Formation of peroxide on poly(vinyl alcohol) and its characteristics

Peroxide formed on poly(vinyl alcohol) (PVA) fiber due to hydrogen peroxide (H₂O₂) treatment was examined in terms of formation conditions, decomposition behavior, and function of graft initiation. By treating aqueous sodium hypochlorite- or periodic acid-oxidized PVA with H₂O₂, formation of peroxide on the substrates was observed which was not on unoxidized PVA. The amount of peroxide increased proportionally to the carbonyl content of the sample, the level of which was higher of NaClO- than for HIO₄-oxidized sample. The peroxide was decomposed by warming the sample in water to separate the H₂O₂. The reaction was easier for the HIO₄- than the NaClO-oxidized sample. The structure of peroxide was assumed to be the α-hydroxy hydroperoxide type for both NaClO- and HIO₄-oxidized samples, which should be distinguished in respect to the location of the group. It is inferred that the peroxide on the NaClO-oxidized sample is situated along the chain of PVA and that the one on the HIO₄-oxidized sample is located mainly at the end of the chain. It was also observed that the peroxides formed on NaClO- and HIO₄-oxidized samples are capable of initiating graft copolymerization of methyl methacrylate by means of heat or light.     

1,2‐propanediol–cellulose–acrylamide graft copolymers

1,2‐Propanediol–cellulose–acrylamide graft copolymers (PCACs) were developed for enhanced oil recovery. They were prepared with acrylamide and 1,2‐propanediol (PDO)–cellulose, which was formed through the addition of glycols to cellulose by the Shotten–Baumann reaction between 3‐chloro‐1,2‐propanediol and cellulose. The graft copolymerization was initiated with a redox system between Ce⁴⁺ and glycols in cellulose. The infrared spectrum of PDO–cellulose had some characteristic absorption bands around 2960 (νC? H) and 1050 cm^?1 (νC? O) that also appeared for the PDO group and pyranose ring of cellulose, respectively. The rate of Ce⁴⁺ consumption by PDO–cellulose was investigated through the calculation of the overall kinetic constant from the slopes of ln(D ? D_R) versus time (where D is the absorbance and D_R is the absorbance of the original polysaccharide solution) The results showed that PDO–cellulose had high reactivity and that there were two mechanisms of oxidation by Ce⁴⁺ with PDO–cellulose. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3022–3029, 2004     

Graft copolymerization of vinyl monomers onto modified cotton. IX. Hydrogen peroxide–thiourea dioxide redox system induced grafting of 2-methyl-5-vinylpyridine onto oxidized celluloses

Cotton cellulose was independently oxidized with potassium periodate, potassium dichromate-sulfuric acid, and potassium dichromate–oxalic acid, and the resulting oxidized celluloses were further modified by treatment with chlorous acid or sodium borohydride. The various modified celluloses so obtained were grafted with 2-methyl-5-vinylpyridine using a thiourea–dioxide–H₂O₂ redox system. It was found that the initiation characteristics of the cellulose samples vary widely with the oxidizing agent used. Further modification of the oxidized celluloses by treating them with chlorous acid enhances considerably their susceptibility toward grafting. The opposite holds true when these oxidized celluloses were modified by sodium borohydride treatment. Excluding thiourea dioxide from the polymerization system offsets grafting onto cotton cellulose while considerable grafting takes place on the various oxidized celluloses and their further modified samples. The work was also extended to study the factors which affect the graft uptake, homopolymer formation, and total conversion. In addition, the reactions involved in initiation of grafting were elucidated.     

Determination of cadmium (II) using H<Subscript>2</Subscript>O<Subscript>2</Subscript>-oxidized activated carbon modified electrode

Pristine activated carbon (AcC) was oxidized by H₂O₂ under ultrasonic conditions. Compared with pristine AcC, the H₂O₂-oxidized AC possesses higher accumulation ability to trace levels of Cd²⁺. Based on this, a highly sensitive, simple and rapid electrochemical method was developed for the determination of Cd²⁺. In 0.01 mol L⁻¹ HClO₄ solution, Cd²⁺ was effectively accumulated at the surface of H₂O₂-oxidized AcC modified paste electrode, and then reduced to Cd under −1.10 V. During the following potential sweep from −1.10 to −0.50 V, reduced Cd was oxidized and a sensitive stripping peak appears at −0.77 V. The stripping peak current of Cd²⁺ changes linearly with concentration over the range 5.0 × 10⁻⁸ to 5.0 × 10⁻⁶ mol L⁻¹. The limit of detection was found to be 3.0 × 10⁻⁸ mol L⁻¹ for 2-min accumulation. Finally, this new sensing method was successfully used to detect Cd²⁺ in waste water samples.     

Oxidation of Ce3+ by HO2 Radical and Ce3+-HO2 Complex Formation

The reaction of Ce⁴⁺ with H₂O₂ in H₂SO₄ is studied as a function of pH, Ce³⁺, SO₄⁼ and the ionic strength. The reaction mechanism proposed assumes the existence of a Ce³⁺ -HO₂ complex. Direct evidence for the reaction, Ce³⁺ + HO₂ + H⁺ → Ce⁴⁺ + H₂O₂ is presented.     

Electroless oxidation of boron-doped diamond surfaces: comparison between four oxidizing agents; Ce, MnO4, H2O2 and S2O8

The electrochemical properties of diamond are very sensitive to the surface terminations. It is still a challenge to successfully produce well-defined “C-O” functions. In this paper, we describe and compare the oxidation of as-grown polycrystalline boron-doped diamond (BDD) films using four different oxidizing agents in aqueous media: Ce⁴⁺, MnO₄⁻, H₂O₂ and S₂O₈²⁻. The different treatments lead to the formation of oxygenated functions at the diamond surface, mainly singly oxidized “C-O” groups such as “C-OH” or “C-O-C”. Processes with Ce⁴⁺ and MnO₄⁻ seem to be particularly interesting as they both lead to the creation of a high amount of oxygenated functions and an improvement of the charge transfer at BDD surfaces.     

Graft copolymerization onto cellulose by ceric ion initiator system: Effects of kind of acid and irradiation with ultraviolet light

The effects of kind of acid and irradiation of ultraviolet light on the graft copolymerization of methyl methacrylate onto cellulose with adsorbed ceric ion were investigated. Irrespective of ultraviolet light irradiation, the amount of reduced ceric ion in the reaction systems was increased in the order HCl > HClO₄ > HNO₃ > H₂SO₄, and the number of grafts formed was increased in the order HClO₄ > HNO₃ > HCl > H₂SO₄. Thus, it was definitely observed that the graft copolymerization is affected by the kind of acid. Ultraviolet light remarkably accelerated the reduction of ceric ion adsorbed on cellulose in the various acid mediums, but decreased the efficiency of graft formation. The most favorable results for the formation of grafts were obtained in the system in which HClO₄ and ultraviolet irradiation was employed. A combination of H₂SO₄ and ultraviolet irradiation resulted in the lowest per cent grafting and average molecular weight of grafts. It was found that H₂SO₄ characteristically dissolves out ceric ion adsorbed into an aqueous solution and accelerates the formation of homopolymer.     

Formation of peroxide on aldehyde cellulose and its ability to initiate graft copolymerization

Cellulose peroxide formed by the treatment of aldehyde cellulose with hydrogen peroxide (H₂O₂) was investigated with respect to formation and decomposition conditions and with respect to graft initiation. Periodic acid-oxidized cellulose was proved to produce the peroxide group on the substrate by subsequent treatment with H₂O₂, whereas no peroxide was produced with unoxidized cellulose. Since the peroxide content of oxidized cellulose increased with increasing carbonyl content of the sample, the peroxide was presumed to be introduced at the site of the aldehyde group of the sample. The peroxide groups formed were proved to revert to aldehyde groups by decomposition upon heating with water to nearly the same level as the original. The structure of the peroxide group was believed therefore to be an α-hydroxy hydroperoxide type. The cellulose peroxide was found to initiate graft copolymerization of methyl methacrylate very easily in thermal initiation and photoinitiation systems.     

Preparation of gelatin–N-vinylpyrrolidone graft copolymer

The graft copolymerization of N-vinylpyrrolidone (VP) onto gelatin was carried out by the following four different initiator systems: AIBN, K₂S₂O₈, H₂O₂—Fe²⁺, and Ce⁴⁺—HNO₃. The last one caused the monomer to lose the double-bond and polymerization ability due to the hydrolysis of the monomer. Using α,α-azobisisobutyronitrile as an initiator, the graft copolymerization of gelatin and N-vinylpyrrolidone in aqueous medium was studied systematically. The relationships between the rate of grafting and the concentration of initiator, monomer, and gelatin were established experimentally. Meanwhile, the rate equation was also derived from the proposed reaction mechanism, and it was similar to the equation previously obtained experimentally. The apparent activation energies for homopolymerization (E_h), graft copolymerization (E_g), and over all polymerization (E_p) were calculated. The graft efficiency and molecular weight of the grafted PVP were measured by hydrolyzing the backbone with hydrochloric acid. The graft copolymers Gel-g-PVP were added into the coating films, and the physical properties of the films, such as hardening ability, dimensional stability, and wetting property were investigated. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1485–1492, 1998     

ESR Study of a Complex Formation Between HO2 Radical and Peroxy-Vanadium (V) Ion

HO₂ radicals were generated in a flow system by the reaction: Ce⁴⁺ + H₂O₂→ Ce³⁺ +HO₂ + H⁺. The HO₂ radicals were mixed with V - H₂O₂ solutions and ESR spectroscopy was used to follow the reaction. It was shown that HO₂ reacts with both VO(O₂)⁺ and VO(O₂)^?₂ complexes. The ESR signal of the complexed radical consists of eight lines, indicating that the unpaired electron interacts with the Vanadium nucleus. The kinetics of the formation and decay reactions of the complexed radical were studied.     

Effect of yttrium and praseodymium on properties of Ce0.75Zr0.25O2 solid solution for CH4–CO2 reforming

Ce_0.75Zr_0.25O₂ solid solutions doped with Y³⁺ or Pr⁴⁺/Pr³⁺ were prepared by the co-precipitation method, and their physicochemical properties were characterized by means of N₂ adsorption, X-ray diffraction, X-ray photoelectron spectroscopy, FT-Raman, and H₂ temperature-programmed reduction and thermogravimetric analysis. Their performance in CH₄–CO₂ reforming was also tested in an atmospheric fixed-bed reactor. Ce_0.75Zr_0.25O₂ and Y³⁺ or Pr⁴⁺/Pr³⁺ doped Ce_0.75Zr_0.25O₂ solid solutions are of CaF₂ structure, and the thermal stability of Ce_0.75Zr_0.25O₂ is enhanced by doping Y³⁺ or Pr⁴⁺/Pr³⁺. Comparing with Ce_0.75Zr_0.25O₂, the migration of bulk lattice oxygen species become easier and the content of surface oxygen species is higher in the doped Ce_0.75Zr_0.25O₂, which is due to either oxygen vacancies or/and structural distortion resulted from the doping. The activity of the solid solutions in CH₄–CO₂ reforming is closely related to the surface oxygen species. Y³⁺ or Pr⁴⁺/Pr³⁺ doped Ce_0.75Zr_0.25O₂, especially the former, show higher activity than Ce_0.75Zr_0.25O₂, and Y³⁺ doped Ce_0.75Zr_0.25O₂ possesses better stability. All of the catalysts have good coke resistance. The catalyst deactivation is mainly due to the catalyst sintering.     

XPS and EIS studies of sputtered Al–Ce films formed on AA6061 aluminum alloy in 3.5% NaCl solution

X-ray photoelectron spectroscopy (XPS) was used to analyze the composition of films at different deposition parameters of sputtered Al-Ce coatings on AA6061 aluminum alloys. By means of electrochemical impedance spectroscopy (EIS) measurements, the protective character of these coatings was studied for 21 days of exposure in a 3.5 wt% NaCl solution and an attempt was made to establish the relationship between film thickness and chemical composition (Al/Ce, Ce³/Ce⁴⁺ ratios) of the surface before and after the electrochemical characterization. XPS studies revealed the presence of the Al^o, Al₂O₃, CeO₂ and Ce₂O₃ compounds, confirming that the sputtered Al-Ce films were deposited in the metallic form and thereafter were superficially oxidized under ambient conditions. The Al–Ce bonds were overlapped with the signal of cerium oxides. The transport phenomena in the oxide film or controlled diffusion process are strongly dependent on the deposition parameters and exposure time in the aggressive medium. It was also found that in the deposited samples at p₄P₂₀₀t₃₀₀, the film was still present after 21 days of exposure, although with visible cracks and erosion areas; however, the Ce³/Ce⁴⁺ ratio almost remained constant before and after the electrochemical characterization, which explained the barrier properties of these samples as compared with others at different deposition parameters.     

以Ce3+/Ce4+为媒质间接电合成1,4-萘醌

探讨了以Ce³⁺/Ce⁴⁺为媒质的1,4-萘醌间接电化学合成反应。考察了液相氧化、Ce³⁺电解氧化过程的影响因素,并进行了萘醌的间接电合成实验。结果发现,硫酸浓度、溶液温度对铈离子的氧化能力和电化学反应活性具有重要的影响;当温度为70℃、硫酸浓度为1.0 mol·L^-1时,液相氧化反应的收率最高(85.8%)。Ce³⁺电解氧化的最优条件为:电流密度50 mA·cm^-2、硫酸浓度1.0 mol·L^-1、温度为50℃,其电流效率可达90.6%;间接电合成实验过程中萘醌的平均收率达85.7%,Ce³⁺电解氧化的平均电流效率达87.8%,并且电解过程具有良好的稳定性,表明该技术具有良好的产业化应用前景。     

Synthesis,Structure and Electrical Properties of Mo‐doped CeO2–Materials for SOFCs

In this paper, we report the synthesis, structure and electrical conductivity of Mo‐doped compounds with a nominal chemical formula of Ce_1–xMo_xO_2+δ (x = 0.05, 0.07, 0.1) (CMO). The formation of fluorite‐like structure with a small amount of Ce₈Mo₁₂O₄₉ impurity (JCPDS Card No. 31‐0330) was confirmed using a powder X‐ray diffraction (PXRD). The fluoride‐type structure was retained under wet H₂ and CH₄ atmospheres at 700 and 800 °C, while diffraction peaks due to metal Mo were observed in dry H₂ under the same condition. AC impedance measurements showed that the total conductivity increases with increasing Mo content in CMO, and among the investigated samples, Ce_0.9Mo_0.1O_2+δ exhibited the highest electrical conductivity with a value of 2.8 × 10^–4 and 5.08 × 10^–2 S cm^–1 at 550 °C in air and wet H₂, respectively. The electrical conductivity was found to be nearly the same, especially at high temperatures, in air, O₂ and N₂. Chemical compatibility of Ce_0.9Mo_0.1O_2+δ with 10 mol‐% Y₂O₃ stabilised ZrO₂ (YSZ) and Ce_0.9Gd_0.1O_1.95 (CGO) oxide ion electrolytes in wet H₂ was evaluated at 800–1,000 °C, using PXRD and EDX analyses. PXRD showed that CMO was found to react with YSZ electrolyte at 1,000 °C. The area specific polarisation resistance (ASPR) of Ce_0.9Mo_0.1O_2+δ on YSZ was found to be 8.58 ohm cm² at 800 °C in wet H₂.     

Kinetic and mechanistic studies on the block copolymerization of methyl methacrylate initiated by Ce4+-poly (ethylene glycol) redox system

The kinetic and mechanistic features of tetravalent cerium-poly(ethylene glycol) (PEG, molecular weight 6000) redox couple initiated block copolymerization of methyl methacrylate (MMA) have been investigated in aqueous acidic medium in the temperature range 30–50°C. The block copolymerization behavior as a function of [Ce⁴⁺], [PEG], [MMA], [H⁺], [NO₃⁻], as well as temperature, have been studied. The overall rate of polymerization (R_p), the rate of disappearance of Ce⁴⁺ (R_Ce), and the number average molecular weight (M _n) have been determined from gravimetry, cerimetry, and gel permeation chromatography, respectively. R_p has been found to bear a square dependence on [MMA] and independent of both [Ce⁴⁺] and [H⁺]. R_Ce has been found to be directly proportional to [Ce⁴⁺] and [H⁺], and independent of [MMA]. Both R_p and R_Ce have been found to be retarded on adding nitrate ions, while increase of temperature accelerated the rates. The M _n of the block copolymer has been found to depend on [Ce⁴⁺], [PEG], [MMA], and [H⁺] as well as on temperature. A plausible reaction scheme has been derived and suitable kinetic expressions have been evaluated based on these observations. It has been concluded that by varying the temperature and concentration of the components of the redox system, it is possible to control the rate of polymerization and the molecular weight of the resulting block copolymer. © 1997 John Wiley & Sons, Inc.     

Site engineering of Ce3+-doped calcium scandate phosphors and understanding of relevant red-shifted emitting from green to yellow

CaSc₂O₄:Ce³⁺ is a well-known green emitting phosphor, but needs to match with suitable red emitting phosphors in practical white lighting. Herein, a site engineering strategy is proposed to modify the local coordination environment of Ce³⁺ by introducing Y³⁺ and Mg²⁺ ions into the CaSc₂O₄ crystal lattice. The obtained results indicate in the modified Ce³⁺-doped samples (CSO-YMg), Y³⁺ ions can occupy both Sc³⁺ and Ca²⁺ sites simultaneously, and the Y³⁺ ions tend to occupy Ca²⁺ sites in low-doped stage and enter into the Sc³⁺ sites in the high-doped stage. The introduction of Y³⁺ ions gives rise to the existence of MgO in as-prepared CSO-YMg samples, and it can be effectively washed through pickling. In the spectral aspect, with the increase of Y³⁺ and Mg²⁺ ions, the main emission peak is red-shifted from 512 nm to 530 nm upon excitation at 450 nm. However, the high-doped sample presents much stronger thermally induced fluorescence quenching than CaSc₂O₄:Ce³⁺. The lattice defects caused by doped ions (Y³⁺ and Mg²⁺) and the non-radiative energy transfer process between the Ca²⁺ (Ce³⁺) and Sc³⁺ (Ce³⁺ or Ce⁴⁺) sites should be responsible for such evident quenching phenomenon in CSO-YMg, which is obviously different from the emitting feature of CaSc₂O₄:Ce³⁺ (only at Ca²⁺ sites). Besides, utilizing the as-prepared CSO-5 phosphors and a blue LED (~450 nm), a WLED was successfully fabricated, yielding a comparable performance to those with commercial Y₃Al₅O₁₂:Ce³⁺ phosphors. What discussed in this study would bring some inspirations in the exploration and understanding of Ce³⁺-based phosphors according to local structural modification.     

Chemical Removal of CeO2 Segregated on the Surface of CeO2–ZrO2 Binary Oxides for Improvement of OSC

A chemical treatment to remove residual CeO₂ phase on CeO₂–ZrO₂ (CZ) solid solution was carried out. A CZ was treated by H₂O₂ for the reduction of Ce⁴⁺ to Ce³⁺ and then HNO₃ for the dissolution of Ce³⁺ compounds (H–CZ). H₂-TPR, TEM-EDX and XPS analyses revealed the removal of CeO₂ phase and the homogeneous distribution of Ce species. About 20% improvement in oxygen storage capacity (OSC) of H–CZ was confirmed at 773 K by the weight measurements under H₂/N₂ and air atmospheres, indicating that the HNO₃/H₂O₂ treatment was effective to avoid the deterioration of the OSC by segregated CeO₂ on the CZ binary oxides.     

ESR Studies of Uncomplexed and Complexed HO2 Radical Formed in the Reaction of H2O2 with Ce4+, Fe2+ and Ti3+ Ions

Excess of H₂O₂ reacting in 0.5N HClO₄ with Ce⁴⁺, Ti³⁺ and Fe²⁺ yields the uncomplexed HO₂ radical. This radical gives a broad ESR signal with a line width of 27±1 gauss and a g-value of 2.0140±0.0015. The HO₂ radical forms a complex with excess of Ce³⁺ which gives an ESR spectrum with a linewidth of 1.3±0.1 gauss and a g-value of 2.0180±0.0005. The equilibrium between complexed [Ce³⁺‥HO₂] and uncomplexed HO₂ was studied. Two complexes are formed between HO₂ and [Ti⁴⁺…H₂O₂]. These complexes give two ESR signals with a linewidth of 0.7 ± 0.1 and 0.5± 0.1 gauss and g-value of 2.0140± ± 0.0005 and 2.0120± 0.0005 respectively.     

Microwave irradiation graft copolymerization of hydroxyethyl methacrylate onto wool fabrics

Hydroxyethyl methacrylate was grafted onto woolen fabrics by microwave irradiation in the presence of catalyst (NH₄)₂S₂O₈. Various parameters of the graft copolymerization reaction, namely, time, microwave intensity, catalyst, and monomer concentration, were optimized. The graft copolymerization was also compared with conventional heating graft copolymerization at the same condition. Microwave irradiation was shown to improve the reactivity of the monomer. The moisture regain decreased as graft add-on increased. The Max load and the strain at Max load increased as graft add-on increased. The infrared spectra showed an additional peak at 1700 cm⁻¹, confirming ester carbonyl groups of the monomer. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2343–2347, 1998     

Preparation for graft copolymers of sawdust/vinyl monomers and their application for removal of dye

A kind of cationic exchanging resin of carboxyl sawdust (CSD) was fabricated through the hydrolysis of graft copolymers of sawdust with acrylonitrile (SAN) and sawdust with acrylamide (SAA) that were made by initiator Fe²⁺/H₂O₂. A study of the graft copolymerization was conducted for initiator usage, vinyl monomer usage, and reaction temperature. The hydrolysis under basic/acid conditions was also studied for the yield and acid value of CSD followed to adsorb Basic Pink dye (BPD). Our results show the following: (1) graft copolymers (SAN and SAA) with a high rate of graft copolymerization are readily prepared by suitable usages of initiator and vinyl monomer under a certain temperature; (2) adsorption capacity of CSD is relative to pH of BPD solution and reaches the most adsorption capacity at pH ≈ 6; (3) adsorption capacity of CSD increases along with the augment of its acid value; and (4) the adsorption capacity of the CSD toward BPD increases along with augment of initial concentration of the adsorbate and reaches about 500 mg/g. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2390–2396, 2002