A series of calcium aluminum layered double hydroxides (LDHs) modified with sodium dodecyl sulfate (SDS) (Ca /Al-SDSLDHs) were synthesized by co-precipitation, and characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and elemental analysis. The Ca /Al-SDS-LDHs enhanced sorption of nitrobenzene and naphthalene from water compared with inorganic LDH (Ca /Al-Cl-LDH). The sorption isotherms for sorption of organic contaminants onto the Ca /Al-SDS-LDHs were linear for the concentration range tested, which implies that the sorption mechanism is mainly by partition. The sorption of naphthalene onto Ca /Al-SDS-LDH was apparently stronger than that of nitrobenzene, but this order reversed after eliminating the hydrophobic effect of these two contaminants. Because naphthalene is non-polar and nitrobenzene is polar, the results indicate that the Ca /Al-SDS-LDHs were selective for polar organic contaminants.
layered double hydroxide, SDS, sorption, nitrobenzene, naphthalene, co-precipitation
Citation:Ruan X X, Sun P, Ouyang X X, et al. Characteristics and mechanisms of sorption of organic contaminants onto sodium dodecyl sulfate modified Ca-Al layered double hydroxides. Layered double hydroxides (LDHs) or hydrotalcite-like compounds are a class of natural and synthetic lamellar compounds with the general formula [M 2+ 1-x M 3+ x (OH) 2 ] x+ [A nx/n ] mH 2 O, where M 2+ = Mg 2+ , Ca 2+ , Ni 2+ , Cu 2+ , Zn 2+ , Co 2+ and M 3+ = Al 3+ , Fe 3+ , Cr 3+ ; and A n-is an anion such as CO 3 2-, SO 4 2-, NO 3 -, or an organic anion [1]. Some of the M 2+ ions in LDHs are substituted by M 3+ ions, which produces positively charged layers with the composition [M 2+ 1-x M 3+ x (OH) 2 ] x+ . To compensate for the positive charges on these layers, A n are intercalated in the structure. LDHs have been investigated because of their potential applications as ion-exchangers [2-6] and catalysts [7].LDHs can be used to remove contaminants from the environment. However, hydrophilic hydroxyl groups on the LDH surface reduce the sorption performance for hydrophobic non-ionic organic contaminants [8,9]. To enhance the sorption of non-ionic organic contaminants, anionic surfactants such as the anions of dodecyl sulfate (DS -) and dodecylbenzenesulfonic acid (DBS -) have been inserted into Mg-Al/Li-Al/Zn-Al LDHs [10][11][12][13][14][15][16][17][18]. Anionic surfactant intercalated LDHs can be prepared by the ion exchange method, using LDH-Cl or LDH-NO 3 as the precursors. The carboxylic acids are believed to assist the intercalation process by facilitating the elimination of carbonate ions [19]. The intercalation capacity of DBS -into Mg/Al-NO 3 -LDH was greater than that of DS -, which indicates that increasing the SO 3 -content on the surfactant will increase its intercalation capacity [20].Modification of anionic surfactants has been used to improve the removal efficiencies of organic contaminants by LDHs. Excellent sorption of 2-naphthol onto SDS-modified Mg-Al-Cl-LDH was used to propose a solubilization theory, in whi...
