Generation Mechanism of Persistent Free Radicals in Lignocellulose-Derived Biochar: Roles of Reducible Carbonyls.

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 C═O and aromatic C═C groups indicated that the generation of PFRs was highly dependent on the C═O and aromatic C═C structures. The reduction of biochars by KBH4 resulted in a 32.2 ± 2.49% decrease in the C═O 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 C═O 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.

Emission factors of environmentally persistent free radicals in PM2.5 from rural residential solid fuels combusted in a traditional stove.

Emission factors (EFs) are crucial for establishing emission inventory and subsequent health risk assessment of pollutants. However, the EFs of environmentally persistent free radicals (EPFRs) in PM2.5 have not been well investigated. We measured EPFRs in PM2.5 from burning of different solid fuels in a traditional stove widely used in rural China and calculated the EFs of EPFRs (EFEPFRs). The characteristics of EPFRs varied greatly with PM2.5 depending on the feedstock, and the EFEPFRs of crop residue, firewood and bitumite was 2.13 ± 1.04, 1.40 ± 0.76 and 1.08 ± 0.39 (1020 spins·kg-1), respectively. The estimated results of EPFRs emission associated with PM2.5 showed that the crop residue was the main contributor to the top four provinces with high EPFRs emissions in China in 2010. A wide range (0.03-4.89 cig·person-1·day-1) of equivalent cigarette number converted by inhaling EPFRs in PM2.5 was observed. Provinces with higher equivalent cigarette number were mainly agricultural provinces, because the rural residents tend to use readily available fuels. Additionally, EPFRs in collected PM2.5 during 2 - month photoaging were more stable in particles with higher organic carbon contents. Our findings provided a new insight into the risk assessment of PM2.5 from different sources by taking EPFRs into consideration.

An integrated study on the pyrolysis mecanism of peanut shell based on the kinetic analysis and solid/gas characterization.

An in-depth understanding of peanut shell pyrolysis reaction is essential for its efficient utilization. Detailed analysis of thermodynamics, kinetics, and reaction products can provide valuable information about pyrolysis reaction. In this work, pyrolytic reaction mechanism was elucidated with the analysis of thermogravimetric-mass spectrometry and the structural characterization of the derived biochar. The thermodynamic and kinetic parameters of three sub-stages were matched well in different model-free methods. The positive ΔH and ΔG values indicated that the pyrolysis reactions for three stages were endothermic and nonspontaneous. The reaction mechanism predicted by integral master-plots were F3 (f(α) = (1-α)3), F1 (f(α) = (1-α), and F3 (f(α) = (1-α)3) for the three sub-stages, respectively. The negative ΔS in the third stage was related to the reduced releasing of low-molecular weight gases and ordered graphite-like carbon structure. This study provides a prospective approach to understand the pyrolysis mechanism of biomass.

Components and Persistent Free Radicals in the Volatiles during Pyrolysis of Lignocellulose Biomass.

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.

Formation of persistent free radicals in biochar derived from rice straw based on a detailed analysis of pyrolysis kinetics.

The presence of persistent free radicals (PFR) in biochars may greatly broaden the application of biochars in pollution control, but may also cause negative impacts to the environment. Understanding the structural basis and the formation mechanisms of PFR is essential for a targeted biochar production and application. This study used rice straw (RS), a ubiquitous agricultural waste, to investigate the generation processes of PFR in relation to RS pyrolysis kinetics. Based on a detailed thermogravimetric (TG) and derivative thermogravimetric (DTG) analysis, the activation energy was calculated by Kissinger-Akahira-Sunose (KAS) and Flynn-Wall-Ozawa (FWO) methods. This work combined pyrolysis kinetics analysis and solid particle characterization. Our results showed that lignin started to pyrolyze at a lower temperature than cellulose and hemicellulose. Lignin was the main factor for PFR generation. Chemical bond breaking contributed only slightly to PFR formation. The reconfiguration of the carbonaceous structures may be a more important contributor to PFR formation, while the cross-linking between different compositions and the interactions between the chemical compositions and inorganic minerals may play a significant role for PFR generation and stabilization in RS. This study provides useful theoretical basis to understand the thermal pyrolysis process of RS and the manipulation of biochar properties.

Inorganic nanotubes formation through the synergic evolution of dynamic templates and metallophosphates: from vesicles to nanotubes.

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.