Exfoliation of Egyptian Blue and Han Blue, Two Alkali Earth Copper Silicate-based Pigments

In a visualized example of the ancient past connecting with modern times, we describe the preparation and exfoliation of CaCuSi(4)O(10) and BaCuSi(4)O(10), the colored components of the historic Egyptian blue and Han blue pigments. The bulk forms of these materials are synthesized by both melt flux and solid-state routes, which provide some control over the crystallite size of the product. The melt flux process is time intensive, but it produces relatively large crystals at lower reaction temperatures. In comparison, the solid-state method is quicker yet requires higher reaction temperatures and yields smaller crystallites. Upon stirring in hot water, CaCuSi(4)O(10) spontaneously exfoliates into monolayer nanosheets, which are characterized by TEM and PXRD. BaCuSi(4)O(10) on the other hand requires ultrasonication in organic solvents to achieve exfoliation. Near infrared imaging illustrates that both the bulk and nanosheet forms of CaCuSi(4)O(10) and BaCuSi(4)O(10) are strong near infrared emitters. Aqueous CaCuSi(4)O(10) and BaCuSi(4)O(10) nanosheet dispersions are useful because they provide a new way to handle, characterize, and process these materials in colloidal form.