Tailoring the hierarchical porous structure within polyethersulfone/cellulose nanosheets mixed matrix membrane to achieve efficient dye/salt mixture fractionation

Mixed matrix concept using cellulose nanosheets (CNs) and polyethersulfone was employed to fabricate hierarchical porous membrane with potential application for efficient dye/salt mixture fractionation. To this end, CNs was extracted by acid hydrolysis of alpha cellulose and incorporated in polyethersulfone casting solutions at four concentration levels. After that, membranes were manufactured by typical nonsolvent induced phase separation method. Effect of CNs incorporation on thermodynamic stability and phase separation behavior of polymer solution was investigated by construction of phase diagram. In addition, the obtained flat-sheet membranes characteristics including surface morphology, cross-section structure, thermal decomposition, porosity, pore size and pure water flux, were investigated. CNs filled membranes were also evaluated for fractionation of direct dye/NaCl binary mixture. Results reveal that, two stages of phase separation process are observed in CNs filled solution, in which the early stage can initiate with lower water content. This leads to fabrication of more porous membranes with longer finger-like cavities which were confirmed by FESEM analysis of the membranes. Results of TGA reveal that, two weight loss steps forms during decomposition process of CNs filled membranes. It was also observed that addition of 1.5 wt.% CNs into polymer solution increases water permeability from 20 to 90 L/m(2) h. Application of 1.5 wt.% CNs filled membranes for fractionation of binary mixture containing direct red 23 (1 g/l) and NaCl (40 g/l) revealed that dye rejection and salt penetration percentages of obtained membranes are 98 % and 97 % respectively. Results confirm the potential of CNs filled membrane as a novel and promising approach for highly efficient fractionation of salt/dye mixtures, owning to its fabrication simplicity and perfect structural features.