Synthesis and characterization of MOF/silica cellulose acetate based membranes: Removal of uremic toxins in haemodialysis spent dialysate

The phase inversion technique associated to the Loeb-Sourirajan membranes made possible the creation of membranes in all the range of pressure-driven membrane processes. The present work addresses the synthesis and characterization of CA/SiO2 and CA/SiO2/MOF membranes specific for the removal of the uremic toxins - urea and p-cresil sulfate - from the spent dialysate fluid of haemodialysis. The MOF (Metal Organic Framework) synthesized - UiO2–66(Zr) - is added to casting solutions that differ on the acetone/formamide ratio – CA22, CA22/SiO2, CA34 and CA34/SiO2. The membranes with the higher acetone/formamide ratio, CA22 and CA22/SiO2, have lower hydraulic permeabilities,1.29 Kg/h/m2/bar and 4.1 Kg/h/m2/bar, respectively. The incorporation of UiO2–66(Zr) leads to the increase of their hydraulic permeabilities. This pattern is not verified for the CA34/SiO2 membranes. The molecular weight cut-off for the series of CA22 membranes ranges from 2.9 to 28.3 kDa and for the CA34 series ranges from 8.9 to 35.7 kDa. The incorporation of UiO2–66(Zr) leads to lower rejection coefficients to the two uremic toxins - urea and p-cresil sulfate. In average over the transmembrane pressure range of 0.5–4.0 bar the rejection coefficients are below 5 %.