Application of Raman and chemometrics to the mechanochemical synthesis of 4,4-bipyridine/cobalt based MOF using twin screw extrusion

The process optimization of 4,4-bipyridine based metal organic framework (MOF) synthesis by twin screw extrusion (TSE) is investigated using cobalt nitrate hexahydrate (Co(NO3)2·6H2O) as metal precursor. The effects of operating parameters including solvent amount added (L/S ratio), screw speed and feeding rate on the product composition are examined. The collected MOF samples were characterized offline by powder X-ray diffraction, Raman spectroscopy, thermogravimetric analysis, and scanning electron microscopy. It is found that the explored feeding and screw rates are insufficient to generate a pure MOF, only obtained by adding an optimum solvent amount, improving wettability and reactants mixing to interact at molecular level, facilitating the reaction inside the extruder. Partial least square based multivariate analysis of the collected Raman spectra is used to obtain predictive models to quantify MOF purity, which reached a maximum of 87.0 wt% at 0.5 L/S, 50 g/h of feeding rate and 100 rpm of screw speed.