CuO／ZrO_2超细粒子催化剂的制备和物性结构表征Ⅱ．煅烧温度的影响

ＣｕＯ／ＺｒＯ２超细粒子催化剂的制备和物性结构表征Ⅱ．煅烧温度的影响师江柳刘金尧朱起明（清华大学化学系一碳化工国家重点实验室，北京１０００８４）张鎏张继炎（天津大学化工系，天津３０００７２）关键词氧化铜，氧化锆，超临界流体干燥，超细粒子，煅烧，物性结...     

焙烧温度对低温水煤气变换Au/Fe2O3催化剂性能的影响

采用改性沉积-沉淀法制备了系列低温水煤气变换Au/Fe2O3催化剂,发现经300℃焙烧的样品具有较好的催化活性和稳定性.并运用N2物理吸附、原位X射线粉末衍射(in situ XRD)、程序升温还原(H2-TPR)和X射线光电子能谱(XPS)等技术,探讨焙烧温度对催化剂性能的影响机制,同时对样品的失活原因进行了分析.结果表明,催化剂性能与焙烧温度引起的金和载体氧化铁的相互作用以及载体还原性质的变化密切相关.XPS表征结果说明,尽管反应后在催化剂表面有碳酸盐或类碳酸盐物种生成,但半定量分析表明这些物种的形成不是催化剂失活的主要原因;根据在低温水煤气变换反应过程中Au/Fe2O3催化剂的比表面积明显下降,载体的结晶度也明显提高,推断Au/Fe2O3催化剂载体的结构性质的变化才是其失活的主要原因.     

Sol–gel synthesis of pure nano sized β-tricalcium phosphate crystalline powders

β-Tricalcium phosphate (β-TCP) nano powders (80 nm) were synthesized using a simple sol–gel route with calcium nitrate and potassium dihydrogenphosphate as calcium and phosphorus precursors, respectively. Double distilled water was used as a diluting media for β-TCP sol preparation and ammonia was used to adjust the pH. After aging, the β-TCP gel was dried at 40 °C and calcined to different temperatures ranging from 200 to 800 °C. The dried and calcined powders were characterized for phase composition using X-ray diffractrometry (XRD) and Fourier transform-infrared spectroscopy (FT-IR). The particle size and morphology was studied using Transmission electron microscopy (TEM). Calcination revealed that with increase in temperature, both the crystallinity and crystallite size of β-TCP particles increased. Particle size distribution analysis of the calcined β-TCP at 800 °C showed a narrow skewed distribution plot centered between 70 and 80 nm. This value was in closed agreement with particle size values obtained from XRD analysis (83 ± 6 nm). The present study showed that narrowly distributed, high crystalline, pure β-TCP could be obtained using this simple technique for biomedical applications.     

Synthesis, characterization and effect of calcination temperature on phase transformation and photocatalytic activity of Cu,S-codoped TiO2 nanoparticles

A novel copper and sulfur codoped TiO₂ photocatalyst was synthesized by modified sol-gel method using titanium(IV) isopropoxide, CuCl₂·2H₂O and thiourea as precursors. The samples were characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), scanning electron microscopy equipped with energy dispersive X-ray micro-analysis (SEM-EDX), transmission electron microscopy (TEM) and Fourier transform infrared (FT-IR) analysis. The XRD results showed undoped and Cu,S-codoped TiO₂ nanoparticles only include anatase phase. Effect of calcination temperature showed rutile phase appears in 650 and 700 °C for undoped and 0.1% Cu,S-codoped TiO₂, respectively. The SEM analysis revealed the doping of Cu and S does not leave any change in morphology of the catalyst surface. The increase of copper doping enhanced “red-shift” in the UV-vis absorption spectra. The TEM images confirmed the dopants suppressed the growth of TiO₂ grains. The photocatalytic activity of samples was tested for degradation of methyl orange (MO) solutions. The results showed photocatalytic activity of the catalysts with 0.05% Cu,0.05% S and 0.1% Cu,0.05% S were higher than that of other catalysts under ultraviolet (UV) and visible irradiation, respectively. Because of synergetic effect of S and Cu, the Cu,S-codoped TiO₂ catalyst has higher activity than undoped and Cu or S doped TiO₂ catalysts.     

焙烧对醛氨缩合催化剂Co-ZSM-5分子筛核磁共振的影响

采用NMR研究了活化焙烧对Co-ZSM-5分子筛结构的影响。结果表明，焙烧使分子筛结构发生了较大变化，焙烧温度高于600℃，分子筛骨架脱铝明显；焙烧温度高于750℃，分子筛骨架结构遭到破坏。     

Humidity sensing properties of ZnO-based fibers by electrospinning

Zinc oxide (ZnO) based fibers with a diameter of 80-100 nm were prepared by electrospinning. Polyvinyl alcohol (PVA) and zinc acetate dihydrate were dissolved in water and the polymer/salt solution was electrospun at 2.5 kV cm⁻¹. The resulting electrospun fibers were subjected to calcination at 500 °C for 2 h to obtain ZnO-based fibers. Humidity sensing properties of the fiber mats were investigated by quartz crystal microbalance (QCM) method and electrical measurements. The adsorption kinetics under constant relative humidity (RH) between 10% and 90% were explained using Langmuir adsorption model. Results of the measurements showed that ZnO-based fibers were found to be promising candidate for humidity sensing applications at room temperature.     

Effect of calcination temperature on porous titania prepared from industrial titanyl sulfate solution

Porous titania with anatase phase was prepared via thermal hydrolysis of industrial titanyl sulfate solution, and subsequent calcination at different temperature. The as-prepared powders were characterized by TG, DSC, XRD, particle size distribution test, N₂ adsorption-desorption isotherm and SEM. Raising calcination temperature could accelerate the crystal growth, enlarge its specific surface area, pore diameter, and improve its photocatalytic activity. While too high temperature could destroy the pore structure even collapse. The optimal calcination temperature is 550 °C, and the obtained sample showed good thermal stability and high photocatalytic activity, with specific surface area of 189.3 m²/g and higher degree of crystallinity, and its photocatalytic degradation rate of methylene blue was of 95.76%.     

焙烧气氛对LiNi0.5Mn0.5O2中Li/Ni混排及电化学性能的影响

用固相法分别在氧气和空气气氛下合成了层状锂离子电池正极材料LiNi_0.5Mn_0.5O₂, 采用X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、电化学阻抗谱(EIS)及充放电性能测试对其结构、形貌和电化学性质进行表征, 用Rietveld精修计算晶体结构中的Li/Ni混排率, 研究了混排率与电化学性能的关系. 结果显示, 在不同的焙烧气氛下均能合成出纯相和结晶性良好的LiNi_0.5Mn_0.5O₂, 但两种材料在电化学性能上存在一定的差异. 氧气气氛下焙烧合成的材料在首次放电容量, 循环稳定性方面均优于空气气氛下合成的材料. 在0.1C充放电条件下氧气气氛下焙烧得到的LiNi_0.5Mn_0.5O₂材料首次放电容量达到178 mAh·g^-1, 充放电循环50圈后容量为165 mAh·g^-1, 容量保持率为92.7%; 而在空气气氛下焙烧得到的LiNi_0.5Mn_0.5O₂材料首次放电容量为164 mAh·g^-1, 充放电循环50圈后容量为137 mAh·g^-1, 容量保持率为83.5%. 氧气气氛下合成的材料具有较优的电化学性能可归因于氧气气氛下焙烧合成的LiNi_0.5Mn_0.5O₂具有较小的Li/Ni混排率.     

抑制β沸石骨架脱铝的焙烧研究

研究了因焙烧过程升温速率对β沸石模板剂的热分解过程的影响 ,不同升温速率下Naβ沸石焙烧的尾气组成 ;还测定了Naβ沸石的TG -DTG谱 ,40 0℃下Naβ沸石的FTIR谱图 ,以及在不同温度下焙烧 4h后的XRD谱图及2 9Si、2 7Al的NMR结果 .根据这些结果 ,提出了分段焙烧脱胺方法 ,使有机胺在 2 6 0～ 42 0℃间的两个恒温段充分发生Hofmann降解反应 ,从而使分解产生的乙烯和水蒸气能够随空气流自然排出焙烧体系 ,可使焙烧过程中产生的热能得到分阶段逐步地释放 ,同时可避免高温下沸石骨架水热脱铝的负作用 ,得到骨架脱铝少、结晶度高的脱胺 β沸石 .     

Synthesis and Structural Characterizations of Ternary Iron(Ⅱ) Mixed Ligand Complex: Low Cost Materialsas a Precursor for Preparation of Nanometric Fe_2O_3 Oxide

The reaction of the ligands, ethylenediaminetetraacetic acid terasodium salt (Na₄EDTA) and N-N heterocyclic diamines like2,2’-bipyridine (bipy) with iron(Ⅱ) sulfate with 1∶2∶2 stoichiometric ratios form the mononuclear ternary complex of formulae, [Fe₂(EDTA)(bipy)₂] at pH~7. The FTIR and Raman laser spectra of the iron(Ⅱ) complex show that 2,2’-bipyridine is present asa bidentate ligand and the ethylenediaminetetraacetic acid terasodium salt as monodentate carboxylate anion. The electronic spectra and magnetic moments data suggest the six coordination number. It has two iron(Ⅱ) centers in octahedral environments, which are interlinked by carboxylato-O atoms of ethylenediaminetetraacetate and by nitrogen atoms of the two 2,2-bipyridine ligands in a chelating mode. Thermal analysis study show thatiron(Ⅱ) complex containing EDTA and 2,2’-bipyridine on its thermalde composition form the corresponding Fe₂O₃ oxide in nano size at the temperature range ~475 ℃. The iron(Ⅱ) complex was performed as a convenient low cost precursor for the preparation of Fe₂O₃ nanoparticles by the the thermal decomposition method. The iron(Ⅲ) oxide composition has been discussedusing FTIR, X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX).