Photocatalytic Oxidation Using TiO2 and UV for Total Organic Carbon Analysis of Water

Abstract

Water quality monitoring is vital for long-duration human missions. In particular, monitoring potable water Total Organic Carbon (TOC) is an important metric to understand water quality. The International Space Station (ISS) currently has this capability with its Total Organic Carbon Analyzer (TOCA) that performs off-line analysis. Currently an effort is underway to develop a Miniature Total Organic Carbon Analyzer (mini-TOCA), which aims to decrease the mass, volume, and power specifications to enable long-duration human exploration without sacrificing analytical capability. The main steps of TOC analysis are oxidation of the water sample and the detection of carbon dioxide. One novel oxidation method for use in a TOCA instrument is photocatalytic oxidation using a titanium dioxide (TiO¬2) coating combined with UV LEDs emitting at the TiO2 bandgap (365 nm). Several reactor prototype configurations using this method were procured and tested. The considered design parameters included various surface geometries of the fluidic channels, catalyst application methods, and UV duration and intensity. The application of catalytic TiO2 was attempted using a commercial coating, and atomic layer deposition (ALD) on machined steel and 3D printed titanium. Direct formation of the catalytic later was also tried with titanium substrate via heat treating. The extent of oxidation for different reactor configurations and coatings was determined by changes in direct conductivity measurements of water samples containing trace organic compounds. The ALD catalyst coating was most effective for oxidizing sample. The amount of UV output was also varied to understand the time required for full oxidation. Further work is planned to introduce more types of samples, perform lifetime testing, and integrate the reactor with a tunable laser spectrometer.