Papers by Author: Titipun Thongtem

Abstract: 0–3 % Ho doped Bi₂MoO₆ samples were synthesized by hydrothermal reaction at 180 °C for 20 h. Their phase, morphologies, atomic vibration and optical properties were characterized by X-ray powder diffraction (XRD), Raman spectrophotometry, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and UV-visible spectroscopy. In this research, the products were orthorhombic Bi₂MoO₆ nanoplates with asymmetric and symmetric stretching and bending modes of MoO₆ octahedrons, and their strong absorption in the UV visible region.

Abstract: Purified cadmium sulfide crystals were successfully synthesized from 1:2 molar ratio of Cd and S powders by a 900 W microwave plasma for 120 min and 140 min. In the present research, XRD and SAED patterns including SEM, TEM, and FIB images were used to indicate phase and morphology of the products, with their Raman peaks at 303 and 605 cm^-1. Photoemission was determined to be 537 nm, and direct energy gap (E_g) to be 2.48-2.51 eV.

Abstract: CaWO4 was prepared by solvothermal reaction of Na2WO4.2H2O and calcium salts (CaCl2.2H2O, Ca(NO3)2.4H2O and Ca(CH3COO)2) in solvent containing a variety of glycerol/water ratios at 160 oC for 6 h. By using XRD, SEM, TEM and ED, the products compose of nano-sized CaWO4 particles with scheelite structure but different morphologies. Interplanar spaces between (101) planes were determined from HRTEM image, ED patterns and XRD spectra are 0.424, 0.474 and 0.476 nm, respectively. Luminescent intensities of the products prepared in pure water are the highest and their central peaks are the same at 444 nm. In addition, Ca, W and O were detected using EDX.

Abstract: MWO4 (M = Ca, Sr, Ba and Pb) was solvothermally prepared using metallic nitrates and sodium tungstate in 25/5 volume ratios of glycerol/water (SGL) and propylene glycol/water (SPG) at 160 oC for 6 h. XRD revealed the presence of MWO4 single phase with tetragonal scheelite structure. The strong W-O stretching band of WO4 tetrahedrons was detected at 705-875 cm-1. The product images show nano-sized particles in basic SGL and SPG solvents and flower-like particles in SPG solvent with pH of 6.7. Central peaks of the luminescent spectra are 445, 446, 443 and 440 nm, respectively.

Abstract: CdS was synthesized by solvothermal reaction of CdCl2.2.5H2O and (NH2)2CS in ammonia solution at 200 oC for 10 h. XRD, TEM and SAED show that the products are nanocrystalline CdS. The phase is 100 % hexagonal (hcp) in pure water, gradually transformed into cubic with the increase of NH3 concentration, and 100 % cubic in 25 % NH3 solution. By using FTIR, no solvents were detected in the products. Raman analysis revealed the presence of 1LO (longitudinal optical) and 2LO phonon peaks at 297.0 and 597.1 cm-1 for CdS (hcp), and 295.9 and 596.9 cm-1 for CdS (cubic), respectively. Strong peaks of the photoluminescent (PL) spectra were detected at 450 nm for hcp, and 519 nm for cubic.

Abstract: Nano-rod ZnWO4 was solvothermally prepared by the reaction of Zn(CH3COO)2.2H2O with Na2(WO4).2H2O in water at 150-200 oC using the pH of 5.0, 7.0, 9.0 and 12.0 for 24, 48 and 72 h. N-cetyl pyridinium chloride was used as a surfactant. By using XRD, SAED, EDX and TEM, nano-rod ZnWO4 containing Zn, W and O was detected. The pH values can play a role in the length of the nano-rods and their crystallinities. FTIR revealed the presence of Zn-O-W, W-O and Zn-O stretching vibrations of the products. Their photoluminescent (PL) spectra are similar and the wavelengths at the highest intensities were detected over the range of 445-450 nm.

Abstract: LiNiVO4 was synthesized using Li2CO3, NH4VO3 and Ni(CH3COO)2.4H2O as starting reagents and citric acid as a chelating agent. Mole ratios of metals to citric acid used for the preparation were 1 : 1 - 1 : 4. Carboxylate precursors were calcined at high temperatures to form powder. TGA data showed weight loss due to the evaporation and decomposition processes. FTIR showed the stretching bands of VO4 tetrahedron at 642, 713 and 813 cm-1. For 1 : 3 and 1 : 4 mole ratios, nano-crystals of inverse spinel LiNiVO4 (produced at 450 oC calcination for 6 h) were detected by XRD, electron diffraction, SEM and TEM.

Abstract: Li1-xNi1+xO2 powder was prepared by using tartaric acid as a complexing agent. A 1 : 1 : 2 mole ratio of Li : Ni : tartaric acid was used to form carboxylate precursors which were calcined at 650–800 oC for 14–48 h. TGA of the precursors showed that formation of Li1-xNi1+xO2 initiates at 600 oC and above. By using XRD, Li1-xNi1+xO2 with 650–800 oC calcination was detected. Calculated intensity ratios of I(003)/I(104) and I(006+102)/I(101) showed that the best condition is at 750 oC for 34 h. The crystallite size was estimated using the Scherrer equation. AAS and titration techniques showed that Ni3+/(Ni3+ + Ni2+) and mean oxidation state of nickel are 66.50 wt% and 2.67 respectively. EDX showed that the powder was comprised by Ni and O. The faceted particles are shown by SEM. TEM and electron diffraction showed the results that are in accordance with the above.

Abstract: Carbon nanotubes (CNTs) were grown on 304 stainless steel using iron as a catalyst. By using the applied voltages of 4-6 kV, iron wire with 0.5 mm in diameter was sparked for 1, 2, 10 and 100 times to form catalytic dots on the steel substrate. CNTs were subsequently grown in a gas mixture of 10 ml/s Ar and 0.1 ml/s C2H2 at a temperature range 700 - 900 K for 300 s (5 min). The dots and CNTs were characterised using AFM, SEM and TEM to determine their characteristics.