Papers by Pasit Pakawatpanurut
Advanced Materials Interfaces, 2017
Different morphologies of manganese oxide/carbon nanotube (MnO 2 /CNT) composites were prepared u... more Different morphologies of manganese oxide/carbon nanotube (MnO 2 /CNT) composites were prepared using ethylenediaminetetraacetic acid (EDTA) or sodium dodecyl sulfate (SDS) as soft templates. Using EDTA, the resulting composite showed hierarchical structure, while an assembly of rod-like structures was obtained when SDS was used. The surface of CNT in the composites was covered with a layer of manganese oxide of 2-3 nm in thickness. The surface area was higher when EDTA was used in the synthesis (246 m 2 /g for EDTA route compared with 227 m 2 /g for SDS route), as is also the case for the specific capacitance (154 F/g based on cyclic voltammetry and 115 F/g based on galvanostatic charge/ discharge for 95% MnO 2 loading of EDTA route compared with 80.3 F/g based on cyclic voltammetry and 79.2 F/g based on galvanostatic charge/discharge for 80% MnO 2 loading of SDS route). Overall, the MnO 2 / CNT composites showed good charge/discharge reversibility. Given these favorable properties along with the simplicity of the preparation, the MnO 2 /CNT/Ni-foam electrode can potentially be used in future large-scale development of the electrochemical capacitors. ß
We report a study of the hydrogen storage properties of materials that result from ball milling C... more We report a study of the hydrogen storage properties of materials that result from ball milling Ca(BH 4) 2 and MNH 2 (M = Li or Na) in a 1:1 molar ratio. The reaction products were examined experimentally by powder X-ray diffraction, thermogravimetric analysis and differential scanning calorimetry (TGA/DSC), simultaneous thermogravimetric modulated beam mass spectrometry (STMBMS), and temperature-programmed desorption (TPD). The Ca(BH 4)/LiNH 2 system produces a single crystalline compound assigned to LiCa-(BH 4) 2 (NH 2). In contrast, ball milling of the Ca(BH 4)/NaNH 2 system leads to a mixture of NaBH 4 and Ca(NH 2) 2 produced by a metathesis reaction and another phase we assign to NaCa(BH 4) 2 (NH 2). Hydrogen desorption from the LiCa(BH 4) 2 (NH 2) compound starts around 150 °C, which is more than 160 °C lower than that from pure Ca(BH 4) 2. Hydrogen is the major gaseous species released from these materials; however various amounts of ammonia form as well. A comparison of the TGA/DSC, STMBMS, and TPD data suggests that the amount of NH 3 released is lower when the desorption reaction is performed in a closed vessel. There is no evidence for diborane (B 2 H 6) release from LiCa(BH 4) 2 (NH 2), but traces of other volatile boron−nitrogen species (B 2 N 2 H 4 and BN 3 H 3) are observed at 0.3 mol % of hydrogen released. Theoretical investigations of the possible crystal structures and detailed phase diagrams of the Li−Ca−B−N−H system were conducted using the prototype electrostatic ground state (PEGS) method and multiple gas canonical linear programming (MGCLP) approaches. The theory is in qualitative agreement with the experiments and explains how ammonia desorption in a closed volume can be suppressed. The reduced hydrogen desorption temperature of LiCa(BH 4) 2 (NH 2) relative to Ca(BH 4) 2 is believed to originate from intramolecular destabilization.
The mixed pine tree seed-like/disc-shaped micro-structures of MnOx (x = 4/3 and 1) were synthesiz... more The mixed pine tree seed-like/disc-shaped micro-structures of MnOx (x = 4/3 and 1) were synthesized using a simple microwave-assisted solvothermal synthesis and heat treatment under N2 atmosphere (heating rate 5 °C/min), without the need for carbon composite. This new mixed morphology showed high specific capacitance, as measured by the cyclic voltammetry (182 F g−1 at 1 mV s−1) and by the constant galvanostatic charge-discharge cycling (195 F g−1 at 0.1 A g−1). During the cycling process the specific capacitance of the material increased, which was caused by the partial electrochemical oxidation of the major phase Mn3O4 (x = 4/3) to MnO2 in a neutral electrolyte of 1 M Na2SO4. According to the galvanostatic charge-discharge cycling tests at 1 A g−1 , this material also showed good capacitance retention for over 1000 cycles. MnOx synthesized herein can thus be a good candidate for the electrode material for electrochemical capacitors.
The charge transfer process within the electrolyte system is an active area for further improving... more The charge transfer process within the electrolyte system is an active area for further improving the conversion efficiency of the dye-sensitized solar cell (DSSC). In this work, micelle formed by cationic surfactant cetylpyridinium (CP) chloride was used in the electrolyte to enhance the ion transport of the redox couple. Using a mixed solvent of ethylene glycol and acetonitrile at 1:9 volume ratio and 0.50 M CP, an 83% improvement in DSSC efficiency was observed. Because of a strong correlation between the efficiency and the current density as a function of the CP concentration, the presence of CP micelle likely caused a favorable shift in the ion transport within the electrolyte. According to the cyclic voltammetry, such improved ion transport can be attributed to a faster diffusion of the redox couple, particularly the I 3-diffusion. In addition, the impedance analysis also revealed a short electron lifetime for the diffusion process in the presence of the CP micelle. From these results, it is plausible that the CP micelle in the electrolyte provides an extensive network of positively-charged interfaces, which facilitates the diffusion of the redox couple and enhances the overall performance of the DSSC.
Journal of Power Sources, 2016
Journal of Electroceramics, 2015
Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics, 2000
We report the results of a study, using digital video microscopy, of the melting transition in a ... more We report the results of a study, using digital video microscopy, of the melting transition in a quasi-two-dimensional suspension of uncharged silica spheres. This system was chosen to further test the dependence of the two-dimensional melting transition on the functional form of the colloid-colloid interaction. Our experimental data show that the solid phase undergoes a first order transition directly to the liquid phase. The system studied yields no evidence of the existence of a hexatic phase interpolating between the solid and liquid phases in the melting process.
Materials Research Bulletin, 2013
ABSTRACT Different morphologies of manganese oxide/carbon nanotube (MnO2/CNT) composites were pre... more ABSTRACT Different morphologies of manganese oxide/carbon nanotube (MnO2/CNT) composites were prepared using ethylenediaminetetraacetic acid (EDTA) or sodium dodecyl sulfate (SDS) as soft templates. Using EDTA, the resulting composite showed hierarchical structure, while an assembly of rod-like structures was obtained when SDS was used. The surface of CNT in the composites was covered with a layer of manganese oxide of 2–3 nm in thickness. The surface area was higher when EDTA was used in the synthesis (246 m2/g for EDTA route compared with 227 m2/g for SDS route), as is also the case for the specific capacitance (154 F/g based on cyclic voltammetry and 115 F/g based on galvanostatic charge/discharge for 95% MnO2 loading of EDTA route compared with 80.3 F/g based on cyclic voltammetry and 79.2 F/g based on galvanostatic charge/discharge for 80% MnO2 loading of SDS route). Overall, the MnO2/CNT composites showed good charge/discharge reversibility. Given these favorable properties along with the simplicity of the preparation, the MnO2/CNT/Ni-foam electrode can potentially be used in future large-scale development of the electrochemical capacitors.
Materials Chemistry and Physics, 2012
A non-conducting, nontoxic poly(acrylic acid-co-acrylonitrile) (PAA) was prepared and used as a s... more A non-conducting, nontoxic poly(acrylic acid-co-acrylonitrile) (PAA) was prepared and used as a supporting matrix for the electrolyte of dye-sensitized solar cells (DSSCs). DSSCs of active area 0.80 cm × 1.10 cm fabricated with PAA, 0.5 M LiI, 0.05 M I 2 , 0.5 M 3-tert-butylpyridine, and 0.1 M 1methyl-3-propylimidazolium iodide in 3-methoxypropionitrile solvent showed an average solar energy conversion efficiency of 1.61% under simulated sunlight illumination of 100 mW cm −2 , AM 1.5. The effects of the gel polymer matrix on the electrochemical properties of DSSCs were studied using the electrochemical impedance spectroscopy. Relative to the non-gel reference cells, the results showed a decrease in charge recombination, ionic diffusion, and double layer capacitance and an increase in electron lifetime. These results could play an important role in determining the future direction for the development of high-performance gel polymer electrolytes.
Journal of Biological Chemistry, 2002
Escherichia coli general NAD(P)H:flavin oxidoreductase (Fre) does not have a bound flavin cofacto... more Escherichia coli general NAD(P)H:flavin oxidoreductase (Fre) does not have a bound flavin cofactor; its flavin substrates (riboflavin, FMN, and FAD) are believed to bind to it mainly through the isoalloxazine ring. This interaction was real for riboflavin and FMN, but not for FAD, which bound to Fre much tighter than FMN or riboflavin. Computer simulations of Fre.FAD and Fre.FMN complexes showed that FAD adopted an unusual bent conformation, allowing its ribityl side chain and ADP moiety to form an additional 3.28 H-bonds on average with amino acid residues located in the loop connecting Fbeta5 and Falpha1 of the flavin-binding domain and at the proposed NAD(P)H-binding site. Experimental data supported the overlapping binding sites of FAD and NAD(P)H. AMP, a known competitive inhibitor with respect to NAD(P)H, decreased the affinity of Fre for FAD. FAD behaved as a mixed-type inhibitor with respect to NADPH. The overlapped binding offers a plausible explanation for the large K(m) values of Fre for NADH and NADPH when FAD is the electron acceptor. Although Fre reduces FMN faster than it reduces FAD, it preferentially reduces FAD when both FMN and FAD are present. Our data suggest that FAD is a preferred substrate and an inhibitor, suppressing the activities of Fre at low NADH concentrations.
We report a study of the hydrogen storage properties of materials that result from ball milling C... more We report a study of the hydrogen storage properties of materials that result from ball milling Ca(BH 4 ) 2 and MNH 2 (M=Li, Na) in a 1:1 molar ratio. The reaction products were examined experimentally by Powder X-Ray Diffraction, Thermogravimetric Analysis and Differential Scanning Calorimetry (TGA/DSC), Simultaneous Thermogravimetric Modulated Beam Mass Spectrometry (STMBMS), and Temperature Programmed Desorption (TPD). The Ca(BH 4 ):LiNH 2 system produces a single crystalline compound assigned to LiCa(BH 4 ) 2 (NH 2 ). In contrast, ball milling the Ca(BH 4 ):NaNH 2 system leads to a mixture of NaBH 4 and Ca(NH 2 ) 2 produced by a metathesis reaction, and another phase we assign to NaCa(BH 4 ) 2 (NH 2 ). Hydrogen desorption from the LiCa(BH 4 ) 2 (NH 2 ) compound starts around 150 °C, which is more than 160 °C lower than pure Ca(BH 4 ) 2 . Hydrogen is the major gaseous species released from these materials, however various amounts of ammonia form as well. A comparison of the TGA/DSC, STMBMS and TPD data suggests that the amount of NH 3 released is lower when the desorption reaction is performed in a closed vessel. There is no evidence for diborane (B 2 H 6 ) release from LiCa(BH 4 ) 2 (NH 2 ), but traces of other volatile boron-nitrogen species (B 2 N 2 H 4 and BN 3 H 3 ) are observed at 0.3 mole % of the hydrogen released. Theoretical investigations of the possible crystal structures and detailed phase diagrams of the Li-Ca-B-N-H system were conducted using the Prototype Electrostatic Ground State (PEGS) method and multiple gas canonical linear programming (MGCLP) approaches. The theory is in qualitative agreement with the experiments and explains how ammonia desorption in a closed volume can be suppressed. The reduced hydrogen desorption temperature of LiCa(BH 4 ) 2 (NH 2 ) relative to Ca(BH 4 ) 2 is believed to originate from intramolecular destabilization.
Journal of Clinical Investigation, 2009
activation. An important physical property of GPI-anchored complement regulatory proteins such as... more activation. An important physical property of GPI-anchored complement regulatory proteins such as DAF is their ability to translate laterally in the plasma membrane. Here, we used singleparticle tracking and tether-pulling experiments to measure DAF lateral diffusion, lateral confinement, and membrane skeletal associations in human erythrocyte membranes. In native membranes, most DAF molecules exhibited Brownian lateral diffusion. Fluid-phase complement activation caused deposition of C3b, one of the products of C3 cleavage, onto erythrocyte glycophorin A (GPA). We then determined that DAF, C3b, GPA, and band 3 molecules were laterally immobilized in the membranes of complement-treated cells, and GPA was physically associated with the membrane skeleton. Mass spectrometry analysis further showed that band 3, α-spectrin, β-spectrin, and ankyrin were present in a complex with C3b and GPA in complement-treated cells. C3b deposition was also associated with a substantial increase in erythrocyte membrane stiffness and/or viscosity. We therefore suggest that complement activation stimulates the formation of a membrane skeletonlinked DAF-C3b-GPA-band 3 complex on the erythrocyte surface. This complex may promote the removal of senescent erythrocytes from the circulation.
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Papers by Pasit Pakawatpanurut