Kien T. Nguyen

Arsenic removal from aqueous solutions by adsorption using novel MIL-53(Fe) as a highly efficient adsorbent

A MIL-53(Fe) analogue was successfully synthesized by a HF free-solvothermal method. The sample was characterized by XRD, N2 adsorption (BET), TEM, FTIR, XPS and AAS. From the N2 adsorption–desorption isotherms, it can be seen that the structure of MIL-53(Fe) in the anhydrous form exhibits closed pores with almost no accessible porosity to nitrogen gas. The XPS results reveal that Fe is really incorporated into the MIL-53(Fe) framework. In the hydrated form, the pores of MIL-53(Fe) are filled with water molecules. Thus, MIL-53(Fe) exhibited a very high adsorption capacity of As(V) in aqueous solution (Qmax of 21.27 mg g−1). Adsorption kinetics data revealed that As(V) adsorption isotherms fit the Langmuir model and obey the pseudo-second-order kinetic equation.

Isomorphous substitution of Cr by Fe in MIL-101 framework and its application as a novel heterogeneous photo-Fenton catalyst for reactive dye degradation

Partial isomorphous substitution of Cr by Fe in the MIL-101 framework was achieved by direct synthesis using a hydrothermal method (conventionally, solvothermal method). The products were characterized by XRD, EDX, N2 adsorption (BET), TEM, UV-vis, FTIR, XPS and testing the photo-Fenton activities in the degradation of the commercial reactive dye RR195. From FTIR and XPS results, it was revealed that Fe is really incorporated into the MIL-101 framework. From EDX results, an amount of ca. 25% of Cr atoms in the MIL-101 framework is substituted by Fe atoms. Fe substituted Cr-MIL-101 showed high adsorption capacity of reactive dye. Moreover, this material exhibited high photo-Fenton activity in reactive dye degradation, opening new applications of MOFs as novel heterogenous photo-Fenton catalysts.

Study on photocatalytic activity of TiO2 and non–metal doped TiO2 in Rhodamine B degradation under visible light irradiation

Highly active photocatalytic TiO2 nanotubes were successfully synthesised by hydrothermal treatment in base medium using commercial TiO2 powder as Ti–source. Non–metal doped TiO2 samples were made by post–synthesis using urea, thio–urea, ammonium fluoride and ethylene glycol as N, S F and C source. The obtained samples were characterised by XRD, FE–SEM, UV–Vis. Photocatalytic activities of the samples were tested in photocatalytic degradation of Rhodamine B and Methylene Blue in liquid phase under visible light irradiation. Both TiO2 nanotubes and doped samples showed high photocatalytic activities in both the Rhodamine B and Methylene Blue degradation. However, non–metal doped TiO2 samples exhibited much higher photocatalytic activity under visible light irradiation as compared to that of non doped TiO2 sample, indicating high photocatalytic performance of non–metal doped TiO2 photocatalysts under visible light irradiation.

Removal of Cd2+ and Cu2+ ions from aqueous solution by using Fe–Fe3O4/graphene oxide as a novel and efficient adsorbent

The nano Fe–Fe3O4/graphene oxide (GO) was successfully synthesized by the precipitation method and followed by chemical reduction using FeCl3 as iron sources and NaBH4 as reducing agent. The products were characterized by x-ray diffraction (XRD), Fourier transform infrared spectroscopy, transmission electron microscopy (TEM), BET, x-ray photoelectron spectroscopy (XPS) and VMS. From the obtained XRD and XPS results, it revealed the formation of both Fe and Fe3O4 nano particles on GO surface. TEM images showed that both Fe3O4/GO and Fe–Fe3O4/GO had small particle size of 10–20 nm and uniform size distribution. Fe3O4/GO and Fe–Fe3O4/GO were used as adsorbents for removal of Cd2+ and Cu2+ ions from aqueous solution. Maximum adsorption capacity (Q max) of Fe–Fe3O4/GO for Cu2+ and Cd2+ are 90.0 mg g−1 and 108.6 mg g−1, respectively. These values are much higher as compared to those of Fe3O4/GO as well as those reported in the literature. Additionally, this novel adsorbent can be reused by washing with diluted Hcl solution and easily recovered by applying the magnetic field. The Cd2+ adsorption isotherm fits better for the Langmuir model that of the Freundlich model and it obeys the pseudo-second order kinetic equation.

Study on synthesis and photocatalytic activity of novel visible light sensitive photocatalyst Ag3PO4

Silver orthophosphate nanoparticles have been synthesised by precipitation of AgNO3 and H3PO4 in presence of oleylamine and other solvents like toluene, and ethanol at room temperature. Particle sizes of silver orthophosphate nanocrystals can be controlled by adjusting the amount of water. The products were characterised by XRD, UV–Vis, FESEM and EDX. The characterisation results showed that the crystal sizes of products were 5–20 nm depending on the content of water. UV–Vis result revealed a strong light absorbance in the visible light region at 465–470 nm. Photocatalytic activities of titania and silver orthophosphate nanocrystals were tested in photocatalytic degradation of Methylene Blue (MB) in liquid phase under visible light irradiation. Samples showed very high photocatalytic activity in the degradation of Methylene Blue. After 2h of reaction, the conversion reached the value of 97%.

Impact of anthropogenic activities on water quality and plankton communities in the Day River (Red River Delta, Vietnam)

Planktons are a major component of food web structure in aquatic ecosystems. Their distribution and community structure are driven by the combination and interactions between physical, chemical, and biological factors within the environment. In the present study, water quality and the community structure of phytoplankton and zooplankton were monthly investigated from January to December 2015 at 11 sampling sites along the gradient course of the Day River (Red River Delta, northern Vietnam). The study demonstrated that the Day River was eutrophic with the average values of total phosphorus concentration 0.17xa0mg/L, total nitrogen concentration 1.98xa0mg/L, and Chl a 54xa0μg/L. Microscopic plankton analysis showed that phytoplankton comprised 87 species belonging to seven groups in which Chlorophyceae, Bacillariophyceae, and Cyanobacteria accounted for the most important constituents of the river’s phytoplankton assemblage. A total 53 zooplankton species belonging to three main groups including Copepoda, Cladocera, and Rotatoria were identified. Plankton biomass values were greatest in rainy season (3002.10-3 cell/L for phytoplankton and 12.573 individuals/m3 for zooplankton). Using principal correspondence and Pearson correlation analyses, it was found that the Day River was divided into three main site groups based on water quality and characteristics of plankton community. Temperature and nutrients (total phosphorus and total nitrogen) are key factors regulating plankton abundance and distribution in the Day River.

Ordered Mesoporous Carbons as Novel and Efficient Adsorbent for Dye Removal from Aqueous Solution

Ordered mesoporous carbons (OMCs) were successfully synthesized by using hard template and soft template methods. These materials were characterized by XRD, TEM, and N2 adsorption-desorption Brunauer-Emmett-Teller (BET). From the obtained results, it is revealed that the obtained OMCs samples showed high surface area (>1000u2009m2/g) with high pore volume, mainly mesopore volume (1.2–2.4u2009cm3/g). Moreover, OMCs samples had similar structure of the SBA-15 silica and exhibited high MB adsorption capacity with of 398u2009mgg−1 for OMCs synthesis with hard template and 476u2009mgg−1 for OMCs synthesis with soft template, respectively. From kinetics investigation, it is confirmed that MB adsorption from aqueous solution obeys the pseudo-second-order kinetic equation.

Catalytic pyrolysis of biomass by novel nanostructured catalysts

Nanostructured catalysts were successfully prepared by acidification of diatomites and the regeneration of used FCC catalysts. The obtained samples were characterized by IR, XRD, SEM, EDX, MAS-NMR (27Al and 29Si), NH3-TPD and tested in catalytic pyrolysis of biomass (rice straw). The results showed that the similar bio-oil yield of 41,4% can be obtained by pyrolysis in presence of catalysts at 450°C as compared to that of the pyrolysis without catalyst at 550°C. The bio-oil yield reached a maximum of 42,55 % at the pyrolysis temperature of 500°C with catalytic content of 20%. Moreover, by catalytic pyrolysis, bio-oil quality was better as reflected in higher ratio of H/C, lower ratio of O/C. This clearly indicated high application potential of these new nanostructured catalysts in the production of bio-oil with low oxygenated compounds.