Gas sensors made from electrospun nanofibers doped by functionalized carbon nanotubes

The objective of this thesis is to investigate various nanostructures doped by functionalized carbon nanotubes and explore their application as wearable room temperature gas sensors.;A preliminary study of electrospinning process of nanofibers was made. Pure tin dioxide nanofibers were fabricated by calcining electrospun nanofibers of PVA/stannic hydroxide sol composite as precursor. A simple method for dispersing MWCNTs into tin oxide precursor solutions has been developed and the hybrid SnO2/MWCNTs nanofibers were synthesized by electrospinning followed by calcination in air at 500°C.;Porous SnO2/MWCNTs composites were successfully fabricated by a PVA fiber-template method. Electrospun PVA fibers were used as sacrificial templates for coating with SnO2/MWCNTs precursor solution using a sol-gel deposition technique. Porous structures were formed after the removal of the PVA fiber templates through heat treatment. FESEM showed that the resulting composite materials exhibited an extended network of features separated by large pores with a diameter of 1-21im approximately. Topological defects including open-ended structures and stepped surface with open edges of graphic sheet were created on the MWCNTs after the calcination process.;Two types of gas sensor devices were made based on flexible PET substrates and evaluated with CO gas of a wide range of concentrations. The measurements were carried out by using the sensors fabricated from SnO2/MWCNTs composite fiber mats at steady state. The results show that the n-type SnO 2/MWCNTs nanofibers were able to detect carbon monoxide at 50 ppm at room temperature, while the pure SnO2 nanofibers were insensitive up to 500 ppm. Sensors fabricated from porous SnO2/MWCNTs composites exhibit a reversible and reproducible response, at a bias voltage of 0.5V, to CO in the range of 45--400 ppm at room temperature.;The mechanistic study by TEM shows that after being pretreated in acidic environment under sonication and calcination in air, abundant defect sites are created on the surface of MWCNTs walls. The defect would serve as a binding site for the CO molecule leading to changes in the electronic structure and subsequently in the adsorbate binding energy and charge transfer between gas molecules and sensing materials.