Metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs) are highly versatile materials based on inorganic modes connected via organic linkers or purely via the connection of organic building blocks, respectively. This results in 3-D nanoporous frameworks, which, due to their combination of high porosity and variability of building blocks, can exhibit exceptional properties that make them attractive. Certain applications (e.g., in electronics and as membranes) require a thin film or even a patterned morphology on various substrates. Inkjet printing of MOFs has emerged as a simple and effective technique for the scalable production of a wide range of MOF (gradient) films and patterns on a wide range of substrates according to specific requirements. This review comprehensively reviews the achievements in inkjet printing of both MOFs and COFs. We discuss the different substrates, ink formulation, and hardware intertwined requirements needed to achieve high-resolution printing and obtain desired properties such as porosity, physical-mechanical characteristics, and uniform thickness. Crucial aspects related to ink formulation, such as colloidal stability and size control of MOFs and COFs, are discussed. Additionally, we highlight potential opportunities for furthering the development of inkjet printing of MOFs/COFs and critically assess the reporting of the printing procedures and characterization of the resultant materials. In this manner, this review aims to contribute to the advancements in understanding and optimization of inkjet printing of MOFs and COFs, as this technique holds great potential for diverse applications and functionalization of MOF/COF films and patterns.

Due to the irreversible tautomerization of imine linkages to their corresponding ketoenamines, β-ketoenamine-linked Covalent Organic Frameworks (COFs) are a stable type of COF that displays high surface areas. In the solvothermal synthesis of such COFs, the use of (acetic) acid is ubiquitous. However, the effect of the added acid on the COF properties (notably their surface area) has never been investigated. Building on an extensive literature overview, we systematically studied the effect of the pK_a of several added acids on COF performance characteristics and extended the investigation by including a series of (organo-)bases with varying pK_a. Interestingly, the highest BET surface areas, above 1400 m²/g, were found in the alkaline region of the pK_a window, with a maximum near pK_a ∼10.8 for triethylamine (TEA) and N,N-diisopropylethylamine (DIPEA). Considering the pK_a values related to the three phenolic hydroxyl groups of 2,4,6-triformylphloroglucinol, one of the COF building blocks, these organobases fully deprotonate two of these hydroxyl groups and partly deprotonate the third one, which optimizes the reaction rate of the β-ketoenamine bond formation, explaining the improved COF crystallinity and associated microporosity. The largely overlooked use of organobases in the synthesis of β-ketoenamine-linked COFs thus offers a promising approach to improve the COF performance.