Surface structure-controlled synthesis of nanocrystals through supersaturation dependent growth strategy

纳米晶体很多重要的物理化学性质与其表面结构密切相关, 纳米晶的表面结构调控及相关理论研究是前沿和热点领域.; 本评述总结了非平衡态过饱和条件下纳米晶体生长热力学相关理论及其在离子晶体、分子晶体、贵金属、氧化物、金属有机框架等5类纳米晶体表面结构控制中的应; 用. 从热力学推导出的"类"Thomson-Gibbs方程可以发现, 晶体裸露晶面的表面能与其生长过程生长基元的过饱和度成正比.; 该理论揭示了过饱和度在纳米晶体表面结构控制中的重要作用, 为合理设计合成具有特定表面结构的纳米晶提供了有效指导.Many physical and chemical properties of nanocrystals are closely; related to their surface structures. Studies on the surface structure; control of nanocrystals and related theories are hot and frontier; research topics recently. In this review, we introduce the; supersaturation control strategy and its application in the surface; structure control of nanocrystals ranging from ionic, molecular,; metallic, metal oxide, to metal-organic frameworks crystals. Deduced; from thermodynamics, it can be found that the surface energy of; nanocrystals is directly proportional to the supersaturation of growth; units. The relationship between supersaturation and surface energy; provides an important theoretical basis for the controlled synthesis of; nanocrystals with specific surface structure.国家重点基础研究发展计划; 国家自然科学基金项目; 中央高校基本科研业务费专项资金资助; 中国博士后科学基

C–X(X = Cl, Br, I) bond dissociation energy as a descriptor for the redispersion of sintered Au/AC catalysts

负载型Au基催化剂在工业过程中具有非常广泛的潜在应用,如催化加氢/脱氢过程、精细化学品合成、能源催化转化及环境保护等过程,表现出很高的催化活性和选择性.Au基催化剂活性物种或活性中心基本由纳米粒子或化合物构成,但在应用过程中因Ostwald熟化效应或粒子迁移作用,尤其是高温高压等苛刻反应条件下,均随应用时间延长从小尺寸粒子逐渐长为大粒子,造成活性降低或完全失活,这也是负载型催化剂失活的最主要原因之一.其中因成本、稀缺等特性,负载型Au催化剂的烧结问题是影响和制约其应用的主要因素.除可通过载体改性、助剂和官能团配位稳定等方法来延缓其失活过程外,对已烧结催化剂的高效、快捷和绿色的再分散/再生过程也具有基础和应用研究的重要意义.活性炭载Au催化剂(Au/AC)广泛应用于乙炔氢氯化反应中,以期替代高毒性的汞基催化剂,但在反应过程中因高活性的Au~(3+)物种易被还原而形成Au~0物种进而烧结导致失活;如新鲜Au/AC催化剂表面的Au粒子尺寸为1-2 nm,经乙炔氢氯化反应后变为33 nm左右;随之在453 K、0.1 MPa、乙炔体积空速(GHSV)为600 h~(-1)、氯化氢与乙炔摩尔比为1.1的反应条件下,乙炔转化率从81.8%降至11.2%.如何有效对大粒子Au再分散/再生可为其应用提供有力支撑.有研究表明,气相CHI_3在甲醇羰基化反应过程中明显改变Au/AC表面的Au粒子尺寸;或采用浓盐酸或王水也可将烧结的Au/AC催化剂进行再分散/再生.但已有的Au基催化剂再分散/再生过程均伴随着强酸、强氧化或高毒性在分散剂的应用,对环境的影响及后续处理有明显的局限性,且再分散机理尚不明确.在前期工作基础上,本文采用系列卤代烃(碘代烃、溴代烃和氯代烃)对烧结的Au/AC进行再分散/再生研究.结果表明,在室温常压条件下CHI_3可以快捷高效地对烧结Au/AC催化剂进行再分散/再生,具有最优的再分散性能;通过对系列碘代烃C-I键的解离能分析,发现C-I解离能越低越有利于大粒子Au的再分散.同时,溴代烃和氯代烃对烧结的Au/AC催化剂也具有再分散能力,但比碘代烃的再分散效率低.C-X键的解离能与再分散效率有高相关性,即C-X键的解离能越低越有利于Au的再分散.总体上,三类卤代烃再分散效率高低顺序为C-I>C-Br>C-Cl.进而,通过不同分散过程中Au粒子分散状态推测了卤代烃对Au粒子的再分散机理,即卤代烃先在Au粒子表面化学吸附,然后C-X键解离,形成Au-X物种,小粒子Au在AC表面聚集并稳定,最后形成高分散Au粒子(粒径<1 nm)催化剂.以乙炔氢氯化反应考察了再生Au/AC催化剂性能,结果表明,该催化剂上乙炔转化率可达79.4%,基本恢复至初始水平,且该方法可对失活催化剂进行多次高效再生.Disintegration or redispersion of supported sintered gold nanoparticles(Au NPs) in the presence of alkyl halide can give catalyst regeneration or redispersion of sintered Au catalysts. The selectivity of alkyl halides, temperature and size distributions were investigated to elucidate the redispersion of Au NPs during halide-induced decomposition. This study proved that the alkyl halide induced the redispersion of sintered Au NPs which depended on the R–X(X = I, Br, Cl) bond dissociation energy(BDE) and thus provided a simple descriptor for the regeneration of inactive supported Au cata-lysts. A correlation between the BDE of R–X and dispersion efficiency was established. The tendency for disintegration and redispersion followed the R–X BDE of the alkyl halide. Compared to alkyl chlorides and bromides, iodides were more efficient for redispersing sintered Au NPs. As a descriptor, the BDE of R–I played a crucial role in particle redispersion. These findings provided insights into the mechanism of organic halide-induced Au NP disintegration and the effect of the halide type on the redispersion of sintered catalysts.国家自然科学基金(21403178,21473145,21503173,91545115);; 教育部创新团队发展计划(IRT_14R31);; 福建省青年教师教学科研基金(JA15003

Preparation and optical properties of ThO2 and Eu-doped ThO2 nanotubes by the sol-gel method combined with porous anodic aluminum oxide template

通讯作者地址: Xie, ZX (通讯作者), Xiamen Univ, Coll Chem & Chem Engn, State Key Lab Phys Chem Solid Surfaces, Xiamen 361005, Peoples R China 地址: 1. Xiamen Univ, Coll Chem & Chem Engn, State Key Lab Phys Chem Solid Surfaces, Xiamen 361005, Peoples R China 2. Xiamen Univ, Coll Chem & Chem Engn, Dept Chem, Xiamen 361005, Peoples R China 电子邮件地址: [email protected] this paper, we report the synthesis of thorium oxide and Eu-doped thorium oxide nanotubes for the first time using the sol-gel method in porous anodic aluminum oxide template. Transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were applied to characterize the morphology and structure of the as-prepared nanotubes. It has been demonstrated that Eu3+ ions were homogeneously doped into the ThO2 crystal lattice. The optical properties resulting from Eu-doped products were investigated by means of photoluminescence spectroscopy. Strong visible light emissions were observed at low doping concentration, and the luminescent intensity decreased at high doping concentration. The luminescent centers were concluded to be the Eu3+ ions in the cubic (O-h) sites rather than the C-3 upsilon sites, which accounted well for the decrease of luminescent intensity at high doping concentration

石墨烯复合材料及其制备方法

本发明提供了一种石墨烯复合材料，包括：基体；复合于所述基体上的石墨烯层；复合于所述石墨烯层上的保护膜层；所述保护膜层由前驱体树脂与导电物质组成。本申请通过在石墨烯表面复合包括前驱体树脂与导电物质的保护膜层，其中前驱体树脂使保护膜层具有良好的耐刮擦性与高透光性，导电物质使保护膜在垂直薄膜方向导电，从而使保护膜具有高透光性、垂直薄膜方向导电以及耐刮擦性。本申请还提供了一种石墨烯复合材料的制备方法

一种保护基底上石墨烯层的方法和石墨烯复合材料

本申请属于石墨烯领域，尤其涉及一种保护基底上石墨烯层的方法和石墨烯复合材料。本发明通过在保护膜和-或石墨烯层施加一定的静电，使保护膜依靠静电力吸附在石墨烯层表面，避免了基底上的石墨烯层在运输和储存过程中出现刮擦和染尘，同时由于静电力远远小于分子间范德华力，使得保护膜在撕脱过程中不会粘附基底上石墨烯，保证了基底上石墨烯层的完好