沉淀法制备CeO2纳米晶与表征

采用乙醇为分散剂和保护剂,用反向沉淀法制备了不同粒径的CeO2纳米晶。XRD分析表明,当焙烧温度为250－800℃时,所合成的CeO2纳米粒子属于立方晶系,空间群为OH^5-FM3M。TEM分析表明,CeO2纳米粒子呈球形,粒度随焙烧温度的增加而增大。热失重分析表明样品的热失重主要受温度的影响,而焙烧时间的影响不大。相对密度分析表明,随CeO2纳米晶粒度的增大,粉末的密度增加。     

掺杂纳米CeO2的纳米玻璃的微观结构研究

采用溶胶-凝胶技术制备了掺杂纳米CeO2的纳米玻璃. XRD分析表明, 掺杂CeO2纳米玻璃为无定形. SEM分析表明, 掺杂纳米CeO2的纳米玻璃中掺杂的纳米粒子分布均匀, 无团聚现象; 玻璃各成分之间混合均匀; 采用不同溶剂所制备的纳米玻璃的致密程度不同. 热分析表明, 掺杂纳米CeO2的纳米玻璃在68 ℃附近有1个吸热峰, 故在该温度时, 应长期保温, 使样品中溶剂充分挥发, 当温度达到500 ℃附近时, 样品几乎不再失重, 仅发生致密化.     

V^5＋离子掺杂纳米氧化铈的合成与表征

以硝酸铈、柠檬酸和偏钒酸铵为原料,采用溶胶-凝胶(sol-Gel)法制备了V5+离子掺杂纳米CeO2粉体.利用X射线粉晶衍射(XRD)和 扫描电镜(SEM)等方法研究了合成反应条件(焙烧温度、V5+掺入量等)对合成物的微观结构、物相组成以及性能的影响.XRD分析表明所合成的CeO2纳米晶粒具有空间群符号为Fm3m的立方晶体结构.随焙烧温度的升高,合成的CeO2晶粒结晶度增高.对甲基蓝的光催化降解试验表明,纳米CeO2对甲基蓝具有较好的光催化降解效果,焙烧温度对纳米CeO2的光催化活性有较大影响,适量V5+的掺入有利于提高纳米 CeO2的光催化降解效果,掺1%V5+离子的CeO2光催化降解甲基蓝6 h,其降解率可达89%以上.     

粒径可控纳米CeO_2的微乳液法合成

以十六烷基三甲基溴化铵(CTAB)/正丁醇/正辛烷/硝酸铈(Ce(NO3)3)水溶液(氨水)所形成的反相微乳液体系合成CeO2前驱体,利用热重(TG)和X射线衍射(XRD)分析方法确定了得到纳米CeO2的适宜焙烧温度为550℃,CeO2前驱体经550℃焙烧后得到纳米CeO2.采用XRD、透射电镜(TEM)、紫外-可见(UV-Vis)分光光度计等表征手段分别对纳米CeO2的晶形、形貌、粒径及紫外吸收性质进行了表征,该纳米CeO2粒子具有立方晶型结构,分散性较好、粒径范围为5-18nm.考察了微乳液中正辛烷与正丁醇质量比、Ce(NO3)3浓度对纳米CeO2粒径的影响,结果表明:利用微乳液法,通过改变微乳液中正辛烷与正丁醇质量比、Ce(NO3)3浓度能够对纳米CeO2粒径进行有效控制;纳米CeO2的粒径均随着正辛烷与正丁醇质量比和Ce(NO3)3浓度的增大而减小.同时,对不同条件下制得的纳米CeO2的紫外吸收性质进行了考察.     

CeO2@Au核壳结构纳米粒子的合成与性质研究

采用沉淀法制备了球形CeO2纳米粒子,将其作为核粒子溶液,然后向其中滴加四氯合金酸溶液,在CeO2胶体表面利用柠檬酸钠还原[AuCl4]-离子,得到了CeO2@Au核壳结构纳米粒子。TEM分析表明,CeO2纳米粒子分散效果好,粒径为5 nm;CeO2@Au核壳粒子为球形,无团聚,平均粒径为15 nm。XRD分析表明,CeO2@Au核壳粒子为晶型结构,属于立方晶系,CeO2空间群为O5H-FM3M,Au的空间群为Fm-3m。UV-vis分析发现,CeO2@Au核壳粒子在300和520 nm处呈现出两个比较强的吸收峰,分别对应于CeO2胶体溶液的吸收峰和金粒子的表面等离子共振吸收峰。EDS分析了核壳结构CeO2@Au纳米粒子中存在Ce,O和Au 3种元素。XPS分析表明,Ce3d3/2和Au4f电子结合能与标准结合能相比发生了变化,说明CeO2与Au之间存在着相互作用。     

透明纳米CeO2的合成与表征

采用胶溶法合成了表面修饰十二烷基苯磺酸钠（DBS）的CeO2纳米粒子有机溶胶，探讨了制轩CeO2纳米有机溶胶的最佳实验条件TEM分析表明，CeO2（DBS）纳米粒子呈球形，约3nm，粒径分布均匀，无团聚现象。ED分析表明，CeO2（DBS）纳米粒子为多晶结构。     

镍基催化剂上乙醇水蒸气重整反应的研究

考察了载体对Ni催化剂乙醇水蒸气重整制氢反应性能的影响。结果表明，Ni/CeO2催化剂具有较好的低温活性和氢气选择性。对Ni担载量和焙烧温度考察发现，400℃焙烧的15%NiCeO2催化剂具有较好的催化性能；继续升高焙烧温度引起NiO和CeO2粒子的显著增大,导致对氢气选择性的降低。较小的Ni和CeO2粒子有利于乙醇水汽重整反应的进行，而大的粒子倾向于乙醇的分解反应。 350℃时,在反应过程中分别添加CO、CO2和CH4的结果表明没有发生CO和CO2甲烷化反应,而发生了一定程度的CH4水汽重整反应。     

纳米CeO2/聚苯乙烯杂化材料的制备及表征

用反相胶束微乳液法制备了纳米CeO2/聚苯乙烯杂化材料 .XRD分析表明,纳米CeO2/聚苯乙烯杂化材料中,CeO2是无定形粒子.XPS分析表明,杂化材料并非简单的物理混合,CeO2纳米粒子与有机物之间存在着一定强度的化学键.FTIR分析表明,CeO2粒子的吸收存在蓝移现象.     

纳米CeO2的形貌控制与表征

以Ce(NO3)3·6H2O和(NH4)2CO3为沉淀源,利用柠檬酸作为络合剂和分散剂,实现了对CeO2前驱体的形貌和尺寸控制,并采用TEM,TGA和XRD等方法对前驱体及其热分解所得纳米CeO2的形貌及结晶性等进行了表征.结果表明,随着柠檬酸加入量的提高,前驱体形貌从纳米线向类球形颗粒变化,焙烧生成的纳米CeO2颗粒的形貌具有明显继承性,所得CeO2属于立方萤石结构,且随焙烧温度的提高,晶化程度增大.     

0,1,3维CeO2的可控制备及CuO/CeO2催化剂上CO氧化反应

以水、乙醇和乙二醇为溶剂,采用溶剂热法可控制备了0,1,3维CeO2.结果表明,0维CeO2由0.2～0.5 μm纳米粒子组成;1维CeO2是直径为25～30 μm,长约500 μm的六方棒;松针型的3维CeO2是由以纳米粒子为单元构成的直径为1～5 μm,长约50 μm的光滑棒组成,其比表面积高达234 m2/g.将...     

A carbanion induced synthesis of highly congested pyrazole and imidazole containing heterocycles

An efficient approach to the synthesis of highly congested di, penta and hexacyclic pyrazoles as well as imidazole fragment containing novel heterocyclic molecule has been developed through a carbanion induced transformation of suitably functionalized 2H-pyran-2-ones, benzo[h]chromene and thiochromeno[4,3-b]pyrans. Due to the presence of fluorescence, we report their prime application metal sensor as off/on switching in ferric ions.     

Selective synthesis of 4,5-dihydroimidazo- and imidazo[1,5-a]quinoxalines via modified Pictet–Spengler reaction

An efficient tandem approach for the selective synthesis of 4,5-dihydroimidazo[1,5-a]quinoxalines 6a–g and imidazo[1,5-a]quinoxalines 7a–h by the reaction of 2-imidazolyl anilines 4a–c with aryl aldehydes 5a–k under mild reaction conditions is described. Introduction of electron releasing alkyl groups in substrates 4a–b was found to be instrumental for the success of the reaction.     

Understanding the Diels-Alder reactivity of 1,2-azaborine analogues

The Diels-Alder reactivity of 1,2-heteroborines (H₄C₄B(H)X, X?=?NH, PH, AsH; O, S, Se) has been computationally explored by means of Density Functional Theory (DFT) calculations. The influence of the HB?=?X fragment on the reactivity of the system has been quantitatively analyzed in detail by means of the so-called Activation Strain Model (ASM) of reactivity. It is found that the interaction between these species and the dienophile is significantly stronger than that computed for their all-carbon isoelectronic counterpart, benzene. In addition, the strain energy plays a key role in the observed reactivity trends. The role of the aromaticity strength of these heteroarenes on the reactivity is also assessed.     

Synthesis of N-substituted carbazolones from α-iodo enaminones via Pd(0)-catalyzed intramolecular coupling under microwave irradiation

A variety of N-aryl and N-alkyl carbazolones were conveniently achieved in good to high yields via Pd₂(dba)₃-mediated intramolecular coupling of N-substituted α-iodo enaminones under microwave irradiation. The Pd(0)-catalyzed cyclization was found to proceed favorably with the more electron-deficient phenyl ring during the reactions involving unsymmetrical N,N-diaryl α-iodo enaminones. This unique property enables the construction of carbazolone skeleton containing nitro substituted benzenoid ring.     

Synthesis of substituted 2,4,5,6-tetrahydrocyclopenta[c]pyrazoles and 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles by intramolecular nitrilimine cycloaddition

Both substituted 2,4,5,6-tetrahydrocyclopenta[c]pyrazoles and 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles have been synthesized by the 3+2 intramolecular dipolar cycloaddition of nitrilimines to alkynes. This cyclization has been extended to more versatile 3-bromo derivatives by the use of alkynylbromides as dipolarophiles.     

Catalyst free,visible-light promoted photoaddition reactions between C60 and N-trimethylsilylmethyl-substituted tertiary amines for synthesis of aminomethyl-1,2-dihydrofullerenes

An efficient and benign method for the preparation of aminomethyl-substituted fullerenes has been developed. The process, involving catalyst free, visible-light irradiation of 10% EtOH-toluene solutions containing fullerene C₆₀ and N-trimethylsilylmethyl-substituted amines by using a 20 W compact fluorescent lamp, leads to formation of aminomethyl-substituted fullerene adducts in a highly efficient manner. The photoaddition reaction takes place via a pathway initiated by visible light absorption by C₆₀, followed by SET from the amine to the triplet excited state of C₆₀. Ethanol-promoted desilylation of the resulting a minimum radical then generates the corresponding α-amino radical which couples with the C₆₀ radical anion to form the anion precursor of the fullerene adducts. The new approach using visible-light takes place under mild conditions and it does not require the use of photocatalysts. Thus, the method developed in this effort could broadens the range of functionalized fullerene derivatives that can be readily prepared.     

Highly efficient and stereoselective cycloaddition of nitrones to indolyl- and pyrrolylacrylates

The reactions of various nitrones with indolyl- and pyrrolylacrylates proceeds regioselectively with high diastereoselectivity in the case of aldonitrones, and represents an effective method for obtaining new indolyl- and pyrrolyl-substituted isoxazolidine carboxylates stabilized by weak (CH?O) and moderate (NH?N) strength intramolecular hydrogen bonding. The resulting cycloadducts exhibit promising in vitro anti-influenza activities.     

Transition metal-free direct amination of benzoxazoles using formamides as nitrogen sources

A transition metal-free method for the direct amination of benzoxazoles using formamides as nitrogen sources is reported, which was mediated by an inexpensive and environmentally friendly tetrabutylammonium iodide/tert-butyl hydroperoxide system and gave the 2-aminobenzoxazole derivatives with moderate to good yields.     

l-Proline-catalyzed five-component domino reaction leading to multifunctionalized 1,2,3,4-tetrahydropyridines

Multifunctionalized 1,2,3,4-tetrahydropyridines are concisely synthesized in good yields via l-proline-catalyzed or l-proline/FeCl₃-cocatalyzed one-pot multicomponent reactions (MCRs). The MCRs involve a domino hydroamination/prins reaction/Mannich-type reaction/intramolecular dehydration-cyclization process. The molecular structure of 5baa, one of multifunctionalized 1,2,3,4-tetrahydropyridines, was confirmed by single-crystal X-ray diffraction.     

Studies of Photoionization of CF3 I by Femtosecond Time-resolved Mass Spectrometry

The multi-photon dissociative photoionization dynamics of CF3I has been studied with femtosecond two-color pump-probe time of flight mass spectra at a pump pulse of 265 nm and a probe pulse of 398 nm. The life constants of CF3I+ and its fragment ions CF3+ and I+ are obtained as (96±7), (198±130) and (167±6)fs, respectively. The multi-photon dynamics leading to these ions differ. CF3I+ corresponds to a (1+2′) transition with one-photon pump excitation to the A band of CF3I. CF3+ are mainly formed by a tow-photon probe excitation to the CF3+ with subsequent dissociation of parent ions. I+ are produced in (2+2′) combined with (1+1′+2′) process. The results provide information on the multi-photon pathways involved.