# Graphene-Based Functional Hybrid Membranes for Antimicrobial Applications: A Review
## 2 Properties and Synthesis of Graphene
### Synthetic Methods  
The development of high-yield and cheap preparation technology are the basis of the wide application of graphene. Many methods, such as mechanical stripping, epitaxial growth, redox, etc., have been proved to be effective methods of graphene synthesis [33].  
Mechanical stripping is the simplest and most primitive preparation method, which makes independent graphene a reality. In this technique, a piece of graphite is stripped off several times and then transferred to the substrate. The number of layers in graphene can then be assessed using characterization methods such as optical microscope, Raman spectroscopy, atomic force microscope and scanning tunneling microscope. This method can still produce the highest quality crystals, but is limited by the inability to scale-up the process and is, therefore, only suitable for laboratory-scale experiments and prototyping [38]. [PERSON] et al. studied the preparation of graphene by tape exfoliation from the perspective of molecular dynamics [39]. This was achieved by using molecular dynamics force field GraFF to represent the dispersion interaction of graphene. For nanoscale graphene sheets, two different exfoliation mechanisms (mixed-shear and positive-mode exfoliation) were observed, depending on the polymer binder used. The exfoliation method under these two mechanisms facilitates the synthesis of graphene rather than multilayer graphite.  
Epitaxial growth is also a common method for the preparation of graphene. [PERSON] et al. demonstrated the growth of graphene thin films with (5 \(\times\) 50) cm\({}^{2}\) size in 20 min, and the ultra-high grain orientation of the graphene films is more than 99% [40]. The growth is the epitaxial growth in graphene on a meter-scale single crystal copper (111) surface as a template, and the seamless fusion of graphene facilitates the ultrafast growth of graphene films with high single crystallinity. This was achieved through the preparation of single crystal Cu (111) from industrial polycrystalline copper foils by temperature-gradient driven annealing and the wonderful effect of a continuous oxygen supply to adjacent oxides.  
Graphite is chemically oxidized to GO and then reduced, which is a common method for the large-scale production of graphene or rGO. Among the high number of chemical-reducing agents used to prepare rGO, hydrazine (N\({}_{2}\)H\({}_{4}\cdot\)H\({}_{2}\)O) is the most famous, which can provide rGO with better electrical and structural properties [41]. [PERSON] et al. reviewed the chemical reduction in GO by ascorbic acid, which is a non-toxic and cheap organic acid [42]. As hthe obtained rGO has high quality, high productivity, and can produce stable dispersions that are necessary for many applications, chemical reduction has a higher priority than non-chemical reduction. [PERSON] et al. investigated the electrical conductivity of rGO preparation by the reduction in GO using sodium borohydride (NaBH\({}_{4}\)) as function of time (2 min to 24 h) and temperature (20 \({}^{\circ}\)C to 80 \({}^{\circ}\)C) [43]. They used an inexpensive water reduction route that relies on sodium borohydride (NaBH\({}_{4}\)), resulting in the highest conductivity of reduced graphene oxide to date.