Aldehyde linkers are functional groups containing a carbonyl group (C=O) bonded to a hydrogen atom, and they play a crucial role in the construction of covalent organic frameworks (COFs). These linkers can undergo condensation reactions with other functional groups, such as amines or hydrazides, to form stable covalent bonds within the COF structure. COFs containing aldehyde linkers typically have high porosity and surface area, making them ideal for applications such as adsorption and catalysis. Aldehyde linkers can also be post-functionalized to introduce additional functionalities, expanding the range of applications of COFs. Due to their reactivity, aldehyde linkers provide a versatile platform for the synthesis of COFs with complex architectures and tailored properties.