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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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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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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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Electrical and dielectric properties of barium titanate–polydimethylsiloxane nanocomposite with 0-3 connectivity modified with carbon nanotube (CNT)
(2019-01-02)
Nawanil, Chanisa
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Makcharoen, Worawut
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Khaosa-Ard, Krittanat
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Maluangnont, Tosapol
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Vittayakorn, Wanwilai
This study explored the preparation and electrical properties of 0–3 barium titanate/polydimethylsiloxane nanocomposites by dispersing barium titanate nanoparticles (BaTiO<inf>3</inf>; BT) into the polydimethylsiloxane (PDMS) matrix phase. The effect of barium titanate nanoparticles on electrical properties has been investigated systematically, and the relative permittivity of nanocomposites was found to increase significantly with increasing barium titanate content. Different theoretical models were used to predict the dielectric constant of these composites and compare their experimental value with the theoretical value in order to find an appropriate equation. The result indicated that the dielectric properties of composites are influenced not only by relative permittivity of the components but also dependence on interactions between ceramics and polymers. Furthermore, the preparation and dielectric properties of BT/PDMS nanocomposites modified with carbon nanotube (CNT) were also studied. The dielectric results demonstrate that adding CNT can enhance the relative permittivity of the BT/PDMS composite via improvement of dispersion and distribution of the BT nanoparticles in the PDMS matrix phase. Moreover, the electrical outputs from the BT/PDMS/CNT nanocomposites generator were measured under periodic knocking. The nanocomposites innovatively expand the feasibility of self-powered energy systems for smart sensor and energy harvesting applications.
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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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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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The study of trivalent-dopants effect on electrical properties of the BaZr0.7In0.3O3-δ system
(2019-01-02)
Poolphol, Phieraya
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Muanghlua, Rangson
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Atiwongsangthong, Narin
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Vittayakorn, Wanwilai
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Vittayakorn, Naratip
Perovskite BaZrO<inf>3</inf> and BaZr<inf>0.7</inf>In<inf>0.3</inf>O<inf>3-δ</inf> (BZI) ceramics were prepared via solid-state reaction. The crystal structure, dielectric and electrical properties of these ceramics were analyzed comparatively. Rietveld analysis indicated that BaZrO<inf>3</inf> and BaZr<inf>0.7</inf>In<inf>0.3</inf>O<inf>3-δ</inf> (BZI) have cubic symmetry with the Pm (Formula presented.) m space group. A small amount of In<inf>2</inf>O<inf>3</inf> was observed in the BZI ceramic. The lattice parameter (a) decreased when a small amount of In3+ was added. The relative permittivity ε<inf>r</inf>(T) and tan δ(T) of BZ and BZI ceramics behaved as plateaus that were independent of frequency and temperature in a temperature range of below 150 ̊C and 50 ̊C, respectively, which ascribed to the intrinsic dielectric properties resulting from electronic and/or ionic polarization. By increasing the temperature further, both ceramics exhibited colossal dielectric constant (CDC) behavior. Conductivity was greater with increasing temperature, which corresponded to Arrhenius behavior. Activation energies were calculated as 0.522 and 0.620 eV for the BZI and BZ system, respectively.
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Giant dielectric constants in K0.8M0.4Ti1.6O4 (M = Ni, Zn) lepidocrocite-type layered titanate ceramics
(2019-01-02)
Maluangnont, Tosapol
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Vittayakorn, Naratip
We reported herein the temperature-dependent dielectric properties of K<inf>0.8</inf>M<inf>0.4</inf>Ti<inf>1.6</inf>O<inf>4</inf> (M = Ni, Zn) lepidocrocite titanate ceramics at the frequency f of 103, 104 and 105 Hz. This titanate is an example of layered alkali titanium oxides possessing two-dimensional (2D) sheets of edge-shared TiO<inf>6</inf> octahedra, in contrast to other widely studied materials with mostly corner-shared TiO<inf>6</inf> motifs. The giant dielectric constants ε′ ∼104 and the dielectric losses tan δ ∼ 0.5–2 were obtained upon heating from RT to 250 °C. These values in our water-free ceramics are comparable to those previously reported in lepidocrocite titanate and related structures containing up to 15%wt water. The results were explained considering (i) Maxwell-Wagner polarization of interlayer species, and (ii) the possible formation of internal barrier layer capacitors (IBLCs) via the oxidized surfaces.

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