Comparison of nano-particles for the photocatalytic destruction of organic pollutants for water recovery

Photocatalysis is used to mineralize water pollutants, providing water treatment without a waste stream. This water treatment method allows for a compact reactor design (i.e., reduced Equivalent Systems Mass (ESM)) that is applicable in future NASA missions that will require water recovery. The reactor would provide a post-processing unit to remove any organic contaminants (e.g., VOCs) not removed in prior water subsystems. Several approaches to the reactor design are being explored. Titanium dioxide (TiO₂) is the chosen photocatalyst based on its proven performance and non-toxicity. Because of their propensity to adsorb pollutants, silica and activated carbon are being investigated as supporting materials for the titania. Three types of particles are being tested for their ability to destroy organic contaminants: silica gel doped with titania, activated carbon coated with titania, and silica gel doped with both activated carbon and titania. Each material has certain advantages. Silica has a high transparency for the activation of the titania by UV light, while activated carbon has a very high adsorption strength, which brings the contaminants in better contact with the titania. The creation of silica-carbon-titania particles is an attempt to utilize the positive aspects of all three materials. The silica gel-based particles are utilized as pellets and packed in a recirculating reactor design. An additional effort is made to incorporate magnets into the particles or coat magnetic media with photocatalysts for use in a magnetically agitated photocatalytic reactor (MAPR). This paper presents the preliminary effectiveness of each design approach gauged by the ability to remove organic contaminants.