Self-assembled manganese dioxide nanowires as electrode materials for electrochemical capacitors

The microstructure and morphology of sol-gel derived manganese dioxide (MnO₂) xerogels were affected by the synthesis conditions and post synthesis heat treatment. Manganese dioxide nanoparticles in sol that were dialyzed to more acidic pH (pH 5.7) value were observed to self-assemble into nanowires, whereas non-dialyzed sols remained nanoparticulate in nature. MnO₂ xerogels of disordered nanowire network exhibited comparatively higher porosity and BET surface areas. The electrochemical properties of both MnO₂ nanowire and nanoparticle thin-film electrodes were evaluated using cyclic voltammetry in a mild aqueous electrolyte (0.1 M Na₂SO₄). The charge capacities of MnO₂ nanowire-based thin-film electrodes were substantially higher (~ 800 F/g) than those of nanoparticulate thin-film electrodes (~ 700 F/g).     

Influence of surfactants on the structure of the adsorption layer in the system: Carboxymethylcellulose/alumina

The influence of surfactants: anionic SDS, nonionic Triton-100 and their mixture (SDS/TX-100) on the structure of the adsorption layer in the system: carboxymethylcellulose (CMC)/alumina (Al₂O₃) was measured. The surface charge density of alumina and its zeta potential were determined in the presence of the CMC macromolecules and the surfactant particles. In order to gain more information about the structure of adsorption layer the amount of CMC adsorption in the presence of surfactants as well as the thickness of the CMC adsorption layer were determined. It was proved that in the presence of surfactants mixture (SDS/TX-100) the amount of adsorption of CMC is the highest and the obtained adsorption layer is the thickest. On the other hand, when Triton X-100 is added to the measured system the polysaccharide conformation is closely packed. The amount of adsorption is large but the thickness of the adsorption layer is relatively low. In the presence of SDS macromolecules of CMC form conformation expanded towards the bulk solution. Such a conformation is characterized by the smaller amount of adsorption of polymer but the larger thickness of the adsorption layer.     

Preparation of MnO<Subscript>2</Subscript>/porous carbon material with core–shell structure and its application in supercapacitor

Tubular manganese dioxide (MnO₂) is synthesized by hydrothermal method, and a silicon dioxide (SiO₂) used as template is wrapped on the as-synthesized MnO₂. Then poly(styrene-co-divinylbenzene) (PS) as heteropolymeric carbon precursor was wrapped on as-prepared MnO₂/SiO₂ to form intermediate product MnO₂@SiO₂@PS. The intermediate products were treated by carbon tetrachloride, stripped template and carbonized, thus the final product MnO₂/porous carbon composite (MnO₂@PC) with core–shell structure was obtained. The core–shell structural composite is used as an electrode of supercapacitors, which combines high conductivity and high surface specific area of porous carbon material and high electrochemical activity of MnO₂. The resulting core–shell MnO₂@PC exhibits a maximum specific capacitance of 196.2 F g^?1 at a discharge density of 1 A g^?1 with capacitance retention of 78.52% over 5000 discharge/charge cycles.     

Reducing dissolution of MnO2 nanofibers by doping with ferric ion

MnO₂ nanofiber was found to possess high adsorption capacities for heavy metal ions such as, arsenic and lead, in water due to its high specific surface area (SSA) and high surface activity. However, a significant amount of manganese was found to leach from MnO₂ nanofibers. Reducing MnO₂ dissolution is very important for improving its applications in drinking water treatment. In this study, MnO₂ nanofiber was doped with Fe³⁺ to reduce its dissolution in water. Dissolution tests were conducted on un-doped and Fe-doped MnO₂ nanofibers. The results revealed that doping with Fe³⁺ significantly reduced MnO₂ dissolution. SSA and defects of MnO₂ materials were analyzed by BET and XRD methods. The effects of Fe³⁺ on MnO₂ dissolution were discussed and the optimal dopant amount was identified.     

Improvement of hydrothermally synthesized MnO2 electrodes on Ni foams via facile annealing for supercapacitor applications

Nanostructured manganese dioxide (MnO₂) is deposited on nickel foams by a hydrothermal synthesis route. As-deposited MnO₂ thin films are largely amorphous. Facile post-deposition annealing significantly improves the electrochemical performance of the MnO₂ thin films via changing their morphology, phase, and crystallinity. The specific capacitance of the MnO₂ electrode increases with the annealing temperature and reaches an optimal value of 244 F g^?1 (at the current density of 1 A g^?1) in a neutral 1 M Na₂SO₄ electrolyte for a specimen annealed at 500 °C. Furthermore, when an alkaline 5 M KOH electrolyte is used, an exceptionally high capacitance of 950 F g^?1 is achieved at the current density of 2 A g^?1. The cost-effective facile synthesis, high specific capacitance, and good cycle stability of these MnO₂-based electrodes enable their applications in high-performance supercapacitors.     

In Vitro and In Vivo Adhesion Testing of Mucoadhesive Drug Delivery Systems

Bioadhesive tablets were prepared by physical mixing of polymers and drug, then granulating and compressing into a tablet. The mucoadhesion was evaluated by shear stress measurement, detachment force measurement, and X-ray photography of the rabbit gastrointestinal tract. The strong interaction between the polymer and the mucous lining of the tissue helps increase contact time and permit localization. Polymers like hydroxypropyl methylcellulose K4M (HPMC K4M), hydroxypropyl methylcellulose 100 cps (HPMC 100 cps), carbopol-934, sodium carboxy methylcellulose (Na CMC), guar gum, and polyvinylpyrrolidone (PVP) were tested by shear stress measurement and detachment force measurement methods. HPMC K4M, showing maximum bioadhesion, was used in further studies. Adhesion was maximum between pH 5 and pH 6. Maximum adhesion was observed in the duodenum, followed by the jejunum and ileum. Barium sulfate (BaSO₄) matrix tablets containing polymer and drug were subjected to X-ray studies in rabbits, and it was found that the tablet was mucoadhesive even after 8 hr. Enteric coating did not show any effect on mucoadhesion after passing from the stomach.     

二氧化锰电极材料的制备及电化学性能研究进展

二氧化锰(MnO₂)作为一种重要的无机功能材料,因成本低、来源广泛、电化学性能优异及对环境友好且理论比电容高等优势,在电化学电容器电极材料的研究中有巨大的应用潜力,已成为超级电容器电极材料的研究热点。目前,制备二氧化锰的方法多样,常用的方法有:固相法、水热法、溶胶凝胶法、液相共沉淀法、电化学沉积法等。且因二氧化锰具有比表面积大、循环稳定性好等优势,用其作为电极材料更易于工业化生产,具有较大的市场价值。本文主要综述了非晶态及晶态二氧化锰电极的制备方法及其用于超级电容器的研究进展,并对其储能机理、温度对其微观结构(表面积)和残余结构水等因素的影响进行了分析。     

Joint Charge Storage for High‐Rate Aqueous Zinc–Manganese Dioxide Batteries

Aqueous rechargeable zinc–manganese dioxide batteries show great promise for large‐scale energy storage due to their use of environmentally friendly, abundant, and rechargeable Zn metal anodes and MnO₂ cathodes. In the literature various intercalation and conversion reaction mechanisms in MnO₂ have been reported, but it is not clear how these mechanisms can be simultaneously manipulated to improve the charge storage and transport properties. A systematical study to understand the charge storage mechanisms in a layered δ‐MnO₂ cathode is reported. An electrolyte‐dependent reaction mechanism in δ‐MnO₂ is identified. Nondiffusion controlled Zn²⁺ intercalation in bulky δ‐MnO₂ and control of H⁺ conversion reaction pathways over a wide C‐rate charge–discharge range facilitate high rate performance of the δ‐MnO₂ cathode without sacrificing the energy density in optimal electrolytes. The Zn‐δ‐MnO₂ system delivers a discharge capacity of 136.9 mAh g^?1 at 20 C and capacity retention of 93% over 4000 cycles with this joint charge storage mechanism. This study opens a new gateway for the design of high‐rate electrode materials by manipulating the effective redox reactions in electrode materials for rechargeable batteries.     

Steric Stabilization of Suspensions

Introduction The vast majority of work on pharmaceutical suspensions is concerned with the electrical stabilization of such systems, incorporating the 0LV0 theory of colloid science to account for the suspensions characteristics observed. Stabilization of particles, produced by the adsorption of polymers at the solid-liquid interface, has not been extensively investigated in the area of pharmaceutical suspensions. It is only recently that theories describing this “steric stabilization” have been (2) introduced and these may be used only with certain restrictions Steric stabilization has one major advantage over electrostatic stabilization in that it is relatively insensitive to the presence of added electrolytes. The addition of ionic exclpients such as colourings, flavourings, buffers and preservatives must be taken into account when formulating a dispersion where stabilization is by electrostatic means alone. Possible leaching of ionic species from glass containers may also cause unwanted changes in suspension appearance and redispersibility. Stabilization of particles through the adsorption of polymers avoids this problem as the steric effect is independent of added electrolyte and high ionic strengths are usually required before the solution properties of nonionic polymers are affected.     

Electrospun carbon nanofibers with manganese dioxide nanoparticles for nonenzymatic hydrogen peroxide sensing

Carbon nanofibers (CNFs) decorated by manganese dioxide nanoparticles (MnO₂NPs) are prepared by an electrospinning technique, followed by thermal treatments in different environments. The obtained MnO₂NPs–CNFs composite was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). SEM images showed that the surface of the CNFs was decorated with homogeneously dispersed nanoparticles with narrow size distribution. XRD and XPS characterizations confirmed the main composition of the nanoparticles was MnO₂. Furthermore, for the strong catalytic oxidation ability of MnO₂ toward hydrogen peroxide, the composite material was used as the matrix for nonenzymatic sensor construction. Cyclic voltammetry and amperometric response were applied to investigate the performance of the sensor. Under the optimum conditions, a wide linear range from 10 μM to 15 mM (R = 0.9994, R represents the correlation coefficient) with a low detection limit of 1.1 μM was obtained. The proposed sensor also displayed short response time, high sensitivity, good reproducibility and stability. These superior performances could be attributed to the large surface area and excellent electrocatalytic activity of the MnO₂NPs–CNFs.     

Nitrogen‐Containing Microporous Conjugated Polymers via Carbazole‐Based Oxidative Coupling Polymerization: Preparation,Porosity, and Gas Uptake

Facile preparation of microporous conjugated polycarbazoles via carbazole‐based oxidative coupling polymerization is reported. The process to form the polymer network has cost‐effective advantages such as using a cheap catalyst, mild reaction conditions, and requiring a single monomer. Because no other functional groups such as halo groups, boric acid, and alkyne are required for coupling polymerization, properties derived from monomers are likely to be fully retained and structures of final polymers are easier to characterize. A series of microporous conjugated polycarbazoles ( CPOP‐2–7 ) with permanent porosity are synthesized using versatile carbazolyl‐bearing 2D and 3D conjugated core structures with non‐planar rigid conformation as building units. The Brunauer–Emmett–Teller specific surface area values for these porous materials vary between 510 and 1430 m² g^?1. The dominant pore sizes of the polymers based on the different building blocks are located between 0.59 and 0.66 nm. Gas (H₂ and CO₂) adsorption isotherms show that CPOP‐7 exhibits the best uptake capacity for hydrogen (1.51 wt% at 1.0 bar and 77 K) and carbon dioxide (13.2 wt% at 1.0 bar and 273 K) among the obtained polymers. Furthermore, its high CH₄/N₂ and CO₂/N₂ adsorption selectivity gives polymer CPOP‐7 potential application in gas separation.     

Development of Polysaccharide-Based Colon Targeted Drug Delivery Systems for the Treatment of Amoebiasis

ABSTRACT

The main focus of this study is to develop colon targeted drug delivery systems for metronidazole (MTZ). Tablets were prepared using various polysaccharides or indigenously developed graft copolymer of methacrylic acid with guar gum (GG) as a carrier. Various polysaccharides such as GG, xanthan gum, pectin, carrageenan, β-cyclodextrin (CD) or methacrylic acid-g-guar (MAA-g-GG) gum have been selected and evaluated. The prepared tablets were tested in vitro for their suitability as colon-specific drug delivery systems. To further improve the colon specificity, some selected tablet formulations were enteric coated with Eudragit-L 100 to give protection in an acidic environment. Drug release studies were performed in simulated gastric fluid (SGF) for 2 hr followed by simulated intestinal fluid (SIF) at pH 7.4. The dissolution data demonstrate that the rate of drug release is dependent upon the nature and concentration of polysaccharide/polymer used in the formulations. Uncoated tablets containing xanthan gum or mixture of xanthan gum with graft copolymer showed 30–40% drug release during the initial 4–5 hr, whereas for tablets containing GG with the graft copolymer, it was 70%. After enteric coating, the release was drastically reduced to 18–24%. The other polysaccharides were unable to protect drug release under similar conditions. Preparations with xanthan gum as a matrix showed the time-dependent release behavior. Further, in vitro release was performed in the dissolution media with rat caecal contents. Results indicated an enhanced release when compared to formulations studied in dissolution media without rat caecal contents, because of microbial degradation or polymer solubilization. The nature of drug transport was found to be non-Fickian in case of uncoated formulations, whereas for the coated formulations, it was found to be super-Case-II. Statistical analyses of release data indicated that MTZ release is significantly affected by the nature of the polysaccharide used and enteric coating of the tablet. Differential scanning calorimetry indicated the presence of crystalline nature of drug in the formulations.     

Preparation and formation mechanism of nano-sized MnOx-CeO2 hollow spheres via a supercritical anti-solvent technique

Manganese and cerium composite oxide (MnO_x-CeO₂) hollow nanospheres were successfully prepared by precipitating manganese acetylacetonate and cerium acetylacetonate from their mixed methanol solution using supercritical carbon dioxide as an anti-solvent. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) were employed to characterize the precursor and as-prepared MnO_x-CeO₂. XRD analysis reveals the cubic fluorite structure of the MnO_x-CeO₂. HRTEM results indicate that the MnO_x-CeO₂ hollow spheres have an average diameter of about 50 nm, and a wall thickness of 10-20 nm. A new formation mechanism of these nano-sized hollow spheres has also been proposed based on the experimental results.     

Effects of guar gum content on structure and properties of multi-crosslinked polyurethane composite films

Films from multi-crosslinked polyurethane with different contents of guar gum (1–10 wt%) were prepared through a solution-casting method, followed by a thermal treatment or natural light exposure crosslinking procedure. Acrylic terminated prepolymers were prepared by capping the NCO groups of polyurethane prepolymers with pentaerythritol triacrylate. The effect of the guar gum content on the miscibility, morphology and physical properties of the blend films was investigated by Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, surface properties and tensile tests. The results reveal that small guar gum content is well embedded in the crosslinked polyurethane network and forms films with good mechanical properties, thermal behavior and hydrophilic properties. These results prove guar gum to be eco-friendly filler for multi-crosslinked polyurethane network. In the case of polyether urethanes, incorporating up to 3 wt% guar gum leads to a slight enhancement of the elongation at break, while for polyester urethanes incorporation up to 3 wt% guar gum slight increases stress at break values. Incorporating guar gum into the polyurethane networks leads to an increase in the hydrophilic nature of the polymer blends and improved surface structure. The properties of guar gum – which can be abundantly found in nature – make it desirable for polymer blends for biomedical applications.     

Y-TZP悬浮液的界面吸附特性

本文利用聚电解质分散剂聚丙烯酸铵（ＮＨ_４ＰＡＡ）制备了稳定的Ｙ－ＴＺＰ悬浮液．通过等温吸附实验和电动特性测定发现,分散剂浓度为２ｗｔ％时,在粉体颗粒表面的吸附达饱和,悬浮液的等电点（ＩＥＰ）向酸性区移动．扫描俄歇能谱（ＳＡＭ）分析和原子力显微镜（ＡＦＭ）研究表明,粉体的表面化学键结构因分散剂的吸附而改变,悬浮颗粒之间的相互排斥能增大．悬浮液的粘度在分散剂饱和吸附时达到最小值,浆料的悬浮稳定性得到了提高.     

Film formation mechanism in glass lubrication by polymer latex dispersions

The stabilization of organic coatings by tin dioxide resulting in glass bottle lubrication was investigated on flat glass. The anchoring function of SnO₂ was assessed for a mixture of polyethylene and polymethylmethacrylate. Friction tests in air confirm the SnO₂ anchoring property with the maintaining of the lubricant effect due to the polymer over large sliding distances. The persistence of the polymethylmethacrylate stretching band ν_C = O on significant sliding distances in infrared microscopy experiments shows that the polymer coating stabilization results from the strong adhesion of the polymer on SnO₂. The impact of roughness and surface chemistry on the stabilization of the polymer coating was tested. The suppression of the lubricant effect by surface chemistry alteration or by roughness modification of SnO₂ suggests that roughness and surface chemistry of SnO₂ are both necessary for lubrication.     

Investigation of the stability of an alumina suspension in the presence of ionic polyacrylamide

The influence of solution pH on the adsorption mechanism of polyacrylamide (PAM) on the alumina surface and stability of its suspension in the presence of polymer were investigated. The structure of polymer adsorption layer was determined from the spectrophotometric, viscosity, surface charge and zeta potential measurements which enable determination of adsorbed amount of polymer, thickness of the polymer adsorption layer, surface charge density and zeta potential of Al₂O₃ particles in the absence and presence of PAM. The measurements of stability of alumina suspension without and with adsorbed polyacrylamide were also carried out using two methods: spectrophotometry and turbidimetry. The obtained results indicate that solution pH influences the structure of PAM adsorption layer (decrease of adsorbed amounts of polymer and increase of its adsorption layer thickness with the increasing pH). These conformational changes of polyacrylamide molecules with the rising pH have an impact on stability of the alumina suspension. The most pronounced effect of polymer on the stabilization properties of investigated systems is observed for PAM addition at pH 6 resulting in a great destabilization of the alumina particles by bridging flocculation.     

Triggering High Capacity and Superior Reversibility of Manganese Oxides Cathode via Magnesium Modulation for Zn//MnO2 Batteries

Aqueous zinc-ion batteries (ZIBs) have attracted extensive attention in recent years because of its high volumetric energy density, the abundance of zinc resources, and safety. However, ZIBs still suffer from poor reversibility and sluggish kinetics derived from the unstable cathodic structure and the strong electrostatic interactions between bivalent Zn²⁺ and cathodes. Herein, magnesium doping into layered manganese dioxide (Mg–MnO₂) via a simple hydrothermal method as cathode materials for ZIBs is proposed. The interconnected nanoflakes of Mg–MnO₂ possess a larger specific surface area compared to pristine δ-MnO₂, providing more electroactive sites and boosting the capacity of batteries. The ion diffusion coefficients of Mg–MnO₂ can be enhanced due to the improved electrical conductivity by doped cations and oxygen vacancies in MnO₂ lattices. The assembled Zn//Mg–MnO₂ battery delivers a high specific capacity of 370 mAh g⁻¹ at a current density of 0.6 A g⁻¹. Furthermore, the reaction mechanism confirms that Zn²⁺ insertion occurred after a few cycles of activation reactions. Most important, the reversible redox reaction between Zn²⁺ and MnOOH is found after several charge–discharge processes, promoting capacity and stability. It believes that this systematic research enlightens the design of high-performance of ZIBs and facilitates the practical application of Zn//MnO₂ batteries.     

Effect of doping cobalt on the micro-morphology and electrochemical properties of birnessite MnO2

Birnessite-type MnO₂ nanoparticles are synthesized by mixing KMnO₄ solution directly with ethylene glycol under ambient conditions. When cobalt exists in the solution, the micro-morphology of the products transforms from conglomeration to dispersive state. The result of transmission electron microscopy (TEM) and field emission scanning electron microscopy (FE-SEM) shows that the product is constructed with nanosphere in sizes of ca. 40 nm. These nanospheres are twisted by nanorods clusters. X-ray diffraction (XRD) pattern shows that the products are birnessite-type. The electrochemical properties of the prepared materials are studied using cyclic voltammetry (CV) and galvanostatic charge–discharge test in aqueous electrolyte. The product shows a very high specific capacity of 326.4 F g⁻¹. These results indicate that cobalt has great effects on the micro-morphology and electrochemical properties of manganese dioxide.     

Chemical and Colloidal Dynamics of MnO2 Nanosheets in Biological Media Relevant for Nanosafety Assessment

Many layered crystal phases can be exfoliated or assembled into ultrathin 2D nanosheets with novel properties not achievable by particulate or fibrous nanoforms. Among these 2D materials are manganese dioxide (MnO₂) nanosheets, which have applications in batteries, catalysts, and biomedical probes. A novel feature of MnO₂ is its sensitivity to chemical reduction leading to dissolution and Mn²⁺ release. Biodissolution is critical for nanosafety assessment of 2D materials, but the timing and location of MnO₂ biodissolution in environmental or occupational exposure scenarios are poorly understood. This work investigates the chemical and colloidal dynamics of MnO₂ nanosheets in biological media for environmental and human health risk assessment. MnO₂ nanosheets are insoluble in most aqueous phases, but react with strong and weak reducing agents in biological fluid environments. In vitro, reductive dissolution can be slow enough in cell culture media for MnO₂ internalization by cells in the form of intact nanosheets, which localize in vacuoles, react to deplete intracellular glutathione, and induce cytotoxicity that is likely mediated by intracellular Mn²⁺ release. The results are used to classify MnO₂ nanosheets within a new hazard screening framework for 2D materials, and the implications of MnO₂ transformations for nanotoxicity testing and nanosafety assessment are discussed.