Sorption of aqueous organic contaminants onto dodecyl sulfate intercalated magnesium iron layered double hydroxide

Abstract

Dodecyl sulfate anion (DS−) intercalated magnesium iron layered double hydroxide (DS–Mg–Fe LDH) was firstly prepared by the co-precipitation method, and was characterized by the means of X-ray diffraction (XRD), Fourier infrared (FT-IR), Total Organic Carbon analysis (TOC), themogravimetric and differential thermal analysis (TG-DTA) and surface characteristics analysis (BET-N2). The sorption characteristics and mechanisms of hydrophobic organic contaminants (naphthalene, nitrobenzene, acetophenone) and hydrophilic contaminant (aniline) on DS–Mg–Fe LDH were investigated, and were subsequently compared with that on the inorganic magnesium iron layered double hydroxides (CO3–Mg–Fe LDH and NO3–Mg–Fe LDH). The greater sorption amount of organic contaminants on DS–Mg–Fe LDH than on CO3–Mg–Fe LDH and NO3–Mg–Fe LDH indicated that organic modified LDHs were potential sorbents for the abatement of organic contaminants. Sorption mechanism on DS–Mg–Fe LDH varied with the types of organic contaminants. The uptake curves of naphthalene, nitrobenzene and acetophenone on DS–Mg–Fe LDH were linear, and sorption capacities for three hydrophobic compounds were in the sequence of their hydrophobicity (refers to water solubility or Kow). These results suggested that the sorption mechanism was the partition between water and the organic interlayer phase composed of the alkyl chain of DS−. After eliminating the influence of the hydrophobicity, the polar compounds (nitrobenzene and acetophenone) exhibited higher affinity to DS–Mg–Fe LDH than nonpolar compound (naphthalene), which demonstrated that both the hydrophobicity and polarity benefited the sorption of hydrophobic compounds on organic LDHs. For hydrophilic compound, aniline, its uptake curve was nonlinear. The sorption process of aniline was the cooperation of the adsorption on hydroxide surface through forming the hydrogen bonding and the weak partition to the interlayer organic phase.