Colorimetric Oxygen Indicator from Titanium Dioxide Nanocomposite by Mechanical Milling Process

Abstract

This research aims to develop the efficiency of colorimetric oxygen indicator by titanium dioxide/methylene blue nanocomposite. The indicator was composed of titanium dioxide (TiO₂) nanoparticles as a semiconductor photocatalyst, methylene blue (MB) as a redox dye, and citric acid as a sacrificial electron donor. TiO₂/MB nanocomposite was synthesized via a mechanical milling process based on crucial parameters of rotation speed and milling time. Rotation speed in the milling process was studied at 200, 250, and 300 rpm with different milling times in the wet process at 15, 30, and 45 min. After that, all conditions of TiO₂/MB nanocomposite in blue ink suspension were pasted on glass slide substrate by screen printing technique and baked at 100°C for 30 min. TiO₂/MB indicators were exposed under UVA irradiation (λ_max at 360 nm) for 3 min until bleaching state. The bleached indicators were placed in an air environment and recovered in a blue state. Switching time at activated TiO₂/MB nanocomposite layer was monitored by the timer that indicated on the colorimetric switching color responsibility recovery with oxygen gas in the environment. Functional groups of TiO₂/MB nanocomposite before/after colorimetric state were analyzed by fourier transform-infrared (FT-IR) spectrometer. Meanwhile, the absorption and diffuse reflection properties of the indicators were monitored by a UV-VIS-NIR spectrophotometer. The mechanism of color switching in the TiO₂/MB indicator depends on the structural changing of methylene blue with the cooperation with TiO₂ photocatalyst in the nanocomposite.