Characterization of nano-to-micron sized respirable coal dust: Particle surface alteration and the health impact

Highlights: • Carbon enhancement and oxygen reduction in nano-sized coal particles. • The asymmetric fit of XPS carbon scan for estimating oxygen content is recommended. • Pore volume and surface area dramatically enhance in nano-coal dust. • Weaker wetting behavior could enhance the toxicity in coal dust nanoparticles. Chemical and physical properties of coal dust particles significantly influence the inhalation of respirable coal dust by miners, causing several lung diseases such as coal workers' pneumoconiosis (CWP) and silicosis. Multiple experimental techniques, including proximate/ultimate analyses, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), laser diffraction, and low-pressure CO₂ and N₂ adsorption, were used to investigate the chemical and physical properties of micron-/nano-coal particles comprehensively. Compared to the micron-scale coal dust, the nano-coal dust (prepared by cryogenic ballmill) shows the increase of carbon content and aromaticity and a decrease of oxygen content along with the reduction of oxygen-containing functional groups. Pore volume and surface area estimated by low-pressure CO₂ and N₂ adsorption have more than five-time increase for the nano-coal dust. The reduction of oxygen functional groups suggests the dropped wetting behavior of coal nanoparticles. The significantly increased pore volume and surface area in coal nanoparticles could be caused by the enhanced pore interconnectivity on the particle surface and the alteration of coal macromolecules. Weaker wettability and the highly enhanced surface area suggest potentially more significant toxicity of nano-coal dust inhaled by coal miners.