Carbon nitride 2D nanosheets enhanced rGO membranes for water treatment: Forward osmosis and photocatalysis

Abstract

Although forward osmosis (FO) offers the advantage of high desalination capacity without additional driving forces, it faces two challenges: the trade-off effect and membrane fouling. Embedding 2D nanosheets into the membrane effectively enhances its properties by modulating the interlayer spacing and imparting catalytic functionality, providing a key strategy to address the outlined challenges. In this work, 2D nanomaterials with photocatalytic properties, specifically carbon nitride (gCN), were intercalated into reduced graphene oxide (rGO) laminates to prepare rGO@gCN composite FO membranes. Atomically 2D gCN nanosheets acted as nanospacers, increasing the interlayer spacing between rGO nanosheets and enhancing the membrane's surface hydrophilicity, thereby providing a direct water transport channel and reducing resistance to water transport. The rGO@gCN membrane exhibited optimal performance, with a water flux of 48.4 LMH (an 11-fold increase compared to the pristine rGO membrane), without sacrificing the rejection of divalent ions and organic dyes, thereby overcoming the constraints of the trade-off effect. Additionally, the rGO@gCN membrane demonstrated self-cleaning capabilities for methylene blue (MB) fouling on the surface during both static and dynamic photocatalytic performance tests. The rGO@gCN membrane maintained 70 % of the initial water flux even after 4 h FO filtration under visible light, and the MB-contaminated membrane could be self-cleaning to restore its original appearance and water permeability. Overall, this work provides a multifaceted strategy and valuable design insights for achieving high FO performance and enhanced resistance to membrane fouling in various potential applications of 2D nanomaterial-based FO membranes.