Persistent free radicals (PFRs) may cause negative impacts to human health and the environment because of the induced reactive oxygen species. We expect that PFRs could be generated in the condensable volatiles formed during lignocellulose biomass pyrolysis. Elucidating the structural origin and the formation mechanism of PFRs is important for an in-depth understanding of air pollutants from the pyrolysis or combustion of lignocellulose biomass. This work selected rice straw and pine sawdust to represent agricultural and forest biomass residues. The pyrolysis mechanism, volatile components, and PFR generation were discussed based on the analysis of thermogravimetry−Fourier transform infrared spectroscopy−mass spectrometry (MS), pyrolysis−gas chromatography/MS, and electron spin resonance (ESR). Levoglucosan, furans, and 2-methoxyphenols were the main pyrolytic compounds for cellulose (CL), hemicellulose (HC), and lignin (LG), respectively. Obvious ESR signals were detected in the condensable volatiles of LG, while no ESR signals were detected for those of CL and HC. Higher ESR signals were detected in lignocellulose with a higher content of LG. Therefore, LG was the main structural basis to generate PFRs in lignocellulose condensable volatiles, mostly attributed to the methoxyphenol components. This study provides useful information regarding the generation mechanisms of and the structures related to PFRs, which is essential to understand the risks of lignocellulose pyrolytic volatiles.
A novel synergic evolution of dynamic assembly, from vesicles to nanotubes, between the metallophosphates and organic amines, is disclosed, by which the multicomponent metallophosphate (Cu(2)(OH)PO(4)) nanotubes are synthesized for the first time.
Persistent free radicals (PFRs) in biochar can influence
biochar
reactivity, promoting organic contaminant degradation or even causing
certain toxic impacts. However, the PFR generation mechanism is not
still well understood. An investigation of the relationship between
PFR formation and the chemical structure of biochar is essential for
understanding the PFR formation mechanism. Our in situ measurement
results showed that PFR intensities increased from 0–509.5
to 146–5678 a.u. after being pyrolyzed at 300 °C for 60
min. The significant positive correlation between PFR intensities
and the peak areas of CO and aromatic CC groups indicated
that the generation of PFRs was highly dependent on the CO
and aromatic CC structures. The reduction of biochars by KBH4 resulted in a 32.2 ± 2.49% decrease in the CO
content and a relative increase in the C–O content, while other
physicochemical properties did not change. Thus, the observed 49.3%
decrease in PFR signals after this reduction suggested that the reducible
CO groups, possibly in aldehydes, aromatic ketones, and quinones,
were closely associated with PFRs in biochars. This study provides
an in situ insight into the PFR generation mechanism and guides the
corresponding biochar design and property manipulation.
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