ONLINE MONITORING OF DISINFECTANTS USING CHEMIRESISTIVE SENSORS

Abstract

To ensure safe and reliable water quality, continuous monitoring of a wide range of water parameters is required. Disinfectants are added to kill the pathogens in water and a sufficient level of disinfectant in water prevents pathogen regrowth. Therefore, monitoring the disinfectant is crucial to prevent waterborne disease. Conventional monitoring techniques rely on colorimetric kits and bulky electrochemical analyzers. These techniques rely either on additional reagents or frequent maintenance. This thesis attempts to solve these issues by incorporating chemiresistive sensor platforms to monitoring of disinfectants. First, the single-walled carbon nanotube (SWCNT) networks were optimized to sense broader range of disinfectants (potassium permanganate) in water. High sensitivity and broader dynamic range of detection were achieved by controlling the density of the SWCNT networks. We have demonstrated that sparce networks (∼25 kΩ) are sensitive to trace concentrations (0.01–0.1 mg/L). Medium density networks (∼15 kΩ) provided stable responses in the intermediate range (0.2–1.6 mg/L) and highly dense networks (∼5 kΩ) were most effective at higher concentrations (1–8 mg/L). Functionalization of the sensors with redox-active molecules further improved the sensitivity and durability. Then, we tackle multivariate sensing of free chlorine at different pHs by utilizing an array of functionalized chemiresistors. We introduced an electrical reset to continuously measure free chlorine in simulated tap water background. Then, we demonstrated the classification and quantification free chlorine and potassium permanganate at different pHs using an array of chemiresistors. Finally, we have demonstrated that this carbon-based chemiresistive array can be extended to graphene-based chemiresistors and to other disinfectants. Differentiation and quantification of monochloramine and free chlorine were demonstrated using few-layer graphene-based functionalized chemiresistors. This thesis advances monitoring of a critical, complex drinking-water parameter and opens an avenue toward multianalyte detection that will ensure safe drinking water.