In-flow optical characterization of flame-generated carbon nanoparticles sampled from a premixed flame

Area of Science:

• Nanoparticle characterization
• Optical physics
• Combustion science

Background:

• Carbon nanoparticles (CNPs) exhibit unique optical properties influenced by their size and formation environment.
• Understanding these properties is crucial for applications in catalysis, energy, and materials science.
• Flame synthesis offers a route to control CNP characteristics.

Purpose of the Study:

• To investigate the optical absorption properties of CNPs synthesized in an ethylene/air flame.
• To determine the spectral absorption coefficient and optical band gap of CNPs at various heights above the burner.
• To evaluate the refractive index absorption function (E(m)) and explore quantum confinement effects.

Main Methods:

• In-flow extinction measurements across a wide spectral range.
• Laser-induced incandescence (LII) measurements at different laser fluences.
• Tauc plot analysis for optical band gap determination.
• Evaluation of E(m) from low laser fluence LII data.

Main Results:

• Absorption coefficient and optical band gap were obtained for CNPs sampled at different flame heights.
• An increase in optical band gap with decreasing height suggests quantum confinement in the flame inception region.
• Laser-induced incandescence revealed distinct particle temperature responses and enabled E(m) evaluation.
• Optical properties, including E(m), showed significant variation with sampling height and excitation wavelength.

Conclusions:

• The study demonstrates a correlation between CNP formation height in a flame and their optical properties.
• Quantum confinement effects influence the optical band gap of nascent CNPs.
• In-flow optical measurements provide valuable insights into the spectral absorption and refractive index of flame-synthesized CNPs.