Michael A. Matthews

University of South Carolina, Columbia, South Carolina, United States

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Publications (44)57.46 Total impact

  • Lin Yu, Michael A. Matthews
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    ABSTRACT: This paper reports new data on the production of hydrogen from water vapor plus NaBH4, or NaBH4 + 10% CoCl2. Data were collected with the aid of an isothermal semi-batch reactor with in-situ H2 rate measurement. The reaction of NaBH4 to generate H2 proceeds via three steps: deliquescence, dissolution and reaction. The deliquescence regime of NaBH4 in the presence of 10 weight percent CoCl2 is defined. The H2 yield is quantified at various reaction conditions (reaction temperature 70–120 °C, relative humidity 31–69%). CoCl2 significantly accelerates the rate of H2 production compared to deliquescence + reaction of pure NaBH4. It is also found that a combination of high temperature and high relative humidity contributes to high H2 rate and yield, and either of the two factors dominates the reaction at different conditions. A two-part reactor model accounting for the mechanism of the steam hydrolysis by NaBH4 is developed. The model captures the dissolution + reaction step as well as reaction-only step and was validated by experimental data.
    International Journal of Hydrogen Energy 01/2014; 39(8):3830–3836. · 3.55 Impact Factor
  • Ping Li, Lin Yu, Michael A. Matthews, Wissam A. Saidi, J. Karl Johnson
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    ABSTRACT: We report a theoretical investigation of H2O adsorption on the NaBH4(100) surface based on first principles density functional theory with inclusion of dispersion corrections in order to explore the initial stages of deliquescence at the molecular level. In the zero coverage limit, H2O is found to bind strongly to sodium sites on NaBH4(100) through O··· Na and O–H···H–B attractions. As the coverage increases H2O molecules adsorb on boron sites. H atoms in the adsorbed H2O monomer adopt tilted down (15°–20°) configurations with respect to the NaBH4(100) surface, which undergoes reconstruction in response to adsorbed H2O by rotations of BH4– groups of up to 90° and slight distortions of the positions of Na+ and BH4–. The adsorption energy per H2O is roughly independent of water coverage up to at least a coverage of four monolayers, suggesting that it is energetically feasible for water to condense on the surface, in agreement with experiments. We have experimentally studied the deliquescence of a mixture of NaBH4 with 10 wt % CoCl2. We found that CoCl2 lowers the deliquescence temperature compared to that for pure NaBH4 at a given vapor phase mole fraction of water; i.e., the deliquescence relative humidity is increased because of addition of CoCl2. Thus, while CoCl2 is a catalyst for aqueous phase hydrolysis of NaBH4, it actually inhibits deliquescence and hence delays the onset of steam hydrolysis.
    Industrial & Engineering Chemistry Research. 09/2013; 52(38):13849–13861.
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    ABSTRACT: We show that the superoxide ion (O2 ) generated electrochemically from oxygen dissolved in room temperature ionic liquids (RTIL's) reacts with primary and secondary alcohols to form the corresponding ketones and carboxylic acids, respectively. Specifically, we study the conversion of benzhydrol to benzophenone and benzyl alcohol to benzaldehyde/benzoic acid. The kinetics (e.g., rate, selectivity and yield) for these reactions are also determined as a function of the variations in the structure of the ionic liquids. The RTIL's used here are imidazolium-based cations where the functional groups on the imidazolium ring are modified. Specifically, 1-butyl-3-methylimidazolium hexafluorophosphate [bmim][PF6], 1-butyl-2,3-dimethylimidazolium hexafluorophosphate [bdmim][PF6], 1-hexyl-3-methylimidazolium hexafluorophosphate [hmim][PF6] are used as the reaction medium. These results are compared to an ammonium-based RTIL (N-butyl-N-trimethylammonium bis(trifluoromethylsulfonyl)imide). The results show that the nucleophilic attack by the O2 of both the RTIL and the alcohol, especially that of the H atom at the R2 position of the [bmim][PF6] and [hmim][PF6] greatly affects the yields. No RTIL degradation products were detected for the reactions in [bdmim][PF6] and N-butyl-N-trimethylammonium bis(trifluoromethylsulfonyl)imide ionic liquids. For the benzyl alcohol oxidation reaction in the RTIL, N-butyl-N-trimethylammonium bis(trifluoromethylsulfonyl)imide, benzaldehyde formed did not undergo further oxidation to form benzoic acid, which may be due to the greater hydrophobicity of this RTIL. The competitive reaction kinetics between the alcohol and RTIL component must be considered in the selection of the RTIL solvent system.
    Synthetic Communications 01/2012; · 1.06 Impact Factor
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    ABSTRACT: Sodium metaborate hydrates are a class of compounds represented by the stoichiometry NaBO2·xH2O. Recently, sodium metaborate has received attention as the byproduct of sodium borohydride hydrolysis, a reaction that is under consideration for hydrogen storage applications. The aim of this work was to understand the disposition of water in the crystal structure of hydrated sodium metaborates and to characterize the thermal stability and dehydration of the various hydrated species to optimize hydrogen storage efficiency as well as recyclability of the borate. Observations from a suite of analytical techniques including thermal analyses (thermogravimetric analysis/differential scanning calorimetry), X-ray diffraction, and Raman spectroscopy were correlated to characterize the dehydration mechanism of commercially available sodium metaborates, with an emphasis on the dihydrate (x = 2). A transformation from tetrahedrally coordinated boron to trigonal boron occurs when NaB(OH)4 (x = 2) is heated between 25 and 400 °C. The first dehydration to Na3[B3O5(OH)2] (x = 1/3) releases 5 mol of water between 83 and 155 °C. The final mole of water is released between 249 and 280 °C, and Na3B3O6 (x = 0) is formed. Raman spectra are reported for x = 2 and 1/3 for the first time. First-principles density functional theory was used to compute Raman spectra of the x = 1/3 and 2 material in order to assign the modes. We found reasonably good agreement between the experimentally measured and calculated vibrational frequencies.
    Industrial & Engineering Chemistry Research. 05/2011; 50(13).
  • Hong Liu, Christopher M. Boyd, Amy M. Beaird, Michael A. Matthews
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    ABSTRACT: Complex chemical hydrides are a means to store hydrogen in the solid state near ambient temperatures and pressures. Hydrolysis of hydrides has the potential to provide high gravimetric and volumetric energy densities if water consumption can be minimized. At low temperatures (110∼140 °C), the product of NaBH4 hydrolysis is NaBO2·2H2O (dihydrate), consuming 2 mol of unutilized water. The objective of this work was to conduct water vapor hydrolysis of NaBH4 at elevated pressure and temperature above 150 °C. It was hypothesized that this would yield a solid borate with decreased water bound in the crystal structure. A series of batch reactions were conducted to verify the hypothesis. Experimental characterization of the sodium metaborate byproducts indicated that the primary product of water vapor hydrolysis was NaBO2·1/3H2O (hemihydrate) under a variety of reaction conditions. For the most cases, the conversion of NaBH4 approached 100%.
    Fuel and Energy Abstracts 01/2011; 36(11):6472-6477.
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    ABSTRACT: Bacterial endotoxins have strong affinity for metallic biomaterials because of surface energy effects. Conventional depyrogenation methods may not eradicate endotoxins and may compromise biological properties and functionality of metallic instruments and implants. We evaluated the solubilization and removal of E. coli endotoxin from smooth and porous titanium (Ti) surfaces and stainless steel lumens using compressed CO(2)-based mixtures having water and/or surfactant Ls-54. The CO(2)/water/Ls-54 ternary mixture in the liquid CO(2) region (25 °C and 27.6 MPa) with strong mixing removed endotoxin below detection levels. This suggests that the ternary mixture penetrates and dissolves endotoxins from all the tested substrates. The successful removal of endotoxins from metallic biomaterials with compressed CO(2) is a promising cleaning technology for biomaterials and reusable medical devices.
    Journal of Supercritical Fluids The 01/2011; 55(3):1052-1058. · 2.73 Impact Factor
  • Lin Yu, Michael A. Matthews
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    ABSTRACT: Sodium borohydride is being commercialized to provide hydrogen storage for portable fuel cells. Prior kinetic studies have focused on catalytic hydrolysis of dilute aqueous solutions at room temperature. This work reports on a new NMR method for studying the kinetics of non-catalyzed sodium borohydride hydrolysis in highly concentrated solutions. The effects of initial NaBH4 concentration, temperature and pH on conversion are studied. It is found that higher initial NaBH4 concentration and higher temperature both improve the reaction rate. The reaction rate is slowed down with increasing pH of basic solutions and is accelerated with decreasing pH of acidic solutions. In addition, temperature effect seems to be more important than that of the acidic pH on the reaction rate.
    Fuel and Energy Abstracts 01/2011; 36(13):7416-7422.
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    Pedro J Tarafa, Michael A Matthews
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    ABSTRACT: It is known that the commercial surfactant Dehypon® Ls-54 is soluble in supercritical CO(2) and that it enables formation of water-in-CO(2) microemulsions. In this work we observed phase equilibrium for the Ls-54/CO(2) and Ls-54/water/CO(2) systems in the liquid CO(2) region, from 278.15 - 298.15 K. In addition, the Peng-Robinson equation of state (PREOS) was used to model the phase behavior of Ls-54/CO(2) binary system as well as to estimate water solubilities in CO(2). Ls-54 in CO(2) can have solubilities as high as 0.086 M at 278.15 K and 15.2 MPa. The stability of the microemulsion decreases with increasing concentration of water, and lower temperatures favor increased solubility of water into the one-phase microemulsion. The PREOS model showed satisfactory agreement with the experimental data for both Ls-54/CO(2) and water/CO(2) systems.
    Fluid Phase Equilibria 11/2010; 298(2):212-218. · 2.38 Impact Factor
  • Amy M. Beaird, Thomas A. Davis, Michael A. Matthews
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    ABSTRACT: The interaction between sodium borohydride (NaBH4) and water vapor leading to hydrolysis and hydrogen generation has been investigated by a visual technique. In situ video monitoring confirms that reaction is preceded by deliquescence of NaBH4 upon exposure to water vapor, forming a viscous liquid solution that releases hydrogen. A regime of temperature and relative humidity under which the deliquescence is favorable has been determined. A relative humidity threshold exists below which NaBH4 powder does not absorb water vapor into the bulk to form a solution and thereby does not undergo reaction to form hydrogen. The deliquescence behavior of NaBH4 in water vapor provides an alternative reaction pathway that has potential to improve hydrogen storage density by reducing excess water and other additives.
    Industrial & Engineering Chemistry Research. 09/2010; 49(20).
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    ABSTRACT: Biomaterials must be both sterile and free of contaminants prior to use, and this is particularly critical for the next generation of implants based on tissue engineering. With increasing complexity of tissue engineering scaffolds and multifunctional devices, there is a need for new approaches to decontamination, i.e. cleaning, disinfection, and sterilization. This work presents our recent results on several aspects of decontamination of both metallic and polymeric biomaterials using compressed carbon dioxide (CO2) technology. We demonstrate the removal of a lubricant oil from titanium surfaces with supercritical CO2. In another application, high level disinfection of a model hydrogel contaminated with Staphylococcus aureus has been achieved with liquid CO2.
    Journal of Supercritical Fluids - J SUPERCRIT FLUID. 01/2010; 53(1):192-199.
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    ABSTRACT: Complex chemical hydrides can be used to store and deliver hydrogen gas to fuel cells, and thus are one of several candidate materials to be used in storage systems for the hydrogen economy. These hydrides have high native hydrogen content, and hydrogen can be released via several chemical pathways. This review summarizes the extensive literature on the kinetic and thermodynamic properties of the various reactions of chemical hydrides, with an emphasis on hydrolysis. These properties are significant because they affect all aspects of system design, as well as the recovery and recycle of the byproducts. Hydrolysis of chemical hydrides takes place at relatively low temperatures and gives promising theoretical hydrogen storage efficiencies. Complications include metastable kinetic pathways as well as inefficient utilization of water in the byproducts.
    Industrial & Engineering Chemistry Research - IND ENG CHEM RES. 04/2009; 48(8).
  • A Jiménez, J Zhang, M A Matthews
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    ABSTRACT: The purpose of the present work is to evaluate a novel CO(2)-based cold sterilization process in terms of both its killing efficiency and its effects on the physical properties of a model hydrogel, poly(acrylic acid-co-acrylamide) potassium salt. Suspensions of Staphylococcus aureus and Escherichia coli were prepared for hydration and inoculation of the gel. The hydrogels were treated with supercritical CO(2) (40 degrees C, 27.6 MPa). The amount of bacteria was quantified before and after treatment. With pure CO(2), complete killing of S. aureus and E. coli was achieved for treatment times as low as 60 min. After treatment with CO(2) plus trace amounts of H(2)O(2) at the same experimental conditions, complete bacteria kill was also achieved. For times less than 30 min, incomplete kill was noted. Several physical properties of the gel were evaluated before and after SC-CO(2) treatment. These were largely unaffected by the CO(2) process. Drying curves showed no significant change between treated (pure CO(2) and CO(2) plus 30% H(2)O(2)) and untreated samples. The average equilibrium swelling ratios were also very similar. No changes in the dry hydrogel particle structure were evident from SEM micrographs.
    Biotechnology and Bioengineering 06/2008; 101(6):1344-52. · 4.16 Impact Factor
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    ABSTRACT: This study reports the effect of exposure to liquid carbon dioxide on the mechanical properties of selected medical polymers. The tensile strengths and moduli of fourteen polymers are reported. Materials were exposed to liquid CO(2), or CO(2) + trace amounts of aqueous H(2)O(2), at 6.5 MPa and ambient temperature. Carbon dioxide uptake, swelling, and distortion were observed for the more amorphous polymers while polymers with higher crystallinity showed little effect from CO(2) exposure. Changes in tensile strength were not statistically significant for most plastics, and most indicated good tolerance to liquid CO(2). These results are relevant to evaluating the potential of liquid CO(2)-based sterilization technology.
    Journal of Supercritical Fluids The 10/2007; 42(3):366-372. · 2.73 Impact Factor
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    ABSTRACT: The present work examines chemical and structural response in B. anthracis spores killed by a mixture of supercritical carbon dioxide (SCCO(2)) and hydrogen peroxide (H(2)O(2)). Deactivation of 6-log of B. anthracis spores by SCCO(2)+H(2)O(2) was demonstrated, but changes in structure were observed in only a small portion of spores. Results from phase contrast microscopy proved that this treatment is mild and does not trigger germination-like changes. TEM imaging revealed mild damage in a portion of spores while the majority remained intact. Dipicolinic acid (DPA) analysis showed that <10% of the DPA was released from the spore core into the external milieu, further demonstrating only modest damage to the spores. Confocal fluorescent microscopy, assessing uptake of DNA-binding dyes, directly demonstrated compromise of the permeability barrier. However, the magnitude of uptake was small compared to spores that had been autoclaved. This work suggests that SCCO(2)+H(2)O(2) is quite mild compared to other sterilization methods, which has major implications in its application. These results provide some insight on the possible interactions between spores and the SCCO(2)+H(2)O(2) sterilization process.
    Journal of Microbiological Methods 09/2007; 70(3):442-51. · 2.16 Impact Factor
  • Jun Li, Thomas A. Davis, Michael A. Matthews
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    ABSTRACT: At U.S. Department of Energy (DOE) sites, significant amounts of job control waste (JCW) need to be disposed. This JCW is generated and contaminated with polychlorinated biphenyls (PCBs) during cleanup operations. A commercial, plant-based absorbent material, “Toxi-dry,” is used extensively for decontamination and decommissioning of DOE waste sites and is classified a hazardous JCW after use. In this investigation, 1,2,4-trichlorobenzene (TCB) was chosen as the surrogate for PCBs. As a promising separation technology, supercritical fluid extraction (SFE) was investigated for removing and recovering PCBs from contaminated of JCW. TCB was extracted from Toxi-dry using both pure and modified supercritical carbon dioxide. It was found that at constant pressure, increasing temperature from 40 to 80°C greatly improved the recoveries, while the pressure effect of SFE was not as clear as the temperature effect. With 5wt% acetone or ethanol added as cosolvent, the efficiency of SFE of TCB was also significantly improved.
    Separation Science and Technology 02/2007; 38(12&13)(pp. 2979–2993 (2003)):2979-2993. · 1.16 Impact Factor
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    ABSTRACT: It was hypothesized that supercritical carbon dioxide (SC-CO(2)) treatment could serve as an alternative sterilization method at various temperatures (40-105 degrees C), CO(2) pressures (200-680 atm), and treatment times (25 min to 6 h), and with or without the use of a passive additive (distilled water, dH(2)O) or an active additive (hydrogen peroxide, H(2)O(2)). While previous researchers have shown that SC-CO(2) possesses antimicrobial properties, sterilization effectiveness has not been shown at sufficiently low treatment temperatures and cycle times, using resistant bacterial spores. Experiments were conducted using Geobacillus stearothermophilus and Bacillus atrophaeus spores. Spore strips were exposed to SC-CO(2) in commercially available supercritical fluid extraction and reaction systems, at varying temperatures, pressures, treatment times, and with or without the use of a passive additive, such as dH(2)O, or an active additive, such as H(2)O(2). Treatment parameters were varied from 40 to 105 degrees C, 200-680 atm, and from 25 min to 6 h. At 105 degrees C without H(2)O(2), both spore types were completely deactivated at 300 atm in 25 min, a shorter treatment cycle than is obtained with methods in use today. On the other hand, with added H(2)O(2) (<100 ppm), 6 log populations of both spore types were completely deactivated using SC-CO(2) in 1 h at 40 degrees C. It was concluded from the data that large populations of resistant bacterial spores can be deactivated with SC-CO(2) with added H(2)O(2)at lower temperatures and potentially shorter treatment cycles than in most sterilization methods in use today.
    Journal of Biomedical Materials Research Part B Applied Biomaterials 02/2007; 80(2):511-8. · 2.31 Impact Factor
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    ABSTRACT: The reaction of sodium borohydride with steam produces hydrogen gas and a hydrated solid. Unlike the reaction in liquid water, up to 95% yield of hydrogen is obtained with pure steam without a catalyst. Liquid promoters (methanol and acetic acid) at concentrations of 1mol% do not enhance the reaction rate, although acetic acid improves the hydrogen yield slightly.
    International Journal of Hydrogen Energy - INT J HYDROGEN ENERG. 01/2007; 32(18):4717-4722.
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    ABSTRACT: Hydrogen can be obtained from hydrolysis of chemical hydrides, making this an interesting option for hydrogen storage. The gravimetric and volumetric energy densities attainable from hydrolysis of chemical hydrides depend in large measure on the amount of water required for the process. The steam hydrolysis of sodium borohydride produces hydrated metaborate byproducts in which the degree of hydration of the metaborate is closely tied to the amount of water in the reaction. Experimental characterization of these sodium metaborate byproducts indicates that the primary byproduct of steam hydrolysis is NaBO2·2H2O under a variety of reaction conditions. A group contribution method is used to estimate the heats and free energies of formation of a variety of hydrated metaborates. This information will be useful in establishing the preferred (stable) hydration state of the byproducts, and in distinguishing these from metastable products.
    International Journal of Hydrogen Energy - INT J HYDROGEN ENERG. 01/2007; 32(18):4723-4730.
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    ABSTRACT: Supercritical carbon dioxide (SC CO(2)) has been evaluated as a new sterilization technology. Results are presented on killing of B. pumilus spores using SC CO(2) containing trace levels of additives. Complete killing was achieved with 200 part per million (ppm) hydrogen peroxide in SC CO(2) at 60 degrees C, 27.5 MPa. Addition of water to SC CO(2) resulted in greater than three-log killing, but this is insufficient to claim sterilization. Neither ethanol nor isopropanol when added to SC CO(2) affected killing.
    Journal of Microbiological Methods 10/2006; 66(3):479-85. · 2.16 Impact Factor
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    ABSTRACT: Supercritical phase CO2 is a promising method for sterilizing implantable devices and tissue grafts. The goal of this study is to evaluate the biocompatibility of titanium implants sterilized by supercritical phase CO2 in a rat subcutaneous implantation model. At 5 weeks post implantation titanium implants sterilized by supercritical phase CO2 produce a soft tissue reaction that is comparable to other methods of sterilization (steam autoclave, ultraviolet light radiation, ethylene oxide gas, and radio-frequency glow-discharge), as indicated by the thickness and density of the foreign body capsule, although there were some differences on the capillary density. Overall the soft tissue response to the implants was similar among all methods of sterilization, indicating supercritical phase CO2 treatment did not compromise the biocompatibility of the titanium implant.
    The International journal of artificial organs 05/2006; 29(4):430-3. · 1.76 Impact Factor