Methane non-oxidative aromatization on Mo/ZSM-5: Effect of adding triethoxyphenylsilanes into the synthesis system of ZSM-5

A series of ZSM-5 zeolites were synthesized by adding triethoxyphenylsilane (PTEOS) into the initial sol of the synthesis system. The samples were studied by XRD, SEM, N₂ adsorption-desorption and acid assessment of d₃-acetonitrile adsorption. Characterization results showed that the crystal size of the ZSM-5 zeolites could be adjusted in a certain range by introducing different contents of PTEOS. Besides, the resultant materials possess hierarchical porosity in addition to those micropores generated by the MFI channels. Moreover, supported Mo/ZSM-5 catalysts were prepared, and their catalytic performances were investigated in the methane non-oxidative aromatization. It was found that the Mo/ZSM-5 catalyst, bearing suitable crystal size and mesoporous characteristic showed relatively high shape-selectivity to benzene and high stability for the reaction of methane aromatization.     

Key factor affecting the structural and textural properties of ZSM-5/MCM-41 composite

ZSM-5/MCM-41 micro/mesoporous composite materials were synthesized by the hydrothermal technique with alkali-treated ZSM-5 zeolite as source of silica and aluminum and characterized by various physico-chemical techniques such as X-ray diffraction (XRD), nitrogen sorption at 77 K, transmission electronic microscopy (TEM), FTIR spectroscopy and NH₃ temperature programmed desorption (TPD) techniques. The effect of concentration of CTAB in the synthesis of these solids has been investigated, the mesopore volume, surface area and surface acidity decrease with increasing the concentration of CTAB. Increasing the CTAB concentration causes the recrystallization of zeolite ZSM-5 and it disadvantage the formation of mesoporous materials MCM-41. The catalytic activity of ZSM-5/MCM-41 materials has been evaluated in the Friedel–Crafts acylation of anisole with benzoyl chloride as alkylating agent. The results revealed the reaction to be influenced by surface area, pore volume and surface acidity.     

Physicochemical characteristics of ZSM-5/SAPO-34 composite catalyst for MTO reaction

SAPO-34 and ZSM-5 are the most well-known catalyst for MTO reaction. A combination of ZSM-5 and SAPO-34 might give rise to optimal catalyst to meet a change of market demand for ethylene, propylene and butadiene. In this study, we have developed ZSM-5/SAPO-34 composite catalysts to control the composition of light olefins in MTO reaction. ZSM-5/SAPO-34 composite catalysts showed very different physicochemical and catalytic properties with respect to ZSM-5 and SAPO-34 synthetic procedure. The physicochemical properties of the composite catalysts have been compared by XRD, SEM, N₂ isotherm, FT-IR and NH₃-TPD. Their catalytic performances were also evaluated for MTO reaction. The series composite catalyst synthesized by successive crystallization of SAPO-34 synthetic gel after ZSM-5 crystallization exhibited relatively high catalytic performance.     

The effect of solvent on the crystal structure and size distribution of cadmium sulfide nanocrystals

CdS nanocrystals with different structures were synthesized by the method of solution precipitation using thiourea and cadmium acetate as starting materials in different solvents: water, methanol and N,N-dimethylformamide (DMF). Our results show that the solvent has direct effect on the structure and size of the final nanoparticles. It was found that using DMF, as a solvent, results in producing smaller nanoparticles with the cubic structures, while using the other solvents gives rise to larger nanoparticles with the hexagonal structure. It was also found that using heat during washing the precipitate results in a more homogenous size distribution of CdS nanocrystals. On the basis of our experimental results we also suggest a critical structure transformation size.     

Bulk heterojunction organic photovoltaic cell fabricated by the electrospray deposition method using mixed organic solvent

A high‐efficiency bulk heterojunction organic photovoltaic cell (OPV) was achieved by the electrospray deposition method. The surface roughness of the P3HT:PCBM thin film can be reduced using the mixed solvent consisting of o‐dichlorobenzene (o‐DCB) and acetone. The effect of acetone concentration is related to its dielectric constant. Under an optimized concentration of acetone in o‐DCB (20 vol%), the P3HT/PCBM active layer with a smooth surface can be formed, and the power conversion efficiency of the OPV was 1.9%.

     

Transport properties of modified Nafion membranes: Effect of zeolite and precursors

Fe-silicalite/Nafion composite membranes with high relative selectivity (as defined by the proton conductivity to methanol permeability ratio) of 5.4 and proton conductivity of 11 mS cm^− 1 were prepared by in situ hydrothermal synthesis of the zeolite within the pores of Nafion membranes. The effects of the zeolite structure and precursor structure were evaluated in terms of transport properties and acidity levels for a series of Nafion membranes modified with silica and tetrapropylammonium (TPA) and tetrabutylammonium (TBA) cations. Introduction of up to 40% (w/w) of silica vs. pure Nafion shows little effect on the transport and acidity properties of the composite membranes. Introduction of tetraalkylammonium (TAA) cations reduces water uptake of the membranes, and results in the appearance of protons that are inaccessible for titration in water media. The selectivity of the composite membranes increases in the order: SiO₂/Nafion < TAA/Nafion < Fe-silicalite/Nafion.     

碳气凝胶薄片的制备及表面密度致密层去除工艺

研究了不同密度和厚度的碳气凝胶薄片的制备及其表面致密层去除工艺。在以间苯二酚、甲醛为原料制备有机及碳气凝胶块体材料的基础上,结合自制活动式微模具成型工艺,制备了厚度在80~350 μm,密度在50~600 mg·cm-3范围内变化的碳气凝胶薄片。采用场发射扫描电镜、X射线相衬成像和表面轮廓仪-台阶仪等手段对其表面和内部微观结构进行了表征。测试结果表明,碳气凝胶薄片与块体的内部结构相同,但薄片表面存在一层和内部结构截然不同的致密层。采用不同粗糙程度的材料对薄片进行了表面微处理,成功去除该致密“皮”层。     

Characterization and corrosion behavior of hydroxyapatite/zirconia composite coating on NiTi fabricated by electrochemical deposition

NiTi alloy is used as biomaterial due to its unique properties, but the high content of Ni (about 50 at.%) in biomedical NiTi is concerned. Hydroxyapatite and hydroxyapatite/zirconia composite coatings were directly electrodeposited on NiTi alloy surface. The coated samples were characterized using X-ray diffraction, scanning electron microscopy, infrared spectroscopy, bonding strength test, polarization and EIS. Results showed that when ZrO₂ was added into the electrolyte, morphology of HAP was changed from thin flake-flower-like crystals to needle-flower-like crystals, and coating was denser. Besides, HAP crystal grains in the coating were preferentially arranged in the [0 0 1] direction. Addition of ZrO₂ could improve the bonding strength between the coating and the substrate. Corrosion resistance of NiTi in the simulated body fluid at 37 °C was significantly improved by almost 60 times by electrodeposition of the hydroxyapatite/zirconia composite coating.     

One-dimensional photonic crystal fabricated by the photochemical etching of silicon

The formation of periodic wall arrays on an n-type (100) Si substrate with V-shaped seed grooves on the surface was investigated. The influence of silicon sidewall roughness on the optical properties of onedimensional (1D) of photonic crystals obtained on the basis of the arrays was studied. The reflection spectra of the 1D photonic crystals exhibit a high modulation level of up to 95% and photonic band gaps of a high order that are in good agreement with calculations over a wide spectral range (1.5—15 μm).     

PVDF–PEO/ZSM-5 based composite microporous polymer electrolyte with novel pore configuration and ionic conductivity

A novel composite microporous polymer electrolyte based on poly(vinylidene fluoride), poly(ethylene oxide), and microporous molecular sieves ZSM-5 (denoted as PVDF–PEO/ZSM-5) was prepared by a simple phase inversion technique. PEO can obviously improve the pore configuration, such as pore size, porosity, and pore connectivity of PVDF-based microporous membranes, results in a high room temperature ionic conductivity. Microporous molecular sieves ZSM-5 can further improve the mechanical strength of PVDF–PEO blends and form special conducting pathway in PVDF–PEO matrix by absorb liquid electrolyte in its two-dimensional interconnect channels. The high room temperature ionic conductivity combined with good mechanical strength implies that PVDF–PEO/ZSM-5 based composite microporous polymer electrolyte can be used as candidate electrolyte and/or separator material for high-performance rechargeable lithium batteries.     

Effect of particle size of graphites on electrical conductivity of graphite/polymer composite

The effect of particle size of graphite particles on the dispersion state of graphite particles and electrical conductivity of graphite/low-density polyethylene (LDPE) composites is investigated. Graphite particles which have plate-like and spherical shapes and mean particle sizes of 2.1 to 82.6 μm are used. Scanning electron microscopy observation showed that graphite particles are not aggregated and ordered along the direction of mixing-roll in the polymer matrix. X-ray diffraction measurements show that crystallite size of the (110) plane of polyethylene crystal and the crystallinity are significantly affected by the particle size of graphite particles. These results were interpreted as due to the orientation of PE crystallites. The electrical conductivity of composites changes discontinuously at the critical volume fraction of particles, Ø_c. The Ø_c values given by the percolation equation increase with decreasing of the particle size of graphites. The plate-like graphite particles with a mean particle size of 2.1 μm could induce conductivity at Ø_c of 0.135. The values of Ø_c increased linearly with increasing of the mean particle sizes of the plate-like graphites. The value of Ø_c of spherical graphite particle is the largest value, 0.292, in all specimens.     

Equilibrated thermodesorption studies of adsorption of n-hexane and n-heptane on zeolites Y, ZSM-5 and ZSM-11

Gravimetric measurements of thermodesorption of n-hexane and n-heptane were performed under quasi-equilibrium conditions. Differential thermodesorption profiles for ZSM-5 and ZSM-11 showed two peaks, but for Y zeolites, only one thermodesorption peak was observed. A model function, derived from the Langmiur adsorption model, was fitted to the experimental data, and the model parameters (the adsorption entropy and enthalpy) were estimated. The two-step desorption profiles observed for ZSM-5 and ZSM-11 were attributed to the commensurate freezing effect, i.e. a transition in the adsorbed phase resulting in ordering of the adsorbed molecules in the zeolite channels. The results observed for ZSM-11 indicate that the zigzag channels typical for ZSM-5 micropore system are not necessary for this transition to occur.     

Effect of Nafion dispersion solvent on the interfacial properties between the membrane and the electrode of a polymer electrolyte membrane-based fuel cell

A new Nafion binder solution was prepared using a different organic solvent, dimethylacetamide (DMAc), and applied to a polymer electrolyte membrane-based fuel cell. Wide angle X-ray diffraction (WAXD), electrochemical impedance spectroscopy (EIS), and polarization of the fuel cell were carried out to determine the crystallinity of the Nafion binder film, the cell resistance, and the fuel cell performance. This new Nafion binder film, which was created using a homemade Nafion solution containing DMAc, dissolved slower than a recast Nafion film that was made using a commercial Nafion solution in methanol (2 M). It was found that the slow dissolution of the homemade Nafion binder film was due to a more highly developed crystalline morphology, which can lead to good structural integrity in the catalyst layer for long-term operation of the fuel cell. The micellar structure of Nafion in the commercial Nafion binder solution is broken by new organic solvent, which leads to higher physical chain entanglement between the Nafion membrane and the Nafion binder during preparation of the membrane/electrode assembly (MEA), thereby improving the interfacial stability between the membrane and the electrode and providing long-term stability of the fuel cell.     

Mn／ZSM-5催化剂及其SCR催化性能研究

采用液态离子交换法制备了不同含量的Mn／ZSM-5型分子筛催化剂,并考察了上述催化剂的物理化学特性及其在NH3-SCR反应中的催化性能。理化分析结果表明：所制备催化剂在Mn含量≤9．2％时具有高度的分散性,分子筛表面团聚的氧化锰颗粒粒径小于4nm;锰元素主要富集于分子筛的浅层及表面。催化性能研究结果表明：Mn含量达到1...     

Effect of solvent type and concentration on size and morphology of arbidol microparticles obtained by supercritical antisolvent precipitation

The capability of arbidol microparticle preparation by supercritical antisolvent (SAS) precipitation was demonstrated. A nonmonotonic dependence of the average particle size on the concentration was found, while the position of the minimum is dependent on the type of solvent used. It is possible to prepare Arbidol particles of various morphology and size from several microns to several hundred microns depending on the conditions.     

界面自组装的金/氧化石墨烯复合材料的表面增强拉曼散射行为研究

采用Frens法制备金纳米粒子溶胶,通过界面自组装技术在掺磷的非晶碳衬底表面构筑三维的金/氧化石墨烯/金复合结构.以罗丹明B为探针分子,考察金/氧化石墨烯/金复合材料的表面增强拉曼散射活性.结果表明,由于氧化石墨烯的化学增强和金纳米粒子的电磁场增强的协同作用,在该三维复合材料上获得了很强的罗丹明B拉曼信号.所设计的三维金/氧化石墨烯/金复合材料在生物分析、环境监测、疾病防控、食品安全等领域具有潜在的应用价值.     

Effect of oxygen annealing on the photoresponse of PbSe thin films fabricated by the pulsed laser deposition method

In this work, we have fabricated lead selenide (PbSe) thin films by the pulsed laser deposition method on Si/SiO₂ substrates and investigated the effect of oxygen annealing (sensitization) in these films. The oxygen-sensitized films show high responsivity in the visible (VIS) and the near-infrared (NIR) region at room temperature without cooling. We also demonstrate the effective surface oxidation of PbSe thin films during the oxygen annealing process without treated with commonly used halogens that leads to a better photoresponse in these PbSe films.     

Effect of ice crystal shape and effective size on snow bidirectional reflectance

We tested the applicability of three rigorous radiative transfer computational approaches, namely, the discrete ordinates radiative transfer (DISORT) method, the adding–doubling approach, and an efficient computational technique based on Ambartsumian's nonlinear integral equation for computing the bidirectional reflectance of a semi-infinite layer. It was found that each of these three models, in a combination with the truncation of the forward peak of the bulk scattering phase functions of ice particles, can be used to simulate the bidirectional reflectance of a semi-infinite snow layer with appropriate accuracy. Furthermore, we investigate the sensitivity of the bidirectional reflectance of a homogeneous and optically infinite snow layer to ice crystal habit and effective particle size. It is shown that the bidirectional reflectance is not sensitive to the particle effective size in the visible spectrum. The sensitivity of the bidirectional reflectance in the near-infrared spectrum to the particle effective size increases with the increase of the incident wavelength. The sensitivity of the bidirectional reflectance to the effective particle size and shape is attributed fundamentally to the sensitivity of the single-scattering properties to particle size and shape. For a specific ice crystal habit, the truncated phase function used in the radiative transfer computations is not sensitive to particle effective size. Thus, the single-scattering albedo is primarily responsible for the sensitivity of the bidirectional reflectance to particle size, particularly, at a near-infrared wavelength.     

Morphologies of a spherical bimodal polyelectrolyte brush induced by polydispersity and solvent selectivity

It is commonly realized that polydispersity may significantly affect the surface modification properties of polymer brush systems. In light of this, we systematically study morphologies of bidisperse polyelectrolyte brush grafted onto a spherical nanocolloid in the presence of trivalent counterions using molecular dynamics simulations. Via varying polydispersity, grafting density, and solvent selectivity, the effects of electrostatic correlation and excluded volume are focused, and rich phase behaviors of binary mixed polyelectrolyte brush are predicted, including a variety of pinned-patch morphologies at low grafting density and micelle-like structures at high grafting density. To pinpoint the mechanism of surface structure formation, the shape factor of two species of polyelectrolyte chains and the pair correlation function between monomers from different polyelectrolyte ligands are analyzed carefully. Also, electrostatic correlations, manifested as the bridging through trivalent counterions, are examined by identifying four states of trivalent counterions. Our simulation results may be useful for designing smart stimuli-responsive materials based on mixed polyelectrolyte coated surfaces.     

Crystal characterization and optical spectroscopy of Eu~(3+)-doped CaGdAlO_4 single crystal fabricated by the floating zone method

A highly transparent Eu~(3+)-doped CaGdAlO_4(CGA) single crystal is grown by the floating zone method.The segregation coefficient,x ray diffraction,and x ray rocking curve are detected,and the results reveal that the single crystal is of high quality.The f –f transitions of Eu~(3+) in the host lattice are discussed.The ~5D_0–~7F_2 emission transition at 621 nm(red light) is dominant over the ~5D_0–~7F_1 emission transitions at 591 and 599 nm(orange light),agreeing well with the random crystal environment of Eu~(3+) ions in a CGA crystal.The decay time of Eu:~5D_0 is measured to be 1.02 ms.All the results show that the Eu:CGA crystal has good optical characterization and promises to be an excellent red-fluorescence material.