Abstract:
Until mid of 1990s there were two kind of porous materials, namely inorganic materials
and carbon based materials. In case of microporous inorganic solids, the largest two
subclasses of porous inorganic solids are aluminosilicates and aluminophosphates.
Zeolites are 3D crystalline, hydrated alkaline or alkaline earth- alumina silicates with the
general formula Mn+
x/n [(AlO2)x(SiO2)y]x-·wH2O.1,2 Their structure built from corner
sharing TO4 tetrahedra (T = Al, Si), defines interconnected tunnels or cages in which
water molecules or Mn+ ions are present. The porosity is generated after removal of the
water molecules, without affecting its structure. The cavities were extensively exploited
for the molecular sieving and catalytic activity. Synthetic zeolites, aluminophosphates
(AlPO4s) were first observed in 1862 which consist of Al3+ and P5+ ion linked by corner
sharing oxygen atoms.3 These are 3D neutral framework with channel and/or pores of
molecular dimension. The first publication of crystalline microporous alumina phosphate
appeared in 1982. Since 1982 not only crystalline oxide materials,
silicoaluminophosphates, metallosilicates, metalloaluminophosphates, metallophosphates
but also porous chalcogenides, nitrides, halides phosphates have also been observed.
Another porous inorganic solid, activated carbon has high open porosity and high specific
surface area, but have a disordered amorphous structure. The structural feature of
activated carbon is a twisted network of defective hexagonal carbon layer, cross linked by
aliphatic bridging groups.
