Synthesis of Two-Dimensional Plasmonic Molybdenum Oxide Nanomaterials by Femtosecond Laser Irradiation

Abstract

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 (H X MoO3), 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 H3 + 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 H3 + 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.

Molybdenum Blues with Tunable Light Absorption Synthesized by Femtosecond Laser Irradiation of Molybdenum Trioxide in Water/Ethanol Mixtures

“…[34,46] When the concentration of ethanol is 90%, the MoO 3-X peaks become dominant in the Raman spectrum, consistent with our previous work that 80-90% ethanol is optimum to prepare MoO 3-X from MoS 2 via femtosecond laser irradiation. [34] In the 100% ethanol sample, almost all the Raman peaks belong to MoO 3 . The photo luminescence excitation and emission spectra of the MBs synthesized in 1% and 30% ethanol solvents were also investigated.…”

“…[32,33] Our previous work also successfully synthesized MoO 3-X nanosheets by irradiating MoS 2 suspended in ethanol/water solvents using a femtosecond laser system. [34] When a femtosecond laser pulse interacts with materials, the high electric field of the laser pulse strips electrons from bulk materials, then the bulk materials are dissociated due to mutual repulsion of the photoionized molecular species. The nanoparticles are formed via nucleation and coalescence of the reactive ionized species.…”

Oxygen deficient α-MoO3 with enhanced adsorption and state-quenching of H2O for gas sensing: a DFT study

“…Our calculation results may explain previous experimental results where light absorption and LSPR effects are significantly promoted by the introduction of V O for photo-thermal synergistic catalytic and photothermal therapy. 53–55 As shown in the schematic diagrams in Fig. 7c and d, the perfect-MoO 3 and MoO 3 –H 2 O only absorb UV light through excitations from the VBM to CBM.…”

Controlled local orientation of 2D nanomaterials in 3D devices: methods and prospects for multifunctional designs and enhanced performance

“…[186][187][188] Thanks to the recent development of a diverse range of lasers, laser irradiation as a method to process nanomaterials is blooming. [189][190][191] Different from most conventional material processing techniques, laser irradiation imparts rapid heat and localized high energy to materials, allowing precise control over the material microstructures. 188 Park et al reported the fabrication method of L-shaped graphene nanostructures with a vertical alignment and reduced defect level through laser irradiation.…”