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The removal of volatile organic compounds (VOCs) from the air aboard spacecrafts is necessary to maintain the health of crewmembers. The use of photocatalysis has proven effective for the removal of VOCs. A majority of studies have focused on thin films, which have a low adsorption capacity for contaminants and intermediate oxidation byproducts. Thus, this study investigates the use of adsorbent materials impregnated or coated with titania to: (1) provide a system that can remove VOCs for a period of time in the absence of UV irradiation to reduce power requirements and/or offer contaminant removal in the event of lamp failure and (2) improve the photocatalytic oxidation efficiency by concentrating VOCs and intermediate oxidation byproducts near the surface of the photocatalyst. Two adsorbent materials (porous silica gel and BioNuchar120 activated carbon) and glass beads were tested as catalyst supports for the destruction of a target VOC, in this case methanol (Co = 50 ppmv).

A magnetically agitated photocatalytic reactor (MAPR) has been developed and tested as a post-processor in the past using phenol and reactive red dye to simulate these waste components, yet these components ignore factors that may hinder a photocatalytic post processor including competitive adsorption of various organic compounds and their oxidation byproducts and the demonstrated detrimental effect of inorganic compounds such as ammonium bicarbonate on photocatalytic oxidation. To assess these effects, this work looks at photocatalytic oxidation of air evaporation subsystem (AES) ersatz water while modifying the photocatalyst mass, magnetic field current and frequency to find the optimal conditions. Additionally, the magnetic photocatalyst has been characterized to observe the assembled structures formed when exposed to the magnetic field array in the MAPR and the crystallinity of the titanium dioxide coating.

NASA will require a safe and efficient method for water recovery on long-term space missions. Photocatalysis represents a promising solution for part of a system designed for recovery of water from humidity condensate, urine, and shower waste. It eliminates the need for chemical oxidants that are dangerous and difficult to transport, and the considerable energy consumption of distillation. In terms of decreasing the equivalent system mass (ESM) with respect to these alternative technologies, considerations for the volume, mass, cooling and crew time are also important. This photocatalytic reactor generates the oxidant in the form of hydroxyl radicals and valence band holes by exposing silica-titania composite particles with a barium ferrite core to ultraviolet light. The magnetic core of the catalyst allows for separation, confinement, and agitation.

NASA has identified a number of water treatment options that have shown promise in space. The water recovery system on any particular mission will be a collection of individual treatment units, with each treatment unit focusing on a select group of contaminants. The project objective has been to develop a microgravity-compatible, compact post processor based on magnetic agitation that is safe and reliable and that provides product water that meets or exceeds NASA's potable water quality requirements. The micron-sized magnetic photocatalytic particles have been proven durable and capable of oxidizing synthetic organic chemicals. The reactor has been optimized with respect to agitation frequency (50 Hz), UV wavelength (312 nm), and geometry (circular coiled reactor cell).

A prototype reactor was designed and tested to oxidize synthetic organic chemicals (SOCs) without the use of expendable chemicals and without the need to separate the catalyst from the water after treatment. An annular continuous flow reactor with a nominal volume of 400 mL was packed with silica gel pellets that were doped with titania (TiO2) (12 wt%). The reactor was configured in a test stand with UV lamps in the center of the reactor. SOC oxidation experiments were performed in a recycle mode and in a single-pass mode. Five target analytes (acetone, chlorobenzene, ethyl acetate, toluene, and methylmethacrylate) were spiked (100 to 300 μg/L) into nano-pure water and recycled through the reactor until adsorption equilibrium was attained. UV lamps, which were shielded, were then uncovered, and effluent concentrations were monitored as a function of time. All of the compounds were degraded to below detection limit (5 μg/L) after an extended reaction period of 23 hours.