Preparation And Characterization Of Chitosan/Hydroxy-aluminum Complex Modified Montmorillonites And Their Adsorption Study Of Contamination From Aqueous Solutions

In this study,chitosan and hydroxy-aluminum cation as intercalation agent were used to prepare a series of chitosan/hydroxy-aluminum modified montmorillonite adsorbents.The conditions of the intercalation reaction and the structure characteristic, surface property of chitosan/hydroxy-aluminum modified montmorillonites were investigated by varies physical chemistry methods and modern instruments analysis. Based on the study of the adsorption property and adsorption thermodynamics of chitosan/hydroxy-aluminum modified montmorillonite for two dyes（Acid Blue 25 and Acid Green 25） and Cr⁶⁺ anion,the adsorption mechanism was discussed.The main study contents and results are as follows:（l）The hydroxy-aluminum pillared montmorillonite was modified with the chitosan.Montmorillonite was not intercalated with the chitosan by ion exchange.The adsorption of the chitosan cation took place onto montmorillonite surface and blocked part of the pores.The specific surface area and pore volume of the modified montmorillonite decreased with adsorption of chitosan.（2）The Na-montmorillonite was modified with the mixture of chitosan and hydroxy-aluminum cation as intercalation agent.Montmorillonite was intercalated with the mixture of chitosan and hydroxy-aluminum cation by ion exchange. Montmorillonites were intercalated with bilayers of chitosan at about 3:lof the chitosan-clay ratio.（3）The surface property of montmorillonite was changed after the adsorption of chitosan onto montmorillonite surface and into the pores.TG-DSC analysis proved the hydrophobic nature of montmorillonite was strengthened.MBET specific surface area analysis proved the specific surface area of the modified montmorillonite decreased with the adsorption of chitosan.Zeta potential analysis proved the zeta potential of the modified montmorillonite increased under an acidic condition.（4）The adsorption capacity for acid dye with the modified montmorillonites was higher than the hydroxy-aluminum pillared montmorillonite.The adsorption capacity of chitosan/hydroxy-aluminum complex pillared montmorillonite was superior to that of the hydroxy-aluminum pillared montmorillonite modified with chitosan.With the increase of pH value of the dye solution,the adsorption capacity reduced.The possible mechanism for the adsorption of acid dye may be electrostatic interaction between the protonated groups of chitosan and the dye. （5）The adsorption capacity for Cr⁶⁺ anion of chitosan/hydroxy-aluminum complex pillared montmorillonite was much larger than that of the hydroxy-aluminum pillared montmorillonite.The effect of solution pH on the adsorption capacity was remarkable and the adsorption property was better under weak acidic condition.The chromium species adsorption on absorbent was found to be governed by the ionic attraction between the protonated groups of chitosan and the negatively charged Cr⁶⁺ anion.