Seminar by Dr. Vu Thi Ngoc Anh and Dr. Wannida Sapyen

On November 3, 2023, the lectures from Dr. Vu Thi Ngoc Anh and Dr. Wannida Sapyen take place in the meeting room B.

Dr. Vu Thi Ngoc Anh presents a talk entitled "Synthesis, characterization, and sorption activity of novel azo-colorants derived from phloroglucinol and antipyrine and their metal complexes"

Abstract:

Two novel azo-colorants derived from phloroglucinol and antipyrine as well as 10 metal complexes with Co(II), Ni(II), Zn(II), Cu(II), and Cd(II) were isolated and studied by a set of methods (1H, 13C NMR, IR, UVVIS, EPR, X-ray structure determination). The azo-coupling of phloroglucinol with a 5-pyrazolone amino-derivative led to the isolation of a colorant H3L1 which was presented in the hydroxy-azo tautomeric form. At nitrosation of H3L1, the product H3L2 was isolated, which can be described as trioxo di-hydroxylamino hydrazone. According to the X-ray structure determination, the Cd-complex of H3L1 exhibited the dimeric form with two unionized organic ligands in the inner sphere. It was also found that chloride anions bridge two cadmium cations to form dimers. According to EPR spectra, the Cu complex with H3L1 exhibited distorted tetragonal symmetry associated with the d_x2-y2 ground state rather than dz2, and the corresponding Cu–H3L2 complex was described by a cubic symmetry of the coordination medium. Both H3L1, H3L2, and their metal complexes show coloristic activity towards wool, polyamide, and polyacetate fibers, which are strongly resistant towards UV-irradiation. The H3L2 compound possessed good sorption activity towards heavy metal cations from aqueous solutions of trace concentrations both under static and dynamic conditions.

TS. Wannida Sapyen presents a talk entitled "Selective colorimetric detection of Cr(VI) using starch-stabilized silver nanoparticles and application for chromium speciation"

Abstract:

Chromium naturally exists in two oxidation states including trivalent chromium (Cr(III)) and hexavalent chromium (Cr(VI)). Cr(III) is an essential nutrient, while Cr(VI) is toxic. Most conventional analytical techniques for chromium speciation that provide high sensitivity, selectivity, and accuracy usually require lengthy analysis, trained personnel, and bulky spaces. Herein, starch-stabilized silver nanoparticles (starch-AgNPs) was proposed to solve this limitation as a fast and selective Cr(VI) sensor via colorimetric detection. Together with inductively coupled plasma atomic emission spectroscopy (ICP-OES), Cr(III) concentration could be accomplished by the subtraction of Cr(VI) concentration from total chromium concentration. To develop a simple and rapid method for a selective Cr(VI) determination by utilizing starch-AgNPs and employ this sensor for chromium speciation in real water samples combined with ICP-OES. The characterization of AgNPs was carried out by transmission electron microscopy (TEM) and UV-Vis spectroscopy. The optimum condition including pH and response time for selective Cr(VI) detection was investigated. The chromium speciation in water samples was determined by the proposed method combined with ICP-OES. The accuracy and precision of the method was evaluated by spiked real water samples and a standard US-EPA Method 7196A. The proposed method showed selectivity toward Cr(VI) in the presence of 50 mM EDTA at the optimum condition (pH 3 and 1 min). In the presence of Cr(VI) ions, the color changed from yellow to colorless and the reduction of UV-Vis signal were observed. Two linear ranges of 0 – 6 μM and 10 – 80 μM with limit of detection of 0.93 μM and 11.57 μM were obtained, respectively. The accuracy and precision of the method was in good agreement with AOAC guidelines. A simple and fast method for selective Cr(VI) detection was developed. The chromium speciation in real samples was successfully applied with acceptable accuracy and precision.