Metal−organic frameworks (MOFs) are a promising class of functional materials with applications in catalysis, separations, electronics, and drug delivery, among others. Despite a range of techniques utilized for MOF synthesis, a generalizable and scalable approach has yet to be developed for producing MOFs without using environmentally damaging organic solvents. Here, we look at MOF synthesis as a reaction in an aqueous medium and propose new methods of measuring conversion and selectivity. We show that controlling reactant speciation via pH is a generalizable approach to producing the prototypical MOFs UiO-66, UiO-66-NH 2 , ZIF-L, and HKUST-1 with space−time yields (STY) of over 2250 kg m −3 day −1 , which is a 1 order of magnitude improvement for zirconium-based MOFs. We show that UiO-66-NH 2 crystallization is complete in 5 min at room temperature, with 70% of the extent of reaction completed by 30 s. Finally, we apply the rapid synthesis approach to coating cotton fabric with up to 20 wt % UiO-66-NH 2 using a sequential dip-coating (SQD) technique and demonstrate particulate matter (PM 1−4 ) filtration up to 85%. This work shows a greenchemistry-based, generalizable pathway to rapid synthesis for multiple MOFs and demonstrates its utility for filtration applications. The ability to produce alternative filtration materials is especially relevant under pandemic conditions, where SQD offers a rapid and high-throughput manner of providing air filtration by modifying commonly available textile materials.

NU-1000, a zirconium (Zr)-based metal–organic framework (MOF), is a promising candidate for heterogeneous catalysis, gas storage, electrocatalysis, and drug-delivery applications due to its large pore size and mesoporous structure. However, the synthesis of NU-1000 may produce another polymorph NU-901, which has a smaller average pore size and pore volume than NU-1000. Similarly, the presence of NU-1000 as a phase impurity in NU-901 crystallites is undesired. Although phase-pure NU-901 and NU-1000 have been successfully synthesized in bulk, multiple applications such as electrocatalysis and separation membranes require the formation of thin films. In this study, we utilize self-assembled monolayers and crystal engineering to control the polymorphism and orientation of NU-901/NU-1000 thin films. We report the fabrication of thin films of NU-901 and NU-1000 via a solvothermal method by functionalizing the substrate with carboxyl (−COOH) tail groups. This synthesis produces phase-pure hexagonal rod-shaped NU-1000 crystals and nearly phase-pure prolate-shaped NU-901 crystal as revealed by scanning electron microscope (SEM), powder X-ray diffraction (PXRD), and nitrogen adsorption isotherm analyses. Furthermore, we control the orientation of NU-1000 crystallites on the fluorine-doped tin oxide (FTO) substrate by controlling the nucleation density of the MOFs on the substrate. We hypothesize that heating the functionalized substrate in a Zr-oxo cluster solution preceding solvothermal synthesis results in the coordination of Zr-oxo clusters to the (−COOH) groups of the substrate, which promotes a higher nucleation density of NU-1000 on the substrate, resulting in the perpendicular growth of NU-1000 during crystal formation.

Synthesis of porous, covalent crystals such as zeolites and metal–organic frameworks (MOFs) cannot be described adequately using existing crystallization theories. Even with the development of state-of-the-art experimental and computational tools, the identification of primary mechanisms of nucleation and growth of MOFs remains elusive. Here, using time-resolved in-situ X-ray scattering coupled with a six-parameter microkinetic model consisting of ∼1 billion reactions and up to ∼100 000 metal nodes, we identify autocatalysis and oriented attachment as previously unrecognized mechanisms of nucleation and growth of the MOF UiO-66. The secondary building unit (SBU) formation follows an autocatalytic initiation reaction driven by a self-templating mechanism. The induction time of MOF nucleation is determined by the relative rate of SBU attachment (chain extension) and the initiation reaction, whereas the MOF growth is primarily driven by the oriented attachment of reactive MOF crystals. The average size and polydispersity of MOFs are controlled by surface stabilization. Finally, the microkinetic model developed here is generalizable to different MOFs and other multicomponent systems.

Thin-film fabrication of metal organic frameworks (MOFs) has been explored for a range of applications, including separations, catalysis, sensing, and charge transport. However, many fabrication techniques have obstacles, including slow crystallization, control over film thickness, and control over crystallinity. Recently, a meniscus-guided coating technique, called solution shearing, has been shown to create MOF thin films within minutes and with control over the film thickness. However, there have been no previous reports of solution shearing based evaporative crystallization of zirconium-based MOFs, which have been widely studied for the aforementioned applications. Here, for the first time, we show that (i) the zirconium 1,4-dicarboxybenzene MOF, UiO-66, can be formed using evaporative crystallization during solution shearing, and (ii) a wide range of parameters can be tuned to control the film thickness, coverage, and crystallinity. Finally, we bring the solution shearing technique closer to separation applications by growing a full film of UiO-66 crystals up to the resolution of scanning electron microscopy (SEM) on anodic alumina oxide (AAO). This is the first instance of UiO-66 crystals being formed using an evaporative crystallization-based flow coating method, and solution shearing shows the promise to be applicable to form large area zirconium-based MOF crystals in a rapid manner (within seconds to minutes).

Illustrated is a continuous-flow microfluidic device with patterned surface to induce faster nucleation of metal–organic frameworks (MOFs) and other slow-growing crystals, where the cyclonic flow allows trapping of crystals to grow them under controlled conditions.