Recent progress in the use of graphene/polymer composites to remove oil contaminants from water
摘要: 频繁的海上溢油事故和工业含油污水的肆意排放严重破坏海洋生态平衡。因此，开发先进的除油材料迫在眉睫。石墨烯（G）及其衍生物氧化石墨烯（GO）因其具有高比表面积、低密度、高孔隙率、表面功能可调等优异的理化性质，在油水分离领域成为研究热点。为充分发挥其优势，近年来，将G或GO与聚合物复合制备成功能化G/聚合物或GO/聚合物纳米复合材料，因其具有良好的除油能力、优异的机械性能、价格低廉、形貌及表面化学组分可调等优势而越来越受到人们的青睐。目前已开发出气凝胶、泡沫、海绵、膜等具有三维结构的G/聚合物或GO/聚合物复合吸油剂和过滤膜。本文系统性地总结了从表面润湿理论到G/聚合物或GO/聚合物复合吸油材料和滤膜材料的最新研究进展。此外，重点归纳了近年来有关油品回收及吸油材料再生的方法策略。最后，提出该研究领域目前面临的挑战和未来研究方向，旨在为该领域的深入探索开辟新的视角。Abstract: Frequent oil spill accidents and the massive discharge of industrial oily sewage have destroyed the ecological balance and threatened marine life. Graphene (G) and graphene oxide (GO) have emerged as important materials in the field of oil/water separation because of their remarkable physicochemical properties including high specific surface area, low density, high porosity and tailorable surface functionality. To take full advantage of G and GO, their incorporation with polymers to build functional G/polymer and GO/polymer composites has recently gained increasing popularity because of their improved oil clean-up capability, outstanding mechanical performance, relatively low cost and adjustable surface chemical composition. Tremendous efforts have contributed to the development of G/polymer and GO/polymer composite oil clean-up sorbents and filtration membranes in 3D structural forms such as aerogels, foams, sponges and membranes. In this review, a comprehensive picture from the basic theory of the surface wettability to the recent advances in G/polymer and GO/polymer composite oil clean-up sorbents and filtration membranes are highlighted. The strategies for oil recovery and regeneration of the sorbents are also summarized. Current challenges and future research directions in this topic are provided, aimed at providing new perspectives for in-depth exploration in this field.
Figure 2. (a) Absorption process of AG-1 towards paraffin oil(Sudan red-stained paraffin oil floating on water was completely absorbed within 62 s, (b) absorption capacities of AG-1 (black) and AG-2 (red) towards various oils and common organic solvents (adapted from Ref with permission. Copyright 2014 The Royal Society of Chemistry), (c) a schematic illustration showing the fabrication procedure of CNF/PVA/GO composite aerogels, (d1) photographs of d-MCPGAby freeze-drying methods, (d2) SEM image showing the vertical section of d-MCPGA, (d3) SEM image showing the cross section of d-MCPGA, (e) water contact angles of d-MCPGA measured from 0 s to 120 s, (f) absorption capacities of MCPGA (d-MCPGA, r-MCPGA, n-MCPGA) for various types of oils and organic solvents, (g1) photograph showing the ultra-light cylindrical d-MCPGA hold up by the young leaves, (g2) the shape of the d-MCPGA before bearing 500 g mass load, (g3) the shape of the d-MCPGA after bearing 500 g mass load and (g4) the state of d-MCPGA when bearing 500 g mass load. (adapted from Ref with permission (Copyright 2019 Multidisciplinary Digital Publishing Institute).
Figure 3. (a) SEM image of a cellulose nanofibrous foam, (b) physical appearance of the cellulose nanofibrous foam, (c,e) SEM images of a cellulose nanofibrous aerogel at different magnifications and (d) physical appearance of the cellulose nanofibrous aerogel. (adapted from Ref with permission. Copyright 2016 PubMed)
Figure 4. (a) The oil and solvent absorption capacities of G/PPy, (b) cyclic absorption capacities of G/PPy foam towards diesel (adapted from Ref with permission. Copyright 2013 The Royal Society of Chemistry), (c) photographs and a schematic illustration showing the fabrication of the rGO@PU foam, (d) absorption capacity of the neat PU and rGO@PU foams towards oils and organic solvents, (e) cyclic absorption capacities of the rGO@PU foam towards oils and organic solvent and (f) oil-removing efficiency of the rGO@PU foam (adapted from Refwith permission. Copyright 2018 Elsevier).
Figure 5. (a) Oil/water separation capacities of GO/PES composite flat sheet (FS) and hollow fiber (HF) membranes at different oil concentrations (adapted from Refwith permission. Copyright 2020 Wiley), (b) a schematic illustration showing the preparation procedure of the GO-Ca2+-SA hybrid mesh by layer-by-layer self-assembly and cross-linking (adapted from Refwith permission. Copyright 2020 Elsevier), (c) TEM image of the hybrid membrane with 7 wt% of GO, (left), the magnified TEM image of the spindle-knot structure (middle), the magnified TEM image of PAN and GO sheets (right), (d) relation curves between flux and permeation volume of PAN/GO membranes (left), relation curves between flux and permeation volume of H-PAN/GO membranes (inset was permeation volume = 200 mL) (right) (adapted from Ref with permission. Copyright 2017 Elsevier) and (e) functionalization of GO with aspartic acid (adapted from Refwith permission. Copyright 2017 Elsevier).
Figure 6. (a) A schematic illustration showing the fabrication procedure of CGQD-incorporated ENCF membrane, (b) toluene permeation flux of the CGQD-incorporated ENCF membrane with various concentrations of CGQD, (c) the permeation flux of the CGQD-incorporated ENCF membrane to several common organic solvents (adapted from Ref with permission. Copyright 2018 Elsevier).
Table 1. The synthetic methods, WCA and oil absorption capacities of G/polymer and GO/polymer composite aerogels and foams.
Material Synthesis method Water contact angle Oil absorption
Number of cycle Ref. G/PVDF aerogels Solvothermal reduction 153.6° 20−70 10  PI-GO aerogel Supercritical drying - 8.0 -  LGA aerogels Hydrothermal treatment and freeze-drying 127° 167−350 10  G/CNC aerogel Lyophilize andcoating 130° 25−58 100  CNF/PVA/GO aerogel Directional freeze-drying technology and hydrophobic treatment 142° 60−96 -  XPAA/rGO aerogel Vacuum heated - 120 -  a-GPCCA aerogel Directional freeze-drying and carbonization 140° 155−288 15  G/PPy foams Hydrothermal method and vacuum freeze Dried - >100 11  rGO@PU foam Solvothermal method 153° 37 50  G/PU foam - 158° 700 200  LPU-rGO-ODAfoam Dried in air 152° 26−28 20  PEI/GO foam Dried at 60 °C - 17 >3  PDMS/GO sponge Amidation reaction and drying under vacuum 174.1 ± 0.6 ° 14.6 10 
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