Rate Of Photooxidation Research Articles

Voltage-Driven Molecular Photoelectrocatalysis of Water Oxidation.

Molecular photocatalysis and photoelectrocatalysis have been widely used to conduct oxidation-reduction processes ranging from fuel generation to electroorganic synthesis. We recently showed that an electrostatic potential drop across the double layer contributes to the driving force for electron transfer (ET) between a dissolved reactant and a molecular catalyst immobilized directly on the electrode surface. In this article, we report voltage-driven molecular photoelectrocatalysis with a prevalent homogeneous water oxidation catalyst, (bpy)Cu (II), which was covalently attached to the carbon surface and exhibited photocatalytic activity. The strong potential dependence of the photooxidation current suggests that the electrostatic potential drop across the double layer contributes to the driving force for ET between a water molecule and the excited state of surface-bound (bpy)Cu (II). Scanning electrochemical microscopy (SECM) was used to analyze the products and determine the faradaic efficiencies for the generation of oxygen and hydrogen peroxide. Unlike electrocatalytic water oxidation by (bpy)Cu (II) in the dark, which produces only O2, the voltage-driven photooxidation includes an additional 2e- pathway generating H2O2. DFT calculations show that the applied voltage and the presence of light can alter the activation energy for the rate-determining water nucleophilic attack steps, thereby increasing the reaction rate of photo-oxidation of water and opening the 2e- pathway. These results suggest a new route for designing next-generation hybrid molecular photo(electro)catalysts for water oxidation and other processes.

Study of Factors Affecting UV-Induced Photo-Degradation in Different Types of Polyethylene Sheets.

Enhancing the degradability of polyethylene plastics could provide a potential solution to the overwhelming crisis of plastic waste. Conventional studies have focused on the degradation of polyethylene thin films. This study investigated UV-induced photo-degradation according to ASTM D5208-14 in polyethylene sheets with thicknesses ranging from 0.4 to 1.2 mm. The impacts of sample thickness, metal pro-oxidants, polyethylene resin types and foaming were explored through the characterization of the carbonyl index, molecular weight, tensile properties and crystallinity. As pro-oxidants, single iron or manganese stearate demonstrated a concentration-dependent trend in accelerating the photo-degradation of polyethylene sheets. The thickness, foaming and resin type-such as low-density polyethylene (LDPE) and high-density polyethylene (HDPE)-significantly impacted the rate of photo-oxidation. Thick polyethylene sheets (1.2 mm) exhibited a heterogenous and depth-dependent degradation profile. As the photo-degradation progressed, the enhanced crystallinity, reduced UV transmittance and formation of crosslinks were able to prevent further oxidative cleavage of the polyethylene chain. This study investigated the time course and factors affecting the photo-degradation of polyethylene sheets, which could provide insights into the formulation design of photo-degradable polyethylene plastics.

Engineering atomic Rb-N configurations to tune radical pathways for highly selective photocatalytic H2O2 synthesis coupled with biomass valorization

Photocatalytic oxygen reduction for hydrogen peroxide (H₂O₂) synthesis presents a green and cost-effective production method. However, achieving highly selective H₂O₂ synthesis remains challenging, necessitating precise control over free radical reaction pathways and minimizing undesirable oxidative by-products. Herein, we report for the visible light-driven simultaneous co-photocatalytic reduction of O2 to H2O2 and oxidation of biomass using the atomic rubidium-nitride modified carbon nitride (CNRb). The optimized CNRb catalyst demonstrates a record photoreduction rate of 8.01 mM h−1 for H2O2 generation and photooxidation rate of 3.75 mM h−1 for furfuryl alcohol to furoic acid, achieving a remarkable solar-to-chemical conversion (SCC) efficiency of up to 2.27%. Experimental characterizations and DFT calculation disclosed that the introducing atomic Rb–N configurations allows for the high-selective generation of superoxide radicals while suppressing hydroxyl free radical formation. This is because the Rb–N serves as the new alternative site to perceive a stronger connection position for O2 adsorption and reinforce the capability to extract protons, thereby triggering a high selective redox product formation. This study holds great potential in precisely regulating reactive radical processes at the atomic level, thereby paving the way for efficient synthesis of H2O2 coupled with biomass valorization.

UV LED ageing of polymers for PV cell encapsulation

Encapsulation polymers in terrestrial solar modules degrade due to ultraviolet radiation from the sun. To assess a polymer’s durability under UV light, accelerated aging tests can be conducted. A new LEDs device allows us to investigate the effects of temperature, irradiation, and UV source spectrum on the photooxidation mechanism and kinetics of two polyethylene-based commercial encapsulants, differentiated by the presence or absence of UV absorbers. The photooxidation rate of the polymer matrix increases as the temperature and irradiance increase between 62 and 82 °C, and 12 and 28 W.m−2, respectively. In the last case, the photooxidation rate is not proportional to the number of photons. Finally, we observed different distributions of degradation products under UVB radiation at 305 nm compared to those under UVA radiation at 365 nm. UVB photons enable Norrish reactions that are not possible with UVA alone. Special care is needed to maintain a balance between UVA and UVB photons to ensure representative durability tests. With a few adjustments to their emission spectrum, UV LED devices appear to be good candidates for accelerated aging of encapsulation polymers.

Synthesis and evaluation of novel mitochondria-targeted, water-soluble phenoxazine-porphyrins for efficient photodynamic therapy

In this study, we use cationic imidazole as the targeting group and phenoxazine as the electron donor, attaching phenoxazine to porphyrin via two different linking methods to synthesize two phenoxazine-porphyrin photosensitizers (PSs), P1 and P2, intended for photodynamic therapy (PDT) applications. Additionally, we synthesized a molecule, P3, that does not contain the cationic imidazole group, to serve as a control PS. We comprehensively evaluate the performance of P1 and P2 through steady-state and transient spectroscopy analysis, theoretical calculations, photooxidation experiments, and in vitro cell experiments. The results showed that P1 and P2 exhibit excellent water solubility, longer triplet state lifetimes (P1 at 200 μs, P2 at 170 μs), outstanding photostability, higher photooxidation rates and quantum yields of singlet oxygen (1O2). Notably, in the photooxidation experiment, P1's photooxidation rate is 1.1 times that of P2, and 1.5 times that of tetraphenyl zinc porphyrin (ZnTPP) without phenothiazine. This may be due to the larger Gibbs free energy difference between the singlet and triplet excited states in P1 (ΔGS-T of P1 is 0.87 eV, compared to 0.83 eV for P2), which results in a greater driving force for intersystem crossing (ISC) in P1 than in P2. The introduction of the cationic imidazole group in P1 and P2 significantly enhances water solubility and tumor cell uptake compared to P3, particularly showing higher intracellular accumulation and 1O2 generation capabilities in HepG2 tumor cells. Flow cytometry test results further confirmed the significant photocytotoxicity of P1 and P2, with a marked decrease in survival rates after light exposure, where the survival rate of P1 nanoparticles (NPs) dropped to 41.7 %, P2 NPs to 35.1 %, and P3 NPs to 75.0 %. The findings of this study provide crucial theoretical support for the design of new PSs.

Effect of diphenylalanine on the functional activity of porphyrin and non-porphyrin photosensitizers solubilized by Pluronic F127

The effect of the diphenylalanine (Phe-Phe) amino acid on the rate of tryptophan photooxidation catalyzed by photosensitizers (PS) of different natures: dimegin (DMG), fluorinated tetraphenylporphyrin (FTPP), photoditazine (PD) and methylene blue (MB) was studied. It was shown that in the presence of Phe-Phe, the effective constant of photooxidation of the substrate catalyzed by DMG, PD and MB in the aqueous phase decreases. However, the introduction of the amphiphilic polymer Pluronic F127 into the systems allows not only to restore, but also to increase the activity of the PS in the processes of photosensitized oxidation. In particular, the activity of dimegin solubilized by Pluronic F127 in the presence of Phe-Phe is higher than the activity of both pure porphyrin and solubilized DMG. In addition, the activity of the hydrophobic FTPP solubilized by Pluronic also increases. At the same time, a study of the luminescence of singlet oxygen generated by solubilized FTPP in the absence and presence of Phe-Phe revealed that the dipeptide does not influence the processes of 1О2 generation. It was suggested that micellar catalysis influences the activity of solubilized PS in the presence of a biologically active dipeptide.

Development of an automatic evaluation system for photooxidation and assessment of polyethylenes containing HALS and UVA

An automatic evaluation system for photooxidation has been developed by utilizing a chemiluminescence apparatus combined with a light irradiation system. The system is composed of a controller, a driving device, and irradiation equipment, which are integrated with the chemiluminescence measurement system. Various measurement conditions can be set independently, including irradiation time (fixed or variable), waiting time from irradiation to measurement, chemiluminescence measurement time, number of repetitions (up to 999 times), and measurement temperature. LLDPEs containing Hindered Amine Light Stabilizers (HALS) and Ultraviolet Absorbers (UVA) were evaluated using this system. The decay of chemiluminescence after UV irradiation was repeatedly measured at r.t. and 105℃, respectively, below the melting point of LLDPE, and the time-course of chemiluminescence was obtained by plotting time against I(t = 0) for each instance. I(t = 0) represent the rate of photooxidation under UV exposure, calculated using second-order analysis of the chemiluminescence decay. The chemiluminescence intensity increased significantly in the initial stage with irradiation time, maintained a stable intensity for a period, and then exhibited a substantial increase in the later stage. We termed the point at which this significant increase in chemiluminescence occurs as the induction time of photooxidation (photo-OIT). Using this system, the photo-OIT of LLDPE samples with HALS and UVA was measured, revealing the potential for assessing the synergistic effects of photooxidation stabilizers.

Influence of irradiance on the photooxidation of HALS stabilized low-density polyethylene

This paper concerns the experimental analysis of the effect of irradiance on the photooxidation of low-density polyethylene (LDPE) stabilized with different HALS. Infrared analysis in transmission mode was used to monitor the extent of oxidation provoked by the exposure of thin samples (100 µm thick) in a SEPAP MHE unit (Atlas/Ametek) at two different irradiances (90 W.m − 2 and 300 W.m − 2 between 300 and 420 nm). The temperature of the samples was maintained constant in order to focus on the impact of irradiance on the kinetics, without interfering with the temperature. The intended goal was to characterize the effect of the irradiance in accelerated testing and the consequences on the lifetime prediction. Previous results obtained in the case of unstabilized LDPE samples showed that no acceleration was obtained when increasing the irradiance from 90 W.m − 2 and 300 W.m − 2 while keeping the temperature constant. In the case of the stabilized samples, the results presented in the present article show that the rates of photo oxidation tended to increase when increasing the irradiance. However, the ratio of these rates never reaches the ratio of the irradiances, and these ratios depends on the stability of the samples.

Panchromatic Light-Absorbing [70]Fullerene-Perylene-BODIPY Triad with Cascade of Energy Transfer as an Efficient Singlet Oxygen Sensitizer.

A panchromatic light-absorbing [70]fullerene-perylene-BODIPY triad (C70-P-B) was synthesized and applied as a heavy atom-free organic triplet photosensitizer for photooxidation. The photophysical processes were comprehensively investigated by the methods of steady-state spectroscopy, time-resolved spectroscopy, as well as theoretical calculations. C70-P-B shows a strong absorption ability from 300-620 nm. Efficient cascading intramolecular singlet-singlet energy transfer in C70-P-B was confirmed by the luminescence study. The backward triplet excited state energy transfer from C70 moiety to perylene then occurs to populate 3perylene*. Thus, the triplet excited states of C70-P-B are distributed on both C70 and perylene moiety with lifetimes of 23 ± 1 μs and 175 ± 17 μs, respectively. C70-P-B exhibits excellent photooxidation capacity, and its yield of singlet oxygen reaches 0.82. The photooxidation rate constant of C70-P-B is 3.70 times that of C70-Boc and 1.58 times that of MB, respectively. The results in this paper are useful for designing efficient heavy atom-free organic triplet photosensitizers for practical application in photovoltaics, photodynamic therapy, etc.

Fabrication of nitrogen doped TiO2/Fe2O3 nanostructures for photocatalytic oxidation of methanol based wastewater

An important industrial process that often occurs on the surface of a heterogeneous catalyst using thermochemical or photochemical could help in the oxidation of methanol-based wastewater to formaldehyde. Titania-based photocatalysts have drawn a lot of interest from scientists because they are a reliable and affordable catalyst material for photocatalytic oxidation processes in the presence of light energy. In this study, a straight-forward hydrothermal method for producing n-TiO2@α-Fe2O3 composite photocatalysts and hematite (α-Fe2O3) nanocubes has been done. By adjusting the ratio of n-TiO2 in the prepared composite photocatalysts, the enhancing influence of the nitrogen-doped titania on the photocatalytic characteristics of the prepared materials was investigated. The prepared materials were thoroughly characterized using common physiochemical methods, such as transmission electron microscope (TEM), scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX), X-ray photoelectrons spectroscopy (XPS), physisorption (BET), and others, in order to learn more about the structure The results obtained showed that nitrogen-doped titania outperforms non-doped titania for methanol photooxidation. The addition of nitrogen-doped titania to their surfaces resulted in an even greater improvement in the photooxidation rates of the methanol coupled with hematite. The photooxidation of methanol in the aqueous solution to simulate its concentration in the wastewater has been occurred. After 3 h, the four weight percent of n-TiO2@α-Fe2O3 photocatalyst showed the highest rate of HCHO production.

Significantly Accelerated Hydroxyl Radical Generation by Fe(III)–Oxalate Photochemistry in Aerosol Droplets

Fe(III)-oxalate complexes are ubiquitous in atmospheric environments, which can release reactive oxygen species (ROS) such as H2O2, O•2-, and OH• under light irradiation. Although Fe(III)-oxalate photochemistry has been investigated extensively, the understanding of its involvement in authentic atmospheric environments such as aerosol droplets is far from enough, since the current available knowledge has mainly been obtained in bulk-phase studies. Here, we find that the production of OH• by Fe(III)-oxalate in aerosol microdroplets is about 10-fold greater than that of its bulk-phase counterpart. In addition, in the presence of Fe(III)-oxalate complexes, the rate of photo-oxidation from SO2 to sulfate in microdroplets was about 19-fold faster than that in the bulk phase. The availability of efficient reactants and mass transfer due to droplet effects made dominant contributions to the accelerated OH• and SO42- formation. This work highlights the necessary consideration of droplet effects in atmospheric laboratory studies and model simulations.

A novel Zn0.5Cd0.5S/WO3·H2O S-scheme heterostructures with one-pot synthesis for significant photodegradation of toxic Cr (VI) and organic RhB pollutants: Kinetics, degradation mechanism and photocatalytic evaluation

The artificial-photosynthetic semiconductor composites have attracted tremendous attention with respect to their enhanced photocatalytic properties. Herein, we reported the facile synthesis of Zn0.5Cd0.5S/WO3·H2O S-scheme photocatalyst via one-pot in situ hydrothermal strategy. Density Functional Theory (DFT) calculation was employed to reveal the S-scheme photogenerated electron transfer mechanism, and the subsequent experimental characterization further illustrated the path for electron-hole transfer and separation under the effect of S-scheme heterojunction. The mass of WO3·H2O accounted for Zn0.5Cd0.5S/WO3·H2O 48 wt% (ZCSW48) was the best high-efficiency S-scheme photocatalyst displayed significant photocatalytic properties on pollution degradation, in detail, with the Cr (VI) photoreduction rate of 2.27 μmol·s−1·g−1cat. and the Rhodamine B (RhB) photooxidation rate of 0.38 μmol·min−1·g−1cat., respectively. The designed Zn0.5Cd0.5S/WO3·H2O photocatalysts have integrated with the three aspects of photocatalytic efficiencies including the visible light response, prolonged photogenerated carrier lifetime and the sufficient surface active sites due to amount of surface defects, therefore, this work provides more insights into the utilization of green energy for environmental treatment by artificial structured semiconductors.

The role of predissociation states in the UV photooxidation of acetylene

We study the photo-induced oxidation of acetylene in two different spectral areas, around 220 and 320 nm. In both spectral areas, the dominant reaction pathways involve the rupture of the acetylene C−H bond, thus primarily generating C2H and H fragments. The released fragments react in O2 presence resulting in glyoxal and other molecular species formation. We observe strong variations in the photooxidation rates, which point to the increased participation of excited, predissociation states, in the oxidation process. Such effects of increased excited state participation in photooxidation should be observed in a variety of photo-induced reactions, affecting the reaction spectral response and eventually the reaction cycles in terrestrial or planetary environments.

Engineering ZnSn(OH)6 with ternary active sites-directed hydroxyl vacancies for robust deep C6H6 photo-oxidation: Experiment and DFT calculations

The removal mechanisms of low concentration benzene series VOCs over photocatalysts are often ascribed to the surface interface charge transfer or hydroxyl radical (OH) oxidation. Typically, reactive oxygen species (ROSs) contribute to the enhanced photoactivity, however, it remains ambiguous at this stage. Herein, ZnSn(OH)6 with hydroxyl vacancies (ZHS160) is examined to identify the specific ROSs for C6H6 photo-oxidation, namely holes, electrons, H2O and O2/O2− except OH. The well-designed ZHS160 possesses ternary active sites: hydroxyl vacancies for localizing electrons and adsorbing H2O molecules, exposed Zn and Sn sites for adsorbing/activating molecular C6H6 and O2, respectively. Therefore, ZHS160 exemplifies an exceptional photo-oxidation rate of low concentration C6H6 reaching 86%, far exceeding that of pristine ZnSn(OH)6 (22%). Impressively, the formed intermediates are confirmed to gain insights into their formation, chemical and electronic features as empowered by the in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), gas chromatography-mass spectrometry (GC–MS) and density functional theory (DFT) simulations. Accordingly, a distinguishing reaction path based on the pristine ZnSn(OH)6 and ZHS160 is elucidated. As such, these results advance the mechanistic understanding of deep photo-oxidation of C6H6 to CO2 over ZnSn(OH)6 with hydroxyl vacancies.

Reversible Metal Ion/Complex Binding to Chitin Controlled by Ligand, Redox, and Photochemical Reactions and Active Movement of Chitin on Aquatic Arthropods

There is strong adsorption of metal ions and their complexes to chitin, which depends on both the oxidation and complexation states of many of the said elements (whereas others display chemical reactions detectable via electrochemical methods while being retained by chitin); thus, ad- and desorption at ambient water concentrations (often in the nMol/L range) are controlled by the presence and photochemical properties (concerning Eu and probably U and Ag) of mainly biogenic organic matter (both DOC and POC, and DON). With chitin forming the outer hull of mobile organisms (animals), this biopolymer is expected to take part in metal distribution in aquatic (limnetic and riverine) ecosystems. Having studied the attachment of many different elements to both crayfish and grafted (marine shrimp) chitin, with the highest accumulations observed in Bi, V, Ni, and LREEs, one should consider secondary biochemical transformations which take place at different water and sediment levels. After chitin had been embedded into sediment, methanogenesis (which requires Ni), Bi, and Sb biomethylations and photodesorption in the illuminated water column will occur if there are appropriate organics, causing the vertical separation of Eu from other REEs, at least during the daytime. Eutrophication will enhance both the production and especially the photooxidation rates of organics in water because phosphorylated sugars and lipids are formed quantitatively within min P, which enter water and undergo Eu-mediated photooxidation much more readily. Another biopolymer, gelatin, acts as an inert matrix-enhancing organic photooxidation product via Eu, producing chemical waves, indicating autocatalysis upon light impact. From the redox-related photodesorption of metal analytes from chitin, both sensors and devices for (light-assisted) electrochemical energy conversion are being developed by our workgroup. The electrochemical determination of adsorption thermodynamics on chitin is thus directly linked to its applications in environmental monitoring and technology.

Characteristics of Surface Ozone Levels at Climatologically and Topographically Distinct Metropolitan Cities in India

Surface ozone (O3) data at Pune (1998–2014) and Delhi (1998–2013) are studied to examine their temporal characteristics. Study also examines role of meteorology and atmospheric boundary layer height (ABLH) in modulating surface O3 at these sites. Using diurnal variability of surface O3, rate of change of surface O3, [d(O3)/dt] is estimated to infer the nature of surface O3 formation/destruction mechanisms. Analysis of data reveals that at both locations, surface O3 concentrations during daytime are significantly high as compared to those during nighttime. Seasonally, at Pune averaged daytime surface O3 concentrations are high during pre-monsoon and low in monsoon while those during winter and post-monsoon are found to be significantly higher than those in monsoon but half as compared to those in pre-monsoon. At Delhi, averaged daytime surface O3 concentration is minimum in winter and maximum in pre-monsoon with monsoon and post-monsoon values being about 0.79–0.82 times with respect to pre-monsoon O3 concentrations. High natural/anthropogenic pollutant concentration, abundance of ozone precursor gases, high temperature and high rate of photo-oxidation of precursor gases due to solar flux are the causal factors for increased surface O3 concentrations in pre-monsoon season. Reduced solar flux decreases photo-dissociation of ozone precursor gases resulting in low O3 concentration during winter season. Occurrence of low surface O3 during early morning hours in monsoon, post-monsoon and winter seasons is because of low ABLH and low stratosphere-troposphere exchange (STE). [d(O3)/dt] values during morning/evening at Pune and Delhi are indicative of asymmetric and symmetric nature of ozone formation/destruction mechanisms.

Spectrally Resolved Single Particle Photoluminescence Microscopy Reveals Heterogeneous Photocorrosion Activity of Cuprous Oxide Microcrystals

Photocorrosion of cuprous oxide (Cu2O) has notably limited its application as an efficient photocatalyst. We report a facile approach to visualize in situ formation of copper and oxygen vacancies on the Cu2O surface under ambient condition. By imaging photoexcited single Cu2O particles, the resultant photoluminescence generated at Cu2O surface enable effective localization of copper and oxygen vacancies. Single particle photoluminescence imaging showed substantial heterogeneity in the rate of defect formation at different facets with the truncated corners achieving the fastest initial rate of photooxidation before subsequently changing to the face and edge sites as the photocorrosion proceeds. The generation of copper or oxygen vacancy is proportional to the photoexcitation power, while pH-dependent studies rationalized alkaline conditions for the formation of copper vacancy. Reaction in an electron-hole scavenger system showed that photooxidation and photoreduction will simultaneously occur, yet heterogeneously on the surface of Cu2O, with rate of copper vacancy formation being fastest.

Interaction effects between macromolecules and photosensitizer on the ability of AlPc and InPc-loaded PHB magnetic nanoparticles in photooxidatizing simple biomolecules

The parameters used in the preparation of polymeric nanoparticles can influence its ability to photooxidate biomolecules. This work evaluated the effects of four parameter to prepare Poly(3-hydroxybutyrate) (PHB) nanoparticle loaded with aluminum and indium phthalocyanine (AlPc and InPc), together with iron oxide nanoparticles, assessing their influence on the size, the entrapment efficiency, and the nanoparticles recovery efficacy. The capability of free, and encapsulated, AlPc and InPc in photooxidating the bovine serum albumin (BSA) and tryptophan (Trp) was monitored by fluorescence. The AlPc-loaded nanoparticles had a larger size and a greater entrapment efficiency than that obtained by InPc-loaded nanoparticles. The free InPc was more efficient than the free AlPc to photooxidize the BSA and Trp; whereas the encapsulated AlPc was more efficient than encapsulated InPc to photooxidize the biomolecules. The higher hydrophobicity of the AlPc, combined with the greater aggregation state and the major interaction with the BSA, quenching the capacity of the free AlPc to photooxidate the biomolecules; whereas the greater interaction of the AlPc with PHB reduce the aggregation effect on the free molecules in the aqueous phase and increase the entrapment efficiency, resulting in an improving of the photodynamic efficiency and an increase of the photooxidation rate constant.

Sulfate-accelerated photochemical oxidation of arsenopyrite in acidic systems under oxic conditions: Formation and function of schwertmannite

The weathering of arsenopyrite is closely related to the generation of acid mine drainage (AMD) and arsenic (As) pollution. Solar radiation can accelerate arsenopyrite oxidation, but little is known about the further effect of SO42− on the photochemical process. Here, the photooxidation of arsenopyrite was investigated in the presence of SO42− in simulated AMD environments, and the effects of SO42− concentration, pH and dissolved oxygen on arsenopyrite oxidation were studied as well. SO42− could accelerate the photooxidation of arsenopyrite and As(III) through complexation between nascent schwertmannite and As(III). Fe(II) released from arsenopyrite was oxidized to form schwertmannite in the presence of SO42–, and the photooxidation of arsenopyrite occurred through the ligand-to-metal charge-transfer process in schwertmannite–As(III) complex along with the formation of reactive oxygen species in the presence of O2. The photooxidation rate of arsenopyrite first rose and then fell with increasing SO42− concentration. In the pH range of 2.0–4.0, the photooxidation rate of arsenopyrite progressively increased in the presence of SO42−. This study reveals how SO42− promotes the photooxidation of arsenopyrite and As release in the AMD environment, and improves the understanding of the transformation and migration of As in mining areas.

Abiotic anoxic iron oxidation, formation of Archean banded iron formations, and the oxidation of early Earth

Iron in the early anoxic oceans of Archean age (4000-2500 million years ago) is believed to have been oxidized to form banded iron formations (BIF). Previously, it has been proposed that iron was oxidized either by free oxygen, H2O2, microbial oxidation, or photo-oxidation. However, these mechanisms are difficult to reconcile with evidence for the oceans at that time having been largely devoid of dissolved oxygen and oxidants, together with the rarity of microbial remains in BIF and restrictively slow rates of photo-oxidation. Experiments reported here show that ferrous iron readily oxidizes in analogs of Archean anoxic seawater following the precipitation of ferrous hydroxide. Once precipitated, ferrous hydroxide undergoes decomposition to elemental iron that reacts with water at room temperature to form ferric iron and release hydrogen gas. The ferric iron may then be incorporated into green rust, a mixed ferrous-ferric phase that ages into iron minerals commonly found in BIF. Our finding suggests that anoxic iron oxidation may have contributed to the formation of oxide-facies BIF, especially Algoma-type BIF that likely formed in semi-restricted basins where ferrous hydroxide saturation was more easily achieved. Additionally, ferrous hydroxide decomposition would have contributed to early Earth's oxidation, as a result of hydrogen escape to space, thus providing new insights into environmental and biological conditions on early Earth.