Layer-by-Layer Self-Assembly of Nano- and Micro-particles as a Catalyst Integration Method for Microreactor Applications(Abstract)

摘要

Commercially available silica spheres in the size range of about 20 nm to 2 µm were initially used as our model catalyst particles for exploring electrostatic layer-by-layer self-assembly, as a novel method of incorporating commercial catalyst powder into a thin-film catalyst structure as an integral part of microreactor fabrication. For the negatively charged SiO_2 surface, this method basically consisted of depositing polyelectrolyte multilayers by alternately dipping the substrate into a polycation solution and a polyanion solution. The final polymer surface was made to be positively charged since the silica particles are negatively charged. Substrates that were coated with the polymer film was dipped into silica colloidal suspension and then rinsed in a cleaning solution to electrostatically attach only one layer of the silica particles. The silica particles were immobilized by applying a 1 µm thick sol-gel alumina layer that contained pores with the size of about 3 nm. The overall procedure was refined by systematically studying the effects of pH, ionic strength, and salt and/or buffer concentrations of the polyelectrolyte solutions, the silica colloidal suspension, and the rinsing solutions. The effects of silica particle size on surface coverage and uniformity were assessed. Also, the self-assembly behavior of the model spheres was compared to that observed for ball-milled commercial catalyst powder to assess the practicality of this self-assembly concept.