Synthesis of Dispersed Metal- Organic Framework Crystals with Controllable Size and Shape in Aqueous Systems Yichang Pan, Dodi Heryadi, Xiang Li, Lan Zhao, Gabriella Lestari, Haibin Su, Zhiping Lai Advanced Membranes and Porous Materials Center, King Abdullah University of Science and Technology Supercomputing Laboratory, King Abdullah University of Science and Technology Division of Materials Science, Nanyang Technological University, Singapore

Abstract We demonstrated that surfactants like CTAB could efficiently manipulate and control the shape and size of MOF (ZIF-8) crystals. The reason is because the long hydrophobic hydrocarbon chain of CTAB can adsorb on the hydrophobic surface of ZIF-8 crystals in aqueous solution and function as capping agent to slow down the crystal growth rate. The growth rate of {100} decreased much more profound than {110} and {111} faces because CTAB molecules adsorbed on {100} much stronger than the other two faces. Thus, not only the absolute value, but also the relative growth rate of {100} to {110} decreased when more CTAB molecules adsorbed on the surface. The present work may open a facile method to control the shape and size of MOF particles that may be very useful in their applications in membranes, optics and building blocks for nano-device assembly, etc. KAUST King Abdullah University of Science and Technology

a) XRD patterns, b-e) SEM images of ZIF- 8 crystals prepared with CTAB at the amount of no CTAB, %, 0.01% and 0.025%, respectively, f) plot of the mean particle size of ZIF-8 crystals versus the concentrations of CTAB added. The insets in the SEM pictures are schematic sketches of the crystal morphology. {110}, {100} and {111} facets are represented in cyan, red and yellow color, respectively. KAUST King Abdullah University of Science and Technology XRD patterns and SEM images

SEM pictures of ZIF-8 crystals prepared by adding TPABr and CTAC at the amount of a) 0.001% TPABr, b) 0.01% TPABr, c) 0.065% TPABr, d) % CTAC, e) 0.01% CTAC, and f) 0.02% CTAC. KAUST King Abdullah University of Science and Technology SEM pictures of ZIF-8 crystals prepared by adding TPABr and CTAC

a) The predicted equilibrium morphology of ZIF-8 crystals based on the minimum total surface energy, b) the predicted growth morphology based on the attachment energies, and c) a snapshot of the MD simulation of CTAB molecules adsorbed on the ZIF-8 {100} surface at 40 ps. KAUST King Abdullah University of Science and Technology predicted equilibrium morphology

Surface Free and Attachment Energies of Various Crystal Facets Calculated Using the Morphology Module of the Material Studio. KAUST King Abdullah University of Science and Technology6 Surface Free and Attachment Energies