MXenes, a class of two-legged transition metal carbides or nitrides, have emerged as highly promising multifunctional platforms for electrochemical energy storage and nanofluidic technologies thanks to their tunable surface composition and diverse intercalation chemistry.

Although ion intercalation in aqueous or organic media has been widely used to regulate the interlayer structure and electronic states of MXenes, the selection of compatible intercalated species currently relies largely on empirical trial and error. To date, a widely accepted theoretical framework for quantitatively evaluating the feasibility of guest molecules entering the MXene host structure has yet to be established.

In response to this challenge, the research team led by Professor Que Wenxiu from the Ministry of Education Key Laboratory of Electronic Ceramics and Devices, School of Electronic Science and Engineering at Xi'an Jiaotong University (XJTU), and the Shaanxi Provincial Engineering Research Center of Advanced Energy Storage Electronic Materials and Devices, published a research article in the journal Advanced Materials. Titled Spatial-Compatibility-Assisted Molecular Intercalation in MXenes, the study proposes a universal steric-compatibility criterion.

According to this criterion, when the effective 3D size of the intercalating molecule is comparable to or smaller than the interlayer spacing (Δd) formed after the removal of the Al element in the parent MAX phase, the intercalation process is geometrically feasible.

Based on this principle, a series of small molecules possessing spatial size compatibility can be screened, effectively rationalizing their intercalation and etching behaviors. Guided by this geometric size-matching principle, the authors successfully synthesized a variety of multilayer MXene materials, including typical 2D transition metal carbide systems such as Ti₃C₂Tₓ, Mo₂TiC₂Tₓ, V₂CTₓ, V₄C₃Tx, Nb₂CTx, and Nb₄C₃Tx, demonstrating the broad universality of this method across different MXene families.

Furthermore, the resulting multilayer Ti₃C₂Tx MXene can be effectively exfoliated into few-layer MXene nanosheets through simple ultrasonication. This indicates that the strategy can simultaneously improve interlayer exfoliation during material preparation, paving the way for the subsequent construction of high-performance 2D material devices.