高活性钒酸铋的尿素沉淀法控制合成及其光催化活性增强机制研究

通过普通尿素沉淀法、超声协助和水热尿素法合成出高结晶度的单斜晶白钨矿型的钒酸铋粉末。利用XRD、SEM、DRS等手段分别对合成材料的晶型、微观形貌及光物理性质等进行研究。结果表明3种方法均能得到结晶度较高的钒酸铋颗粒,但微观形貌上有较大差异。在可见光下对难生化降解的红色染料FN-3G的降解效果表明,所合成的三种BiVO₄样品的光催化性能均较好,超声协助法和水热法合成的样品光催化活性增强的机制主要归因于结晶度的提高和比表面积的增大。结晶度的提高可降低电子和空穴复合几率,从而增强光电转换效率;而比表面积的增大主要提高了染料分子的吸附能力。     

ZSM-5分子筛结晶度及晶粒大小的影响因素

以硅溶胶为硅源,偏铝酸钠为铝源,用晶种法制备ZSM-5分子筛.考察了物料混合方式、陈化时间、晶化时间、晶化温度、碱度和水量等对ZSM-5分子筛相对结晶度和晶粒大小的影响.用X射线衍射仪(XRD)、扫描电子显微镜(SEM)和激光粒度分析等对所合成样品进行了表征.结果表明:在一定的高碱度条件下形成高浓度的硅铝酸盐凝胶,才能合成出晶化良好的样品,ZSM-5分子筛是按固相机理形成的;合成ZSM-5分子筛的相对结晶度和平均颗粒度均随晶化温度的升高及硅铝酸盐凝胶浓度的增加而增大,在室温陈化24 h、180℃晶化12～24 h时相对结晶度最高,平均颗粒度基本上与陈化时间无关.     

Pure-silica-zeolite MEL low-k films from nanoparticle suspensions

Following our previous works on pure-silica-zeolite (PSZ) MFI, in this study we explore PSZ MEL as a new option for low-k dielectric films. Our motivation has been to increase the microporosity of the spin-on films by moving to structures with a framework density (FD) lower than MFI. Nanoparticle PSZ MEL suspensions were synthesized by a two-stage method that allowed the yield of nanocrystals to be significantly enhanced, while the zeolite nanocrystals remain small. For the first time zeolite nanocrystals of about 50 nm were synthesized with a yield as high as 57%. Nanoparticle suspensions with different particle sizes and crystallinities were spun on silicon wafers to prepare continuous thin films. An ultralow-k value as low as 1.5 was obtained with MEL nanoparticle suspension of high relative crystallinity. The surface roughness of the PSZ MEL film with high relative crystallinity is greatly improved (R(rms) approximately 5.6 nm) compared to MFI films with high relative crystallinity (R(rms) approximately 12 nm).     

高表面积MCM-41的合成与性能

通过易于控制的手段，合成出了超高表面积的MCM 41分子筛，并采用XRD、N2吸附脱附、热重 差热分析、SEM等测试手段对合成样品进行分析表征，主要考察了晶化时间对分子筛表面积的影响.其XRD结果表明,合成的固体产物具有六方排列的孔道结构，结晶度高.氮吸附脱附实验表明，产物具有单一的孔径分布，其BET表面积可达1300 m2•g－1左右，合成样品的平均孔径约3.2 nm，适宜的晶化时间是50～100 h.热重分析表明，样品热稳定性好，吡啶升温脱附曲线表明合成的样品具有弱酸性.     

Urea Decomposition Method to Synthesize Hydrotalcites

The urea decomposition property at high temperature has been used to control the pH value in the synthesis of layer compounds. The hydrotalcites of Mg-Al and Ni-Al with high crystallinity were synthesized by using this property.     

Studies on the formation of todorokite-type manganese oxide with different crystalline birnessites by Mg2+-templating reaction

The formation of todorokite-type manganese oxide (TodMO) by hydrothermal soft chemical reaction (Mg2+ exchange followed by hydrothermal treatment) was studied using three kinds of Na-type birnessite (Na-BirMO) with different crystallinities. Buserite (BusMO) formation by Mg2+ exchange and TodMO formation by hydrothermal treatment progressed in a similar manner regardless of the crystallinity of the initial Na-BirMO, but the crystallinity of the synthesized TodMO depended on that of the initial Na-BirMO. Particle morphology of the synthesized TodMO was related to the crystallinity of the initial Na-BirMO. The amounts of fibrous morphology were gradually increasing, accompanied by increased crystallinity of the initial Na-BirMO. TodMO with a neat fibrous morphology was obtained using a high crystalline Na-BirMO as precursor. Most of the interlayer metal ions (Na+ and Mg2+) were extracted from Na-BirMO and BusMO by treatment with a 0.1 M HCl solution, while only 37% of Mg2+ was extracted from TodMO. Both the acid treatment and the particle morphology may be the most convenient method to distinguish TodMO from BusMO.     

Preparation of Eu-Doped Y(2)O(3) Luminescent Nanoparticles in Nonionic Reverse Microemulsions

In this study, Y(2)O(3):Eu luminescent nanoparticles were prepared by precipitation of aqueous yttrium nitrate/europium nitrate solution using ammonium hydroxide in the reverse microemulsions based on polyoxyethylene (5) nonylphenyl ether/polyoxyethylene (9) nonylphenyl ether, cyclohexane, and water. With Eu-doped Y(2)O(3) nanoparticles obtained, particle size, shape, chemical composition, crystalline formation rate, crystallinity, and photoluminescence were measured and compared with those of particles formed by a bulk precipitation method. The nanoparticles synthesized in microemulsion showed a narrow size distribution, spherical shape, fast crystalline formation rate, high crystallinity, and strong photoluminescence. This stronger photoluminescence of particles formed in a microemulsion might be attributed to more densely packed particles with very few voids and higher crystallinity at a relatively low temperature than those synthesized through a bulk precipitation method. Copyright 2000 Academic Press.     

干粉合成中氟离子对ZSM—5沸石的结构定向作用

考察了Ｎａ２Ｏ－ＳｉＯ２－Ａｌ２Ｏ３－ＥＤＡ干粉体系中是否加入ＮａＦ以及加入量对产品物相及结晶度的影响。结果表明,当反应体系不加ＮａＦ时,产物为结晶度高的单一晶相的ＺＳＭ－３５沸石,而体系中加入ＮａＦ时,产品中有ＺＳＭ－５沸石物相出现,而且随着ＮａＦ加入量的增加,产品物相完全转化为具有很高结晶度的单一相ＺＳＭ－５沸石。说明氟离子对干粉体系中ＺＳＭ－５沸石的生成具有明显的结构定向作用     

Dye-sensitized solar cells based on two-dimensional TiO2 nanosheets as the scattering layers

Research on Chemical Intermediates - Two-dimensional (2D) TiO2 nanosheets with high crystallinity and good light scattering properties were synthesized via a simple solvothermal process using...     

两种杂原子复配对Y型分子筛结晶性能的影响

分子筛作为催化剂或催化剂的载体材料广泛应用于各种催化反应过程中,将杂原子引人分子筛骨架中形成杂原子分子筛,可在较大的范围内调节分子筛表面的酸性中心和氧化还原催化活性中心.     

Mo-MCM-48中孔分子筛微波辐射合成的研究

在微波辐射下快速合成含Mo离子的MCM-48分子筛,考察了微波反应釜压力和反应时间对Mo-MCM-48合成的影响,并用XRD,TEM,FT-IR和N2吸附进行表征。结果表明：微波辐射下能快速合成结晶良好的Mo-MCM-48分子筛;合成时以0.481MPa压力、反应2h为宜;Mo离子进入MCM-48分子筛的骨架;焙烧结果表明Mo-MCM-48热稳定性较好。苯乙烯催化氧化结果表明Mo-MCM-48具有一定的催化氧化活性。     

VDF/TFE/PMVE三元共聚物的结构与性能研究

控制不同单体的起始组成合成了一系列偏氟乙烯 (VDF) 四氟乙烯 (TFE) 全氟甲基乙烯基醚 (PMVE)三元共聚物 ,通过1 9F NMR测定了这类三元共聚物的组成 ,结果与按竞聚率的计算结果吻合 .进一步分别用DSC和WAXD表征了玻璃化温度和结晶度 ,实验结果发现用这类三元共聚物制成的硫化胶的性能与其组成和微观结构密切相关     

两阶段晶化合成复合分子筛

采用低温与高温相结合的两阶段晶化方式合成了一系列ZSM-5(core)/SAPO-5(shell)双结构分子筛, 研究了合成条件对核壳结构分子筛的形成及性质的影响, 并采用X射线衍射、扫描电镜、X射线能量散射谱、红外光谱及N₂静态吸附等手段对样品进行表征. 实验结果表明, 与直接高温晶化相比, 两阶段晶化方式在短晶化时间内合成的复合材料中SAPO-5的结晶度较低, 而合成纯SAPO-5分子筛的结晶度却明显较高; 两阶段晶化的方式能适当促进核壳结构型复合分子筛的形成, 减少SAPO-5的独立生长.     

锌皂石的非水热合成与插层组装性能研究

以尿素为羟基缓释剂和pH值控制剂, 在常压和低于100 ℃的温和实验条件下, 用非水热法合成出了八面体片阳离子为Zn^2＋的皂石, 研究了原料的硅铝配比(n_Si/n_Al), 溶液pH值、晶化温度和晶化时间对锌皂石合成的影响, 利用XRD, TEM, IR等手段对样品进行了表征. 结果表明: 合成样品具有三八面体皂石结构; 在比较宽的投料范围内 (n_Si/n_Al＝5.67～19), 合成皂石的晶相和晶形无明显变化; 在初始pH＝6的体系中, 90 ℃晶化12.5 h即可获得结构完整、晶相单一的锌皂石; 非水热条件下, 锌皂石在a向和b向上择优生长, c向生长速度相对较慢; 另外, 利用层间域离子的可交换性和层板带电荷的相反性, 将带正电荷的类水滑石客体层板引入到带负电荷的皂石层间, 形成了c向上单个皂石主体层板与单个类水滑石客体层板交叉堆垛的结构方式.     

Polyethylene Aerogels with Combined Physical and Chemical Crosslinking: Improved Mechanical Resilience and Shape‐Memory Properties

While the introduction of polymers into aerogels strongly enhances their toughness, truly elastic monolithic aerogels which restore their dimensions upon extensive compression are still challenging to synthesize. In this context hydrophobic semi‐crystalline polymers with low glass transition temperatures, and combined stiffness and flexibility, have only recently attracted attention. Shown here is that polyethylene aerogels with a low density, and combined chemical crosslinking and high crystallinity, display high moduli and excellent mechanical resilience. To maximize the crystallinity of these aerogels while maintaining a high crosslinking density, polyethylene networks with well‐defined segments were synthesized by hydrosilylation crosslinking of telechelic, vinyl‐functionalized oligomers obtained from catalyzed chain‐growth polymerization. Recoverable deformations both above and below the melting temperature of polyethylene affords remarkable shape‐memory properties.     

Offretite Zeolite Single Crystals Synthesized by Amphiphile-Templating Approach

Offretite zeolite synthesis in the presence of cetyltrimethylammonium bromide (CTABr) is reported. The offretite crystals were synthesized with a high crystallinity and hexagonal prismatic shape after only 72 h of hydrothermal treatment at 180 °C. The CTABr has dual-functions during the crystallization of offretite, viz. as structure-directing agent and as mesoporogen. The resulting offretite crystals, with a Si/Al ratio of 4.1, possess more acid sites than the conventional offretite due to their high crystallinity and hierarchical structure. The synthesized offretite is also more reactive than its conventional counterpart in the acylation of 2-methylfuran for biofuel production under non-microwave instant heating condition, giving 83.5% conversion with 100% selectivity to the desired product 2-acetyl-5-methylfuran. Hence, this amphiphile synthesis approach offers another cost-effective and alternative route for crystallizing zeolite materials that require expensive organic templates.     

二乙酸甘油酯封端的齐聚L-丙交酯增塑改性聚L-丙交酯薄膜

以二乙酸甘油酯(GD)引发L-丙交酯(LLA)开环聚合合成了二乙酸甘油酯封端的齐聚L-丙交酯(OGLA),并以此为增塑剂,以溶液共混法制备了OGLA与高分子量聚L-丙交酯(PLLA)的共混膜.采用DSC研究了共混膜的T_g和结晶性变化,考察了共混膜的力学性能和渗出性.结果表明:随着OGLA含量的增加,共混物T_g下降,结晶度降低,柔性提高;与聚乳酸相比,随着OGLA含量的增加,拉伸强度、弹性模量有一定程度降低,但断裂伸长率有较大程度的提高,力学性能得到较好的平衡;OGLA增塑体系与GD增塑体系相比较,优势在于避免了小分子增塑剂的渗出.     

SAPO-34分子筛晶化过程的研究

采用XRD、SEM、ICP-AES和MAS NMR等手段系统地研究了SAPO-34分子筛在常规水热合成过程和干胶液相转化过程中的组成和骨架结构的变化.结果表明,常规水热合成法在制备SAPO-34分子筛过程中,硅溶胶缩聚和解聚速率快,活性硅物种数量较少,产品易出现杂晶;采用干胶液相转化法,固体硅源解聚速率较慢,活性硅物种数量逐步增加,SAPO-34分子筛成核和成长的速率得到了控制,抑制了杂晶相的生成,SAPO-34分子筛结晶度逐渐增加.     

锂离子电池正极材料LiFePO4的微波合成及结构表征

以乙酸锂、草酸亚铁、磷酸二氢铵为原料,利用微波法制备出锂离子正极材料磷酸亚铁锂,同时在不同的时间下研究其对反应物合成的影响.用X射线衍射技术、扫描电子显微镜等对产品的晶体结构进行表征,结果表明：微波合成法具有反应时间短、能耗小、合成效率高等优点,其合成的磷酸亚铁锂的晶体结晶度较好、粒度分布较均匀、晶粒比较完整;同时也证实了微波合成是一种比较好的合成方法.     

晶种和溶剂对复合分子筛形成的影响

采用包埋法合成ZSM-5/SAPO-5核壳结构复合分子筛,研究了凝胶组成对该材料性能的影响,并利用X射线衍射和扫描电镜等手段对其进行了表征。结果表明,合成的分子筛是以ZSM-5为核,SAPO-5为壳的双结构复合分子筛。通过向凝胶中加入晶种或者调节溶剂性质可以明显改变复合材料的结晶度和颗粒形貌。引入晶种合成材料的颗粒形貌以椭圆型为主,分子筛的结晶度增加;以醇和水混合物为溶剂合成分子筛的颗粒仍以球形为主,分子筛的结晶速率降低,结晶度的最高值降低。