One-pot graphitic encapsulation of Fe7C3 nanoparticles enabling enhanced photothermal performance.

Here, we report a one-pot solvothermal synthesis that enables Fe7C3 nanoparticles (NPs) to direct the in situ formation of conformal graphitic carbon shells under comparatively mild conditions. Comprehensive structural analyses reveal that the resulting Fe7C3@C nanostructures consist of a crystalline carbide core encapsulated within a few-layer graphitic carbon shell, with small γ-Fe2O3 NPs by-products. Systematic variation of reaction parameters shows that both a reducing atmosphere and the Fe7C3 phase are essential for promoting graphitization, while Fe5C2 and Fe3C NPs prepared under analogous solvothermal conditions develop only amorphous carbon shells. This structural feature directly translates into superior photothermal behavior: Fe7C3@C NPs exhibit enhanced photothermal heating under 808 nm irradiation, even after 10 irradiation cycles, and a photothermal conversion efficiency (PCE) exceeding those of other iron carbides and several noble-metal nanostructures. These findings establish Fe7C3 as a uniquely capable phase for promoting in situ carbon ordering and highlight phase-dependent surface chemistry as a powerful tool for designing high-performance photothermal materials.