# Graphene-Based Functional Hybrid Membranes for Antimicrobial Applications: A Review
## 4 Functional Tailoring of Graphene-Based Membranes
### Metals and Metal Oxides  
The doping of graphene films with alkali, transition or noble metals results in increased binding energy [60]. Compared with other nanoparticles, Ag NPs have shown good performance in water purification because they limit the growth of microorganisms such as algae, bacteria and fungi [44]. Silver ions can penetrate cells, destroy cell membranes and inactivate bacteria. In order to improve the anti-biofouling performance of polyvinyl-dene fluoride (PVDF) membranes, [PERSON] et al. synthesized GO-Ag composites as membrane antibacterial agents using a simple and environmentally friendly method [63]. GO-Ag composite films were prepared by phase inversion method using GO-silver composites with different concentrations (0.00-0.15%) as raw materials. Compared with the unmodified PVDF membrane, the hydrophilicity, mechanical properties and permeability of the GO-Ag composite modified membrane were improved. Silver phosphate (AP), as a silver ion (Ag\({}^{+}\)) source, has a higher bactericidal effect than silver nanoparticles in membrane applications. [PERSON] et al. synthesized AP-supported GO quantum dots (GOQDs) multifunctional nanocomposites via a facile electrostatic drive method. Subsequently, GOQDs/APs were intercalated into dense polyamide (PA) layers via interfacial polymerization [64]. The results show that the thin film nanocomposite (TFN)-GOQD/AP membrane has a strong bactericidal performance against _Escherichia coli_, with a sterilization rate of 99.9%, good stability and excellent antifouling performance during reverse osmosis. [PERSON] et al. synthesized rGO-copper (rGOC) nanocomposites by in situ reduction as a novel and efficient biocide [65]. A loose NF membrane was designed using a fast (2 h) biomimetic strategy, in which the rGOC nanocomposite was tightly co-deposited with polydopamine (PDA) on the ultrafiltration support. After the PDA-rGOC-modified membrane was contacted with _Escherichia coli_ for 3 h, the rGOC-functionalized membrane exhibited strong antibacterial properties, reducing the number of viable _Escherichia coli_ bacteria by 97.9%. Combined with the release of Cu ions, the antibacterial activity of GO-functionalized films was enhanced by subsequent ROS-induced oxidative stress in the rGOC composite. The photocatalytic properties of metal oxide-graphene composites have also been exploited for antibacterial applications, and increasing the heterojunction density can improve antibacterial activity due to enhanced absorption in the visible region [5]. Metal oxides can kill bacteria by releasing metal ions and generating ROS upon contact with bacteria. The adhesion of graphene oxide to bacterial membrane surfaces is inherently repulsive, and these studies demonstrate that graphene nanostructures can disrupt bacterial membranes to a degree that depends on their size and composition. [PERSON] et al. prepared a multifunctional thin-film nanocomposite (MTFN) by incorporating a novel nanocomposite-structured rGO@TiO\({}_{2}\)@Ag into the PA active layer [66]. This film has a high desalination performance, dye retention and antimicrobial properties. The special properties of graphene-based nanocomposites synthesized by a microwave-assisted irradiation process facilitate water channelization and provide superhydrophilic and antibacterial properties for MTFN membranes. [PERSON] et al. fabricated GO-based composite films with high antifouling properties using a phase inversion process [67]. Strongly hydrophilic GO and antibacterial copper oxide (Cu\({}_{\text{x}}\)O) were used as nanofillers and blended with PVDF to obtain hybrid membranes with excellent antibacterial properties. Due to the hydrophilic and bactericidal properties of the membrane surface, the composite membrane exhibits excellent antifouling properties, including higher flux recovery, better resistance to accumulated pollutants, and lower filtration resistance, especially lower irreversible resistance.