Regeneration Of Fe2 Research Articles

Study on removal of NO from flue gas by ferrous cysteine solution and analysis of reaction process

Wet denitrification technology has been extensively researched for its benefits in synergistically treating pollutants. As a representative complexing agent, ferrous cysteine (Fe2+(CyS)2) solution in the complex absorption method has attracted the attention of researchers. In this study, the influence of c(Fe2+):c(CySH) ratio, complexation time, initial pH value, and temperature on the NO removal efficiency and reaction process of Fe2+(CyS)2 in a bubbling reactor were investigated. The results highlighted the significance of the initial pH of the Fe2+(CyS)2 solution in denitrification efficiency, with higher pH leading to improved NO removal. The denitrification efficiency showed a volcano-like variation with increasing temperature and was not much affected by NO inlet concentration and Fe2+(CyS)2 solution complexation time. Under optimal conditions, the denitrification efficiency remained above 80 % for 3 h of continuous reaction, peaking at 98.4 %. Calculations of NO absorption capacity indicated the regeneration of Fe2+(CyS)2 solutions. Testing with iodometric and bromine-ferrous titration methods revealed that the reaction product of cysteine is cystine, maintaining material balance before and after the reaction. Experimental results validate Fe2+(CyS)2 as an effective and stable denitrification method, laying the foundation for potential industrial application.

Synergies of Mn modified Fe-based MOF enhanced catalytic ozonation: charge transfer and multiple sites mechanism

The conjoint improvement of catalytic ozonation activity and stability for MOFs materials has always been an urgent challenge. Metal doping offers a viable approach to inspire the interaction between active components and O3 due to the optimization of electronic structure and introduction of surface-active sites. In this work, 88A-Mn catalyst derived from MIL-88A was prepared by loading Mn to MIL-88A with a simple pyrolysis method. The structure and physical characterizations confirmed the coexistence of Fe and Mn in the catalyst. The 88A1-Mn1-350 exhibited the efficient degradation of ibuprofen in catalytic ozonation system, with its degradation rate showing 3.6 times and 2.6 times higher than those of the O3 system and the 88A-T/O3 system, respectively. Mechanism analysis indicated the synergistic effect among Fe/Mn interaction, surface hydroxyl group, and O-C=O group promoted the continuous generation of ROS, including ·OH and ·O2-. Specifically, the regeneration of Fe2+ derived from the Mn doping contributed to the recovery of catalytic activity and played an indispensable role in maintaining high efficiency. In addition, 88A1-Mn1-350 possessed outstanding stability in a wide range of pH (3-11) and the coexistence of anions. It also exhibited the superiority compared with traditional catalysts. This finding provides a feasible modification approach to enhance the property of MOFs materials, and achieves the efficient remove of refractory organics in catalytic ozonation system.

Exploring the impact of ultrasound on antibiotic-resistant bacteria inactivation in the sulfidated zero valent iron/persulfate system

Antibiotic resistance poses huge challenge on human beings. In this study, we evaluated the removal of antibiotic-resistant E. coli and antibiotic-resistant genes through sulfidated zero valent iron activated persulfate system under ultrasound (33 kHz, 40 W). In the proposed system, the inactivation efficiency was significantly improved, 7.8 log AR E. coli were inactivated in 30 min. And antibiotic-resistant genes (ampC and TetB) were also removed after treatment by the system. Impressively, a switch in the AR E. coli decay model from pseudo second order kinetics (R2 = 0.969) to first order kinetics (R2 = 0.981) was found with the introduction of ultrasound. Ultrasound changes in cellular and S-ZVI/PDS reaction processes are the main reason. Ultrasound converted the system from a heterogeneous process to a homogeneous process. Fe2+ played the main role in the radical generation and the fate of Fe2+ was explored by XPS and XRD. Not only sulfidation promoted the release and regeneration of Fe2+, but also ultrasound accelerated the migration of Fe2+ from the S-ZVI surface to the solution. Reactive oxygen species (OH·, SO4-·, and O2-·) were the vital reasons for antibiotic-resistant E. coli elimination. TEM and FTIR analyses illustrated the changes in cell structure and substance after treatment. Ultrasound boosted cell membrane deformation and rupture which accelerated their inactivation under free radical attack.

Fe3S4/biochar catalysed heterogeneous Fenton oxidation of organic contaminants: Hydrogen peroxide activation and biochar enhanced reduction of Fe (III) to Fe (II)

Greigite and biochar are two important materials recently gaining importance in Fenton catalysis to remove organic contaminants. Each material, however, has significant drawbacks. For instance, biochar is challenging to remove from reaction media despite having good Fenton activities, whereas greigite (FS) exhibits limited Fenton activities in the absence of light. To make both materials useful, we prepared Fe3S4/ biochar (FSBC) composite to enhance the reactivity, stability, and reusability, which could be used for large-scale applications in organic pollutant degradation. At room temperature, the developed catalysts demonstrated good Fenton degradation efficiency toward cationic and anionic dyes as well as phenols. About 90.2 % of Eriochrome Black T (EBT) degradation was accomplished at pH 4 within 1 h without light irradiation. The activation of H2O2 to generate hydroxyl radicals was enhanced by the addition of biochar to the Fe3S4 for the degradation of pollutants. The electrons produced by the biochar and the S-generated specie on the Fe3S4 surface boost the surface iron redox cycle with the regeneration of Fe2+ ions. The biochar has a crucial role in enhancing the activity by 10 % in 1 h in the presence of magnetic Fe3S4 with a rate constant of 0.0372 min−1.The biochar provides stability to the Fe3S4/ biochar composite with minimum Fe leaching and is recovered magnetically from the reaction mixture by using external magnets, which can be used for five catalytic cycles without significant loss of catalytic activity. The reported catalyst, which overcame the individual limitations of both the FS and biochar to improve catalyst activity and magnetic separation, will serve as the foundation for creating novel catalyst systems for the future degradation of organic pollutants.

Disclosing the mutual influence of photocatalytic fuel cell and photoelectro-Fenton process in the fabrication of a sustainable hybrid system for efficient Amaranth dye removal and simultaneous electricity production.

Photocatalytic fuel cell (PFC) was employed to provide renewable power sources to photoelectro-Fenton (PEF) process to fabricate a double-chambered hybrid system for the treatment of azo dye, Amaranth. The PFC-PEF hybrid system was interconnected by a circuit attached to the electrodes in PFC and PEF. Circuit connection is the principal channel for the electron transfer and mobility between PFC and PEF. Thus, different circuit connections were evaluated in the hybrid system for their influences on the Amaranth dye degradation. The PFC-PEF system under the complete circuit connection condition attained the highest decolourization efficiency of Amaranth (PFC: 98.85%; PEF: 95.69%), which indicated that the complete circuit connection was crucial for in-situ formation of reactive species in dye degradation. Besides, the pivotal role of ultraviolet (UV) light irradiation in the PFC-PEF system for both dye degradation and electricity generation was revealed through various UV light-illuminating conditions applied for PFC and PEF. A remarkable influence of UV light irradiation on the production of hydrogen peroxide and generation and regeneration of Fe2+ in PEF was demonstrated. This study provided a comprehensive mechanistic insight into the dye degradation and electricity generation by the PFC-PEF system.

Concentration Dependence of Anti- and Pro-Oxidant Activity of Polyphenols as Evaluated with a Light-Emitting Fe2+-Egta-H2O2 System.

Hydroxyl radical (•OH) scavenging and the regeneration of Fe2+ may inhibit or enhance peroxidative damage induced by a Fenton system, respectively. Plant polyphenols reveal the afore-mentioned activities, and their cumulative net effect may determine anti- or pro-oxidant actions. We investigated the influence of 17 phenolics on ultra-weak photon emission (UPE) from a modified Fenton system (92.6 µmol/L Fe2+, 185.2 µmol/L EGTA (ethylene glycol-bis(β-aminoethyl-ether)-N,N,N′,N,-tetraacetic acid) and 2.6 mmol/L H2O2 pH = 7.4). A total of 8 compounds inhibited (antioxidant effect), and 5 enhanced (pro-oxidant effect) UPE at all studied concentrations (5 to 50 µmol/L). A total of 4 compounds altered their activity from pro- to antioxidant (or vice versa) along with increasing concentrations. A total of 3 the most active of those (ferulic acid, chlorogenic acid and cyanidin 3-O-glucoside; mean UPE enhancement by 63%, 5% and 445% at 5 µmol/L; mean UPE inhibition by 28%, 94% and 24% at 50 µmol/L, respectively) contained catechol or methoxyphenol structures that are associated with effective •OH scavenging and Fe2+ regeneration. Most likely, these structures can determine the bidirectional, concentration-dependent activity of some phenolics under stable in vitro conditions. This is because the concentrations of the studied compounds are close to those occurring in human fluids, and this phenomenon should be considered in the case of dietary supplementation with isolated phenolics.

Sustainable Electrochemical NO Capture and Storage System Based on the Reversible Fe2+/Fe3+-EDTA Redox Reaction

The removal of nitric oxide (NO), which is an aggregation agent for fine dust that causes air pollution, from exhaust gas has been considered an important treatment in the context of environmental conservation. Herein, we propose a sustainable electrochemical NO removal system based on the reversible Fe2+/Fe3+-ethylenediamine tetraacetic acid (EDTA) redox reaction, which enables continuous NO capture and storage at ambient temperature without the addition of any sacrificial agents. We have designed a flow-type reaction system in which the NO absorption and emission can be separately conducted in the individual reservoirs of the catholyte and anolyte with the continuous regeneration of Fe2+-EDTA by the electrochemical reduction in Fe3+-EDTA. A continuous flow reaction using a silver cathode and glassy carbon anode showed that the concentrations of Fe2+ and Fe3+-EDTA in the electrolyte were successfully maintained at a 1:1 ratio, which demonstrates that the proposed system can be applied for continuous NO capture and storage.

Solar photo-assisted electrochemical processes applied to actual industrial and urban wastewaters: A practical approach based on recent literature

The application of electrochemical processes for wastewater treatment has increase significantly in the last two decades. However, most of the works are focused on lab-scale systems testing in saline simulated solutions spiked with a reference organic compound, evidencing the scarcity of studies on actual wastewaters through a more realistic practical approach. The aim of the present work is assessing the performance of electrochemical treatments in actual matrices, considering the formation of different oxidants species, apart from hydroxyl radicals, from dissolved ions contained in target effluents as well as both, the regeneration of Fe2+ and their combination with a light irradiation source. The degradation of a mix of microcontaminants in water matrices with different complexity by solar photoelectron-Fenton at natural pH and at pilot scale has been carried out at Plataforma Solar de Almería. Higher degradation rates were obtained when focusing on the more complex and saline matrices. In addition, complex industrial wastewaters mineralization was also studied by means of solar assisted electro-oxidation, showing the crucial role of ammonium concentration in the effluent, since it acts as a competitor for active chlorine species and so reducing the mineralization rate.

Converting Ag3PO4/CdS/Fe doped C3N4 based dual Z-scheme photocatalyst into photo- Fenton system for efficient photocatalytic phenol removal

In this work, a dual Z-scheme Ag3PO4/CdS/Fe-g-C3N4 (AP/CdS/FeCN) photocatalyst was prepared by precipitation- deposition method. AP/CdS/FeCN photocatalyst was converted into the heterogenous photo-Fenton system with the addition of H2O2. The synergistic coupling between AP/CdS/FeCN and H2O2 resulted in enhanced for phenol degradation, with a rate constant of constant 6.2×10−4s-1, which is 1.31 and 1.61 times than that of AP/CdS/FeCN and Fe2O3/H2O2. The enhancement in photodegradation was attributed to (i) more regeneration of Fe2+ ions, (ii) enhanced visible light absorption, (iii) elevated redox potential due to more hydroxyl radical’s formation, and (iv) low Fe leaching in the reaction solution. As indicated by EIS, PL, and trapping experiments, photoinduced CB electrons of g-C3N4 and CdS were transferred entirely to Fe3+ to regenerate Fe2+ ions to accelerate the Fenton cycle. In comparison to the conventional Fe2O3/H2O2 Fenton process, Fe ion leaching in AP/CdS/FeCN/H2O2 catalytic system was almost negligible. It confirmed strong chemical interaction of Fe3+ with g-C3N4. AP/CdS/FeCN/H2O2 displayed significant catalytic efficacy and firmness for five successive catalytic cycles. Moreover, the AP/CdS/FeCN/H2O2 nanocomposite exhibited substantial mineralization perfomance for other phenolic pollutants. The results demonstrate that AP/CdS/FeCN/H2O2 catalytic system has the potential for water purification.

Mechanism investigation of carboxyl functional groups catalytic oxidation in coal assisted water electrolysis cell

The electric energy consumption for H2 production can be significantly reduced by integrating chemical energy of coal in the coal assisted water electrolysis (CAWE) process. While the oxidation mechanism of coal has not been comprehensively demonstrated. In this work, the oxidation mechanism of carboxyl group, a typical oxygen-functional group of coal, was systematically investigated by preparing a model compound of carboxylated graphene. For direct oxidation of carboxylated graphene (GCM), the onset potential was close to 1.2 V at ambient temperature. The apparent activation energy for hydrogen production was dramatically diminished by electrolysis of GCM slurry. The products analysis indicated that carboxyl groups can be oxidized to CO and CO2 at 90 °C around 1.6 V Fe3+ was sufficient to oxidize carboxyl groups to generate Fe2+ at 90 °C. The chemical oxidation of carboxyl groups was a first-order reaction accompanied by adsorption, oxidization and desorption stages. In the presence of Fe2+/Fe3+, electrolysis initiated at about 0.5 V. A gentle slope of voltage from 0.6 V to 1.2 V was observed in the continuous electrolysis and the regeneration of Fe2+ became the limiting step for a long period of time. The results are essential to guide the application of CAWE.

Electrochemical-assisted leaching of active materials from lithium ion batteries

The development of a circular economy for lithium-ion batteries (LIB) is essential to realize decarbonization and an electrified energy market. However, the current commercial operations that recover valuable constituents from LIBs require significant energy and reagents, which create toxic emissions and additional waste. We report an electrochemical-based method for leaching valuable metals from the active materials of mixed shredded LIBs. In this process, the use electrons, as green reagent, allows the use and regeneration of Fe2+ in low concentrations as substitute for hydrogen peroxide as a reducing agent. Leaching in a membrane separated two-compartment electrochemical cell contributes to decrease the acid requirements as H+ can be generated electrochemically. With this design, leaching efficiencies over 96% for the active metals (Li, Co, Mn, and Ni) were demonstrated at pulp densities up to 240 g/L. Copper present in the active material is electrowon and recovered separately. Preliminary cost analyses demonstrate ca. 80% reduction in energy and chemical costs as compared to traditional hydrometallurgical routes.

β-FeOOH catalyzed peroxymonosulfate for organic pollutant degradation in water: radical and non-radical mechanism

Iron-based catalysts as peroxymonosulfate (PMS) activator are commonly used to oxidize and degrade azo dye. However, there are still some issues such as low catalytic performance, relatively less reactive oxygen species and high metal iron dissolution. As such, a novel iron oxyhydroxide (FeOOHs) with four crystal form was synthesized and employed as efficient PMS activator for AO7 degradation in this study. It was found that the crystal form of catalyst had significant influence on its catalytic performance. β-FeOOH exhibited the best catalytic performance, owing to its smallest lattice size, maximum specific surface area and highest surface hydroxyl density. β-FeOOH/PMS system possessed a great high apparent reaction rate constant (1.3919 h−1), which was about 17, 3, 31, 20, 14, 49 and 23 times higher than that in β-FeOOH/persulfate(PS), Fe0/PMS, Fe0/PS, Fe2O3/PMS, Fe2O3/PS, Fe3O4/PMS and Fe3O4/PS system, respectively. More importantly, radical quenching tests and Electron spin resonance (ESR) analysis revealed that OH., SO4.−, O2.− and 1O2 were involved in the reaction process. The catalytic mechanism proposed that β-FeOOH had the effective electron transfer rate performance, and Fe3+ underwent a reduction to Fe2+ during the β-FeOOH/PMS catalytic oxidation process. Then, the regeneration of Fe2+ on the hydroxylated surface of FeOOH promoted the formation of FeOH+, which was crucial for PMS activation and reactive oxygen species (ROS) generation. The recyclability tests proved good stability and reusability of β-FeOOH. This study provides a kind of new understanding of peroxymonosulfate activation for environmental remediation and advances the study of iron-based oxyhydroxide in heterogeneous catalysis.

Decolorization of Crystal Violet from Aqueous Solution Using Electrofenton Process

In recent years, advance oxidation processes (AOPs) have been widely interested for treatment of industrial wastewater and organic matter. At among, Electrofenton has been proposed as a strong oxidative method. So, the aim of this work was purification of colored aqueous containing crystal violet by electrofenton process and steel mesh electrodes. All regents and methods were prepared from analytical grad and standard methods. The amounts of crystal violet were determined by colorimetric using a spectrophotometer at a maximum wavelength about 586 nm. The main parameters such as pH, applied current, dye concentration, reaction time and supporting electrolyte dose were investigated. Experimental data analysis was also performed using excel software. The results of this study showed that the better dye degradation is occurred in acidic pH (pH3), contact time of 5 minutes, initial concentration of crystal violet 50 mg/l, applied current 0.8 A and an electrolyte level about 0.1 g/L of NaCl. Higher electrical current and lower pHs were caused to generate the higher amount of oxidative radical and regeneration of Fe2+. Under optimal condition, crystal violet was removed around 99.72%. Referring to the results, it can be concluded that the electrofenton is a suitable in situ hydrogen peroxide generation technology for treatment of colored wastewater.

Development of a synthesis method for odor sesquiterpenoid, (-)-rotundone, using non-heme Fe2+-chelate catalyst and ferric-chelate reductase.

(-)-Rotundone, a sesquiterpenoid that has a characteristic woody and peppery odor, is a key aroma component of spicy foodstuffs, such as black pepper and Australian Shiraz wine. (-)-Rotundone shows the lowest level of odor threshold in natural compounds and remarkably improves the quality of various fruit flavors. To develop a method for the synthesis of (-)-rotundone, we focused on non-heme Fe2+-chelates, which are biomimetic catalysts of the active center of oxygenases and enzymatic supply and regeneration of those catalysts. That is, we constructed a unique combination system composed of the oxidative synthesis of (-)-rotundone using the non-heme Fe2+-chelate catalyst, Fe(II)-EDTA, and the enzymatic supply and regeneration of Fe2+-chelate by ferric-chelate reductase, YqjH, from Escherichia coli. In addition, we improved the yield of (-)-rotundone by the application of cyclodextrin and glucose dehydrogenase to this system, and thus established a platform for efficient (-)-rotundone production.

Fe(II)-promoted activation of peroxymonosulfate by molybdenum disulfide for effective degradation of acetaminophen

In this study, it was demonstrated that the Fe ion was an effective promoter of bulk MoS2 for the activation of peroxymonosulfate (PMS) to degrade acetaminophen (ACT). ACT removal rate constant in the presence of 5 mg/L FeSO4·7H2O (0.1099 min−1) was approximately 20 times as that in the absence (0.0045 min−1) with 0.1 g/L MoS2 of FeSO4·7H2O at pH0 3. Both electron paramagnetic resonance (EPR) characterization and quenching experiment suggested the key role of singlet oxygen (1O2), acting as dominant reactive species responsible for ACT degradation in the Fe2+/MoS2/PMS system. Besides, the chemical state and composition of MoS2, the ion (Fe and Mo) concentrations and the speciation of Mo(VI) were investigated. Results suggested that the promoting effect of Fe(II) ion originated from the regeneration of Fe2+ mediated by MoS2, and the formation of molybdenum(VI) peroxo complex species in Fe2+/MoS2/PMS system. The present study not only provides an insight into PMS activation by MoS2 accelerated by Fe(II) ion, but also suggests an high-efficiency, easy-to-handle and environmentally friendly method to treat refractory wastewater.

Near‐neutral Electro‐Fenton Treatment of Pharmaceutical Pollutants: Effect of Using a Triphosphate Ligand and BDD Electrode

AbstractIn this work, a mixture of pharmaceutical pollutants was successfully treated by electro‐Fenton (EF) at near‐neutral pH using the inorganic ligand triphosphate (TPP). The effect of the ligand and the reactivity of its Fe complexes were thoroughly investigated under different conditions of TPP : Fe2+ ratio, Fe2+ and TPP concentrations, current density, and nature of the anode material (Ti/IrO2−RuO2 and boron doped diamond, BDD). The mineralization of organics was mainly controlled by the EF reaction promoted by the continuous electrochemical formation of H2O2 and regeneration of Fe2+ (as Fe2+‐TPP), while the main role of the ligand was to keep active Fe2+ ions dissolved in solution to catalyze the Fenton's reaction at near‐neutral pH. The results contrasted with previous works that reported the ability of Fe‐TPP to enhance the oxidation performance of Fenton‐like systems. Moreover, the remarkable oxidative properties of diamond electrodes enhanced the mineralization efficiency and TPP was not detrimental to oxidation with BDD. Finally, the degradation kinetics of all the compounds under investigation were determined, and a pathway for the antidepressant amitriptyline (ATTL) was proposed.

Effects of Fe and V States on the Fenton Catalytic Activity of Natural Rutile

AbstractAs a common mineral phase on Earth and Martian regolith, natural rutile was reported as a potential candidate for use as a Fenton catalyst in this study. The influences of Fe and V in various chemical states on the generation of reactive oxygen species (ROSs) and the catalytic activity of rutile were examined. A series of rutile samples with various surface and bulk states of Fe and V were obtained initially by hydrogen annealing of natural rutile at ~773–1173 K. X-ray diffraction, electron paramagnetic resonance spectra, and X-ray photoelectron spectroscopy demonstrated that the atomic fractions of Fe(III) and V(V) decreased sharply with increasing temperature, along with the accumulation of surface Fe(II) and bulk V(III). All as-prepared materials showed enhanced Fenton degradation efficiency on methylene blue (MB) compared with P25-TiO2, and the treated samples exhibited up to 3.5-fold improvement in efficiency at pH 3 compared to the untreated sample. The improved efficiency was attributed mainly to Fenton catalysis involving Fe(II) and V(III). The dissolved Fe2+ played a crucial role in the homogeneous Fenton reaction, while the bound V(III) favored adsorption primarily and may have facilitated heterogeneous Fenton reaction and the regeneration of Fe2+. The pH regulated the reaction mechanism among homogeneous (pH = 3) and heterogeneous (pH = 3.7) Fenton catalysis and physical adsorption (pH = 5, 6). The aim of the present study was to improve the understanding of the potential role of natural rutile with advanced oxidation functions in Earth systems and even on Mars, which also provide an inspiration for screening natural rutile and any other similar, Earth-abundant, low-cost minerals for environmental application.

The role of quinone cycle in Fe2+–H2O2 system in the regeneration of Fe2+

ABSTRACTThe reaction between Fe2+ and H2O2 generates highly reactive ·OH. However, the weak conversion from Fe3+ to Fe2+ limits its continuous reaction. Here, the difference between the Fenton system and modified Fenton system for the regeneration of Fe2+ was analyzed. A UV-vis spectrometer and redox potential measurements were used to detect Fe2+ concentration. Results indicated that Fe2+ could be better regenerated in the modified Fenton system. The regeneration of Fe2+ was facilitated by the consumption of NH2OH, while in hydroquinone (HQ)- and 1,4-bezoquinone (1,4-BQ)-modified Fenton systems, the quinone cycle could be built up and Fe3+ could be converted to Fe2+ continuously. However, results showed that HQ and 1,4-BQ reacted with ·OH, which caused a gradual decline in the enhancement effect. In order to keep Fe2+ concentration stable for a longer time, the influence of [HQ/1,4-BQ]0/[Fe2+]0 on Fe2+ concentration was carefully studied. When the mole ratio was 5:1, Fe2+ concentration remained nearly 90% of total iron at 40 min. But when the mole ratios were 0.5:1 and 0.1:1, Fe2+ concentration decreased to a very low level at 20 min. Oxidation–reduction potential (ORP) results further confirmed the role of quinone cycle.

Semiconducting Mineral Photocatalytic Regeneration of Fe2+ Promotes Carbon Dioxide Acquisition by Acidithiobacillus ferrooxidans

Abstract:Chemoautotrophic organisms have once been excluded from the development of universally applicable CO2 fixation technology due to its low production yields of biomass. In this study, we used Acidithiobacillus ferrooxidans (A.f.) as a model chemoautotrophic microorganism to test the hypothesis that exogenetic photoelectrons from semiconducting mineral photocatalysis can enable the regeneration of Fe2+ that could be then used by A.f. and support its growth. In a simulated electrochemical system, where exogenetic electrons were provided by an electrochemical approach, an accelerated growth rate of A.f. was observed as compared with that in traditional batch cultivation. In a coupled system, where light‐irradiated natural rutile provided the primary electron source to feed A.f., the bacterial growth rate as well as the subsequent CO2 fixation rate was demonstrated to be in a light‐dependent manner. The sustaining flow of photogenerated electrons from semiconducting mineral to bacteria provided an inexhaustible electron source for chemoautotrophic bacteria growth and CO2 fixation. This finding might contribute to the development of novel effective CO2 fixation technology.

Influence of Chelating Agents on Fenton-Type Reaction Using Ferrous Ion and Hypochlorous Acid

Iron-based advanced oxidation technologies, such as the Fenton process, are widely used for industrial wastewater treatment. However, wastewater sometimes contains chelating agents such as detergents, stabilizers, and masking agents for metallic ions, which have a potential to inhibit the iron-based advanced oxidation process through the masking of iron. In this research, we investigated the influence of chelating agents on Fenton-type reaction using ferrous ion (Fe2+) and hypochlorous acid (HOCl). Chelating agents tested were oxalic acid, ethylenediaminetetraacetic acid (EDTA) and 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP). Hydroxyl radicals generated were determined by 1,4-dioxane degradation. When HOCl was reacted with Fe2+ at pH 6.0, oxalic acid and EDTA strongly inhibited the 1,4-dioxane degradation. However, the inhibition effect declined at acidic pH because of the protonation of carboxyl groups in the chelating agents. The HEDP differed from the other chelating agents in the inhibition effect. It showed the inhibition effect only under the low dose at pH 6.0. On the contrary, the higher dose and acidic pH enhanced the 1,4-dioxane degradation efficiency. The regeneration of Fe2+ from ferric ion (Fe3+) by the degradation of Fe3+-HEDP complex was inferred to be responsible for the enhancement effect.