Effect of titanium precursors used in the preparation of graphene oxide/TiO2 composite for gas sensing utilizing quartz crystal microbalance

Abstract Graphene oxide/TiO2 (GO/TiO2) composites were prepared from four Ti precursors, namely, ammonium hexaflourotitanate (AHFT), titanium(IV) chloride, titanium(IV) isopropoxide, and titanium(IV) butoxide. These composites were used to determine the precursor dependence of the gas sensing ability of GO/TiO2 composites using quartz crystal microbalance (QCM). The X-ray diffraction (XRD) analysis indicated that the non-annealed TiO2 obtained from AHFT has the highest crystallinity of the anatase phase. Further, the X-ray photoelectron spectroscopic (XPS) and Fourier transform infrared (FT-IR) spectroscopic analyses confirmed that F and N present in the precursor has been attached to the specific sites of the TiO2 surface via ligand exchange reactions but not substituted into the TiO2 lattice. Although TiO2 alone does not show significant gas adsorption ability, when GO is modified with TiO2, the replacement of surface hydroxyl groups by fluoride groups on the TiO2 surface aids for increased gas adsorption due to the presence of additional surface-active sites. The results conclude that among different TiO2 precursor materials used for the GO/TiO2 composite preparation, the composite prepared with AHFT has the highest vapor sensing ability. The sensitivity of the composite functionalized QCM resonator for the EtOH vapor ranged from 20,000 ppm to 12 ppm. In this sensor, the GO amount in the range between 30% and 50% gives the highest sensor sensitivity for all the gases and vapors examined. It was found that a single sensor for different gases can be prepared using the same materials in the composite but with different mass ratios.