通讯波段禁带胶体光子晶体的制备及实验参数研究

采用直径为700nm的二氧化硅微球,通过垂直沉积法在玻璃基片上制备了位于光通讯波段的禁带胶体光子晶体。研究了不同蒸发温度、湿度条件、干燥过程对样品晶体质量的影响。用扫描电子显微镜(SEM)对其形貌进行了观测。实验结果表明,在温度为65℃,相对湿度为70%,缓慢干燥条件下制备出的样品具有较好的晶体质量,晶体在大范围内保持了面心立方(FCC)单晶结构,其(111)面平行于生长基片。     

Engineering and characterization of mesoporous silica-coated magnetic particles for mercury removal from industrial effluents

Mesoporous silica coatings were synthesized on dense liquid silica-coated magnetite particles using cetyl-trimethyl-ammonium chloride (CTAC) as molecular templates, followed by sol-gel process. A specific surface area of the synthesized particles as high as 150 m²/g was obtained. After functionalization with mercapto-propyl-trimethoxy-silane (MPTS) through silanation reaction, the particles exhibited high affinity of mercury in aqueous solutions. Atomic force microscopy (AFM), zeta potential measurement, thermal gravimetric analysis (TGA), analytical transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and atomic absorption spectroscopy (AAS) were used to characterize the synthesis processes, surface functionalization, and mercury adsorption on the synthesized magnetite particles. The loading capacity of the particles for mercury was determined to be as high as 14 mg/g at pH 2. A unique feature of strong magnetism of the synthesized nanocomposite particles makes the subsequent separation of the magnetic sorbents from complex multiphase suspensions convenient and effective.     

Ce-MCM-48立方介孔分子筛结构的光谱表征

在碱性条件下,以混合模板剂pH调节水热合成了掺入铈的介孔分子筛Ce-MCM-48,并采用XRD,DRUV-Vis(紫外-可见漫反射),FTIR,XRF结合BET等测试手段对样品进行表征。实验结果表明,采用本方法所合成的掺铈介孔材料仍保持立方介孔的有序结构,同时适量的铈的掺入和pH调节使分子筛的有序性及吸附性能得到改善,晶胞参数增大,孔径更均一,孔壁增厚。从而可推出Ce-MCM-48的热稳定性、水热稳定性、催化活性及择形选择性可得到提高。掺入的铈以四配位状态高度分散在介孔的有序结构当中。红外光谱表明不同量的铈的掺入对骨架硅的各种振动扰动程度不同。     

掩埋式多模干涉型分束器的反射性能

通过束传播方法(BPM)模拟了SiO2基掩埋式波导结构多模干涉(MMI)型分束器的反射性能,模拟结果表明,MMI工作在分束模式时存在最优的多模干涉长度实现最大输出和最小反射,而在合束模式下实现最大输出时反射也达到最大,这是由自映象原理决定的。SiO2基掩埋式波导结构MMI分束器对反射具有良好的抑制作用,其最大反射功率为-60dB。分析表明,多模干涉区末端的界面反射率决定了器件的反射强弱,SiO2基掩埋式波导的界面反射率非常低,这是其低反射的原因。     

二维衰减全反射红外光谱研究水在聚酰亚胺/二氧化硅纳米高分子复合膜中的吸附扩散行为

考虑到基于聚酰亚胺衍生物的电子器件的稳定性和性能,运用二维衰减全反射红外相关光潜研究了水在聚酰亚胺衍生物:poly(4’4- oxydiphenylene pyromellitimide)和二氧化硅的纳米高分子复合膜中的动态吸附和扩散行为．二维相关光谱区分出了三种不同氢键强度的水分子状态,同时,氢键的数量和强度还对不同状态水分子的扩散速率起了决定性的作用,和PI聚合物本身以及PI表面残留的硅酸形成氢键的水分子的扩散速度则最慢.     

熔融石英玻璃无水环境固结磨粒抛光特性

为了克服游离磨粒抛光的随机性、磨料浪费以及产生的水合层等问题,提出了一种无水环境下熔融石英玻璃固结磨粒抛光技术。研究实现了稳定的抛光轮烧结工艺,并应用于熔融石英玻璃抛光加工,通过对加工产物和抛光轮粉末进行EDS能谱分析和XRD衍射分析,从微观上初步阐述了固结磨粒抛光的去除机理;从宏观上探索压力和转速对去除效率和表面粗糙度的影响。实验结果表明：加工过程中,在法向力和剪切力作用下,CeO₂磨粒和熔融石英发生化学反应,CeO₂将SiO₂带出玻璃,实现材料去除;同时,压力和转速对加工效率影响并不遵循Preston公式,温升和排屑成为决定去除效率的关键。     

Surface characterization by nitrogen adsorption of silica aerogels synthesized from various Si(OR)4 and R″Si(OR′)3 precursors

We report the surface characterization by nitrogen adsorption-desorption technique of organically surface-modified silica aerogels. These solids were prepared through a sol-gel process from various combinations of silicon precursors and co-precursors with the aim of obtaining identically modified materials. The silicon precursors are based on four identical hydrolysable alkoxy groups (methoxy or ethoxy) whereas one of the alkoxy groups in the co-precursors is substituted by a non-hydrolysable alkyl group (methyl, ethyl, n-propyl, iso-butyl, n-octyl, vinyl or phenyl). Obtained alcogels were dried under carbon dioxide supercritical conditions and their specific surface area, pore volume, mesoporosity and pore size distribution were investigated. Mesoporous materials exhibiting high specific surface areas and total pore volumes were obtained, revealing a decreasing porosity along with the use of co-precursors having larger side chains.     

Emulsion Combustion and Flame Spray Synthesis of Zinc Oxide/Silica Particles

Two flame spray methods, emulsion combustion method (ECM) and flame spray pyrolysis (FSP), were compared for synthesis of pure and mixed SiO₂ and ZnO nanoparticles. The effect of silicon precursor was investigated using liquid hexamethyldisiloxane (HMDSO) or SiO₂ sol, while for ZnO zinc acetate (ZA) was used. Gas phase reaction took place when using HMDSO as Si precursor, forming nanoparticles, whereas the SiO₂ sol used as Si source was not evaporated in the flame, creating large aggregates of the sol particles (e.g. 1 m). The FSP of ZA produced ZnO homogeneous nanoparticles. Lower flame temperatures in ECM than in FSP resulted in mixed gas and liquid phase reaction, forming ZnO particles with inhomogeneous sizes. The FSP of HMDSO and ZA led to intimate gas-phase mixing of Zn and Si, suppressing each other's particle growth, forming nanoparticles of 19 nm in BET-equivalent average primary particle diameter. Nucleation of ZnO and SiO₂ occurred independently by ECM of HMDSO and ZA as well as by FSP of the SiO₂ sol and ZA, creating a ZnO and SiO₂ mixture. The reaction of ZnO with SiO₂ was likely to be enhanced by ECM of the SiO₂ sol and ZA where both Zn and Si species were not evaporated completely, resulting in ZnO, -willemite and Zn_1.7SiO₄ mixed phase.     

Enhanced nonlinearity in photonic crystal fiber by germanium doping in the core region

Germanium doping in silica can be used as a method for nonlinearity enhancement.Properties of the enhanced nonlinearity in photonic crystal fiber(PCF)with a GeO2-doped core are investigated theoretically by using all-vector finite element method.Numerical result shows that the nonlinear coefficient of PCF is greatly enhanced with increasing doping concentration,furthermore,optimal radius of the doped region should be considered for the desired operating wavelength.     

Green approaches via nanocatalysis with nanoporous materials: Functionalization of mesoporous materials for single site catalysis

Among the various green keys, catalysis, especially using heterogeneous catalysts, has been powerfully applied to achieve greener chemical processes. Here are presented nanoporous materials which have mesoporosity with the functional groups on the inner pore walls. The materials were synthesized via a rather greener process, such as microwave synthesis, and over these nanocatalysts some of the green chemical reactions were carried out with high activities and selectivities. Cobalt species has been successfully functionalized and stabilized as a Co(III) complex onto SBA-15 support and proven to be an active catalyst in alkylaromatic oxidation with molecular oxygen, styrene epoxidation with tert-butyl hydroperoxide (TBHP), and allylic oxidation of cycloolefins with H₂O₂. Short-channeled amino-functionalized SBA-15 catalyst with hexagonal plate morphology was synthesized directly by using microwave synthesis from the co-condensation of aminopropyl triethoxysilane (APTES) and sodium metasilicate under a strong acidic condition. The catalyst showed high catalytic activity in liquid-phase Knoevenagel condensation reactions, due to easy diffusion and mass transfer of substrates into the short mesopore channel. The HO₃S–SBA-15 was prepared by grafting of mercaptopropyl trimethoxysilane onto the calcined mesoporous silica surface and subsequently oxidized with H₂O₂. The resulting catalyst was applied as a Bronsted solid-acid catalyst for the esterification of oleic acid with methanol.