Hybrid Materials: A Metareview

Abstract

The field of hybrid materials has grown so wildly in the last 30 years that writing a comprehensive review has turned into an impossible mission. Yet, the need for a general view of the field remains, and it would be certainly useful to draw a scientific and technological map connecting the dots of the very different subfields of hybrid materials, a map which could relate the essential common characteristics of these fascinating materials while providing an overview of the very different combinations, synthetic approaches, and final applications formulated in this field, which has become a whole world. That is why we decided to write this metareview, that is, a review of reviews that could provide an eagle's eye view of a complex and varied landscape of materials which nevertheless share a common driving force: the power of hybridization.

Figure 1

Graphical representation of hybrid materials: from their chemical roots to the wide variety of final applications. The numbers indicated for each application correspond to the number or reviews found for “hybrid materials” AND the corresponding application (Web of Science). These figures are intended as a mere estimate of the relative abundance of specialized reviews, but they are not mutually exclusive (i.e., a review on “implants” could also be included in “biomed”).

Figure 2

Hybrid materials are general classifications. On the left, classification based on the differences between the interactions of the components, having class I and class II hybrid materials. On the right, the classification according to the matrix and filler component nature, being divided into four classifications: I–O, O–I, I–I, and O–O types.

Figure 3

Schematic representation of different types of hybrid materials where the dispersion of organic and inorganic components takes place at various levels. Hybrid composites (left) are not mere physical mixtures, since the interface between organic (black lines denoting a polymer) and inorganic (orange lines representing a layered phase or aggregated rods) has an enhanced relevance. Nevertheless, in these cases, domains of the individual components remain. In a hybrid nanocomposite (middle), those domains are blurred or vanished. It is in this particular case that Organic–Inorganic or Inorganic–Organic materials could be distinguished depending on the matrix dominating the structure. Finally in hybrid compound materials like polysiloxanes or MOFs (right), organic and inorganic moieties are orderly bonded at the molecular level.

Figure 4

Word cloud generated from the text contained in the abstracts of reviews referenced in this metareview. Only terms related to the composition were kept. This image provides a semiquantitative picture of the relative importance of several types of materials and chemicals in the preparation of the hybrid materials referenced. It should not be taken as a statistical estimate given the relatively reduced size of the sampled text.

Figure 5

Examples of metal–organic framework hybrid materials (MOFs) with groundbreaking conducting properties (from REF Freund et al. Angew Chem 2021). Intrinsically hybrid materials, MOFs have grown into a category on their own and have led to the development of hybrids for which they act as the host framework, even leading to MOF-COF hybrids. Reprinted with permission from ref (85). Copyright 2021 John Wiley & Sons.

Figure 6

An example of the importance of microstructure in the field of hybrid nanocomposite electrodes: The top images show a real SEM photograph and a schematic rendering of the improper agglomeration of carbon and binder. The bottom images represent the corresponding SEM and diagram of a sample electrode with a proper coating of the active material, resulting in improved performance. Reprinted with permission from ref (123). Copyright 2015 John Wiley & Sons.

Figure 7

Encapsulation as a primary structuration method in hybrids. From drugs for acne treatment to UV-filters for sunscreens, silica microcapsules provide optimal delivery. Reprinted with permission from ref (12). Copyright 2009 Royal Society of Chemistry.

Figure 8

Oligonucleotide-functionalized gold nanoparticles aggregate in the presence of complementary target DNA (A), resulting in a color change from red to blue (B), which can be monitored by UV–vis spectroscopy (C). Reprinted with permission from ref (127). Copyright 2005 American Chemical Society.

Figure 9

(a) Scheme showing working principle of Au nanoparticle capped-mesoporous silica as responsive controlled drug delivery systems. TEM images of these particles in the (b) before and (c) after being exposed to ATP rich environment. Adapted with permission from ref (131). Copyright 2011 American Chemical Society

Figure 10

Acidic montmorillonite-immobilized primary amines as acid–base bifunctional catalysts for cascade reaction. Reprinted with permission from ref (15). Copyright 2009 American Chemical Society.

Figure 11

(a) Dynamic response of Cu₂O nanowires, rGO-Cu₂O, and rGO materials under increasing NO₂ concentrations, showing the synergistic effect of both phases. (b) Sensitivities of NO₂ sensors for the three devices. (c) Mechanism of NO₂ sensing of rGO-Cu₂O. Reprinted with permission from ref (32). Copyright 2012 American Chemical Society.

Figure 12

(a) Scheme of the in situ synthesis process and (b) of the resulting structure of a UiO-66 MOFs-wood hybrid membrane for efficient organic pollutant removal. (c) Filter built with 3 membranes for large-scale operation. Reprinted with permission from ref (104). Copyright 2019 American Chemical Society.