ABSTRACT
Halloysites are dioctahedral 1:1 layered aluminosilicates with a chemical composition and a structure similar to that of kaolinite, dickite, or nacrite. They consist of adjacent sheets of gibbsite octahedra (Al (OH)3) and tetrahedrally coordinated silicon dioxide. They also incorporate a monolayer of water molecules between their layers. Because of the mismatch between the sheets and the weak interactions between the adjacent layers, because of the interlayer water, the sheets are often rolled over to form a nanotubular structure with few layers (5-6) within the wall of the nanotubes (Figure 15.1). They are then known as halloysite nanotubes (HNTs). Unlike platy kaolinites, most of the Al-OH groups are mainly located between the rolled-up layers of HNTs and they are inaccessible in the ideal formula (Pavlidou and Papaspyrides, 2008; Deng et al., 2008; Joussein et al., 2005).
