Tuning the performance of ultrathin graphene oxide membrane via surface morphology control of support

Abstract

In this study, nanofiltration performance of an ultrathin graphene oxide (GO) membrane (<20 nm thickness) was significantly improved by optimizing the surface morphology of polycarbonate (PC) support via ion beam treatment. Ion beam can precisely generate and control the dimensions of the wrinkled structure by adjusting the exposure time. The wrinkle formation can be attributed to an increased degree of polymer cross-linking and heat generation by the penetrating $Ar^+$ ions that result in a stiff skin layer. Upon filtration testing, the water flux of the GO membrane with 20 nm thickness was enhanced by 6.4 times with the use of a wrinkled PC support structure. The root mean square (RMS) of the height was 0.83 nm for the flat PC and 11.5 nm for the wrinkled PC. A high rejection rate (greater than 90%) was also observed with dye molecules of sub-nanometer size. The influence of support morphology on the water flux was found to be especially significant when the thickness of the GO membrane was below 10 nm, which enhances the water flux from $4.21 L m^{−2} h^{−1} bar^{−1}$ at an RMS of 0.827 nm to $26.9 L m^{−2} h^{−1} bar^{−1}$ at an RMS of 11.5 nm. These results indicate that the support morphology is a critical parameter that determines the performance of ultrathin graphene-based membranes.