Kinetics and mechanism of metalorganic framework thin film growth: systematic investigation of HKUST-1 deposition on QCM electrodesElectronic supplementary information (ESI) available: General experimental aspects, details of QCM measurements, and additional characterization of Cu3(btc)2 coatings. See DOI: 10.1039/c2sc20065a

We describe a systematic investigation of the factors controlling step-by-step growth of the metalorganic framework (MOF) [Cu 3 (btc) 2 (H 2 O) 3 ] x H 2 O (also known as HKUST-1), using quartz crystal microbalance (QCM) electrodes as an in situ probe of the reaction kinetics and mechanism. Electrodes coated with silica, alumina and gold functionalized with OH and COOHterminated self-assembled monolayers (SAMs) were employed to determine the effects of surface properties on nucleation. Deposition rates were measured using the high sensitivity available from QCM-D (D = dissipation) techniques to determine rate constants in the early stage of the process. Films were characterized using grazing incidence XRD, SEM, AFM, profilometry and reflectionabsorption IR spectroscopy. The effects of reaction time, concentration, temperature and substrate on the deposition rates, film crystallinity and surface morphology were evaluated. The initial growth step, in which the surface is exposed to copper ions (in the form of an ethanolic solution of copper( ii ) acetate) is fast and independent of temperature, after which all subsequent steps are thermally activated over the temperature range 2262 C. Using these data, we propose a kinetic model for the Cu 3 (btc) 2 growth on surfaces that includes rate constants for the individual steps. The magnitude of the activation energies, in particular the large entropy decrease, suggests an associative reaction with a tight transition state. The measured activation energies for the step-by-step MOF growth are an order of magnitude lower than the value previously reported for bulk Cu 3 (btc) 2 crystals. Finally, the results of this investigation demonstrate that the QCM method is a powerful tool for quantitative, in situ monitoring of MOF growth in real time. The kinetics of HKUST-1 surface nucleation and growth are observed using in situ QCM measurements, from which a detailed reaction mechanism is proposed.