Synthesis and characterisation of boron and gallium substituted saponite clays below 100 °C at one atmosphere

Abstract

This paper describes a simple procedure for the synthesis of saponites with isomorphous substitution of Si 4+ by B 3+ and Ga 3+ below 100 °C and at 1 atmosphere. The XRD pattern of the Ga- and B-substituted saponites are similar to Al-substituted saponites. The 71Ga MAS-NMR spectra of Ga 3+ containing Mg- and Zn-saponite show two broad peaks at approximately 25 and 180–195 ppm, attributed to Ga 6 and Ga 4, respectively. the dimensions of Mg-saponite particles are considerably smaller than those of Zn-saponites. The lateral dimensions of the platelets of B 3+ containing Mg-saponites range between 40 and 100 nm, exhibiting hardly any stacking after 20 h of synthesis, while the platelets of the Zn-saponites are 200–350 nm in length with some degree of stacking. B 3+ containing Mg-saponite exhibits a broad double signal at 12.6 and 9.0 ppm of a low intensity, together with a sharp peak at −0.8 ppm, presumably corresponding to BO 3 and BO 4, respectively. 29Si MAS-NMR on the B 3+ containing saponites reveals two signals at approximately −85 due to Q 2 Si(OB) and −96 ppm corresponding to Q 3 Si(OB).