Tunable gating graphene oxide (GO) membranes with high water permeance and precise molecular separation remain highly desired in smart nanofiltration devices. Herein, bioinspired by the filtration function of the renal glomerulus, we report a smart and high-performance graphene oxide membrane constructed via introducing positively charged polyethylenimine-grafted GO (GO-PEI) to negatively charged GO nanosheets. It was found that the additional GO-PEI component changed the surface charge, improved the hydrophilicity, and enlarged the nanochannels. The glomerulus-inspired graphene oxide membrane (G-GOM) shows a water permeance up to 88.57 L m–2 h–1 bar–1, corresponding to a 4 times enhancement compared with that of a conventional GO membrane due to the enlarged confined nanochannels. Meanwhile, owing to the electrostatic interaction, it can selectively remove positively charged methylene blue at pH 12 and negatively charged methyl orange at pH 2, with a removal rate of over 96%. The high and cyclic water permeance and highly selective organic removal performance can be attributed to the synergic effect of controlled nanochannel size and tunable electrostatic interaction in responding to the environmental pH. This strategy provides insight into designing pH-responsive gating membranes with tunable selectivity, representing a great advancement in smart nanofiltration with a wide range of applications.

No abstract

No abstract

Carbon nanomaterials have proven their wide applicability in molecular separation and water purification techniques. Here, an unzipped carbon nanotubes (CNT) embedded graphene oxide (GO) membrane (uCNTm) is reported. The multiwalled CNTs were longitudinally cut into multilayer graphene oxide nanoribbons by a modified Hummer method. To investigate the varying effects of different bandwidths of unzipped CNTs on their properties, four uCNTms were prepared by a vacuum-assisted filtration process. Unzipped-CNTs with different bandwidths were made by unzipping multiwalled CNTs with outer diameters of 0–10, 10–20, 20–30, and 30–50 nm and named uCNTm-1, uCNTm-2, uCNTm-3, and uCNTm-4, respectively. The uCNTms exhibited good stability in different pH solutions, and the water permeability of the composite membranes showed an increasing trend with the increase of the inserted uCNTm’s bandwidth up to 107 L·m–2·h–1·bar–1, which was more than 10 times greater than that of pure GO membranes. The composite membranes showed decent dye screening performance with the rejection rate of methylene blue and rhodamine B both greater than 99%.

No abstract

Graphene-oxide (GO) is an oxidized derivative of graphene. GO has a large number of oxygen-containing functional groups, including hydroxyl, carboxyl, and epoxy groups. The introduction of these groups makes its physical and chemical properties more complicated. For example, although GO films are impermeable to other liquids and even gases, they exhibit abnormally high permeance of water through the GO film. As a three-dimensional hollow material, metal-organic frameworks (MOFs) have a very large specific surface area and pore volume, and have a wide range of applications in catalysis, adsorption, and separations. Combining GO with MOFs can alter the distance between the layers of the GO to affect the transport and screening of specific molecules. This gives composites many potential applications in areas such as gas treatment and water treatment. This review summarizes the current status of GO/MOF composites, expanding on the following aspects: (1) We begin by reviewing the current status of research on GO and MOF with a focus on the physical properties. The mechanical strength of single-layer graphene is very weak, and in most solvents, GO spontaneously aggregates and is very difficult to effectively disperse. On the other hand, MOFs have high specific surface area, high crystallinity, and high porosity, but relatively low stability. Their relative instability greatly limited their practical applications. The formation of GO/MOF composites can take advantage of desirable properties of both material types, while improving their physical characteristics.(2) We next review the characteristics, preparation and applications of GO/MOF composites. At present, various GO/MOF composite materials, such as GO/ZIF-8, GO/MOF-5 have been prepared by in-situ synthesis and other methods. They are widely used in gas adsorption and separation, wastewater treatment applications, and molecular sieve applications. (3) We conclude this review by summarizing the opportunities for achieving composites materials with hydrophilic, antifouling, high-throughput, and high-repulsion properties by efficient, controllable, and low-cost methods. As GO/MOF technology improves, we suggest that these versatile materials have additional prospective applications in other areas, including as materials for medical applications.

Advanced membrane separation technology plays an important role in achieving excellent water treatment, which can help solve the freshwater crisis. However, there remains a trade-off between membrane permeability and selectivity. An emerging candidate to address this issue is graphene oxide (GO), a two-dimensional (2D) laminated graphene derivative with abundant oxygen functional groups. Furthermore, the transport channels of GO-based membranes can be artificially modified and manipulated, exhibiting great promise for GO in the field of water purification and molecular separation. This review comprehensively summarizes the research advances on 2D GO-based membranes for high-performance nanofiltration (NF). It begins with an elaboration on the preparation methods of GO-based membranes, followed by a detailed summary of the chemical modification and physical manipulation of transport channels. Then we reviewed the current research progress of theoretical calculation and molecular dynamics simulation. Also, the high NF performance of GO-based membranes is presented. Finally, the remaining challenges and future prospects in order to develop advances in membrane technology are provided.

Water pollution has long been a threat to human sustainability, and the development of nanofiltration membrane materials for water treatment is receiving increasing attention. Graphene oxide (GO) nanomaterials have demonstrated their widespread applicability in molecular separation and water purification technologies in recent years. However, the separation performance of the GO membrane (GOM) will decrease with long-term humidity. In this paper, we report a zeolite imidazole framework-8 (ZIF-8) nanoporous material embedded in a GOM, namely, GOZMs. After the positively charged ZIF-8 is compounded with GO, the separation and permeability of the composite nanofiltration membrane significantly improve, and it can remain stable during the long-term permeation process. Besides, four different ZIF-8 sizes were successfully prepared to investigate the effects of different porous particle sizes on composite nanofiltration membranes. The water permeability of the composite nanofiltration membrane increases monotonically with the increase of the ZIF-8 particle size, reaching 136.4 L m–2 h–1 bar–1, which is about 6 times higher than that of the pure GOM. The composite nanofiltration membrane exhibits decent dye screening performance while ensuring high water permeability. The rejection of rhodamine B and methylene blue was close to 100%, and the rejection of methyl orange was consistently lower. Therefore, the successful preparation of GOZMs paves a unique way for designing and developing novel nanofiltration membranes for water treatment and dye separation.