Grafting of dodecylsulfate groups on gadolinium hydroxocation nanosheets for self-construction of a lamellar structure?

Journal of Materials Chemistry Pub Date: 2011-01-11 DOI: 10.1039/C0JM03149F

Abstract

The self-stacking of gadolinium hydroxocation nanosheets to form a layered structure was achieved by using the dodecylsulfate (DS) group as an anionic surfactant at room temperature. DS-assisted construction behavior of layered gadolinium hydroxocations (LGdH) differed significantly depending on the pH of the solutions. At pH < 7, the interlayer distances of self-constructed lamellar structures were in the range of 34～36 ?, which is explained by a tilted bilayer arrangement of the DS groups. The lamellar products obtained at this pH range formed a Gd2(SO4)3 phase when heated at 300 °C and subsequently transformed to Gd2O2SO4 above 600 °C. Based on a significant shift of the IR band assigned to the S–O asymmetric stretching mode, it is proposed that LGdH nanosheets are grafted with DS?groups at low pH so that some Gd3+ ions in each hydroxocation layer are coordinated by sulfate groups instead of hydroxyl groups. LGdH nanosheets grafted with DS groups are then assembled to precipitate as a lamellar form. In contrast, the layered structure obtained at pH > 7 showed an interlayer spacing of 24～25 ?, which can result from an interdigitated monolayer packing of the DS groups. The products obtained at this pH range were directly transformed to Gd2O2SO4 without formation of Gd2(SO4)3 with increasing temperature and showed no shift of the S–O asymmetric stretching band in the IR spectra. Thus, no strong interaction between the sulfate headgroups and the LGdH layers suggested that typical restacking of the exfoliated nanosheets and DS groups leads to the lamellar structure at pH > 7.

Graphical abstract: Grafting of dodecylsulfate groups on gadolinium hydroxocation nanosheets for self-construction of a lamellar structure
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