Low Temperature Synthesis of Zeolite Films on Glassy Carbon: Towards Designing Molecularly Selective Electrochemical Devices

Faujasite‐type zeolite films have been grown on glassy carbon electrode surfaces embedded in an epoxy resin matrix by a quasi ambient temperature hydrothermal synthesis. The resulting zeolite modified electrodes are mechanically stable and provide an advantageous combination of electrochemical detection with charge and size selectivities at the molecular level, as demonstrated with the aid of some model electroactive probes or analytes (Ru(NH₃)₆³⁺, Fe(CN)₆^3?, Ru(bpy)₃²⁺, dopamine, ascorbic acid). To act efficiently as a physical molecular sieve barrier between the electrode surface and the external solution, these films must have a thickness of about 0.7 μm. These results open the door for further development of molecular sieving electrochemistry.     

A Relative Method For The Determiniation Of The Adsorption Capacity Molecular Sieves

Abstract

A new method for the determination of the absorption capacity of molecular sieves is described. The method is based on the functional priniciple of the vacuum pump with molecular sieves. The principle of the method consists in that the pumpdown time for a vacuum (for example 10^?2 mm Hg) is inversely proportional to the adsorption capacity of molecular sieves. The method is relative since it requires a standard (a molecular sieve whose adsorption capacity is determined by a standard method). For the molecular sieves that must be studied it is sufficient to measure the pumpdown time of the same vacuum level obtained in the case of the standard molecular sieve. The adsorption capacity was obtained from a relation of the form: T_e/T_x = C_x/C_e.     

Carbon Molecular Sieve Membrane Preparation by Economical Coating and Pyrolysis of Porous Polymer Hollow Fibers

Dip coating and pyrolysis processes are used to create multi‐layer asymmetric carbon molecular sieve (CMS) hollow fiber membranes with excellent gas separation properties. Coating of an economical engineered support with a high‐performance polyimide to create precursor fibers with a dense skin layer reduces material cost by 25‐fold compared to monolithic precursors or ceramic supports. CMS permeation results with CO₂/CH₄ (50:50) mixed gas feed show attractive CO₂/CH₄ selectivity of 58.8 and CO₂ permeance of 310 GPU at 35 °C.     

Influence of Vapor Phase Pretreatments of Epoxy Surfaces on the Nucleation of MOCVD Copper Thin Films

Vapor phase pretreatments of epoxy composite material reinforced with carbon fibers were carried out prior to the growth of Cu thin films by metal-organic chemical vapor deposition (MOCVD) using Cu (hfa)(COD) as copper precursor. These dry surface oxidation processes include H₂O/UV, O₂/UV and O₂/Plasma treatments. Oxygen plasma method is the most efficient to oxidize the surface and it has the greatest effect to improve the wettability of epoxy samples. As a consequence, the higher hydrophilicity of the plasma-modified epoxy surface induces a higher nucleation density in the Cu film. Furthermore, this treatment reduces drastically the induction period observed for the growth of the metal. Even though the O₂/UV pretreatment incorporates almost the same amount of oxygen in the epoxy surface than the plasma treatment, the functional groups are different, as revealed by XPS analyses, and the surface is less hydrophilic. Correlations between oxidation, wettability and nucleation density of the Cu films are discussed.     

(MCM-41)-La_2O_3纳米复合材料的制备、表征及光学性质

借助水热法,以正硅酸乙酯为硅源,十六烷基三甲基溴化铵为模板剂,在碱性条件下制备了纳米MCM-41分子筛。通过固相热扩散法将La2O3组装到MCM-41介孔孔道中,制备出含La2O3不同浓度的(MCM-41)-La2O3主-客体纳米复合材料。采用化学分析、粉末XRD、FTIR、77K低温N2吸附-解吸附、固体扩散漫反射吸收光谱、拉曼光谱、扫描电镜和发光光谱对主-客体复合材料进行表征。粉末XRD结果表明,La2O3组装到MCM-41分子筛的孔道后并未破坏分子筛骨架,在所制备的(MCM-41)-La2O3主-客体纳米复合材料中MCM-41骨架结构仍然具有较高的有序性,并且,随着植入客体材料浓度的增加复合材料的有序度有所降低。红外光谱表明所制备的纳米复合材料主体分子筛骨架完好;低温氮气吸附-解吸附技术表明La2O3已经部分地占据了MCM-41分子筛孔道,导致分子筛的比表面积和孔体积都有所降低;固体扩散漫反射吸收光谱表明吸收光谱的吸收峰发生了蓝移现象,并表现出量子限域效应,说明La2O3已经组装到了MCM-41分子筛的孔道中;拉曼光谱表明所制备的复合材料没有出现新的特征峰,表明La2O3已经组装到了MCM-41分子筛的孔道中;扫描电镜表明(MCM-41)-La2O3样品的外观非常规整,主要呈现的是球状结构,La2O3含量为10%时,(MCM-41)-La2O3的平均粒径为(114±10)nm。发光光谱研究结果表明,所制备的复合材料(MCM-41)-La2O3样品在396nm处具有较好的发光性质,因而具有作为发光材料潜在应用前景。     

Synthesis, characterization and in vitro oxidative stability of poly(3,3,3-trifluoropropyl)methylsiloxane modified polyurethaneurea

A series of α,ω-bis(3-hydroxypropyl)-poly[(3,3,3-trifluoropropyl)methylsiloxane] (FPS) with different molecular weights were synthesized and characterized, then the FPS modified polyurethaneurea (FSPUU) elastomers were further synthesized with poly(tetramethylene glycol)/FPS as soft segments and 4,4′-diphenylmethane diisocyanate/ethylene diamine as hard segments. The surface properties of the FSPUU films were measured. It was found that the surface hydrophobicity of these FSPUU films was enhanced with increasing the molecular weight of FPS, due to the enrichment of FPS segments at the surface region. Oxidative stability of the FSPUU films was examined in vitro by immersing the films with 200 μm thickness in oxidative solution (H₂O₂/CoCl₂) for 21 days. The experimental results showed that the degree of degradation of all FSPUU films was lower than that of polydimethylsiloxane modified polyurethaneurea (MSPUU), and the oxidative stability of these FSPUU films was fair enhanced with increasing the molecular weight of FPS, which could be attributed to the lowering of swelling ratios in H₂O and 20% H₂O₂, as well as the permeation rate of H₂O in FSPUU films. Furthermore, the tensile strength of all FSPUU films is higher than that of MSPUU film.     

Alumina nanofibers obtained via electrospinning of pseudo-boehmite sol/PVP solution

Alumina nanofibers were fabricated by calcination of the polyvinylpyrrolidone (PVP)/pseudo-boehmite nanocomposite precursor fibers formed by electrospinning PVP/ethanol solution of dispersed pseudo-boehmite nanoparticles with and without additive of silica. The evolution of the phase, mechanical property and morphological features of the calcined fibers were studied and the effect of adding SiO₂ on the phase transformation of alumina was discussed. Adding SiO₂ can retard the phase transformation of γ-Al₂O₃ to α-Al₂O₃ and therefore inhibit the growth of alumina grains during calcination. Upon calcining the precursor fibers with 4 wt% SiO₂ additive at 1,300 °C, continuous alumina nanofibers with diameter ranging from 300 to 800 nm were obtained. These continuous nanofibers exhibited good flexibility and could be very promising for applications in filtration and catalyst support.     

Atomic Force Microscopic Studies of Porous TiO2 Thin Films Prepared by the Sol-Gel Method

Porous titanium dioxide thin films were prepared from alkoxide solutions with and without polyethylene glycol (PEG) by the sol-gel method on soda-lime glass. The effects of PEG addition to the precursor solution on the microstructure and roughness of the resultant thin films were investigated by atomic force microscopy (AFM). It was found that TiO₂ films prepared from the precursor solution without PEG had granular microstructure and flat texture, and was composed of about 100 nm spherical particles. With an increase in the times of coating cycles, the roughness of films decreased and the size of TiO₂ particles increased. On the other hand, the larger the amount and molecular weight of the added PEG in precursor solutions, the larger the diameter and the depth of pores in the resultant films on the decomposition of PEG during heat-treatment. The surface of the films was also rougher, and fewer pores were produced during heat-treatment. The mechanism of porous structure formation in the TiO₂ films was explained using the principle of spinodal phase separation.     

High‐Flux Carbon Molecular Sieve Membranes for Gas Separation

Carbon membranes have great potential for highly selective and cost‐efficient gas separation. Carbon is chemically stable and it is relative cheap. The controlled carbonization of a polymer coating on a porous ceramic support provides a 3D carbon material with molecular sieving permeation performance. The carbonization of the polymer blend gives turbostratic carbon domains of randomly stacked together sp² hybridized carbon sheets as well as sp³ hybridized amorphous carbon. In the evaluation of the carbon molecular sieve membrane, hydrogen could be separated from propane with a selectivity of 10 000 with a hydrogen permeance of 5 m³(STP)/(m²hbar). Furthermore, by a post‐synthesis oxidative treatment, the permeation fluxes are increased by widening the pores, and the molecular sieve carbon membrane is transformed from a molecular sieve carbon into a selective surface flow carbon membrane with adsorption controlled performance and becomes selective for carbon dioxide.     

High-Flux Carbon Molecular Sieve Membranes for Gas Separation

Carbon membranes have great potential for highly selective and cost-efficient gas separation. Carbon is chemically stable and it is relative cheap. The controlled carbonization of a polymer coating on a porous ceramic support provides a 3D carbon material with molecular sieving permeation performance. The carbonization of the polymer blend gives turbostratic carbon domains of randomly stacked together sp² hybridized carbon sheets as well as sp³ hybridized amorphous carbon. In the evaluation of the carbon molecular sieve membrane, hydrogen could be separated from propane with a selectivity of 10 000 with a hydrogen permeance of 5 m³(STP)/(m²hbar). Furthermore, by a post-synthesis oxidative treatment, the permeation fluxes are increased by widening the pores, and the molecular sieve carbon membrane is transformed from a molecular sieve carbon into a selective surface flow carbon membrane with adsorption controlled performance and becomes selective for carbon dioxide.     

NaY分子筛的改性及吸附脱氮性能

采用离子交换法用NH⁺₄、Zn²⁺、Cu²⁺、Cr³⁺阳离子改性NaY分子筛,并利用XRD、FT-IR和低温N₂吸附-脱附等方法对改性的分子筛进行了表征。XRD 和FT-IR表征结果表明,改性后的分子筛骨架完好。Cr改性Y分子筛(CrY)的比表面积、孔体积及平均孔径均较小,但存在部分介孔。研究了改性分子筛对含喹啉模拟燃料的吸附脱氮,喹啉分子尺寸的模拟结果为0.711 6 nm×0.500 2 nm,说明其并不易进入Y型分子筛0.74 nm的微孔。吸附脱氮结果表明,CrY的脱氮效果最好,CuY和ZnY次之,NH₄Y效果最差,改性分子筛的吸附脱氮性能与金属离子的价态有关,同价金属离子改性后的分子筛,吸附时间对其影响趋势相同,且金属离子价态越高,改性分子筛的吸附脱氮性能越好。吸附温度对CrY和NH₄Y分子筛吸附脱除喹啉的影响不大,可在室温下使用,但高温有利于CuY和ZnY吸附脱氮。XRD表征结果表明,焙烧后CrY分子筛骨架已完全塌陷失去了绝大部分吸附脱氮性能。     

TiO2/activated carbon fibers photocatalyst: Effects of coating procedures on the microstructure, adhesion property, and photocatalytic ability

In order to more easily separate TiO₂ photocatalyst from the treated wastewater, TiO₂ film was immobilized on the surface of activated carbon fibers (ACFs) by employing two kinds of coating procedures, dip-coating, and hydrothermal treatment. The effects of coating procedures on microstructure of TiO₂-coated ACFs (TiO₂/ACFs), such as morphology, porous property, crystal structure, and light absorption characteristics were investigated in detail. The adhesion property between TiO₂ film and ACFs was evaluated by ultrasonic vibration, and the photocatalytic activity of TiO₂/ACFs was tested by the photocatalytic decoloration of methylene blue solution. The results show that hydrothermal treatment presented many advantages to obtain high-performance TiO₂/ACFs photocatalyst in comparison with dip-coating. Hydrothermal treatment could improve the binding property between TiO₂ films and ACFs, which endowed the as-obtained TiO₂/ACFs photocatalyst with improved reusable performance, and TiO₂/ACFs synthesized by hydrothermal treatment presented higher photocatalytic activity.     

Variations in the Electrokinetic Potential of Magnesium Hydrosilicate Fibers upon Treatment with Ammonium Chloride

The effect of the treatment of magnesium hydrosilicate (Mg₃Si₂O₅(OH)₄) fibers with an aqueous 5% ammonium chloride solution at 37?40 and 57?60°C on their electrokinetic potential (ζ potential) is studied. The maximum time of exposure in the NH₄Cl solution was 100 min, while the ζ potential was measured every 20 min. It is shown that the treatment of the initial magnesium hydrosilicate fibers with the NH₄Cl solution leads to a reversal of their surface charge and a rise in the absolute value of the negative charge, which is explained by magnesium leaching out of the surface layer of the fibers. Washing of the treated fibers with distilled water leads again to the sign reversal of the ζ potential. Therewith, the character of the dependences of the fiber ζ potential on the time of the treatment with the 5% NH₄Cl solution at T = 37?40°C is the same before and after washing.     

Preparation and Photocatalytic Activity of TiO2 Films on Silica Glass Substrates by Assembly Technique

Nanostructured TiO₂ coating films on silica glass substrates were prepared by the assembly technique. TiO₂ colloids were synthesized employing the sol‐gel method using TiCl₄ as a precursor. The effect on the surface structures which was caused by the polyethylene glycol (PEG) added to the precursor solution and the photocatalytic activity were studied. The experimental results showed that the cobble‐like TiO₂ coating films were synthesized at 500 °C. On the surface of the samples, TiO₂ films exhibited uniform shape and a narrow size distribution. The result of proper PEG added to the precursor solution led to the decreasing of the size of TiO₂ particles and the increasing of the surface area of the samples. The photocatalytic activity of TiO₂ films with PEG was higher than that of samples without PEG.     

Polyoxyalkylated diethylenetriamine polymeric surfactants: molecular structure effect on thin wetting films

Thin wetting films from aqueous solution of four polyoxyalkylated diethylenetriamine (DETA) polymeric surfactants (named A, B, C, and D) are studied. Surfactants A, B, and C have a star-like structure differing only by the number of polymeric branches: four, six, and nine in the mentioned order while the forth one, D, is of a dendritic type with four to six primary and two to three secondary branches. The receding contact angles θ _r of the solution on hydrophilic SiO₂ glass surface and the contact angle θ _aq of a drop of doubly distilled water on SiO₂ glass surface pretreated with DETA polymeric surfactant solution are measured. The θ _r values on hydrophobicity of SiO₂ glass surface, respectively, increase in the following order: surfactant A, surfactant C, surfactant B, and surfactant D. The equilibrium thickness h _eq of wetting films from DETA aqueous solution on hydrophilic SiO₂ glass surface is measured using the micro-interferometric method. Results show an unexpected course of the h _eq vs. C _s curves with a maximum. Results from the studies indicate that differences in polymeric surfactant molecular structure affect the properties exhibited at air/liquid and solid/liquid interfaces, such as the value of surface tension, degree of hydrophobicity of solid surface, equilibrium film thickness, etc.     

Fine pore mouth structure of molecular sieve carbon with GCMC-assisted supercritical gas adsorption analysis

N₂ adsorption isotherms of molecular sieve carbon were measured at 77 K and 303 K. The Ar adsorption isotherms of molecular sieve carbon samples were also measured at 303 K. The grand canonical Monte Carlo (GCMC) simulation technique was applied to calculate the N₂ and Ar adsorption isotherms at 303 K using the ultramicropore volume determined by H₂O adsorption. The comparative method of experimental and simulated isotherms of supercritical N₂ and Ar at 303 K gave the width of the micropore mouth of the molecular sieve carbon, which can be applied to the ultramicropore width determination for other noncrystalline porous solids.     

Role of Organic Additives in the Sol-Gel Synthesis of Porous CaF2 Anti-Reflective Coatings

Porous CaF₂ anti-reflective coating films were prepared by the sol-gel method. Effects of organic additives on deposition and optical properties of the films were investigated. Amino alcohols (2-aminoethanol, 2-dimethylaminoethanol, and triethanolamine) and alcohols with larger molecular weights (ethyleneglycol, 2-methoxyethanol, cyclohexanol, and 2-(2-n-butoxyethoxy)ethanol) were chosen as the organic additives. Among these additives, cyclohexanol was the most effective to control the surface morphology and the optical properties of the films. By changing the amount of cyclohexanol in the coating solution, it was possible to control the optical thickness of the CaF₂ films. Accordingly, the wavelength giving the maximum transmittance could be changed in the UV region.     

锰氧八面体分子筛室温同时去除甲醛和臭氧的性能研究

通过回流法、无溶剂法及水热法合成了3种锰氧八面体分子筛催化剂（OMS-2）,并对其室温同时去除甲醛和臭氧的反应活性进行了研究.结果表明无溶剂法制备的锰氧八面体分子筛（OMS-2-S）具有最高的甲醛转化率,且水气的加入对3种OMS-2催化剂的二氧化碳产率均具有明显的促进作用.并通过XRD、SEM和XPS等技术对催化剂进行表征,考察了催化剂物理化学性质对其催化活性的影响.从表征结果可得,较强的吸附能力、丰富的氧空位及较强的氧物种移动性是OMS-2-S催化剂活性较高的原因.     

Preparation and Formation Mechanism of Porous TiO2 Films Using PEG and Alcohol Solvent as Double-Templates

Porous nanocrystalline TiO₂ anatase thin films have been synthesized on glass substrates via a sol-gel dip-coating method. The coating sol was obtained by suppressed hydrolysis of Ti(OC₄H₉)₄ through the addition of complexing molecules as stabilizers in an alcohol solution containing polyethylene glycol (PEG). Chemical changes taking place during the sol-gel process were discussed based on IR spectra analysis. A model concerning the pore formation was established to explain the role of PEG and solvent with core-shell configuration as double-templates. The structural characteristics of porous TiO₂ films were found to greatly depend on the concentration and molecular weight of PEG, the types of stabilizing agents and solvents. The pore size of the films was tunable in the range of 10–500 nm and their surface area varied from 51 to 72 m²·g^–1.     

Nanocomposites based on LaCoO3 and mesoporous molecular sieves: Preparation and physicochemical and catalytic properties

Individual perovskite-like LaCoO₃ obtained by the citrate method and LaCoO₃ supported onto the mesoporous molecular sieve MSM-41 have been characterized by X-ray powder diffraction, EPMA, low-temperature nitrogen adsorption, H₂ TPR, and EXAFS. The catalytic activity of the supported cobaltate in methanol oxidation is two orders of magnitude higher than the activity of the bulk cobaltate owing to nanosized LaCoO₃ particles in the pores of the molecular sieve.