Adsorption of phenanthrene and 1,3-dinitrobenzene on cation-modified clay minerals

Nonpolar nonionic compound (phenanthrene, PHE) and polar nonionic compound (1,3-dinitrobenzene, DNB) were used as probes to explore the dominant mechanism responsible for adsorption of nonionic organic compounds on different cation-modified clay minerals (i.e. smectite, kaolinite, and vermiculite). Batch experiments were conducted, and possible adsorption mechanisms were inferred from adsorption isotherms and characteristics of the modified clay minerals. The results demonstrate that cation-modified clay minerals can adsorb a larger amount of DNB than PHE. Smectite and vermiculite, 2:1 type layered silicate minerals, have a higher adsorption capacity for DNB than the 1:1 type layered kaolinite. K+-modified clay minerals have greater adsorption capacities for DNB than Na+- and Ca2+-modified clay minerals; while Ca2+-modified clay minerals with the exception of vermiculate have greater adsorption capacities of PHE than K+- and Na+-modified clay minerals. The results of this study suggest that hydrophobic interaction and inter-layer accommodation are likely to be the dominant mechanisms of PHE adsorption by clay minerals, whereas electrostatic interactions through hydrogen bond and formation of electron donor–acceptor complexes are responsible for DNB adsorption by clay minerals. This study will benefit understanding the adsorption mechanisms of nonionic organic compounds on minerals in the environments.