Graduation Year

2025

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Electrical Engineering

Major Professor

Arash Takshi, Ph.D.

Committee Member

Stephen Saddow, Ph.D.

Committee Member

Jing Wang, Ph.D.

Committee Member

Cai Mike Wang, Ph.D.

Committee Member

Ioannis Spanopoulos, Ph.D.

Keywords

Chemical sensing, Electrochemical detection, Electrochemistry, Perovskite, Photocurrent, Phthalocyanine

Abstract

Volatile Organic Compounds (VOCs) present significant health risks to both humans and animals. Long term exposure to certain VOCs belonging to certain chemical classes can cause both short- and long-term effects including nausea, damage to the central nervous system, and cancer. VOCs can be found in various everyday products like varnishes, paints, cooking items, cleaning products, nail polishes etc. Because of their ubiquitous nature, health concerns and risks regarding VOC exposure have become even more pressing. In this study, the VOC sensing capabilities and trends of novel 2D, and 3D materials (perovskite, and phthalocyanines) have been explored through electrochemical and thin-film fashion. Methylammonium lead iodide (MAPbI3) perovskite has been tested at first, against acetone, ethanol, isopropanol, and methanol, both under dark and illuminated conditions. MAPbI3 showed a good degree of selectivity toward methanol under illuminated condition. The work later focused on phthalocyanines; results indicate that copper phthalocyanine (CuPc) exhibits exceptional selectivity toward formic acid (FA), with a sensitivity of 0.643 µA/ppm. The nitrogen atom of CuPc macrocycles had been protonated by formic acid which led to this enhanced sensitivity toward FA. The material was tested against three other carboxylic acids (acetic acid, benzoic acid, and trifluoroacetic acid) with varying Pka in a 3-electrode fashion to confirm the protonation hypothesis. In the later phase of the work, 6 phthalocyanines (5 metalated, and one metal-free) had been tested against 4 analytes (acetone, acetic acid, ethanol, and isopropanol) in a thin-film fashion, fabricated on interdigitated Au electrodes. Among the metalated phthalocyanines, one has an alkaline earth metal (magnesium phthalocyanine: MgPc), and the rest are transition metal phthalocyanines (TMPcs), namely: cobalt phthalocyanine, (CoPc), copper phthalocyanine (CuPc), iron phthalocyanine (FePc), and zinc phthalocyanine (ZnPc). The responses of the metalated phthalocyanines (MPcs) were compared with that of the metal-free variant (H2Pc) to assess the effect of the metalation in identifying VOC responses. Comparative investigation suggests that even in the absence of the metal cores, the Pc thin-film conductivity changes upon exposure to the VOCs, however, the responses cannot be distinguished from one another, suggesting that the metal core may not be the dominant factor in identifying particular VOC signature. Test results suggested that the conductivity changes were governed by adsorption mechanism, which had been verified by 3-probe electrochemical tests. Based on the findings, it can be concluded that an appropriate choice of the materials according tothe target analytes’ chemical class can solve the problem of identifying VOC signatures responses for ensuring a safer environment.

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