Optical Sensors for the Determination of Concentrated Hydroxide. Characterization of the Sensor Materials and Evaluation of the Sensor Performance

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Abstract
Optical sensors for the determination of highly concentrated bases such as NaOH (1-10 M) and materials to make these sensors have been characterized by X-ray photoelectron spectroscopy, 29Si solid-state NMR, FT-IR, and measurements of film porosity, surface area, and thickness. The bonding character and composition of the Si-Zr mixed oxides-organic polymer composites were evaluated. These studies suggest that there are Si-O-Zr matrixes in the mixed oxides, and that the Si-O-Zr matrixes contribute to the durability of the base sensors in highly alkaline solutions. The performance of these base sensors has been studied in detail as well. These sensors were stable for approximately 120 days, exhibited short response times (typically <10 s), and were fully reversible with minimal hysteresis effects in NaOH-ROH-H2O solutions (R = Me, Et, and i-Pr).