Vietnam Journal of Chemistry

Mesostructure aluminosilicate materials assembled from ZSM-5 (MFI), beta (BEA) zeolite seeds have synthesized successfully from metakaolin under basic medium. They were characterized by XRD, nitrogen adsorption isotherm, TEM, FTIR, TPD_NH3. The results exhibit character of the ordered hexagonal mesostructures assembled from ZSM-5, Beta zeolite seeds with the wall thickness of ~8 Å, pore size of 38 Å, BET surface area of 723m2/g and 700 m2/g, respectively. These materials contain both strong and weak acidic sites.

The effects of hypochlorite level (NaOCl, 1%, 2% and 4% w/w) on the structures and physicochemical properties of oxidized tapioca starch were investigated. Carboxyl and carbonyl group contents of oxidized starch increased with increasing NaOCl level. Oxidation caused the outer layer of the starch grain surface to erode away and X-ray diffraction patterns of all the starches remained unchanged after oxidation.

Six known compounds daphneresinol (1), (+)-neo-olivil (2), methyl gallate (3), bergenin (4), asiatic acid (5) and blumenol A (6) were obtained from the organic extract of the leaves of Dipterocarpus obtusifolius Teijsm. Ex Miq. by various chromatographic techniques. Structural elucidation of the metabolites was carried out by analysis of their spectroscopic data and by comparison with those reported in the literature. Compounds 1-4 and 6 were isolated from this plant for the first time.

Nano thin films of tin oxide are synthesized by sputtering for gas sensors application. The fabrication includes of deposition tin metal thin films on thermally oxidized SiO2 followed by thermal oxidation at 300oC, 400oC, 500oC and 600oC in air. The effect of oxidized temperatures on the morphologies; microstructure and gas sensing properties are investigated. Tin oxide tin films showed very high sensitivity to NOx at ppm level. The nano thin film oxidized at 400 oC showed highest sensitivity compared to others.

Some new compounds of 2-amino-4,6-diarylpyrimidines  have been synthesized from corresponding substituted chalcones and guanidine hydrochloride using two different synthetic methods in  microwave oven. The products formed were equally available and confirmed by IR, 1H-NMR and mass spectral data.

Mixed oxides of La, Sr, Co and Ag were prepared by sol-gel method using acid citrat as solvent. Two kinds of obtained mixed oxides A = La1-xSrxCoO3+La2O3+SrO+Co3O4+ SrCoOx and B = A+Ag were characterizied by X-Ray Diffraction analysis (XRD), Field Emision Scanning Electron Microscope (FESEM), Energy Dispersive X-ray Spectroscopy (EDS). Their catalytic activity was studied by Temperature Programmed Surface Reaction (TPSR). The results shown that the mixed oxide A exhibits a weak DeNOx activity, but in the addition of a little of metal silver (Ag), the NOx conversion increases remakably from 29.4% (in absence Ag) to 82.4% at 220oC.

Localized surface plasmon resonance of nanoparticles, especially AuNP and AgNP, has been extensively exploited in many applications related to chemical and biological sensing. AgNP shows the best dominant plasmon resonance characteristic compared to other nano metals. Thereforce, it is quite sensitive to changes in the size and shape of nano particles, as well as external medium on the particle surface. This is the basis for exploiting this nature in the development of sensor systems. This work presents a chemical method to prepare AgNP colloidal systems which was then exammined the physical characteristics through physical analyzes, including surface plasmon resonance characteristic, X-ray diffraction analysis (XRD) and TEM. Experimental results showed that the color of AgNP solution was changed, accompanying with a decrease in size of AgNP and a blue shift in absorption wavelength in the presence of Hg2+, due to the chemical reaction between Hg2+ and AgNPs. The positive results of this work can be applied to the development of sensors based on the color change for quick screening Hg2+ in water samples. Keywords. Silver nanoparticle, plasmon resonance, sensor, mercury, mercury analysis in water sample.

Maytensifolin B, α–amyrin and clerolsterol were isolated from stem bark of Arnicratea cambodiana (Pierre) N. Hall. for the first time. Their structures were elucidated by means of spectroscopic methods and comparison with reported data.

By the reaction of o-acylphenols with ethyl acetoacetate a new series of 3-acetylcoumarine derivatives were obtained. Some α,β-unsaturated ketones were also synthesized via 3-acetylcoumarine derivatives by Claisen-Schmidt condensed reaction. Ketones formed via 3-acetyl-4-methylcoumarine derivatives have interesting structures. The structures of these compounds were confirmed by IR, 1H-NMR and MS spectroscopic data.

A new method to prepare mesoporous material Ti-SBA-15, which was expected to be a commercial synthesis was presented. The obtained Ti-SBA-15 with hexagonal structure were successfully prepared by using sodium silicate and nontoxic precursors, which are low cost and available in Vietnam. These materials were characterized by different techniques such as XRD, IR, BET, SEM, HRTEM, UV-VIS. It shown that Ti-SBA-15 have very uniform pore size (3.5- 9.5 nm). These catalysts were tested in the oxidation reaction α-pinene with hydrogen peroxide as oxidation agent. The results shown that Ti-SBA-15 had activity and stability higher than Ti-MCM-41 under lower reaction temperature than other oxide catalysts. This commercial preparation method is a great potential background to scale-up and apply mesoporous material Ti-SBA-15 in fine chemistry and pharmaceutical chemistry.