Decontamination of Cr(Ⅵ) from water using sewage sludge-derived biochar: Role of environmentally persistent free radicals

Biochar is a well-known material for pollutant removal owing to its low cost and rich surface functionality. A kind of highly active substance, called environmentally persistent free radicals(EPFRs), can be produced in the preparation process of biochar, playing an important role in the removal of pollutants.In this study, sludge-derived biochars(SBC_(120) and SBC_(270)) were prepared by the hydrothermal carbonization under two temperatures(120℃ and 270℃) to investigate their removal abilities of Cr(Ⅵ). The maximum removal amounts of Cr(Ⅵ) by SBC_(120) and SBC_(270) were 16.58 and 22.93 mg·g^(-1), respectively. It was further revealed that the appearance of Cr(Ⅲ), as a result of EPFRs on sludge-derived biochar(SBC) transferred electrons to Cr(Ⅵ) in neutral solutions. That is to say, oxygen-centered(O-centered) EPFRs on SBC_(120) and carbon-centered(C-centered) EPFRs on SBC_(270) all could be used as electron donors to Cr(Ⅵ) to make it become Cr(Ⅲ). This study not only provides a theoretical basis for the mechanism of pollutants removal by sludge-derived biochar but also offers a new perspective on the direct effect of EPFRs on pollutants.

Light-induced variation in environmentally persistent free radicals and the generation of reactive radical species in humic substances

Environmentally persistent free radicals(EPFRs)in humic substances play an essential role in soil geochemical processes.Light is known to induce EPFRs formation for dissolved organic matter in aquatic environments;however,the impacts of light irradiation on the variation of EPFRs in soil humic substances remain unclear.In this study,humic acid,fulvic acid,and humin were extracted from peat soil and then in situ irradiated using simulated sunlight.Electron paramagnetic resonance spectroscopy results showed that with the increasing irradiation time,the spin densities and g-factors of humic substances rapidly increased during the initial 20 min and then gradually reached a plateau.After irradiation for 2h,the maximum spin density levels were up to 1.63×10^17,2.06×10^17,and 1.77×10^×10^17 spins/g for the humic acid,fulvic acid,and humin,respectively.And the superoxide radicals increased to 1.05×10^l4-1.46×10^14spins/g while the alkyl radicals increased to 0.47×10^14-1.76×10^14 spins/g.The light-induced EPFRs were relatively unstable and readily returned back to their original state under dark and oxic conditions.Significant positive correlations were observed between the concentrations of EPFRs and reactive radical species(R2=0.65-0.98,/?<0.05),which suggested that the newly produced EPFRs contributed to the formation of reactive radical species.Our findings indicate that under the irradiation humic substances are likely to be more toxic and reactive in soil due to the formation of EPFRs.

Environmentally persistent free radicals in PM_(2.5):a review

Environmentally persistent free radicals(EPFRs)are a new class of pollutants that are long-lived in fine particles(PM_(2.5)),i.e.,their 1/e lifetime ranges from days to months(or even infinite).They are capable of producing harmful reactive oxygen species such as hydroxyl radicals.The redox cycling of EPFRs is considered as an important pathway for PM_(2.5) to induce oxidative stress inside the humans,causing adverse health effects such as respiratory and cardiovascular diseases.Conse-quently,research regarding their toxicity,formation and environmental occurrences in PM_(2.5) has attracted increasing atten-tions globally during the past two decades.However,literature data in this field remain quite limited and discrete.Hence,an extensive review is urgently needed to summarize the current understanding of this topic.In this work,we systematically reviewed the analytical methods and environmental occurrences,e.g.,types,concentrations,and decay behaviors,as well as possible sources of EPFRs in PM_(2.5).The types of pretreatment methods,g-values of common EPFRs and categories of decay processes were discussed in detail.Moreover,great efforts were made to revisit the original data of the published works of EPFRs in airborne particulate matter and provided additional useful information for comparison where possible,e.g.,their mean and standard deviation of g-values,line widths(ΔHp-p),and concentrations.Finally,possible research opportunities were highlighted to further advance our knowledge of this emerging issue.

大气细颗粒物中环境持久性自由基的分子特征与形成机理的研究

Aerosol-bound organic radicals,including environmentally persistent free radicals(EPFRs),are key components that affect climate,air quality,and human health.While putative structures have been proposed,the molecular characteristics of EPFRs remain unknown.Here,we report a surrogate method to characterize EPFRs in real ambient samples using mass spectrometry.The method identifies chemically relevant oxygenated polycyclic aromatic hydrocarbons(OxPAH)that interconvert with oxygen-centered EPFR(OC-EPFR).We found OxPAH compounds most relevant to OC-EPFRs are structurally rich and diverse quinones,whose diversity is strongly associated with OC-EPFR levels.Both atmospheric oxidation and combustion contributed to OC-EPFR formation.Redundancy analysis and photochemical aging model show pyrolytic sources generated more oxidized OC-EPFRs than photolytic sources.Our study reveals the detailed molecular characteristics of OC-EPFRs and shows that oxidation states can be used to identify the origins of OC-EPFRs,offering a way to track the development and evolution of aerosol particles in the environment.