MXene Sheet Size as a Synthesis-encoded Variable: A Critical Review of Processing–Structure–Property Relationships

Abstract

MXenes are solution-processable two-dimensional carbides and nitrides whose macroscopic performance is often attributed to composition and surface terminations, while the lateral dimensions of individual sheets are treated as a secondary processing detail. This review critically examines the more consequential interpretation that sheet size is a synthesis-encoded structural variable, jointly determined with thickness, edge density, basal-plane defects, oxidation state, intercalants, surface terminations and assembly history. Literature published from the emergence of MXenes in 2011 to 30 May 2026 was selected through transparent searches of accessible scholarly indexes, DOI records, institutional repositories and citation networks. The evidence is strongest for Ti₃C₂Tₓ and shows a recurrent trade-off. Larger, less damaged sheets usually reduce interflake junctions, support liquid-crystalline alignment, increase film conductivity and mechanical integrity, and improve dimensional stability in electromagnetic and electrochemical devices. Smaller sheets provide more edge sites, shorter diffusion distances, greater colloidal accessibility and, in some contexts, stronger photothermal or interfacial activity. These tendencies are not universal because the synthesis routes used to change size simultaneously alter termination chemistry, defect density, oxidation, layer number, ionic residues and film packing. Consequently, many published comparisons cannot isolate a true causal size effect. Hydrofluoric-acid and in situ fluoride etching, electrochemical and hydrothermal routes, Lewis-acid molten-salt chemistry, delamination intensity and post-synthetic fractionation each generate distinctive bundles of structural attributes rather than size alone. A process–structure–assembly–property framework is therefore proposed in which size distributions, rather than single mean values, are interpreted alongside chemistry and orientation. The field now requires matched-batch experiments, harmonised metrology, distribution-aware reporting and application-specific optimisation. Controlling sheet size is not a universal route to ‘better’ MXenes; it is a means of selecting the balance among transport, reactivity, stability and manufacturability required by a particular device architecture.