2D Zeolite Coatings: Langmuir–Schaefer Deposition of 3 nm Thick MFI Zeolite Nanosheets

Stable suspensions of zeolite nanosheets (3 nm thick MFI layers) were prepared in ethanol following acid treatment, which partially removed the associated organic structure‐directing agent. Nanosheets from these suspensions could then be dispersed at the air–water interface and transferred to silicon wafers using Langmuir–Schaefer deposition. Using layer‐by‐layer deposition, control on coating thickness was demonstrated. In‐plane X‐ray diffraction (XRD) revealed that the deposited nanosheets contract upon calcination similar to bulk MFI crystals. Different methods for secondary growth resulted in preferentially oriented thin films of MFI, which had sub‐12‐nm thickness in certain cases. Upon calcination, there was no contraction detectable by in‐plane XRD, indicating well‐intergrown MFI films that are strongly attached to the substrate.     

Synthesis of highly ordered mesoporous alumina thin films and their framework crystallization to γ-alumina phase

Here we report the preparation of highly ordered mesoporous alumina films existing both as P6(3)/mmc and Fm-3m mesostructures by using triblock copolymer Pluronic P123 as the structure-directing agent. 2D grazing-incidence small-angle X-ray scattering (GI-SAXS) completely proves the existence of two different mesopore structures (i.e., [001]-oriented P6(3)/mmc and [111]-oriented Fm-3m symmetries). After calcination at 1000 °C, the amorphous alumina framework is successfully converted to γ-alumina crystals. During the crystallization process, large uniaxial shrinkage occurs along the direction perpendicular to the substrate with the retention of horizontal mesoscale periodicity, thereby resulting in formation of partially vertical mesoporosity in the film. Through detailed electron microscopic study, we discuss the formation mechanism for the vertical mesoporosity upon calcination. The obtained mesoporous γ-alumina film shows high thermal stability up to 1000 °C, which is highly useful in wide research areas such as catalyst supports and separators.     

薄片状MFI晶体无凝胶蒸汽辅助晶化制备b轴取向沸石膜

采用新型薄片状MFI沸石晶体作为晶种,通过无凝胶蒸汽辅助晶化法(gel-less steam-assisted crystallization,GLSAC)在烧结氧化硅多孔载体上制备了致密平整、b轴取向的MFI沸石膜。考察了GLSAC中模板剂浓度、釜底水量、生长温度及时间对MFI沸石膜的影响。扫描电子显微镜和X射线衍射结果显示,适量的模板剂和釡底水量能抑制晶种的面外生长。成功制备了厚度750 nm、致密平整的MFI沸石膜。制备的对丁烷异构体气体分离测试表明,25℃时,等物质的量的丁烷异构体的分离因子(SF_A/B)可达36,对正丁烷的渗透速率为1.5×10^-7mol·m^-2·s^-1·Pa^-1。     

Single‐Mode Microwave Heating‐Induced Concurrent Out‐of‐Plane Twin Growth Suppression and In‐Plane Epitaxial Growth Promotion of b‐Oriented MFI Film under Mild Reaction Conditions

In this study, single‐mode microwave heating was applied in epitaxial growth of b‐oriented MFI seed monolayer prepared by facile manual assembly, resulting in the formation of well‐intergrown and highly b‐oriented MFI film with few twins. It exhibited a precise molecular sieving property at a reaction temperature no higher than 100 °C within 2 hours, therefore making it possible for easy operation in an open environment. The capability for concurrent suppression of undesired out‐of‐plane twin growth and promotion of in‐plane epitaxial growth rate under mild reaction conditions was attributed to the obvious superiority of single‐mode microwave heating in comparison with conventional multi‐mode microwave heating in aspects of microwave field uniformity and intensity. Our research indicated that the single‐mode microwave heating technique could potentially be a useful tool for improving the microstructure and therefore the performance of diverse zeolite films.     

Functionalisation of the template-free and template-structured silica films synthesised on glass substrates by sol–gel technique

Possibility of the post-synthesis functionalisation of the template-free and template-structured silica films of ca. 200 nm thickness on glass slides was evaluated. The films were prepared by dip-coating from TEOS sol–gel precursor in the absence or presence of CTAB template. It has been found out that the template-structured silica films can be functionalised with Ag nanoparticles via [Ag(NH₃)₂]NO₃ ion-exchange or with adsorbed Methylene Blue (MB) cationic dye due to the presence of the well-organised mesopores after template removal. In contrast, only the external geometric surface of the template-free silica films appeared to be accessible for modifier molecules. Possibility of functionalisation of the multi-layered template-structured silica film depends on the sequence of dip-coating and calcination steps upon their preparation. When preparation includes reiteration of dip-coating and calcination steps, only the latest top silica film appears to be accessible to modifier molecules. When preparation includes successive dip-coating cycles accomplished by calcination of the final multi-layered film, all pores appear to be accessible since their formation occurs via simultaneous removal of the template molecules over the whole thickness of the multi-layered template-structured silica film.     

Facile Preparation of Hydrophobic Colloidal MFI and CHA Crystals and Oriented Ultrathin Films

We report novel routes for synthesis of defect‐free, hydrophobic and monodispersed 10 nm (5 unit cells) thick MFI crystals and 100 nm CHA crystals. The crystals are obtained in high yield and display very high 1‐butanol adsorption from aqueous solution. These crystals are assembled in monolayers for the growth of ultrathin and uniformly oriented films with thicknesses of 36 nm and 330 nm, respectively, using a synthesis gel in the form of a powder. This method is very simple and may open up for industrial preparation of materials with improved performances.     

Synthesis of submicron polycrystalline MFI zeolite films on porous ceramic supports

This paper reports preparation and properties of ultra-thin MFI-type zeolite (silicalite) films on sol–gel derived mesoporous 8 mol% yttria doped zirconia (YZ) supports by the in situ synthesis method. Only non-continuous zeolite films were obtained on the as-synthesized YZ supports (calcined at 450°C). Continuous polycrystalline pure silicalite films, with a thickness of 0.5–0.7 μm, could be grown on the YZ supports pretreated at 700°C. The difference in the oxygen vacancy defect concentrations in these two types of YZ supports is suggested to explain the different results of growing silicalite films. Moreover, defect free 2–3 μm thick silicalite films were also prepared on the α-alumina supports under the same synthesis conditions. The silicalite layer on the YZ support offers a significantly lower mass transfer resistance as compared to that on the alumina support. Single gas permeation data of hydrogen, methane and ethane through these membranes were measured and compared with those of silicalite membranes prepared by other groups. The alumina supported silicalite membranes prepared in this work show better separation factors than the literature values. The zeolite film on the YZ support is less resistant to the stress induced in the step of template removal as compared to the zeolite film on the alumina support.     

Effects of substrate constraint on crack pattern formation in thin films of colloidal polystyrene particles

Crack formation and the evolution of stress in drying films of colloidal particles were studied using optical microscopy and a modified cantilever deflection technique, respectively. Drying experiments were performed using polystyrene particles with diameters of 47 ± 10 nm, 100 ± 16 nm, and 274 ± 44 nm that were suspended in water. As the films dried, cracks with a well-defined spacing were observed to form. The crack spacing was found to be independent of the particle size used, but to increase with the film thickness. The characteristic crack spacing was found to vary between 20 and 300 μm for films with thickness values in the range 3-70 μm. Cantilever deflection measurements revealed that the stresses that develop in the film increase with decreasing film thickness (increasing surface-to-volume ratio). The latter observation was interpreted in terms of the effects of a substrate constraint which causes the build up of stresses in the films. This interpretation was confirmed by crack formation experiments that were performed on liquid mercury surfaces in which removal of the substrate constraint prevented crack formation. Experiments were also performed on compliant elastomer surfaces in which the level of constraint was varied by changing the substrate modulus. The cracking length scale was found to increase with decreasing substrate modulus. A simple theory was also developed to describe the substrate modulus dependence of the cracking length scale. These combined experiments and theory provide convincing evidence that substrate constraints are an important factor in driving crack formation in thin colloidal films.     

Basic aluminium succinate: An alumina precursor formed by precipitation from homogeneous solution

Precipitation from a homogeneous solution of aluminium nitrate by neutralisation using urea in presence of succinic acid leads to the formation of a well-defined alumina precursor, basic aluminium succinate, which on calcination yields microspheroidal γ-alumina with excellent free-flowing characteristics.     

Do directional primary and secondary crack patterns in thin films of maghemite nanocrystals follow a universal scaling law?

Cracks due to a shrinking film restricted by adhesion to a surface are observed in nature at various length scales ranging from tiny crack segments in nanoparticle films to enormous domains observed in the earth's crust. Here, we study the formation of cracks in magnetic films made of maghemite (gamma-Fe2O3) nanocrystals. The cracks are oriented by an external magnetic field applied during the drying process which presents a new method to produce directional crack patterns. It is shown that directional and isotropic crack patterns follow the same universal scaling law with the film height varying from micrometer to centimeter scales. Former experimental studies of scaling laws were limited to small variations in height (1 order of magnitude). The large variation in height in our experiments becomes possible due to the combined use of nanocrystals and electron microscopy. A simple two-dimensional computer model for elastic fracture leads to structural and scaling behaviors, which match those observed in the experiments.     

Hierarchical Mesoporous Metal–Organic Frameworks for Enhanced CO2 Capture

Hierarchical porous materials are promising for catalyst, separation and sorption applications. A ligand‐assisted etching process is developed for template‐free synthesis of hierarchical mesoporous MOFs as single crystals and well‐intergrown membranes at 40 °C. At 223 K, the hierarchical porous structures significantly improve the CO₂ capture capacity of HKUST‐1 by more than 44 % at pressures up to 20 kPa and 13 % at 100 kPa. Even at 323 K, the enhancement of CO₂ uptake is above 25 % at pressures up to 20 kPa and 7 % at 100 kPa. The mesoporous structures not only enhance the CO₂ uptake capacity but also improve the diffusion and mass transportation of CO₂. Similarly, well‐intergrown mesoporous HKUST‐1 membranes are synthesized, which hold the potential for film‐like porous devices. Mesoporous MOF‐5 crystals are also obtained by a similar ligand‐assisted etching process. This may provide a facile way to prepare hierarchical porous MOF single crystals and membranes for wide‐ranging applications.     

Nanostructure Analysis of Anodic Films Formed on Aluminum-Focusing on the Effects of Electric Field Strength and Electrolyte Anions

In this review, the research conducted by the authors on anodic oxide films on aluminum is described, paying particular attention to how the electric field strength, as a factor other than voltage, controls the nanostructures and properties of the films. It will also be indicated what factors contribute to the formation of defects, which, in contrast to the ideal or model film structure, contains a significant number of defects in the film. In addition to electrochemical measurements, the films were examined with a variety of advanced instruments, including electron microscopes, to confirm the “reality of film nanostructure” from a slightly different angle than the conventional view. The following topics on anodic films formed in four types of major anodizing electrolytes are discussed: pore initiation process, steady-state porous structure, sealing mechanism, the relationship between cell parameters and voltage/electric field strength, amount and depth of anion incorporation, electrolyte types, radial branching of pores, atypical pore structures, defect formation mechanism, self-ordering, Al coordination number, and the creation of α-alumina membranes.     

TEM investigation of formation mechanism of monocrystal-thick b-oriented pure silica zeolite MFI film

The first direct transmission electron microscopic (TEM) observation has been carried out on the continuous monocrystal-thick b-oriented pure silica zeolite MFI films produced by in situ crystallization. The self-supporting film samples for TEM study were fabricated by dissolving the steel substrate with acid. This TEM study is free of those artifacts that are typically associated with TEM sample preparations, and allows us to investigate the "true" structure and texture of a very large area of the film and at the same time to focus at will on each individual zeolite crystal in the film. Abundant TEM information including crystallographic orientation relationships among crystals in the film (both out-of-plane and in-plane), grain boundaries, and each crystal grain was obtained. This TEM investigation provides direct unambiguous new evidence to support the homogeneous nucleation mechanism, by which the films form through homogeneous nucleation and crystal growth in the bulk to form equal-sized disk-shape crystals, followed by self-assembly of these crystals onto the substrate to produce a two-dimensional close-packed structure. The last stage of the film formation involves simultaneous space-limited growth and rotation of the individual crystals to realize the in-plane crystallographic control within the film.     

Formation of thin calcium carbonate films with aragonite and vaterite forms coexisting with polyacrylic acids and chitosan membranes

CaCO3 crystallization on a chitosan membrane was studied using diffusion of (NH4)2CO3 vapors into a CaCl2 solution containing differing added amounts of two polyacrylic acids (PAAs) with molecular weights of ca. 2.0 x 10(3) and ca. 4.5 x 10(4). The coexistence of PAA and the chitosan membranes produced thin CaCO3 island crystals, which developed into a continuous CaCO3 film on the membranes. Continuous CaCO3 films consisting of only aragonite formed on the chitosan membranes at the optimum amount of PAA. When the amount of PAA is not optimum, the polymorph of CaCO3 switches from aragonite to vaterite, and the morphology has a tendency to become an isolated island structure. The formation of the aragonite and vaterite island crystals and the appearance of a range of added PAA suitable for their formation are explained by the action of two parallel phenomena: (a) the high concentration of Ca2+ ions in the chitosan membrane vicinity is achieved by the interaction between the -COO- groups of PAA adsorbed by the -NH3+ groups of the chitosan membrane through an electrostatic force and free Ca2+ ions in the CaCl2 solution, which produces the high supersaturation with CaCO3 in the membrane vicinity during CO2 diffusion; (b) PAA, remaining as mobile carboxylic anions in the CaCO3 solution, inhibits the growth of the CaCO3 island crystals by its adsorption. The CaCO3 supersaturation in the membrane vicinity is controlled by regulating the balance of these phenomena, which leads to the formation of the desired CaCO3 polymorph.     

聚(ε-己内酯)薄膜结晶形貌及分子取向研究

用匀胶机通过溶液铸膜方法在硅片和铝箔基板上分别制备具有不同厚度的聚(ε-己内酯)(PCL)薄膜. 通过原子力显微镜(AFM)和偏光衰减全反射傅里叶红外光谱(ATR-FTIR)对薄膜中PCL的结晶形貌、 片晶生长方式及分子链取向进行了研究. AFM结果表明, 在200 nm或更厚的薄膜中, PCL主要以侧立(edge-on)片晶的方式生长; 对于厚度小于200 nm的薄膜, PCL片晶更倾向于以平躺(flat-on)的方式生长. 这种片晶生长方式的改变在硅片和铝箔基板上都表现出同样的倾向. 此外, 在15 nm或更薄的薄膜中, PCL结晶由通常的球晶结构变为树枝状晶体. 偏光ATR-FTIR结果表明, 当膜厚小于200 nm时, 薄膜结晶中PCL分子链沿垂直于基板表面方向取向, 并且膜越薄, 取向程度越高, 与AFM的观测结果一致.     

Effect of Ion Energy on Structure and Composition of Cathodic Arc Deposited Alumina Thin Films

The effect of energy supplied to the growing alumina film on the composition and structure has been investigated by varying substrate temperature and substrate bias potential. The constitution and composition were studied by X-ray diffraction and elastic recoil detection analysis, respectively. Increasing the substrate bias potential from −50 to −100 V caused the amorphous or weakly crystalline films to evolve into stoichiometric, crystalline films with a mixture of the α- and γ-phase above 700 ^oC, and γ-phase dominated films at temperatures as low as 200 ^oC. All films had a grain size of <10 nm. The combined constitution and grain size data is consistent with previous work stating that γ-alumina is thermodynamically stable at grain sizes <12 nm [McHale et al., Science 277, 788 (1997)]. In order to correlate phase formation with synthesis conditions, the plasma chemistry and ion energy distributions were measured at synthesis conditions. These results indicate that for a substrate bias potential of −50 V, ion energies in excess of 100 eV are attained, both from a high energy tail and the accelerated ions with charge >1. These results are of importance for an increased understanding of the evolution of film composition and microstructure, also providing a pathway to γ-alumina growth at temperatures as low as 200 ^o C.     

Effect of sol-gel preparation method on particle morphology in pure and nanocomposite PZT thin films

Double-scale composite lead zirconate titanate Pb(Zr_0.52Ti_0.48)O₃ (PZT) thin films of 360 nm thickness were prepared by a modified composite sol-gel method. PZT films were deposited from both the pure sol and the composite suspension on Pt/Al₂O₃ substrates by the spin-coating method and were sintered at 650°C. The composite suspension formed after ultrasonic mixing of the PZT nanopowder and PZT sol at the powder/sol mass concentration 0.5 g mL⁻¹. PZT nanopowder (≈ 40–70 nm) was prepared using the conventional sol-gel method and calcination at 500°C. Pure PZT sol was prepared by a modified sol-gel method using a propan-1-ol/propane-1,2-diol mixture as a stabilizing solution. X-ray diffraction (XRD) analysis indicated that the thin films possess a single perovskite phase after their sintering at 650°C. The results of scanning electron microscope (SEM), energy-dispersive X-ray (EDX), atomic force microscopy (AFM), and transmission electron microscopy (TEM) analyses confirmed that the roughness of double-scale composite PZT films (≈ 17 nm) was significantly lower than that of PZT films prepared from pure sol (≈ 40 nm). The composite film consisted of nanosized PZT powder uniformly dispersed in the PZT matrix. In the surface micrograph of the film derived from sol, large round perovskite particles (≈ 100 nm) composed of small spherical individual nanoparticles (≈ 60 nm) were observed. The composite PZT film had a higher crystallinity degree and smoother surface morphology with necklace clusters of nanopowder particles in the sol-gel matrix compared to the pure PZT film. Microstructure of the composite PZT film can be characterized by a bimodal particle size distribution containing spherical perovskite particles from added PZT nanopowder and round perovskite particles from the sol-matrix, (≈ 30–50 nm and ≈ 100–120 nm), respectively. Effect of the PZT film preparation method on the morphology of pure and composite PZT thin films deposited on Pt/Al₂O₃ substrates was evaluated.     

Effect of calcination temperature on the microstructure of porous TiO<Subscript>2</Subscript> film

To obtain porous TiO₂ film, the precursor sol was prepared by hydrolysis of Ti isopropoxide and then complexed with trehalose dihydrate. The porous TiO₂ film was fabricated by the dip-coating technique on glass substrates using this solution. The TiO₂ film was calcined at 500 °C. The maximum thickness of the film from one-run dip-coating was ca. 740 nm. The film was composed of nanosized particle and pores. The porosity of the TiO₂ film was increased by addition of trehalose dihydrate to the sol. The porous TiO₂ films were calcined at different temperatures. The effects of calcination temperature on the microstructure of the porous TiO₂ film were investigated. The porous film prepared from sol containing trehalose still kept the porous structure after calcination at 950 °C. The phase transition temperature of the film from anatase to rutile was shifted from 650 to 700 °C by addition of trehalose to the sol.     

Electrocatalytic oxidation of nitric oxide at TiO2–Au nanocomposite film electrodes

Structured films of TiO₂ (anatase) nanoparticles (ca. 6 nm diameter) and gold nanoparticles (nominal 20 nm diameter) are formed via a layer-by-layer deposition procedure. TiO₂ nanoparticles are deposited with a Nafion polyelectrolyte binder followed by calcination to give a mesoporous thin film electrode. Gold nanoparticles are incorporated into this film employing a poly(diallyldimethylammonium chloride) polyelectrolyte binder followed by calcination to give a stable mesoporous TiO₂–gold nanocomposite. This methodology allows well-defined and structured films to be formed which are re-usable after a 500 °C heat treatment in air.Electrochemical experiments are performed in aqueous KCl and buffer solutions and for the oxidation of nitric oxide, NO, and nitrite in phosphate buffer solution. It is shown that the NO oxidation occurs as a highly effective electrocatalytically amplified process at the surface of the gold nanocomposite probably with co-evolution of oxygen, O₂. In contrast, the oxidation of nitrite to nitrate occurs at the same potential but without oxygen evolution. A mechanistic scheme for the amplified NO detection process is proposed.     

Sputtered,electroless, and rolled palladium–ceramic membranes

Three techniques were used to produce palladium–ceramic (Pd–ceramic) composite membranes for hydrogen separation and production. They are sputtering, electroless deposition and rolling of thin Pd alloy films over ceramic porous tubes.After studying and developing the three coating techniques, an extensive testing and characterizing work was carried out on these thin film composite membranes. The results show that in the sputtered (0.5–5 μm) and electroless (2.5–20 μm) composite membranes, the thermal cycling of the hydrogenated metallic layer produces membrane failures. Such failures are characterized by crack formation and metal film peeling. This fact has been explained by an evaluation of the shear stresses at the metal–ceramic interface due to the differential elongation between the palladium (Pd) coating and the ceramic support under thermal cycling and hydrogen loading. The rolled membranes (50–70 μm), however, because of the particular coating solution, have shown a complete hydrogen selectivity and good chemical and physical stability in long-term tests.