History and Classification of Non-Siliceous Hybrid Materials - Mesoporous Organic-Inorganic Non-Siliceous Hybrid Materials - page 11

organosulfonate groups has remained relatively unstudied, which can be due to the
weak interaction or non-interaction capacity with the majority of transition metal
ions or complexes.
Nowadays, the research of hybrid materials has shifted toward much more
sophisticated nanocomposites with higher added values. The field of organic-inor-
ganic material has been broadened to a multidisciplinary area, including orga-
nometallics, colloids and nanoobjects, soft matter and polymers, coordination
polymers such as MOFs, sol/gel, aerosol/aerogel, catalysis and interfaces, porous
materials, clays and lamellar compounds, nanocomposites, biomaterials, and bio-
engineering. Furthermore, a very significant trend is the growing research interest
in the rational design of functional hybrids, which extends the field even further.
Hybrid materials represent an inexhaustible source of inspiration for us to explore
and discover.
2.2 Classification of Non-Siliceous Hybrid Materials
Organic-inorganic hybrids can be defined as nanocomposite materials with inti-
mately linked organic bridging groups and inorganic units. The versatile changes
in composition and structure can bring various physicochemical properties that are
not the simple sum of the individual contribution of both construction phases. As
a result, the nature of the interface and the interactions between the organic and
inorganic units can be employed to categorize the hybrids into two main classes
[ 15 , 40 , 41 ]. Class I is associated with the hybrid systems that involve no covalent
or weak chemical bonding. In this class, only hydrogen bonding, van der Waals or
electrostatic forces are usually present. Conversely, Class II hybrid materials show
strong chemical interactions between the components, which are formed when the
discrete inorganic building blocks are covalently bonded to the organic polymer or
inorganic and organic polymers are covalently connected with each other [ 42 , 43 ].
On the other side, hybrids can also be characterized by the type and size of the
organic or the inorganic precursors [ 15 , 40 ]. Precursors can be two separate
monomers or polymers and even covalently linked ones. Because of the mutual
insolubility between inorganic and organic components, phase separation will
occur. However, homogeneous or single-phased hybrids can be obtained through
judiciously choosing bifunctional monomers that contain organic and inorganic
components, or by combining both types of components in the phases where one
of them is in large excess [ 44 ].
The chemical strategies to construct Class II hybrid frameworks are depend-
ent on the relative stability of the interactions between the components and the
chemical linkages that connect different components. PMOs represent the typical
examples of Class II hybrids. The stable Si-C bonds under hydrolytic conditions
allow for the easy incorporation of a large variety of organic bridges in the sil-
ica network during the solgel process. Nowadays, the potential of hybrid materi-
als is further strengthened due to the fact that many of them are entering various