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Feng et al. Chem Synth 2023;3:37 https://dx.doi.org/10.20517/cs.2023.26 Page 3 of 16

structures. Moreover, this approach suffers from complex procedures, low yield, and poor controllability,
which limits its application performance [27,28] . On the contrary, bottom-up strategies have high versatility,
generally do not require complex operation steps, and provide a pathway to obtain a large number of hybrid
and composite materials from inorganic, organic, and even biological starting components [29,30] . Especially, a
series of 2DMMs with controllable structures, compositions, and morphology have been constructed at the
nanoscale or even molecular level by combining the “bottom-up” synthesis concept with a self-assembly
strategy.

In the following section, we have systematically summarized the synthesis work of 2DMMs in recent years;
according to different self-assembly synthesis processes, the synthesis methods of 2DMMs are classified into
five classes: molecular self-assembly methods, single micelle assembly methods, multi templates methods,
surface-limited co-assembly (SLCA) methods, and template free methods.

MOLECULAR SELF-ASSEMBLY METHOD
It is well known that molecular self-assembly exists widely in nature and living systems. Based on the
assembly principle of amphiphilic molecules, various novel functional nanostructured materials, especially
ordered mesoporous materials, can be designed and created. This material possesses high surface areas,
regular arrangement, and uniform nanopores and exhibits broad application prospects in catalysis,
separation, energy, and other fields [31,32] . Due to their unique nanoscale effect, mesoporous materials exhibit
excellent properties, such as unique surface acidity, high electronic mobility, and improved coordination
catalysis abilities. In addition, these mesoporous materials possess high porosity, which is conducive to the
loading and diffusion of ions, molecules, and even nanoparticles within the porous structure, providing rich
interfaces and active sites for a variety of applications [33,34] .

Molecular self-assembly is an effective method for directly preparing structurally precise nanomaterials and
molecular scale materials. Due to its advantages of controllable preparation, precise thickness control, and
easy removal of templates without residue, this method provides an ideal platform for the construction of
complex and layered 2D structures, such as mesoporous nanosheets . The key issue of the molecular self-
[35]
assembly method is to establish an interface that allows the micelles to self-assemble in two dimensions;
diverse interfacial scales exhibit various characteristics in the directional interfacial assembly of 2DMMs,
resembling the classical chemical vapor deposition synthesis of graphene on metal catalysts. The gas-liquid,
liquid-liquid, and solid-liquid two-phase interfaces provide infinite space for the 2D growth process [36-38] .

For instance, Zu et al. reported a novel layered phase separation behavior using amphiphilic block
copolymers [polystyrene b polyethylene oxide (PS-b-PEO)] to form stable terminated layered micelles (i.e.,
nanoconfined self-assembly strategies) with precursors in a layered colloidal confined nanospace
[39]
[Figure 1]. The fabrication of ordered mesoporous iridium (Ir)-IrO /C catalysts by nano-limited self-
x
assembly has mainly undergone three stages: Firstly, tetrahydrofuran (THF) is preferentially volatilized at
40 °C, causing liquid-liquid microphase separation of different components (step 1); Then, amphiphilic
block copolymer PS-b-PEO was assembled with an iridium precursor and acetylacetone (acac) to form an
organic-inorganic layered composite micelle. The residual THF and water were continuously evaporated at
3+
100 °C to obtain an organic-inorganic PS-b-PEO/Ir hybrid layered composite (step 2). After slowly
calcining the hybrid layered composite under argon atmosphere at 450 °C, an ordered mesoporous
Ir-IrO /C layered catalyst (step 3) was formed in situ. A series of 2D Ir-based catalysts with highly ordered
x
interlayer channels (~20 nm), high specific surface areas, and uniform distributions of Ir-based
nanoparticles (~2 nm) were synthesized.