide range of potential scan rate (V = 0.001–8 V/s). Using the diagnostic criteria of cronovoltammetric method, based on the original experimental data, the mechanism of electrooxidation of manganese ions in the acidic medium with subsequent reaction of disproportionation of the product of irreversible electrode reaction and hydrolysis yielding manganese dioxide is proposed. The kinetics of cathodic reduction of electrolytic manganese dioxide in the 0.5 M Na₂SO₄ solution is studied under the steady-state and non-steady-state potentiodynamic polarization conditions. From the experimental data, it is found that, in the acidic medium (pH 1–3), the mechanism of the electrode process changes depending on the cathodic potential scan rate: at the scan rate V < 0.5 V/s, MnOOH forms via one-electron transition leading, in its turn, to the partial deactivation of electrode surface with subsequent disproportionation of manganite. At the relatively high potential scan rates, manganite has no time to form, and the two-stage reduction via one-electron transitions at each stage is well pronounced. The parameters of the electrode processes are calculated.     

Pre-concentration of trace amounts of manganese in water samples based on (1-(2-pyridylazo)-2-naphthol) modified magnetic nanoparticles

A simple procedure based on magnetic nanoparticles has been developed for analytical purposes. In this method, 1-(2-pyridylazo)-2-naphthol (PAN)-modified magnetic nanoparticles (MNPs) were used for separation and pre-concentration of manganese(II) ions from aqueous samples. This method combines the use of a solution solvent with separation of magnetic nanoparticles from sample solution using a magnet. The influence of different parameters, such as amount of extractant (PAN) loaded on the nanoparticles, pH of solution, adsorption time, amount of modified nanoparticle, type and amount of eluents for desorption of manganese from magnetic nanoparticles were evaluated. The effect of various cationic and anionic interferences on the percentage recovery of manganese was also studied. Manganese ions were adsorped from a solution at pH 9.5 and desorbed from nanoparticles with 10?mL of DMSO?:?HNO₃ (1?:?1, v/v). The detection limit of the proposed method was found to be 0.11?µg?L^?1. The method was employed to recover and determine the level of manganese in different water samples.     

Carbon Nanotubes as Catalyst Supports for Oxygen Electrodes

Carbon nanotubes modified with manganese dioxide were prepared. Manganese dioxide was deposited by reduction of KMnO₄ in solution using formic acid or nanotube carbon. The electrochemical properties of oxygen electrodes containing nanotubes modified with manganese dioxide were studied.     

Radiotracer technique in adsorption studies

Hydrous manganese oxide (HMO) was synthesized and its adsorption properties with respect to Ba(II) ions investigated as a function of contact time, adsorptive concentration, temperature and pH, using a radiotracer technique. The adsorption equilibrium is achieved quickly in ca. 30 min and the steady state values of adsorption at various concentrations (10^–2–10^–7M) agree well with the classical Freundlich isotherm. The adsorption increases with increasing pH and reaches a maximum followed by a plateau over a fairly wide pH range. The temperature markedly affects the extent of adsorption and the process is thermodynamically found to be irreversible.     

高度分散二氧化锰纳米纤维的水热合成和对双氧水电流检测

采用水热还原氧化法合成了高度分散的具有纳米纤维结构的钾矿型二氧化锰,并将其用来制作检测双氧水浓度的传感器.运用X射线衍射(XRD)仪、电子扫描显微镜(SEM)、透射电子显微镜(TEM)和比表面积(BET)及孔隙度分析仪观察和表征二氧化锰纳米纤维的结构和表面形貌;用电化学工作站(EW)检测其传感性能.结果表明:在pH为7.4的磷酸缓冲溶液中,开路电压为0.2V的条件下对0.1%(w,质量分数)的二氧化锰纳米纤维修饰的玻碳电极(GCE)进行测试,测试结果为随着双氧水的浓度每增加0.1mmo·lL-1,响应电流的峰值就增加约1.3μA,在双氧水的浓度在0.1-1.5mmo·lL-1范围内得到的线性相关系数为0.996,这种电极的高灵敏度和优异的电化学活性可能归因于钾矿型二氧化锰纳米纤维的特殊纳米结构.这种传感器有很高的灵敏度和很好的重现性.综上说明这种廉价并且有很好的电化学活性的材料为设计新型电极生物传感器提供了更大可能.     

Catalytic air oxidation of manganese in synthetic waters

An attempt was made to study the oxidation of manganese by air in synthetic waters. A series of batch experments were performed at differnet values of concentration, temperature and pH. Unoxidized manganese in the solution was determined by formaldoxime spectrometric method. Results of these studies indicated that the air oxidation of manganese soluble in water can be effectively performed in basic media and that oxidation yield increasedwith an increase in pH and concentration. The yield was very high in the presence of manganese dioxide, sepiolite or clinoptilolite in solution and, the oxidation was almost completed especially at high values of pH and concentration. The reaction was found to be first order with respect to Mn²⁺ with a very low activation energy. A yield of 62% was obtained for the air oxidation of wastewater taken from the treatment plant of Corum Municipality.     

Effect of Precipitation pH and Heat Treatment on the Properties of Hydrous Zirconium Dioxide

The effect of the precipitation pH and subsequent heat treatment is studied on the properties of hydrous zirconium dioxide precipitated by ammonia from nitrate solutions. Precipitation at pH ≤ 6 generates hydrous zirconium dioxide, which contains excess sorbate nitrate ions; the product precipitated at pH ≥ 7 contains excess ammonium ions. This distinction considerably affects the course of thermolysis and the morphology of products. The exotherm associated with the formation of the crystal structure of zirconia becomes more pronounced with rising precipitation pH. In addition, the samples prepared at pH ≥ 7 have a more developed surface. The morphologic and microstructural evolution of hydrous zirconium dioxide samples during thermolysis is described.     

Sorption rate of uranyl ions by Hyphan cellulose exchangers and by hydrated titanium dioxide

Summary Sorption of uranyl ions by the cellulose exchanger Hyphan proceeds rather fast. Two steps are observed with half-times of the order of 10 s and 2 min. The majority of the uranyl ions is bound in 1 min. Sorption of uranyl ions by titanium dioxide is a very slow process. For particle sizes between 0,1 and 0.5 mm the half-time is about 3 h and equilibrium is attained in about 1 day. The effect of stirring suspensions of inorganic sorbents like titanium dioxide in solution is investigated in detail. Sorption of uranyl ions by titanium dioxide and change in pH in solution are measured simultaneously as a function of time.Alexander von Humboldt fellow     

Etude du comportement électrochimique du manganèse dans le tampon borate

The anodic behavior of the manganese electrode in borate buffer solutions have been studied by potentiostatic and galvanostatic electrochemical techniques. Three distinct steps determined on the charging curves are attributed to the formation of Mn (OH)₂, MnOOH and MnO₂. The manganese dioxide formed anodically in pH 11 borate solution may be reduced cathodically with high faradaic efficiency.     

Characteristics of manganese-coated sand using SEM and EDAX analysis

"Manganese-coated sand" is a type of silica medium coated with manganese oxides, formed from the sorption of manganese oxides during long-term filtration via the process of rapid sand filtration, followed by aeration in a water treatment plant. Locally available manganese-coated sand, both for packing and as a byproduct of filtration processes for water treatment plants in Taiwan, was found to be a low-cost and promising adsorbent for removal of Mn(2+) from raw water. This study was conducted to build the basic data for coating hydrated manganese oxide on the sand surface to utilize the adsorbent properties of the coating and the filtration properties of the sand. In this study, gas adsorption porosimetry and scanning electron microscopy analyses were used to investigate the surface properties of the coated layer. An energy dispersive X-ray (EDAX) technique of analysis was used to characterize metal adsorption sites on a manganese-coated sand surface. Results indicated that manganese-coated sand had more micropores and higher specific surface area, owing to attachment of manganese sand. Manganese ions penetrated into the micropores and mesopores of manganese oxide on a sandy surface; regeneration of manganese-coated sand could be achieved by soaking with pH < 2.0 acid solution. Results of EDAX analysis showed that the interfacial layer constructed the interface of manganese-coated sand. Acid and alkali resistance tests interpret a wide application range of pH for manganese-coated sand, and general temperature conditions do not affect the performance of this sand. Manganese-coated sand is potentially suitable for application as a packed bed for treatment of heavy metals from water. The results of this study can also benefit plant operational capacity data for engineering design.     

Synthesis of a MnO2/multiwalled carbon nanotube nanocomposite and its application as a sorbent for removing Cu2+ ions from aqueous media

In this research, a manganese dioxide/multiwalled carbon nanotube (MnO₂/MWCNT) was firstly synthesized and characterized and then was applied as an effective sorbent for removing Cu²⁺ ions from aqueous solution. The effects of initial concentration, temperature, contact time, pH solution, and sorbent dosage were investigated and the optimum value of each was determined. The Langmuir isotherm model, Freundlich model, and Temkin model were used to fit our experimental results. Ultimately, using the Van't Hoff approach, the thermodynamic functions of the intended adsorption phenomenon such as ΔH°_ad, ΔS°_ad, and ΔG°_ad were estimated.     

棉杆纤维素的改性(Ⅲ)——多乙撑多胺纤维素醚的制备及其吸附性能

化学改性制备纤维素衍生物对金属离子的富集分离［１～３］,膜分离［４,５］等方面的研究已有不少报道．我们近期研究［６,７］表明,由农业废弃物棉杆纤维制得的含氮纤维素醚衍生物对有毒的金属离子,尤其是对Ｈｇ２＋、Ｃｄ２＋、Ｃｒ３＋、Ｐｂ２＋离子有较好的吸附...     

Polyurethane-pyridylazonaphthol foams in the preconcentration and separation of trace elements

The feasibility of using PAN—polyether and polyester polyurethane foams in batch and column operations has been examined. The effects of pH, plasticizer and various anions present in the aqueous solution on the extraction behaviour of cobalt, iron and manganese have been investigated. In dynamic systems, the effect of flow rate on the extraction efficiencies of these metal ions has been investigated. The uptake of cobalt(III) and manganese(II) on PAN—polyester foam columns is quantitative at flow rates up to 10 ml min^-1 and 2 ml min^-1, respectively. The retention of iron(III) by the foam column is not quantitative even at a flow rate of 1 ml min^-1. Preconcentration of cobalt and its separation from various concentrations of manganese are successful..     

Ion exchange of some transition metal cations on hydrated titanium dioxide in aqueous ammonia solutions

The adsorption of transition metal cations on hydrated titanium dioxide in complexing ammonia and amine solutions has been studied as a function of ammonia (amine) concentration. The relationships between the distribution coefficients and ammonia concentration as well as the effects of various amines on sorption of transition metals indicate that a coordinate bond is formed between the metal ions and the hydroxy groups of the sorbent. The distribution coefficients of silver(I) and cobalt(III), which form strong ammonia complexes in aqueous solutions, decrease with increasing concentration of ammonia already at concentrations exceeding 10^–3. mol·dm^–3. Cations of zinc, manganese and mercury which form much weakerammonia complexes do not exhibit any effect of ammonia concentration in the whole range investigated. In the case of sorption of macroamounts of ammonia or amine complexes of silver, the molecular sieve effect plays an important role. The differences in the affinity of hydrated titanium dioxide for ammonia solvates of various transition metal ions can serve as a tool for effective separation of these ions in ammonia solutions.