# Two-Dimensional Metal-Organic Frameworks and Their Derivative Electrocatalysts for Water Splitting
## 2 Fabrication Strategy of 2D MOF and Their Derivatives
### Fabrication Strategy of 2D MOF
#### 2.1.2 Bottom-Up Fabrication
Solid-gas interface synthesis encounters limitations due to challenging synthesis conditions and methods. However, the liquid-gas, solid-liquid, and liquid-liquid interface methods have gained significant attention due to their milder synthesis conditions. [PERSON] et al. [115] demonstrated the synthesis of highly conductive 2D MOF films through a liquid-liquid interface reaction, combining the organic ligand benzhexanethiol (BHT) with Au or Ag ions (Figure 4a). The Ag\({}_{3}\)BHT\({}_{2}\) MOF film produced showed excellent conductivity of up to 363 S cm\({}^{-1}\). X-ray diffraction analysis revealed a hexagonal lattice structure in Ag\({}_{3}\)BHT\({}_{2}\), which enables planar conjugation and \(\pi\)-\(\pi\) superposition, contributing to its high conductivity. In contrast, Au\({}_{3}\)BHT\({}_{2}\), with its disordered structure, exhibited nearly insulating properties (Figure 4b,c). The Ag\({}_{3}\)BHT\({}_{2}\) 2D MOF thin film offers promising applications in electronic devices and sensors due to its excellent conductivity and straightforward synthesis method. In 2021, [PERSON] et al. [116] reported the synthesis of 2D Ni-MOF nanosheets through a liquid-liquid interface reaction. By controlling the molar ratio of organic linkers and metal ions in different solvents, they precisely controlled the coordination mode of Ni-MOF nanosheets. This led to highly efficient 2D MOF nanosheets with near-zero overpotential and approximately 98% selectivity for H\({}_{2}\)O\({}_{2}\) when the metal ion/organic ligand concentration was 6. The average thickness of Ni-MOF nanosheets was approximately 5 nm (Figure 4d). Although the liquid-liquid interface synthesis presents an advantage of simple synthesis and controllable product components or morphology, the limited contact interface area between the two-phase solutions restricts its synthesis efficiency. [PERSON] et al. [117] proposed an interfacial synthesis method involving three solvent layers and two pure solvents:--acetonitrile and dimethylformamide (DMF), which are miscible--and a mixed layer of DMF and acetonitrile. BDC ligands in the bottom layer and copper ions in the top layer gradually diffuse into the middle DMF and acetonitrile mixed layer, forming 2D nanosheets with a thickness of approximately 5-25 nm and lateral dimensions of 0.5-4 um. This method mitigates the limited interfacial contact area issue of liquid-liquid interfacial synthesis, but the limited space still presents a constraint, making it less favorable for large-scale applications. Surface-Active Agent-Assisted MethodsSurface-active agent-assisted synthesis methods have proven effective in directing the growth of MOF crystals. In this method, surfactants bind to the surface of MOF crystals, inhibiting their vertical growth and enhancing growth in the 2D direction. For instance, [PERSON] et al. [118] successfully prepared ultra-thin 2D Zn-TCPP (TCPP = tetrakis(4-carboxyphenyl)porphyrin) nanosheets with a thickness of less than 10 nm using a surface-active agent-assisted method. They used polyvinylpyrrolidone (PVP) as a surfactant to limit the expansion of MOF crystals in-plane by adhering to the MOF surface during the synthesis of Zn-TCPP. This resulted in different growth rates of the MOF in different directions. The C=O group in the PVP surfactant strongly interacts with the metal ions in MOF, facilitating PVP's attachment to the MOF's outer layer post-nucleation and restraining its expansion. The scanning transmission electron microscopy (STEM) images show Zn-TCPP nanosheets with an area of approximately 1.2 \(\pm\) 0.4 um, while the high-resolution TEM (HRTEM) image reveals an interplanar distance of 1.64 nm for Zn-TCPP nanosheets. Figure 4: (**a**) Ag\({}_{3}\)BHT\({}_{2}\) thin slice formed via liquid–liquid interfacial approach. (**b**) Thin slice Ag\({}_{3}\)BHT\({}_{2}\) SEM image. (**c**) Thin slice Au\({}_{3}\)BHT\({}_{2}\) SEM image. Reproduced with permission [115] Copyright 2018, American Chemical Society. (**d**) Ni-MOF nanosheets-6 AFM image and the corresponding height profiles.