Mg/Al金属氧化物的物化性质及吸附特性

为研究微波煅烧和常规煅烧下的Mg/Al金属氧化物的物化性质、吸附特性及机理,通过XRD(X射线衍射)、SEM(扫描电镜)、BET-BJH(比表面积-孔结构)和pH_ZPC(零电荷点)等表征手段分析了微波煅烧对水滑石结构、形貌、纹理性质及表面电荷性质的影响.结果表明:微波煅烧可获得结晶度更高、片状结构更规整的Mg/Al金属氧化物；微波煅烧使Mg/Al金属氧化物的比表面积由184 m2/g增至205 m2/g,孔容和孔径分别由0.245 cm3/g和2.15 nm增至0.263 cm3/g和2.19 nm；pH_ZPC由12.3增至12.6.微波煅烧和常规煅烧下的Mg/Al金属氧化物的对Cr(Ⅵ)吸附的ΔH(标准焓变)分别为42.86和41.23 kJ/mol,E_a(吸附活化能)分别为21.82和22.59 kJ/mol,二者的吸附过程均为化学吸附且受扩散控制,在该研究条件下的二者理论吸附量最大值分别为93.51和90.31 mg/g,微波煅烧提升了Mg/Al金属氧化物吸附能力,但并不显著；微波煅烧使得Mg/Al金属氧化物更易发生结构还原,其对Cr(Ⅵ)的吸附实质就是结构还原过程.研究显示,微波煅烧并没有改变Mg/Al金属氧化物吸附特性和机理. 

Physico-Chemical and Adsorption Properties and Mechanism of Mg/Al Metallic Oxides

The physico-chemical and adsorption properties and mechanism of Mg/Al metallic oxides originated from calcined Mg/Al hydrotalcite by microwaves(WHT) were investigated through parallel experiments. The effects of microwaves on the structure, surface profile, texture properties and surface charge property of Mg/Al metallic oxides were studied by XRD, SEM, BET-BJH and PT methods. The results showed that Mg/Al metallic oxides with high isotacticity and crystallinity were prepared by microwave calcination. The surface area, pore volume and pore diameter of the Mg/Al metallic oxides originated from calcined Mg/Al hydrotalcite(CHT) were 184 m2/g, 0.245 cm3/g and 2.15 nm, respectively. Microwave calcination made the surface area, pore volume and pore diameter of the Mg/Al metallic oxides increase to 205 m2/g, 0.263 cm3/g and 2.19 nm. Similarly, pH_ZPC increased from 12.3 to 12.6. The adsorption thermodynamics and kinetics were investigated, and the adsorption mechanism discussed from the XRD spectra.Based on thermodynamics and kinetics, ΔH values for Cr(Ⅵ) adsorption by WHT and CHT were 42.86 and 41.23 kJ/mol, and E_a values were 21.82 and 22.59 kJ/mol. Cr(Ⅵ) adsorption process of WHT and CHT were chemisorption and controlled by diffusion. The theoretical adsorption amounts of WHT and CHT under the experimental conditions were 93.51 and 90.31 mg/g, respectively.Microwave calcination increased the Cr(Ⅵ) adsorption capacities of Mg/Al bimetallic oxides, but the strength enhancing efficiency was not noteworthy. Microwave calcination could be beneficial to the recovery of the LDH crystalline structure from the Mg/Al metallic oxides from XRD analysis. The Cr(Ⅵ) adsorption mechanism of Mg/Al bimetallic oxides was structure reconstruction. Microwave calcination did not change the adsorption properties and mechanism for Cr(Ⅵ).