Sujitra Wongkasemjit

MgAl2O4 spinel powders from oxide one pot synthesis (OOPS) process for ceramic humidity sensors

Abstract MgAl 2 O 4 spinel powders can be prepared via the oxide one pot synthesis (OOPS) process. Porous ceramic oxide bodies can be produced with these powders and used as humidity-sensing materials. Pellets were characterized by SEM and their electrical properties were measured using impedance spectroscopy in the frequency range from 10 −2 to 10 5 Hz at different relative humidity (RH) levels in the range 4–90%. The spinel pellets made of powder from the OOPS process exhibited good humidity sensitivity with a linear response of the logarithm of resistance with RH in the whole RH range tested.

Release of monomeric sugars from Miscanthus sinensis by microwave-assisted ammonia and phosphoric acid treatments.

Microwave-assisted ammonium hydroxide (NH4OH) followed by phosphoric acid (H3PO4) treatments were used to release monomeric sugars from Miscanthus sinensis grown in Cha-Chueng-Sao province, Thailand. Treatment with 1.0% (w/v) NH4OH, 15:1 liquid-to-solid ratio (LSR) at 120 °C temperature for 15 min liberated 2.9 g of monomeric sugars per 100 g of dried biomass, whereas the corresponding yield for a treatment with 1.78% v/v H3PO4, 15:1 LSR at 140 °C for 30 min was 62.3 g/100 g. The two-stage pretreatment, treatment with NH4OH at 120 °C temperature for 15 min followed by treatment with H3PO4 at 140 °C for 30 min, impressively provided the highest total monomeric sugar yield of 71.6 g/100 g dried biomass.

Sol-gel processing of silatranes

Silatrane complexes are organosilicon compounds synthesized by direct reaction of SiO2 and trialkanolamines. Here, we explore their potential as ceramic precursors via the hydrolytic sol–gel processing method. Viscoelastic analysis is used to characterize the gelation behavior of silatranes based on triisopropanolamine, under different hydrolysis conditions. Pyrolyzed ceramic products are characterized in terms of surface area and morphology and found to have a homogeneous microporous structure with high surface areas (313–417 m2/g). Faster hydrolysis rates lead to shorter gelation times, and smaller pore sizes in the derived ceramic.

MFI zeolite synthesis directly from silatrane via sol–gel process and microwave technique

Abstract Silatrane was synthesized from the reaction of SiO 2 and triethanolamine using ethylene glycol as solvent under N 2 atmosphere. The obtained silatrane complex was further used as a Si source for MFI zeolite synthesis. The effect of Na + , OH − , and tetrabutyl ammonium hydroxide (organic template) concentration in the reaction mixture was studied. The reaction temperature was varied using the microwave heating technique. The effect of aging the reaction mixture at room temperature for varying times was also investigated. The rate of MFI formation decreases with increasing Na + , decreasing OH − , or lower template concentration. Higher temperatures correlate to shorter aging and heating times. At fixed temperature, longer aging times lead to shorter heating times. It was found that a longer aging time is more important to achieve high crystallinity than the heating time.

Morphology study of MFI zeolite synthesized directly from silatrane and alumatrane via the sol–gel process and microwave heating

Silatrane and alumatrane were prepared via the oxide one-pot process, and used as precursors for synthesis of MFI. The effect on MFI morphology of tetra-butyl ammonium hydroxide (TBA) and tetra-propyl ammonium bromide (TPA) as organic templates was compared. The influence of aging time, and of the sodium and hydroxide content of alumatrane were also investigated. TPA shows better performance as a template for the MFI synthesis than TBA by decreasing aging and heating times. Different templates produce different morphologies and growth directions of MFI crystals due to the steric effect of the template molecule. Increase of alumatrane loading retards MFI crystal formation, but no significant effect is observed on varying sodium and hydroxide concentrations as previously found for pure silicate MFI.

Efficient process for ethanol production from Thai Mission grass (Pennisetum polystachion).

Mission grass (Pennisetum polystachion) obtained from Tak Province, Thailand, possesses the potential to become a lignocellulosic biomass for bioethanol production. After the grass underwent milling and alkaline pretreatments, it was subjected to acid and enzymatic hydrolysis. The glucose hydrolyzate from the grass was detoxified to remove inhibitory compounds and degradation products such as furfural and 5-hydroxymethylfurfural. Overliming at pH 10 produced the highest ethanol yield. Among various strains of bakers yeasts, Saccharomyces cerevisiae TISTR 5596 with a yeast concentration of 10% v/v produced the maximum ethanol yield at 16 g/L within 24h, which is among one of the fastest ethanol producing microorganisms compared to other strains of S. cerevisiae as well as other ethanol-producing microorganisms.

Effect of Sr substituted La2−xSrxNiO4+δ (x = 0, 0.2, 0.4, 0.6, and 0.8) on oxygen stoichiometry and oxygen transport properties

Stoichiometry and oxygen diffusion properties of La2−xSrxNiO4±δ with x = 0.2, 0.4, 0.6, and 0.8 prepared via a sol–gel method were investigated in this study. Iodometric titration and thermogravimetric analysis were used to determine the oxygen non-stoichiometry. Over the entire compositional range, the samples exhibit oxygen hyperstoichiometry with the minimum value δ = 0.14 at x = 0.4. Mixed effects of reduction of oxygen excess and increasing valence of Ni were found to serve as charge compensation mechanisms; the former dominated at a low level of substitution, x < 0.4, while the latter dominated at higher levels of Sr (0.4 < x < 0.8). The highest oxygen diffusion coefficient was found for the minimum amount of Sr substitution, x = 0.2, continuously decreasing with x until x = 0.6. An unusual increase in D* was observed when the Sr content increased up to x = 0.8.

Enhanced butanol production by immobilized Clostridium beijerinckii TISTR 1461 using zeolite 13X as a carrier

Butanol production by cell immobilization onto porous materials-brick and zeolite 13X-was investigated using Clostridium beijerinckii TISTR 1461. Characterization results of two materials were completed to evaluate their potential as an immobilization carrier. Although zeolite has greater porosity than brick, it cannot be used for cell aggregation without treating with chemical. After immobilization, both materials can enhance butanol titers from 5.29 to 5.80g/L and 8.58g/L using brick and zeolite, respectively. Butanol to glucose yield also improved from 0.14 to 0.16g/g after immobilization. It was found that butanol production significantly increased due to an increase in buffering capacity, strong bonding between the zeolite surface and cell, and butanol tolerance. In addition, repeated batch fermentation was performed, demonstrating that cells immobilized onto zeolite 13X have high stability and potential for long-term use in continuous fermentation.

Interactions between CO and Poly(p-phenylene vinylene) as Induced by Ion-Exchanged Zeolites

The effects of zeolite type, ion-exchanged level, and ion type on the electrical conductivity responses of poly(p-phenylene vinylene) (PPV), doped poly(p-phenylene vinylene) (dPPV) and zeolite composites under CO exposures were investigated. The electrical sensitivity of dPPV/Cu+-ZSM5(Si/Al = 23) system shows a negative sensitivity value of −0.154, while the Na+ system gives a positive sensitivity of 1.48. Based on FTIR and TPD data, the positive response of PPV/Na+-ZSM5 stems from the CO molecules acting as a secondary dopant. On the other hand, the negative response of PPV/Cu+-ZSM5 originates from the fact that CO molecules are selectively adsorbed on Cu+ sites rather than C+ sites of doped PPV.

Sol-gel processing of spirosilicates

Abstract The sol-gel transition of tetra-coordinated spirosilicate via hydrolysis and condensation under acidic and basic conditions is examined to elucidate the effect of catalyst, reaction time and temperature on the properties of obtained gel. The main advantage of this process is the low temperature employed, producing a solid network with a high specific surface area. FTIR spectroscopy and TGA analysis were used to characterize the formation of siloxane bonds (Si–O–Si). It is found that spirosilicate can be hydrolyzed under both acid and base catalyzed conditions. The condensation rate to silicates is shown to be at a minimum in 0.001M HCl, which is the iso-electric point of silica. The prepared xerogel has a low-density and is an amorphous material with a specific surface area of 596 m 2 /g. Besides the catalyst media, the type of precursor also has a strong influence on the gel formation. An aminospirosilicate, six-membered ring, containing methyl and amino groups as substituents, was chosen for this study. The resulting xerogel is determined by the fact that to obtain the Si–O–Si bonds, a higher concentration of solvent and higher temperature are more favorable, due to the length and branching of alkyl portion.