Quartz Crystal Microbalance Based Sensors for Detection and Discrimination of Volatile Organic Compounds Using Ionic Materials

Volatile organic compounds (VOCs) are prevalent in everyday life, ranging from household chemicals, naturally occurring scents from common plants and animals, to industrial-scale chemicals. Many of these VOCs are known to cause adverse health and environmental effects and require regulation to prevent pollution. Detecting VOCs plays a critical role in food quality control, environmental quality control, medical diagnostics, and explosives detection. Thus, development of adequate sensing devices for detection and discrimination of VOCs is of great importance. In recent years, use of quartz crystal microbalance (QCM) based sensor arrays for analyses of VOCs has attracted significant interest. Detection of VOCs using QCM-based sensors is dependent upon coating materials; hence, development of suitable coating materials is also of great importance. Over the years, QCM-based sensors have provided great promise for detecting VOCs; however, they have not provided this same potential for discrimination between different VOCs. Thus, this dissertation is focused on development of reusable QCM-based sensor arrays for detection and discrimination of VOCs using ionic liquids (ILs) and a group of uniform materials based on organic salts (GUMBOS) as coating materials. GUMBOS and ILs are similar classes of ionic materials, where GUMBOS represent solid phase organic salts with melting points between 25°C and 250°C, while ILs are organic salts with melting points below 100°C and are typically liquid at room temperature. Within this dissertation the synthesis and characterization of novel ILs and GUMBOS are discussed. Moreover, composite materials using IL-polymer blends are also presented. Vapor sensing properties of all ILs, GUMBOS, and composites were evaluated for use as coating materials in sensor arrays for detection and discrimination towards a wide range of VOCs. Two different sensor array schemes, multisensor array (MSA) and virtual sensor array (VSA), are described and examined throughout this dissertation. Finally, statistical techniques, such as principal component analysis (PCA) and discriminant analysis (DA), were used to develop predictive models to quantify the accuracy of MSAs and VSAs. The first reports of a QCM-based MSA to discriminate VOCs by classes, and a QCM-based VSA for discrimination of closely related chlorinated VOCs are presented within this dissertation. Overall, these studies demonstrate capabilities of QCM-based vapor sensor arrays with ionic coating materials for accurate discrimination and detection of VOCs

Group of Uniform Materials Based on Organic Salts (GUMBOS): A Review of Their Solid State Properties and Applications

Ionic liquids (ILs) are defined as organic salts with melting points below 100 °C. Such ionic compounds are typically formed using bulky cations and/or bulky anions in order to produce liquids or lower melting solids. ILs have been widely explored in several research areas including catalysis, remediation, solvents, separations, and many others. The utility of such compounds has also been recently broadened to include solid phase ionic materials. Thus, researchers have pushed the boundaries of ILs chemistry toward the solid state and have hypothesized that valuable properties of ILs can be preserved and fine-tuned to achieve comparable properties in the solid state. In addition, as with ILs, tunability of these solid-phase materials can be achieved through simple counterion metathesis reactions. These solid-state forms of ILs have been designated as a group of uniform materials based on organic salts (GUMBOS). In contrast to ILs, these materials have an expanded melting point range of 25 to 250 °C. In this chapter, we focus on recent developments and studies from the literature that provide for fine tuning and enhancing properties through transformation and recycling of diverse ionic compounds such as dyes, antibiotics, and others into solid state ionic materials of greater utility

Quartz crystal microbalance based sensor arrays for detection and discrimination of VOCs using phosphonium ionic liquid composites

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. Herein, we examine two sensing schemes for detection and discrimination of chlorinated volatile organic compounds (VOCs). In this work, phosphonium ionic liquids (ILs) were synthesized and vapor sensing properties examined and compared to phosphonium IL‐polymer composites. Pure IL sensors were used to develop a QCM‐based multisensory array (MSA), while IL‐polymer composites were used to develop an MSA and virtual sensor arrays (VSAs). It was found that by employing the composite MSA, five chlorinated VOCs were accurately discriminated at 95.56%, which was an increase in accuracy as compared to pure ILs MSA (84.45%). Data acquired with two out of three VSAs allowed discrimination of chlorinated VOCs with 100% accuracy. These studies have provided greater insight into the benefits of incorporating polymers in coating materials for enhanced discrimination accuracies of QCM‐based sensor arrays. To the best of our knowledge, this is the first report of a QCM‐based VSA for discrimination of closely related chlorinated VOCs