Polymerization of acrylamide initiated with electrogenerated cerium (IV) in the presence of EDTA

Polymerization of acrylamide was carried out with cerium (IV)-EDTA redox initiator system with and without electrolysis. The effect of temperature, time, cerium (IV), and EDTA concentrations on the polymerization yield and molecular weight were studied and compared with electrolytic conditions. At low concentrations of cerium (IV) the electrolytic method continuously supplying Ce (IV) from Ce (III) has an advantage over the nonelectrolytic method for which polymerization did not occur under these conditions. A possible polymerization mechanism is suggested.     

Electrolytic oxidation of Ce(III) in nitric acid and sulfuric acid media using a flow type cell

The electrochemical oxidation behavior of Ce(III) in nitric acid and sulfuric acid media with various concentrations and compositions were investigated by cyclic voltammetry (CV) and potentiostatic electrolysis. In nitric acid media, the peak potential separation for the redox reactions of the Ce(III)/Ce(IV) couple shifted to base side with the increasing concentration of nitric acid from 1 to 6 M. The kinetics of the Ce(III)/Ce(IV) couple is rapid in high concentration nitric acid. The formal potential is independent of both proton and nitrate concentrations while the standard rate constant increases with added protons but is independent of nitrate concentration. Constant-potential electrolysis also shows that a high proton concentration is electrochemically favorable for the electron transfer of the Ce(III)/Ce(IV) couple and for a high Ce(IV) yield in nitric acid media. The current efficiency was ca. 75% for the oxidation process of Ce(III) at 298 K. A Ce(IV) yield of ca. 80% was achieved for the electrolysis of 100 mM Ce(III) in 6 M HNO₃ solution. In sulfuric acid media, the peak potential separation for the redox reactions of the Ce(III)/Ce(IV) couple shifted to noble side with rising concentration of sulfuric acid from 0.1 to 2 M and then shifted to base side with further increase in the concentration. A Ce(IV) yield of ca. 95% was achieved for the potentiostatic electrolysis of 100 mM Ce(III) in 3 M H₂SO₄ solution.     

Electrochemical cell current requirements for toxic organic waste destruction in Ce(IV)-mediated electrochemical oxidation process

The electrochemical cell for cerium oxidation and reactor for organic destruction are the most important operation units for the successful working mediated electrochemical oxidation (MEO) process. In this study, electrochemical cells with DSA electrodes of two types, single stack and double stack connected in series, were used. The performances towards the electrochemical generation of Ce(IV) in nitric acid media at 80 °C were studied. The current-voltage curves and cerium electrolysis kinetics showed the dependence on number of cell stacks needed to be connected in series for the destruction of a given quantity of organic pollutant. The presence of an optimum region for Ce(III) oxidation with a contribution of oxygen evolution, especially at low Ce(III) concentration (high conversion ratios), was found. The cells were applied for the Ce(IV) regeneration during the organic destruction. The cell and reactor processes were fitted in a simple model proposed and used to calculate the current needed in terms of Ce(III) oxidation rate and the number of cell stacks required for maintaining Ce(IV)/Ce(III) ratio at the same level during the organic destruction. This consideration was based on the kinetic model previously developed by us for the organic destruction in the MEO process.     

Ce(III)/Ce(IV) in methanesulfonic acid as the positive half cell of a redox flow battery

The characteristics of the Ce(III)/Ce(IV) redox couple in methanesulfonic acid were studied at a platinum disk electrode (0.125 cm²) over a wide range of electrolyte compositions and temperatures: cerium (III) methanesulfonate (0.1–1.2 mol dm⁻³), methanesulfonic acid (0.1–5.0 mol dm⁻³) and electrolyte temperatures (295–333 K). The cyclic voltammetry experiments indicated that the diffusion coefficient of Ce(III) ions was 0.5 × 10⁻⁶ cm² s⁻¹ and that the electrochemical kinetics for the oxidation of Ce(III) and the reduction of Ce(IV) was slow. The reversibility of the redox reaction depended on the electrolyte composition and improved at higher electrolyte temperatures. At higher methanesulfonic acid concentrations, the degree of oxygen evolution decreased by up to 50% when the acid concentration increased from 2 to 5 mol dm⁻³. The oxidation of Ce(III) and reduction of Ce(IV) were also investigated during a constant current batch electrolysis in a parallel plate zinc–cerium flow cell with a 3-dimensional platinised titanium mesh electrode. The current efficiencies over 4.5 h of the process Ce(III) to Ce(IV) and 3.3 h electrolysis of the reverse reaction Ce(IV) to Ce(III) were 94.0 and 97.6%, respectively. With a 2-dimensional, planar platinised titanium electrode (9 cm² area), the redox reaction of the Ce(III)/Ce(IV) system was under mass-transport control, while the reaction on the 3-dimensional mesh electrode was initially under charge-transfer control but became mass-transport controlled after 2.5–3 h of electrolysis. The effect of the side reactions (hydrogen and oxygen evolution) on the current efficiencies and the conversion of Ce(III) and Ce(IV) are discussed.     

Aqueous polymerization of acrylamide initiated by 4,4′-azobis (4-cyano pentanol) and chain extension of polyacrylamide by means of ceric ion redox systems

Summary The polymerization of acrylamide (AA) initiated by 4,4-azobis (4 cyanopentanol) (ACP) was investigated in aqueous solution at 60°C. The molecular weight and the conversion depend on polymerization duration and initiator concentration. Polymerization of AA initiated by ACP yields polyacrylamide (PAA) with hydroxyl terminal groups. Redox polymerization of AA initiated by hydroxyl terminated PAA in conjuction with Ce(IV) provided increase in the molecular weight of the initial polymer.     

Aqueous polymerization of methyl methacrylate initiated by ceric ion reducing agent systems in sulfuric acid medium

Polymerization of methyl methacrylate (MMA) was carried out in aqueous sulfuric acid medium at 30°C using ammonium ceric sulfate (ACS)/methyl ethyl ketone (MEK) and ammonium ceric sulfate/acetone as redox initiator systems. A short induction period was observed with both the initiator systems, as well as the attainment of limiting conversion for polymerization reactions. The rate of ceric ion consumption, R_ce, was first order with respect to Ce(IV) concentration in the concentration range (0.5–5.5) × 10⁻³M, and 0.5 order with respect to reducing agent concentration in the concentration ranges (0.0480–0.2967M) and (0.05–0.3912M) for Ce(IV)–MEK and Ce(IV)–acetone initiator systems, respectively. A fall in R_ce was observed at higher reducing agent concentrations. The plots of R_ce versus reducing agent concentrations raised to the half power yielded straight lines passing through the origin, indicating the absence of complex formation between reducing agents and Ce(IV). The addition of sodium sulfate to maintain constant sulfate ion concentration in the reaction medium could bring down the R_ce values in the present reaction systems. The rate of polymerization of MMA, R_p, increased with increase in Ce(IV), reducing agent, and monomer concentrations for the Ce(IV)–MEK initiator. The rate of polymerization of MMA is independent of Ce(IV) concentration and increased with an increase in reducing agent and monomer concentrations for the Ce(IV)–acetone initiator. At higher concentrations of reducing agent (0.4–0.5M), a steep fall in R_p values was observed with both the initiator systems. The orders with respect to Ce(IV), MEK, and MMA using the Ce(IV)–MEK initiator were found to be 0.23, 0.2, and 1.29, respectively. The orders with respect to Ce(IV), acetone, and MMA using the Ce(IV)–acetone initiator were found to be zero, 0.42, and 1.64, respectively. Maintaining constant [SO²⁻₄] in the reaction medium could bring down R_p values for the Ce(IV)–MEK initiator system. On the other hand, a rise in R_p values with an increase in [Na₂SO₄] could be observed when constant [SO²⁻₄] was maintained in the reaction medium for the Ce(IV) on reducing agent, production of radicals, initiation, propagation, and termination of the polymeric radicals by bimolecular interaction is proposed. An oxidative termination of primary radicals by Ce(IV) is also included. © 1996 John Wiley & Sons, Inc.     

A study of the Ce(III)/Ce(IV) redox couple for redox flow battery application

In this study, the electrochemical behavior of the Ce(III)/Ce(IV) redox couple in sulfuric acid medium with various concentrations and the influence of the operating temperature were investigated. A change of the concentration of sulfuric acid mainly produced the following two results. (1) With an increase of the concentration of sulfuric acid the redox peak currents decreased. (2) The peak potential separation for the redox reactions increased with rising concentration of sulfuric acid from 0.1 to 2 M and then decreased with further increase of the concentration. Elevated temperature was electrochemically favorable for Ce(III)/Ce(IV) couple, which caused an increase of the peak currents for the redox reactions and a decrease of the peak potentials separation. Constant-current electrolysis shows that the current efficiency was 73% for the oxidation process of Ce(III) and 78% for the reduction process at 298 K, and could be improved by elevating the temperature. The open-circuit voltage of the Ce-V cell, after full charging, remained constant at 1.870±0.005 V for more than 48 h, and is about 29% higher than that of the all-vanadium batteries. The coulombic efficiency was approximately 87%, showing that self-discharge of the Ce-V battery was small. The preliminary exploration shows that the Ce(III)/Ce(IV) couple is electrochemically promising for redox flow battery (RFB) application.     

Low Temperature Initiation by 3-Mercaptopropionic Acid-Ce(IV) or -KMnO4 Redox System for Polymerization of Acrylamide Monomer

Polymerization of acrylamide monomer was performed at low temperatures using 3-mercaptopropionic acid-cerium(IV) sulfate and 3-mercaptopropionic acid-KMnO₄ redox systems in acid aqueous medium. Water soluble polyacrylamides containing 3-mercaptopropionic acid end groups were synthesized. The effects of mole ratio of acrylamide to initiator(n_MSA= n_Ce(IV)), polymerization time, temperature, and concentration of sulfuric acid on the yield and molecular weight of polymer were investigated. The decrease in the mole ratio of acrylamide/Ce(IV) at constant monomer concentration resulted in an increase in the yield but a decrease in molecular weight of polymer. The increase of reaction temperature from 20° to 70°C resulted in a decrease in the yield but indicated generally a constant value for the molecular weight of polymer. With increasing of polymerization time, the yield and molecular weight of polymer did not change mainly. Ce(IV) and Mn(VII) ions are reduced to Ce(III) and Mn(II) ions, respectively in the polymerization reaction. The existence of Ce(III) ion bonded to polymer was investigated by UV-visible spectrometry and fluorescence measurements. The amount of Mn(II) that is incorporated to the polymer was determined using graphite furnace atomic absorption spectrometry. The mechanism of this phenomenon is discussed.     

Influence of the doping agent on the corrosion protection properties of polypyrrole grown on aluminium alloy 2024-T3

The corrosion protection properties of polypyrrole (PPy) electrodeposited onto aluminium alloy 2024-T3 substrates were investigated as a function of the doping agent. We used camphor sulfonic acid (CSA), para toluene sulfonic acid (p-TSA), phenylphosphonic acid (PPA), oxalic acid (OA) and cerium nitrate salt (Ce(NO₃)₃) as doping agents. The resulting coatings have been evaluated towards corrosion protection of aluminium alloy 2024-T3 using electrochemical impedance spectroscopy (EIS). Complementary, scanning electron microscopy (SEM) provided images on the morphology and the thickness of the coatings. The results showed that coatings formed using Ce(NO₃)₃ solution protect the substrate more efficiently compared to the other coatings.     

Polymerization of methyl methacrylate in micellar phase: A kinetic study

Polymerization of methyl methacrylate (MMA) using Ce(IV) as initiator in aqueous nitric acid solution in the presence of sodium lauryl sulphate (NaLS) has been studied kinetically at a temperature range of 25–35°C. The rate of polymerization (R_p) increases with increasing concentration of NaLS, and it was also proportional to [MMA]²; but, in the presence of NaLS, the change of R_p with respect to [Ce(IV)] and [H⁺] were not linear and similarly the rate of Ce(IV) disappearance was not proportional to its original concentration. The overall activation energy of the polymerization process in presence of 0.01M NaLS was found to decrease by ～ 7.0 kcal mol^?1. The monomer–micelle association constant has been calculated to be 5.135 × 10⁴ mol^?1 L. The polymer obtained in surfactant medium is sparingly soluble in benzene and DMSO. From infrared spectra clear evidence of vinyl polymerization was obtained.     

铝基复合材料表面四价铈转化膜的研究

研究了铝基复合材料Ａｌ６０６１／ＳｉＣｐ表面四价铈转化膜的成膜工艺,讨论了各工艺参数对转化膜性能的影响。利用湿热试验、盐水浸渍试验和电化学方法评价了转化膜的耐腐蚀性能并与其它类型转化膜进行了比较,结果表明四价铈转化膜的耐腐蚀性能优于复合材料Ａｌ６０６１／ＳｉＣｐ表面的化学氧化膜和阳极氧化膜。     

Aqueous polymerization of ethyl acrylate initiated by ceric ion‐reducing agent systems in nitric acid medium

Kinetic study of aqueous polymerization of ethyl acrylate (EA) was carried out at 30 °C in dilute nitric acid medium by employing ammonium ceric nitrate (ACN)–methyl cellosolve (MC) and ACN–ethyl cellosolve (EC) as redox initiator systems. The ceric ion consumption was found to be first order with respect to ceric ion concentration with both initiator systems. The formation of complexes between Ce(IV) and reducing agents (RA) was observed. The order with respect to Ce(IV), reducing agents and monomer was evaluated for aqueous polymerization of EA by Ce(IV)–MC and Ce(IV)–EC redox initiator systems. The overall activation energy, E_overall, for aqueous polymerization of EA was evaluated in the temperature region of 27–40 °C with both initiator systems. A kinetic mechanism for aqueous polymerization of EA initiated by redox initiator systems is presented. © 2001 Society of Chemical Industry     

Kinetic study of the polymerization of ethyl acrylate in an aqueous nitric acid medium

A kinetic study of the aqueous polymerization of ethyl acrylate (EA) was carried out at 30°C in a dilute nitric acid medium with ammonium ceric nitrate (ACN)–n‐propanol (nPA) and ACN–ethanol as redox initiator systems. The ceric‐ion consumption was first‐order with respect to the ceric‐ion concentration with both initiator systems. The formation of complexes between Ce(IV) and reducing agents was observed. The orders with respect to the Ce(IV), reducing agents, and monomer were evaluated for aqueous polymerizations of EA initiated by Ce(IV)–nPA and Ce(IV)–ethanol redox initiator systems. The overall activation energy for the aqueous polymerization of EA was evaluated in the temperature region of 27–40°C with both initiator systems. A kinetic mechanism for the aqueous polymerization of EA initiated by redox initiator systems is presented. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 218–224, 2006     

The production of oxalic acid from CO2 and H2O

Oxalic acid has been prepared on a preparative scale in an undivided cell with sacrificial anodes and an aprotic electrolyte. Optimum current efficiencies (>90%) have been obtained in cells with zinc anodes, stainless steel cathodes and acetonitrile with tetrabutylammonium perchlorate as the electrolyte. Micro-pilot experiments revealed that a continuous electrochemical cell can be set up and that the reaction product can be removed by filtration. A complete process is designed by a combination of the oxalic acid production with a zinc electrolysis. No unwanted by-products appear, which is recently of increasing importance. Economic consideration shows that the process may become interesting in the future.     

Anodic oxidation of 2,4-dihydroxybenzoic acid for wastewater treatment

Dihydroxybenzoic acid (2,4-DHBA) is used as an intermediate chemical reactant in industrial synthetic processes. Disinfection of water contaminated by 2,4-DHBA, using chlorinating techniques, generates trihalomethane compounds, so that alternative degradation techniques are of interest. The electrochemical oxidation of 2,4-dihydroxybenzoic acid (2,4-DHBA) at a platinized titanium electrode was investigated. An electroanalytical study by linear and cyclic voltammetry showed adsorption of the reagent at the electrode surface. Mathematical treatment of cyclic voltammetry curves indicates Langmuir type adsorption. For electrolysis, working in the oxygen evolution region causes an increase in electroactive electrode surface area and better mass transfer at the electrode. For example, for an initial 2,4-DHBA concentration of 0.3 kg m^–3 and a current density of 300 A m^–2, almost complete conversion of the pollutant is obtained after passing 4 A h, together with a TOC decrease of 30%. Byproducts of electrodegradation include 2,3,4- and 2,4,5-trihydroxybenzoic acids (THBA), maleic acid, glyoxalic acid and oxalic acid. The faradaic yield is less than 18%, due to oxygen evolution during electrolysis.     

不同阴离子的四丁基季铵盐对草酸在铅电极上电解还原的影响

用恒电流电解法研究了四丁基氢氧化铵和不同的阴离子在草酸电解还原过程中的作用。四丁基铵阳离子可以提高电流效率,但电流效率的增加值不受浓度变化的影响。阴离子对电流效率的作用可以忽略。通过测量电极溶液界面的电容值,发现电流效率和季铵盐在电极表面的吸附相关。     

Grafting vinyl monomers onto silk fibers. VIII. Graft copolymerization of methyl methacrylate onto silk using tetravalent manganese–oxalic acid redox system

The graft copolymerization of methyl methacrylate onto silk fibers was investigated in aqueous solution using the Mn(IV)–oxalic acid redox system. The copolymerization reaction was carried out under a variety of conditions such as different monomer, initiator, oxalic acid, acid concentrations, and temperatures. The graft yield increases with increasing initiator concentration up to 5 × 10^?2M, and with further increase of the initiator concentration it decreases. The graft yield also increases with increasing sulfuric acid concentration up to 15 × 10^?2M, and decreases thereafter. The rate of grafting also increases with increase in oxalic acid concentration up to 1.5 × 10^?2M and 84.592 × 10^?2M, respectively, and thereafter the rate of grafting shows down. The effect of temperature, solvents, and salts on graft yield has also been investigated and a plausible rate expression has been derived.     

Graft copolymerization of vinyl monomers with modified cotton. II. Grafting of acrylonitrile and methyl methacrylate on acetylated cotton

Ce(IV)-induced polymerization of acrylonitrile and methyl methacrylate with acetylated cotton having different acetyl contents was investigated. The extent of interaction between the cotton and monomer is dependent upon the acetyl content of the former as well as on the reaction conditions. Increasing the acetyl content caused a significant decrease in the graft yield. Increasing the acrylonitrile concentration was accompanied by a substantial increase in the graft yields. The same effect was found with the initiator up to a certain concentration, but beyond it there was a reversal. The rate of grafting increased by rising the temperature and follow the order 60° > 40° > 30°C. The Ce(IV) consumption during grafting is greater than that consumed during oxidation. The consumption of Ce(IV) by the cellulosic materials was favorably influenced by the concentrations of monomer and initiator, time, and temperature. Rates of grafting and Ce(IV) consumption during oxidation of acetylated cottons having different acetyl contents strongly support the postulated mechanism of grafting using the Ce(IV)–cellulose redox system. Ce(IV) oxidation had practically no effect on the acetyl groups (expressed as per cent combined acetic acid) of the modified cotton.     

二氧化碳在P^＋／P—Si半导体电极上光电化学还原的研究

1870年,Royer使用Zn电极将CO_2还原为HCOOH。近年来,人们对CO_2在几十种金属电极上的电化学还原进行了深入的研究。但普遍存在的问题是CO_2在金属电极上还原的过电位较大,导致耗电较多。而半导体电极能吸收光能降低CO_2还原的过电位,所以人们对CO_2在半导体电极上的光电还原进行了探讨,使用的光阴极材料有P-GaP,P-GaAs,P-InP,P-CdTe。半导体Si的禁带宽度E_g=1.12eV,     

Kinetic study of aqueous polymerization of methyl methacrylate initiated by Ce(IV)-maltose redox system

Polymerization of methyl methacrylate initiated by ceric ammonium nitrate-maltose has been investigated in aqueous nitric acid under nitrogen in the temperature range 20.5-35°C. The dependence of the initial rate of polymerization and the initial rate of ceric ion consumption on maltose, Ce(IV), and monomer concentrations has been determined. The reaction orders were found to depend on ceric ion concentration. At a moderately high Ce(IV) concentration (1 × 10^?3mol litre^?1) the orders were 1/2 and 3/2 with respect to maltose and monomer concentration, respectively, and independent of Ce(IV) concentration. But at a low Ce(IV) concentration (4 × 10^?4mol litre^?1) the orders with respect to monomer and Ce(IV) changed to 1 and 1/2, respectively. The effect of temperature was also examined. The average molecular weight, as determined by size-exclusion chromacography, was found to depend on maltose, Ce(IV), and monomer concentrations, as well as on temperature.