Synthesis of zirconium disulphide nanomaterials and their nanocomposites with radially aligned nanorutile and polyaniline for room temperature sensing of volatile organic compounds
Date
2022
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Abstract
Integration of 2D nanomaterials with a polymer or semiconductor metal oxide could help in the development of low-cost sensors for rapid detection of volatile organic compounds (VOCs) at room temperature.
This study focuses on the fabrication of robust room temperature sensors of pristine radially aligned nanorutile, and zirconium disulphide/polyaniline (PANI) nanocomposites for chemical sensing of VOCs.
ZrS2 was fabricated using both bottom-up and top-down methods of synthesis. Heat up and hot injection methods were employed to fabricate arrays of morphologies of ZrS2 nanomaterials using the colloidal method. However, the nanomaterials showed high oxophilicity which was confirmed by both XRD and XPS. The XPS peak of S2p was conspicuously absent while the peak Zr3d was very noticeable in the XPS spectra. XPS and EDS measurements indicated replacement of sulphur atom by the O atom on the surface of the nanomaterials. The stability study showed the nanomaterials were not stable in ambient environment.
Nanoparticles of 11 nm and few layered nanosheets were obtained when bulk crystal samples of ZrS2 were exfoliated in cyclohexyl-2-pyrrolidone and N-methyl (-2-) pyrrolidone. Isopropanol served as a green solvent for the exfoliation of few-layered ZrS2 from the bulk crystal sample compared to amide solvents which are not environmentally friendly. However, the pristine ZrS2 nanomaterials could not sense VOCs at room temperature, this could be as a result of low conductivity and number of layers of the nanomaterials obtained using nanomaterials exfoliated in isopropanol. The sensitivity of raw PANI was greatly enhanced with loading of ZrS2 nanomaterials. The sensor displayed responses of 0.43, 0.58, 1.04 and 0.34% which correspond to methanol, ethanol, isopropanol, and acetone vapours respectively. The relatively better responses of the sensor were credited to the synergistic effect of ZrS2/PANI composite structure. The sensor showed good response to low concentrations (7.7 ppm, 11 ppm, 5.8 ppm and 6.1 ppm) which correspond to methanol, ethanol, isopropanol, and acetone respectively. The sensor was more sensitive to isopropanol compared to other alcohols tested for in this work. The behaviour of the sensor changed from p-type to n-type on exposure to ethanol vapour at elevated relative humidity. The sensor displayed good sensitivity, reproducibility, rapid response and recovery times towards alcohols and stability over 60 days.
The hierarchical morphology, high surface area, high porosity and humidity contributed immensely to the titania sensor in the sensing of VOCs at room temperature. The TiO2 sensor showed high sensitivity with responses of -38.27, -86.75, -9.83 and 1.24% which correspond to methanol, ethanol, isopropanol, and acetone respectively. The sensor is more sensitive to ethanol gas compared to other chemical vapours tested. The sensor displayed good sensitivity, reproducibility, rapid response and recovery times towards alcohols and stability over 45 days.
The surface area of the nanorutile decreased by 35% on loading of ZrS2, this could the main reason there was no response observed when the nanocomposite of TiO2-ZrS2 was tested for chemical sensing at room temperature. The active sites for adsorption of the vapour were not available probably due to the covering of pores of the nanorutile as well as low conductivity of ZrS2 at room temperature.
Both sensors of nanocomposite of zirconium disulphide and polyaniline as well as titania could find application in breath analysers since the least detection for a breath analyser is reported to be 200 ppm.
Description
A thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy to the Faculty of Science, University of the Witwatersrand, 2023
Keywords
Zirconium disulphide nanomaterials, Polyaniline, Semiconductor metal oxide