# Graphene-Based Functional Hybrid Membranes for Antimicrobial Applications: A Review
## 3 Fabrication Techniques of Graphene-Based Membranes
### Layer-by-Layer Self-Assembly  
LBL allows for more precise control of the concentration, the geometry of the film to be deposited, the elasticity of the monolayer, etc., and the surface state. The LBL self-assembly  
Figure 2: (**a**) Schematic diagram of two graphene-based films, including NPG film (left) and GO film (right). (Printed image with permission from Ref. [45], copyright 2021, American Chemistry Society). (**b**) Vacuum filtration method. (Printed image with permission from Ref. [49], copyright 2018, Elsevier Ltd.). (**c**) Coating-assisted assembly. (Printed image with permission from Ref. [52], copyright 2016, Nature Publication). (**d**) Schematic diagram of the procedure for constructing LbL GO framework films. (Printed image with permission from Ref. [50], copyright 2016, Elsevier Ltd.). technique, which can construct multilayer films at the nanoscale, has received increasing attention in the fields of biomimicry, clean energy, and microelectronics [57]. [PERSON] et al. used the LBL self-assembly technique to construct ordered dispersed GO and polymer multilayers, demonstrating an efficient and facile method to improve the quality of proton-exchange membranes. (PU/GO/PDDA/GO)\({}_{200}\) films were prepared by the alternate deposition of polyurethane (PU), positively charged poly(diallyldimethylammonium chloride) PDDA, and negatively charged GO. In addition to electrostatic attraction, intermolecular hydrogen bonding can also drive the completion of the LBL self-assembly process. Furthermore, due to the presence of intermolecular hydrogen bonds, phosphoric acid (PA) molecules are trapped and form PA-doped films. As expected, the (PU/GO/PDDA/GO)\({}_{200}\)/PA membrane showed high and stable proton conductivity, benefiting from the formation of free PA molecular chains and the reduced resistance to proton conduction. The excellent performance of LBL self-assembly technology in terms of proton conductivity, assembly, and mechanical stability provides a new strategy for the application of GO in the field of anhydrous proton-exchange membranes. [PERSON] et al. [58] prepared porous carbon nitride nanosheets (MCU-C\({}_{3}\)N\({}_{4}\)) with excellent photocatalytic properties using the supramolecular polymerization of melamine (C), melamine (M), and urea (U) in dimethyl sulfoxide (DMSO). They used the LBL assembly method for the first time to intercalate MCU-C\({}_{3}\)N\({}_{4}\) and carbon nanotubes (CNTs) into GO on PVDF films, and the CNT/MCU-C\({}_{3}\)N\({}_{4}\)/GO materials were immobilized on the polymer. Three-dimensional heterostructured photocatalytic membranes (PMs) were fabricated on polyelectrolyte (PE)-modified PVDF [58]. Compared with pristine GO film and an MCU-C\({}_{3}\)N\({}_{4}\)/GO film prepared using the same method, the PMs with abundant nanochannels have excellent mechanical strength, good water permeability (14.35 L m\({}^{-2}\) h\({}^{-1}\) bar\({}^{-1}\)) and synergetic removal efficiency of rhodamine B (RhB, 98.31%). In long-term operations, Rhodamine B is extremely harmful to the human body. It can cause acute and chronic poisoning injuries when it is ingested and when it comes into contact with the skin. It can be used as a model pollutant. [PERSON] et al. assembled GO nanosheets with polycations on a polyacrylamidenitte substrate using a LBL self-assembly strategy to form a multilayer film [59]. The migration and rearrangement of PE chains are restricted due to the confinement effect of adjacent GO nanosheets. As a result, the anti-swelling properties of the polycation/GO multilayer films are enhanced, making their properties more stable. Due to the anti-fouling ability of GO nanosheets, the fouling resistance of the multilayer films was also improved. Compared with pure PE multilayers, the separation performance, stability, and fouling resistance of polycation/GO membranes were improved. [PERSON] et al.