| Hollow micro nanostructures are widely used in biomedical engineering,chemical catalysis and photonics due to their characteristics of high specific surface area,low density and strong load-bearing capacity.In particular,compared with solid noble metal nanomaterials,hollow noble metal nanomaterials can be exposed more active sites and effectively improve their catalytic performance due to their high specific surface area,internal pore structure and surface defects.At present,the preparation of hollow micro nanostructures mainly adopts the hard template method,and Au,Ag,Cu,ZnO,Cu2O,etc.are usually used as hard template agents.There are some shortcomings:1)high cost;2)there are few types of template morphologies and harsh preparation conditions;3)the template needs to be removed by means of high-temperature calcining,strong acid(such as royal water)and strong alkali dissolution,which are harmful to human body and potentially harmful to the environment.However,calcium carbonate is rich in sources,low in price,environmentally friendly,diverse in morphology,and easy to be removed by dissolving in acid and decomposed at high temperature.It is expected to be an ideal hard template agent for hollow micro-nano materials.The paper aims at preparing hollow Pd and Pt structures.Firstly,the preparation method of submicron spherical calcium carbonate suitable for large-scale synthesis of narrow distribution and monodisperse is explored.Then,by selecting suitable precious metal precursors,reducing agents and adjusting reaction conditions,a layer of Pd and Pt were coated on the surface of calcium carbonate hard template.Finally,the core of calcium carbonate was removed by acid solution to obtain hollow Pd sphere and hollow Pt sphere.The catalytic performance of hollow Pd sphere in formic acid oxidation reaction and the catalytic performance of hollow Pt sphere in methanol oxidation reaction were preliminarily studied.The main research contents are as follows:(1)To explore the preparation method of narrow distribution and monodisperse spherical calcium carbonate,and to explore the method of preparing narrow distribution and monodisperse spherical calcium carbonate based on CO2 carbonization and reversed phase microemulsion method.In the CO2 carbonization method,calcium chloride is used as the calcium source,and NH3·H2O-NH4Cl buffer solution is used as the precipitant to prepare micron-sized spindle,cube,regular hexagon,and irregular and agglomerated spherical calcium carbonate by passing CO2.Furthermore,by using the reversed phase microemulsion system,using calcium chloride as the inorganic calcium source and NH3·H2O as the precipitant,the spherical calcium carbonate of sub-micron size with the uniform morphology,narrow particle size distribution and porous structure was prepared by using external CO2.(2)Hollow Pd sphere structure was prepared based on hard template of calcium carbonate.Hollow Pd spheres were prepared by vacuum reduction of ascorbic acid with K2PdCl4 as Pd source and ascorbic acid as reducing agent.(3)Hollow Pt sphere structure was prepared based on hard template of calcium carbonate.Hollow Pt spheres were prepared by vacuum reduction of ascorbic acid with K2PtCl4 as Pt source and ascorbic acid as reducing agent.(4)Preliminary study on the catalytic properties of hollow Pd and Pt spheres.Compared with the commercial Pd,the oxidation of formic acid by hollow Pd spheres showed higher catalytic activity and stability.Compared with Pt black,hollow Pt spheres showed higher catalytic activity and stability in the oxidation of methanol. |
PDF Full Text Request