Intercalation and separation of isomeric nitrophenols using the anionic clay, Mg2Al(OH)6(CO3)0.5•nH2O and the structurally related layered hydroxy salt, Ni3Zn2(OH)8(CH3COO)2•mH2O

Intercalative sorption of isomeric nitrophenolates (NP) was investigated in two different layered hydroxide materials - anionic clay, magnesium aluminium layered double hydroxide (MgAl-LDH) through reconstructive mechanism and the structurally related layered hydroxy salt, Ni3Zn2(OH)8(CH3COO)2 & BULL;mH2O (NiZn-LHS) through ion-exchange. Intercalation of NP isomers was confirmed by powder X-ray diffraction and infrared spectroscopy. The NP uptake by the layered hydroxide materials was quantified by high performance liquid chromatography. Both the layered hydroxide materials exhibit selective intercalation from the nitrophenolate mixtures. The order of preference is 4-NP > > 2-NP > 3-NP in MgAl-LDH and 4-NP > 2-NP > > 3-NP in NiZnLHS. The bias in intercalation could be attributed to (1) the concentration of the phenolate ions influenced by the pKa of the isomer and (2) extent of H-bonding of the nitro group of the isomer with the hydroxide slabs. The 4isomer with lower pKa and better H-bonding with the adjacent hydroxide slabs is preferentially intercalated. The anionic clays can be used to sorb out nitrophenols as well as separate them from their mixtures.