Dual stimuli pH-responsive nanofiltration membranes with tunable permeability and selectivity during separation of antitumor drug doxorubicin

Abstract

This research aims to separate doxorubicin (as a pH-sensitive antitumor-drug) by dual pH-responsive-membranes (pH-Res-Mems). Since the trade-off between flux and rejection is a limiting factor for pH-Res-Mems with pH alteration, the focus of this research is to apply a novel approach i.e., inducing pH sensitivity to both membrane surface and sub-layer, to resolve the mentioned problem. To this aim, metal-oxides with Close-Gate (CG) mechanism (changing pore-size based on OH- functional-group) including copper-oxide (Cu-pH-Res) and silicon-oxide (Si-pH-Res) or metal-organic-frameworks with Open-Gate (OG) mechanism (changing pore-size based on H+ functional-group) including ZIF-8 (Zn-pH-Res) and ZIF-67 (Co-pH-Res) were added to both membrane layers simultaneously, where SurCun/SubSim and SurZnn/SubCom membranes were synthesized. Addition of Zn-pH-Res and Cu-pH-Res to the surface-layer led to improved superficial properties including hydrophilicity and roughness, while adding Co-pH-Res and Si-pH-Res to the sub-layer resulted in improvement of structural properties such as porosity and pore tortuosity. Furthermore, investigation of the pH sensitivity of membranes indicated that for the SurCu3/SubSi3 membrane, with pH reduction, the overall performance (OP) was enhanced from 2.17 to 6.40, while for the SurZn3/SubCo3 membrane, with pH elevation, OP was enhanced from 2.19 to 16.8. Eventually, the investigations revealed that the SurZn3/SubCo0 single pH-Res-Mem at neutral pH offered rejection of 89%, permeability of 4.41 LMH, and fouling of 70.4%. Meanwhile, these values for the SurZn3/SubCo3 dual pH-Res-Mem at pH= 5.5 were 95%, 21.9 LMH, and 27.2%, respectively. Overall, SurCu3/SubSi3 and SurZn3/SubCo3 membranes succeeded in 91.9% and 94.5% DOX removal from actual hospital wastewater, respectively, indicating the high-efficiency of pH-Res-Mems.