Mesoporous Titania Thin Film with Highly Ordered and Fully Accessible Vertical Pores and Crystalline Walls

We report the preparation of mesoporous titania thin films with the R m pore structure derived from the Im m self‐assembled ordering of the titania species and an EO₁₀₆PO₇₀EO₁₀₆ triblock copolymer. The films were spin‐cast and then aged at 18 °C at a relative humidity of 70 %, which led to the orientation of the Im m structure with the [111] direction perpendicular to the substrates. The [111] body‐diagonal channels became vertical channels upon calcination at 400 °C, thus leading to thin films with vertical channels. The pores are ordered over a large area of up to 1 μm². The titania films can be formed on various types of substrates. By using a titania film formed on a Pt‐coated Si wafer as a template, we produced by an electrochemical‐deposition technique arrays of gold nanowires, whose morphology suggests that most of the pores of the titania thin films are accessible. The pore structure of vertical channels is stable up to 600 °C, at which temperature the wall materials crystallize into anatase.     

纳米TiO2介孔薄膜的模板组装制备研究

以TiCl₄为无机前驱体、三嵌段高分子共聚物EO₂₀PO₇₀EO₂₀为模板剂，在非水条件下制备了有序的锐钛矿TiO₂纳米晶介孔薄膜。通过热重-差热（TG-DTA）分析、X射线衍射（XRD）分析、原子力显微观察（AFM）及N₂吸附-脱附等测试对样品进行了表征。结果表明，薄膜具有均一的大介孔孔径（～10 nm），其BET比表面积为150 m²·g^-1，薄膜较宽的无机壁厚显著提高了介孔结构的热稳定性。通过红外（IR）光谱分析考察了溶胶-凝胶过程中发生的物理化学变化。在对薄膜表面形貌进行AFM观察的基础上初步探讨了嵌段共聚物EO₂₀PO₇₀EO₂₀对薄膜孔结构形成的导向机理。     

Ordered Mesoporous Thin Films of Rutile TiO2 Nanocrystals Mixed with Amorphous Ta2O5

Ordered mesoporous thin films of composites of rutile TiO₂ nanocrystals with amorphous Ta₂O₅ are fabricated by evaporation‐induced self‐assembly followed by subsequent heat treatment beyond 780 °C. Incorporation of selected amounts of Ta₂O₅ (20 mol %) in the mesoporous TiO₂ film, together with the unique mesoporous structure itself, increased the onset of crystallization temperature which is high enough to ensure the crystallization of amorphous titania to rutile. The ordered mesoporous structure benefits from a block‐copolymer template, which stabilizes the mesostructure of the amorphous mixed oxides before crystallization. The surface and in‐depth composition analysis by X‐ray photoelectron spectroscopy suggests a homogeneous intermixing of the two oxides in the thin film. A detailed X‐ray absorption fine structure measurement on the composite film containing 20 mol % Ta₂O₅ and heated to 800 °C confirms the amorphous nature of the Ta₂O₅ phase. Photocatalytic activity evaluation suggests that the rutile nanocrystals in the synthesized ordered mesoporous thin film possess good ability to assist the photodegradation of rhodamine B in water under illumination by UV light.     

Effect of physical aging of poly(1‐trimethylsilyl‐1‐propyne) films synthesized with TaCl5 and NbCl5 on gas permeability,fractional free volume,and positron annihilation lifetime spectroscopy parameters

The effect of physical aging on the gas permeability, fractional free volume (FFV), and positron annihilation lifetime spectroscopy (PALS) parameters of dense, isotropic poly(1‐trimethylsilyl‐1‐propyne) (PTMSP) films synthesized with TaCl₅ and NbCl₅ was characterized. As‐cast films were soaked in methanol until an equilibrium amount of methanol was absorbed by the polymer. When the films were removed from methanol, film thickness initially decreased rapidly and was almost constant after 70 h in air for both catalysts. This timescale was much longer than the timescale for complete methanol desorption (ca. 5 h). From the film‐thickness data, the reduction in FFV with time was estimated. For samples prepared with either catalyst, the kinetics of FFV reduction were well‐described by a simple model based on the notion either that free‐volume elements diffuse to the surface of the polymer film and are subsequently eliminated from the sample or that lattice contraction controls polymer densification. Methane permeability decreased rapidly during the first 70 h, which was the same timescale for the thickness change. The decrease in methane permeability was smaller in films prepared with NbCl₅ than with TaCl₅. The logarithm of methane permeability decreased linearly as reciprocal FFV increased, in accordance with free‐volume theory. The PALS results indicate that the concentration of larger free‐volume elements (as indicated by the intensity I₄) decreased with aging time and that the other PALS parameters were not strongly influenced by aging. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1222–1239, 2000     

Study on the capacity of mesoporous alumina with different pore sizes absorb silane inhibitors

By modifying and optimizing the procedures, which were well described and understood for the synthesis of macroporous alumina, mesoporous alumina–based film has been successfully prepared, In this paper, the orderly mesoporous Al₂O₃ thin film was prepared by electrochemical workstation, and via supported N‐octyltriethoxysilane (NOS) coupling agent, corrosion inhibitors be loaded into the different pore sizes of mesoporous alumina films. The physicochemical properties of this thin inhibitors carrier film were characterized. Corrosion resistance of mesoporous alumina and honeycomb ceramic macroporous alumina were compared; the conclusion shows that mesoporous alumina film can be used as good corrosion inhibitors carrier and bring out a high‐efficiency inhibition result. Simultaneously, by compared with corrosion inhibition of different pore sizes (20‐50 nm) mesoporous alumina who absorbed NOS, and a general relationship between the different mesoporous alumina pore sizes and the adsorption capacity of NOS was obtained.     

Unexpected Molecular Weight Dependence to the Physical Aging of Thin Polystyrene Films Present at Ultra‐High Molecular Weights

The physical aging behavior, time‐dependent densification, of thin polystyrene (PS) films supported on silicon are investigated using ellipsometry for a large range of molecular weights (MWs) from M_w = 97 to 10,100 kg mol^?1. We report an unexpected MW dependence to the physical aging rate of h < 80‐nm thick films not present in bulk films, where samples made from ultra‐high MWs ≥ 6500 kg mol^?1 exhibit on average a 45% faster aging response at an aging temperature of 40 °C compared with equivalent films made from (merely) high MWs ≤ 3500 kg mol^?1. This MW‐dependent difference in physical aging response indicates that the breadth of the gradient in dynamics originating from the free surface in these thin films is diminished for films of ultra‐high MW PS. In contrast, measures of the film‐average glass transition temperature T _g(h) and effective average film density (molecular packing) show no corresponding change for the same range of film thicknesses, suggesting physical aging may be more sensitive to differences in dynamical gradients. These results contribute to growing literature reports signaling that chain connectivity and entropy play a subtle, but important role in how glassy dynamics are propagated from interfaces. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1224–1238     

Gas permeability and hydrocarbon solubility of poly[1‐phenyl‐2‐[p‐(triisopropylsilyl)phenyl]acetylene]

The effects of film thickness, physical aging, and methanol conditioning on the solubility and transport properties of glassy poly[1‐phenyl‐2‐[p‐(triisopropylsilyl) phenyl]acetylene] are reported at 35 °C. In general, the gas permeability coefficients are very high, and this polymer is more permeable to larger hydrocarbons (e.g., C₃H₈ and C₄H₁₀) than to light gases such as H₂. The gas permeability and solubility coefficients are higher in as‐cast, unaged films than in as‐cast films aged at ambient conditions and increase to a maximum in both unaged and aged as‐cast films after methanol conditioning. For example, the oxygen permeability of a 20‐μm‐thick as‐cast film is initially 100 barrer and decreases to 40 barrer after aging for 1 week at ambient conditions. After methanol treatment, the oxygen permeabilities of unaged and aged films increase to 430 and 460 barrer, respectively. Thicker as‐cast films have higher gas permeabilities than thinner as‐cast films. Propane and n‐butane sorption isotherms suggest significant changes in the nonequilibrium excess free volume in these glassy polymer films due to processing history. For example, the nonequilibrium excess free volume estimated from the sorption data is similar for as‐cast, unaged samples and methanol‐conditioned samples; it is 100% higher in methanol‐conditioned films than in aged, as‐cast films. The sensitivity of permeability to processing history may be due in large measure to the influence of processing history on nonequilibrium excess free volume and free volume distribution. The propane and n‐butane diffusion coefficients are also sensitive to film processing history, presumably because of the dependence of diffusivity on free volume and free volume distribution. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1474–1484, 2000     

Tuning the wall thickness and pore orientation in mesoporous titania films prepared with low-temperature aging

Porous titania thin films with well-ordered mesostructures are prepared by using Pluronic surfactant P123 as the pore template and aging the films in a high-humidity environment at −6 °C. These structures are stable enough to undergo calcination at 400 °C to generate nanocrystalline TiO₂ walls with retention of mesoporosity. Under the aging conditions used, the films have well-ordered mesostructures even with a molar ratio of P123 to titanium (R) as small as 0.006. Because the P123 micelle diameter remains constant across a range of compositions, the pore diameter also remains fixed but the wall thickness of the titania thin films increases as the P123 concentration decreases without decreasing the long-range order of the products. Furthermore, mesoporous titania thin films with hexagonal close-packed channels oriented perpendicular to the substrate can be obtained R values of 0.008–0.012 by sandwiching the as-prepared films between glass slides modified with crosslinked P123. Analysis of the mesophases obtained here indicates that a transition from films containing significant 2D hexagonal channels to 3D hexagonal structure occurs below P123/Ti = 0.008. This does not match the expected volume fraction for this transition based on the mesophases behavior of aqueous P123 at room temperature, suggesting that a more detailed model would be needed to predict mesostructure in titania films aged below the freezing point of water.     

Low‐Temperature Route to Crystalline Titania Network Structures in Thin Films

A low temperature route to crystalline titania nanostructures in thin films is presented. The synthesis is performed by the combination of sol‐gel processes, using a novel precursor for this kind of application, an ethylene glycol‐modified titanate (EGMT), and the structure templating by micro‐phase separation of a di‐block copolymer. Different temperatures around 100 °C are investigated. The nanostructure morphology is examined with scanning electron microscopy, whereas the crystal structure and thin film compositions are examined by scattering methods. Optoelectronic measurements reveal the band‐gap energies and sub‐band states of the titania films. An optimum titania thin film is created at temperatures not higher than 90 °C, regarding sponge‐like morphology with pore sizes of 25–30 nm, porosity of up to 71 % near the sample surface, and crystallinity of titania in the rutile phase. The low temperature during synthesis is of high importance for photovoltaic applications and renders the resulting titania films interesting for future energy solutions.     

Gold Nanoparticles Supported on Mesoporous Titania Thin Films with High Loading as a CO Oxidation Catalyst

In the present work, 2.4 nm gold nanoparticles (Au NPs) are uniformly dispersed on mesoporous titania thin films which are structurally tuned by controlling the calcination temperature. The gold content of the catalyst is as high as 27.8 wt %. To our knowledge, such a high loading of Au NPs with good dispersity has not been reported until now. Furthermore, the reaction rate of the gold particles is enhanced by one order of magnitude when supported on mesoporous titania compared to non‐porous titania. This significant improvement can be explained by an increase in the diffusivity of the substrate due to the presence of mesopores, the resistance to agglomeration, and improved oxygen activation.     

Room temperature synthesis of Ti-SBA-15 from silatrane and titanium-glycolate and its catalytic performance towards styrene epoxidation

A novel room temperature sol–gel synthesis of Ti-SBA-15 is described using moisture stable silatrane and titanium glycolate precursors, and poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymer (EO₂₀PO₇₀EO₂₀) as the structure directing agent. Catalyst performance was optimized by systematically investigating the influence of acidity, reaction time and temperature, and titanium loading. Small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) showed well-ordered 2D mesoporous hexagonal structures, while N₂ adsorption/desorption measurements yielded high surface areas (up to 670 m²/g), with large pore diameters (5.79 nm) and volumes (0.83 cm³/g). Diffuse reflectance UV–visible spectroscopy (DRUV) was found that tetravalent titanium as Ti⁴⁺O₄ tetrahedra were incorporated in the framework through displacement of Si⁴⁺O₄ after calcination (550°C/6 h) to loadings of 7 mol% Ti without perturbation of the ordered mesoporous structure, or decoration by extra-framework anatase containing Ti⁴⁺O₆ octahedra. The catalytic activity and selectivity of styrene epoxidation using hydrogen peroxide (H₂O₂) showed that the conversion of styrene increases significantly at higher titanium contents. The only products of this reaction were styrene oxide and benzaldehyde, with selectivity of 34.2 and 65.8%, respectively, at a styrene conversion of 25.8% over the 7 mol% Ti-SBA-15 catalyst. Beyond this titanium loading, anatase is deposited on the framework and catalytic activity degrades. The performance of the new catalyst is also shown to be superior to conventional materials produced by incipient wetness impregnation where Ti resides on the surface of SBA-15, giving a styrene conversion of 11.9% under identical reaction conditions.     

Preparation of WO<Subscript>3</Subscript>-SBA-15 mesoporous molecular sieve and its performance as an oxidative desulfurization catalyst

The tungsten-containing mesoporous molecular sieve WO₃-SBA-15 (SBA: Santa Barbara Amorphous type materials) was prepared under conventional hydrothermal conditions in strong acidic solution using H₂WO₄ as tungsten source, tetraethyl orthosilicate as silicon source, and a mixture of P123 tri-block copolymer (EO₂₀PO₇₀EO₂₀) and cetyltrimethylammonium bromide as structure-directing agent. The catalyst was tested for oxidative desulfurization and characterized by X-ray diffraction and nitrogen adsorption–desorption. The catalyst had the highest desulfurization performance (i.e., 91.3%) after oxidation under the following reaction conditions: 20 mL gasoline with 540 ppm sulfur, 6 mol H₂O₂/sulfur, reaction temperature 333 K, reaction time 80 min, and three extraction cycles.     

Effect of adjacent hydrophilic polymer thin films on physical aging and residual stress in thin films of poly(butylnorbornene‐ran‐hydroxyhexafluoroisopropyl norbornene)

The properties of thin supported polymer films can be dramatically impacted by the substrate upon which it resides. A simple way to alter the properties of the substrate (chemistry, rigidity, dynamics) is by coating it with an immiscible polymer. Here, we describe how ultrathin (ca. 2 nm) hydrophilic polymer layers of poly(acrylic acid) and poly(styrene sulfonate) (PSS) impact the aging behavior and the residual stress in thin films of poly(butylnorbornene‐ran‐hydroxyhexafluoroisopropyl norbornene) (BuNB‐r‐HFANB). The aging rate decreases as the film thickness (h) is decreased, but the extent of this change depends on the adjacent layer. Even for the thickest films (h > 500 nm), there is a decrease in the aging rate at 100 °C when BuNB‐r‐HFANB is in contact with PSS. In an effort to understand the origins of these differences in the aging behavior, the elastic modulus and residual stress (σ_R) in the films were determined by wrinkling as a function of aging time. The change in the elastic modulus during aging does not appear to be directly correlated with the densification or expansion of the films, but the aging rates appear to roughly scale as hσ_R^1/3. These results illustrate that the physical aging of thin polymer films can be altered by adjacent polymers. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 992–1000     

Hierarchically porous titania thin film prepared by controlled phase separation and surfactant templating

Poly(propylene glycol) (PPG) of moderately high molecular weight (M(n) = 3500 Da) exhibits amphibious behavior in aqueous solution in that it is hydrophilic at low temperature but hydrophobic at high temperature. This property is utilized to generate porous titania thin films with a hierarchical structure consisting of macroporous voids/cracks in films with mesoporous walls. The smaller mesopores result from the self-assembly of the Pluronic block copolymer P123 to form micellar templates in well-ordered arrays with hexagonal symmetry. The larger pores are generated from the phase separation of PPG during aging of the films. The PPG acts to a limited degree as a swelling agent for the P123 micelles, but because the films are aged at a low temperature where PPG is hydrophilic, much of the PPG remains in the polar titania phase. Upon heating, the PPG phase separates to form randomly dispersed, large pores throughout the film while retaining the ordered mesoporous P123-templated structure in the matrix of the material. TEM and SEM imaging confirm that calcined titania thin films have interconnected hierarchical porous structures consisting of ordered mesopores 4-12 nm in diameter and macroporous voids >100 nm in size. The density and size of the voids increase as more PPG is added to the films.     

Amperometric Tyrosinase Biosensor Based on Carbon Nanotube–Titania–Nafion Composite Film

A highly sensitive and stable amperometric tyrosinase biosensor has been developed based on multiwalled carbon nanotube (MWCNT) dispersed in mesoporous composite films of sol–gel‐derived titania and perfluorosulfonated ionomer (Nafion). Tyrosinase was immobilized within a thin film of MWCNT–titania–Nafion composite film coated on a glassy carbon electrode. Phenolic compounds were determined by the direct reduction of biocatalytically‐liberated quinone species at ?100 mV versus Ag/AgCl (3 M NaCl) without a mediator. The present tyrosinase biosensor showed good analytical performances in terms of response time, sensitivity, and stability compared to those obtained with other biosensors based on different sol–gel matrices. Due to the large pore size of the MWCNT–titania–Nafion composite, the present biosensor showed remarkably fast response time with less than 3 s. The present biosensor responds linearly to phenol from 1.0×10^?7 M to 5.0×10^?5 M with an excellent sensitivity of 417 mA/M and a detection limit of 9.5×10^?8 M (S/N=3). The enzyme electrode retained 89% of its initial activity after 2 weeks of storage in 50 mM phosphate buffer at pH 7.0.     

Novel Flower‐Like Ag‐SiO2‐MgO‐Al2O3 Material: Preparation,Characterization and Catalytic Application in Methanol Dehydrogenation

Catalytic direct dehydrogenation of methanol to formaldehyde was carried out over Ag‐SiO₂‐MgO‐Al₂O₃ catalysts prepared by sol‐gel method. The optimal preparation mass fractions were determined as 8.3% MgO, 16.5% Al₂O₃ and 20% silver loading. Using this optimum catalyst, excellent activity and selectivity were obtained. The conversion of methanol and the selectivity to formaldehyde both reached 100%, which were much higher than other previously reported silver supported catalysts. Based on combined characterizations, such as X‐ray diffraction (XRD), scanning electronic microscopy (SEM), diffuse reflectance ultraviolet‐visible spectroscopy (UV‐Vis, DRS), nitrogen adsorption at low temperature, temperature programmed desorption of ammonia (NH₃‐TPD), desorption of CO₂ (CO₂‐TPD), etc., the correlation of the catalytic performance to the structural properties of the Ag‐SiO₂‐ MgO‐Al₂O₃ catalyst was discussed in detail. This perfect catalytic performance in the direct dehydrogenation of methanol to formaldehyde without any side‐products is attributed to its unique flower‐like structure with a surface area less than 1 m²/g, and the strong interactions between neutralized support and the nano‐sized Ag particles as active centers.     

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.     

Chemical Preparation of Ferroelectric Mesoporous Barium Titanate Thin Films: Drastic Enhancement of Curie Temperature Induced by Mesopore‐Derived Strain

Mesoporous barium titanate (BT) thin films are synthesized by a surfactant‐assisted sol–gel method. The obtained mesoporous BT thin films show enhanced ferroelectricity due to the effective strains induced by mesopores. The Curie temperature (T_c) of the mesoporous BT reaches approximately 470 °C.     

Effect of post‐deposition annealing on surface morphology and gas sensing properties of palladium phthalocyanine thin films

The effect of post‐deposition annealing on surface morphology and gas sensing properties of palladium phthalocyanine (PdPc) nanostructured thin films has been studied. PdPc thin films were deposited on polyborosilicate substrate by thermal evaporation technique at room temperature. The surface morphology of thin films was investigated by SEM, X‐ray diffraction, and optical absorption. X‐ray diffraction patterns showed a phase transition from α to β based on post‐deposition annealing at temperatures above 200 °C. The SEM and optical absorption confirmed that annealing strongly influenced the surface morphology of nanostructured thin films. Sandwich devices (Au|PdPc|Al) were fabricated and exposed to different concentrations of NO₂ and NH₃ as oxidizing and reducing gases at different temperatures, and the sensitivity of devices were obtained versus gases. Obtained results showed α‐PdPc thin film devices had higher sensitivity in comparison with devices in β‐phase. In particular, it was found that the sensitivity of devices is temperature dependent and the best operating temperature range of devices was measured at about 90–100 °C. Devices showed good reversibility, response, and recovery time at room temperature. Finally, the stability of sensors was investigated for a period of about 1 year; results showed that the sensors were stable for 2 months and lost about 30% of their sensitivity after 1 year. Copyright © 2012 John Wiley & Sons, Ltd.     

Experimental Design for Modeling and Multi‐response Optimization of Catalytic Cyclohexene Epoxidation over Polyoxometalates

An experimental design methodology was applied to optimize cyclohexene epoxidation with hydrogen peroxide in the presence of acid‐activated montmorillonite clay supported on 11‐molybdovanado‐phosphoric acid, with the Keggin structure H₄[PVMo₁₁O₄₀] · 13H₂O (PVMo) as catalyst. The statistical study of the process was achieved through a two‐level, full‐factorial experimental design with five process parameters. The significant input variables (key factors) that influenced the performance of cyclohexene oxidation are the catalyst weight, catalyst loading, temperature, H₂O₂ concentration, and the reaction time. The effect of the individual parameters and their interaction effects on the cyclohexene conversion, as well as the selectivity of cyclohexane‐1,2‐diol, was determined, and a statistical model of the process was developed. The process was optimized by considering the two responses simultaneously, which allows defining the optimal regions for the significant process variables. The optimal conditions were obtained for the catalyst weight of 0.05 g, temperature of 70°C, and reaction time of 9 h, with 20% PVMo as the active phase and hydrogen peroxide as oxidant.