The Preparation And Characterization Of Cr-Al-Pillared Montmorillonite

Ca-montmorillonite from Xinyang Henan province was sodium-modified,and then the Cr-Al-pillared montmorillonite was prepared by ion-exchange method.X-ray diffraction analysis, Fourier-transform infrared absorption spectrum analysis,thermal analysis and N₂ adsorption analysis were applied to study the properties of Cr-Al-pillared montmorillonite.At the same time,the crystal structure of hydroxyl-chromium-aluminum oligocation has been discussed.The experiment took the basal spacing d₀₀₁ value as standard to judge the pillaring effect of Cr-Al-pillared montmorillonite.The better conditions of preparation were selected with Cr/Al molar ratio molar ratio =2:1,OH/(Cr+Al) molar ratio=2.0,(Cr+Al)/montmorillonite=10mmol/g, the reactive temperature=60℃,aging time of pillaring agent=48h and aging time of pillaring product=48h.The XRD results indicated that the d₀₀₁ value of Cr-Al-pillared montmorillonite varied from 1.2726nm to 2.0535nm.It showed hydroxyl-chromium-aluminum oligocation had been already inserted in the layered structure of morillionite.The FTIR results of Cr-Al-pillared montmorillonite showed that the basic structure of montmori- llonite remained unchanged,and that Cr³⁺ tended to adopt octahedral coordination instead of tetrahedral to enter into the layers of montmorillonite.The N₂ adsorption analysis results of samples showed that the specific area,average pore diameter and pore volume of Cr-Al-pillared montmorillonite were 170.4m²/g,3.840nm,and 0.1841cm³/g,respectively.It indicated that Cr-Al-piUared montmorillonite had larger specific area,relatively larger micropore diameter and smaller mesopore diameter.The thermal treatment results showed when the thermal treatment temperature of Cr-Al-pillared montmorillonite reached 355℃,the hydroxy chromium oligocation began to dehydrate hydroxyl.When thermal treatment temperature of Cr-Al-pillared montmorillonite reached 477℃,the hydroxy aluminium oligocation began to dehydrate hydroxyl. The data of XRD showed that the d₀₀₁ value of Cr-Al-pillared montmorillonite had varied from 2.5035nml to 1.7902nm after calcined at 500℃.The FTIR results of Cr-Al-pillared montmorillonite showed that the hydroxyl-Al-Cr oligocations were introduced into the montmorillonite through Si-O-Al or Si-O-Cr chemical bonds after calcined at 500℃.Cr³⁺ in the Cr-Al-pillared agent may substitute partial Al³⁺ in Al-O octahedron in the Keggin ions in the form of Cr-O octahedron or distorted Cr-O octahedron.It may exist in the interlayer of montmorillonite in the form of the structure model of hydroxyl-silico-aluminum oligocation.