Supercritical CO₂‐Induced Amorphization in 2D Materials: Mechanism and Applications

Abstract

Supercritical carbon dioxide (SC CO2)‐assisted chemical and material processing has shown great success in the fabrication of 2D amorphous materials, while the amorphization mechanism in SC CO2 is quite complicated to be understand. In this review, we introduce different kinds of 2D amorphous materials prepared with SC CO2 and discuss the possible amorphization mechanism and how they affect the structures and properties of 2D materials. Their applications are further presented and discussed. In addition, the prospective of future development of SC CO2‐assisted fabrication of 2D amorphous materials is also involved. The investigation of SC CO2 induced amorphization not only provides theoretic understanding of amorphization process, but also directs to the preparation and application of 2D amorphous materials with specific structure and property, suggesting the promising future of SC CO2‐assisted process in material design and engineering.

Adsorption of fluorine from lepidolite hydrometallurgy wastewater by aluminum modified zeolite

“…The SAED pattern shows two different diffraction rings, indicating that the selected area of Al@zeolite is amorphous structure. Due to the stronger adsorption capacity of amorphous materials (Ge et al, 2023), the amorphous structure formed by Al@zeolite is bene cial to the removal of uoride ions.…”

Emerging Amorphized Metastable Structures to Break Limitations of 2D Materials for More Promising Electrocatalysis

“…It is also suggested that the thinner 2D metastable material is more suited to being stabilized compared to thicker ones (γ f/s and γ el are all minimized in eq ). With these principles, the stabilization of metastable structure with a “surfactant” layer has been demonstrated in many cases. − For example, in the supercritical fluid system, the surface energy of the fluid can be sensitively regulated in a broad region (an example of the plot of the surface energy close to the critical condition can be found in ref ), allowing the formation and stabilization of some metastable phases and amorphous surfaces. − …”

“…Direct fabrications of 2D HA metastable materials have rarely been reported. In contrast, in traditional materials, the creation of HA metastable surface was well established, which can be classified as the in situ growth (e.g., size confined, , high pressure/high temperature condition, epitaxial growth, solvent mediation, − , and their combinations), intermediate solidification, − and post-treatment (e.g., electrochemical process, high-temperature surface redox reaction, , cold H 2 plasma reduction, Joule heating, surface etching, and ion exchange ,,,− ) (Figure ). We now focus on these techniques, aiming to guide potential strategies for the fabrication of 2D HA metastable materials.…”

“…For instance, a diagram depicting the surface energy of pure H 2 O illustrates that surface energy levels below 150 mJ m –2 are achievable only under critical conditions, albeit with sensitive regulation . The CO 2 supercritical fluid presents a different scenario, as it has demonstrated success in fabricating certain 2D metastable phases. − Du et al demonstrated that amorphous surface of 2D carbon nitride can be created with this technique . Nevertheless, the fabricated 2D material was still not thin enough (suggested by the X-ray diffraction analysis), where the amorphous surface may be stabilized by additional layers with lower surface energies (see eq and eq described above), which is the same to the metastable materials fabricated with the solvothermal technique .…”

“…Some techniques are more suited for the amorphization (e.g., ion etching through CVD), while others are more suited for the stabilization of metastable structures (e.g., solvent mediation with ionic liquid). − Direct fabrication of 2D HA metastable materials, particularly ultrathin structures, with the above techniques is highly challenging. The main reason is the high surface energy of the 2D HA metastable material, which may be formed in critical conditions and treatments (e.g., the CO 2 supercritical fluid, − high pressure/high temperature, and ion etching through CVD), but must be relaxed or stabilized to a more stable structure under ambient conditions. Therefore, aside from developing more feasible approaches for amorphization and stabilization, their combinations are suggested for fabricating 2D HA metastable materials.…”