层间阴离子对镁铝水滑石吸附甲基橙性能的影响

Effect of Interlayer Anions on the Methyl Orange Adsorption by Mg-Al Hydrotalcite

采用恒pH共沉淀法制备了层间为四种不同无机阴离子的水滑石MgAl-水滑石类层状化合物(LDH)-X(X=CO_(3)^(2-),NO^(-)_(3),Cl-和SO_(4)^(2-)),并通过X射线衍射仪(XRD)、傅里叶变换红外光谱仪(FT-IR)、比表面分析(BET)、X射线光电子能谱(XPS)和Zeta电位对样品的结构及性能进行表征。结果表明,合成的水滑石结晶度较高,层间阴离子对镁铝水滑石的比表面、孔容孔径、表面酸碱性和荷电性能都有较大的影响,因而影响其对甲基橙(MO)的吸附性能;MgAl-LDH-Cl对MO的吸附量最大(660.75 mg/g),MgAl-LDH-CO_(3)对MO的吸附量最小(233.55 mg/g)。MgAl-LDH-X对MO的吸附过程可以用拟二级动力学模型来描述,Langmuir模型可以较好地拟合吸附等温式。水滑石对MO的吸附既有表面、孔吸附,也有静电吸附。

Magnesium-aluminum hydrotalcites of MgAl-LDH(Layered double hydroxides)-X with four different interlayer inorganic anions(X=CO_(3)^(2-),NO^(-)_(3),Cl^(-)and SO_(4)^(2-))were prepared by constant pH co-precipitation method,and the structure and adsorption properties of samples were analyzed and characterized by XRD(X-ray diffraction),FT-IR(Fourier transform infrared spectroscopy),BET(Brunauer-Emmett-Teller),XPS(X-ray photoelectron spectroscopy)and zeta potential.The results showed that the synthetic hydrotalcites have high crystallinity.The interlayer anion of MgAl-LDH-X has a great influence on their specific surface,pore volume,pore size,surface acidity or basicity and charging properties,thus produces an effect on their adsorption for methyl orange(MO).MgAl-LDH-Cl possesses the largest MO adsorption capacity of 660.75 mg/g,while MgAl-LDH-CO_(3) has the smallest one of 233.55 mg/g.The adsorption process can be described by pseudo-second-order kinetic model and the adsorption isotherm fits well with Langmuir isotherm model.The adsorption of MO on hydrotalcite includes surface adsorption,pore adsorption and electrostatic adsorption.