Robust GQDs Modified Thermally Reduced Graphene Oxide Membranes for Ultrafast and Long‐Term Purification of Dye‐Wasted Water

Abstract

Graphene‐related membranes have shown promising potential for water purification. However, both high stability and efficient separation performance of graphene‐related membranes for long‐term operation are urgently requested for their real applications. Here, a robust graphene quantum dots (GQDs) modified thermally reduced graphene oxide (TRG) (GQDs‐TRG) membrane is assembled from GQDs modified TRG aqueous dispersion. The GQDs‐TRG membrane demonstrates an excellent long‐term continuous separation performance in cross‐flow module, with a water permeance of 2000 ± 70 L per hour per square meter per bar (LHM bar−1) and 96 ± 0.2% rejection of Evans Blue (EB). The water permeance is 27 times higher than that of graphene oxide membrane and about two orders of magnitude higher than those of commercial filtration membranes with similar rejection. The gravity‐driven separation experiments on a dead‐end setup and nonequilibrium molecular dynamics simulation further confirm the surface cross flow is beneficial to enhancing the durability of GQDs‐TRG membrane on cross‐flow system. On gravity‐driven separation system, under 10 cm liquid column, the GQDs‐TRG membrane (2.34 µm thickness and 12.56 cm2 effective area) exhibits a water permeance of 800 ± 30 LHM bar−1, EB rejection above 95 ± 0.4%, and durability more than 7 month operation. These GQDs‐TRG membranes show the great potential for the long‐term purification of dye‐wasted water with high stability and suitability.

Towards sustainable ultrafast molecular-separation membranes: From conventional polymers to emerging materials

“…Unlike polymers, 2D materials comprise rigid lamellar layers. Solvents can pass through the pores of lamellar layers, the edges of adjacent 2D materials and the nanochannels that are created through functionalization 58,[62][63][74][75][76]. The rejection performance depends on the interval between two lamellar layers, surface charge and the total number of lamellar layers, i.e., membrane thickness.…”

“…Intervals between the lamellar layers provide solvent passageways and play crucial roles in solute rejection [32][33][34][35][36][37][52][53]62,[74][75][76]. The pore size, porosity and thickness of the membranes can be tailored through adjustments in the intervals between lamellar layers, size of lamellar layers and content of filtration solutions during membrane fabrication [32][33][34][35][36][37][52][53][55][56]62]. Pores can be etched in 2D materials using strong oxidants [35], enhancing membrane porosity.…”

“…This is because the nanochannels between GO layers for solvent transport are easier to create and manipulate. This can be achieved by adjusting inter-lamellar layer distance, pore etching, incorporating nanostrands and enlarging lamellar layer intervals [32][33][34][35][36][37][52][53][55][56]62]. Thermal reduction can also be deployed to obtain robust carbonaceous composite GO-based membranes containing graphene quantum dots (GQDs) and thermally reduced graphene oxide (TRG) (GQDs-TRG).…”

Factors affecting the separation performance of graphene oxide membranes: mechanical support, properties of graphene oxide, and exotic species

“…The protruding oxygen‐containing functional groups keep apart the adjacent GO nanosheets to form nanocapillaries suitable for separation at the NF level . It has been reported that the GO membrane can reject dye molecules, humic acids, micro‐organic pollutants, heavy metal ions such as Pb 2+ /Ni 2+ /Zn 2+ , and also be used for desalination …”

“…11 The protruding oxygen-containing functional groups keep apart the adjacent GO nanosheets to form nanocapillaries suitable for separation at the NF level. 7,11 It has been reported that the GO membrane can reject dye molecules, [12][13][14] humic acids, 15,16 micro-organic pollutants, 17 heavy metal ions 14,18,19 such as Pb 2+ /Ni 2+ /Zn 2+ , and also be used for desalination. 20,21 Manipulating the separation performance of the GO membranes has presented a challenge and aroused the interest of the researchers.…”