Preparation and characterization of graphene oxide and cellulose nanofibers/ polyvinyl alcohol nanocomposite film

Polyvinyl alcohol (PVA) is well-known in the packaging industry, especially in the food and medical fields with the ability to be completely biodegradable and easily soluble in cold water therefore products made from it are the environmentally friendly materials. However, the disadvantages of this polymer as quick dissolubility in water, poor moisture retention, weak mechanical properties reduce its applications. In this study, PVA, reinforced by “green” components at the nanometer-level such as nanocellulose fibers (CNF), graphene oxide (GO) nanosheets showed improvements in properties. Mechanical properties of all of nanocomposite films showed improvements in stress at break and modulus. Especially, reinforced GO and CNF films increased almost doubled and improved more 40% in modulus than the pure PVA film and films reinforced by only GO or CNF. When immersed in water (neutral pH) at room temperature, graphene oxide-reinforced films not only had effective improvements in swelling time but also supported to decrease water retension of film added CNF. The combined reinforcement also indicated a benefit in reducing the rate of water vapor loss of the film as well as the efficiency in declining the moisture absorption of the nanocomposite films. The PVA films reinforced by nanocellulose fibers and graphene oxide sheets overcomed some of the PVA's shortcomings. This helped expanding its applications in the field of environmentally friendly nanocomposite films.

Groundwater modeling from Tien Thanh to Ke Ga area, Binh Thuan province

The coastal area, from Tien Thanh to Ke Ga including Thuan Quy and Tan Thanh communes, is among the regions having a high economic growth rate of Ham Thuan Nam district, Binh Thuan province. The economic growth rate thanked to the development of coastal tourist sites and cultivating areas of dragon fruit, resulted in the increased water demand. Due to the limitation of the water supply system and surface water, the region's main supply comes from the groundwater. The massive and uncontrolled exploitation could lead to the exhaustion and pollution of water reservoirs in the coastal Quaternary aquifer. To serve the management and use of groundwater resources, we calculated the used reserves of the entire area by modeling the layer containing water in the area using the Modflow module of GMS software 10.4 (Groundwater Modeling System). The input data were collected through the suction pump experiment, water samples, survey on exploitation, and results of research reports of nearby areas. The normalized steady-state models showed that aquifers in the area were recharged by rainwater, and re-fed to rivers, partly forming the flows to the sea. If the amount of wasted water into the sea was considered as the total exploitable reserve, the used reserve of underground water in this area is 70,158 m3/day.

Chemical constituents and theira-glucosidase inhibitory activity of the stem of Salacia chinensis L.

Salacia chinensis L., known as “Chop mao” in Vietnam, is a climbing shrub that belongs to the Celastraceae family. The stem of S. chinensis L. is used as a traditional medicine for the treatment of diabetes, rheumatoid arthritis, back pain, … The dried powdered stem of S. chinensis L. was collected in Phu Yen province and was extracted with methanol to yield methanol extract. The methanol extract was suspended in H2O and partitioned successively with n-hexane, CHCl3, EtOAc to obtain n-hexane, CHCl3, EtOAc, and H2O fractions, respectively. The CHCl3 fraction was subjected to a series of chromatographic separation to afford four purified compounds including 3-oxolup-20(29)-en-30-al (1), betulin-3-caffeate (2), 2-(4-hydroxy-3,5-dimethoxylphenyl)ethanol (3), and acetosyringone (4). Their structures were elucidated on the basis of the spectroscopic analysis and comparison with literature data. The isolated compounds were tested for their α-glucosidase inhibitory activity. The result indicated that all compounds (1-4) possessed significant α-glucosidase at the testing concentration of 100 µM with the percent inhibition values of 9.5 ± 1.3, 70.89 ± 0.25, 44.2 ± 1.6, and 6.7 ± 1.7 %, respectively. In addition, betulin-3-caffeate (2) and 2-(4-hydroxy-3,5-dimethoxylphenyl)ethanol (3) show more potent α-glucosidase inhibitory activity, with IC50 values of 69.7 and 152.0 µM, respectively, than that of positive control acarbose (IC50 = 214.5 µM).

Chemical constituents and their alpha-glucosidase inhibitory activity from the stems of taxotrophis ilicifolius

Taxotrophis ilicifolius, called "Gai quít" in Vietnam, belonged to the family of Moraceae. The stems of T. ilicifolius are used in traditional medicine to cure pimples, anti-inflammatory, antibacterial... By column chromatography method together with thin layer chromatography on the ethyl acetate extract of its stems, six compounds were isolated including wogonin (1), 4-hydroxybenzoic acid (2), vanillic acid (3), vanillin (4), syringic acid (5), and syringaldehyde (6). Their chemical structures were elucidated by extensive NMR spectroscopic analysis and comparison with the literature data. The isolated compounds were tested fora-glucosidase inhibitory activity. All compounds showed more potent inhibitory activity with IC50 values 42–142 mM, than that of a positive control acarbose (IC50, 214.5 mM). Among all isolates, compounds 2, 4 and 6 exhibited significant a-glucosidase inhibitory activity with the IC50 values of 49.7, 42.6 and 55.9 mM, respectively. From the present investigation, all these compounds were isolated for the first time as well as their a-glucosidase inhibitoryactivity of T. ilicifolius. These results suggested that the traditional use of T. ilicifolius for the treatment of diabetes disease in Vietnam may be due to thea-glucosidase inhibitory activity of its phenolic constituents.

Chemical constituents and their alpha-glucosidase inhibitory activity of Solanum procumbens

Solanum procumbens called ``Cà gai leo'' in Vietnam, belonged to the family of Solanaceae, which is a prickly diffuse, bright green perennial shrub, woody at the base. This plant has been sought for plenty of Vietnamese folk remedies for diseases such as rheumatism, back pain, detoxification, cough, pain relief, hemostasis, hepatitis, and cirrhosis. Chemical reports revealed the presence of lots of secondary metabolites such as steroids, triterpenoids, alkaloids, and phenolic compounds that have good biological activities such as antibacterial, antidiabetic, antioxidant, and antimicrobial... By column chromatography method together with thin layer normal-phase chromatography on the ethyl acetate extract of its entire plant, we isolated four compounds including dioscin (1), b -sitosterol (2), daucosterol (3) and 6'-O-acetyl-b -daucosterol (4). The result of theira-glucosidase inhibitory activity showed that compounds 2 and 4 had strong inhibition with IC50 values of 35.2 and 209.5 mM, comparing to the positive control, acarbose with an IC50 value of 214.5 mM. The results of this study have contributed to the scientific data of chemical compositions of Vietnamese medicinal plants, among them S. procumbens would potentially be developed as a plant-based drug to decrease the blood glucose level.

Monitoring techniques for algae blooms from space

Microalgae blooms are one of the most serious environmental problems that greatly affect the living environment of aquatic organisms. They deplete the oxygen source in the water, seriously depleting the respiratory oxygen source for organisms living in the water body. Some species of microalgae are also capable of producing toxins, typically blue-green algae, poisoning aquatic organisms and causing death, health effects on human life when ingested. This paper presents the results of research on mapping algae concentration distribution to support water quality assessment for Dau Tieng reservoir. Landsat satellite imagery was used for qualitative and quantitative assessment of algae presence in the lake area. Calculation results showed that algae concentration had a linear correlation with the band ratio of the 3-band algorithm (3BDA (2), and was a combination of spectral reflective bands in the green wavelength bands GREEN, RED and near infrared NIR. We simulated the spatial distribution of algae concentrations on the entire lake area on 3 points of time when satellite images had been collected. Result of this study showed that remote sensing technology can be used for monitoring the appearance and change of algae concentration in water, which is an essential measurement for timely providing warnings as well as assisting in monitoring and managing water environment quality to minimize damages to people and the ecosystem.

Chemical constituents of the whole plant of PHLOGACANTHUS TURGIDUS (FUA EX HOOK.F.) LINDAU

The genus Phlogacanthus belongs to the family Acanthaceae and consists of more than 49 species, These species are widespread in tropical and subtropical zones such as Bangladesh, Bhutan, China, Indonesia, India, Myanmar and Vietnam. In Vietnam, the genus contains about 06 species. The extracts from some species in this genus have been evaluated for biological activities as analgesic, antiinflammatory, antimicrobial, antioxidant, antihyperglycemic and cytotoxic activities. In this study, the whole plant of Phlogacanthus turgidus was collected, dried, cut into small species, and extracted with ethanol to yield the ethanolic extract. Isolation of chemical constituents was performed using column chromatography on silica gel; their structures were elucidated by HRESI-MS, 1D & 2D-NMR and compared with published data. Six compounds, including two nor-isoprenoids: (+)-dehydrovomifoliol (1), (3S,5R,6R,7E,9S)-megastiman-7-ene-3,5,6,9-tetrol (2), two steroids b - sitosterol (3), daucosterol (4), one lignan (+)-syringaresinol (5), a derivative of phenylethanoid glycosides: martynoside (6) were isolated from the ethyl acetate extract of the whole plant of P. turgidus. Among them, 1, 2 were reported for the first time from the genus Phlogacanthus, while 3, 4, 5, 6, were found for the first time from this species.

Effects of auxin and cytokinin on the regeneration and growth of shoot tomato ( Solanum lycopersicum L.) in drought stress

Tomato is one of the most popular foods in the world. However, drought stress has strongly decreased the growth and yield of tomatoes. Therefore, the study on drought-tolerant tomatoes is essential. In this paper, tomato cultivar TN704, which is popularly grown in Vietnam's Southeast and Vietnam's Mekong Delta was selected. The combination of auxin (IAA, indoleacetic acid) and cytokinin (zeatin) at different concentrations was investigated to determine the effective regeneration media. Then, the drought pretreatment was applied to obtain drought-tolerant shoots. The drought tolerance of regenerated shoots was checked by culture in the drought stress condition after two generations (F1 and F2). The physiological and biochemical changes of regenerated shoots in the drought stress condition were analyzed. The MS 1 2 medium supplemented with 0.2 mg/L IAA and 0.5 mg/L zeatin was the effective medium for in vitro shoot regeneration from tomato leaves. The drought pretreatment (MS 1 2 with 20 g/L mannitol) increased the number of regenerated shoots which can develop in the drought stress condition. The regenerated shoots in the F1 and F2 generations grew strongly under drought conditions. The content of chlorophyll, carotenoid and proline, the intensity of respiration and photosynthesis, and the activity of auxin and cytokinin in leaves of F1 and F2 plant were higher than the control.

Synthesis, characterization and photo-Fenton catalytic activity of magnetic CuFe2O4/Fe2O3 materials

In this work, we proposed to immobilize Fe2O3 nanoparticles on the surface of magnetic CuFe2O4 particles by a facile impregnation – annealing method at different annealing temperatures (200, 300, 400 and 500°C) in order to create new heterogeneous photo-Fenton catalysts with enhanced catalytic performance for the oxidation of organic dyes. The influences of annealing temperatures used in the synthesis procedure on the phase composition, the morphology, the particle size and the surface functional groups of our catalysts were investigated by XRD, FE-SEM and FTIR techniques, respectively. The photo-Fenton catalytic performance was evaluated by the degradation of methylene blue under both UVA and visible light illumination in the presence of H2C2O4 as radical-producing source. According to the experimental results, Fe2O3 nanoparticles were successfully coated on CuFe2O4 surface, which successfully formed the α-Fe2O3 phase in the phase composition and also increased the Fe3+ content on the surface. As a consequence, the rate constant of photo-Fenton catalytic degradation of methylene blue over these samples were clearly improved. More especially, owing to the good magnetic property of CuFe2O4 component, our CuFe2O4/Fe2O3 samples were easy to be separated from the solution by a magnet, making them more feasible in practical applications of environmental treatment. Among our catalytic samples, the CuFe2O4/Fe2O3 sample annealed at 300°C showed the best performance with the highest rate constants under both UVA light and visible light. Its catalytic activities was found to be 6.8 times higher than CuFe2O4 under UVA light and 2.1 times higher than CuFe2O4 under visible light. However, when the annealing temperature was up to 500°C, the catalytic activity was reduced, which can be explained by the growth of particles and the stabilization of surface Fe-O bonds.

Green one-step synthesis of cellulose nanocrystal/ ZnO nanohybrid with high photocatalytic activity

In this work, nanohybrid of zinc oxide/ cellulose nanocrystals (ZnO/CNC) was successfully prepared by using a low cost and green method for photocatalytic degradation of methylene blue (MB). CNC had been derived through the hydrolysis reaction by citric/hydrochloric acid from the pure cellulose isolated from Vietnamese Nypa fruticans trunk. The obtained CNC with carboxyl groups could act as a stabilizing and supporting agent to anchor ZnO nanoparticles. The chemical and crystal structures, morphology, thermal and photocatalytic properties of the ZnO/CNC nanohybrid were characterized by FESEM, FTIR, XRD, FESEM, BET, EDX, TGA, DRS and photocatalytic tests. Analyses of FTIR spectra, XRD, and FESEM indicated that the ZnO nanocrystals with the size of 50 nm formed and loaded on the surface of CNC. The TGA analysis demonstrated that the ZnO loading sample (ZnO/CNC) had the thermal degradation onset temperature higher than that of neat CNC. ZnO/CNC cuold be absorpted ultraviolet light and have high value of specific surface area (SBET), based on the DRS spectra and the nitrogen adsorption – desorption isotherms analysis, respectively. ZnO/CNC displayed more photocatalytic activity than pure ZnO upon degradation of methylene blue due to strong interaction between the CNC and ZnO nanoparticles. The maximum degradation of MB was about 95% in 150 minutes for the ZnO/CNC.