两种络合剂对Ce-Sn-O复合氧化物结构与性能的影响

分别以柠檬酸、葡萄糖为络合剂, 用溶胶-凝胶法制备了CeO2和掺杂少量Sn的Ce-Sn-O复合氧化物, 利用XRD、TPR、FT-IR、比表面法、TEM等方法表征了四种催化剂的物理化学性质, 同时以甲烷催化燃烧反应为探针对其进行了活性评价. 结果表明, 以葡萄糖为络合剂合成的掺杂锡后的样品其甲烷完全转化温度较低, 比表面积较大, 通过透射电子显微镜观察, 平均晶粒大小为14 nm 左右, 且分散性良好, 而相比之下柠檬酸为络合剂合成的样品出现明显的团聚现象.     

Characterization of the transition between the monohydrate and the anhydrous citric acid

The knowledge of the thermodynamic parameters related to the hydration of organic solid phases is paramount to exert a very good control over this transition during industrial production or storage. To study this phenomenon, the citric acid was chosen as a model compound. By an original combination of gravimetric and thermal analyses (dynamic vapor sorption and discontinuous isoperibolic thermal analysis, respectively) with structural determination (prototype of in situ X-ray diffractometer) the hydrate/anhydrate transition of the citric acid was thermodynamically characterized by determining: (i) the temperature associated to the peritectic transition <CA, 1H₂O> ? <CA> + H₂O_l, as well as (ii) the minimum relative humidity of hydration, and (iii) the critical relative humidity of deliquescence versus temperature. All these studies lead to the proposition of phase diagram between citric acid and water as a function of temperature and partial vapor pressure of water.     

溶胶-凝胶法制备Ni_2V_2O_7的丙烷氧化脱氢催化性能

以柠檬酸为配位剂,溶胶-凝胶法制备Ni2V2O7,采用X射线衍射、氮气物理吸附、电感耦合等离子体原子发射光谱、氢气程序升温还原、X射线光电子能谱和透射电子显微镜等技术对催化剂进行了表征.通过差热-热重分析,考察干凝胶分解为Ni2V2O7的温度以及分解过程的热效应并研究了不同焙烧温度与Ni2V2O7的形成、晶化程度之间的关系以及对丙烷氧化脱氢(ODH)制丙烯反应催化性能的影响.     

Electrospun Nickel Oxide Hollow Nanostructured Fibers

The citric acid/nickel acetate composite hollow fibers were prepared by using sol-gel processing and co-electrospinning technique. The polycrystalline NiO hollow nanostructured fibers were prepared after calcination. The obtained hollow nanostructured fibers made up of 17～25 nm nanocrystals were about 150 nm to several micrometers in outer diameter. The hollow NiO nanostructured fibers have been characterized by TG, DSC, SEM, FTIR, and XRD techniques. The results showed that the morphology of NiO hollow fibers was obviously influenced by the calcination temperature.     

Redox-responsive gel-sol/sol-gel transition in poly(acrylic acid) aqueous solution containing Fe(III) ions switched by light

Redox-responsive gel-sol/sol-gel transition in aqueous PAA system containing Fe(III)-citrate complex was realized by switching the redox states of Fe(III)/F(II) ions conjugated with photoreduction and oxidation. This reversible transition can be indicated chromatically by the Fe(III) ions and repeated many times as long as there is sufficient citric acid.     

Rheological properties of reversible thermo-setting in situ gelling solutions with the methylcellulose–polyethylene glycol–citric acid ternary system

Colloid and Polymer Science - The composition of vehicle on the reversible sol-gel transition temperature in a ternary system made up of methylcellulose (MC), polyethylene glycol (PEG), and citric...     

钙钛矿型复合氧化物CaVO3的制备及对氧还原反应的电催化性能

以五氧化二钒、硝酸钙、柠檬酸和草酸为原料,采用溶胶-凝胶法制备出CaVO₃的前驱体,在氩气保护下1000 ℃煅烧2 h,成功制备出目标产物CaVO₃.对前驱体和目标产物分别进行了傅里叶变换红外(FTIR)光谱、热重(TG)分析、X射线衍射(XRD)和电导率等表征.在1 mol·L^-1的KOH电解质溶液中测试了样品的氧还原反应(ORR)催化性能.结果表明,修饰电极上(ORR)的电子转移数是1.5-1.7,发生的是2电子还原.     

Investigation of sol-gel transition in pluronic F127/D2O solutions using a combination of small-angle neutron scattering and monte carlo simulation

Physical gelation in the concentrated Pluronic F127/D2O solution has been studied by a combination of small-angle neutron scattering (SANS) and Monte Carlo simulation. A 15% F127/D2O solution exhibits a sol-gel transition at low temperature and a gel-sol transition at the higher temperature, as evidenced by SANS and Monte Carlo simulation studies. Our SANS and simulation results also suggest that the sol-gel transition is dominated by the formation of a percolated polymer network, while the gel-sol transition is determined by the loss of bound solvent. Furthermore, different diffusion behaviors of different bound solvents and free solvent are observed. We expect that this approach can be further extended to study phase behaviors of other systems with similar sol-gel phase diagrams.     

锂离子电池正极材料xLi2MnO3·(1-x)Li[Ni1/3Mn1/3Co1/3]O2的制备及表征

以过渡金属乙酸盐和乙酸锂为原料,柠檬酸为螯合剂,通过溶胶-凝胶法结合高温煅烧法制备了锂离子电池富锂锰基正极材料xLi2MnO3·(1-x)Li[Ni1/3Mn1/3Co1/3]O2,采用X射线衍射(XRD),扫描电子显微镜(SEM)和电化学性能测试对所得样品的结构,形貌及电化学性能进行了表征.结果表明:x=0.5时,在900°C下煅烧12h得到颗粒均匀细小的层状xLi2MnO3·(1-x)Li[Ni1/3Mn1/3Co1/3]O2材料,并具有良好的电化学性能,在室温下以20mA·g-1的电流密度充放电,2.0-4.8V电位范围内首次放电比容量高达260.0mAh·g-1,循环40次后放电比容量为244.7mAh·g-1,容量保持率为94.12%.     

Effect of Molar Ratio of Citric Acid to Metal Nitrate on the Structure and Catalytic Activity of NiO Nanoparticles

NiO nanoparticles were prepared by means of sol-gel method via varying the ratio of citric acid to nickel nitrate. The samples were characterized by powder X-ray diffraction(XRD), Fourier transform infrared(FTIR) spectroscopy, transmission electron microscopy(TEM) and X-ray photoelectron spectroscopy(XPS). It was found that the molar ratio of citric acid to nickel nitrate has a great effect on the crystal structure and particle size of NiO. The increase of the molar ratio of citric acid to nickel nitrate is favorable to the formation of NiO smaller particles within the range tested. Compared to bulk NiO obtained by thermal decomposition, NiO nanoparticles possess more surface oxygen species O^-. The activity test indicates that surface oxygen species O^- plays a crucial role in the hydroxylation of benzene to phenol with hydrogen peroxide as oxidant. The active site may be originated from Ni²⁺ on the surface of the samples, while Ni⁰ does not contribute to the hydroxylation reaction.     

改性沸石H-BEA催化4-苯基丁酸分子内付克反应合成1-萘满酮

以乙二胺四乙酸二钠（EDTA）、柠檬酸、草酸、酒石酸改性制备了H-BEA,并根据XRD和NH3-TPD对沸石H-BEA进行表征。 采用上述改性沸石催化4-苯基丁酸分子内付克反应合成1-萘满酮进行催化剂反应活性评价。 实验结果表明,以柠檬酸改性沸石H-BEA具有较高的催化活性。 进一步对催化剂用量、反应温度、反应时间等工艺条件优化得到最佳工艺条件,在最佳工艺条件下,产物1-萘满酮产率达到94.3%。     

锂离子电池MnO/TiN负极研究

以乙酸锰和钛酸四丁酯为原料,柠檬酸为络合剂,采用溶胶-凝胶法制备钛酸锰（MnTiO3）粉体,而后将其粉体高温氨气氮化,可得到MnO/TiN复合材料. 使用X射线衍射（XRD）、X射线能量色散谱（EDS）和场发射扫描电子显微镜（FESEM）表征材料的物相结构与组分、观察其形貌. 采用循环伏安、恒流充放电和电化学阻抗方法测试电极电化学性能. 结果表明,MnO/TiN电极在100 mA?g-1和1 A?g-1倍率放电下,比容量分别为394 mAh?g-1和146 mAh?g-1,均高于单纯MnO电极比容量和倍率性能,这归因于复合材料中的TiN提供了导电网络,并有效地抑制了电极在充放电过程中的体积膨胀效应.     

Production of radiolanthanides and radiotherapy research at MURR

Positron annihilation lifetime measurement was applied to study the sol-gel transition of anionic polysaccharide aqueous solutions in terms of free-volume parameters the size, intensity, and size distribution of free volumes of the gelation of K-formk-carrageenan solutions as a function of temperature. Slight variations of free volume size and intensity against temperature were observed near 295 K. The correlation of free-volume data with other physical properties vibrational spectra (IR and Raman), conductivity, SAXS, elastic measurement, differential scanning calorimetry were investigated to understand the mechanism of sol-gel transition of carrageenan.     

La_2NiBO_6催化剂的制备及其对甲烷燃烧反应的催化性能

以柠檬酸为络合剂,采用溶胶-凝胶法制备了一系列双钙钛矿型催化剂La_2NiBO_6(B=Mn,Fe,Co,Cu,Ce),其结构经SEM,XRD,N2-BET和H2-TPR表征。以甲烷燃烧反应为模板反应,研究了La_2NiBO_6的催化性能。结果表明:La_2NiCeO_6催化性能最好,起燃温度T_(10%)为461℃,最终转化温度T_(90%)为565℃。     

Rheological study of physical cross-linked quaternized cellulose hydrogels induced by β-glycerophosphate

As a weak base, β-glycerophosphate (β-GP) was used to spontaneously initiate gelation of quaternized cellulose (QC) solutions at body temperature. The QC/β-GP solutions are flowable below or at room temperature but gel rapidly under physiological conditions. In order to clarify the sol-gel transition process of the QC/β-GP systems, the complex was investigated by dynamic viscoelastic measurements. The shear storage modulus (G') and loss modulus (G″) as a function of (1) concentration of β-GP (c(β-GP)), (2) concentration of QC (c(QC)), (3) degree of substitution (DS; i.e., the average number of substituted hydroxyl groups in the anhydroglucose unit) of QC, (4) viscosity-average molecular weight (M(η)) of QC, and (5) solvent medium were studied by the oscillatory rheology. The sol-gel transition temperature of QC/β-GP solutions decreased with an increase of c(QC) and c(β-GP), the M(η) of QC, and a decrease of the DS of QC and pH of the solvent. The sol-gel transition temperature and time could be easily controlled by adjusting the concentrations of QC and β-GP, M(η) and DS of QC, and the solvent medium. Gels formed after heating were irreversible; i.e., after cooling to lower temperature they could not be dissolved to become liquid again. The aggregation and entanglement of QC chains, electrostatic interaction, and hydrogen bonding between QC and β-GP were the main factors responsible for the irreversible sol-gel transition behavior of QC/β-GP systems.     

La2CoAlO6催化剂的制备及其甲烷催化燃烧性能

采用溶胶-凝胶法, 以柠檬酸为络合剂制备了新型稀土双钙钛矿催化材料La₂CoAlO₆, 利用X射线粉末衍射(XRD)、H₂-程序升温还原(H₂-TPR)、比表面(BET)、扫描电镜(SEM)、傅里叶变换红外(FT-IR)光谱和磁性测试等手段对其进行了表征, 以甲烷催化燃烧反应为探针考察了其催化活性. 结果表明, 在空气气氛中, 经过1100 °C焙烧3 h后, 可以形成稳定的单相稀土双钙钛矿型化合物La₂CoAlO₆, 且该化合物表现出较好的甲烷催化燃烧活性, 起燃温度(T₁₀)和完全转化温度(T₉₀)分别为434.1和657.4 °C. 与稀土单钙钛矿型催化剂LaCoO₃和LaAlO₃相比, 其T₁₀分别降低了56.5和138.2 °C, T₉₀分别降低了84.6和108.9 °C. H₂-程序升温还原结果表明, 稀土双钙钛矿型化合物La₂CoAlO₆有较低的还原温度, 并且经过H₂-程序升温还原反应后, La₂CoAlO₆样品XRD图中的所有衍射峰均向小角度方向发生了移动. 扫描电子显微镜的结果表明, 稀土双钙钛矿型催化剂La₂CoAlO₆表现出无规则的片状形貌及较强的抗烧结性. 此外还发现稀土双钙钛矿型催化剂La₂CoAlO₆的磁滞回线较为特殊.     

MgFe2O4纳米颗粒及其气敏性研究

利用Sol-gel燃烧法合成氧化物MgFe2O4对氯气有很高的灵敏度,并利用XRD对产品的物相进行了分析;用TEM对粉体晶粒和形貌进行检测,将产物粉体制成气敏元件,采用静态配气法在气敏测试仪上进行了灵敏度和响应-恢复曲线的测试,研究证明镁铁复合氧化物对氯气有很好的气敏特性。     

Effects of acidic catalysts on the microstructure and biological property of sol–gel bioactive glass microspheres

Sol–gel bioactive glasses have been developed for bone tissue regeneration and drug delivery systems as they have the unique mesoporous structure and high bioactivity in vitro. To develop more reliable drug delivery and bone tissue repair systems, it is necessary to control the morphology and microstructure of bioactive glasses. For this purpose, bioactive glass microspheres (BGMs) were prepared by a sol–gel co-template technology using acids as catalysts. We studied the effects of different acids (citric acid, lactic acid and acetic acid) on the microstructure and apatite-forming bioactivity of BGM. The apatite-forming bioactivity was carried out in simulated body fluid (SBF). The microstructure and apatite-forming bioactivity of BGMs were characterized by various methods. Results showed that acetic acid had little effect on the structure and bioactivity of BGMs. Differently, the morphology and microstructure of BGMs could be controlled by changing citric acid and lactic acid concentrations. In vitro bioactivity test indicated that citric acid and lactic acid derived BGMs possessed the better apatite-forming capacity than that derived by acetic acid.     

Effect of ortho-methoxycinnamic acid on the sol-gel transition of methylcellulose solutions in the presence of cetyltrimethylammonium bromide

The sol-gel transition of methylcellulose (MC) solutions in the presence of ortho-methoxycinnamic acid (OMCA) or cetyltrimethylammonium bromide (CTAB) and in the coexistence of OMCA and CTAB was determined by the rheological measurement. It has been found that the sol-gel transition temperature of MC solutions increases linearly with the concentration of either OMCA or CTAB in solution, respectively. However, in the coexistence of OMCA and CTAB, the sol-gel transition temperature of MC solutions remains invariable, independent of the concentration of CTAB in solution. The experimental results show that OMCA has priority to adsorb on the methyl group of MC chains to form polymer-bound aggregates. In particular, these aggregates inhibit the hydrophobic interaction between CTAB and the methyl group of MC chains completely. Taking into account the fact that OMCA is almost insoluble in MC-free solutions but dissolves very well in aqueous MC solutions, we propose the formation of the core-shell architecture prompted by OMCA and the methyl group of MC chains, with the methyl group of MC chains serving as the core and the self-assembly of OMCA molecules serving as the shell. Obviously, the formation of the core-shell structure increases the solubility of OMCA, improves the stability of methyl groups of MC chains at high temperatures and inhibits the hydrophobic interaction between CTAB and the methyl group of MC chains in solution. The abnormal behavior relating to the sol-gel transition of MC solutions in the presence of OMCA or in the coexistence of OMCA and CTAB is therefore explained. Upon UV irradiation, the sol-gel transition temperature of MC solutions in the presence of OMCA, or in the coexistence of OMCA and CTAB, decreases notably. However, the dependence of the sol-gel transition temperature of MC solutions as a function of OMCA concentration, or CTAB concentration in the presence of OMCA, does not change after UV irradiation.     

Phase Transitions in Pure and Hybrid Hydrogels: A Fluorescence Study

Summary: Recent observations on phase transitions around the critical point showed that the critical exponents differed drastically from percolation results and classical results for pure hydrogel systems, depending on monomer concentration. In addition to pure hydrogels, the sol-gel phase transition during radical crosslinking copolymerization of acrylamide (AAm) and N-isopropylacrylamide (NIPA) hybrid was studied by using the steady state fluorescence (SSF) technique. N,N′-methylenebis(acrylamide) (BIS) and ammonium persulfate (APS) were used as crosslinker and initiator, respectively. Pyranine (trisodium 8-hydroxypyrene-1,3,6-trisulfonate acid, HPTS) was added as a fluoroprobe for monitoring the polymerization. It was observed that pyranine binds to AAm and NIPA chains on the initiation of the polymerization, thus the fluorescence spectra of the bonded pyranines shift to shorter wavelengths. Fluorescence spectra of the bonded pyranines allowed to monitor the sol-gel phase transition without disturbing the system mechanically and to test the universality of the sol-gel transition as a function of polymer concentration ratios. The observations around the gel point of PAAm-PNIPA hybrid show that the gel fraction exponent β obeyed the percolation result.