Al3+ Modification of Graphene Oxide Membranes: Effect of Al Source

Abstract

Graphene oxide (GO) membranes are promising materials for water filtration applications due to abundant nanochannels in the membrane structure. Because GO membranes are unstable in water, metal cations such as Al3+ are often introduced to the membrane structure to promote cross-linking between individual GO sheets. Here, we describe a simple yet versatile method to incorporate Al3+ into GO membranes formed via a slow self-assembly process. Specifically, we directly added aluminum to acidic GO sheet solutions from a variety of sources: Al2O3, AlCl3 and Al foil. Each species reacts differently with water, which can affect the GO solution pH and thus the density of carboxylate groups on the sheet edges available for cross-linking to the Al3+ cations. We demonstrate through characterization of the GO sheet solutions as well as the as-formed membranes’ morphologies, hydrophobicities, and structures that the extent to which the Al3+ cross-links to the GO sheet edges vs. the GO sheet basal planes is dependent on the Al source. Our results indicate that greatest enhancements in the membrane stability occur when electrostatic and coordination interactions between Al3+ and the carboxylate groups on the GO sheet edges are more extensive than Al3+–π interactions between basal planes.

Impact of Aluminum Modification on the Dielectric Properties of Graphene Oxide Membrane: Different Al Source

“…In the low frequency range(0.01~1Hz), where the interfacial polarization dominates, the d-space between parallel GO sheets dominate the through-plane dielectric constant and dielectric loss. As discussed in our previous work, among three Al 3+ AlCl 3 is most effect in tailoring the interlayer structure of the GO membrane [10]. Similarly, among the three AGO membrane serves as the dielectric separator in between carbon paper, the AGO (AlCl 3 ) shows the highest dielectric constant.…”

“…This method allows for controllable introducing Al 3+ (0.5mmol concentration in the membrane) to the solution from sources that react differently in acidic solution before membrane formation. Free-standing GO and AGO membranes were prepared through an ambient evaporation drying process (21°C, humidity of 50~60%) in a Teflon evaporating dish [10]. GO and AGO membranes were sandwiched in between two 1cm*1cm carbon paper electrodes as spacers in the dielectric capacitor.…”

“…The interaction of Al 3+ with the oxygenated functional groups (OFGs) on the edge and basal plane of GO sheets is uneven [8,9]. In addition, difference aluminum source will react with acidic GO solution differently, which will impact the aqueous stability of as-prepared AGO membrane differently [10]. Therefore, a difference in the effect of Al modification on the GO membrane when the Al source are difference can be anticipated.…”

Graphene Oxide Membranes—Synthesis, Properties, and Applications

“…To improve stability, metal cations are often introduced to the membrane structure to promote crosslinking between individual GO planes. In paper [ 5 ], GO membranes were modified with Al 3+ from three different sources: alumina, aluminum chloride, and aluminum foil. It was showed that the membranes functionalized with Al 3+ from aluminum foil were the most stable in water under mechanical stress; hence, the source of the modifier matters greatly.…”