Jithin John Varghese

Two-dimensional metal organic frameworks (2D MOFs) are a class of next generation materials for adsorbents,membranes and sensors; however, many 2D MOF synthesis methods lack the scalability and precision required for translation to industrial scales. Furthermore, the engineering of 2D MOF structures is challenged by complex environment-surface interactions that arise from their high anisotropy, thinness and functionally diverse surfaces. In this work we developed new understandings and methods of engineering such structures by using accelerated, high shear synthesis, and solvent exchange. With the recently developed annular flow microreactor we synthesized 2DMOFs more efficiently than conventional batch methods, by up to 5 orders of magnitude in terms of reactor space-time-yield. To accurately characterize particle size and dynamics in various organic solvents, we used liquid cell transmission electron microscopy. This technique not only visualized the oriented attachment of nanosheets, but also showed that the rate and direction of attachment is significantly influenced by solvent-surface interactions. These techniques and understandings provide rational bases for 2D MOF engineering and process design.

Solvents are crucial components in specialty chemical and pharmaceutical industries and in electrochemical and photoelectrochemical processes, and are increasingly being used in catalytic reactions. Solvents significantly influence the kinetics and thermodynamics of reactions and can alter product selectivity markedly. While such solvent effects are observed routinely, identification of the root causes of such effects is less frequent. Solvents can influence reaction rates, conversion and product selectivity by 1) directly participating in the reaction steps and opening alternate reaction pathways, 2) competing with the reactant for interaction with the catalysts, 3) changing the relative stabilization of the reactant, the transition state (TS) and/or the product, 4) altering intra-pore diffusion characteristics in porous catalysts, 5) exhibiting entropic confinement effects altering free energy barriers of reactions, 6) changing the solubility of different components in the reaction mixture, and 7) inhibiting undesired reactions. Their indirect influences may be due to 1) changes brought on to active sites on catalysts and 2) altered structure/stability of catalysts. This article discusses these fundamental reasons behind observed solvent effects with suitable examples. Advances in computational chemistry have led to the development of multiple tools and techniques, considering solvents either as implicit or as explicit molecules, providing molecular insights into complex solvent effects in catalysis. This article provides an overview of some of these methods with suitable examples to demonstrate their application and potential. This mapping of the solvent effects and their origins is believed to aid in the rational selection of solvents for catalytic reactions. The description of the computational tools, their application and their potential is likely to encourage widespread use of these techniques to investigate solvent effects.

Due to their high anisotropy and tunable chemical composition, two-dimensional metal organic frameworks (2D MOFs) have great potential as building blocks for next-generation materials in a diverse range of applications - from electrochemical catalysis to membrane separation. However, the controllable synthesis is complicated by the environment-surface interactions that arise from the high anisotropy, thinness, and functionally diverse surfaces of 2D MOFs. Liquid cell transmission electron microscopy (LCTEM) offers a unique opportunity to study these interactions in situ. In this work, we analyzed the effects of different solvent environments on the structure and aggregation dynamics of copper benzene dicarboxylic acid (CuBDC) nanosheets, which were synthesized using a high shear annular microreactor. LCTEM revealed that 2D MOF nanosheets undergo oriented attachment and that the rate and direction of oriented attachment is controlled by solvent-surface interactions. We investigated the nature of these solvent interactions using density functional theory calculations, which suggest that the binding energy of solvents to different MOF surfaces is likely responsible for this behavior. The CuBDC nanosheets were then applied as adsorbents in organic solvents, in which we showed how solvent-mediated oriented attachment could significantly affect adsorption properties.