# 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
Reproduced with permission [116]. Copyright 2021, Wiley-VCH. [PERSON] et al. [119] fabricated bimetallic 2D Co/Zn-porphyrin MOF nanomaterials using a surfactant-assisted method (Figure 5a). SEM and TEM images (Figure 5b,c) depict that Co/Zn-porphyrin displayed wrinkled nanofilm structures. Introducing PVP to Co/Zn with different molar ratios limited the vertical expansion of MOFs and promoted the 2D growth of MOFs, resulting in bimetallic 2D MOF nanomaterials with thicknesses of 4-5 nm (Figure 5d). With the exception of PVP, other surface-active agents, such as CTAB [120], sodium dodecyl sulfate [121], and sorbitol-alkylamine [122], were also used to synthesize 2D MOF nanomaterials. Surfactant-assisted methods have both benefits and drawbacks for 2D MOF nanomaterials. However, surfactant-assisted methods have the advantages of higher yields and producing ultrathin 2D MOF nanosheets compared to template-assisted and interfacial synthesis methods. Although surfactant-assisted methods yield higher quantities of ultrathin 2D MOF nanosheets compared to template-assisted and interfacial synthesis methods, they also confine the metal on the 2D MOF surface with the surfactant. This restricts the surface metal's activity and limits its utility in catalysis. Therefore, researching ways to automatically deactivate and shed the surfactant post-synthesis in the surfactant-assisted synthesis process could be a productive direction. Molecular Modulation-Assisted Synthesis  
The molecular modulation-assisted method refers to the addition of small molecules that are not ligands and can be coordinated with metal centers to regulate the growth of MOFs. [PERSON] et al. [123] synthesized hexagonal nanoplates (HXPS) by coordinating Ni ions with BDC anions and DABCO (DABCO = 1,4-diazabicyclo[2.2.2]octane), where Ni cations and BDC anions coordinated in-plane to build a 2D architecture, and Ni ions and DABCO molecules formed out-of-plane coordination. The added small pyridine molecule replaced part of the DABCO on the crystal surface (Figure 6a). The pyridine, which has  
Figure 5: (**a**) Synthetic process of 2D Co/Zn-porphyrin MOF nanosheets. (**b**) Co/Zn-porphyrin SEM image. (**c**) Co/Zn-porphyrin TEM image. (**d**) Co/Zn-porphyrin AFM image. Reproduced with permission [119]. Copyright 2021, Springer Nature. only one N to coordinate with the Ni ions, inhibited the vertical expansion of the MOF crystals and promoted the formation of a 2D structure with a lateral dimension of 600 to 800 nm (Figure 6b,c) and a thickness of 20 nm (Figure 6d). In addition to pyridine, [124] lauric acid [125] and formic acid [126] can also be employed as molecular regulators to modulate the preparation of MOF nanosheets. For example, lauric acid can modulate the synthesis of MOF crystals by controlling the dispersal rate of organic ligands and metal ions. While molecular modulation-assisted synthesis provides precision in controlling synthetic morphology, it shares a drawback with surfactant-assisted methods--the small molecules that attach to the MOF surface invariably interfere with the activity of the metal. Therefore, optimizing the molecular modulation-assisted synthesis process to allow for the detachment of these molecules during synthesis could present a promising solution. Numerous scientists have, so far, unraveled various synthetic strategies for 2D MOFs, primarily falling into two categories: top-down and bottom-up methods. The top-down exfoliation approach is generally straightforward to implement, but it typically yields low output, and the exertion of irregular forces can result in 2D MOFs with uneven morphologies and uncontrollable thickness. On the other hand, the bottom-up synthesis method allows for control over the morphology and thickness of the synthesized 2D MOFs through the manipulation of growth conditions and reaction environments, thereby improving yield. However, the presence of impurities, such as additives in the reaction, can encapsulate the catalyst surface post-reaction, influencing its performance.