Date of Award

2023

Document Type

Thesis

Publisher

Edith Cowan University

Degree Name

Doctor of Philosophy

School

School of Science

First Supervisor

Magdalena Wajrak

Second Supervisor

Kamal Alameh

Abstract

The measurement of pH value is crucial parameter in various fields like, drinking water monitoring, food preparation, biomedical and environmental applications. The most common device for pH sensing is the conventional pH glass electrode. While glass electrodes have several advantages, such as Nernstian sensitivity, superior ion selectivity, excellent stability, and extensive operating range, they have several key disadvantages. pH glass electrodes need to be stored in buffer solutions, they are fragile and have limited size and shape, making them impractical for some applications, such as being potentially used as miniature pH sensors for capsule endoscopy and ambulatory esophageal pH monitoring. To address these issues of limitations of glass electrodes, various metal oxides have been investigated and proposed as potential electrode materials for the development of pH sensors. Solid metal sensors offer unique features such as insolubility, stability, mechanical strength, and possibility of miniaturization. However, the main drawback of the metal oxide pH sensors is the interference caused by oxidizing and reducing agents present in some sample solutions.

To reduce the redox interference, metal nitride solid sensors were investigated in this project with the potential for the development of high-sensitivity pH sensing electrodes. Metal nitrides are refractory, have high melting points and interstitial defects, and, at room temperature, they are chemically stable and resist hydrolysis caused by weak acids. There are many reports on different metal nitrides electrodes in literature, of which several have been previously investigated for use as pH sensors. Here, specifically, thin films of titanium nitride (TiN) were manufactured using radio frequency magnetron sputtering. The effect of sputtering parameters (e.g., thickness, sputter power, gas composition) were investigated to optimize the materials for use as pH sensor. Additionally, the underlining mechanism governing the pH sensitivity of these metal nitrides was investigated by examining the pH sensing properties (i.e., sensitivity, hysteresis, and drift) and the effect of redox agents. The successfully optimized material was then used to construct and demonstrate the concept of a solid-state pH sensor using an appropriate reference electrode.

The solid-state TiN sensor paves the way for future development of a miniaturised pH sensor capsule for biomedical applications or lab-on-a-chip pH sensor for environmental and industrial applications. Expending the realms of pH monitoring, currently limited by the glass pH electrode.

DOI

10.25958/ek86-5d42

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