Page 4 - Read Online

Page 2 of 27 He et al. Soft Sci 2024;4:37 https://dx.doi.org/10.20517/ss.2024.32

INTRODUCTION
The design and development of porous materials has demonstrated vast applications in various fields. A
primary characteristic of these materials is their low density, which results from a significant amount of void
space. This property can be leveraged to develop a wide range of functionalities, depending on the intended
applications. Porous materials such as metal-organic frameworks (MOFs)/covalent organic frameworks
(COFs)/hydrogen-bonded organic frameworks (HOFs) play significant roles due to their distinctive
[1]
characteristics .
In this regard, MOFs, recognized as porous coordination polymers, have witnessed considerable
advancements in recent years. They represent a distinct category of porous crystalline materials created
[2,3]
through the coordination bond interactions between organic ligands and metal-containing nodes . The
current landscape features thousands of MOFs with a wide range of molecular compositions, topological
[4]
structures, crystal forms, and pore architectures . Moreover, the physical properties, topological structures,
ligands, and metal nodes in MOFs can be tailored to enhance their characteristics and practical performance
[5]
through interweaving motifs, mixed ligand strategies, and functionalization . Nonetheless, the practical
applications of MOFs (such as in water treatment) are constrained by the processability challenges
associated with their inherently fragile and powdered crystalline forms. In response to this impediment,
MOF composite materials have emerged as a focal point in research, leveraging their adaptability and
unique microporous structure. However, challenges such as material compatibility, MOF matrix
decomposition, and other factors continue to impede the effective application of MOF composite
materials .
[6-9]

MOFs have highly controllable pore structures, large specific surface areas, and diverse functionalities,
making them extensively utilized in gas adsorption, separation, storage, and other areas. Compared to
conventional materials used for gas adsorption, MOFs offer tunable pore sizes, high surface areas, and a
variety of functional groups, enhancing their ability to adsorb and store gas molecules. By altering the
composition and structure of metal ions and organic ligands, it is possible to optimize gas adsorption and
energy storage performance [10-12] .

COFs are another type of porous material formed by covalent bonding of conjugated organic molecules.
They typically feature a two- (2D) or three-dimensional (3D) arrangement structure, excellent conductivity
and chemical stability, making them suitable for applications in electronic devices, sensors, catalysis, and
other fields. Their structures and properties can be regulated through synthesis methods and the design of
organic molecular structures, offering high customizability and application potential. In the field of
electronic devices and sensors, traditional materials include organic semiconductor materials, metal oxides,
2D materials, etc. In contrast, COFs exhibit excellent chemical stability and can withstand varying
environmental conditions, ensuring their suitability for the long-term reliable operation of these devices and
sensors .
[13]

Another class of porous materials, HOFs, is formed by non-covalent interactions between supramolecular
assembly units. HOFs typically have a molecular-level pore structure and affinity, rendering them
appropriate for applications such as molecular recognition, catalysis, and separation. Their structure and
properties can be regulated through intra- or intermolecular interactions, with unique characteristics. HOFs
[14]
can recognize specific molecules, enabling their use in molecular separation and detection . Additionally,
the synthesis of HOFs is typically straightforward and environmentally sustainable, requiring no extreme
temperatures or pressures, thereby promoting green synthesis methods.