Changing interfaces: Photoluminescent ZnO nanoparticle powders in different aqueous environments

Area of Science:

• Materials Science
• Nanotechnology
• Surface Chemistry

Background:

• ZnO nanoparticles synthesized via vapor phase present unique surface properties.
• Transitioning from solid-vacuum to solid-liquid interfaces alters nanoparticle microstructure and properties.
• Understanding these changes is crucial for applications involving ZnO nanoparticles in dispersions.

Purpose of the Study:

• To investigate the spectroscopic property changes of ZnO nanoparticles during the transition from solid-vacuum to solid-liquid interfaces.
• To identify photoluminescence (PL) indicators for early-stage ZnO nanoparticle dissolution.
• To evaluate characterization challenges in assessing nanoparticle properties across different interfaces.

Main Methods:

• Photoluminescence (PL) spectroscopy to probe oxygen interstitials and near-band-edge emissions.
• Fourier Transform Infrared (FT-IR) spectroscopy.
• Dynamic Light Scattering (DLS) for particle size analysis.
• Zeta potential measurements for surface charge characterization.

Main Results:

• Oxygen adsorption affects PL intensity in the gas phase, but O2 contact at the solid-liquid interface does not.
• Near-band-edge emission (3.2 eV) gains relative intensity compared to visible light emissions.
• ZnO nanoparticle dissolution and formation of zinc formate species were tracked via PL, FT-IR, DLS, and zeta potential.
• No specific PL features were found for early-stage dissolution, but overall spectral changes indicated dissolution.

Conclusions:

• The solid-liquid interface significantly influences ZnO nanoparticle spectroscopic properties compared to the solid-vacuum interface.
• PL spectroscopy is sensitive to surface changes but requires complementary methods for robust dissolution tracking.
• Careful consideration of characterization methods and potential pitfalls is essential when assessing nanoparticles in liquid dispersions.