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Page 10 of 16 Feng et al. Chem Synth 2023;3:37 https://dx.doi.org/10.20517/cs.2023.26

[66]
To solve the above dilemma, the “SLCA” strategy was proposed , which is a universal, controllable, and
suitable method for the preparation of 2D single-layered ordered mesoporous materials on a large scale. The
SLCA uses block copolymers and precursors to assemble on the surface of salt particles in order to form a
single layer micelle bound to the surface of salt particles so as to obtain 2DMMs.

For the first time, the surface of inorganic salt (such as NaCl) particles was used as the substrate for
assembly [Figure 7A]. Combined with the method of vacuum filtration to remove excess precursor liquid,
the interaction between block copolymer guide agent and crown ether on the surface of salt particles and
the synergistic co-assembly between them and precursor molecules/nanocrystals was utilized [Figure 7B]. It
is noteworthy that the flexible polyether PEO segments of structural directing agents can play a role similar
+
+
to crown ethers during the assembly process, complexing with cations (Na , K , etc.) on the surface of
inorganic salt particles and generating strong interactions with the surface of inorganic salt particles,
thereby ensuring that the block copolymers and precursors are orderly assembled on the surface of salt
particles under synthetic conditions, forming a single layer of micelles bound by the surface of salt particles.
The controllable synthesis of 2D mesoporous carbon, silica, and metal oxides (TiO , CeO , Al O , ZrO ,
2
2
2
2
3
Ce Zr O , ZrTiO , etc.) was realized [Figure 7C-I]. The salt solution recovered from washing can be
0.5
0.5
4
2
recycled by recrystallization, and the amplified synthesis can be achieved by passing through the column
[Figure 7J]. The resulting monolayer mesoporous materials (SOMMs) have the advantages of rapid mass
transfer, short mass diffusion distance, highly accessible surfaces, and fully exposed active sites, which make
their performance better than conventional bulk mesoporous materials.
Due to the diverse accessible surfactants and precursors, this SLCA method provides new possibilities for
the designed synthesis of various kinds of 2DMMs , including the application of multi-component metal
[67]
oxides, metal sulfides, and carbide nanosheets.
TEMPLATE-FREE METHOD
The template-free method is a simple and general method for preparing 2DMMs without the use of 2D and
mesoporous structural guiding agents [68-71] . The 2D framework is spontaneously formed through self-
assembly, ion/molecular intercalation, calcination, or gas induced detachment, together with mesoporous
cavities generated by the precursor decomposition, gas release, structural defects, and nanoparticle
aggregation.

For instance, Hu et al. reported a template-free synthesis strategy for the preparation of highly crystalline
[72]
2D mesoporous transition metal oxide nanosheets with abundant surface defects . The method is based on
the crystal-crystal transition to convert the highly crystallized basic carbonate 2D nanosheets into the highly
crystallized transition metal oxide 2D nanosheets at low temperatures. During the thermal transition
process, due to the removal of small molecules (carbon dioxides and water molecules), a double-through
mesoporous structure is generated in situ, which results in highly crystallized 2D mesoporous transition
metal oxides with regular morphology. The method is simple and universal and can realize the controllable
preparation of a variety of high crystalline mesoporous transition metal oxides. Moreover, different from
the conventional crystalline mesoporous metal oxides, the mesoporous transition metal oxides obtained by
this method have abundant surface-step defects.

[73]
Recently, Kaneti et al. synthesized 2D mesoporous mixed oxide nanosheets by a template-free method .
The simple long-term reaction of metal glyceric acid nanospheres in water at room temperature resulted in
the gradual decomposition of organic groups in the glyceric acid nanospheres, which were subsequently
replaced by hydroxyl nanosheets and self-deconstructed/reconstructed into 2D Co glyceric acid/hydroxide