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Nam N.H.,Vietnam Academy of Science and Technology | Van Bay D.,Hanoi National University of Education | Khue D.N.,New Technology Institute | Van Chung T.,Institute of Chemistry and Materials
Asian Journal of Chemistry

The adsorbents based on Fe(OH) 3 containing SiO2 and Fe(0) powders (denoted 3TP) were prepared and used for removal of 2,4-dichlorophenoxyacetic acid from water. The characteristics of this adsorbents were determined and indicated that the presence of SiO2 and Fe(0) powders can enhance the amorphous structure of adsorbents, desired for the adsorption. The adsorption of 2,4-dichlorophenoxyacetic acid onto adsorbents was studied. The adsorption process occurs predominantly via chemisorptions of 2,4-dichlorophenoxyacetic acid onto adsorbents. The adsorption characteristics including kinetic thermodynamic parameters were examined. The experimental data shown that this is an endothermic, spontaneous adsorption process. Source

Tien V.V.,Hanoi National University of Education | Bay D.V.,Hanoi National University of Education | Thu D.X.,Hanoi National University of Education | Chung T.V.,Institute of Chemistry and Materials
Asian Journal of Chemistry

Arsenic present in water may be determined by many methods such as atomic adsorption spectroscopy, inductively coupled plasma atomic emission spectroscopy, electrochemistry and spectrophotometry with silver diethyldithiocarbamate. This study presents the determination of arsenic present in water by spectrophotometric method based on molybdate reagent. This method is highly sensitive and selective but has not been studied in detail. The obtained results exhibited the experimental optimum conditions for arsenic determination by spectrophotometric method using molybdate reagent. The method consists of two steps (i) arsinization producing AsH3, (ii) AgNO3, H2O2 oxidized AsH3 reacting with molybdate reagent to produce molybdenum blue. The absorbance of molybdenum blue at the wavelength of λ = 878 nm has been used for arsenic determination. The limit of detection and limit of quantitation of the method are 2 and 7 ppb respectively. Source

Chung T.V.,Institute of Chemistry and Materials | Anh T.Q.,Hanoi University | Phung D.Q.,Hanoi National University of Education | Luong T.D.,Hanoi National University of Education
Asian Journal of Chemistry

The properties of zero-valent iron is useful in remediation of aromatic nitro compounds by reducing them to convert onto the amino products which may also lead to oxidize or mineralize them with the presence of persulfate anion (S 2O 8 2-). In practice, with the zero-valent iron, persulfate anion (E° = 2.01 V) may be activated to produce free sulfate radical (SO 4 - • ) with the higher standard reduction potential (E0 = 2.60 V). It is an active reagent for the mineralization of nitrobenzene in the studied samples. The activation process of persulfate in solution with zero-valent iron to produce SO4 - •, may be implemented by the following pathways: In the heterogeneous system the activation reaction was implemented on iron surface: Fe(0) + 2S 2O 8 2- → Fe 2+ + 2SO 4 - • + 2SO 4 2-, In homogeneous case, the activation process was implemented in solution: Fe 2+ + S 2O 8 2- • → Fe 3+ + SO 4 - • + SO 4 2- In the studied system zero-valent iron is a source producing Fe 2+ to keep the activation of persulfate anion. The free sulfate radical formed in situ oxidizes nitrobenzene causing the decrease of the total organic carbon in the samples. The experimental data have shown that the nitrobenzene concentration of 80 mg/L in the system consisting of 500 mg/L of Na2S2O8 and 1 g/L of zero-valent iron, pH = 5, the efficiency of nitrobenzene mineralization may reach for 98 % for 40 min. The nitrobenzene was first reduced with zero-valent iron then transported for the further oxidation with free sulfate radical, the mineralization nitrobenzene may reach for 95 % for 0.5 h. This means that amine products are easily oxidized than its nitro compounds. The obtained experimental data have suggested that the reduction of nitrobenzene by zero-valent iron may be combined with the oxidation process with persulfate activated with zero-valent iron to enhance the nitrobenzene degradation efficiency and the efficiency of zero-valent iron used. The factors such as ratios of persulfate/zero-valent iron/ nitrobenzene, pH, the addition of Fe 2+ influencing on the efficiency of nitrobenzene mineralization have been investigated. Source

le Trung Q.,Institute of Chemistry and Materials | Duc Hung N.,Institute of Chemistry and Materials | Nam N.H.,Institute of Chemistry and Materials | van Chung T.,Institute of Chemistry and Materials | And 2 more authors.
Asian Journal of Chemistry

This paper describes the character of the reduction of 2,4.6-trinitroresorcine (TNR) by zero-valent iron (ZVI) in anaerobic conditions and the oxidative reaction of amine resorcine in the system of ZVI-EDTA-O2. The products of TNR by ZVI in anaerobic conditions were amine resorcine compounds. These compounds tend to be easier to be oxidized by the free radical OH• generated in the system of ZVI-EDTA-O2. HPLC method and COD analysis have been used for monitoring efficiency of reactions. The experiments suggested that the removal of TNR from groundwater is likely implemented by two steps. The first step is reduction of TNR by ZVI to form amine resorcine. The second step is oxidation of amine resorcine in system consisting of ZVI-EDTA-O2. From the obtained results a model for TNR contaminated groundwater treatment has been suggested. Source

Chung T.V.,Institute of Chemistry and Materials | Quang D.S.,Institute of Chemistry and Materials | Bay D.V.,Hanoi National University of Education | Luong T.D.,Hanoi National University of Education
Analele Universitatii Bucuresti Chimie

2,4,6-Trinitroresorcine (TNR) with molecular formula C 6H 3N 3O 8 is one of the aromatic nitro compounds ranging slight to strong oxidizing agents causing environmental contamination. The persulfate anions activated by ZVI were used to oxidize organic compounds like trichloroethylene (TCE), methyl tertiary butyl ether (MTBE). The content of this paper was to demonstrate if the ZVI activated persulfate oxidation of TNR was a viable method. The experimental data have shown that the TNR compounds in aqueous media were oxidized by the persulfate anions activated by ZVI. The reaction participated in components such as TNR; its oxidized products were measured by Voltammetry square wave and TOC analysis. The TOC values in the samples reduced have demonstrated that the final oxidized products were CO 2 + H 2O + other mineral compounds. The activation of the persulfate anions by ZVI may be implemented through the reactions between S 2O 8 2- and ZVI to form sulfate free radicals (SO4 _). The mineralization of TNR by the persulfate anions activated by ZVI is favor in the pH range from 3 to 5. © 2011 Analele Universitǎţii din Bucuresti. Source

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