ORIGINAL PAPER Tailoring the hierarchical porous structure within polyethersulfone/cellulose nanosheets mixed matrix membrane to achieve efficient dye/salt mixture fractionation F. Lessan 1 & M. Karimi 1 & M. Arami 1 Received: 1 February 2016 /Accepted: 22 June 2016 # Springer Science+Business Media Dordrecht 2016 Abstract Mixed matrix concept using cellulose nanosheets (CNs) and polyethersulfone was employed to fabricate hierar- chical 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 poly- ethersulfone casting solutions at four concentration levels. After that, membranes were manufactured by typical nonsolvent in- duced phase separation method. Effect of CNs incorporation on thermodynamic stability and phase separation behavior of poly- mer 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 mem- branes 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 permeabil- ity 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 fabri- cation simplicity and perfect structural features. Keywords Cellulose nanosheets . Mixed matrix membrane . Thermodynamic stability . Dye/salt mixture fractionation Introduction Over the last several decades, developments of polymeric mem- branes via phase inversion methods have been increasingly promising in dealing with water treatment problems including eliminating organic and inorganic pollutants from wastewater [1, 2]. Therefore, nowadays membrane separation process is a well-established and environmentally attractive technology in many industrial sectors, such as textile, pharmaceutical, food, pulp and paper industries, wherein wastewater reuse is achieved by implementation of the membrane separation systems [3, 4]. Apart from effluents reclamation which has gained great attention in global separation market, it is worth mentioning that specific polymeric membrane can be tailored for fraction- ation of different solutes. The purpose of fractionation process is to concentrate and extract valuable waste constituents which can be achieved either by the steric (sieving) or electrical (Donnan) mechanisms using an appropriate membrane [5]. In this regard, potential applications of polymeric membranes Highlights •PES/CNs mixed matrix membranes were prepared. •CNs can induce two-stage phase separation during the nonsolvent in- duced phase separation process. •CNs filled membranes have more porous skin layer and longer finger- like cavities than unfilled case. •Addition of CNs greatly improves water permeability of membranes. •Dye/salt aqueous mixture can be efficiently fractionated by CNs filled membranes. * M. Karimi mkarimi@aut.ac.ir 1 Department of Textile Engineering, Amirkabir University of Technology, Hafez Avenue, Tehran 15914, Iran J Polym Res (2016) 23:171 DOI 10.1007/s10965-016-1034-1