AgPd双金属纳米空心球的合成及其催化性能

Synthesis and catalytic properties of hollow AgPd bimetallic nanospheres

以Ag纳米颗粒为牺牲模板,H_(2)PdCl_(4)为前驱体,抗坏血酸为还原剂,聚乙烯吡咯烷酮为表面活性剂,在70℃下采用电偶置换法结合还原法制备出AgPd双金属纳米空心球。采用紫外可见光谱、粉末X射线衍射、透射电镜结合能量色散等手段对由不同体积的0.01 mol·L^(-1)H_(2)PdCl_(4)溶液制备的产物进行结构表征。结果表明,随着H_(2)PdCl_(4)溶液体积的增加,产物的空心化程度逐渐升高,晶粒的尺寸逐渐增大。当H_(2)PdCl_(4)溶液体积为120μL时,合成的AgPd双金属纳米空心球组成和结构较为均匀,其粒径约为25 nm,壳层厚度2~3 nm。双金属中,由于Ag和Pd电负性的差异,电子从Ag转移到了Pd,使Pd表面出现电子富集区,显著提高了其催化效率。将所合成的AgPd双金属以及纯金属Ag和Pd作为催化剂,分别用于硼氢化钠催化还原4-硝基苯酚的反应,发现AgPd双金属的催化性能远高于纯金属Ag和Pd,其中AgPd-120纳米空心球(H_(2)PdCl_(4)溶液体积120μL)作催化剂时的反应速率常数最高,是同等尺寸纯Ag纳米球的24.0倍,纯Pd纳米立方体的14.7倍。

The paper reports the synthesis of AgPd bimetallic hollow nanospheres at 70℃by galvanic replacement reaction(GRR)coupled with a co‐reduction method using Ag nanoparticles as sacrificial templates,H_(2)PdCl_(4) as precursor,ascorbic acid as reductant,and polyvinyl pyrrolidone as capping agent.To characterize the structures,compositions,and morphologies of the products prepared with different H_(2)PdCl_(4) solution volumes,UV‐Vis spectra,powder X‐ray diffraction,and transmission electron microscope coupled with an energy dispersive spectrometer were used.The results indicate the interior caves of nanospheres gradually become big and densities decrease with the increase of volume of the H_(2)PdCl_(4) solution.Simultaneously,the sizes of nanoparticles increase.When the volume of the H_(2)PdCl_(4) solution was increased to 120μL,we synthesized the uniform hollow AgPd bimetallic nanospheres with outer sizes of about 25 nm and wall thicknesses of 2‐3 nm.The catalytic activities of Ag,Pd,and AgPd bimetals were evaluated using the catalytic hydrogenation of 4‐nitrophenol by an excess of NaBH4 at room temperature.The AgPd bimetals showed superior catalytic activities than pure Ag and Pd due to electron transfer from Ag to Pd.The reaction rate constant of AgPd‐120 nano hollow sphere(120μL of H_(2)PdCl_(4) solution)as a catalyst was the highest,which was 24.0 times that of pure Ag nanospheres of the same size and 14.7 times that of pure Pd nanocubes。