Abstract
Inorganic layered crystals exemplified by clay minerals can be exfoliated in solvents to form colloidal dispersions of extremely thin inorganic layers that are called nanosheets. The obtained “nanosheet colloids” form lyotropic liquid crystals because of the highly anisotropic shape of the nanosheets. This system is a rare example of liquid crystals consisting of inorganic crystalline mesogens. Nanosheet colloids of photocatalytically active semiconducting oxides can exhibit unusual photoresponses that are not observed for organic liquid crystals. This review summarizes experimental work on the phase behavior of the nanosheet colloids as well as photochemical reactions observed in the clay and semiconducting nanosheets system.
Highlights
Inorganic layered compounds are crystalline solids built up from stacked inorganic sheets of around1-nm thickness
We describe below some fundamental characteristic properties of the nanosheet colloids represented by liquid crystalline phase behavior
As to experimental studies of anisotropic colloid, liquid crystalline behavior of the colloids of virus rods [26], V2O5 rods [27], and clay plates [28] had been reported in early 20th century; the Onsager theory was established on the basis of these observations
Summary
Exfoliation (and subsequent restacking) has been recognized as a method alternative to intercalation for immobilizing functional molecules in the interlayer spaces of stacked inorganic nanosheets. We have investigated colloidal states of crystalline nanosheets prepared by exfoliation of inorganic oxides in recent years, and found that the “nanosheet colloids” exhibit various unusual properties which are not observed in layered solids such as parent layered crystals and exfoliated–restacked assemblies of nanosheets. We summarize our researches and related works of the nanosheets colloids of layered clay minerals and semiconducting oxides It covers experimental results of liquid crystal formation and physical gelation as well as photochemical electron transfer reactions observed in the nanosheet colloids
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