电催化氧化甲醇反应低成本高活性的Pd核@Pt壳纳米粒子的光化学合成与表征研究(英文)

研究了PEG-丙酮体系中光化学合成Pd纳米粒子并在同一体系内在获得的Pd纳米粒子表面光化学还原Pt(IV)离子获得Pd核@Pt壳纳米粒子。通过改变Pd晶种对Pt(IV)的比例,能够有效调节复合粒子的Pt壳厚度。经HR-TEM和XPS分析,结果表明,获得的纳米粒子的平均粒径为5.3~7.1 nm,具有核-壳复合结构。电化学分析表明Pd:Pt摩尔比1:1、4:1的Pt核@Pt壳纳米粒子具有与Pt相似的催化活性和稳定性,且成本更低,可能被用作直接甲醇燃料电池阳极催化材料。     

铅纳米薄膜熔化温度尺寸效应的分子动力学研究

利用紧束缚分子动力学的方法研究厚度为0.5~10.4 nm自由表面铅纳米薄膜的熔化温度。结果表明,铅纳米薄膜的熔化温度随着薄膜厚度的减小而降低,定量的数值结果与热力学模型预测相一致。薄膜厚度大于3个原子层时才有确定的熔化温度,而单原子层膜和双原子层膜在熔化前就已经破裂。对于自由表面的纳米薄膜,薄膜的熔化从上下表面开始,并逐渐向薄膜的中心逼近,这不同于自由表面纳米粒子的熔化过程,即先表层熔化后内部瞬间熔化。薄膜的熔化开始温度要低于熔化结束温度,这和相应块体材料的熔化温度明显不同。     

FeBP@SiO2核壳结构纳米复合材料的可控制备及其吸波性能

提出一种简便易行的方法制备核壳型FeBP@SiO₂纳米粒子,该方法利用化学还原和溶胶凝胶相结合,实现复合粒子的核壳结构可控。通过改变SiO₂壳厚度,研究了壳层厚度对吸波性能的影响,并对微波吸收机制进行分析和解释。结果表明,随着SiO₂壳层厚度的增加,粒子微波吸收能力先增大后减小。当SiO₂壳层厚度为38 nm时,FeBP@SiO₂样品具有最强的微波吸收性能,在吸收涂层厚度为2.19 mm下反射损耗获得较好的吸收性能(-52.66 dB),这种增强的微波吸收性能主要来自新增磁-介电界面,从而提高了材料的阻抗匹配以及介电损耗的能力,通过设计复合粒子的核壳结构,可以实现复合吸波剂的性能调控,因此本研究为设计下一代新型复合微波吸收材料提供了重要参考。     

在柠檬酸盐溶液体系中金核@铂壳纳米粒子的光化学合成

在含有不同Au:Pt摩尔比的双金属离子和单一Pt(Ⅳ)离子的柠檬酸盐溶液体系中,分别利用光化学共还原和Au晶种生长法合成了Au核@Pt壳纳米粒子。借助于透射电子显微镜的表征,研究了在2种制备方法中复合纳米粒子的尺寸变化规律;利用X射线光电子能谱(XPS)分析了复合纳米粒子的表面化学态和它们的结构,证实形成的Au@Pt纳米粒子为核-壳结构。     

基于紫外光辐照法制备CuSe/ZnSe核壳结构纳米粒子

本文成功制备出以CuSe为核心、ZnSe为壳层,具有核壳结构的CuSe/ZnSe纳米粒子。首先采用回流冷凝法制备出CuSe纳米粒子（NPs）。然后,采用一种简单、快速的光化学方法即紫外光辐照法,室温下在CuSe NPs外包覆ZnSe壳层,最终得到CuSe/ZnSe核壳结构纳米粒子。利用X射线衍射(XRD)、能量色散谱仪(EDS)、透射电镜(TEM)、高分辨透射电镜(HRTEM)和光致发光光谱(PL)对合成的CuSe/ZnSe核壳NPs进行了表征。结果分析表明,合成的CuSe纳米粒子具有六方相结构,粒径平均大小在12 nm。制备出的CuSe/ZnSe纳米粒子的核壳结构清晰,生长的ZnSe壳层为立方闪锌矿结构,粒径大小约为15~45 nm。通过ZnSe壳层的包覆使CuSe在475 nm处产生蓝光发射,同时荧光强度显著增强。     

PS@Au核壳复合粒子的可控合成及粒径对催化性能的影响

采用适当的化学镀工艺,通过对核层聚苯乙烯微球粒径的调制,可控合成了粒径连续可调的PS@Au核壳复合粒子,其球形度较高,无团聚,催化活性优良。利用SEM、XRD和UV-Vis,结合催化性能测试,研究了粒径对PS@Au核壳复合粒子催化性能的影响。结果表明:PS@Au核壳复合粒子较大的比表面积是其取得优良催化性能的物理本质,此外,粒径对其表面微观形貌、Au纳米粒子的生长方式及其催化性能都有显著影响。粒径较小时,核层曲率较大,Au纳米粒子呈发散式生长,表现出孤立的纳米颗粒状结构。此时,比表面积和表面能最大,催化活性最高。随着粒径增大,曲率逐渐减小,Au纳米颗粒表现出近似的薄膜状结构,比表面积和表面能逐渐降低,催化性能逐渐下降。核壳复合粒子的粒径达到400 nm时,Au纳米粒子的表面形貌开始由孤立的颗粒状结构向连续薄膜状过度。     

纳米TiO2包覆SiO2粒子的制备与表征

以微乳法制备的SiO2凝胶粒子(100℃干燥)为核,通过溶胶-凝胶工艺包覆纳米TiO2层,并对纳米TiO2包覆SiO2粒子进行相组成和结构表征.实验结果表明纳米TiO2包覆SiO2所形成的复合粒子的粒径为250 nm左右,其中纳米TiO2包覆壳层较均匀,厚度约为20 nm～40 nm.随煅烧温度的提高(550℃→850℃),包覆纳米TiO2壳层的晶粒尺寸可控制在20 nm以下,且为锐钛矿晶型结构.XPS和FT-IR证实所制备的纳米TiO2壳层与所包覆的SiO2粒子之间形成了Ti-O-Si化学键合.     

原位一步法合成Ag/Fe2O3磁性核壳纳米粒子

采用原位法在低温下一步合成Ag/Fe2O3磁性核壳纳米粒子,并采用XRD,TEM和UV光谱研究了Ag-Fe2O3核壳纳米复合材料的结构。结果表明,纳米银粒子表面被Fe2O3层包覆,Ag核的平均粒径大约为35nm,Fe2O3壳层平均厚度约为7.5nm或15nm,形成了核壳结构的电磁复合纳米粒子。在室温下,饱和磁化强度达到0.98(A·m2)·kg-1,矫顽力8.48×103A/m;Ag/Fe2O3核壳粒子的导电率达到0.62S/cm。通过此法可以比较容易的控制核和壳的尺寸以及复合粒子的单分散性,并得到较高的产率,在催化剂、医药、光电等领域有着广阔的应用前景。     

银纳米粒子熔化的尺寸效应研究

采用分子动力学方法对银纳米粒子进行了熔化过程的模拟,研究分析了银纳米粒子熔化的尺寸效应问题。仿真结果表明,银粒子固-液相变时,其系统势能在某一温度范围内具有明显的突变,熔化过程类似于非晶体,并且银纳米粒子的熔化温度明显低于块状材料,随着纳米粒子尺寸的减小,其熔点也随之降低,根据仿真结果及理论分析建立了纳米粒子熔点与粒径之间的数值关系,并分析了相关的主导机制。     

铂纳米颗粒的XRD和XAS研究

用乙醇还原法制备了PVP包裹的Pt纳米颗粒.X射线衍射(XRD)显示了Pt纳米颗粒的衍射谱与块体铂相同.用X射线吸收谱(XAS)对Pt纳米颗粒的近邻结构进行了研究,发现Pt纳米颗粒的配位数和晶胞参数减小.Pt-L_(2,3)"白线"强度增加,模拟纳米颗粒表面效应的XANES计算不能重现Pt-L_(2,3)实验谱,因此作者把"白线"强度的改变归结为Pt纳米颗粒的重构.     

碳包覆氧化镍纳米颗粒制备与电化学性能研究

采用直流电弧放电等离子体技术制备了核壳结构碳包覆氧化镍纳米颗粒,并采用X射线衍射、高分辨透射电子显微镜、X射线能量色散分析谱仪和表面物理吸附仪等测试技术对样品的微观结构进行研究。并利用循环伏安法、恒电流充放电以及交流阻抗等技术研究其作为超级电容器电极材料的电化学性能。结果表明:直流电弧等离子体技术制备的碳包覆氧化镍纳米颗粒具有典型的核壳结构,内核为面心立方结构的氧化镍纳米颗粒,外壳为碳层。颗粒形貌主要为立方体结构,粒度均匀,分散性良好,粒径分布在30～70 nm范围,平均粒径为50 nm,外壳碳层的厚度为5 nm。碳包覆氧化镍纳米颗粒具有较高的比容量和良好的电化学活性。     

喷雾干燥法制备碳载铂钴镍合金催化剂及其甲醇催化氧化性能研究

本文以氯铂酸、氯化镍和硝酸钴为原料，XC-72炭黑为载体，通过雾化干燥法结合煅烧还原制备碳载铂基（PtCo Ni）分散性好的多元合金纳米粒子催化剂。重点研究表面经过改性的炭黑对合金纳米粒子形成和分散的影响规律，研究碳载PtCoNi（原子比为1:1:1）合金纳米粒子的甲醇催化氧化活性、抗CO中毒能力和耐久性，以及不同原子比对催化氧化甲醇活性和抗CO中毒能力的影响规律。研究结果表明，采用表面改性后的炭黑作为载体，制备的碳载铂基（PtCoNi）催化剂为合金纳米粒子，且纳米粒子在炭黑表面分散均匀，粒径分布在1-4nm，平均粒径为2.3nm；与商用的Pt/C催化剂相比，PtCoNi/C（原子比为1:1:1）催化剂具有更高的甲醇催化氧化活性、耐久性和抗CO中毒性；不同原子比铂基多元催化剂在催化氧化甲醇活性上的顺序为：PtCoNi/C>Pt3CoNi/C>Pt5CoNi/C，抗CO中毒性顺序为：PtCoNi/C>Pt3CoNi/C>Pt5CoNi/C。     

Fabrication and characteristics of spindle Fe2O3@Au core/shell particles

The fabrication and characteristics of spindle Fe2O3@Au core/shell particle were investigated, and the effect of the core/shell nanoparticles as the surface enhanced Raman spectroscopy (SERS)-active substrates was studied. By using the seed-catalyzed reduction technique, anisotropic Fe2O3@Au core/shell particles with spindle morphology were successfully prepared. The Fe2O3 particles with spindle morphology were initially prepared as original cores. The Au nanoparticles of 2 nm were attached onto the Fe2O3 particles through organosilane molecules. Uniform Au shell formed onto Fe2O3 core modified by Au nanoparticles through the in-situ reduction of HAuCl4. The shell thickness was controlled through regulating the concentration of HAuCl4 solution. The results of TEM, XRD and UV-vis characterization show that the core/shell particles with the original shape of the Fe2O3 particles are obtained and these surfaces are covered by Au shell completely. The surface enhanced Raman spectrum of the probe molecules adsorbed on these core/shell substrates is strong and the intensity is enhanced with the increase of the thickness of Au shell or the aspect ratio of particles. The spindle Fe2O3@Au core/shell particles exhibit optimum (SERS) activity.     

金核/铂壳纳米粒子的光化学合成及电催化活性

在含不同摩尔比的Au(Ⅲ)和Pt(Ⅳ)离子的PEG(聚乙二醇)-丙酮溶液中,采用光化学共还原法合成了一组Au@Pt复合纳米粒子,并以炭黑分别对其负载制成Au@Pt/C催化剂。借助于UV-Vis、TEM和HR-TEM的表征,证实复合纳米粒子为球形的核/壳结构;分别以XPS、EDS和电化学方法分析了复合粒子的化学状态、结构特点和Au@Pt/C催化剂的催化性质。结果表明,不同Au:Pt摩尔比的Au@Pt/C催化剂对甲醇氧化反应具有良好的催化活性和稳定性,其中Au:Pt=1:1时形成的Au@Pt/C催化剂电催化活性最高,约为商品Pt/C催化剂的4倍。简要讨论了核/壳结构产生高催化活性的主要原因。     

Expansion of interatomic distances in platinum catalyst nanoparticles

We study the atomistic structure of Pt catalyst nanoparticles using HRTEM (high-resolution transmission electron microscopy). The particles exhibit a faceted, cubo-octahedral shape, extended planar defects, and mono-atomic surface steps. HRTEM imaging with negative spherical aberration yielded atomic-resolution images with a minimum of artifacts. Combining digital image processing, quantitative image analysis, and HRTEM image simulations to determine local variations of the spacing between neighboring Pt atom columns, we have found an expansion of the lattice parameter in the particle core and even larger, locally varying expansion of Pt–Pt next-neighbor distances at the particle surface. The latter likely originates from an amorphous oxide on the nanoparticle surface and/or dissolution of oxygen on subsurface sites. These structural features may significantly impact the catalytic activity of Pt nanoparticles.     

Preparation of novel core-shell nanoparticles by electrochemical synthesis

Nanostructural gold/polyaniline core/shell composite particles on conducting electrode ITO were successfully prepared via electrochemical polymerization of aniline based on 4-aminothiophenol （4-ATP） capped Au nanoparticles. The new approach to the fabrication included three steps： preparation of gold nanoparticles as core by pulse electrodeposition; formation of ATP monolayer on the gold particle surface, which served as a binder and an initiator; polymerization of aniline monomer initiated by ATP molecules under controlled voltage lower than the voltammetric threshold of aniline polymerization, which assured the formation of polyaniline shell film occurred on gold particles selectively Topographic images were also studied by AFM, which indicated the diameter of gold nanoparticles were around 250 run. Coulometry characterization confirmed the shell thickness of polyaniline film was about 30 nm A possible formation mechanism of the Au/polyaniline core-shell nanocomposites was also proposed. The novel as-prepared core-shell nanoparticles have potential application in constructing biosensor when bioactive enzymes are absorbed or embedded in polyaniline shell film.     

Monte Carlo simulations of the structure of Pt-based bimetallic nanoparticles

Pt-based bimetallic nanoparticles have attracted significant attention as a promising replacement for expensive Pt nanoparticles. In the systematic design of bimetallic nanoparticles, it is important to understand their preferred atomic structures. However, compared with unary systems, alloy nanoparticles present greater structural complexity with various compositional configurations, such as mixed-alloy, core–shell, and multishell structures. In this paper, we developed a unified empirical potential model for various Pt-based binary alloys, such as Pd–Pt, Cu–Pt, Au–Pt and Ag–Pt. Within this framework, we performed a series of Monte Carlo (MC) simulations that quantify the energetically favorable atomic arrangements of Pt-based alloy nanoparticles: an intermetallic compound structure for the Pd–Pt alloy, an onion-like multishell structure for the Cu–Pt alloy, and core–shell structures (Au@Pt and Ag@Pt) for the Au–Pt and Ag–Pt alloys. The equilibrium nanoparticle structures for the four alloy types were compared with each other, and the structural features can be interpreted in terms of the interplay of their material properties, such as the surface energy and heat of formation.     

聚苯胺增强 Pt / C 催化剂活性和稳定性研究

目的制备一种具有高稳定性和高催化活性的Pt/C@PANI"核/壳"结构催化剂。方法利用原位化学氧化聚合法制备聚苯胺修饰Pt/C@PANI"核/壳"结构催化剂,采用循环伏安加速寿命实验,结合电化学活性表面积、氧还原活性、X-射线光电子能谱和透射电镜,考察所制备催化剂的活性和稳定性,通过密度泛函理论探究PANI增强Pt/C催化剂活性和稳定性的量子化学本质原因。结果电化学测试表明, Pt/C@PANI催化剂的催化活性与聚苯胺包覆层含量和厚度密切相关,Pt/C@PANI(30%)催化剂具有最好的催化活性,其质量比活性和比表面比活性分别为商业化Pt/C催化剂的1.6和1.8倍。加速寿命实验表明,Pt/C@PANI(30%)催化剂具有很好的稳定性,经过1500圈CV扫描后,其电化学活性表面积仅下降了30%,而商业化Pt/C催化剂降低了83%。理论计算表明,PANI将电子转移给载体C,导致自身空穴增加,PANI部分氧化,导电性增强;PANI的存在使Pt/C@PANI体系的HOMO能级升高,减小了与氧气分子LUMO能级的差异,有利于电子从催化剂HOMO转移到氧分子的LUMO轨道,使得氧容易得到电子;PANI吸附后,Pt原子d带中心显著降低,利于中间物种的脱附,催化活性更高。结论 PANI包覆层抑制了Pt纳米粒子在载体表面的迁移、团聚长大和溶解/再沉积,有效地解决了Pt/C催化剂的Ostwald肿大,催化剂的活性和稳定性得到显著提升。     

直流电弧等离子体制备NiO包覆Ni纳米颗粒

采用直流电弧等离子体技术制备NiO包覆Ni纳米颗粒,对初产物经过钝化处理得到有氧化膜保护的NiO包覆Ni纳米颗粒.采用高分辨透射电子显微镜(HRTEM)、X射线衍射(XRD)、透射电子显微镜(TEM)、选区电子衍射(SAED)、热重和差示扫描量热分析仪(TGA/DSC)以及傅里叶变换红外光谱 (FTIR)等手段对试样的成分、表面组成、形貌、晶体结构、粒度、红外吸收性能和氧化特性进行了分析.结果表明:经过表面钝化处理的NiO包覆Ni纳米颗粒具有明显的核-壳结构,内核为纳米Ni,外壳为NiO氧化物;颗粒呈球形,粒度均匀,分散性良好,粒径分布在20～70 nm范围,平均粒径为44 nm,壳层氧化膜的厚度为5～8 nm;壳核结构可防止纳米Ni颗粒的进一步氧化和团聚,且使红外吸收峰发生蓝移.     

Electrochemical preparation and characterization of gold-polyaniline core-shell nanocomposites on highly oriented pyrolytic graphite

A simple electrochemical method for the in situ preparation of homogeneously dispersed gold-polyaniline core/shell nanocomposite particles with controlled size on the highly oriented pyrolytic graphite(HOPG)was demonstrated.The HOPG surface was modified preferentially by covalent bonding of a two-dimensional 4-aminophenyl monolayer employing diazonium chemistry.AuCl4 -ions were attached to the Ar-NH2 termination and reduced electrochemically.This results in the formation of Au nuclei that could be further grown into gold nanoparticles.The formation of polyaniline as the shell wrap of Au nanoparticle was established by localized electro-polymerization.These core-shell nanocomposites prepared were characterized by AFM and cyclic voltammetry.The results show that the gold-polyaniline core-shell composites on HOPG have a mean particle size of 100 nm in diameter and the polyaniline shell thickness is about 15 nm.