二氧化硅微球的制备与形成机理

在酯-醇-水-碱体系中以正硅酸乙酯为硅源、氨水为催化剂、乙醇为溶剂,采用改进的溶胶-凝胶法合成了二氧化硅球形颗粒。采用红外光谱、BET吸附曲线、扫描电镜等手段重点研究了正硅酸乙酯加料方式对二氧化硅粒径和形貌的影响。分析表明,采用正硅酸乙酯分步滴定法能提高二氧化硅微球的球形度、窄分布、单分散与致密性。同时,在反应温度25℃、正硅酸乙酯浓度0.12mol/L、氨浓度为15.0mol/L、去离子水浓度0.90mol/L、无水乙醇浓度2.35mol/L、pH值为9～12的条件下,获得了直径约200～250nm、粒径一致性约为0.5、分布偏差约为7.5%的球形二氧化硅单分散颗粒;研究和讨论了二氧化硅微球的形成机理。     

微米二氧化硅微球的制备研究进展

以聚合诱导胶体凝聚法、种子生长法、模板法和反相乳液法等制备方法为主线,综述制备微米二氧化硅微球的最新研究进展,同时以所得微球的性能为考察重点,对各种方法进行评价与展望;提出通过硅酸钠等低成本硅原料取代硅酸酯制备高性能硅微球是未来研究重点;改变种子生长法中溶剂的种类、制备粒径更大的单分散微球并进行理论探究成为种子生长法的研究方向;采用模板法对聚合诱导胶体凝聚法制备的微球孔结构进行重组完善,得到纯度较高、机械强度和比表面积较大的微米有序介孔二氧化硅微球,进而用于高性能色谱柱的制备以及生物催化等领域,发展前景可观。     

单分散纳米二氧化硅微球的制备及羧基化改性

采用改进工艺条件的Stober法制备纳米SiO_2微球.用场发射扫描电镜(FESEM)分析了纳米二氧化硅的形貌、粒径.结果表明,通过温度梯度法和控制氨水浓度变化制备出高圆度、单分散、粒径可控的纳米级二氧化硅微球.用KH-550硅烷偶联剂和丁二酸酐对纳米二氧化硅表面羧基化改性.采用X射线能谱仪(EDS)、热重(TGA)、傅里叶红外(FTIR)等手段对改性后纳米二氧化硅的结构、元素种类及含量进行了表征.结果表明,纳米二氧化硅表面成功接枝了羧基官能团.     

二氧化硅/壳聚糖复合微球的制备及性能

通过溶胶-凝胶法制备出3种不同粒径的SiO₂微球,利用扫描电镜分析了微球的粒径分布情况,SiO₂微球粒径分别在140nm、208nm、336nm左右,在一定范围内,硅球的粒径随正硅酸四乙酯(TEOS)/氨水的添加量增加而增大。选取粒径在336nm左右的SiO₂微球,使用硅烷偶联剂3-(2,3-环氧丙氧基)丙基三甲氧基硅烷(GPTMS)将壳聚糖(CS)接枝在SiO₂微球上,得到SiO₂@CS复合微球。通过红外光谱分析、X射线衍射等对微球进行了表征。接枝CS后对SiO₂微球的结晶特性没有影响,微球仍为无定形晶体。元素分析结果表明CS的接枝量为1.03%。使用振荡法进行抗菌测试,SiO₂@CS复合微球对金黄色葡萄球菌(S.aureus)和大肠杆菌(E.coil)的抑菌率分别为85.52%和47.14%,表明复合微球有一定的抗菌效果。     

P(St-EA-MAA)模板法制备中空二氧化硅微球

以种子乳液聚合制得的P(St-EA-MAA)共聚物微球为模板,γ-氨丙基三甲氧基硅烷(APS)为助结构导向剂,正硅酸四乙酯(TEOS)为硅源,制备了P(St-EA-MAA)/SiO2复合微球,经高温煅烧除去聚合物模板,得到了中空二氧化硅微球。热重分析(TGA)表明模板剂的最佳脱除温度为600℃。高分辨透射电镜(HRTEM)观察显示所制得的二氧化硅微球具有典型的中空结构和良好的单分散性,其尺寸主要取决于共聚物微球的大小,通过调节微球模板的尺寸可以有效控制中空微球的大小。N2吸附-脱附曲线显示二氧化硅壁具有丰富的微孔,比表面积、平均孔径和孔容分别为117.87m2/g、1.98nm和0.21cm3/g。在制备复合微球的过程中加入一定量的CTAB可以调整中空微球的壁厚和壁的孔结构,使其比表面积、平均孔径和孔容增加到219.79m2/g、3.89nm和0.25cm3/g。     

二氧化硅纳米管的制备及表征

用表面活性剂十六烷基三甲基溴化铵(C16TMAB)为模板剂,以原硅酸四乙酯(TEOS)为原料,在酸性介质的催化条件下进行水解、缩合,制得了二氧化硅纳米管(平均管径30～60nm),并用FTIR、XRD、TEM对所制备的二氧化硅纳米管进行了表征。此外,讨论了二氧化硅纳米管的形成机理。     

两步法制备醋酸纤维素微滤膜的研究

以二醋酸纤维素酯为制膜材料，以DMF／丙酮为混合溶剂体系，采用两步法制备微滤膜，第一步在水蒸气气氛中吸湿并挥发溶剂而分相凝胶，第二步浸入水中固化制膜．研究了聚合物浓度、溶剂比例、添加剂含量、吸湿时间等因素对膜性能的影响，制备了孔径约0．5μm的微孔滤膜，其性能指标可基本达到商业膜的标准．     

两步沉淀聚合法制备表面具有羧基的核-壳微球

以高交联的聚二乙烯基苯-55(poly(DVB-55))为核,甲苯/乙腈(体积比1∶3)混合溶剂,采用两步沉淀聚合法,在核的表面接枝了具有羧基官能团的较低交联度的壳,得到了单分散或窄分散微米尺度的poly(DVB55)/poly(DVB55-co-methacrylic acid)核-壳微球。结果表明,以甲苯/乙腈混合物替代纯乙腈作为反应介质可以获得比表面积、孔容、接枝量和粒径相对较大的核-壳微球;随着poly(DVB-55)核的用量的增加或反应时间的缩短或单体和交联剂投料浓度的减小,所得的核-壳微球的粒径减小、接枝量降低、粘连程度减小,微球的均匀性则升高。     

分散聚合法制备二氧化硅/ 聚苯乙烯单分散复合微球

在醇/ 水混合介质中用分散聚合方法制备二氧化硅/ 聚苯乙烯单分散复合微球。探讨了分散聚合法制备无机/ 有机复合微球的过程, 考察了分散聚合反应的动力学过程。SEM 和TEM 观察结果表明: 在醇/ 水混合介质中, 用PVP K-30 作为稳定剂, 用分散聚合法制备了单分散的以二氧化硅为核、聚苯乙烯为壳的复合微球,成功实现了聚苯乙烯对二氧化硅的包覆, 复合微球的平均粒径为1.25μm , 分散系数ε为0.035 , 达到了单分散水平。还考察了稳定剂的浓度对复合微球粒径的影响, 当稳定剂PVP K-30 浓度增加时, 发现微球的粒径有所减小, 而微球的单分散性提高。      

单因素对单分散二氧化硅微球制备的影响

以氨水为催化剂、正硅酸乙酯为硅源、醇为溶剂,采用改进的溶胶-凝胶工艺制备单分散SiO2微球,通过扫描电镜、激光粒度分析仪着重研究了正硅酸乙酯添加方式、反应温度、溶剂类型等单因素对SiO2的颗粒大小和形貌的影响.结果表明,正硅酸水解对醇溶剂是有选择性的,乙醇作为溶剂合成SiO2的单分散性和球形度最好.连续滴定和分步滴定更有利于单分散SiO2微球的形成.水解温度升高,生成的颗粒粒径将运渐增大,最佳反应温度为常温25℃或恒温水浴25～35℃.     

CaCl2电解质对制备二氧化硅微球的影响

对比研究了微量CaCl2电解质对直接法生长和以种子法生长制备二氧化硅微球的影响.随着CaCl2加入量的增加,两种制备途径所得球体粒径的大小和分散度都出现明显变化,当Ca2+的浓度达到3.3mmol/L时,颗粒已不能保持球体形状,开始成絮状物.通过对结果的对比分析,为理解二氧化硅球体生长机理提供了帮助.     

A facile method for the preparation of hollow silver spheres

A new method for the preparation of hollow silver spheres was proposed. In the preparation process the mercapto groups played an important role in the process of forming starch/silver core-shell structure, which provided nucleation sites for the growth of a silver shell. Removal of the starch core is realized by degrading the starch template with α-amylase. The morphology of the starch/silver core-shell nanocomposite and the hollow silver spheres was characterized by TEM and AFM.     

Fabrication of hollow silver spheres by MPTMS-functionalized hollow silica spheres as templates

In this study, we provide a strategy to prepare the hollow silver spheres by accumulating the silver nanoparticles on the surface of 3-mercaptopropyltrimethoxysilane (MPTMS)-functionalized silica as templates, which was accomplished by the chemisorption between silver nanoparticles and thiol groups. Then, the resulting hollow silver spheres were obtained through the chemical wet etching process with 10 M HF solution. In conventional method, the fabrication of hollow silver spheres from core-shell spheres was not easy due to the difficulties in retaining the shell structures during core removal. The method in this paper could overcome this limitation. The major focus of study is on understanding the mechanism of formation of the hollow silver spheres through the self-assembly behavior by chemisorption between silver nanoparticles and thiol groups. The silver-coated silica and hollow silver spheres were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high-resolution TEM (HR-TEM), and X-ray photoelectron spectroscopy (XPS).     

Zinc sulfide nanocoating of silica submicron spheres using a single-source method

A chemical method to coat submicron silica particles with nanocrystalline zinc sulfide is described. The ZnS nanocoating was obtained by the thermalysis of zinc diethyldithiocarbamate in the presence of morphologically well defined silica particles. The powders obtained were isolated and were characterized by UV/visible optical reflectance, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The results showed that the silica surfaces became homogeneously coated with ZnS as the reaction time was increased. This coating consists in clusters of small ZnS particles whose dimensions are within the nanometric range.     

Phosphonic acid-functionalized hollow silica spheres by nitroxide mediated polymerization

A new strategy to prepare phosphonic acid-functionalized hollow silica spheres is proposed via nitroxide mediated polymerization of diisopropyl p-vinylbenzyl phosphonate on the surface of hollow silica spheres (HSSs) and hydrolysis thereafter. The thickness of the organic layer of PVBPA can be controlled by the quantity of the monomers. The structure and morphology of poly(vinylbenzyl phosphonic acid) (PVBPA) grafted HSSs (HPSSs) are confirmed by FTIR and TEM. The addition of HPSS in PVBPA membranes can improve the water retentivity of the composite membranes. The composite membranes with HPSSs exhibit higher water uptake and proton conductivity than the pure PVBPA membranes.     

A facile method for rapid preparation of individual titania nanotube powders by a two-step process

Present study reports a facile method for preparing individual TiO₂ nanotube (NT) powders by a two-step process, which includes that TiO₂ NT bundles are rapidly synthesized by an electro-chemical process in perchlorate-containing electrolyte and then they are disaggregated into individual TiO₂ NT powders under an assistance of ultrasonic oscillation treatment. Morphological and microstructural properties of the individual TiO₂ NT powders are characterized by field emission scanning electron microscopy and transmission electron microscopy. Results indicate that the individual TiO₂ NT powders, which have an outer diameter of about 20 nm and an inner diameter of 10 nm, can be easily obtained from the disaggregation of the TiO₂ NT-bundles by combining the electrochemical process with the physical processing. Furthermore, the individual TiO₂ NT powders exhibit higher photocatalytic activity than the TiO₂ NT-bundle powders.     

Study of the preparation process for BaO-Al2O3-SiO2 powders by a two-step method

BaO-SiO₂ and Al₂O₃-SiO₂ dried gel powders were prepared by the sol-gel process using TEOS, aluminium nitrate and barium acetate as raw materials. By using these starting materials, -BaAl₂Si₂O₈ (hexacelsian) powders with small particle size were obtained after calcining at 1000 °C. The effects of solvents and prehydrolysis of TEOS on the gelation were studied. The physical and chemical changes, and phase transformation of the gel powders for BaO (Al₂O₃)-SiO₂ and BaO-Al₂O₃-SiO₂ systems during heating were examined using differential thermal analysis, gas chromatography and X-ray diffraction. The particle sizes of the gel powders obtained were also observed by SEM and TEM.     

Facile preparation of monodisperse micrometer-sized hollow silica spheres with tunable size and commendable surface topography

The fabrication of hollow silica spheres (HSS) is of great importance due to its plenty of implications. Till now, several methods to prepare HSS have been reported, which existed some drawbacks. Herein, a facile and efficient approach was developed to successfully fabricate micrometer-sized monodisperse HSS based on templating method. The approach was achieved by changing the initial water volume and using ethylene glycol dimethacrylate (EGDMA) as the crosslinking agent. The alteration of water volume was the key factor in controlling the size of HSS, and EGDMA was used to accessorily enlarge the bulk of template spheres. In this way, the uniform HSS were controlled in micrometer scale, which simultaneously possessed the favorable surface topography. This method could achieve high reproducibility and would become a general method to systematically manipulate the size and shape of inorganic spheres as we expected. Most importantly, the formation mechanism for HSS was presented and some key influencing factors were analyzed.