Traditional solid state synthesis methods rely on high temperatures (greater than 600 deg. C) to mobilize solid reactants. These conditions generally favor the formation of highly crystalline and structurally simple phases. However, it is desirable in some cases to trap a structure in a metastable state in order to enhance surface reactivity and/or tune the bulk properties of the material. This inherently limits the use of thermal energy for reaction initiation, so alternative techniques must be employed (e.g., solvothermal synthesis, ion exchange, etc.). The synthesis of metal sulfides presents an especially difficult challenge, as the bonding in these compounds is relatively weak compared to metal oxides, and sulfur may adopt a multitude of oxidation states, complicating redox reactions. A survey of different approaches used in our laboratory will be presented, with an emphasis on the use of photochemical reductants for the synthesis of metal sulfides, exemplified by ZnS and FexS.
This seminar will also present a study of the complex self-assembly behavior of aluminosilicate platelets on a surface driven by convective assembly. Strong particle-particle interactions and stick-slip phenomena cause fractal-like patterns of defects to form. A ‘phase diagram’ of patterns observed under different assembly conditions will be presented, along with our use of shape and surface charge manipulation to alter the self-assembly behavior.