Influences of cross-linking agents with different MW on the structure of GO/CNTs layers, membrane performances and fouling mechanisms for dissolved organic matter

Abstract

This study evaluated the impacts of cross-linking agents with different molecular weight (MW) on the structure of graphene oxide (GO)/carbon nanotubes (CNTs) layers and fouling mechanisms. The GO/CNTs-modified membrane was fabricated by chemical activation and vacuum filtration methods and exhibited excellent stability in antifouling performance and rejection rates. Increasing the external diameter of CNTs and MW of cross-linking agents improved the water flux through enlarging the interlayer spacing of GO/CNTs layers, showing the highest water flux of about 1280 kg/m2h. The large external diameter of CNTs deteriorated the antifouling performance and removal efficiency. The small cross-linking agents, i.e. ethanediamine with 60.1 Da or polyethyleneimine with 600 Da, maintained the regular lamellar structure of GO/CNTs layers, causing the high flux and DOC rejection. However, polyethyleneimine with 1800 Da promoted GO/CNTs aggregation and created non-uniform lamellar structure with high surface roughness, resulting in the severest flux decline and the lowest DOC rejection. The fouling model was also influenced by the MW of cross-linking agents; the small agents caused complete blocking while the large agent caused intermediate fouling for humic acid (HA) solution. The bridging effect of Ca2+ resulted in intermediate fouling for all the membranes in the case of HA + Ca2+ solution.