镁铁水滑石的表面化学性质及电化学行为

Surface chemical performances and electrochemical behavior of Mg-Fe hydrotalcite

利用X射线衍射(XRD)、傅里叶变换红外光谱(FT-IR)、零电荷点pHpzc、循环伏安(CV)和电化学阻抗(EIS)等手段,研究镁铁水滑石(MgFe-LDHs)的表面化学性质,揭示其表面酸碱性与电化学性能的关系。结果表明:当Mg与Fe的摩尔比(n(Mg)/n(Fe))为3时MgFe-LDH(LDH-3)的结晶度最高,碱性最强,且远强于n(Mg)/n(Fe)为2的MgFe-LDH(LDH-2)和n(Mg)/n(Fe)为4的(LDH-4)的碱性。LDH-2的碱性略强于LDH-4的,但差异微小。层间CO_3^(2-)与LDH层板金属离子主要形成单齿和双齿配位,其中,单齿配位体与强碱位点配位,形成Lewis碱位。表面碱性取决于Lewis强碱性位(CO_3^(2-)单齿配位)的含量。用镁铁水滑石煅烧产物(MgFe-LDOs)修饰玻碳电极来研究其电化学性能。碱性越强(如LDO-3),其氧化还原可逆性及导电性能越好。

The surface chemical characteristics of the Mg-Fe hydrotalcites （MgFe-LDHs） were determined using X-ray diffractometry （XRD）, Fourier transform-infrared spectrometer （FT-IR）, point of zero charge （pHPZC）, cyclic voltammetry （CV） and electrochemical impedance spectroscopy （EIS）. The relationship between the surfaceacid-base and electrochemical properties of the MgFe-LDHs was clarified. The results show that the MgFe-LDH with molar ratio of Mg to Fe （n（Mg）/n（Fe）） being 3 （LDH-3） has the highest crystallity structure with symmetrical crystals, indicating that the surface basicity of the LDH-3 is the strongest. And its basicity is much higher than those of ones with n（Mg）/n（Fe） of 2 （LDH-2） and 4 （LDH-4）. The basicity of LDH-2 is slightly stronger than that of LDH-4. The monodentate and bidentate coordinations are formed by the interlayer CO32- anions coordinating with the metal ions in the brucite-like layers. The monodentate ligand coordinates with the strong basic sites, then Lewis basic sites form. The basicity depends on the content of Lewis basic sites. Mg-Fe hydrotalcite calcined samples （MgFe-LDOs） were used to modify glassy carbon electrode to study its electrochemical properties. The stronger the basicity （such as those of the LDO-3） is, the better the oxidation-reduction reversibility and conductivity are.