Graphene Loading Method for Water Filtration Media
Materials and Coatings
Graphene Loading Method for Water Filtration Media (MSC-TOPS-150)
Facilitates filtration-boosting application of graphene nanoparticles to filtration beds
Overview
Innovators at NASA Johnson Space Center have developed a novel method to load filter media substrates with pristine graphene nano-particles that significantly boosts water-filtering performance. Although this proof-of-concept was originally developed to apply the graphene to existing filtration media, it could also be used for graphene-only filtration.
Ensuring the longevity of water-filtration media is crucial to providing potable water throughout space-based mission timelines along with decreasing upmass and increasing precious cargo volume for other payloads during resupply missions to the International Space Station (ISS). Future manned deep-space missions will have an even greater dependency on efficient water reclamation systems as filtration media resupply may not be feasible.
The graphene nanoparticle loading technique presented was developed to facilitate the extended life of inert or active filtration media by signif-icantly increasing its contaminant-trapping ability. This method is designed for flow-through packed bed filtration systems and allows graphene to be incorporated into ion-exchange resins, polymer foams, or other substrates, potentially enabling applications across multiple terrestrial product lines.
The Technology
NASA and the US Army Engineer Research and Development Center (ERDC) co-developed advanced graphene materials designed to improve the filtration rate of spacecraft water contaminants which could significantly extend the service life of existing media filtration beds. Traditional granulated activated carbon (GAC) media is characterized by having a polymodal pore structure and contains micro-, meso-, and macropores that trap and contain contaminants. By using the referenced method to add graphene nanoparticles to an existing GAC filtering substrate, additional filtering can be achieved due to graphene’s mostly mesoporous nature.
A high-level overview of the graphene loading process is thus: The unloaded graphene nanoparticles are mixed with a water-based graphene suspension for an extended time at room temperature. This “graphene bath” process is repeated several times before the now graphene-loaded (up to ~ 1% by mass) filtration media is dried and prepared for packing into a filter cartridge. The graphene suspension used during the loading process may be reused multiple times, reducing consumables in the process. Laboratory testing has shown a 40x improvement in contaminant removal per mass of the absorbent (i.e., graphene) over the state of the art (granulated activated carbon) at lower loading rates, suggesting significant promise of the treated filter media posing a potential solution to the demands of an entire mission lifecycle.
Potential commercial applications for this graphene loading method may lay in four distinct market segments that rely on filtration media beds (outside of aerospace): industrial filtration such as ultra-pure water refining for the semiconductor industry, commercial filtration, residential filtration, and filtration-as-a-service. Graphene nano-particles’ tunable pore sizing, in conjunction with this loading method, could offer tailored filtration boosting for existing water filter substrates.
The Graphene Loading Method for Water Filtration Media has a technology readiness level (TRL) 4 (Component and/or breadboard validation in laboratory environment), and it is now available for patent licensing. Please note that NASA does not manufacture products itself for commercial sale.
Benefits
- Designed to facilitate drop-in graphene nanoparticle compatibility with other inert or active water filtration media
- Supports graphene-only filtration
- Allows graphene tunability for application-specific filtration targeting
- Scalable method could facilitate higher production volume
- Could be integral to space-based water filtration systems aiming to enhance longevity
- Facilitates the reduction of upmass for terrestrial-based resupply
Applications
- Aerospace
- Industrial
- Commercial
- Military
- Residential
- Filtration as-a-service
Technology Details
Materials and Coatings
MSC-TOPS-150
MSC-27798-1
Patent Pending
Similar Results
Filtering Molecules with Nanotube Technology
This water filtration innovation is an acoustically driven molecular sieve embedded with small-diameter carbon nanotubes. First, water enters the device and contacts the filter matrix, which can be made of polymer, ceramic, or metallic compounds. Carbon nanotubes within the matrix allow only water molecules to pass through, leaving behind any larger molecules and contaminants. The unique aspect of the technology is its use of acoustics to help drive water through the filter.
An oscillator circuit attached to the filter matrix propagates acoustic vibration, further causing water molecules to de-bond and move through the filter. This use of acoustics also eliminates dependence on gravity (and thus filter orientation) to move water through the device. When water exiting the system diminishes to a pre-determined set point, a cleaning cycle is triggered to clear the sediment from the inlet of the filter, reestablishing the standard system flow rate. Unlike other filtration systems, flushing of the filter system is not required. The combination of acoustics and small-diameter carbon nanotubes in this innovation make it an effective and efficient means of producing contaminant-free, clean water.
Holey Carbon Allotropes
This invention is for scalable methods that allows preparation of bulk quantities of holey nanocarbons with holes ranging from a few to over 100 nm in diameter. The first method uses metal particles as a catalyst (silver, copper, e.g.) and offers a wider range of hole diameter. The second method is free of catalysts altogether and offers more rapid processing in a single step with minimal product work-up requirements and does not require solvents, catalysts, flammable gases, additional chemical agents, or electrolysis. The process requires only commercially available materials and standard laboratory equipment; and, it is scalable. Properties that can be controlled include: surface area, pore volume, mechanical properties, electrical conductivity, and thermal conductivity.
Contaminated Water Treatment
This invention is a system and associated method that is a two step process. It provides a contaminant treatment pouch, referred to as a urine cell or contaminant cell that converts urine or another liquid containing contaminants into a fortified drink, engineered to meet human hydration, electrolyte and caloric requirements. It uses a variant of forward osmosis (FO) to draw water from a urine container into the concentrated fortified drink as part of a recycling stage. An activated carbon pretreatment removes most organic molecules. Salinity of the initial liquid mix (urine plus other) is synergistically used to enhance the precipitation of organic molecules so that activated carbon can remove most of the organics. A functional osmotic bag is then used to remove inorganic contaminants. If a contaminant is processed for which the saline content is different than optimal for precipitating organic molecules, the saline content of the liquid should be adjusted toward the optimal value for that contaminant.
Multi-Stage Filtration System
While HEPA filter elements can last for years without intervention, pre-filtering systems that remove larger particles before they reach the HEPA filter need to be treated (most often by cleaning or replacement) as often as once a week. These treatments can be resource-intensive and expensive, especially in extreme environments. Glenn's innovative system combines a pre-filtration impactor and a scroll filter that reduces the need to replace the more sensitive or expensive filters, extending the system's working life. The system uses an endless belt system to provide the impaction surface. A thin layer of low-toxicity grease is applied to the impaction surface to increase particle adhesion. A high flow turning angle near the impaction surface causes relatively large particles to impact and stick to the surface while smaller particles stay within the air flow. When the surface is covered with particles - or if a layer of particles has grown to a thickness that impairs adhesion - the surface is regenerated. The band is rotated so that the loaded surface passes by a scrapper, removing the layer of particles and a clean segment of the band revolves to become the new impaction surface.
A further innovation is the scroll filter which allows the filtration media to be rotated out of the airflow when fully loaded, providing multiple changes of the filter through a motorized scrolling or indexing mechanism. When nearly fully loaded with dust particles, the exposed media is mechanically rolled up on one side of the filter to both contain and compactly store the dust. The spools that hold the clean and spent filter media are mounted on roller bearings to facilitate the scrolling operation and reduce motor power requirements. Nearly any grade of filter media can be used to meet the desired filtration specification. Additional media rolls can be added after the original roll is spent to further increase filter life.
Air Revitalization for Vacuum Environments
The NASA life support system uses a regenerable vacuum swing adsorption process, known as Sorbent-Based Air Revitalization (SBAR), to separate water and carbon dioxide for disposal. The SBAR system is an adsorbent-based swing bed system that has been optimized to provide both humidity and carbon dioxide control for a spacecraft cabin atmosphere.
The system comprises composite silica gel and zeolite-packed beds for adsorption and a bypass system for flow control. Under normal operating conditions, the disposal system would require a high-quality vacuum environment to operate. Improvements to the SBAR system include an enhanced inherent capacitance that extends the operation time within a non-vacuum environment for up to 4.5 hours. Flight time can be further expanded with multiple SBAR systems to allow for system regeneration. By scheduling periodic thermal regenerations—nominally during sleep periods—the SBAR technology may be suitable for missions of unlimited duration.
