pH-Responsive graphene oxide/poly (methacrylic acid) hybrid nanofiltration membrane performance for water treatment

Graphene oxide (GO) membranes have been proposed for water treatment. GO can be used to prepare membranes that remove organic molecules, such as model dyes from contaminated wastewater. In practical applications, wastewater is often acidic or alkaline. The physico-chemical properties of GO are only weakly affected by pH, and this can lead to poor membrane performance for the removal of positively charged model compounds. In this work, we used pH-responsive poly (methacrylic acid) (PMAA) to prepare GO-PMAA materials through chemical crosslinking. GO-PMAA materials with different compositions were used to prepare membranes via physical intercalation. The membranes were tested for removal of five different dyes of different sizes and valency (including those that are positively charged, negatively charged, and neutral at neutral pH). We identify a membrane composition that works well for the removal of negatively charged methyl orange and Evans blue under acidic conditions (with 73.1% and 99.7% rejection, respectively) with improved water permeance compared to membranes prepared with GO alone. In addition, we evaluated the long-term stability of the nanofiltration membrane. After continuous operation for 20 h, the rejection rate of MnB by 5p-nGOM was about 85.37%, and the water permeance relatively stable, while the rejection rate of MnB by nGOM was about 26.59%, and the water permeance changed greatly. These findings indicate that GO membranes modified with pH-responsive polymers can achieve superior performance with respect to separation, water permeance, long-term operation, and pressure resistance, compared to GO membranes.