Green Synthesis of Inorganic–Organic Hybrid Materials: State of the Art and Future Perspectives

Abstract

The term "inorganic-organic hybrid materials" designates inorganic building blocks in the colloidal domain (1-1000 nm) embedded in an organic, typically polymeric, matrix. Owing to their outstanding properties, hybrid materials have the potential to improve human life significantly. In the last two decades, the importance of reorienting chemical syntheses in the direction of more sustainable, less harmful and energy-consuming procedures, referred to as green chemistry, has been[a] defines a hybrid material as a "material composed of an intimate mixture of inorganic components, organic components, or both types of components", noting that "the components typically interpenetrate on scales of less than 1 μm". [6] This definition includes, for example, polymer-polymer composites (aka blends), metal-metal composites, metal-ceramic composites, metal-polymer, and ceramic-polymer composites. The plethora of powerful hybrid materials cannot be covered in one review article. This paper will thus focus on one subclass of hybrid materials: namely, inorganic-organic hybrid materials in which the amount of organic polymeric component is a majority over that of the inorganic component. Note that the term "composite" historically tends to be associated with macroscopic hybrid materials with the dispersed phase typically greater than 1 mm. Others associate "composite" with hybrid materials in which the components interact through noncovalent bonding, and "hybrids" with cases in which the components are connected by covalent bonding. [7] In recent years, this distinction has faded more and more, and both terms are often used interchangeably. This review addresses exclusively inorganic-organic hybrid materials with the minor component in the colloidal range, and the term "composite" is used occasionally.Depending on the strength of interaction between the dispersed inorganic phase and the organic matrix, hybrid materials are commonly subdivided into two categories. [2] In class I hybrid materials there are weak interactions -namely, van der Waals (vdW), hydrogen bonding, and electrostatic interactions -between the components (Scheme 1, a). [2] Class II hybrid materials display strong bonding (i.e., covalent or iono-covalent interactions, Scheme 1, b; [2] iono-covalent interactions are covalent bonds with a considerable ionic character often found, e.g., in binary or mixed metal oxides). [8] In class II hybrids, the strong Eur.

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