Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) represent new and promising classes of ordered porous materials that have garnered significant research attention since their discoveries in 1995 and 2005 [1,2]. The remarkable structural features and advantageous properties of crystalline MOFs and COFs, such as their high specific surface area, pore size adjustability, easily accessible building blocks, and customizable structures, have captured widespread attention [3,4]. Since their initial report in 2005, COFs have followed the developmental path established by MOFs. Over time, they have evolved from a focus on synthesis to a growing emphasis on practical applications. Numerous applications, including gas separation and adsorption, photocatalysis, electrocatalysis, energy storage, ion- batteries, controlled delivery, and biosensing, have been studied for these materials [[5], [6], [7], [8]].

MOFs have drawn much attention as a new category of highly crystalline, porous materials throughout the last 20 years. MOFs are often made up of metal clusters or ions precisely coordinated with organic ligands [9]. Researchers have created thousands of MOFs with various crystal systems, pore designs, molecular structures, and topologies by varying their chemical constituents, such as metal centers and organic linkers (Fig. 1). They have established themselves as highly adaptable materials for a variety of applications due to their remarkable structural, physical, and chemical properties [10,11]. The diversity of MOF-based composite materials can be increased through the combination of MOFs and additional functional components, including COFs, magnetic nanoparticles (NPs), and carbon nanotubes. By incorporating these materials, their performance and stability are improved, opening the door for previously unheard-of breakthroughs in the sector [12]. Despite their potential, MOFs' range of applications is rather limited because of some inherent restrictions. The comparatively low coordination bond strength is a significant obstacle that may impair their functionality, particularly in challenging circumstances [13].

COFs constitute an emerging category of porous crystalline organic polymers assembled through the polymerization of organic monomers composed of light elements, such as carbon, nitrogen, oxygen, hydrogen, and boron, via strong bonds [14,15]. In addition to having higher thermochemical stability than coordination-based MOFs, schiff-base COFs are distinguished by their intrinsic qualities, which include high porosity, tunable pore sizes, ordered pore architectures, and readily customizable functions [[16], [17], [18]]. Using reticular synthesis principles, COFs may be designed with significant surface areas (4210 m2g−1), exceptionally low densities (0.17 g cm−3), and extensive pore diameters (up to 4.7 nm). This class of material have demonstrated broad applicability in gas separation, catalysis, energy storage, and electronics, by integrating variable pore sizes through the framework's functionalization via pre- and post-synthetic adjustments.

Recently, there has been increased interest in integrating functional constituents to form composites with core-shell structures or doping. This technique seeks to improve the properties of specific materials by combining their physical, chemical, and functional characteristics [19]. MOF integrated hybrid materials are created by mixing MOFs with diverse functional components including polymers [20], metal NPs [21], silica [22], enzymes [23], carbon materials [24], and other MOFs [25]. These hybrids retain the structural characteristics of the constituent elements while exhibiting novel, improved properties. Core-shell MOFs, for example, which are made by enclosing one MOF inside another, exhibit improved gas separation capabilities and have a major impact on gas adsorption behaviour. COF-based hybrid materials have also been developed, similar to MOFs. The lack of solubility and inadequate dispersion of powders of the microcrystalline COF in the majority of solvents are two fundamental constraints of COFs, the same as those of MOFs. Significant attempts have been made to functionalize COFs by mixing them with other materials, such as metal nanoparticles [26], carbon materials [27], polymers [[28], [29], [30]], various COFs [31], and quantum dots [32], in order to get over these difficulties. This tactic improves the original COFs' qualities while reducing their disadvantages. The subject of covalent organic frameworks (COFs) is still in its early stages, with great prospects for foundational research as well as advances in scaling up and refining production procedures [33]. When utilized alone, MOFs and COFs' intrinsic properties preclude them from meeting the specific needs of a variety of disciplines, despite substantial study on their synthesis, nanostructure development, and varied applications. For instance, pure MOFs exhibit inherent shortcomings, including poor stability, limited electrical conductivity, and restricted functionality. In addition, while COFs offer improved chemical stability, they suffer from low specific surface areas and limited crystallinity. As a result, considerable research has focused on hybridizing MOFs and COFs to achieve enhanced performance. While some COFs, which are recognized for their efficient photothermal transformation or generation of reactive oxygen species, show promise as agents for photothermal therapy (PTT) along with photodynamic therapy (PDT), MOFs with high specific surface areas are well-suited for transporting medications, photosensitizers, and near-infrared dyes [34]. These hybrids provide synergistic characteristics, including photothermal therapy (PTT), chemotherapy, photodynamic therapy (PDT), and imaging capabilities, by combining the advantages of their respective constituents [[35], [36], [37]].

Furthermore, mutual cross-functionalization allows the integration of functional components in MOFs and COFs, allowing for their combination. Composites that combine the special qualities of both materials can be produced by embedding the secondary building units (SBUs) of MOFs within the structural units of COFs. In addition to promoting the development of MOF and COF research, this method offers novel functions that are not possible with either material alone. By adding individual metal ions or mononuclear metal complexes to their sturdy structures, metal-covalent organic frameworks (MCOFs), for instance, overcome the drawback of COFs without active metal centres. Only a few chapters particularly concentrate on MOF/COF hybrids in-depth, despite the fact that numerous reviews have recently addressed the synthesis techniques and uses of MOF/COF-based composites [27,38]. Since MOF/COF composites have advanced significantly between 2016 and 2024, this is the perfect opportunity for a thorough analysis that looks at their synthesis techniques, current advancements, and possible future paths [39] (Fig. 2).

In this light, this review presents a comprehensive overview of state-of-the-art design for diverse MOF-COF architectures and hybrid variants, highlighting their innovative fabrication methodologies that enhance selectivity and enable adaptable topologies. It thoroughly explores the sophisticated characterization techniques employed to assess the structural, morphological, thermal, and elemental properties of these hybrids. Considerable efforts have been dedicated in unravelling the interfacial chemistries underpinning MOF/COF hybrids, which integrate the complementary strengths of both frameworks in a synergistic manner. Moreover, this study systematically showcases the pioneering advancements, spanning catalysis—such as molecular, photocatalysis, and energy-transfer photocatalysis—as well as broader areas, including chemical sensing, gas adsorption and separation, biosensing, and biomedical technologies. Finally, the existing challenges and future directions for MOF/COF composites are sketched, aiming to inspire further innovation in diversifying this hybrid material family and unlocking their potential for cross-disciplinary applications.