Fe Valence State Research Articles

Unraveling the mechanism and the key role of amorphous structure C-O-Fe in tetracycline degradation by activation of persulfate in lotus leaf-based red mud-modified biochar

In the present study, red mud modified lotus leaf biochar was synthesized using a low-cost and concise method. The experimental results showed that when RM-HBC=0.4 g/L, PDS=4 mM, pH=5.0, the RM-HBC-PDS system exhibited the best degradation effect on TC, with the highest removal rate of 98.61 %, the highest degradation kinetics of 0.0229 min−1. Advanced characterization and density functional theory have demonstrated that the emergence of the C-O-Fe structure led to the redistribution of the surface charge of RM-HBC. This charge redistribution caused the electrons on the surface of RM-HBC to transfer from C to Fe through the C-O-Fe structure, forming an electron-rich center centered on Fe. The C-O-Fe structure facilitated the transformation of the Fe valence state within the RM-HBC while transmitting electrons, thus maintaining the regeneration of Fe(II). This further promoted the adsorption and activation ability of RM-HBC for PDS, thereby improving the degradation effect of TC in the system. XRD detection showed that the Fe3O4 crystal strength in RM-HBC after the reaction was significantly enhanced. This was due to the C-O-Fe present on the surface of RM-HBC in the process of degradation of TC, which accelerated sustained electron transfer at C-O-Fe, leading to structural fracture, recombination, and ultimately the formation of Fe3O4 crystals. Intermediate detection and toxicity prediction showed that the toxicity of TC was significantly reduced. All the above results confirmed that this study not only achieved the efficient treatment of antibiotic wastewater but also realized the rational utilization of lotus leaf and red mud resources.

Voltage Control of Multiple Electrochemical Processes during Lithium Ion Migration in NiFe2O4 Ferrite.

Li-ion-based electric field control has been attracting significant attention, since it is able to penetrate deep into materials to exhibit diverse and controllable electrochemical processes, which offer more degrees of freedom to design multifunctional devices with low power consumption. As opposed to previous studies that mainly focused on single lithiation/delithiation mechanisms, we reveal three Li-ion modulation mechanisms in the same NiFe2O4 spinel ferrite by in situ magnetometry, i.e., intercalation, conversion, and space charge, which are respectively demonstrated in high, medium, and low voltage range. During the intercalation stage, the spinel structure is preserved, and a reversible modulation of magnetization arises from the charge transfer-induced variation of Fe valence states (Fe2+/Fe3+). Conversion-driven change in magnetization is the largest up to 89 emu g-1, due to the structural and magnetic phase transitions. Although both intercalation and conversion exhibit sluggish kinetics and long response times, the space charge manifests a faster switching speed and superior durability due to its interface electrostatic effect. These results not only provide a clear and comprehensive understanding on Li-based modulation mechanisms but also facilitate multifunctional and multiscenario applications, such as multistate memory, micromagnetic actuation, artificial synapse, and energy storage.

Modulating the pore and electronic structure for targeted recovery of platinum: Accelerated kinetic and reinforced coordination

Adsorption for recovery of low-concentration platinum (Pt) from the complex composition of acidic digestates was challenging because of slow kinetic and poor affinity. It was expected to be overcome by the improvement of pore size distribution and adsorption site activity. Herein, a series of Prussian blue etchings (PBE) with porosity-rich and activity-high cyano (CN) was synthesized to recover low-concentration Pt. The N2 isotherm results showed that the pore structure evolved from mesoporous to microporous. The Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations results revealed that the modulation of electronic structure converted FeII to FeIII in [FeII(CN)6]4−. The coexistence of micro- and meso-pore structures provided channels to accelerate adsorption and ensured PtII enrichment. The regulation of Fe valence state activated CN, which reinforced the strength of coordination interaction between Pt and Fe-CN- at N-atom. The adsorption rate and maximum capacity of PBE1 were 4.4 and 2.5 times higher than those of PB, respectively, due to the dual efficacy of accelerated kinetic and reinforced coordination. This study systematically analyzes the pivotal role of pore and electronic structure modulation in adsorption kinetic and affinity, which provides a novel strategy for PtII targeted recovery.

Intervention of HCHO on the FeSx structure transition during sulfidation of zero-valent iron

Iron sulfides (FeSx) enhancing the properties of sulfidated zero-valent iron (SZVI) to contaminants removal has been extensively studied, however, it is difficult to further regulate the FeSx species to control the SZVI properties. Based on the transformation of formaldehyde (HCHO) on FeSx, this work introduced HCHO into SZVI preparation process to regulate the FeSx structure. Results show that the HCHO-intervened SZVI (SZVIHCHO) has better Cr(VI) removal performance, which is due to the batter electrochemical properties. The FeSx structure of SZVIHCHO is evidently changed by HCHO, that is flaky FeSx transforms into granular FeSx and locally aggregated on SZVIHCHO surface. The composition of FeSx species shows that HCHO can weaken the conversion of FeS to FeS2, but directionally induce the conversion of FeS to Fe3S4. The electrostatic attraction of Fe atom in FeSx to the –CHO and the electron-withdrawing property of –CHO are the causes of electron loss from Fe atom and thus increase the Fe valence state. This study provides the inspirations for the future regulation of SZVI by inserting organics with specific structure and functions during SZVI preparation.

A novel sugarcane residue-derived bimetallic Fe/Mn-biochar composite for activation of peroxymonosulfate in advanced oxidation process removal of azo dye: Degradation behavior and mechanism

Metal-biochar composites with varying Fe/Mn ratios were synthesized for activating peroxymonosulfate (PMS) oxidative degradation of azo dye Orange G (OG) were investigated. The 1Fe2Mn-BC composite based on 1:2 molar ratio impregnation of Fe/Mn salt concentrations of efficient sugarcane harvest residue showed the best catalytic performance under aqueous pH 3–10 and had the least impacts from coexistence of inorganic anions and humic acids. The OG degradation by 1Fe2Mn-BC/PMS system optimized at catalyst:oxidant:pollutant ratio of 1:1.25:0.5 on g/L basis was found to follow pseudo-first-order kinetic and achieved 100 % degradation efficiency within 30 min. Apparent activation energy for OG degradation by 1Fe2Mn-BC/PMS was 16.91 kJ mol−1, and increasing reaction temperature from 293 to 313 K enhanced degradation rate constant by 49 %. Electron paramagnetic resonance (EPR) and radical quenching experiments revealed dominant non-radical 1O2 and radical O2− pathways in the OG oxidation removal by the 1Fe2Mn-BC/PMS system, although SO4− and OH radicals also participated. XPS spectra of 1Fe2Mn-BC before and after OG degradation indicated dominant surface composition of Fe(III) and Mn(II) valence states over other FeMn-biochar composites. The novel optimized one-step pyrolysis Fe/Mn bimetal biochar composite provides an efficient PMS activation for advanced oxidation process (AOP) treating of azo dyes in wastewater decontamination.

Synthesis of NiFe-layered double hydroxides using triethanolamine-complexed precursors as oxygen evolution reaction catalysts: effects of Fe valence.

The synthesis of highly efficient NiFe-layered double hydroxides (NiFe-LDHs) to catalyze the oxygen evolution reaction (OER) is urgent and challenging. Herein, NiFe-FeCl3-x and NiFe-FeCl2-x samples (where FeCl3 and FeCl2 represent the Fe sources and x represents the imposed reaction time: 6, 12, and 24 h) were prepared via one-pot hydrothermal synthesis using Fe sources characterized by Fe(III) or Fe(II) valence states. In the presence of triethanolamine, when FeCl3 was used as the Fe source, pure NiFe-LDH was obtained, whose crystallinity increased with increasing hydrothermal treatment time. In contrast, when FeCl2 was used as the Fe source, a mixture of NiFe-LDH, Fe2O3, and trace amounts of Fe3O4 was obtained. The content of NiFe-LDH in the mixture increased under longer hydrothermal treatment and NiFe-FeCl3-x catalysts exhibited better OER performance than NiFe-FeCl2-x catalysts. Specifically, NiFe-FeCl3-6 afforded the highest OER performance with an overpotential of 246.8 mV at 10 mA cm-2 and a Tafel slope of 46.1 mV dec-1. Herein, we investigated the effects of the valence state of Fe precursors on the structures and OER activities of the prepared catalysts; the mechanism of NiFe-LDH formation via hydrothermal synthesis in the presence of triethanolamine was also proposed.

Fe acting as functionalized auxiliary agents in nitrogen-doped carbon supported Ni-based catalysts for electrocatalytic CO2 Reduction: Effect of valence state

Converting CO2 into useful chemicals is an effective measure to address the energy crisis and the greenhouse effect. CO2RR has become a research hotspot due to its mild conditions. Ni-N-C catalysts are known as promising electrocatalysts, while achieving atomic level dispersion of Ni on the surface of the carrier is still facing challenges. In this work, various N-doped carbon supported Ni-based catalysts were synthesized by selecting Fe2+/Fe3+ as functionalized auxiliary agents in precursors. Different coordination situations of Fe(III)/Ni@NC and Fe(II)/Ni@NC are formed which derived from the valence state of Fe. During the synthesis process of Fe(III)/Ni@NC, Ni2+ replaced Fe3+ through competitive complexation, thereby achieving atomic level dispersion of Ni atoms on the catalyst surface. XAS confirms that Fe(III)/Ni@NC is a Ni-single-atom catalyst with Ni-N4 coordination. In contrast, Fe(II)/Ni@NC contains Ni3C/Ni nanoparticles coated with carbon layer, which shows a characteristic peak approaching to 2.12 Å related to the metallic Ni-Ni bonds. In the H-type cell, the FECO of Fe(III)/Ni@NC achieves 97.8 % at −0.83 V and maintains over 95 % in a wide potential window. The in-situ Fourier transform infrared (FTIR) spectroscopy confirms that the excellent product CO selectivity in CO2RR is due to the accumulation of *COOH intermediates at the active sites. Significantly, Fe(III)/Ni@NC shows excellent performance in the flow cell with FECO over 96 % from −40 to −140 mA cm−2. This work reveals the impact of Fe valence state of functionalized auxiliary agents on the electrocatalytic performance of materials, which provides a new approach for designing high-performance atomically dispersed electrocatalysts.

Characterization of iron oxides: Valence states and naturally occurring polymorphs using chemical shift of X–ray FeLβ1 line by WD–XRF

In X–ray spectroscopic studies of 3d transition metals, Kβ1,3 lines have been extensively used for the examination of chemical states. This is because Kβ1,3 lines are the second most intense X–ray lines and are more sensitive to changes in chemical state of 3d transition metals since the valence shell 3p is involved in the transition. In order to characterize iron oxides in natural iron ores, we determined the chemical shift, asymmetric index and FWHM of the third order FeKβ1,3 lines using WD–XRF technique. Unfortunately, none of these parameters exhibited good agreement with the chemical state of iron which was desired for characterization of iron oxides. Alternatively, FeL-lines were inspected because it involves the valence shell 3d electrons and moreover Fe(II) and Fe(III) have different number of unpaired electrons in the 3d shell. Hence, FeL-lines are anticipated to represent signature of different chemical states of iron. The study established a linear relationship between chemical shift of FeLβ1 line (δβ) and spin multiplicity (2S+ 1) in iron oxide ores having both Fe(II) and Fe(III) valence states. Since (2S + 1) is an intrinsic property of valence state, the study of δβ facilitated speciation of iron. The δβ also contained potential information on structural framework of iron oxides whereby it enabled characterization of various polymorphic phases of iron oxides irrespective of their crystalline/amorphous forms and structure. The δβ was found to increase with increase in Fe(III)/Fetotal ratio in the iron oxide CRMs. Hematite (α–Fe2O3) was observed to have higher δβ than maghemite (γ–Fe2O3) which is attributed to differences in their packing structure. Magnetite (Fe3O4), on the other hand, showed an anomalous behavior due to structural resemblance with maghemite, but both were characterized successfully.

Effect and mechanism of Fe2O3 decomposition in the preparation of foaming ceramics from industrial solid waste

AbstractMgO–Al2O3–SiO2 foam ceramics were prepared by direct sintering of asbestos tailings and coal fly ash by spontaneous bubble process. By X‐ray diffraction, scanning electron microscopy, Fourier‐transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and thermodynamic analysis, the effect of Fe2O3 decomposition on the preparation of foaming ceramics from industrial solid waste and the pore‐forming process was studied. The results show that the foaming effect of foaming ceramics with higher raw iron content is better when the roasting temperature is higher. Increasing the content of iron is beneficial to the formation of cordierite, and increasing the roasting temperature is beneficial to the relative content of spinel in foaming ceramics. Combined with the change in the Fe valence state, content in porous ceramic samples, and thermodynamic analysis of the product, it is found that Fe2O3 decomposition is the fundamental cause of ceramic foaming at high temperature. Fe2+ produced after decomposition replaces Mg2+ into spinel and cordierite structures, and the O2 produced by decomposition cannot be discharged in time to cause ceramic foaming. The research results can provide theoretical basis for the preparation of industrial solid waste foamed ceramics.

Enhanced Magnetization in CoFe2O4 Through Hydrogen Doping

AbstractMagnetic spinel oxides have attracted extensive research interest due to their rich physics and wide range of applications. However, these materials invariably suffer suppressed magnetization, due to structural imperfections (e.g., disorder, anti‐site defects, etc.). Herein, a dramatic enhanced magnetization is obtained with an increasement of 5 µB/u.c in CoFe2O4 (CFO) through ionic liquid gating induced hydrogen doping. The intercalated hydrogen ions lead to both distinct lattice expansion of ≈0.7% and notable Fe valence state reduction through electron doping, in which ≈17% Fe3+ is reduced into Fe2+. These facts collectively trigger a site‐specific spin‐flip on tetrahedrally coordinated Co2+ sites that enhances the net ferrimagnetic moment nearly to its theoretical maximum for perfect CFO.

Improving the magnetic and dielectric properties of Cu1−xHoxFeO2 nanoceramics by tuning the vacancy defects and Fe valence state

In this study, Cu1−xHoxFeO2 nanoceramics were synthesized by sol-gel method to investigate the influence of the vacancy defects and Fe valence state tuning on the magnetic and dielectric properties of Cu1−xHoxFeO2 nanoceramics. XRD and Raman analysis indicated that Cu1−xHoxFeO2 nanoceramics with single-phase delafossite structure were synthesized by sol-gel method; Ho3+ ions had replaced the Cu ions in CuFeO2 and resulted in lattice deformation. XPS analysis indicated that Ho3+ substitution could tune the Fe valence state, but did not cause significant change in oxygen vacancy concentration. The results of positron annihilation lifetime spectroscopy revealed that cation vacancies concentration in the interface region could be effectively tailored by Ho3+ substitution. The magnetic measurements indicated that Ho3+ substitution enhanced the magnetic transition temperatures and magnetization of Cu1−xHoxFeO2 samples, which could be mainly attributed to the cation vacancies concentration in the interface region and Fe2+ concentration. Most interestingly, the Cu1−xHoxFeO2 nanoceramics exhibited giant dielectric characteristic, which was attributed to the charge ordering of Fe3+ and Fe2+.

Low-temperature Mossbauer studies of substituted La-=SUB=-0.67-=/SUB=-Sr-=SUB=-0.33-=/SUB=-FeO-=SUB=-3-γ-=/SUB=- lanthanum ferrite

The valence states of Fe atoms and the formation of oxygen vacancies in substituted La0.67Sr0.33FeO3-γ orthoferrite have been studied in detail by low-temperature Mossbauer spectroscopy under oxygen removal. It has been shown that the averaged valence state of Fe atoms is not revealed with a decreasing measurement temperature. This makes it possible to reveal Fe4+ ions. The Analysis of the obtained data allows us to conclude that the presence of several Zeeman sextets associated with Fe3+ ions is related to the appearance of oxygen vacancies and Fe4+ ions in the nearest ionic surrounding of Fe ions. Using the Mossbauer data, the number of oxygen vacancies and oxygen ions has been determined for all the studied samples depending on the vacuum annealing temperature. Keywords: perovskites, substituted lanthanum ferrites, X-ray diffraction analysis, Mossbauer spectroscopy, Fe valence states, oxygen vacancies.

Crystal Structure-Controlled Electrocatalysis on Iron-Based Oxides Toward Oxygen Evolution in Alkaline Media: Trend and Mechanism

Present energy issues have increasingly stimulated the demand for the development of clean and sustainable energy platforms which can achieve net zero carbon emissions. Renewable energy resources are quite promising candidates for the construction of sustainable decarbonized society. One of examples of harnessing renewable energy-derived electricity is the electrolysis of earth-abundant water into hydrogen, which is a prominent carbon-free chemical fuel with a high weight energy density. Compared with polymer electrolyte water electrolysis in acidic environment, electrochemical alkaline water splitting can employ inexpensive nonprecious metals as electrocatalysts, which can make this technology a large-scale and cost-effective process. However, the anodic oxygen evolution reaction (OER) in the water splitting has a large overpotential, and it is a great bottleneck for widespread use. Thus, highly active and inexpensive electrocatalysts for OER are desired to overcome this concern.Iron (Fe) is a very earth-abundant element that is a quite cheap and non-toxic metal, and thus it is a potential candidate as electrocatalyst for OER. Previous studies have reported several multimetal oxides with Fe and other metallic elements, such as perovskite and brownmillerite types, which have attracted great attentions due to their facile synthesis and easily tunable OER activities by element substitution and doping. However, most of these studies focused on the choice of elements. Contrarily, the effects of crystal structures on OER activity have not yet been sufficiently interpreted, and it can be a crucial aspect to understand the OER electrocatalysis on Fe-based oxides and for the rational design of outstanding OER catalysts.In this study, we aim to comprehensively understand the effects of crystal structures on electrocatalytic OER activities on Fe-based oxides. To obtain versatile insights into OER electrocatalysis, we collected OER performances of Fe-based simple and bimetal oxides from our experiments and literature, and their structural characteristics were obtained from databases for inorganic compounds. Thus, we found that OER efficiencies on the Fe-based oxides were correlated with Fe–O bond lengths in their crystals; i.e., a shorter Fe–O bond length led to a higher OER activity.[1] We then exploited databases to mine potential candidates based on the structure–activity relationship and selected unreported Fe-based bimetal and trimetal oxides with various structures, which can dramatically accelerate our catalyst research. We synthesized these Fe-based multimetal oxides and evaluated their OER activity in alkaline media; remarkably, the OER efficiency on the unreported Fe-based multimetal oxides also exhibited excellent correlation with Fe–O bond lengths, as plotted in Figure 1. It is notable that the trend in the Fe–O bond length and OER activity is applicable to a wide variety of Fe-based simple, bimetal, and trimetal oxides regardless of chemical compositions, crystal categories, and Fe valence states. Furthermore, machine learning analysis proved that Fe–O bond length is the most dominant structural descriptor for OER efficiency compared with other structural parameters.[2] However, it is required to overcome the abovementioned catalytic trend because theoretical Fe–O bond length in Fe-based oxides is limited, and superior OER catalysts cannot be achieved according to this design guideline. Hence, we attempted to switch the OER electrocatalytic mechanism on a Fe-based oxide by the arrangement of crystal structure because different mechanisms should be involved in different descriptors; i.e., the mechanism switch could surpass the abovementioned catalytic trend. Thus, we found post-spinel CaFe2O4 that comprises a large amount of edge-shared FeO6 connectivity in its crystal. DFT calculations unveiled that the structural characteristics induced an unprecedented OER mechanism, multi-iron-site mechanism, where OER process goes through a reaction intermediate with an O–O bridge on multiple Fe sites as depicted in upper side in Figure 1. Consequently, CaFe2O4 exhibited prominent OER activity despite long Fe–O bond length in its crystal.[3] These findings provide a novel insight into the OER electrocatalysis on Fe-based oxides and contribute to the innovation of electrochemical hydrogen production.The part of this paper is based on results obtained from a project, JPNP14021, commissioned by the New Energy and Industrial Technology Development Organization (NEDO). Authors acknowledge the PRESTO program (No. JPMJPR15S3) of the JST. The part of DFT calculations was carried out on the supercomputers at NIMS, Hokkaido Univ., Kyushu Univ., and the HPCI systems (project codes: hp180115, hp200131). The part of this work was supported by JSPS KAKENHI Grant Number 20H00314 and 20K15087.

New Insight of Fe Valence State Change Using Leaves: A Combined Experimental and Theoretical Study

Fe2+ is of considerable importance in plant growth and crop production. However, most Fe elements in nature favor existing in the trivalent state, which often causes the deficiency of Fe2+ in plants. Here, we report the Fe valence state change from Fe3+ to Fe2+ by using leaves. This valence state change was confirmed by x-ray photoelectron spectroscopy in Fe-Cl@leaves. Fourier transform infrared and ultraviolet-visible spectroscopy demonstrated that aromatic ring groups were included in leaves, and cation-π interactions between Fe cations and the components containing aromatic rings in leaves were measured. Further, density functional theory calculations revealed that the most stable adsorption site for hydrated Fe3+ cation was the region where hydroxyl groups and aromatic rings coexist. Moreover, molecular orbital and charge decomposition analysis revealed that the aromatic rings took the major part (59%) of the whole net charge transfer between leaves and Fe cations. This work provides a high-efficiency and eco-friendly way to transform the Fe valence state from Fe3+ to Fe2+, and affords a new insight into the valance change between plant organisms with cations.

Exotic FeII/FeIII Local Environments in the Hexagonal Channels of Hydroxyapatite.

In this fundamental solid-state chemistry study, two sample series were investigated in depth: iron(III)-doped hydroxyapatite (HA) compounds obtained from a co-sintering process of hematite and pure HA under air and iron(III)-doped HA compounds obtained from a co-sintering process from iron(II) acetate and pure HA under an argon atmosphere. X-ray diffraction, UV-visible, Fourier transform infrared, 1H and 31P NMR, electron paramagnetic resonance (EPR,) and Mössbauer spectroscopy methods were coupled to unravel the Fe valence states, the interactions with other anionic species (OH- and PO43-), and finally the complex local environments in hexagonal channels in both the series. In particular, we highlighted the associated mechanism to ensure electroneutrality with a focus on deprotonation versus calcium substitution. By diverging mechanisms, Fe3+ and Fe2+ ions were found to be located in different coordinated sites: 4(+1) coordinated site for Fe3+ and 2(+3) coordinated site for Fe2+ and clearly associated with very different Mössbauer and EPR signatures as various absorption bands (leading to different sample colors).

Boosting the bifunctional electrocatalytic activity of cobalt free perovskite oxide (La0.8Sr0.2)0.95MnO3 via iron doping for high-efficiency Zn–air batteries

The representative Mn-based perovskite La0.8Sr0.2MnO3 has drawn extensive interests to substitute noble metal as oxygen reduction and evolution reaction (ORR and OER) in Zn-air battery (ZAB) due to its high oxygen kinetics. However, researches concerning the catalytic activity of the A-site deficient La0.8Sr0.2MnO3 with Fe doping are still scare. In this work, (La0.8Sr0.2)0.95Mn1-xFexO3(x = 0, 0.1, 0.3 and 0.5) perovskites are prepared and developed as bifunctional electrocatalysts. Their structure, morphology, surface adsorbed element state and electrochemical behaviors are characterized. The results demonstrate that Fe doping can increase surface oxygen vacancies, tailor Mn and Fe valence state of the perovskite and thus improve electrocatalytic activity. Among all the perovskite samples tested, (La0.8Sr0.2)0.95Mn0.7Fe0.3O3 (LSMF2) performs the best ORR/OER activity. Except for the good electrocatalytic activity, it also achieves excellent long-term durability compared with Pt/C catalyst. When LSMF2 is applied as the cathode electrocatalyst, a peak power density of 104 mW cm−2 is achieved for the ZAB. Meanwhile, a much lower charge–discharge voltage gap of only 0.9 V than Pt/C catalyst (1.13 V) is obtained. Besides, the proposed ZAB exhibited remarkably high stability during cycling in performance up to 100 cycles. These results highlight perovskite LSMF2 as a very promising electrocatalyst in ZAB.

NiFe layered double hydroxide nanosheet arrays for efficient oxygen evolution reaction in alkaline media

Exploring efficient oxygen evolution reaction (OER) catalysts synthesized from low-cost and earth-abundant elements are crucial to the progression of water splitting. In this paper, NiFe layered double hydroxide (LDH) nanosheets were grown on Ni foam (NF) through a straightforward hydrothermal method. The Fe doping effects were systematically investigated by controlling Ni/Fe ratios and Fe valence states, and the in-depth influence mechanisms were discussed. The results indicate that, through controlling structure morphology and enhancing Ni2+ oxidation, NiFeIII(1:1)-LDH displays the best and outstanding OER performance, with a low over potential of 382 mV at 50 mA cm−2, a low Tafel slope of 31.1 mVdec−1 and only 20 mV increase after 10 h continuous test at 50 mA cm−2. To our knowledge, this is one of the best OER electrocatalysts in alkaline media to date. This work provides a facile and novel strategy for the fabrication of bimetallic LDH catalysts with desired structures and compositions.

Enhanced performance and recyclability for peroxymonosulfate activation via g-C3N4 supported CoFe layer double oxide

CoFe layered double oxide (CoFe LDO) anchored on g-C3N4 was prepared by mixing appropriate amounts of CoFe layer double hydroxide and melamine at moderate synthesis temperatures. The resulting CoFe LDO/g-C3N4 composite has superior properties in peroxymonosulfate (PMS) activation, resulting in remarkable activity in catalyzing paracetamol degradation. It has been able to degrade 10 mg/L paracetamol in less than 10 min in darkness by using 0.2 g/L catalyst and 0.5 mM PMS dosages. The effects of PMS and catalyst dosage, initial pH and coexisting anions were also investigated. Negligible cation leaching, enhanced reusability and enhanced stability make CoFe LDO/g-C3N4 an attractive compound for environmental pollution abatement. The influence of g-C3N4 on lowering Co and Fe valence states in CoFe LDO compounds by covalent stimulates the oxidant radical (SO4− and OH) production and concomitantly paracetamol degradation. Electro magnetic resonance experiments and a so-called chemical probe were used to identify SO4− as the dominant radical in the degradation processes. Interestingly, X-ray absorption spectroscopy and electrochemical measurements revealed the existence of a second contributing mechanism, based on a pure electron transfer process from the pollutant to PMS mediated by the catalyzer. These findings, pioneer a new method for the mechanism of coupling radical and electron transfer processes that act synergistically to promote paracetamol degradation in scarcely 10 min in darkness.

Impact of growth conditions on the structural and magnetic properties of (Zn,Fe)Te thin films grown by molecular beam epitaxy (MBE)

We have investigated the effect of growth conditions on the structural and magnetic properties of (Zn,Fe)Te. Thin films of Zn1-xFexTe are grown by molecular beam epitaxy (MBE) with an almost same Fe composition, x = 1.4% but under two different growth conditions: (a) Te-rich (Te/Zn flux ratio of 2.3) and (b) Zn-rich (Te/Zn flux ratio of 0.7). Structural analysis by using x-ray absorption fine structure (XAFS) reveals that both films are mainly composed of pure diluted phase with substitutional Fe atoms on the Zn-site, but the valence state of Fe atoms in the film grown under Zn-rich condition has deviated more from isoelectronic Fe2+ as compared to the one grown in Te-rich condition. Accordingly, the magnetization measurement using SQUID confirms a significant difference in magnetic properties among these films; a linear dependence of magnetization on magnetic field (M−H), typical of van-Vleck paramagnetism under Te-rich growth condition turns into ferromagnetic behaviors with hysteretic M−H curve in the Zn-rich condition. The ferromagnetism exhibited by the Zn-rich growth film may reflect the deviation of substitutional Fe valence state from Fe2+ to Fe2+/3+ mixed states.

Activation of permonosulfate by Co-Fe3O4 composite catalyst for amino acid removal: Performance and mechanism of Co-Fe3O4 nanoparticles

Dissolved organic nitrogen (DON) derived from amino acids has been a major concern in drinking water treatment because of its potential to form nitrogenous disinfection byproducts (N-DBPs). The degradation performance of amino acids by peroxymonosulfate (PMS) activated by Co-Fe3O4 composite catalyst in heterogeneous catalytic process was elucidated in our study. The sole and combined catalytic performance of PMS and Co-Fe3O4 were evaluated for two amino acid species (i.e., histidine and phenylalanine) separately and validated under varying levels of PMS dose, Co-Fe3O4 dose, initial pH. The removal of histidine (62%) and phenylalanine (33%) was achieved with 0.1 g/L Co-Fe3O4, 1.5 mM PMS in the PMS/Co-Fe3O4 system. In contrast, only 19% and 16% histidine removal were obtained under individual application of PMS and Co-Fe3O4, respectively, confirming the preferable performance in the Co-Fe3O4/PMS system. Moreover, the reusability of the Co-Fe3O4 was elucidated after four successive runs. Radical quenching experiments revealed •OH and SO4•− were active while SO4•− was the dominant radical species. Examination of degradation intermediates and N-DBPs in Co-Fe3O4/PMS system showed that the increase of DCAN in histidine was attributed to histamine formation which produced more DCAN. Finally, the mechanism by the Co-Fe3O4/PMS system for the degradation of amino acids was proposed. The catalyst Co-Fe3O4 exhibited a unique adsorption of amino acids and the electron donor ability of Fe2+ enhanced the Co3+/Co2+ cycle which promoted the generation of free radicals according to the conversion of Fe and Co valence states.