Synthesis Of Two-Dimensional Plasmonic Molybdenum Oxide Nanomaterials By Femtosecond Laser Irradiation

A novel process to synthesize plasmonic MoO3-x nanosheets is demonstrated, in which MoS2 powders suspended in ethanol/water are irradiated with pulses from a femtosecond laser, resulting in simultaneous Coulomb explosion, photoexfoliation, and oxidation. The oxidation process is found to start with the formation of hydrogen-bonded molybdenum oxide (HxMoO3), followed by the release of -OH2 groups to create oxygen vacancies, and finally, MoO3-x is oxidized to MoO3 after extended irradiation. The formation of H x MoO3 is the critical step to create enough oxygen vacancies for localized surface plasmon resonance (LSPR), and this step is attributed to H-3(+) dissociated from ethanol under femtosecond laser irradiation. It is found that 80-90% ethanol is the optimal concentration to synthesize plasmonic MoO3-x, where the balance of water facilitates the release of the -OH2 groups to create the required vacancies. It is shown that different organic solvents like methanol, 1-propanol, and isopropyl alcohol that were reported to generate large amounts of H-3(+) under femtosecond laser irradiation can also oxidize MoS2 into plasmonic MoO3-x. The LSPR properties of the synthesized MoO3-x are evaluated by UV-vis spectroscopy and photothermal conversion measurements. A photothermal conversion efficiency of 33% is observed under near-infrared irradiation, suggesting a potential application in photothermal cancer therapy.