Defect electrons accelerate iron cycle of novel Fe-based Fenton:Long-term effective quinoline degradation

Heterogeneous Fenton has been widely used in the disposal of organic pollutants,however,slow regeneration of≡Fe(II)remains limitation for its practical application of long-term treatment.Herein,we come up with a novel Fe-based heterogeneous Fenton catalyst named as FeS_(x)O_(y)-X(X is the ratio of ethylene glycol to N,N-dimethylformamide).With the help of the abundant defect electrons in Sulfur vacancies,≡Fe(Ⅱ)regeneration on the surface of FeS_(x)O_(y)-1:1 was accelerated,resulting in a stable proportion of≡Fe(Ⅱ)on the surface,which maintained continuously stable generation of hydroxyl radical(·OH)and singlet oxygen(^(1)O_(2)).Thus,without any organic reagents or cocatalysts,FeS_(x)O_(y)-1:1 based Fenton system achieved effective long-term degradation of 560 mg/L quinoline within only 7 days,which was evidently better than reported Fe S and SV-Fe S_(2)(SV:Sulfur vacancy).The system had excellent adaptability to water quality and the COD removal rate of biochemical wastewater was as high as 79.8%.

Efficient decomposition of sulfamethoxazole in a novel neutral Fered-Fenton like/oxalate system based on effective heterogeneous-homogeneous iron cycle

In this study,efficient sulfamethoxazole(SMX) degradation was demonstrated in a novel neutral FeredFenton like/oxalate(electro-Fe^2+/PDS/Ox,Fered-FL/Ox) system adopting pre-anodized Ti@Ti02 cathode.Optimization of operational parameters was conducted and the whole reaction mechanism based on the critical solid-liquid interfacial reactions was explored.An efficient neutral heterogeneous-homogenous iron cyclewould exist in the Fered-FL/Ox system,depending on the formation of specific C-O-Ti bonds through the inner sphere surface complex(ISSC) of Fe(C2 O4)3^3-.It would induce ultrafast electron transfer from the cathode to the FeⅢ core,effectively accelerating the neutral Fenton-like reactions and complete mineralization of SMX with relative low dosage of ferrous catalyst and applied voltage.The result of this study is expected to supply a good alternative in treating complex neutral industrial wastewaters.

The sources and transport of iron in the North Paci?c and its impact on marine ecosystems

The limitation of iron(Fe)makes the North Pacific a typically high-nitrate,low-chlorophyll(HNLC)region in comparison with other oceanic regions of the world.Iron inputs from land via river discharge and atmospheric dust deposition are the primary processes introducing Fe into the ocean.Also,subsequent physical processes are crucial in transporting biologically available Fe into the upper ocean.As anthropogenic dust increases,the Fe from anthropogenic activities is expected to become more important in terms of impacting marine ecosystems.To investigate the Fe cycle and its impact on ecosystems,a project entitled‘The sources and transport of Fe in the North Pacific and its impact on marine ecosystems’has been funded by the National Natural Science Foundation of China.The project will focus on three major scientific questions:(1)What are the major sources of Fe in the North Pacific?(2)What is the influence of the Fe-binding ligand cycle on marine ecosystems?(3)What is the likely influence of global change in the future?The distribution of Fe and its corresponding impact on the marine ecosystem in current and future environmental conditions will be investigated.The results of the project are expected to improve our understanding of the marine ecosystem in the North Pacific.

Release the iron: does the infection of magnetotactic bacteria by phages play a role in making iron available in aquatic environments?

Magnetotactic bacteria(MTB)are ubiquitous prokaryotes that orient along magnetic field lines due to magnetosomes’biomineralization within the cell.These structures are ferrimagnetic organelles that impart a magnetic moment to the cell.To succeed in producing magnetosomes,MTB accumulate iron in(i)cytoplasm;(ⅱ)magnetosomes;and(ⅲ)nearby the organelle.It has already been estimated that a single MTB has an iron content of 10 to 100-fold higher than Escherichia coli.Phages are the most abundant entity in oceans and are known for controlling nutrient flow such as carbon and nitrogen by viral shunt and pump.The current work addresses the putative role of phages that infect MTB on the iron biogeochemical cycle.Can phage infection in MTB hosts cause a biogenic iron fertilization-like event in localized microenvironments?Are phages critical players in driving magnetosome biomineralization genes(BGs)horizontal transfer?Further investigation of those events,including frequency of occurrence,is necessary to fully comprehend MTB’s effect on iron cycling in aqueous environments.

Effect of iron transformation on Acidithiobacillus ferrooxidans bio-leaching of clay vanadium residue

The acid bio-leaching process of vanadium extraction from clay vanadium water-leached residue was studied and the effect of the performance of iron transformation was investigated.Acidithiobacillus ferrooxidans affects the dissolution of vanadium through the catalytic effect on Fe^3+/Fe^2+couple and material exchange.The passivation of iron settling correlates with ferrous ion content in bio-leaching solution.In medium containing A.ferrooxidans and Fe(Ⅲ),the increment in Fe(Ⅱ)concentration leads to the formation of jarosite,generating a decline in vanadium extraction efficiency.Analysis of cyclic voltammetry shows that Fe(Ⅱ)ion is apt to be oxidized and translated into precipitate by A.ferrooxidans,which strongly adsorbed to the surface of the residue.Fe(Ⅲ)ion promotes the vanadium extraction due to its oxidizing activity.Admixing A.ferrooxidans to Fe(Ⅲ)medium elevates the reduction of low valence state vanadium and facilitates the exchange of substance between minerals and solution.This motivates 3.8%and 21.8%increments in recovery ratio and leaching rate of vanadium compared to the Fe(Ⅲ)exclusive use,respectively.Moreover,Fe(Ⅱ)ion impacts vanadium extraction slightly in sterile medium but negatively influences vanadium leaching in the presence of bacteria.

Hematite-facilitated microbial ammoxidation for enhanced nitrogen removal in constructed wetlands

Constructed wetlands(CWs)are widely applied for decentralized wastewater treatment.However,achieving efficient removal of ammonia(NH+-N)has proven challenging due to insufficient oxygen.In this study,natural hematite(Fe,O3)was employed as a CW substrate(H-CWs)for the first time to drive anaerobic ammonia oxidation coupled with iron(I)reduction(Feammox).Compared to gravel constructed wetlands(G-CWs),ammonia removal was enhanced by 38.14%to 54.03%and nitrous oxide(N_(2)0)emissions were reduced by 34.60%in H-CWs.The synergistic removal of ammonia and nitrate by H-CWs also resulted in the absence of ammoxidation by-products.Inhibitor and 15N isotope tracer incubations showed that Feammox accounting for approximately 40%of all ammonia removal in the H-CWs.The enrichment of iron phosphate(Fe_(3)Fe_(4)(PO_(4))_(6))promoted the accumulation of the Feammox intermediate compound FeOOH.Microbial nanowires were observed on the surface of H-CW substrates as well,suggesting that the observed biological ammoxidation was most likely related to extracellular electron transfer(EET).Microbial and metagenomics analysis revealed that H-CWs elevated the integrity and enhanced the abundance of functional microorganisms and genes associated with nitrogen metabolism.Overall,the efficient ammonia removal in the absence of O2 together with a reduction in N_(2)O emissions as described in this study may provide useful guidance for hematite-mediated anaerobic ammonia removal in CWs.

Visible light induced efficient activation of persulfate by a carbon quantum dots(CQDs)modifiedγ-Fe_(2)O_(3) catalyst

In this study,a carbon quantum dots modified maghemite catalyst(CQDs@γ-Fe_(2)O_(3))has been synthesized by a one-step solvothermal method for efficient persulfate(PDS)activation under visible light irradiation.Transmission electron microscopy(TEM),scanning electron microscopy(SEM)and UV-vis diffuse reflectance spectroscopy(UV-vis DRS)characterization indicated that the formation of heterojunction structure between CQDs and y-Fe_(2)O_(3) effectively reduced the catalyst band gap(Eg),favoring the separation rate of electrons and holes,leading to remarkable efficient sulfamethoxazole(SMX)degradation as compared to the dark-CQDs@γ-Fe_(2)O_(3)/PDS and vis-γ-Fe_(2)O_(3)/PDS systems.The evolution of dissolved irons also demonstrated that CQDs could accelerate the in-situ reduction of surface-bounded Fe^(3+).Electron paramagnetic resonance(EPR)and radical scavenging experiments demonstrated that both*OH and SO_(4)·were generated in the reaction system,while*OH was relatively more dominant than SO_(4)·for SMX degradation.Finally,the reaction mechanism in the vis-CQDs@y-Fe_(2)O_(3)/PDS system was proposed involving an effective and accelerated heterogeneous-homogeneous iron cycle.CQDs would enrich the photo-generated electrons from y-Fe_(2)O_(3),causing efficient interfacial generation of surfacebond Fe^(2+)and reduction of adsorbed Fe3+.This visible light induced iron cycle would eventually lead to effective activation of PDS as well as the efficient degradation of SMX.

A collaborative strategy for enhanced reduction of Cr(Ⅵ) by Fe(0) in the presence of oxalate under sunlight:Performance and mechanism

Nanometer-size zero-valent iron(NZVI)is an efficient reducing agent,but its surface is easily passivated with an oxide layer,leading to reaction inefficiency.In our study,oxalate(OA)was introduced into this heterogeneous system of NZVI,which could form ferrioxalate complexes with the NZVI surface-bound Fe3+and dissolved Fe3+in the solution.Photolysis of ferrioxalate complexes can facilitate the generation of Fe2+from Fe3+and CO2·-radical,both species have strong reduction capacity.Hence,a"photo-oxalate-Fe(0)"system through sunlight induction was established,which not only prohibited the formation of a surface passivation layer,but also displayed a synergetic mechanism of ferrioxalate photolysis to enhance reduction,exhibiting remarkably higher degradation activity(several times faster)toward the model pollutant Cr(Ⅵ)than the mechanism with NZVI alone.Factor tests suggested that both NZVI dosage and OA content markedly affected the reduction rate.Low pH was beneficial to the reduction efficiency.Moreover,recyclability experiment showed that the reduction rate decreased from 0.21706 to 0.03977 min-1 after three cycles of reuse due to the NZVI losing reaction activity generally,but the system still maintained considerable reduction capacity.Finally,a mechanism was revealed whereby NZVI would transform to Fe oxides after the exhaustion of its reductive power,and the photolysis of ferrioxalate to promote the cycling of iron species played the predominant role in providing extra reduction ability.These features confirm that introduction of OA into Cr(Ⅵ)reduction by NZVI through sunlight induction is advantageous and promising.

Distinct roles of pH and organic ligands in the dissolution of goethite by cysteine

Electron shuttles such cysteine play an important role in Fe cycle and its availability in soils,while the roles of pH and organic ligands in this process are poorly understood.Herein,the reductive dissolution process of goethite by cysteine were explored in the presence of organic ligands.Our results showed that cysteine exhibited a strong reactivity towards goethite-a typical iron minerals in paddy soils with a rate constant ranging from 0.01 to0.1 hr^(-1).However,a large portion of Fe(Ⅱ) appeared to be "structural species" retained on the surface.The decline of pH was favorable to generate more Fe(Ⅱ) ions and enhancing tendency of Fe(Ⅱ) release to solution.The decline of generation of Fe(Ⅱ) by increasing pH was likely to be caused by a lower redox potential and the nature of cysteine pH-dependent adsorption towards goethite.Interestingly,the co-existence of oxalate and citrate ligands also enhanced the rate constant of Fe(Ⅱ) release from 0.09 to 0.15 hr-1;nevertheless,they negligibly affected the overall generation of Fe(Ⅱ) in opposition to the pH effect.Further spectroscopic evidence demonstrated that two molecules of cysteine could form disulfide bonds(S-S) to generate cystine through oxidative dehydration,and subsequently,inducing electron transfer from cysteine to the structural Fe(Ⅲ) on goethite;meanwhile,those organic ligands act as Fe(Ⅱ) "strippers".The findings of this work provide new insights into the understanding of the different roles of pH and organic ligands on the generation and release of Fe induced by electron shuttles in soils.

Regulating Lewis Acid-Base Sites over Fenton System for Enhancing Degradation of Pollutants in Saline and Buffered Wastewater

The saline and buffered environment in actual wastewater imposes higher demands on Fenton and Fenton-like catalytic systems.This study developed a MoS_(2)co-catalytic Fe_(2)O_(3)Fenton-like system with controllable Lewis acid-base sites,achieving efficient treatment of various model pollutants and actual industrial wastewater under neutral buffered environment.The acidic microenvironment structured by the edge S sites(Lewis basic sites)in the MoS_(2)/Fe_(2)O_(3)catalyst is susceptible to the influence of Lewis acidic sites constructed by Mo and Fe element,affecting catalytic performance.Optimizing the ratio of precursor amounts ensures the stable presence of the acidic microenvironment on the surface of catalyst,enabling the beneficial co-catalytic effect of Mo sites to be realized.Furthermore,it transcends the rigid constraints imposed by the Fenton reaction on reaction environments,thereby expanding the applicability of commonplace oxides such as Fe_(2)O_(3)in actual industrial water remediation.