Sol-gel chemistry has spread worldwide since the 70’s for the possibility of making ceramic materials under soft experimental conditions. The use of molecular precursors under water-based reaction conditions at room temperature has completely transformed the way of conceiving hard matter both in term of chemistry and in term of shaping. Nevertheless, one may ask oneself the question, may the low-energy sol-gel process be pushed further and re-analyzed in terms of the recent “green chemistry” principles?
The review from Coradin et al. proposes an alternative point of view over the basics of sol-gel chemistry and some of its applications in material science for silica systems. Many aspects of the sol-gel processing of materials is analyzed through the 12 principles of green chemistry and a life cycle approach. How are alkoxides synthesized? Which is the limit for their use? Are there valid alternatives? Which constraints should one consider when choosing an alternative route? At the moment, silicon alkoxides are manufactured from either metallurgical grade silicon or from silicon tetrachloride. In both cases either energetic or health-disrupting arguments may be used to contrast this approach. At the moment, alternatives to these processes can be found in the use of aqueous silicates, modified silica or use of silica-containing plant-based resources.
In line with these thoughts, catalysis, processing and use of organics in the process of material making is reviewed and existing counter-examples or possible alternatives are depicted to provide an overview of what a green sol-gel chemistry may look like in the forthcoming years, provided that the final performance keeps up with expectations.