Multi-walled carbon nanotubes: sampling criteria and aerosol characterization

Area of Science:

• Occupational Health and Safety
• Nanomaterial Characterization
• Aerosol Science

Background:

• Multi-walled carbon nanotubes (MWCNTs) are increasingly used, necessitating robust methods for assessing workplace exposure.
• Complex MWCNT aerosols, containing soot and catalysts, pose challenges for accurate characterization.
• Existing sampling and characterization protocols may not fully address the complexities of MWCNT aerosols.

Purpose of the Study:

• To develop and validate protocols for sampling and characterizing multi-walled carbon nanotube (MWCNT) aerosols.
• To establish reliable methods for assessing MWCNT particle size, concentration, and morphology in exposure settings.
• To provide guidance for designing inhalation studies and workplace monitoring of MWCNT aerosols.

Main Methods:

• Aerosols were generated using an acoustical generator from a dry powder mixture of MWCNTs, soot, and metal catalysts.
• Sampling was performed using filters and a cascade impactor within an exposure chamber.
• Microscopic (particle counting, sizing) and gravimetric analyses were employed for characterization.

Main Results:

• Filter sampling density of 0.008-0.10 particles/µm² was found adequate for particle analysis.
• Resuspended MWCNT aerosols (10 mg/m³) contained 2.7 × 10⁴ particles/cm³, with an average of 18 nanotubes per particle.
• Mass median aerodynamic diameter was 1.5 µm; mean effective density of isometric particles ranged from 0.71-0.88 g/cm³; nanotube shape factor was 1.94-2.71.

Conclusions:

• The developed protocols provide a reliable framework for sampling and characterizing MWCNT aerosols.
• The findings are applicable to designing animal inhalation exposure studies and workplace safety assessments.
• This measurement scheme is relevant for characterizing any carbon nanotube aerosol, ensuring worker safety and research integrity.