以酸解正硅酸乙酯为硅源合成ZSM-5分子筛的过程调控

正硅酸乙酯（TEOS）作为合成ZSM-5分子筛的常用硅源,其在不同酸碱介质中水解的前驱体聚合状态对ZSM-5分子筛的粒径和孔径分布具有调控作用。以酸性介质TEOS水解缩合的前驱体为硅源,在水热条件下合成ZSM-5分子筛,并利用XRD、SEM、BET、FI-IR等方法对反应不同阶段的样品进行表征分析。主要考察了水解程度、水解时间、合成过程的pH、晶化温度、晶化时间及模板剂用量对ZSM-5分子筛合成过程的调控,结果表明：以乙醇为共溶剂,以TEOS在硫酸介质pH=2.0时水解20 h的前驱体为硅源,水热合成过程中加入模板剂四丙基氢氧化铵（TPAOH）,铝源为氢氧化铝,180 ℃晶化30 h合成了粒径约为200 nm的ZSM-5分子筛,其比表面积提高了35.6%,平均孔径降低了48.6%。     

Silicalite-l Synthesis from Silicate Aqueous Solutions Including Amines as a Base

Aqueous silicate solutions could be prepared from a silicon alkoxide using amines as a base. The synthesis of silicalite-1 conducted by hydrothermally treating the solutions after the addition of NPrⁿ₄Br (TPABr), was examined focusing on triethylamine (NEt₃) as the amine. The aqueous solutions with chemical compositions of Si(OEt)₄ (TEOS) : NEt₃ : TPABr : H₂O = 1 : ≥0.5 : ≥0.8 : 200 led to silicalite-1 crystallization upon hydrothermal treatment at 130C for 4 days. The resulting crystals had a small thin coffin shape. With increasing the added amounts of NEt₃ and TPABr, the crystal size decreased. Among the investigated conditions, the smallest silicalite-1 crystal measuring about 1.0 × 0.7 × 0.4 um was obtained at starting compositions of NEt₃/TEOS ≥2.0 and TPABr/TEOS ≥3.2. The increase in the TPA content of the starting solutions accelerated the crystal nucleation of silicalite-1, so that the obtained crystals became smaller. During the hydrothermal synthesis, an amorphous silica gel was formed before the crystallization commenced. The increase in the NEt₃ content may suppress the formation of the silica gel, and/or facilitate its dissolution, thereby the supersaturation degree of silicate species in the solution was increased, giving small silicalite-1 crystals. When an aqueous suspension of the smallest silicalite-1 crystals was spread onto a glass substrate by a dip-coating method, an ordered mono-grain layer of the silicalite-1 crystals oriented with the straight channels normal to the substrate surface was obtained.     

硅源对全硅ＭＣＭ-４１中孔分子筛结构的影响研究

以十六烷基三甲基溴化铵、硅酸钠和正硅酸乙酯等为原料,研究了不同硅源对ＭＣＭ-４１分子筛合成的影响,并以ＸＲＤ、ＩＲ、热分析进行了表征,讨论了可能的机理。实验表明,用正硅酸乙酯比硅酸钠合成的全硅ＭＣＭ-４１分子筛的结构性能更好些。     

Some New Features on Synthesis of Titanium Silicalite-1 in a Non-TPAOH Inorganic Reactant Synthetic System

Various effects on the synthesis of titanium silicalite-1 (TS-1) were discussed in the non-TPAOH (tetrapropyl ammonium hydroxide) inorganic reactant synthesis system, in which cheap colloidal silica and TiCl₃ aqueous solution, TiCl₄ were used as the silicon and titanium sources, respectively, TPABr (tetrapropyl ammonium bromide) as the template reagent, and weak organic bases as the base source to provide the alkalinity needed for crystallization. The influence of diverse synthesis parameters such as different base sources, SiO₂/TiO₂ ratio, silicon source, titanium source, amounts of template, N₂ protection, seed crystals, aging period, amount of water, crystallization temperature, and crystallization time have been investigated in detail.     

Hydrothermal synthesis of gallosilicate (MFI) zeolite: Factors influencing crystallization kinetics and crystal size/growth

The kinetics of the hydrothermal synthesis of gallosilicate (MFI) zeolite (under autogeneous pressure at 180°C) from a gel containing a source of silica (Na-trisilicate or fumed silica), gallium nitrate, templating agent (TPA-Br or TPA-OH), deionized water and sulfuric acid have been thoroughly investigated in order to understand the influence of various synthesis parameters (viz. gel composition, source of silica, template, method of gel preparation and pH of gel) on the crystallization kinetics and crystal size/growth of the zeolite. The zeolite samples were characterized for their crystallinity by XRD and crystal size and morphology by SEM. The crystallization rate and crystal size of the zeolite were found to be strongly influenced by the above synthesis parameters. © 1998 SCI     

Bioactive assessment of bioactive glass nanostructures synthesized using synthetic and natural silica resources

The sol-gel route of synthesizing bioactive glasses of composition 45S5 has shown higher compatibility than the melt casting method. In bioactive glass synthesis, a major silica source is derived from the synthetic tetraethyl orthosilicate precursor. This work demonstrates the sol–gel-derived bioactive glass prepared from rice husk and TEOS as silica sources. In this study, the effect of crystallization with respect to the silica source in bioactive glass composition was investigated to gain further understanding on the processes involved in the fabrication of bioglass. The in vitro biodegradation and apatite formation of the bioactive glass in simulated body fluid was investigated by spectroscopic and morphological studies. Both the bioactive glasses show a change in morphology toward nanostructured apatite formation after in vitro immersion studies. Further, the hemocompatibility of bioactive glass prepared using rice husk is similar to bioactive glass prepared from organic silica sources. This promises the possibility of synthesizing low cost and biocompatible bioactive glass 45S5 system for tissue engineering applications.     

Dry gel conversion synthesis of shape controlled MFI type zeolite materials

Acid treated silica fibers, coming either from asbestos cord waste or calcium aluminosilicate glass, were engaged as reactants to product MFI type zeolite fibers applying a dry gel conversion (DGC) type synthesis. The impact of amorphous silica fiber shape and synthesis conditions on morphology of the final product was investigated. Enhanced zeolite nucleation and restricted crystal growth are necessary to maintain the initial fiber morphology. Whereas a DGC type crystallization in hydroxide media results in the formation of zeolite fibers, the use of fluoride ions leads to the formation of large individual zeolite particles. Synthesis conditions have to be adapted to form zeolite particles with an average size smaller than the silica fiber diameter to allow a good conservation of the fiber morphology. Final zeolite fibers have textural properties comparable to a standard zeolite product and are promising for adsorption applications.     

羟基磷酸铜的合成及催化氧化染料脱色

以磷酸氢二铵、氯化铜或乙酸铜为原料,采用水热合成法,在不同配比下合成了羟基磷酸铜纯结晶相。合成温度120℃~180℃,晶化时间24~72h。羟基磷酸铜晶体形貌随合成条件而变化,在合成体系中加入少量正硅酸乙酯可使产物粒径小且均匀。将合成的羟基磷酸铜作为催化剂用于催化过氧化氢氧化8种染料脱色,发现具有较高的催化活性,2h脱色率可达70%~90%。     

高岭土微球原位合成纳米Y沸石

喷雾干燥成型的苏州高岭土经不同温度焙烧活化后在水热条件下原位晶化为纳米尺度的NaY沸石微球。采用X射线荧光光谱（XRF）分析合成前后微球的化学组成;采用X射线衍射光谱（XRD）表征微球的晶相组成;采用扫描电子显微镜（SEM）表征合成前后微球的形貌。考察了合成过程中投料硅铝物质的量比、晶种导向剂用量、碱量、体系水加入量和高岭土焙烧温度等条件对原位晶化合成的影响,并讨论了合成过程出现的问题,制备了纯相且生长完好的纳米尺度的Y沸石微球。     

A new synthesis procedure for titanium-containing zeolites under strong alkaline conditions and the catalytic activity for partial oxidation and photocatalytic decomposition

A new synthesis procedure for titanium-containing aluminosilicate zeolites has been obtained using a clear colloidal dispersion (sol) which was prepared with titanium isopropoxide, water, hydrochloric acid and colloidal silica, Ludox. When NaY, KL, offretite, mordenite and ZSM-5 zeolites were crystallized from the sol following conventional hydrothermal crystallization procedures, all the aluminosilicate zeolites showed the same X-ray absorption fine structure at the Ti K edge indicating framework Ti. The zeolites showed remarkable catalytic activity for the partial oxidation of cyclohexene using H₂O₂ as an oxidant and the photocatalytic decomposition of trichloroethene using water.     

Crystallization and morphology studies of biodegradable poly(ε‐caprolactone)/silica nanocomposites

Biodegradable poly(ε‐caprolactone) (PCL)/silica nanocomposites at various silica loadings were prepared via direct melt compounding method in this work. Scanning electron microscopy observation indicated that when the silica content was < 3 wt%, the nanoparticles dispersed evenly in the PCL matrix and exhibited only aggregates with particle size of less than 100 nm. The results of nonisothermal melt crystallization showed that the crystallization peak temperature was higher in the nanocomposites than in neat PCL; moreover, the overall crystallization rate was faster in the nanocomposites than in neat PCL during isothermal melt crystallization. Both nonisothermal and isothermal melt crystallization studies suggested that the crystallization of PCL was enhanced by the presence of silica and influenced by the silica loading. The effect of silica on the crystallization behavior was twofold: the presence of silica may provide heterogeneous nucleation sites for the PCL crystallization while the aggregates of silica may restrict crystal growth of PCL. However, the crystal structure of PCL remained almost unchanged despite the presence of silica in the nanocomposites. POLYM. COMPOS., 2013. © 2012 Society of Plastics Engineers     

Multiple paths to nanocrystalline high silica beta zeolite

Several principles from nanozeolite synthesis lore were investigated in order to prepare discrete pure silica nanocrystalline BEA zeolite. It was discovered that lowering reaction temperature to 100 °C results in a significant reduction in nano-BEA crystal size, that lowering synthesis mixture water content to the lowest possible level for a ‘pourable’ gel provides nano-BEA crystals, that tetraethylorthosilicate (TEOS) more consistently provides smaller crystals than fumed silica as a raw material, that increasing the level of structure-directing agent resulted in more discrete and smaller crystals (25–30 nm), and that ‘surfactant’ addition could generate even smaller nano-BEA crystals or nanocrystalline domains, but mild to severe aggregation was still a problem. Nearly pure silica nanocrystalline BEA zeolites were prepared from Al-containing products by a calcination followed by acid extraction procedure. The calcination step is critical for more complete Al removal. Defects generated by acid extraction could be healed by treatment of resultant powder with a hexamethyldisilazane (HMDS). Another key finding was that Al-containing synthesis mixtures could provide nanocrystalline BEA zeolite with 4,4′-trimethylenebis(N-methyl, N-benzyl-piperidinium) dihydroxide (TMP(OH)₂) as organic structure-directing agent. Interestingly, adjusting synthesis parameters in TMP and Al-containing synthesis mixtures provided some differences to pure Si BEA products. For example, stirring or lowering reaction temperature did not decrease crystal size, but did shorten crystallization time. The smallest crystals from TMP-based, Al-containing reaction mixtures were prepared when a freeze–dried colloidal silica was utilized as silica source.     

Effect of in situ prepared silica nano-particles on non-isothermal crystallization of polypropylene

The crystallization behavior of PP/silica nanocomposites prepared in-situ via solid-state modification and sol-gel reaction is investigated. The crystallization behavior studied with DSC shows that in situ formed silica nano-particles act as nucleating agents. The non-isothermal crystallization kinetics of PP/silica nanocomposites is studied using a combined Avrami-Ozawa approach and shows a two-stage crystallization process: the primary stage is characterized by nucleation and spherulitic growth and the secondary stage is characteristic of the perfectioning of crystals. Silica speeds up the primary stage, resulting in a more narrow lamellar thickness distribution. The crystallization activation energy decreases with increasing silica content in the PP/silica nanocomposites. The nucleating efficiency of the in-situ prepared silica particles based on the scale as proposed by Lotz and co-workers is found to be 20% in the low concentration range and is higher compared to silica nano-particles as well as other nano-fillers studied. The melting behavior indicates the formation of more perfect crystals with a narrow lamellar thickness distribution and the WAXD patterns show that silica nano-particles induce the formation of crystals with the β-modification in PP at high silica content (ca. 5 wt%). DMTA analysis shows a marginal lowering of the T_g and an increased mobility of the amorphous phase.     

含氟体系中合成条件对MCM-48分子筛结构性能的影响

在合成过程中引入F~-可以缩短MCM-48分子筛的晶化时间,考察以正硅酸乙酯(TEOS)为硅源、十二烷基三甲基溴化铵(CTAB)为模板剂的合成体系中加入F~-后,n(CTAB)∶n(Si)、晶化时间和晶化温度等合成条件对MCM-48结构性能的影响。XRD、N_2吸附脱附和TEM等表征结果表明,在n(CTAB)∶n(Si)=0.65、晶化温度120℃和反应时间24 h条件下,合成的MCM-48分子筛结晶度较高,比表面积为1 305 m~2·g~(-1),平均孔径3.416 nm,为MCM-48分子筛的适宜合成条件。     

Effect of ZnO/K2O ratio on the crystallization sequence and microstructure of lithium disilicate glass-ceramics

The effect of ZnO/K₂O (Z/K) ratio on the crystallization sequence and microstructure of lithium disilicate (Li₂Si₂O₅: LS2) glass-ceramics was carefully investigated for the SiO₂-Li₂O-K₂O-ZnO-P₂O₅ system. The Z/K ratios of precursor glasses were varied from 0 to 3.5 while the nucleating agent of P₂O₅ and glass modifiers of ZnO plus K₂O were fixed to have 1.5 and 4.5 mol% relative to LS2, respectively. For the samples prepared by two-stage heat treatments of 500 °C for 1 h and 800 °C for 2 h in air, the LS2 nucleation rate was increased with increasing the Z/K ratio due to the variation in crystallization sequence from type II (Li₂SiO₃: LS) to type I (LS + LS2) in addition to an amorphous phase separation in base glass. Consequently, with increasing the Z/K ratio, the LS2 crystalline phase within the glass matrix continuously changed from larger acicular ones to smaller equiaxed ones.     

微波辅助高效水热合成SAPO-11分子筛

采用微波辅助的方法,以拟薄水铝石、硅溶胶等为原料,合成出纯相SAPO-11分子筛,大大减少了晶化时间,节约了合成成本。通过X射线衍射（XRD）,扫描电子显微镜（SEM）对合成的样品进行表征,详细考察了硅源、模板剂、硅铝比及晶化条件（晶化时间、晶化温度、pH）对合成的影响。结果表明,pH及晶化时间的影响较为显著,以硅溶胶为硅源,以二正丙胺为模板剂,在n(SiO2)∶n(Al2O3)=0.6、pH=5.7、晶化温度为185 ℃、晶化时间为10 h的条件下,采用微波辅助可以高效地合成纯相的SAPO-11分子筛。     

有机弱碱体系中介孔分子筛MCM-41的合成与表征

在有机弱碱无水乙二胺为碱介质的条件下(pH≈10) ,以阳离子表面活性剂十六烷基三甲基溴化铵(CTAB)为模板剂,以正硅酸乙酯(TEOS)为硅源,在室温下合成了介孔分子筛MCM-41。与在强碱水热体系中合成的样品相比,室温弱碱体系中合成的样品具有孔道短程有序度高等特点。详细考察了晶化时间、表面活性剂浓度和晶化温度对产物结构的影响。用XRD对所合成的产物进行表征,结果表明,晶化时间越长,所得到产物的有序度越高;随着表面活性剂质量分数的增加,所合成产物的结构和晶型的完整性越高,但并不是表面活性剂的质量分数越大越好,当表面活性剂的质量分数大于6%时,就呈现下降的趋势;随着晶化温度的升高,所得样品的规整性变差,但晶格参数a₀随温度的升高而呈现变大的趋势。     

TS-1分子筛催化剂的制备和表征

以四丙基氢氧化铵为模板剂,正硅酸乙酯为硅源,钛酸四丁酯为钛源,异丙醇为络合剂,碳酸铵为晶化调节剂,对经典水热法进行改进,制备出形貌规则且粒径约为200 nm的TS-1分子筛,考察晶化时间、正硅酸乙酯水解时间及络合剂种类对骨架Ti含量的影响,并采用XRD、SEM、FTIR和UV-Vis等对合成的样品进行表征。结果表明,当正硅酸乙酯水解2 h和晶化时间3天时,异丙醇的加入可有效阻止TiO_2沉淀的产生,同时加入(NH_4)_2CO_3能够促进钛物种进入TS-1分子筛骨架,提高骨架中的Ti含量。     

Nonisothermal crystallization behavior and mechanical properties of poly(butylene succinate)/silica nanocomposites

Silica nanoparticles and poly(butylene succinate) (PBS) nanocomposites were prepared by a melt‐blending process. The influence of silica nanoparticles on the nonisothermal crystallization behavior, crystal structure, and mechanical properties of the PBS/silica nanocomposites was investigated. The crystallization peak temperature of the PBS/silica nanocomposites was higher than that of neat PBS at various cooling rates. The half‐time of crystallization decreased with increasing silica loading; this indicated the nucleating role of silica nanoparticles. The nonisothermal crystallization data were analyzed by the Ozawa, Avrami, and Mo methods. The validity of kinetics models on the nonisothermal crystallization process of the PBS/silica nanocomposites is discussed. The approach developed by Mo successfully described the nonisothermal crystallization process of the PBS and its nanocomposites. A study of the nucleation activity revealed that the silica nanoparticles had a good nucleation effect on PBS. The crystallization activation energy calculated by Kissinger's method increased with increasing silica content. The modulus and yield strength were enhanced with the addition of silica nanoparticles into the PBS matrix. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of hydrogen bonding on the crystallization behavior of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)/silica hybrid composites

Biodegradable poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHB-HHx)/hydrophobically modified silica hybrid composites were prepared using simple melt compounding and the effect of hydrogen bonding on their crystallization behavior was observed. The intermolecular hydrogen bonding between PHB-HHx and silica increased gradually with the increase of silica content of the hybrid composites. However, the extent of intermolecular hydrogen bonding was not directly proportional to the silica content. Although, the crystallization rates of the PHB-HHx/silica hybrids decreased as the strength of intermolecular hydrogen bonding increased, the constant value of the Avrami exponent indicates that the presence of silica does not alter the nucleation mechanism or the geometry of the crystal growth of the PHB-HHx hybrids. The calculated crystallization activation energy increased with the addition of silica, suggesting that silica retards the overall crystallization rate of the PHB-HHx hybrid composites as a result of the existence of intermolecular hydrogen bonding. The relationship between the extent of intermolecular hydrogen bond and crystallization rate is described by the empirical second-order equation.