Tailoring of Sol−Gel Films for Optical Sensing of Oxygen in Gas and Aqueous Phase

TLDR

Sol‑gel optical sensors for gas‑phase and dissolved oxygen use fluorescence quenching of a ruthenium complex entrapped in a porous silica film. The study aimed to determine optimal film‑processing parameters for both sensing environments. The authors employed tetraethoxysilane and organo‑modified precursors (methyltriethoxysilane, ethyltriethoxysilane) and varied the water/precursor molar ratio to tailor film microstructure. Higher modified‑precursor content and longer aliphatic chains increased film hydrophobicity, enhancing dissolved‑oxygen sensitivity and diffusion, which resulted in excellent gas‑phase and DO sensor performance and 6‑month quenching stability.

Abstract

Sol-gel-based optical sensors for both gas-phase and dissolved oxygen have been developed. Both sensors operate on the principle of fluorescence quenching of a ruthenium complex which has been entrapped in a porous sol-gel silica film. A comprehensive investigation was carried out in order to establish optimal film-processing parameters for the two sensing environments. Both tetraethoxysilane and organically modified sol-gel precursors such as methyltriethoxysilane and ethyltriethoxysilane were used. Film hydrophobicity increases as a function of modified precursor content, and this was correlated with enhanced dissolved oxygen (DO) sensor performance. Extending the aliphatic group of the modified precursor further improved DO sensitivity. The influence of water/precursor molar ratio, R, on the sol-gel film microstructure was investigated. R value tailoring of the microstructure and film surface hydrophobicity tailoring were correlated with oxygen diffusion behavior in the films via the Stern-Volmer constants for both gas phase and DO sensing. Excellent performance characteristics were measured for both gas-phase and DO oxygen sensors. The long-term quenching stability of DO sensing films was established over a period of 6 months.