Abstract
Coal, as one of the most economic and abundant energy sources, remains the leading fuel for producing electricity worldwide. Yet, burning coal produces more global warming CO2 relative to all other fossil fuels, and it is a major contributor to atmospheric particulate matter known to have a deleterious respiratory and cardiovascular impact in humans, especially in China and India. Here we have discovered that burning coal also produces large quantities of otherwise rare Magnéli phases (TixO2x–1 with 4 ≤ x ≤ 9) from TiO2 minerals naturally present in coal. This provides a new tracer for tracking solid-state emissions worldwide from industrial coal-burning. In its first toxicity testing, we have also shown that nanoscale Magnéli phases have potential toxicity pathways that are not photoactive like TiO2 phases, but instead seem to be biologically active without photostimulation. In the future, these phases should be thoroughly tested for their toxicity in the human lung.
Highlights
Coal, as one of the most economic and abundant energy sources, remains the leading fuel for producing electricity worldwide
Based on HNO3–HClO4–HF digestion followed by inductively coupled plasma mass spectrometer (ICP-MS) analyses of these samples, titanium concentrations are 0.28–0.42 g kg−1, 6.1–6.6 g kg−1, 4.6–5.2 g kg−1, and 4.7–6.1 g kg−1
Compared with diffraction peaks reported in International Centre for Diffraction Data (ICDD) files, as well as transmission electron microscopy (TEM) observations (Supplementary Fig. 4), we found that the dominant phase for converted P25, heated in the presence of coal powder at 900 °C, is the Ti6O11 Magnéli phase, and the dominant phase for coal-annealed P25 at 1100 °C, is the Ti4O7 Magnéli phase
Summary
As one of the most economic and abundant energy sources, remains the leading fuel for producing electricity worldwide. Burning coal produces more global warming CO2 relative to all other fossil fuels, and it is a major contributor to atmospheric particulate matter known to have a deleterious respiratory and cardiovascular impact in humans, especially in China and India. Over the last 50 years, as world coal use continues to increase as one of the most economic, abundant, and utilized fuel sources, in parallel, environmental scientists have been discovering the severe detrimental aspects of this particular energy source. With the development of environmental nanoscience and technology, this is more often no longer the case It is the rise of coal, and the rise of incidental environmental nanoscience, that have come together to create the study presented in this article, that is, the discovery of titania suboxides, Magnéli phases (TixO2x−1), as an incidental nanomaterial consequence of coal combustion. We determined in this study that TixO2x−1 is produced in the coal combustion process from stoichiometric titanium oxide, TiO2, which very commonly occurs as an accessory (minor, by abundance) mineral in many coals with different coal ranks and sources worldwide[11,12,13,14,15,16]
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