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Papers by Kontad/Suriya Ounnunkad

A green and simple synthetic route via a thermal hydrolysis of titanyl sulphate (TiOSO4) has been... more A green and simple synthetic route via a thermal hydrolysis of titanyl sulphate (TiOSO4) has been employed to prepare nanocrystalline anatase titanium dioxide (TiO2) without further calcination. X-ray diffraction (XRD) clearly showed that the anatase crystalline structure was already formed under the reaction conditions at 80.0±2.0 °C. The obtained anatase TiO2 showed high thermal stability as the anatase-to-rutile transformation in only 25 wt% occurred at 900 °C. Scanning electron (SEM) and transmission electron (TEM) micrographs revealed that TiO2 secondary particles comprised irregular primary particles with diameters of 8–22 nm depending on the calcination temperature. Superior UV-light absorption intensity compared with the commercial P25 TiO2suggested the great potential of the obtained material for use as a highly efficient photocatalyst under UV irradiation.

Nanocrystalline Cu0.5Co0.5Fe2O4 powders were prepared via a metal-cellulose precursor synthetic r... more Nanocrystalline Cu0.5Co0.5Fe2O4 powders were prepared via a metal-cellulose precursor synthetic route. Cellulose was used as a fuel and a dispersing agent. The resulting precursors were calcined in the temperature range of 450–600 °C. The phase development of the samples was determined by using Fourier transform infrared (FT-IR) spectroscopy and powder X-ray diffraction (XRD). The field-dependent magnetizations of the nanopowders were measured by vibrating sample magnetometer (VSM). All XRD patterns are of a spinel ferrite with cubic symmetry. Microstructure of the ferrites showed irregular shapes and uniform particles with agglomeration. From XRD data, the crystallite sizes are in range of 16–42 nm. Saturation magnetization and coercivity increased with increasing calcining temperature due to enhancement of crystallinity and reduction of oxygen vacancies.

La or Pr substituted barium hexaferrites, Ba1−x(La or Pr)xFe12O19, x=0.00–0.20, were successfully... more La or Pr substituted barium hexaferrites, Ba1−x(La or Pr)xFe12O19, x=0.00–0.20, were successfully prepared by a citrate combustion process. The sintered bodies were structurally and magnetically studied by powder X-ray diffraction (XRD) and vibrating sample magnetometry (VSM). All XRD patterns show the single phase of the magnetoplumbite barium ferrite without other intermediate phases. Magnetization (MS) and coercive field (HC) could be improved by substitutions of La or Pr ions on Ba ion basis sites. The MS reveal magnetic behavior with respect to La or Pr ions content, showing an increase at first and then a decrease. The HC increases remarkably with increasing La or Pr ions content.

The construction of and the electrochemical characteristics of a novel freestanding biomedical po... more The construction of and the electrochemical characteristics of a novel freestanding biomedical polymersingle walled carbon nanotube (SWCNT) nanocomposite electrode, formed via an intercalation process, have been described. The SWCNT Buckypapers are prepared from SWCNT dispersion solution via a filtration process, followed by soaking in a 5%w/v insulating poly(styrene-βisobutylene-β-styrene) (SIBS) solution. The intercalated platforms represent randomly dispersed CNT bundles and individual CNTs which are partially surrounded by an insulating polymer. This arrangement leads to an improvement in the Faradaic to capacitive charging ratio, relative to electrodes derived from non-intercalated samples. The electrochemical behaviour of freestanding SIBS intercalated SWCNT Buckyelectrodes have been investigated via analysis of DC and Fourier transformed AC voltammetries in order to determine the composites ability to serve as an electrode platform. In comparison with the bare sample, significantly faster electron transfer reaction rates and improved Faradaic to capacitive background charging current ratios, suggest that the devices made from this novel nanocomposite electrode should offer improved performance in electroanalytical applications, and possibility also in bio-/chemo-sensors, biofuel cell type devices and as a biocompatible platform for cell culturing.

Journal of Electroceramics, 2006

The properties of magnesium ferrites, Mg 1−x Zn x Fe 2 O 4 with 0.0 ≤ x ≤ 0.5, were investigated ... more The properties of magnesium ferrites, Mg 1−x Zn x Fe 2 O 4 with 0.0 ≤ x ≤ 0.5, were investigated by means of powder X-ray diffraction, magnetization, Mössbauer spectroscopy, and scanning electron microscopy. The ferrites were prepared by conventional solid-state reaction using a mixed oxide method. All XRD patterns revealed only the monophasic spinel characteristic structure of MgFe 2 O 4 . The lattice parameters increased with the increasing of Zn content. Saturation magnetization (M S ) of the ferrites was discussed with respect to Zn substitution. M S values increased with Zn content up to x = 0.35 and then decreased thereafter. Mössbauer results showed Fe 3+ ion distribution between tetrahedral and octahedral sites and the effect of Zn ions on ferrimagnetic order. The line-broadening of the Mössbauer spectra increased with substituting Mg with Zn ions due to disruption of the local magnetic order. The SEM micrographs of the sintered bodies showed irregular shape in the order of ∼5-6 μm.

Putting insulating polymers into a highly conductive single-walled carbon nanotube paper leads to... more Putting insulating polymers into a highly conductive single-walled carbon nanotube paper leads to excellent electrochemical performance; fast redox reactions and high signal to background noise ratio. The ability of such composites to serve as superior electrochemical platforms was investigated by using DC and AC cyclic voltammetry. The electrochemical platforms show benefits in sensing applications with fast signal generation and low limits of detection.

physica status solidi (b), 2007

PACS 61.10 Nz, 75.50. Gg, 75.60.Ej, 76.80.+y Site preference of Cr in the M-type barium ferrite c... more PACS 61.10 Nz, 75.50. Gg, 75.60.Ej, 76.80.+y Site preference of Cr in the M-type barium ferrite ceramics was monitored by powder X-ray diffraction (XRD), magnetization measurements and Mössbauer spectroscopy. The calcined BaFe 12-x Cr x O 19 powders ( x = 0.0 -0.8) obtained by the sol gel method were die-pressed into pellets and then sintered at 1300°C in a oxygen atmosphere for 12 hrs. All the phases of the ceramics were of the pure magnetoplumbite structure. The saturation magnetization ( M s ) is found to be a function of Cr ion content. The M S of the ceramics decreases due to the dilution of the magnetic interaction with increasing Cr concentration. The coercivity ( H c ) of the ceramics increases due to finer grain observed by scanning electron microscopy (SEM). Fitted Mössbauer spectra show that Cr ions preferentially occupy into the 2 a , 12k and 4 f 2 Fe crystallographic sites.

Journal of Electroanalytical Chemistry, 2011

The performances of freestanding carbon nanotube (buckypaper) and polymer-intercalated buckypaper... more The performances of freestanding carbon nanotube (buckypaper) and polymer-intercalated buckypaper electrodes in an electroanalytical chemistry context were evaluated via analysis of direct current and Fourier Transform large-amplitude alternating current voltammograms derived from the ferrocenemonocarboxylic acid (FMCA 0/+ ), ruthenium hexamine ([Ru(NH 3 ) 6 ] 3+/2+ ) and ferricyanide ([Fe(CN) 6 ] 3À/4À ) redox couples. The composite polymer-intercalated buckypaper electrodes exhibit substantially superior Faradaic-to-capacitive background charging current ratios under both dc and ac conditions compared and display close to ideal voltammetry for all three processes. A significant difference was detected in midpoint potentials determined by cyclic voltammetry at buckypaper and polymer-intercalated buckypaper electrodes, commensurate with different mass transport mechanisms. It is proposed that the porosity of the buckypaper gives rise to a restricted diffusion model of mass transport within the pores and a large electrode over that generates a large capacitance current. Thus, polymer intercalation is required to achieve high quality electroanalytical performance. Simulations of voltammograms obtained at porous polymer-intercalated buckypaper electrodes are consistent with the composite electrodes consisting of a randomly arranged array of nano-/micro-electrode domains, implying that significant surface heterogeneity is present. However, under slow scan rate conditions, when significant overlap of diffusion layers occurs, voltammograms may be approximately interpreted in terms of a linear diffusion based mass transport model.

A green and simple synthetic route via a thermal hydrolysis of titanyl sulphate (TiOSO4) has been... more A green and simple synthetic route via a thermal hydrolysis of titanyl sulphate (TiOSO4) has been employed to prepare nanocrystalline anatase titanium dioxide (TiO2) without further calcination. X-ray diffraction (XRD) clearly showed that the anatase crystalline structure was already formed under the reaction conditions at 80.0±2.0 °C. The obtained anatase TiO2 showed high thermal stability as the anatase-to-rutile transformation in only 25 wt% occurred at 900 °C. Scanning electron (SEM) and transmission electron (TEM) micrographs revealed that TiO2 secondary particles comprised irregular primary particles with diameters of 8–22 nm depending on the calcination temperature. Superior UV-light absorption intensity compared with the commercial P25 TiO2suggested the great potential of the obtained material for use as a highly efficient photocatalyst under UV irradiation.

Nanocrystalline Cu0.5Co0.5Fe2O4 powders were prepared via a metal-cellulose precursor synthetic r... more Nanocrystalline Cu0.5Co0.5Fe2O4 powders were prepared via a metal-cellulose precursor synthetic route. Cellulose was used as a fuel and a dispersing agent. The resulting precursors were calcined in the temperature range of 450–600 °C. The phase development of the samples was determined by using Fourier transform infrared (FT-IR) spectroscopy and powder X-ray diffraction (XRD). The field-dependent magnetizations of the nanopowders were measured by vibrating sample magnetometer (VSM). All XRD patterns are of a spinel ferrite with cubic symmetry. Microstructure of the ferrites showed irregular shapes and uniform particles with agglomeration. From XRD data, the crystallite sizes are in range of 16–42 nm. Saturation magnetization and coercivity increased with increasing calcining temperature due to enhancement of crystallinity and reduction of oxygen vacancies.

La or Pr substituted barium hexaferrites, Ba1−x(La or Pr)xFe12O19, x=0.00–0.20, were successfully... more La or Pr substituted barium hexaferrites, Ba1−x(La or Pr)xFe12O19, x=0.00–0.20, were successfully prepared by a citrate combustion process. The sintered bodies were structurally and magnetically studied by powder X-ray diffraction (XRD) and vibrating sample magnetometry (VSM). All XRD patterns show the single phase of the magnetoplumbite barium ferrite without other intermediate phases. Magnetization (MS) and coercive field (HC) could be improved by substitutions of La or Pr ions on Ba ion basis sites. The MS reveal magnetic behavior with respect to La or Pr ions content, showing an increase at first and then a decrease. The HC increases remarkably with increasing La or Pr ions content.

The construction of and the electrochemical characteristics of a novel freestanding biomedical po... more The construction of and the electrochemical characteristics of a novel freestanding biomedical polymersingle walled carbon nanotube (SWCNT) nanocomposite electrode, formed via an intercalation process, have been described. The SWCNT Buckypapers are prepared from SWCNT dispersion solution via a filtration process, followed by soaking in a 5%w/v insulating poly(styrene-βisobutylene-β-styrene) (SIBS) solution. The intercalated platforms represent randomly dispersed CNT bundles and individual CNTs which are partially surrounded by an insulating polymer. This arrangement leads to an improvement in the Faradaic to capacitive charging ratio, relative to electrodes derived from non-intercalated samples. The electrochemical behaviour of freestanding SIBS intercalated SWCNT Buckyelectrodes have been investigated via analysis of DC and Fourier transformed AC voltammetries in order to determine the composites ability to serve as an electrode platform. In comparison with the bare sample, significantly faster electron transfer reaction rates and improved Faradaic to capacitive background charging current ratios, suggest that the devices made from this novel nanocomposite electrode should offer improved performance in electroanalytical applications, and possibility also in bio-/chemo-sensors, biofuel cell type devices and as a biocompatible platform for cell culturing.

Journal of Electroceramics, 2006

The properties of magnesium ferrites, Mg 1−x Zn x Fe 2 O 4 with 0.0 ≤ x ≤ 0.5, were investigated ... more The properties of magnesium ferrites, Mg 1−x Zn x Fe 2 O 4 with 0.0 ≤ x ≤ 0.5, were investigated by means of powder X-ray diffraction, magnetization, Mössbauer spectroscopy, and scanning electron microscopy. The ferrites were prepared by conventional solid-state reaction using a mixed oxide method. All XRD patterns revealed only the monophasic spinel characteristic structure of MgFe 2 O 4 . The lattice parameters increased with the increasing of Zn content. Saturation magnetization (M S ) of the ferrites was discussed with respect to Zn substitution. M S values increased with Zn content up to x = 0.35 and then decreased thereafter. Mössbauer results showed Fe 3+ ion distribution between tetrahedral and octahedral sites and the effect of Zn ions on ferrimagnetic order. The line-broadening of the Mössbauer spectra increased with substituting Mg with Zn ions due to disruption of the local magnetic order. The SEM micrographs of the sintered bodies showed irregular shape in the order of ∼5-6 μm.

Putting insulating polymers into a highly conductive single-walled carbon nanotube paper leads to... more Putting insulating polymers into a highly conductive single-walled carbon nanotube paper leads to excellent electrochemical performance; fast redox reactions and high signal to background noise ratio. The ability of such composites to serve as superior electrochemical platforms was investigated by using DC and AC cyclic voltammetry. The electrochemical platforms show benefits in sensing applications with fast signal generation and low limits of detection.

physica status solidi (b), 2007

PACS 61.10 Nz, 75.50. Gg, 75.60.Ej, 76.80.+y Site preference of Cr in the M-type barium ferrite c... more PACS 61.10 Nz, 75.50. Gg, 75.60.Ej, 76.80.+y Site preference of Cr in the M-type barium ferrite ceramics was monitored by powder X-ray diffraction (XRD), magnetization measurements and Mössbauer spectroscopy. The calcined BaFe 12-x Cr x O 19 powders ( x = 0.0 -0.8) obtained by the sol gel method were die-pressed into pellets and then sintered at 1300°C in a oxygen atmosphere for 12 hrs. All the phases of the ceramics were of the pure magnetoplumbite structure. The saturation magnetization ( M s ) is found to be a function of Cr ion content. The M S of the ceramics decreases due to the dilution of the magnetic interaction with increasing Cr concentration. The coercivity ( H c ) of the ceramics increases due to finer grain observed by scanning electron microscopy (SEM). Fitted Mössbauer spectra show that Cr ions preferentially occupy into the 2 a , 12k and 4 f 2 Fe crystallographic sites.

Journal of Electroanalytical Chemistry, 2011

The performances of freestanding carbon nanotube (buckypaper) and polymer-intercalated buckypaper... more The performances of freestanding carbon nanotube (buckypaper) and polymer-intercalated buckypaper electrodes in an electroanalytical chemistry context were evaluated via analysis of direct current and Fourier Transform large-amplitude alternating current voltammograms derived from the ferrocenemonocarboxylic acid (FMCA 0/+ ), ruthenium hexamine ([Ru(NH 3 ) 6 ] 3+/2+ ) and ferricyanide ([Fe(CN) 6 ] 3À/4À ) redox couples. The composite polymer-intercalated buckypaper electrodes exhibit substantially superior Faradaic-to-capacitive background charging current ratios under both dc and ac conditions compared and display close to ideal voltammetry for all three processes. A significant difference was detected in midpoint potentials determined by cyclic voltammetry at buckypaper and polymer-intercalated buckypaper electrodes, commensurate with different mass transport mechanisms. It is proposed that the porosity of the buckypaper gives rise to a restricted diffusion model of mass transport within the pores and a large electrode over that generates a large capacitance current. Thus, polymer intercalation is required to achieve high quality electroanalytical performance. Simulations of voltammograms obtained at porous polymer-intercalated buckypaper electrodes are consistent with the composite electrodes consisting of a randomly arranged array of nano-/micro-electrode domains, implying that significant surface heterogeneity is present. However, under slow scan rate conditions, when significant overlap of diffusion layers occurs, voltammograms may be approximately interpreted in terms of a linear diffusion based mass transport model.