The synthesis of colloidal zeolite TPA–silicalite-1

The synthesis of colloidal TPA–silicalite-1 from a clear xTPAOH–yH₂O–TEOS precursor sol, with x=0.01–0.443 and y=20–80, has been studied at 115°C. Both the starting sol and the reaction products at various times were examined by dynamic light scattering (DLS) to determine the size of the colloidal (or sub-colloidal) particles presented. In addition, the pH of the system has been measured. The observations made with the DLS were consistent with the literature results. In essence, uniform particles of colloidal zeolite were formed during the reaction, and their size grew linearly with reaction time. At the same time, sub-colloidal particles smaller than 5 nm were also observed that persisted throughout the process. The measured pH, on the other hand, could be satisfactorily modeled by the equilibrium theory, suggesting that an equilibrium distribution of dissolved silicates was established before the reaction, and a different equilibrium was attended when colloidal zeolites, as well as the co-existing sub-colloidal particles, were observed. The number density of the colloidal particles ρ was found to depend on the 3.4 power of the silica concentration and the ratio x.     

The Chemistry of Porous Polymers: The Holey Grail

Porous polymers have been evolving continuously since the introduction of foam rubber in 1929. Today, pore diameters ranging from sub-nanometre to millimetre can be generated controllably. Cutting-edge porous polymers are now being applied at the forefront of critical problems with societal and environmental impact including advanced systems for biomedicine, water purification, energy storage, and gas purification and storage. The commonly-used pore generation approaches include macromolecular design, self-assembly, phase separation, solid and liquid templating, sol-gel formation, and foaming. In each, The Chemistry of Polymers, both the polymerization chemistry and the macromolecular structural chemistry, must be applied advantageously to generate the empty volume within the polymer and then fix it in place. This essay will traverse the various pore size scales, describing the chemistries involved and discussing their implications.     

Preparation and characterization of three dimensionally ordered macroporous Li4Ti5O12 anode for lithium batteries

Three dimensionally ordered macroporous (3DOM) Li₄Ti₅O₁₂ membrane (80 μm thick) was prepared by a colloidal crystal templating process. Colloidal crystal consisting of monodisperse polystyrene particles (1 μm diameter) was used as the template for the preparation of macroporous Li₄Ti₅O₁₂. A precursor sol consisting of titanium isopropoxide and lithium acetate was impregnated into the void space of template, and it was calcined at various temperatures. A macroporous membrane of Li₄Ti₅O₁₂ with inverse-opal structure was successfully prepared at 800 °C. The interconnected pores with uniform size (0.8 μm) were clearly observed on the entire part of membrane. The electrochemical properties of the three dimensionally ordered Li₄Ti₅O₁₂ were characterized with cyclic voltammetry and galvanostatic charge and discharge in an organic electrolyte containing a lithium salt. The 3DOM Li₄Ti₅O₁₂ exhibited a discharge capacity of 160 mA h g⁻¹ at the electrode potential of 1.55 V versus Li/Li⁺ due to the solid state redox of Ti^3+/4+ accompanying with Li⁺ ion insertion and extraction. The discharge capacity was close to the theoretical capacity (167 mA h g⁻¹), which suggested that the Li⁺ ion insertion and extraction took place at the entire part of 3DOM Li₄Ti₅O₁₂ membrane. The 3DOM Li₄Ti₅O₁₂ electrode showed good cycle stability.     

Synthesis of mesoporous alumina TUD-1 with high thermostability

Mesoporous alumina, TUD-1, was prepared via a sol-gel process by using tetraethylene glycol (TEG) as template. The effect of TEG and solvents on the pore structure of the final products was studied. A mechanism using non-surfactant template was proposed. It was found that TUD-1 has amorphous framework, high surface area, large pore volume and narrow pore size distribution together with high thermal stability upon prolonged heat treatment at high temperatures, which is essential for applications in adsorption and catalysis.     

在壳聚糖改性的硅锆复合中间层上原位水热合成b-轴取向silicalite-1分子筛膜

引言 分子筛是一类具有特殊孔道或笼状结构的多孔介质,可以根据分子的动力学尺寸大小、形状以及极性等进行选择性吸附.     

A facile preparation of highly interconnected macroporous PLGA scaffolds by liquid-liquid phase separation II

A regular and well-interconnected macroporous (from 50 to 200 μm) poly(d,l-lactic acid-co-glycolic acid) (PLGA) scaffold was fabricated by means of the thermally induced phase separation (TIPS) method. Poly(l-lactic acid) (PLLA) was blended with PLGA to increase the viscosity of polymer solution; a block copolymer of poly(ethylene glycol) (PEG) with PLGA was added as a surfactant to decrease the interfacial tension between the polymer-rich and polymer-lean phases. The effect of TIPS parameters including the concentration of diblock copolymer and PLGA/PLLA ratio was also studied. The cloud-point curve shifted to higher temperatures with both increasing the PLLA composition in the PLGA/PLLA blend and the PEG contents in the additives (PEG itself and PEG-PLGA diblocks). This shifting to higher temperature increases the quenching depth during phase separation. Addition of a PEG-PLGA diblock copolymer (0.5 wt% in solution) to the PLGA/PLLA (1/1) blend polymer in a dioxane/water solution stabilized the morphology development during TIPS with respect to interconnection and macropores, and avoided segregation or sedimentation in the late stage.     

Preparation of templated mesoporous silica membranes on macroporous α-alumina supports via direct coating of thixotropic polymeric sols

A simple method for depositing mesoporous silica films directly on macroporous α-alumina supports is reported. A polymeric silica sol was prepared by hydrolysis of tetraethylorthosilicate in acid propanol in presence of hexadecyltrimethylammonium bromide as template. The rheology of the sol was changed by a modified urea-based thixotropic agent, which was used in a concentration range between 2% and 10% on volume. The dynamic viscosity of the sol was measured as a function of shear rate. The rheology modifier was found to increase the viscosity of the sol and confer at the same time a thixotropic behavior to it. Long range order in the unmodified and modified materials was analyzed by XRD on powders after calcination at 500 °C. It was found that the pore size increased with increasing concentration of additive, while the degree of order decreased until eventually, at high concentrations, the ordered porous structure collapsed completely. The gradual pore size increase at lower concentration is thought to be caused by swelling of the surfactant micelles by the rheology modifier.The modified sols were deposited via dip-coating on α-alumina disks. The morphology of the silica top layers was characterized by SEM. Pore size distributions and permeances of the prepared membranes were assessed by permporometry and single gas permeation measurements, respectively. The membranes had narrow pore size distributions, with an average diameter of about 2 nm. Permeabilities of H₂, He, CH₄ and O₂ were compared. Hydrogen permeances up to 6 × 10⁻⁷ mol s⁻¹ m⁻² Pa⁻¹ were measured at 473 K. The gas flux across the membrane follows a Knudsen-type mechanism, as shown by the permselectivities.     

Impregnation synthesis of a novel macroporous silica-based crown ether polymeric material modified by 1-dodecanol and its adsorption for strontium and some coexistent metals

4,4′,(5′)-Di-(tert-butylcyclohexano)-18-crown-6(DtBuCH18C6) is a chelating agent having high selectivity mostly for Sr(II). To significantly reduce its leakage by molecular modification, a macroporous silica-based DtBuCH18C6 polymeric composite (DtDo/SiO₂–P) was synthesized. It was performed by impregnating and immobilizing DtBuCH18C6 and 1-dodecanol molecules into the pores of the SiO₂–P particles utilizing an advanced vacuum sucking technique. The adsorption of a few fission and non-fission products Sr(II), Ba(II), Cs(I), Ru(III), Mo(VI), Na(I), K(I), Pd(II), La(III), and Y(III) onto DtDo/SiO₂–P was investigated. It was done by examining the effects of contact time and the HNO₃ concentration in a range of 0.1–5.0 M at 298 K. At the optimum concentration of 2.0 M HNO₃, DtDo/SiO₂–P exhibited strong adsorption ability and high selectivity for Sr(II) great over all of the tested elements, which showed very weak or almost no adsorption except Ba(II). Meanwhile, It was found that the quantity of total organic carbon (TOC) leaked from DtDo/SiO₂–P in 2.0 M HNO₃, 187.5 ppm, was lower than 658.4 ppm that leaked from DtBuCH18C6/SiO₂–P, which was not modified. This was ascribed to the effective association of DtBuCH18C6 and 1-dodecanol through intermolecular interaction. The reduction of DtBuCH18C6 leakage by molecular modification with 1-dodecanol was achieved. It was of great benefit to application of DtDo/SiO₂–P in chromatographic partitioning of Sr(II), one of the main heat generators, from high level liquid waste (HLLW) in reprocessing of nuclear spent fuel in the MAREC (Minor Actinides Recovery from HLLW by Extraction Chromatography) process developed recently.     

Direct synthesis of mesoporous silicalite-1 supported TiO2–ZrO2 for the dehydrogenation of EB to styrene with CO2

Direct synthesis route was developed to support TiO₂–ZrO₂ binary metal oxide onto the carbon templated mesoporous silicalite-1 (CS-1). Metal hydroxide modified carbon particles could play a role as hard template and simultaneously support metal components on the mesopores during the crystallization of zeolites. Such supported TiO₂–ZrO₂ binary metal oxides (TZ/CS-1) showed better resistance to deactivation in the oxidative dehydrogenation of ethylbenzene (ODHEB) in the presence of CO₂. These catalysts were found to be active, selective and catalytically stable (10 h of time-on-stream) at 600 °C for the dehydrogenation of ethylbenzene (EB) to styrene (Sty).