Kinetics and mechanism of the sulfite-induced autoxidation of Fe(II) in acidic aqueous solution

A spectrophotometric study employing stopped-flow techniques was performed of the sulfite-induced autoxidation of Fe(II) in acidic aqueous solution (pH < 3.9). In the presence of an excess Fe(II), simultaneous autoxidation of Fe(II) and sulfite occurs, and completes the catalytic cycle for the Fe(III) catalyzed autoxidation of sulfite. In the presence of an excess sulfite, the rapid formation of Fe(III) is followed by a slower redox process during which Fe(II) and sulfate are produced. The sulfite-induced autoxidation of Fe(II) is independent of the Fe(II) concentration. The suggested mechanism involves the rate-determining formation of SO₃⁻, followed by the formation of SO₅⁻and the subsequent oxidation of Fe(II).     

Aqueous S(IV) oxidation—I. Catalytic effects of some metal ions

Catalytic effect of metal ions [Fe(III), Mn(II), Cu(II), Pb(II) and Zn(II)] on the oxidation of S(IV) in aqueous solution at concentrations of metal ions and S(IV) as found in an urban atmosphere were studied under controlled experimental conditions (T, pH air flow rate, mixing, concentration of reactant, etc.). The following rate expressions were obtained: −r_S(IV) = k [Fe(III)] [S(IV)], −r_S(IV) = k [Mn(II)] [S(IV)]^0.65, −r_S(IV) = k [Cu(II)] [S(IV)]². The activation energy equals 104 kJ mol⁻¹ for Fe(III), 63.3 kJ mol⁻¹ for Mn(II), and 116.8 kJ mol⁻¹ for Cu(II) catalysed S(IV) oxidation.     

南京夏季大气臭氧光化学特征与敏感性分析

对流层臭氧（O₃）主要由氮氧化物（NO_x）和挥发性有机物（VOCs）经过一系列光化学反应生成,反应过程呈现复杂的非线性关系.为深入了解O₃的光化学特征及生成机制,利用2018年夏季大气O₃与VOCs的观测数据,结合大气零维框架模拟模型F0AM-MCM,研究O₃超标日和非O₃超标日的O₃光化学特征之间的差异性.观测结果表明,O₃超标日期间φ（O₃）和φ（TVOCs）的平均值分别为47.8×10^-9和49.0×10^-9,为非O₃超标日期间O₃（26×10^-9）和TVOCs（30×10^-9）体积分数的1.8倍和1.6倍.使用F0AM模型,借助EKMA曲线和RIR分析等识别O₃敏感性,发现南京市O₃超标日和非O₃超标日O₃的形成均主要受VOCs和NO_x的协同控制.F0AM-MCM模拟结果表明,在O₃超标日,·OH和HO₂的日平均混合比分别是非O₃超标日的1.3倍和1.8倍,表明O₃超标日期间具有更强的大气氧化能力,且·OH和HO₂的形成和损失速率也有明显的增加,表明自由基循环的增强.此外,O₃超标日的O₃生成速率明显高于非O₃超标日,从而导致了O₃超标日的O₃净生成速率明显高于非O₃超标日.以上发现提高了对南京夏季O₃超标日大气O₃光化学特征的认识.     

Determination of photochemically-generated reactive oxygen species in natural water

Reactive oxygen species(ROS) can be produced by interactions between sunlight and light-absorbing substances in natural water environment.ROS may participate in the indirect photolysis of trace organic pollutants,therefore resulting in changes in their environmental fates and ecological risks in natural water systems.Bisphenol A(BPA),an endocrine-disrupting chemical,exits widely in natural waters.The photodegradation of BPA promoted by ROS(.OH,1O2,HO2./O2·-),which were produced on the excitation of ubiquito...     

Ligand effects on arsenite removal by zero-valent iron/O2: Dissolution, corrosion, oxidation and coprecipitation

Ligands may increase the yields of reactive oxygen species (ROS) in zero-valent iron (ZVI)/O₂ systems. To clarify the relationship between the properties of ligands and their effects on the oxidative removal of contaminants, five common ligands (formate, acetate, oxalate, ethylenediaminetetraacetic acid (EDTA), and phosphate) as well as acetylacetone (AA) were investigated with arsenite (As(III)) as the target contaminant at three initial pH values (3.0, 5.0, and 7.0). The addition of these ligands to the ZVI/O₂ system resulted in quite different effects on As(III) removal. EDTA enhanced the oxidation of As(III) to arsenate (As(V)) but inhibited the removal of As(V). Oxalate was the only ligand in this work that accelerated both the removal of As(III) and As(V). By analyzing the ligand effects from the four aspects: dissolution of surface iron (hydr)oxides, corrosion of ZVI, reaction with ROS, and interference with precipitation, the following properties of ligands were believed to be important: ability to provide dissociable protons, complexation ability with iron, and reactivity with ROS. The complexation ability is a double-edged sword. It could enhance the generation of ROS by reducing the reduction potential of the Fe(III)/Fe(II) redox couple, but also could inhibit the removal of arsenic by coprecipitation. The elucidated relationship between the key property parameters of ligands and their effects on the ZVI/O₂ system is helpful for the rational design of effective ZVI/ligand/O₂ systems.     

Influence factors for the oxidation of pyrite by oxygen and birnessite in aqueous systems

The oxidation of exposed pyrite causes acid mine drainage, soil acidification, and the release of toxic metal ions. As the important abiotic oxidants in supergene environments, oxygen and manganese oxides participate in the oxidation of pyrite. In this work, the oxidation processes of natural pyrite by oxygen and birnessite were studied in simulated systems, and the influence of pH, Fe(II) and Cr(III) on the intermediates and redox rate was investigated. SO₄^2 − and elemental S were formed as the major and minor products, respectively, during the oxidation processes. Ferric (hydr) oxides including Fe(OH)₃ and goethite were formed with low degree of crystallinity. Low pH and long-term reaction facilitated the formation of goethite and ferric hydroxide, respectively. The rate of pyrite oxidation by birnessite was enhanced in the presence of air (oxygen), and Fe(II) ions played a key role in the redox process. The addition of Fe(II) ions to the reaction system significantly enhanced the oxidation rate of pyrite; however, the presence of Cr(III) ions remarkably decreased the pyrite oxidation rate in aqueous systems. The introduction of Fe(II) ions to form a Fe(III)/Fe(II) redox couple facilitated the electron transfer and accelerated the oxidation rate of pyrite. The present work suggests that isolation from air and decreasing the concentration of Fe(II) ions in aqueous solutions might be effective strategies to reduce the oxidation rate of pyrite in mining soils.     

广州城市大气HOx化学过程初步研究

根据广州城市大气中OH自由基和其它污染物同步测量结果,计算了城市大气HO_x(OH+HO₂)化学过程中主要反应的转化速率,分析了城市大气化学过程的主要特征,并与清洁大气中的化学过程进行了对比.研究结果表明:广州城市大气中OH和HO₂总的生成速率分别约为4.5×10⁸分子/(cm³·s)和3.8×10⁸分子/(cm³·s),比清洁大气中要快得多;城市大气中的OH净生成主要来自气相HNO₂的光解,而OH的去除主要与VOCs、HCHO、NO₂和CO反应,有别于清洁大气.     

无定形Fe (OH)3 和Fe3 O4 共沉淀态As的化学提取

无定形铁氧化物结合态砷的迁移性和生物可利用性易受环境变化影响.分别以1 mol·L-1盐酸和0.2 mol·L-1草酸铵缓冲溶液为提取剂,以新制备和室温老化(3个月、6个月)的共沉淀态Fe(OH)3-As和Fe3O4-As为提取对象,研究提取时间、液固比、Fe/As摩尔比和室温老化对As提取效率的影响.结果表明,1 mol·L-1盐酸提取Fe(OH)3-As、Fe3O4-As共沉淀时液固比应分别为50、200左右,0.2 mol·L-1草酸铵缓冲溶液提取Fe(OH)3-As、Fe3O4-As共沉淀时需保证加入的草酸根与固相中Fe的摩尔比分别为4、2.5;盐酸和草酸铵缓冲溶液提取时间2 h即可.样品Fe/As摩尔比和室温老化对Fe(OH)3-As共沉淀的溶解提取影响不大,但对Fe3O4-As共沉淀的提取影响比较大,Fe/As摩尔比越大,Fe3O4-As共沉淀越不易被提取;老化时间越长,其中共沉淀的As越不易被溶解提取.值得注意的是:盐酸和草酸铵缓冲溶液提取过程中如果有不溶固相存在,会发生As的再吸附,使无定形铁氧化物共沉淀态砷的测定不准确.     

Cu-Al2O3中骨架铜类芬顿催化去除水中有机污染物

为解决传统铁基芬顿催化剂在水体通常酸碱(pH6)条件下活性低的问题,采用简单共沉淀法制备了Cu掺杂的Al_2O_3类芬顿催化剂.通过X射线衍射(XRD)、X射线光电子能谱(XPS)和紫外可见(UV-vis)吸收光谱分析表明,Cu-Al_2O_3中铜掺杂的质量分数低于4.77%时,催化剂中铜主要以Cu~(2+)和Cu~+的形式共存于Al_2O_3的骨架结构中,形成Al—O—Cu键;过量的铜掺杂会导致外骨架铜物种如铜氧化物团簇的存在.以难降解有机污染物2-氯苯酚(2-chlorophenol,2-CP)和染料罗丹明B(Rhodamine B,Rh B)为目标污染物,对Cu-Al_2O_3的类芬顿催化性能进行了详细地研究.结果表明,骨架铜物种在中性温和条件下对2-CP和Rh B显示出很高的催化去除效率和稳定性,反应2 h,Cu-Al_2O_3(Cu质量分数4.77%)对2-CP的去除率达到54%,相应的TOC去除率达到49%,而铜离子溶出浓度仅为0.025 5 mg·L-1,而Cu-Al_2O_3(Cu质量分数7.58%)由于外骨架铜的存在导致催化活性增加缓慢和稳定性下降.ESR测试结果表明,·OH和HO_2~-/O_2~-·是反应中主要的活性物种.     

Identification of close relationship between atmospheric oxidation and ozone formation regimes in a photochemically active region

Understanding ozone (O₃) formation regime is a prerequisite in formulating an effective O₃ pollution control strategy. Photochemical indicator is a simple and direct method in identifying O₃ formation regimes. Most used indicators are derived from observations, whereas the role of atmospheric oxidation is not in consideration, which is the core driver of O₃ formation. Thus, it may impact accuracy in signaling O₃ formation regimes. In this study, an advanced three-dimensional numerical modeling system was used to investigate the relationship between atmospheric oxidation and O₃ formation regimes during a long-lasting O₃ exceedance event in September 2017 over the Pearl River Delta (PRD) of China. We discovered a clear relationship between atmospheric oxidative capacity and O₃ formation regime. Over eastern PRD, O₃ formation was mainly in a NO_x-limited regime when HO₂/OH ratio was higher than 11, while in a VOC-limited regime when the ratio was lower than 9.5. Over central and western PRD, an HO₂/OH ratio higher than 5 and lower than 2 was indicative of NO_x-limited and VOC-limited regime, respectively. Physical contribution, including horizontal transport and vertical transport, may pose uncertainties on the indication of O₃ formation regime by HO₂/OH ratio. In comparison with other commonly used photochemical indicators, HO₂/OH ratio had the best performance in differentiating O₃ formation regimes. This study highlighted the necessities in using an atmospheric oxidative capacity-based indicator to infer O₃ formation regime, and underscored the importance of characterizing behaviors of radicals to gain insight in atmospheric processes leading to O₃ pollution over a photochemically active region.     

One-step preparation of a novel graphitic biochar/Cu0/Fe3O4 composite using CO2-ambiance pyrolysis to activate peroxydisulfate for dye degradation

Herein,a one-step co-pyrolysis protocol was adopted for the first time to prepare a novel pyrogenic carbon-Cu⁰/Fe₃O₄ heteroatoms (FCBC) in CO₂ ambiance to discern the roles of each component in PDS activation.During co-pyrolysis,CO₂ catalyzed formation of reducing gases by biomass which facilitated reductive transformation of Fe³⁺ and Cu²⁺ to Cu⁰ and Fe₃O₄,respectively.According to the a...     

Atmospheric coarse particulate concentrations and dry deposition fluxes for ten metals in two urban environments

The atmospheric coarse particle concentrations of ten metals (Al, Ca, Cd, Cu, Fe, Mn, Ni, Pb, Si and Zn) were measured with the Noll Rotary Impactor (NRI) in the Los Angeles Basin (Claremont) California, and in Chicago, Illinois. The dry deposition fluxes were also measured for the ten elements at the Chicago site. An evaluation of the data demonstrates that the coarse particle mass could be divided into two categories: (1) material that was primarily of crustal origin (Al, Ca, Fe and Si) and (2) material that was primarily of anthropogenic origin (Cd, Cu, Mn, Ni, Pb and Zn). The mass of crustal material varied between 15 and 50% of the total coarse particle mass, while the mass of anthropogenic material was <1%. The dry deposition fluxes for the crustal material were between 20 (Al) and 200 (Si) ng m⁻² s⁻¹ while the fluxes for the anthropogenic material were between 1 and 7 ng m⁻¹ s⁻¹ for Cu, Mn, Pb and Zn. The cadmium (Cd) flux averaged 0.02 ng m⁻² s⁻¹.     

Polynuclear aromatic hydrocarbon degradation by heterogeneous reactions with N2O5 on atmospheric particles

The degradation of particulate polynuclear aromatic hydrocarbons (PAH) on atmospheric soot particles in the presence of gas phase dinitrogen pentoxide (N₂O₅) was explored. Dilute diesel and wood soot particles containing PAH were reacted with∼10ppm of N₂O₅ in a 200 ℓ continuous stirred tank reactor (CSTR). To provide a stable source of particles for reaction in the CSTR, diesel or wood soot particles were injected at night into a 25 m³ Teflon outdoor chamber. The large chamber served as a reservoir for the feed aerosol, and the aerosol could then be introduced at a constant flow rate into the CSTR. PAH-N₂O₅ heterogeneous rate constants for wood soot at 15°C ranged from2 × 10⁻¹⁸to5 × 10⁻¹⁸ cm³ molecules⁻¹ s⁻¹. For diesel soot the rate constants at 16°C were higher and ranged from5 × 10⁻¹⁸to30 × 10⁻¹⁸ cm³ molecules⁻¹ s⁻¹. Comparisons with other studies suggest that sunlight is the most important factor which influences PAH decay. This is followed by ozone, NO₂, N₂O₅ and nitric acid. The rate constants of nitro-PAH formation from a parent PAH and N₂O₅ were of the order of1 × 10⁻¹⁹−1 × 10⁻¹⁸ molecules⁻¹s⁻¹. The uncertainty associated with all of these rate constants is± a factor of 3. Given, however, the small magnitude of the rate constants and the low levels of N₂O₅ present in the atmosphere, we concluded that PAH heterogeneous reactions with gas phase N₂O₅ degrade particle-bound PAH or to form nitro-PAH from PAH arenot very important. (Direct application of the specific rate constants derived in this study to ambient atmospheres should not be undertaken unless the ambient particle size distributions and chemical composition of the particles are similar to the ones reported in this study.)     

Metal ion catalyzed oxidation of SO2 in the presence of trace H2O2 in aqueous solution under environmental reaction conditions

Aqueous phase oxidation of SO₂ or S(IV) by H₂O₂-metal ions at a H₂O₂ concentration much lower than S(IV), was studied using a continuously flowing stirred reactor. Of the metal ions, Fe²⁺ showed the highest catalytic activity, i.e. the oxidation of S(IV) continued after most of the H₂O₂ was consumed. The dependence of the rate on the concentration of S(IV), H₂O₂, Fe²⁺ or H⁺ and temperature was determined. The following rate expression and low apparent activation energy of 40.7 kJ mole⁻¹ were evaluated,−d[S(IV)]/dt=620[S(IV)]²[Fe²⁺]^0.5(molel⁻¹S⁻¹). The significance of this reaction as the sulfate formation in atmospheric water droplets is discussed and a comparison of the rate with others using H₂O₂, O₃ and dissolved O₂ catalyzed by metal ions is made.     

上海市大气中HO2自由基的测定与特征

为研究上海市大气中ＨＯ２自由基的分布特征,建立了化学放大法测定ＨＯ２自由基系统,对上海市大气中ＨＯ２自由基浓度进行了没定邦等结果表明,ＨＯ２自由基的典型日变化基本上为双峰型,峰值出现在阳光辐射较强的中午时分,实验测得ＨＯ２自由基最大浓度达２．２４×１０＾８分子·ｃｍ＾－３,ＨＯ２自然基民ＮＭＨＣ,Ｃ烽Ｏ２等具有一定的相关性,ＨＯ２自由基的研究对于大气光化学烟雾的研究具有重要意义     

Sensitive voltammetric and amperometric responses of respiratory toxins at hemin-adsorbed carbon-felt

A hemin [iron-Fe(III) protoporphyrin IX chloride] was adsorbed onto a carbon-felt (CF), which is a microelectrode ensemble of micro carbon fiber (ca. 7 μm diameter). The resulting hemin-adsorbed-CF (hemin-CF) showed a well-defined redox wave based on the hemin-Fe(III)/Fe(II) redox process with the formal potential of -0.225 V vs. Ag/AgCl in deoxygenated phosphate/citrate buffer solution (0.1 mol/L, pH 5.0). The apparent heterogenous electron transfer rate constant was estimated to be 8.6 sec^-1. In air-saturated electrolyte solution, the hemin-CF exhibited an excellent electrocatalytic activity for the reduction of dioxygen (O₂). This activity was reversibly inhibited by respiratory toxins such as cyanide and azide, which bind sixth coordination position of iron active center of hemin. The electrocatalytic O₂ reduction current at the hemin-CF was modulated by the toxins in a concentration-depending manner. Based on the relationship between the inhibition and the toxin concentration, apparent inhibition constants of cyanide and azide were evaluated to be 4.52 and 1.98 μmol/L, respectively. When the hemin-CF was used as a working electrode unit of the CF-based electrochemical flow-through detector with air-saturated carrier, the injection of the azide induced peak-shape current responses, which allowed rapid and continuous flow-amperometric determination of azide with high sensitivity.     

Studies on the formation of H2O2 in the ozonolysis of alkenes

The formation of H₂O₂ in the reactions of ozone with alkenes, isoprene and some terpenes has been studied with tunable diode laser absorption spectroscopy. The measured yields of H₂O₂ were found to be considerably enhanced in the presence of water vapour. H₂O₂ is thought to be formed in the ozonolysis of the alkene with O₃ by direct reaction of an intermediate with water vapour. The yield of H₂O₂ relative to the reacted alkene in the ozonolysis of trans-2-butene in the presence of water vapour was also studied with long path FTIR spectroscopy. Irrespective of the analytical methods and reaction conditions applied, the H₂O₂ yields in the reaction of O₃ with the different alkenes in the presence of water vapour were found to be in the range of a few per cent or less. Under the assumption that the reactive species forming H₂O₂ in the ozonolysis is the Criegee biradical, the overall rate constants for the reactions of some biradicals with water vapour were measured relative to the rate constant of the biradical with SO₂. For the H₂COO biradical a rate constant of (5.8 ± 2.5) × 10⁻¹⁷ cm³ s⁻¹ was determined and for the (CH₃)₂COO biradical (2.9 ± 1.5) × 10⁻¹⁷ cm³ s⁻¹; in the latter case with the assumption that (CH₃)₂COO reacts with SO₂ as fast as CH₂COO.     

Anaerobic oxidation of arsenite by bioreduced nontronite

The redox state of arsenic controls its toxicity and mobility in the subsurface environment. Understanding the redox reactions of arsenic is particularly important for addressing its environmental behavior. Clay minerals are commonly found in soils and sediments, which are an important host for arsenic. However, limited information is known about the redox reactions between arsenic and structural Fe in clay minerals. In this study, the redox reactions between As(III)/As(V) and structural Fe in nontronite NAu-2 were investigated in anaerobic batch experiments. No oxidation of As(III) was observed by the native Fe(III)-NAu-2. Interestingly, anaerobic oxidation of As(III) to As(V) occurred after Fe(III)-NAu-2 was bioreduced. Furthermore, anaerobic oxidization of As(III) by bioreduced NAu-2 was significantly promoted by increasing Fe(III)-NAu-2 reduction extent and initial As(III) concentrations. Bioreduction of Fe(III)-NAu-2 generated reactive Fe(III)-O-Fe(II) moieties at clay mineral edge sites. Anaerobic oxidation of As(III) was attributed to the strong oxidation activity of the structural Fe(III) within the Fe(III)-O-Fe(II) moieties. Our results provide a potential explanation for the presence of As(V) in the anaerobic subsurface environment. Our findings also highlight that clay minerals can play an important role in controlling the redox state of arsenic in the natural environment.     

Simultaneous Fe(III) reduction and ammonia oxidation process in Anammox sludge

In recent years, there have been a number of reports on the phenomenon in which ferric iron (Fe(III)) is reduced to ferrous iron [Fe(II)] in anaerobic environments, accompanied by simultaneous oxidation of ammonia to NO₂^-, NO₃^-, or N₂. However, studies on the relevant reaction characteristics and mechanisms are rare. Recently, in research on the effect of Fe(III) on the activity of Anammox sludge, excess ammonia oxidization has also been found. Hence, in the present study, Fe(III) was used to serve as the electron acceptor instead of NO₂^-, and the feasibility and characteristics of Anammox coupled to Fe(III) reduction (termed Feammox) were investigated. After 160days of cultivation, the conversion rate of ammonia in the reactor was above 80%, accompanied by the production of a large amount of NO₃^- and a small amount of NO₂^-. The total nitrogen removal rate was up to 71.8%. Furthermore, quantities of Fe(II) were detected in the sludge fluorescence in situ hybridization (FISH) and denaturated gradient gel electrophoresis (DGGE) analyses further revealed that in the sludge, some Anammox bacteria were retained, and some microbes were enriched during the acclimatization process. We thus deduced that in Anammox sludge, Fe(III) reduction takes place together with ammonia oxidation to NO₂^- and NO₃^- along with the Anammox process.     

UV强化草酸络合Fe3+活化过硫酸盐氧化降解苯胺

采用UV-草酸络合Fe~(3+)[UV-Fe(C_2O_4)3-3]活化过硫酸钠(PS)氧化降解苯胺,研究了Fe(C_2O_4)3-3浓度,PS浓度,pH对PS活化效率及苯胺氧化降解效果的影响机制.结果表明,Fe(C_2O_4)3-3浓度和pH决定了UV-Fe(C_2O_4)3-3体系中Fe~(3+)向Fe2+的转化过程,并对活化PS氧化降解苯胺产生显著影响.随着Fe(C_2O_4)3-3浓度增加,PS的分解率不断提高,但当浓度高于0.75 mmol·L~(-1)时,草酸根离子(C2O_2-4)对硫酸根自由基(SO·-4)的竞争以及SO·-4之间的相互淬灭作用降低了苯胺的降解效果,降解速率大小顺序为5 mmol·L~(-1)0.25 mmol·L~(-1)0.5 mmol·L~(-1)1 mmol·L~(-1)0.75 mmol·L~(-1);中性和碱性条件不利于Fe(C_2O_4)3-3发生光化学反应生成Fe2+,但当初始pH为7和9时,由于PS活化分解过程降低反应体系pH,反应300min时PS的活化率可分别达到74%和67%,苯胺去除率分别高达91%和97%,均高于初始pH为酸性条件下的结果;苯胺降解率随初始PS浓度增加而增大,当PS浓度大于10 mmol·L~(-1)时,苯胺降解过程由二级反应变为准一级反应,但此时过量的PS因与SO·-4发生反应而显著降低PS用于氧化降解苯胺的利用率.