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Ultrasonically-assisted surface modified TiO2/rGO/CeO2 heterojunction photocatalysts for conversion of CO2 to methanol and ethanol
(2019-11-01)
Seeharaj, Panpailin
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Kongmun, Panyata
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Paiplod, Piyalak
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Prakobmit, Saowanee
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Sriwong, Chaval
Converting CO<inf>2</inf> to usable fuel may contribute to lowering of global warming, thus this study developed effective heterojunction photocatalysts for the photoreduction of CO<inf>2</inf> with water into methanol and ethanol fuels. The photocatalysts were prepared from combining surface modified titanium dioxide (TiO<inf>2</inf>) nanoparticles with reduced graphene oxide (rGO) and cerium oxide (CeO<inf>2</inf>). The TiO<inf>2</inf> surfaces were firstly modified via the sono-assisted exfoliation, with high intensity ultrasonic waves (ultrasonic horn, 20 kHz, 150 W/cm2) in 10 M NaOH for 1 h. Highly reactive nanosheets delaminated from outer surfaces of the primary TiO<inf>2</inf> crystals leading to an increase in specific surface active area, light absorption and decrease in electron-hole recombination rate, which enhanced photocatalytic activity. Then, 0.75 wt% rGO and 1 wt% CeO<inf>2</inf> were incorporated into the surface modified TiO<inf>2</inf> to promote photogenerated charge separation, electron mobility and CO<inf>2</inf> absorptivity. The modified TiO<inf>2</inf>/rGO/CeO<inf>2</inf> photocatalysts exhibited superior photocatalytic performance by producing methanol at 641 μmol/g<inf>cat</inf>h and ethanol at 271 μmol/g<inf>cat</inf>h, almost 7 times higher than rates from pure TiO<inf>2</inf>. The significant improvement in CO<inf>2</inf> photoconversion activity was mainly attributed to the high interfacial contact area and strong connection between the reactive delaminated TiO<inf>2</inf> nanosheets, rGO and CeO<inf>2</inf>, which, in turn, facilitated the flow of large number of photogenerated charge carriers to react with the absorbed species, and the multi-step charge transportation due to the heterojunction effect that effectively retarded electron-hole recombination.
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Giant suppression of dielectric loss in BaZrO3
(2019-11-01)
Kolodiazhnyi, T.
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Pulphol, P.
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Vittayakorn, W.
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Vittayakorn, N.
We report the effect of precursor's purity and heterovalent substitution on the microstructure and dielectric properties of BaZrO<inf>3</inf> ceramics. We find that independent of the purity or raw materials, the dielectric loss of BaZrO<inf>3</inf> at microwave frequencies is rather high with a Q factor in the range of 1000–3000 at 10 GHz. All stoichiometric ceramics studied show up to three types of low-T dielectric relaxations in the 2–250 K range. All these dielectric anomalies can be suppressed by partial substitution of Zr for Nb. By alloying of BaZrO<inf>3</inf> with a hypothetical BaGa<inf>1/2</inf>Nb<inf>1/2</inf>O<inf>3</inf> phase the Q × f value of ceramics at microwave frequency can be improved significantly. The origin of this remarkable improvement is attributed to the effect of the donor ions on the random electric fields and antiferrodistortive instability. Ceramic with a chemical composition of BaZr<inf>0.96</inf>Ga<inf>0.02</inf>Nb<inf>0.02</inf>O<inf>3</inf> sintered at 1600 °C shows dielectric constant, ε′ = 36.7, temperature coefficient of the resonance frequency, τ<inf>f</inf> = +110 ppm/°C and Q × f = 172 THz.
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Acid modified multiwalled carbon nanotubes condition by reflux
(2019-09-25)
Jirakittidul, Kittimon
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Vittayakorn, Naratip
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Manrean, Rawijee
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Pornteeranawapat, Natchanun
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Neamyooyong, Saichon
Nanomaterials, especially carbon nanotubes (CNTs), show excellent combinations of thermal, mechanical and electrical properties. However, as-produced CNTs are entangled and form agglomerates, due to their several micron lengths. Therefore, the dispersion efficiency of CNTs is limited. We decreased the length and improved dispersion with acid modified multiwall-CNTs (A-MWCNTs) formed by a reflux method. MWCNTs were modified with an acid mixture of sulfuric acid and nitric acid at the ratio of 3:1 by volume. The reflux temperature and time were varied between 80 to 120 °C and 10 to 30 min. FTIR found an increase in carboxylic acid groups on the surfaces with increasing reflux temperature and time. Therefore, A-MWCNTs showed good dispersion in polar solvents; i.e. water, DMF and DMAc. Furthermore, A-MWNCT lengths were shortened with increased reflux temperature and time. Carboxylic acid groups on A-MWCNT surfaces decreased the electrical conductivity by two orders of magnitude. However, epoxy resin in which the A-MWCNTs, modified at 120 °C and 30 min were encapsulated, showed better conductivity, since the shortest MWCNT lengths and the carboxylic groups on the A-MWCNT surfaces allowed good dispersion in epoxy resin.
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High-Performance Hybridized Composited-Based Piezoelectric and Triboelectric Nanogenerators Based on BaTiO3/PDMS Composite Film Modified with Ti0.8O2 Nanosheets and Silver Nanopowders Cofillers
(2019-05-28)
Sriphan, Saichon
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Charoonsuk, Thitirat
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Maluangnont, Tosapol
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Vittayakorn, Naratip
In order to commercialize the rapidly developing technology of energy harvesters, the following devices need to be developed further for enhancing output performance, flexibility, scalability, facile fabrication, and cheaper price. The composite-based triboelectric nanogenerator (CTENG), which contains the above properties, is a promising technology that has attracted special interest for a decade. Focus has been placed on the hybrid concept between the composite-based piezoelectric nanogenerator (CPENG) and CTENG in order to enhance CTENG efficiency. This study presented a high-performance hybridized CPENG and CTENG device, which operated from the composite film of Ti<inf>0.8</inf>O<inf>2</inf> nanosheets (Ti NSs)/silver nanoparticles (Ag NPs) co-doped BaTiO<inf>3</inf> nanopowders (BT NPOs) inside the polydimethylsiloxane (PDMS) host. The 0.3 vol % of Ti NSs and 1.5 vol % of Ag NPs exhibited the optimum harvesting performance in all compositions, with an output voltage and current density reaching approximately 150 V and 0.32 μA/cm2, respectively. Their harvesting performance was approximately 60 and 32 times higher than that of the CPENG constructed from pure PDMS. In addition, practical demonstration of the proposed device was investigated. The hybridized CPENG and CTENG device could operate in a long-term cyclic operation, charge the capacitor for storing energy, and also drive LEDs to brighten. This work suggested facile device fabrication and made a guideline to develop high-performance nanogenerators, which is crucial for device development and practical usage in the future.
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Electrical conductivity, magnetism, and optical properties of reduced BaCeO 3
(2019-03-01)
Pulphol, Phieraya
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Vittayakorn, Naratip
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Vittayakorn, Wanwilai
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Kolodiazhnyi, Taras
BaCeO <inf>3</inf> -based perovskites are well-known proton and oxygen ion conductors. For practical applications as electrolytes in solid oxide fuel cells, these compounds must be robust towards reduction of cerium ion. In this work, we explore the effect of reducing atmosphere on the physical properties of undoped and Nb-doped BaCeO <inf>3</inf> . The BaCeO <inf>3</inf> perovskite structure is thermodynamically stable at least up to 1450 ∘ C upon annealing in H <inf>2</inf> -containing atmosphere. Annealing at 1550 ∘ C causes a decomposition of the BaCeO <inf>3</inf> . The higher annealing temperature leads to higher concentration of Ce 3 + ions and a higher electrical conductivity. With increasing the annealing temperature from 1300 to 1450 ∘ C , the activation energy of conductivity decreases from E <inf>a</inf> = 0.31–0.263 eV. We attribute the electrical conductivity in reduced BaCeO <inf>3</inf> to the activation of the small polaron hopping in agreement with the recent first-principles calculations. However, in contrast to the theoretical predictions, we find no evidence of the Ce 3 + –Ce 3 + spin-singlet small bipolarons.
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Analysis of Sb-doped ceria: Magnetism, conductivity, dielectric, specific heat and optical properties
(2019-02-01)
Kolodiazhnyi, T.
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Charoonsuk, T.
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Spreitzer, M.
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Vittayakorn, N.
We report on magnetism, charge transport, dielectric properties and specific heat of Ce<inf>1−x</inf>Sb<inf>x</inf>O<inf>2</inf> ceramics sintered at 1650 ∘C with a final antimony content of 0 ≤ x ≤ 0.0017. In contrast to other donor dopants, such as Nb, Ta, U and W, charge compensation of antimony in Ce<inf>1−x</inf>Sb<inf>x</inf>O<inf>2</inf> does not involve the formation of the Ce3+ ions as revealed by the magnetic susceptibility data. Therefore, we conclude that antimony is mainly present as Sb3+ ion and acts as an acceptor dopant in Ce<inf>1−x</inf>Sb<inf>x</inf>O<inf>2</inf>. This conclusion is also supported by a very low electrical conductivity of the Sb-doped ceria that shows an activation energy E<inf>σ</inf> ∼ 0.97 eV. This activation energy is close to that observed in oxygen conducting acceptor-doped ceria and is significantly higher than the typical E<inf>σ</inf> ∼ 0.1–0.3 eV values reported for n-type CeO<inf>2</inf>. Below 10 K, both an anomaly in the dielectric loss and a small specific heat surplus in Sb-doped ceria indicate a low-energy dipolar relaxation probably associated with a local dynamics of the off-centered Sb3+ point defects.
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Disentangling small-polaron and Anderson-localization effects in ceria: Combined experimental and first-principles study
(2019-01-23)
Kolodiazhnyi, Taras
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Tipsawat, Pannawit
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Charoonsuk, Thitirat
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Kongnok, Thanundon
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Jungthawan, Sirichok
By comparison of the electrical conductivity of ceria doped with penta- and hexavalent ions, we separate the total electron localization energy into the two contributions originating from the small polaron effects and the Coulomb interaction with the donor ions. The upper bound of the itinerant small polaron hopping energy is estimated at 66±20 meV. The binding energy of the Ce3+-M5+/6+ defect complex increases from 121 meV for M=Nb5+/Ta5+ to 243 meV for M=W6+/U6+. The first-principles simulations are in qualitative agreement with the experimental findings. At low temperatures the f electrons bound to the donor defects show dielectric relaxation with the lowest activation energy of 2.7 and 17 meV for Nb(Ta)- and W-doped ceria, respectively. Remarkably, these energies are significantly smaller than the hopping energy of the itinerant small polarons. While both the electron-lattice and the electron-defect interactions cause the f electron localization in real-case ceria, the latter effects seem to be the dominant.
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Synthesis of BaTiO3@TiO2-sheet Core-Shell Structured Nanocomposites
(2019-01-02)
Nawanil, Chanisa
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Panprom, Parinya
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Makcharoen, Worawut
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Khaosa-Ard, Krittanat
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Maluangnont, Tosapol
Core-shell structure nanocomposites have been of interest, as they can exhibit unique properties arising from the combination of peculiar characteristics of each component. In this research, core-shell structured nanocomposites, comprising barium titanate (BaTiO<inf>3</inf>; BT) nanoparticles as the core and titanate (TiO<inf>2</inf>) nanosheets as the shell, were prepared. The surface of barium titanate (BT) nanoparticles was modified chemically by hydrogen peroxide (H<inf>2</inf>O<inf>2</inf>) to create hydroxyl groups. TiO<inf>2</inf> nanosheets were deposited on the surface of the functionalized BT core, via alternate adsorption with oppositely charged polyelectrolyte poly(diallyl dimethylammonium) (PDDA) cations to produce an ultrathin TiO<inf>2</inf> shell layer that encapsulates BaTiO<inf>3</inf> nanoparticles. The structure of the core-shell particles was investigated in order to illustrate their formation mechanisms. Furthermore, this work reported the advance in utilizing a core-shell nanostructure to enhance relative permittivity and maintaining a low loss of polymer nanocomposites. A significant improvement in relative permittivity is attributed to the TiO<inf>2</inf> shell, which acts as polarizable dipoles and consequently enhances interfacial polarization. The results indicated that the structure of core-shell nanocomposites is attractive as a novel structural building block for fabricating novel materials and electronic devices.
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Dielectric properties of nanocrystalline barium zirconate titanate synthesized by glycine-nitrate autocombustion
(2019-01-02)
Seeharaj, Panpailin
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Charoonsuk, Thitirat
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Vittayakorn, Naratip
Dielectric properties of nanocrystalline barium zirconate titanate (Ba(Zr<inf>x</inf>Ti<inf>1-</inf><inf>x</inf>)O<inf>3</inf>; BZT for x = 0.1 and 0.3) synthesized by glycine-nitrate autocombustion method were investigated in this study. The phase formation examined by TGA-DTA, XRD, FT-IR and Raman spectroscopy confirmed that high purity single-phase BZT with perovskite structure was obtained by using glycine-to-nitrate molar ratio of 2.2:4 and calcining in air at 1100 °C for 4 h. TEM analysis showed that BZT had agglomerate particles consisted of primary spherical nanocrystals with the size of 8-11 nm. The diffuse phase transition behavior of BZT ceramics increased with increasing Zr concentration and for x = 0.3, the Curie temperature; T<inf>c</inf>, shifted to below room temperature. The BZT ceramics for x = 0.1 had relatively high dielectric constant (ε), 13007, low T<inf>c</inf>, 76 °C and comparable dielectric loss (tan δ) at T<inf>c</inf>, 0.012 which caused by the high degree of Zr diffuseness into the perovskite structure. These results suggest that glycine-nitrate autocombustion is the effective method for preparing high quality BZT ceramics.
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High piezoelectric activity in lead-free BaTiO3-BaZrO3-CaTiO3 ceramics with near polymorphic phase boundary
(2019-01-02)
Sutapun, Manoon
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Vittayakorn, Naratip
Lead-free 0.88BaTiO<inf>3</inf>–(0.12-x)BaZrO<inf>3</inf>–xCaTiO<inf>3</inf> (BT-BZ-xCT) ceramics were fabricated via solid state reaction. The effect of CaTiO<inf>3</inf> content on crystal structure, phase transition, and electrical properties was investigated systematically. The crystal structure and phase transition of ceramics were characterized by X-ray diffraction (XRD), Raman spectra and dielectric measurement. Results show that ceramic in the composition, x = 0.02, exhibits a rhombohedral structure. Ceramics with increasing CT content transformed from a rhombohedral to orthorhombic structure in the composition, x = 0.04, and eventually became a tetragonal structure at the composition, x ≥ 0.08. The polymorphic phase boundary (PPB) was observed at the composition, x = 0.06, with coexistence of orthorhombic and tetragonal phases showing at almost room temperature. This PPB composition exhibited a high piezoelectric response (d<inf>33</inf>*) of 1,150 pm/V at 10 kV/cm as an electric field was applied. These results indicate that the materials studied have potential as candidates for lead-free piezoelectric ceramics.

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