• Successful production of 2D NbOCl2 nanosheets with controllable size using liquid phase exfoliation and centrifugation-based size selection.
• Nanosheets exhibit high crystalline quality (defect-free) and remarkable stability in isopropyl alcohol due to solvation shell protection.
• NbOCl2 demonstrates a robust photothermal conversion efficiency exceeding 30%, indicating strong photothermal agent performance.
• These findings highlight the material's promising applications in photothermal therapy, thermal energy conversion, and advanced nanophotonics.