Optical determination of Cr(VI) using regenerable, functionalized sol-gel monoliths.

Transparent, pyridine-functionalized sol-gel monoliths have been formed and their use in Cr(VI) sensing applications is demonstrated. The monoliths were immersed in acidic Cr(VI)-containing solutions, and the Cr(VI) uptake was monitored using UV-vis and atomic absorption spectroscopies. At concentrations at the ppm level, the monoliths exhibit a yellow color change characteristic of Cr(VI) uptake, and this can be measured by monitoring the absorption change at about 350 nm using UV-vis spectroscopy.

Optical sensors for the determination of concentrated hydroxide. Characterization of the sensor materials and evaluation of the sensor performance.

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.

Reactions of d0 group 4 amides with dioxygen. Preparation of unusual oxo aminoxy complexes and theoretical studies of their formation.

Reactions of d0 amides M(NMe2)4 (M = Zr, 1; Hf, 2) with O2 have been found to yield unusual trinuclear oxo aminoxide complexes M3(NMe2)6(mu-NMe2)3(mu3-O)(mu3-ONMe2) (M = Zr, 3; Hf, 4) in high yields. Tetramethylhydrazine Me2N-NMe2 was also observed in the reaction mixtures. Crystal structures of 3 and 4 have been determined.

High-acidity determination in salt-containing acids by optical sensors. The scope of a dual-transducer approach and the Hammett acidity function.

A dual-transducer approach based on sol-gel optical sensors was recently reported to measure acid and salt concentrations, C(acid) and C(salt), in concentrated aqueous LiCl-HCl, CaCl2-HCl, and AlCl3-HCl solutions (C(acid) at 5-6 M; C(salt) < or = 2 M). The scope of this new approach has been studied in salt-containing HCl solutions with C(acid) at 2-9 M, and factors that influence sensor responses and accuracy have been investigated. A linear relationship between (deltaA/deltaC(salt))C(acid) and (dA/dC(acid))C(salt)=0, which is the basis of this dual-transducer approach, was found to lead to an empirical linear relationship between (deltaH0)C(acid) and (deltaC(salt))C(acid) (H0: Hammett acidity function of the indicator encapsulated in the sensor).