The Fabrication of Au@C Core/Shell Nanoparticles by Laser Ablation in Solutions and Their Enhancements to a Gas Sensor.

A convenient and flexible route is presented to fabricate gold noble metal nanoparticles wrapped with a controllable ultrathin carbon layer (Au@C) in one step based on laser ablation of the noble metal targets in toluene-ethanol mixed solutions. The obtained metal nanoparticles were <20 nm in size after ablation, and the thickness of the wrapped ultrathin carbon layer was 2 nm in a typical reaction. The size of the inner noble metal nanoparticles could be controlled by adjusting the power of laser ablation, and the thickness of the ultrathin carbon layer can be controlled from 0.6 to 2 nm by laser ablation in different components of organic solution. Then the resultant Au@C core/shell nanoparticles were modified on the surface of In₂O₃ films through a sol-gel technique, and the hydrogen sulfide (H₂S) gas-sensing characteristics of the products were examined. Compared to pure and Au-modified In₂O₃, the Au@C-modified In₂O₃ materials exhibited a revertible and reproducible performance with good sensitivity and very low response times (few seconds) for H₂S gas with a concentrations of 1 to 5 ppm at room temperature. Evidence proved that the ultrathin carbon layer played an important role in the improved H₂S sensor performance. Other noble metals wrapped by the homogeneous carbon shell, such as Ag@C, could also be prepared with this method.