Nanohybrids of Mg/Al layered double hydroxide and long-chain (C18) unsaturated fatty acid anions: Structure and sorptive properties

Long-chain (C18) unsaturated fatty acid anions, elaidate (ELA), oleate (OLE), linoleate (LINO), and linolenate (LINOLEN), were intercalated into Mg/Al (3:1) layered double hydroxide (LDH) and the resultant organo-LDH nanohybrid materials were characterized and subsequently evaluated as sorbents of six pesticides (clopyralid, imazethapyr, diuron, atrazine, alachlor, and terbuthylazine). The effect of the degree (18:1, 18:2, 18:3) and type (cis/trans) of unsaturation in the fatty acid alkyl chain on both the structure and sorptive properties of the LDH-unsaturated fatty acid nanohybrids was determined. All fatty acid anions were readily intercalated into the LDH, yielding structures with basal spacing values ranging between 32 Å (LDH-LINOLEN) and 40 Å (LDHELA). The bend imposed by the cis geometry of the double bonds present in OLE, LINO and LINOLEN was identified as a major factor determining the arrangement of these anions in the LDH interlayer space. Intercalation of cis-unsaturated fatty acid anions led to less densely packed structures and reduced the interlayer distance of the resultant nanohybrid compared to the structures resulting from intercalation of the linear, trans-unsaturated elaidate anion. All organo-LDHs displayed higher affinity to uncharged pesticides as compared to unmodified LDH, but double bonds in the fatty acid alkyl chain, particularly when present in cis configuration, reduced the affinity of the organo-LDHs to all pesticides, presumably because they led to structures with reduced hydrophobicity as compared to those resulting from the incorporation of linear organic anions.