IRG I: Life Support Systems
In 2002, the NASA Advanced Life Support Division (ALS) defined as the primary goal for future manned long duration missions that it is essential to: "...provide life support self sufficiency for human beings to carry out research and exploration productively in space for benefits on Earth and to open the door for extended on-orbit stays and planetary exploration." In support of this ALS Division goal, the proposed work presented in this section is aimed atproducing superior sorbents suitable for the deep and bulk removal of CO2 from spacecraft breathing air and a novel biochemical system for water recycling during space missions.
C. R. Cabrera*, K.H. Griebenow*, A. Hernandez-Maldonado (IRG I Leader)+, Y. Ishikawa*, R. G. Raptis*;
University of Puerto Rico at Rio Piedras (UPR-RP)* and University of Puerto Rico at Mayaguez (UPR-M)+
NASA Collaborators: B. Luna and M. Flynn, NASA Ames Research Center
IRG I Expertise:
Synthesis and study of porous sorbent materials;1-7 separations via adsorption;3,8-17 transition metal pyrazolate complexes;18-24 ab initio calculations;25-45 protein stability and formulation;46-54 chemical modification of proteins to improve long-term stability, investigation of the relationship between protein structure, function, stability and dynamics;46- 48,50,51,54-58 non-aqueous enzymology;49,52,55,57 protein folding;59-61 computational modeling;56 various spectroscopic methods to study protein structure and dynamics (CD, FTIR microcopy, FT-Raman, fluorescence);48,51,57,59-64 electrochemical characterization and electrochemistry.65-69
IRG I Facility Description:
Access to standard chemical characterization techniques (NMR, IR, XPS, XRD) and surface analysis techniques at the Materials Characterization Center (XRD, XPS, SEM, AFM) and Nanoscopy Facility (TEM, FIB) at UPR-RP. Specialized volumetric and gravimetric (low pressure) instruments for gas sorption measurements and in situ DSC/High Temperature XRD at UPR-M. Extensive set of mild chemical methods to anchor proteins on surfaces; formulation and chemistry tools to improve protein long-term stability; extensive spectroscopic tools available in the laboratory (3 FTIR units; 1 FT-Raman; 1 fluorimeter; 2 UV-vis spectrometers; 1 circular dichroism spectrometer); biochemistry methods to investigate protein functionality (2 HPLCs for aggregation, gel electrophoresis); electrochemical techniques are available for the urea removal studies (10 potentiostats/galvanostat, 2 rotating disk electrode systems).
IRG I Development Plan:
The synthesis and characterization of new porous materials will be carried out in the laboratories of Dr. Raptis and Dr. Hernández-Maldonado. Determination of gas sorption properties will be carried out in the laboratory of Dr. Hernández-Maldonado, while Dr. Ishikawa's group will be responsible for the theoretical work. All the groups have access to the infrastructure of the Puerto Rico NSF EPSCoR Institute of Functional Nanomaterials (IFN).
In order to evaluate the materials performance under conditions approaching those that occur in actual missions, we will rely on the infrastructure provided by the Atmosphere Revitalization Group at NASA Ames Research Center (ARC). The preparation of robust enzymatic electrodes for organic substance removal will be done in the laboratories of Dr. Cabrera and Dr. Griebenow. Initially, the efficiency and mechanism of hydrolysis of urea to ammonia and eventual oxidation to nitrogen will be studied in detail by our research groups. The integration of the bioelectrochemical device in the existing water recycling device at NASA will be done in strong collaboration with NASA ARC Laboratory. This will lead to modifications and continued iterations of results and conceptual designs for scaling-up.
Sub-Theme A:Selective Porous Gas Sorbents for Space Life Support Systems - A Combined
Experimental and Theoretical Approach:
We will carry out the design, preparation and study of superior sorbents for the selective removal of CO2 gaseous mixtures during short and long term space missions,70-72 including Extra-Vehicular Activities (EVA). For exploration missions lasting between 7 and 180 days, the current CO2 levels are limited to 7,000 ppm, but NASA continues to analyze the possibilities of lowering the allowable CO2 levels due to the evident results from short- and long-term effects on human physiology.71,72 Another concern is that high CO2 levels also contribute to decompression sickness (DCS). Astronauts face possible DCS during space walks, since the spacesuit operates at a pressure lower than that of the cabin.
Nanoporous Sorbents for Spacecraft Air Ultrapurification:
Sorbents will be designed based on advanced solid-state ion exchange (SSIE) techniques11,73-75 and will offer structural characteristics that synergistically enhance the net surface potential by relying on interactions between extra-framework functional species and the sorbate gas. The considerable differences in the sorbates (i.e., CO2, N2 and O2) quadrupole moments and the surface potential overlapping resulting from the material small pore dimensions (ca. 4 Ã…) will be the driving force for the separation. In addition, since the surface interaction is at the physisorption and/or weakchemisorption levels, regeneration of the sorbents will be accomplished via temperature swing and/or process pressure reduction, which is feasible for long-duration and EVA space missions. Figure 2.1.1 shows preliminary sorption data obtained with a CO2 selective porous material developed by Hernandez-Maldonado's group based on the aforementioned principles and using liquid phase ion exchange (LPIE) techniques (surface interaction ~ 10 kcal/mol).76 SSIE will provide more sorption sites per unit cell (Figure 2.1.1). These sorbents would be an option to replace materials currently used by NASA, which coincidentally rely on weak adsorption processes (i.e., type-A zeolites and activated carbon) and are currently part of the"Carbon Dioxide Removal Assemblies" or CDRA.77
Figure 2.1.1. Actual and expected (dashed line) adsorption isotherms of CO2 on [Na+Sr2+H+]- and [Sr2+]-SAPO-34, respectively, at 298 K. Also shown in the figure are isotherms for N2 and O2 and the schematics of the partially and fully ion-exchanged (i.e., one and two Sr2+ ions per cage, respectively) frameworks.
Nanoporous Sorbents for Bulk Gas Separations:
We will investigate the use of a redox-active, extended-lattice host for the redox-controlled sorption/desorption of bulk CO2. Two of the envisioned applications that provide the impetus for current research efforts into the design of new Metal Organic Frameworks (MOFs) are their potential use in gas-storage and purification.78-82 Several research groups worldwide are pursuing the synthesis of such materials and their efforts are focused either on increasing the pore size, or tailoring the pore surface as to improve the host-guest interaction.83-85 In a recent study related to this project, the use of polyoxometallate-based MOFs has been proposed for use as an electrochemical capacitor.86
The central hypothesis of this project is that a redox-active MOF, with at least two stable oxidation states - MOFRed and MOFOx -- will have different affinity for a guest species at each one of those states (Figure 2.1.2). Such a sorbent will be loaded/unloaded at constant temperature and pressure by switching between its two oxidation states, with Δ%-loading defining its useful capacity. New MOFs will be prepared using well-characterized, redox-active Fe8, Cu3- and Cu6-complexes already at hand in the Raptis group, as structural building units (SBU).18-24 The short-term goal of this project is to study the guest-host interaction at different MOF oxidation states, in order to identify the parameters that influence that interaction and will, therefore, allow maximization of Δ%. Initially, studies will focus on the sorption/ desorption of guest species from solution -- e.g. solvent molecules, or solutes - and will continue to the sorption of gaseous guests from a solid/liquid or solid/gas interface. The longterm goal is to understand the fundamental chemical and physical properties of redoxcontrolled sorbents that will allow the design of materials for CO2 bulk separations. It should be mentioned that these novel MOF materials could be used as a combined CO2 storage and delivery system for O2 production via reduction. NASA is interested in recovering oxygen by using an adsorption compressor to take the CDRA regeneration main product at low pressure and deliver it at higher pressure to a reduction system (source: Dr. B. Luna, NASA ARC)
Figure 2.1.2. Gas sorption isotherms for the reduced and oxidized MOF forms.
Density-functional theoretical (DFT) studies of small gas molecule interactions with the nanoporous sorbents with specific framework topologies and novel compositions will be carried out. The extant DFT with the commonly used local density approximation (LDA) and generalized gradient approximations (GGA) fails to describe van der Waals (vdW) forces, such as the sorbate-surface interaction, since the long-range exchange andcorrelation effects are not correctly taken into account.87 To remedy the description of vdW interaction, a scheme based on a long-range/short-range decomposition of the electron interaction will be employed.88,89 In the new DFT computational scheme, the long-range correction for generalized gradient approximation (GGA) exchange functional was combined with a vdW correlation functional to describe accurate dissociation potentials of rare-gas dimers and vdW complexes.88,89 The proposed theoretical modeling and simulation will provide the understanding of the sorbate interactions with the porous surfaces at the nanoscale, and predict and design enhanced performance of the porous material. The major long-term emphasis of the proposed study will be to gain fundamental understanding of sorbate-porous sorbent interactions, so that enhanced devices can be identified and designed.
Sub-Theme B: Degradation of Urea for Bioregenerative Applications.
Water is the most massive component aboard spacecrafts, making it imperative to completely recycle wastewater into useful resources. It is estimated that during a long duration mission of four crew members, human wastes will contribute 54% to the total wastes, 81.4% of it being urine,90 and with urea and NaCl being the most predominant urine contaminants (36.2% and 21.6%, respectively.91 Common wastewater treatment technologies in spaceships include reverse osmosis (RO), nanofiltration (NF), and vapor compression distillation (VCD). However, urea is a very small and neutral molecule and thus difficult to reject by either size or charge. Investigations on the rejection performance of several RO membranes used presently in space missions revealed that urea is still hard to reject by present membranes and still accounts for more than 39% of carbon in treated transit mission wastewater (TMW).92 In addition, separated urea still has to be stored. Biochemical reactors have also been evaluated for water reclamation and recycling of urea using the enzyme urease.93 Urease (EC 126.96.36.199, urea amidohydrolase) is a nickel metalloenzyme that catalyzes the hydrolysis of urea to ammonia and carbon dioxide.94,95 In the work of Schussel, urease was immobilized in diatomaceous earth and urea was continuously fed into the bioreactor with the byproducts being discarded. Although the work cited above provides evidence that the enzyme urease is useful in water reclamation systems, the long-term stability has not been investigated and how to efficiently use the highly toxic byproduct ammonia is unclear. Ammonia oxidation on Pt is a structurally selective process that takes place almost exclusively at Pt (100) sites.96
The ammonia oxidation mechanism proposed by Oswin et al established that the rate determining step for the alkaline anodic oxidation at high currents is the desorption of Nads. With the intention of increasing the catalytic activity of platinum for the anodic alkaline oxidation, Pt alloys have been tested. Endo reported that bimetallic platinum alloys, including Ir and Ru, increase the electrocatalytic activity. The reason why these enhance the activity might be explained by their activity at the dehydrogenation catalytic steps of NH3 at a lower potential compared to pure Pt.97 To overcome the aforementioned problems, our long-term goal is to incorporate a continuous flow biochemical regenerator reactor, along with existing space mission technologies, to degrade urea and to be able to perform in-situ resource recovery with minimum energy consumption through the use / reuse of the reaction products (Figure 2.1.3). Although we will focus on urea initially, it is expected that future work will address enzymatic degradation of other organics, such as ethanol, methanol, and other organic residuals commonly found in ROtreated spacecraft wastewater. We hypothesize that we can integrate a bioreactor and a fuel cell into one efficient recycling system. Nevertheless, the main innovation will be on the development of an ambient temperature/pressure reactor. This is because NASA has a funded line item to do this and it is clearly of interest to NASA. The fuel cell will be a secondary or coinnovation. This is based on previous results that expose the importance of chemical immobilization to attain robust systems, and that the urease reaction product ammonia is highly energetic and can be oxidized to molecular nitrogen. To make the organic bioreactor functional, we will covalently attach the enzyme urease onto platinized boron doped diamond electrodes to minimize losses by enzyme desorption, which plague alternative systems.
Furthermore, we will explore surface modification of the enzyme with sugars and poly(ethylene glycols) to assure long-term enzyme stability.48 Lastly, we will consider using the reaction products as energy containing fuel by integrating the above system into a fuel cell. The latter proposition will address the well-mentioned in-situ resource recovery by producing inert nitrogen gas and carbon dioxide in the same process; both of these gases are completely reusable in a Biomass subsystem (i.e., bacterial N2 fixation and CO2 for photosynthesis) for manned long duration missions. It is important to note that our technology is also applicable as a post-treatment device for urine wastewater reclamation systems in combination with the activated carbon technology ("bag project") used by Flynn and co-workers. Urease can be immobilized on activated carbon and stabilized as described in this context. The innovation described herein will allow biochemical urea removal for the long periods required in future manned space explorations
IRG I Path to Innovation:
By using bottom-up strategies for designing sorbents, IRG I will provide new insights at the fundamental and applied levels to tackle difficult separations at ambient conditions and/or with minimal energy input. The inclusion of a theoretical calculation component will provide a unique tool to further enhance the materials design process. The combination of the enzyme urease and a fuel cell to remove urea from urine is a highly innovative and a fundamentally new idea. Lastly, the enzyme modification by glycans to improve long-term stability is a fundamentally new methodology.