Transition metal iron and persistent free radicals(PFRs)both affect the redox properties of biochar,but the electron transfer relationship between them and the coupling reduction mechanism of Cr(Ⅵ)requires further in...Transition metal iron and persistent free radicals(PFRs)both affect the redox properties of biochar,but the electron transfer relationship between them and the coupling reduction mechanism of Cr(Ⅵ)requires further investigation.To untangle the interplay between iron and PFRs in biochar and the infuences on redox properties,FeCl_(3)-modified rice husk biochar(FBCs)was prepared and its reduction mechanism for Cr(Ⅵ)without light was evaluated.The FBCs had higher surface positive charges,oxygen-containing functional groups,and PFRs compared with pristine rice husk biochar(BC).Phenoxyl PFRs with high electrondonating capability formed in biochar.The pronounced electron paramagnetic resonance signals showed that the PFRs preferred to form at lower Fe(Ⅲ)concentrations.While a high concentration of Fe(Ⅲ)would be reduced to Fe(Ⅱ)and consumed the formed PFRs.Adsorption kinetics and X-ray photoelectron spectroscopy analysis indicated that the FBCs effectively enhanced the Cr(Ⅵ)removal efficiency by 1.54-8.20 fold and the Cr(Ⅵ)reduction efficiency by 1.88-9.29 fold compared to those of BC.PFRs quenching and competitive reductant addition experiments revealed that the higher Cr(Ⅵ)reduction performance of FBCs was mainly attributed to the formed PFRs,which could contribute to~74.0%of Cr(Ⅵ)reduction by direct or indirect electron transfer.The PFRs on FBCs surfaces could promote the Fe(Ⅲ)/Fe(Ⅱ)cycle through single electron transfer and synergistically accelerate~52.3%of Cr(Ⅵ)reduction.This study provides an improved understanding of the reduction mechanism of iron-modified biochar PFRs on Cr(Ⅵ)in environments.展开更多
In addition to the adsorption and immobilization capacities of iron-modified biochars,these materials produce persistent free radicals(PFRs)that can carry out metal[i.e.,Cr(VI)]redox transformations,but the primary fo...In addition to the adsorption and immobilization capacities of iron-modified biochars,these materials produce persistent free radicals(PFRs)that can carry out metal[i.e.,Cr(VI)]redox transformations,but the primary forms and active species of PFRs involved are not well understood.Here,we investigated the key species of PFRs ofα-Fe2O3-modified biochar(MBC)and their influence on Cr(VI)reduction under anaerobic conditions simulating paddy soil environments.MBC produced bulk phenoxyl PFRs that promoted Cr(VI)reduction due to the catalytic effect of the transition metal Fe.In addition,MBC was more efficient in reducing Cr(VI)under anaerobic conditions than under aerobic conditions due to the more active and accessible dissolved PFRs present in the dissolved organic matter(DOM).The electron transfer capacity of DOM was demonstrated by excitation-emission matrix(EEM)spectrophotometry combined with parallel factor analysis,which showed that the protein-like and humic-like components of DOM were involved in Cr(VI)reduction.Furthermore,Fourier transform ion cyclotron resonance mass spectrometry(FTICR-MS)analysis indicated that reduced-S compounds(O/S<4)and carboxylic acid(-COO)groups in the unsaturated aliphatic and lignin-like compounds are potentially the main active species accelerating Cr(VI)reduction under anaerobic conditions.Our results provide new insights into the role of dissolved PFRs from iron-modified biochar in promoting Cr(VI)reduction under anaerobic conditions such as flooded soils.展开更多
基金supported by the National Key Research and Development Program of China (No.2020YFC1808500)the National Natural Science Foundation of China (Nos.42107046 and 41907119)+2 种基金the GDAS’Project of Science and Technology Development (Nos.2022GDASZH-2022010105,and 2019GDASYL-0102002-5)the Postdoctoral Science Foundation of China (No.2020M682634)the Guangdong Basic and Applied Basic Research Foundation (No.2021A1515011540)。
文摘Transition metal iron and persistent free radicals(PFRs)both affect the redox properties of biochar,but the electron transfer relationship between them and the coupling reduction mechanism of Cr(Ⅵ)requires further investigation.To untangle the interplay between iron and PFRs in biochar and the infuences on redox properties,FeCl_(3)-modified rice husk biochar(FBCs)was prepared and its reduction mechanism for Cr(Ⅵ)without light was evaluated.The FBCs had higher surface positive charges,oxygen-containing functional groups,and PFRs compared with pristine rice husk biochar(BC).Phenoxyl PFRs with high electrondonating capability formed in biochar.The pronounced electron paramagnetic resonance signals showed that the PFRs preferred to form at lower Fe(Ⅲ)concentrations.While a high concentration of Fe(Ⅲ)would be reduced to Fe(Ⅱ)and consumed the formed PFRs.Adsorption kinetics and X-ray photoelectron spectroscopy analysis indicated that the FBCs effectively enhanced the Cr(Ⅵ)removal efficiency by 1.54-8.20 fold and the Cr(Ⅵ)reduction efficiency by 1.88-9.29 fold compared to those of BC.PFRs quenching and competitive reductant addition experiments revealed that the higher Cr(Ⅵ)reduction performance of FBCs was mainly attributed to the formed PFRs,which could contribute to~74.0%of Cr(Ⅵ)reduction by direct or indirect electron transfer.The PFRs on FBCs surfaces could promote the Fe(Ⅲ)/Fe(Ⅱ)cycle through single electron transfer and synergistically accelerate~52.3%of Cr(Ⅵ)reduction.This study provides an improved understanding of the reduction mechanism of iron-modified biochar PFRs on Cr(Ⅵ)in environments.
基金supported by the National Natural Science Foundation of China(42025705 and 42107046)the GDAS’Project of Science and Technology Development(2022GDASZH-2022010105 and 2020GDASYL-202001102019)the Guangdong Basic and Applied Basic Research Foundation(2021A1515011540).
文摘In addition to the adsorption and immobilization capacities of iron-modified biochars,these materials produce persistent free radicals(PFRs)that can carry out metal[i.e.,Cr(VI)]redox transformations,but the primary forms and active species of PFRs involved are not well understood.Here,we investigated the key species of PFRs ofα-Fe2O3-modified biochar(MBC)and their influence on Cr(VI)reduction under anaerobic conditions simulating paddy soil environments.MBC produced bulk phenoxyl PFRs that promoted Cr(VI)reduction due to the catalytic effect of the transition metal Fe.In addition,MBC was more efficient in reducing Cr(VI)under anaerobic conditions than under aerobic conditions due to the more active and accessible dissolved PFRs present in the dissolved organic matter(DOM).The electron transfer capacity of DOM was demonstrated by excitation-emission matrix(EEM)spectrophotometry combined with parallel factor analysis,which showed that the protein-like and humic-like components of DOM were involved in Cr(VI)reduction.Furthermore,Fourier transform ion cyclotron resonance mass spectrometry(FTICR-MS)analysis indicated that reduced-S compounds(O/S<4)and carboxylic acid(-COO)groups in the unsaturated aliphatic and lignin-like compounds are potentially the main active species accelerating Cr(VI)reduction under anaerobic conditions.Our results provide new insights into the role of dissolved PFRs from iron-modified biochar in promoting Cr(VI)reduction under anaerobic conditions such as flooded soils.
