Study on the mechanism of hydrogel formation between silver ion and chitosan
Objective Chitosan has a strong coordination ability for silver ions. In this paper,chitosan molecules (CTS) interact with silver ions (Ag+) in alkaline atmosphere (NH3) to form hydrogels and the mechanism is studied. Methods Firstly,chitosan silver nitrate solution was crosslinked in ammonia atmosphere with AgNO3 and CTS to prepare chitosan silver ionized hydrogels with different concentrations of silver ions. Then,the microstructure of the crosslinked hydrogels was studied by infrared spectroscopy,X-ray photoelectron spectroscopy and wide-angle X-ray diffraction. Results A wide absorption band at 3500 cm-1 to 3200 cm-1 was observed in the IR spectrum of hydrogel,representing the stretching vibration of O—H and N—H. The absorption bands at 1640 cm-1 and 1570 cm-1 represented the stretching vibration of C=O in the amide Ⅰ band and the bending vibration of amino group in chitosan, respectively. As the content of Ag+in hydrogel gradually increased,The peak intensity ratio between 1640 cm-1 and 1570 cm-1 decreased. The absorption peak corresponding to silver (Ag3d) could be observed in X-ray photoelectron spectroscopy. The narrow scanning N1s spectrum of hydrogel showed two peaks of 400. 3 eV and 398. 1 eV,corresponding to N in NH-acetyl group and N on free amino group,respectively. The diffraction peaks of CTS at 2θ=13° and 20° in the wide-angle X-ray diffraction pattern corresponded to intermolecular and intramolecular hydrogen bonds respectively. After the formation of CTS/NH3 hydrogel,the diffraction peak was enhanced. Due to the interaction between free amino group and Ag+,the new diffraction peaks of 29. 6°,36. 2°, 39. 8° and 43. 6° corresponded to Ag+. Conclusions When the chitosan-silver ion solution is exposed to an alkaline ammonia atmosphere,the acidic —NH3+ deprotonates and associates with Ag+ to form a cross-linked chitosan network. The formation of CTS—Ag+/NH3 hydrogel is a physical complexation process,which consists of the hydrogen bond between chitosan molecules and the coordination bond between —NH2 and Ag+. Ag+was used as a physical crosslinker to form non-covalent bonds bound to chitosan.
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维普
