Recently European producers of synthetic zeolites have commissioned scientific assessment, analysis and measurement of synthetic zeolites in line with the EU recommendation on the definition of nanomaterials (Commission Recommendation 2011/696/EU). Two independent experts have been in charge of these studies: Prof. Dr. Javier Pérez-Ramirez, ETH Swiss Federal Institute of Technology Zürich, and Prof. Dr.-Ing. Michael Stintz, Technische Universität Dresden.
Both experts have reached the same conclusion based on evaluation and analysis of their respective results that synthetic zeolites (or crystalline aluminosilicates) are not to be considered as nanomaterials according to the EU recommendation.
Synthetic zeolites, CAS No. 1318-02-1, comprise a group of synthetic, crystalline aluminosilicates made out of silicon dioxide (SiO2) and aluminum oxide (Al2O3) in various compositions, together with metal oxides. They are normally produced by mixing the starting materials (an aluminate, a silicate, sodium hydroxide and optionally further metal oxides and templates) in an aqueous solution and crystallized at elevated temperature to form a slurry of crystals. These crystals are separated by filtration, washed with water and dried. Through partial ion exchange (surface modification) the initial product may be modified. As zeolites are porous substances, containing defined pores (channels) up to 1 nm, they may be looked at as materials with an internal nanostructure.
Commercially available synthetic zeolites were analyzed in different ways (e.g. X-Ray powder diffraction, laser diffraction, dispersing systems and ultrasonic treatment) to show that the EU recommendation on the definition of nanomaterials does not apply to synthetic zeolites. In conclusion, commercially produced synthetic zeolites do not fulfill the definition given in Commission Recommendation 2011/696/EU. The zeolite crystals are larger than 100 nm and do not disintegrate upon application of dispersing systems (ultrasonic waves or shear forces).
NB: Using modified synthesis procedures, it is possible to manufacture zeolite crystals smaller than 100 nm. These zeolite crystals are stable in diluted suspensions only. These zeolites are a niche product and are neither covered by EUZEPA nor by the existing REACH registrations of the Synthetic Zeolite Consortium.