Preparation And Gas Sensing Properties Of Pt@CNTs Nano-composite

Nanotechnology is a new branch of science developed from the1980s. Nanomaterials have distinct physical and chemical properties due to small size effect, surface effect, quantum size effect and macroscopic quantum tunneling effect, and have potential applications in electronic integration, sensing, detection, display, catalysis, medicine, energy, environment, aerospace and national defence. One-dimensional (1D) nanostructures, such as carbon nanotubes (CNTs), have been demonstrated to be an ideal material system in fabricating nanodevices.CNTs, with small sizes and high surface-to-volume ratio, have been widely focused on due to their applications in sensors, especially gas sensors. CNTs have relatively high gas sensing performance against strong oxidizing and reducing gases. However, there are still many problems in practical applications. Firstly, the sensitivity is not satisfied, which need to be further improved. Secondly, the work temperature of CNTs gas sensors is high, which limits their applications in many situations.In this paper, Pt@CNTs are synthesized, and high sensitivity and low operating temperature maybe be obtained. Details are as follows:CNTs are uniformly coated with Pt nanoparticles by a simple wet chemical method (using formic acid, sodium hydroxide, sodium borohydridc and chloroplatinic acid as reagents). The CNTs are Multi-walled CNTs with lengths of5～15μm and diameters of30～40nm. The average diameter of Pt nanoparticles is about4nm, which have the face-centered cubic crystal structure.Such high gas sensing can be attributed to the electrical effects and Chemical mechanism of Pt nanoparticles. Electrical effects:in the regions nearby the contact between Pt and CNTs, the electron transfer from CNTs to Pt results in an electron depletion layer at CNTs surface, which increases surface-hole-concentration and the sensor conductance. Chemical mechanism: three-phase boundary of Pt/CNTs/Air has more chemical-activity, and the adsorbed oxygen molecules are dispersed with higher rate. More oxygen molecules capture electrons from CNTs and become oxygen ions, which enhance the electron depletion and increase the sensor conductance. As the sensors are exposed to ethanol, the reaction between oxygen ions and ethanol is accelerated by the Pt catalysis effect, which results in high sensitivity and low work temperature. The relationship between sensitivity and ethanol concentration of p-type semiconducting nanomaterials has been investigated with the conductance model, and a universal equation is obtained.Our results indicate that the wet chemical method is an effective method for uniformly coating nanomaterials with Pt nanoparticles; We speculate Pt@CNTs nano-composites have great application in gas sensors with high sensitivity and low work temperature; Pt1D nanostuctures have been obtained by using CNTs as templates, which can be used in other catalysis fields, such as cathode catalyst in the fuel cell.