(90f) Nanofiltration Membrane Consisting of a Sulfonated Pentablock Copolymer Selective Layer for the Removal of Heavy Metals

Heavy metal pollution has become a major problem in numerous countries due to the indiscriminate discharge of untreated wastewater. The situation is expected to be further aggravated in the near future by rapid population growth and economic development. As heavy metals are toxic and non-biodegradable, their bio-accumulation in human body will cause the life dysfunction. As such, there is an urgent need to address the current situation to prevent further damage to the environment and human health. Among the methods available for wastewater treatment, nanofiltration (NF) is a feasible and promising option. However, the development of new membrane materials is constantly required for the advancement of this technology. In this study, we attempt to develop a composite NF membrane consisting of a molecularly designed pentablock copolymer rejection layer for the removal of heavy metal ions. The resultant NF membrane has a reasonably high pure water permeability (A) of 2.4 LMH/bar but a relatively small mean effective pore diameter of 0.50 nm, and a molecular weight cut-off of 255 Da. . The newly developed NF membrane can effectively remove heavy metal cations such as Pb²+, Cd²⁺, Zn²⁺ and Ni²⁺ with a rejection greater than 98.0%. In addition, the membrane also shows reasonably high rejections towards anions such as HAsO₄^2- (99.9%) and HCrO₄^- (92.3%). This performance can be attributed to (1) the pentablock copolymer’s unique ability to form a continuous water transport passageway with a defined pore size and (2) the incorporation of polyethyleneimine (PEI) as a gutter layer between the selective layer and the substrate. To the best of our knowledge, this is the first reported NF membrane comprising this pentablock copolymer as the selective material. The promising preliminary results achieved in the current study may provide a useful platform for the development of new NF membranes for heavy metal removal.