Ag@SiO_2核壳纳米粒子的制备与表征

以NaBH4作还原剂,TEOS为前体,采用反相微乳液法制得粒径50～100nm的Ag@SiO2核壳纳米粒子,其中Ag核为面心立方结构,壳层为无定形SiO2。考察催化剂加入的先后和微乳液R值(R=n水/n表面活性剂)对Ag@SiO2核壳纳米粒子形成的影响。用TEM、UV-Vis、XRD对纳米粒子的形貌及性质进行表征。结果表明:催化剂若先于TEOS加入,易得到Ag@SiO2核壳纳米粒子,随着R值的增加,Ag核的粒径变大,纳米粒子逐渐由单核变成多核。催化剂若后于TEOS加入,则形成负载型Ag/SiO2复合物。Ag核被SiO2壳包覆后的等离子共振吸收峰发生了微弱红移。而当壳厚80nm时,由于SiO2的散射作用,吸收峰会发生蓝移。

Preparation and characterization of Ag@SiO_2 core-shell nanoparticles in microemulsions

Ag@SiO_2 core-shell nanoparticles were fabricated via water-in-oil (W/O) reverse microemulsion process. Using sodium borohydride (NaBH_4) as reducing agent, the silver core was formed in water droplets and packed with amorphous silicon dioxide (SiO_2 shell) formed by the hydrolysis of tetraethyl orthosilicate (TEOS) at the water/oil interface. The obtained nanoparticles were characterized by TEM, UV-Vis and XRD measurements respectively. The diameter of the obtained nanoparticles is approximately from 50 to 100 nm. The size of inner silver core varies by altering the R value (the molar ratio of water to surfactant). The formation of core-shell nanoparticles is affected by the order of ammonia addition. UV-Vis spectra indicated that the plasma resonance absorption of silver core wrapped with SiO_2 has a red shift. XRD pattern proved that the nanoparticles have a structure with a crystalline silver core and an amorphous SiO_2 shell.