Synthesis, characterization, and sol-gel kinetic studies of colloidal silica particles using Stöber’s method: a teaching laboratory activity

Abstract

In the last decades, alkoxide sol-gel chemistry provided an exceptional tool for the synthesis of nanostructured building blocks and designing application of novel materials. To keep up with the latest advancements in this field, a group of Argentine researchers established the Buenos Aires School of Materials Synthesis and Sol-Gel Processes, which has been held every 2 years at Buenos Aires—Argentina, since 2003. The course, aimed at young graduate students, postdoctoral researchers, and industry professionals, focuses on both the fundamentals and the newest developments of sol-gel processes. Also, during 40 h of laboratory-based work, they become immersed in the typical techniques and skills in sol-gel synthesis and materials characteriza tion. These “hands-on” experiment al sessions are the defining feature of this school as they explore key sol-gel related processes: hydrolysis and condensation kinetics, wet-lab synthetic approaches, and materials characterization techniques. In the work presented here, the stude nts employ the well-known Stöber´s method for obtaining SiO 2 colloidal particles. Tetraethoxysilane hydrolysis and condensation kinetics are foll owed using a conductometer, and the time-dependent data obtained are interpreted using a simple consecutive reaction kinetics mechanism. Later, the students explore simple one-pot post-grafting colloidal surface chemical modifications, which are confirmed through infrared spectrometry and zeta-potential measurements. Carefully controlled additions of the alkoxide precursor allow for experimentation on increasing particle diameter, which can be readily confirmed using scanni ng electron microscopy. Moreover, encapsulation within the SiO 2 framework with cationic luminescent dyes as [Ru(bpy) 3 ] 2+ results in photochemical hybri d platforms. In essence, this labor atory activity encompasses several sol-gel and colloidal chemistry concepts suited for an advanced chemical course on materials synthesis.