河姆渡、罗家角两遗址水稻硅酸体形状特征之比较

对长江下游迄今为止发现的最古老的新石器时代遗址———河姆渡遗址、罗家角遗址进行了植物硅酸体分析 ,结果在两遗址出土的陶器碎片中发现了起源于水稻叶片运动细胞硅酸体。硅酸体的形状解析结果表明 :来自两遗址的硅酸体断面形状大致相同 ,而在大小方面存在显著差异。利用硅酸体形状亚种判别函数进行判别 ,结果河姆渡遗址的稻为粳稻 ,罗家角遗址的稻为籼稻。研究结果表明两遗址的栽培稻群体具有不同系统特性 ,为长江下游的水稻系统演化及稻作起源研究提供了有意义的实证数据。     

Enhanced photocatalytic performance of nanocrystalline TiO2 membrane by both slow photons and stop‐band reflection of photonic crystals

An nc‐TiO₂/SnO₂ inverse opal composite membrane was fabricated, the photo‐activity of which was significantly enhanced by utilizing both slow photons and stop‐band reflection of the photonic crystal layer. The materials of the photonic crystal layer must be transparent in the area of adsorption edge of the nc‐TiO₂, so that SnO₂, having much greater electronic band gap than TiO₂, was used for the materials of the photonic crystal layer. The photonic band‐gap of the SnO₂ photonic crystal was designed at the semiconductor band gap of TiO₂ to harvest slow photons in the interface between the SnO₂ layer and the TiO₂ layer. The two layer structure makes it possible to couple the stop‐band reflectivity of the photonic layer to the photocatalyst. Composite membranes can improve solar energy harvesting and substantially improve photocatalysts for photolysis and photochemical degradation of environmental pollutants. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Facile synthesis of Ag nanoparticles supported on TiO2 inverse opal with enhanced visible-light photocatalytic activity

TiO₂ inverse opal films loaded with silver nanoparticles (ATIO) were synthesized on glass substrates. TiO₂ inverse opal (TIO) films were prepared via a sol-gel process using self-assembly of SiO₂ colloidal crystal template and a facile wet chemical route featuring an AgNO₃ precursor solution to fabricate silver nanoparticles on the TIO films. The inverse opal structure and Ag deposition physically and chemically modify titania, respectively. The catalysts were characterized by Raman spectroscopy, field-emission scanning electron microscopy, high-resolution transmission electron microscopy (HRTEM), UV-vis absorption spectra, X-ray photoelectron spectroscopy and photoluminescence spectroscopy. The HRTEM results show that Ag nanoparticles measuring 5-10 nm were evenly distributed on TIO. Both the UV- and visible-light photocatalytic activities of the samples were evaluated by analyzing the degradation of methylene blue (MB) in aqueous solution. The results reveal that the apparent reaction rate constant (k_app) of MB degradation of the sample ATIO under UV-light irradiation is approximately 1.5 times that of the conventional Ag-loaded TiO₂ film (ATF) without an ordered porous structure at an AgNO₃ concentration of 5 mM in the precursor solution. At an AgNO₃ concentration of 10 mM, the sample exhibits a k_app value approximately 4.2 times that of ATF under visible-light irradiation. This enhanced visible-light photocatalytic performance can be attributed to the synergistic effect of optimized Ag nanoparticle deposition and an ordered macroporous TIO structure. Repeated cycling tests revealed that the samples showed stable photocatalytic activity, even after six repeated cycles.     

Hydrogen activity tuning of Pt-doped WO3 photonic crystal

A photonic crystal responsive to H₂ has been fabricated by replicating polystyrene colloidal crystal template with WO₃ sol-gel, followed with subsequent Pt sputter-deposition. Under H₂ stimulation, the reflection peak of the photonic crystal rapidly shifted to short wavelength and its intensity declined accordingly. The reflection peak returned to its original location after exposure to oxygen atmosphere. The Pt-WO₃ photonic crystal also exhibited excellent, tunable optical performance with high sensitivity to hydrogen in the range of 100% to 0.1%.     

Concept of Templated Lattices of Semiconductor Nanostructures

Design of ordered nanostructured solids by template approach is reviewed. A variety of lattices of semiconductor nanoparticles was formed in the synthetic opal. The impact of an ensemble periodicity upon the electron and photon transport in opal-based lattices has been demonstrated. The conductivity of such lattices is the product of individual transmission characteristics of nanostructures, whereas specific collective properties can be seen as the small additives. In contrast, the photon transport shows strong collective behaviour and the photonic energy band structure is formed in addition to the electronic band structure. If the optical range photonic bandgap is tuned in the resonance with the fundamental electronic gap of a composite, their interference leads to the conjugated equilibrium state of the system.     

混凝土中碱-硅反应的膨胀机理研究

利用高碱活性的蛋白石和低碱活性的天然水晶研究碱—硅反应的膨胀力来源。试样粉磨至40￣80μm后与0.7 mol/L的NaOH溶液混合,至反应达平衡,反应产物用真空干燥。取约1 g产物,压制成直径14 mm,厚约3￣4 mm的薄片后,采用自行设计的FLM1-凝胶膨胀自动测量仪分别在无半渗膜和有半渗膜条件下测量其吸水膨胀量。在无半渗膜条件下,反应产物的吸水膨胀量都很小;在有半渗膜条件下,反应产物吸水后都表现出明显的膨胀现象,其中蛋白石反应产物的膨胀量达85.5%,水晶的膨胀量有5.1%,这与反应溶液的pH值降低趋势相对应,也与样品本身的碱活性大小一致。结果表明,产物吸水肿胀所引起的膨胀量是很有限的,渗透压是碱-硅酸反应的主要膨胀来源,从而为碱-硅反应的渗透压假说提供试验论据。     

三维光子晶体的化学方法制备与应用

描述了光子晶体的基本概念、特征及其材料组成。并详细介绍了用自组装制备三维半导体光子晶体的方法；为了提高电解质的折射率反差，以合成蛋白石为模板剂制备反相蛋白石的方法，最后论述了光子晶体的应用前景。     

A method for determining void arrangements in inverse opals

The periodic arrangement of voids in ceramic materials templated by colloidal crystal arrays (inverse opals) has been analysed by transmission electron microscopy. Individual particles consisting of an approximately spherical array of at least 100 voids were tilted through 90° along a single axis within the transmission electron microscope. The bright‐field images of these particles at high‐symmetry points, their diffractograms calculated by fast Fourier transforms, and the transmission electron microscope goniometer angles were compared with model face‐centred cubic, body‐centred cubic, hexagonal close‐packed, and simple cubic lattices in real and reciprocal space. The spatial periodicities were calculated for two‐dimensional projections. The systematic absences in these diffractograms differed from those found in diffraction patterns from three‐dimensional objects. The experimental data matched only the model face‐centred cubic lattice, so it was concluded that the packing of the voids (and, thus, the polymer spheres that composed the original colloidal crystals) was face‐centred cubic. In face‐centred cubic structures, the stacking‐fault displacementvector is . No stacking faults were observed when viewingthe inverse opal structure along the orthogonal <110>‐type directions, eliminating the possibility of a random hexagonally close‐packed structure for the particles observed. This technique complements synchrotron X‐ray scattering work on colloidal crystals by allowing both real‐space and reciprocal‐space analysis to be carried out on a smaller cross‐sectional area.     

在乙醇介质中制备SiO2光子晶体及其表征

以乙醇为介质,用二氧化硅球沉降法制备有序性较好的人工欧泊(Opal),并对二氧化硅球排布进行了显微形貌及透射谱表征.结果显示二氧化硅微球有序堆积,其结构为类面心立方晶型,与目前的理论研究结果符合得很好.