Natural clinoptilolite nanoplatelets production by a friction-based technology

Adhesion is a crucial factor in the functionalization of a substrate by nanoparticles. The planar geometry is the most convenient shape since it provides the maximum contact area with substrate. Some nature-made materials present a nanostructured texture that may include nanosized-lamellas. Consequently, these lamellas could be cleaved by using an appropriate milling technology which is capable to apply a force in the most convenient way. In the pollution control, nanosized molecular traps have to be supported on a certain type of substrate (e.g., paper), and zeolites are frequently used for such a purpose. Indeed, zeolites-based molecular traps have been used for removing gaseous air pollutant such as SO₂, H₂S, NO_x, etc.

The clinoptilolite is a very common type of natural zeolite having a lamellar texture. Here, an effective technique for the clinoptilolite delamination has been used. This approach is based on the applying of mild friction force to the mineral surface to progressively detach the aggregated lamellas, thus achieving both small lamellar aggregates and single crystals. It must be pointed out that small aggregates are more convenient than single lamellar crystals since the presence of a meso-porosity allows trapping of larger gaseous molecules too. Differently from other milling methods the selected approach allowed to achieve a product made of larger lamellas, that is important to enhance the adhesion.

Transmission Electron Microscopy is a powerful technique for the morphological characterization of the clinoptilolite aggregates because silico-aluminate minerals result semi-transparent to the electron beam, thus allowing the visualization of the mineral inner structure. Number of aggregated lamellas, average sizes of the aggregates and lamellas, aggregate thickness, lamellas boundary shape, etc. could be determined by the quantitative analysis of the TEM micrographs. Additional morphological information has been obtained by the Scanning Electron Microscopy analysis performed on the same samples.