A novel 3-dimensional graphene-based membrane with superior water flux and electrocatalytic properties for organic pollutant degradation

Abstract

Graphene-based separation membranes exhibit great potential for the application of wastewater purification, but it is difficult to achieve a balance between water flux and rejection. To overcome the “trade-off” effect between permeability and selectivity, a novel 3-dimensional graphene-based membrane with superior water flux was fabricated using a simple, viable and green method. In addition, electrocatalytic technology is coupled to the membrane separation process. Comprehensive characterization indicates that the TiO₂ nanoparticles were successfully mounted on the moderately reduced graphene oxide (rGO) surface. By introducing oxygen-functionalized carbon nanotubes (oCNTs), the rGO-TiO₂/oCNT membrane has more pronounced 3-dimensional water channels. More importantly, the rGO-TiO₂/oCNT membrane acts as both a separation membrane and an anode to couple the membrane process to the electrocatalytic technique. The small-molecule contaminants that are difficult to remove by physical exclusion would be degraded when the matter passes through the channels with the electrocatalyst. The TiO₂ nanoparticles act as both a nano-wedge to expand the water channels and an electrocatalyst to promote the degradation of the contaminants. The rGO-TiO₂/oCNT membranes showed a removal rate up to 95% at a high liquid hourly space velocity of 88 h⁻¹ under the applied electrocatalysis conditions, which is two times more than that obtained without the electrocatalyst. The rGO-TiO₂/oCNT membrane could not only achieve a superior water flux (the maximum was 44.14 L m⁻² h⁻¹ bar⁻¹) but also maintain excellent dye removal performance (>90%) via membrane process coupling electrocatalysis. The optimum component ratio of the rGO-TiO₂/oCNT membrane was investigated, and it was found that 30% oCNT content accounts for a stable catalytic performance. The graphene-based membrane coupled electrocatalysis in this study would provide a new approach to break the bottleneck of the trade-off effect and inspire the design of a functional membrane.