蒙脱石对水溶液中甘氨酸的吸附特性及机理

Adsorption characteristics and mechanism of glycine on montmorillonite in aqueous solutions

研究蒙脱石对不同浓度甘氨酸在水溶液中的吸附特性及机理。采用X线衍射（XRD）、全反射傅里叶变换红外光谱（ATR-FTIR）和等离子体发射光谱（ICP-AES）等手段对吸附样品进行性质表征。研究结果表明：蒙脱石平衡吸附量随甘氨酸浓度升高而增加,在甘氨酸浓度为0.01~0.20 mol/L范围内,蒙脱石吸附甘氨酸符合Freundlich等温吸附模型。蒙脱石层间阳离子解吸总量小于其对甘氨酸的平衡吸附量,且蒙脱石d（001）由1.528 nm减小到1.446 nm,揭示蒙脱石吸附甘氨酸是通过层间阳离子交换机制,但阳离子交换非惟一方式。蒙脱石吸附甘氨酸存在阳离子交换和端面吸附2种机制：通过COO-与蒙脱石端面正电基团间的静电作用力吸附甘氨酸两性离子;通过NH3＋与蒙脱石层间基面氧原子形成氢键吸附甘氨酸正离子。

Adsorption characteristics and mechanism of different concentrations of glycines adsorbed on the surface of montmorillonite from aqueous solutions were studied. The reaction products were characterized using X-ray diffraction（XRD） and attenuated total reflectance Fourier-transform infrared（ATR-FTIR） spectroscopy and inductively coupled plasma-atomic emission spectrometry（ICP-AES）. The results show that the equilibrium amount of glycine adsorbed by montmorillonite increases with the variable glycine concentrations from 0.01 to 0.20 mol/L. And the dependence of glycine adsorption with its aqueous concentration fits for a Freundlich equation at the studied concentration range of glycine. The total amount of the desorbed interlayer cations is less than the equilibrium amount of glycine adsorbed by montmorillonite, and the cation exchange reaction produces a decrease of the montmorillonite interlayer space from 1.528 to 1.446 nm, demonstrating that the glycine adsorbed by montmorillonite mainly through cation exchange mechanism, but the cation exchange is not the only adsorption way. ATR-FTIR results confirm two adsorption mechanisms, one is the glycine cation exchange through hydrogen bonding between the NH3＋ group and the basal oxygen of the interlayer surface, and the other mechanism is edge adsorption by electrostatic force between the COO-group and the positively charged groups at the edge surface of montmorillonite.