Abstract
The study aimed to enhance the textural properties of the synthetic hectorite clay Laponite RD. In the early 1990s Mobil Research and Development Corporation produced the first ordered mesoporous molecular sieves. This family of materials, M41S, were fabricated via liquid crystal templating (LCT), a technique involving the condensation and hydrolysis of a silica source around an organic template. As clays are primarily silicates, the question arises "Why not apply the same principles to enhance porosity characteristics of other silicates such as clays?" Optimization of reagent concentrations, template choice, synthesis protocol and template removal strategy led to a maximum total pore volume of 0.95 cm3 g-1. This was achieved through templating Laponite RD with the neutral surfactant polyoxyethylene (20) sorbitan trioleate (Tween 85). This more than trebled the original total pore volume of Laponite RD, 0.27 cm3 g-1. An increase in modal pore diameter was also observed after use of this template; from 36.6 A to 52.3 A. Synthesis of Laponite-like compounds within the laboratory led to enhancement of porosity characteristics without templating; a total pore volume of 0.44 cm3 g-1 was observed for this synthetic hectorite (KP). Use of a template further enhanced the porosity characteristics of these samples. The cationic surfactant CTMA+ (used in the original Mobil synthesis) led to a total pore volume of 0.60 cm3 g-1 for modified hectorite KP. A similar result, 0.65 cm3 g-1, was achieved through templating Laponite RD with this same surfactant. Sorption and exchange properties of the newly modified hectorites were assessed by simple equilibrium batch testing methods using both single metal and multi-metal solutions. Hectorite KP samples removed a greater percentage of metal ions from aqueous solution than its Laponite RD analogues. For 5 mg dm-3 single element solutions CTMA+ modified hectorite removed > 95% of all eight metals tested. For solutions containing higher concentrations of ions the removal efficiency of all tested clays were reduced due to greater competition between ions. Partial interlayer collapse was observed during powder XRD studies, due to the acidic nature of the metal ion solutions.