Fluorinated and unsubstituted phthalocyanine nanowire chemiresistors for environmental gas monitoring at parts-per-billion levels.

Abstract

This work focuses on developing chemiresistors based on hexadecafluorinated and non-hexadecafluorinated metal phthalocyanine Nanowires (F_xMPc, x= 0 and 16, M = Fe, Co, Cu, Zn, and Ni) to detect gases at extremely low levels, of the order parts per billion (ppb). The thesis describes the synthesis and purification process of the F_xMPc precursor materials and the preparation of sensitive devices by direct growth of nanowires through the physical vapor transport method on interdigitated electrodes. These materials were characterized to validate their composition, structure, and morphology at both stages, after synthesis, and as nanowires. Finally, experiments were carried out to evaluate its performance in detecting and monitoring toxic gases such as NH₃, CO, and NO₂ in ppb and ppm (parts per million).<br /> <br /> For the F₁₆FePc, the response and recovery times adjusted using a double exponential model gave two rate constants: a fast one, in the order of minutes for concentrations higher than 500 ppb, and a slow one, in the order of hours. These rate constants are suitable for industrial gas detection and environmental monitoring in reclamation zones, where longer exposure times are critical in the sampling process. Our F₁₆FePc-nanowire sensor prototypes show a normalized response of ∼10% towards NH₃ at 40 ppb over a measurement time of ∼2.5 h at room temperature and measurable responses at concentrations as low as 5 ppb. For the FePc, experiments were carried out to corroborate their selectivity and detection of CO; an excellent sensitivity of 80 % was obtained for 1 ppm during 4 hours of exposure. For MPc (M= Cu, Zn, and Ni), preliminary detection tests were carried out at 10 ppm for NO₂ during an exposure of approximately 20 min, with promising results, for NiPc a response of 300%, for ZnPc of 3000% and 45,000% of CuPc.<br /> <br /> What finally turns this work into innovative research for developing highly sensitive and selective chemical sensors for detecting different polluting gases using phthalocyanine nanowires. The results obtained in the experiments suggest that these sensors could be helpful in a wide range of industrial and environmental applications, which makes this research of great relevance and of interest for the scientific community. Moreover, the sensors operate with power consumption in the order of a fraction of microwatt, and at room temperature so, no heating is needed making them ideal for developing self-powered, reduced size gas detection devices.<br /> <br />