# Graphene-Based Functional Hybrid Membranes for Antimicrobial Applications: A Review
## 4 Functional Tailoring of Graphene-Based Membranes
### Polymers  
Graphene can be coupled with a variety of polymers to form membrane materials [68, 69, 70, 71]. By optimizing the properties of graphene and polymers and the way of conjugation, the physical and chemical properties of graphene composite membranes can be optimized. [PERSON] et al. prepared covalently cross-linked GO membranes using a facile vacuum filtration method, and cross-linked tannic acid-functionalized GO (TA-GO) and hyperbranched polyethyleneimine (PEI) [72]. The cross-linked GO membrane exhibits good dimensional stability and ion separation performance. TA-containing cross-linked GO films exhibited excellent antibacterial activity against _Escherichia coli_ due to the inherent bactericidal properties of the TA moiety. [PERSON] et al. prepared covalently cross-linked GO membranes by vacuum-assisted filtration self-assembly after the functionalization of dopamine (GO-PDA) and branched polyethyleneimine (GO-PDA-PEI) [73]. Compared with GO and GO-PDA, the GO-PDA-PEI film exhibited extraordinary stability. Notably, Graphene oxide exhibits excellent photothermal properties under 795 nm near-infrared laser irradiation. Under 795 nm near-infrared (NIR) laser irradiation, the GO-PDA-PEI membrane exhibited excellent antibacterial properties against both Gram-positive _Staphylococcus aureus_ and Gram-negative _Escherichia coli_, with an antibacterial efficiency of over 99%.  
[PERSON] et al. developed a facile method to graft biocidal GO onto chemically inactive membrane materials using benzophenone as an anchor [74]. The GO nanosheets undergo an amide coupling reaction and are functionalized with benzophenone. Then, the functionalized GO nanosheets were grafted onto the inert membrane surface via benzophenone-induced cross-linking, which was irreversible under UV irradiation (Figure 3a). When exposed to model bacteria (_Escherichia coli_), the GO-functionalized PVDF and polysulfone membranes exhibited robust antibacterial activity, reducing the number of viable cells by 90% and 75%, respectively, compared to the pristine membrane. [PERSON] et al. prepared a bilayer polymer membrane with blood compatibility and antibacterial properties by coating a GO and sulfonated polyanion co-doped hydrogel film (GO-SPHF) on the underlying membrane substrate [75]. The double-layer membrane showed strong antibacterial ability, and had an excellent bactericidal ability for both _E. coli_ and _S. aureus_. [PERSON] et al. developed an ultrafiltration PES membrane with dual antifouling and antibacterial properties (Figure 3b) [76]. First, the ampholyte hydrogel was UV-grafted onto the PES membrane surface (p-PES membrane). Then, the hydrogel was loaded into GO nanosheets using a vacuum filtration strategy (GO-p-PES membrane). Static adsorption and dynamic filtration experiments showed that p-PES membranes had similar organic fouling propensities to GO-p-PES membranes. Furthermore, the GO loading induced the antibacterial properties of the membrane, as demonstrated by contact kill and antibiotic fouling filtration experiments.