Orthorhombic LiMnO_(2)nanoparticles and LiMnO_(2)nanorods have been synthesized by hydrothermal methods.LiMnO_(2)nanoparticles were synthesized by simple one-step hydrothermal method.To obtain rod-like LiMnO_(2),γ-MnOOH nanorods were first synthesized and then the H+ions were completely replaced by Li+resulting in LiMnO_(2)nanorods.Their electrochemical performances were thoroughly investigated by galvanostatic tests.Although the LiMnO_(2)nanoparticles have smaller size than LiMnO_(2)nanorods,the latter exhibited higher discharge capacity and better cyclability.For example,the discharge capacities of LiMnO_(2)nanorods reached 200 mA·h/g over many cycles and remained above 180 mA·h/g after 30 cycles.However,the maximum capacity of LiMnO_(2)nanoparticles was only 170 mA·h/g and quickly decreased to 110 mA·h/g after 30 cycles.Nanorods with one-dimensional electronic pathways favor the transport of electrons along the length direction and accommodate volume changes resulting from charge/discharge processes.Thus the morphology of LiMnO_(2)may play an important role in electrochemical performance.
Xiaoling XiaoLi WangDingsheng WangXiangming HeQing PengYadong Li
Shape control of nanocrystals has become a significant subject in materials science.In this work,we describe a convenient way to achieve morphology-controllable synthesis of CoO nanocrystals including octahedrons and spheres as well as LiCoO_(2) polyhedrons and spheres.In particular,we explain the formation of CoO octahedrons exposing only high-energy(111)facets using theoretical calculations;these should also be a useful tool for directing future face-controlled preparation of other nanocrystals.More importantly,the as-obtained LiCoO_(2) nanocrystals showed different electrochemical performance depending on their morphology,indicating that Li-insertion/deintercalation dynamics might be crystal face-sensitive.
The catalytic activity of crystallites depends mainly upon the arrangement of surface atoms,the number of dangling bonds,and defect site distribution on different crystal planes.Here,we report the shape-controlled synthesis of CuCl crystallites,including tetrahedra,face-centered-etched tetrahedra,tripod dendrites,and tetrapods.These different morphologies of CuCl crystallites expose different proportions of{111}and{110}crystal planes,and materials with a preponderance of{111}crystal planes have better catalytic activity in aniline coupling than those with more{110}planes.
Ting XieMing GongZhiqiang NiuShuai LiXiaoyu YanYadong Li
Nanocrystalline intermetallics and alloys are novel materials with high surface areas which are potential low-cost and high-performance catalysts.Here,we report a general approach to the synthesis of a large variety of nanocrystalline intermetallics and alloys with controllable composition,size,and morphology:these include Au-,Pd-,Pt-,Ir-,Ru-,and Rh-based bi-or tri-metallic nanocrystals.We find that only those intermetallics and alloys whose effective electronegativity is larger than a critical value(1.93)can be prepared by co-reduction in our synthetic system.Our methodology provides a simple and convenient route to a variety of intermetallic and alloyed nanomaterials which are promising candidates for catalysts for reactions such as methanol oxidation,hydroformylation,the Suzuki reaction,cyclohexene hydroconversion,and the selective hydrogenation of acetylene.
CO oxidation has been performed on Co_(3)O_(4) nanobelts and nanocubes as model catalysts.The Co_(3)O_(4) nanobelts which have a predominance of exposed{011}planes are more active than Co_(3)O_(4) nanocubes with exposed{001}planes.Temperature programmed reduction of CO shows that Co_(3)O_(4) nanobelts have stronger reducing properties than Co_(3)O_(4) nanocubes.The essence of shape and crystal plane effect is revealed by the fact that turnover frequency of Co3+sites of{011}planes on Co_(3)O_(4) nanobelts is far higher than that of{001}planes on Co_(3)O_(4) nanocubes.
Nearly monodisperse spherical amorphous Se colloids are prepared by the dismutation of Na_(2)SeSO_(3)solution at room temperature;by altering the pH of the solution,amorphous Se colloid spheres with sizes of about 120 nm,200 nm,300 nm,and 1μm can be obtained.Se@Ag2Se core/shell spheres are successfully synthesized by using the obtained amorphous Se(a-Se)spheres as templates,indicating the potential applications of these Se nanomaterials in serving as soft templates for other selenides.Meanwhile,selenium nanowires are obtained through a“solid-solution-solid”growth process by dispersing the prepared Se spheres in ethanol.This simple and environmentally benign approach may offer more opportunities in the synthesis and applications of nanocrystal materials.
Nanocrystals are emerging as key materials due to their novel shape-and size-dependent chemical and physical properties that differ drastically from their bulk counterparts.The main challenges in this field remain rationally controlled synthesis and large scale production.This article reviews recent progress in our laboratory related to solution-based synthesis of various nanostructures,including zero-dimensional(0-D)nanocrystals,1-D nanowires and nanorods,hollow structures,and superlattice materials.On the other hand,the essential goal for nanoresearchers is to achieve industrial applications of nanostructured materials.In the past decades,these fascinating materials have been widely used in many promising fields such as nanofabrication,nanodevices,nanobiology,and nanocatalysis.Herein,we focus on their applications as nanocatalysts and try to illustrate the main problems and future directions in this area based on our recent endeavors in catalytic applications of nanocrystals.
Synthesis of tubular nanomaterials has become a prolific area of investigation due to their wide range of applications.A facile solution-based method has been designed to fabricate uniform Bi_(2)S_(3)nanotubes with average size of 20 nm×160 nm using only bismuth nitrate(Bi(NO_(3))_(3)·5H_(2)O)and sulfur powder(S)as the reactants and octadecylamine(ODA)as the solvent.Powder X-ray diffraction(XRD),transmission electron microscopy(TEM),high-resolution TEM(HRTEM),and energy dispersive spectroscopy(EDX)experiments were employed to characterize the resulting Bi_(2)S_(3)nanotubes and the classic rolling mechanism was applied to explain their formation process.
Dingsheng WangChenhui HaoWen ZhengXiaoling MaDeren ChuQing PengYadong Li
