Controllable Synthesis and Magnetic Properties of Monodisperse Fe_3O_4 Nanoparticles

Magnetite(Fe_3O_4) nanoparticles with different sizes and shapes are synthesized by the thermal decomposition method.Two approaches,non-injection one-pot and hot-injection methods,are designed to investigate the growth mechanism in detail.It is found that the size and shape of nanoparticles are determined by adjusting the precursor concentration and duration time,which can be well explained by the mechanism based on the LaMer modei in our synthetic system.The monodisperse Fe_3O_4 nanoparticles have a mean diameter from 5nm to 16 nm,and shape evolution from spherical to triangular and cubic.The magnetic properties are size-dependent,and Fe_3O_4nanoparticles in small size about 5nm exhibit superparamagnetic properties at room temperature and maximum saturation magnetization approaches to 78 emu/g,whereas Fe_3O_4 nanoparticles develop ferromagnetic properties when the diameter increases to about 16 nm.

Theoretical Investigation of Influence of Mechanical Stress on Magnetic Properties of Ferromagnetic/Antiferromagnetic Bilayers Deposited on Flexible Substrates

Effect of mechanical stress on magnetic properties of an exchange-biased ferromagnetic/antiferromagnetic bilayer deposited on a flexible substrate is investigated.The hysteresis loops with different magnitudes and orientations of the stress can be classified into three types.The corresponding physical conditions for each type of the loop are deduced based on the principle of minimal energy.The equation of the critical stress is derived,which can judge whether the loops show hysteresis or not.Numerical calculations suggest that except for the magnitude of the mechanical stress,the relative orientation of the stress is also an important factor to tune the exchange bias effect.

Synergistic effect of Ni^(Ⅱ)and Co/Fe^(Ⅲ)in doped mixed-valence phosphonate for enhancing electrocatalytic oxygen evolution

Metal organophosphonates have been explored in energy-related fields due to their high chemical and thermal stability as a type of uniformly precursor,but only few of pristine metal organophosphonate are directly used for oxygen evolution reaction(OER)catalysts.Here,a mixedvalence iron phosphonate(Fe_(3)-ppat)has been constructed and applied to OER catalysis considered the potential active sites in pillars Fe^(Ⅱ)(-H_(2)O)_(4)(COO)_(2)and inorganic layers Fe^(Ⅲ)(μ_(2)–OH)PO_(3).Specifically,isostructural trimetallic framework Fe_(1.7)Co_(0.3)Ni_(1.0)-ppat possesses a minimum overpotential(291 mV),small Tafel slope(91.65 mV dec^(-1)),and high stability up to 83 h.The enhanced catalytic performance could be mainly ascribed to the synergistic effect of Ni^(Ⅱ)equivalent occupancy in pillars and Co/Fe^(Ⅲ)in layers.

Electron modulation of cobalt carbonate hydroxide by Mo doping for urea-assisted hydrogen production

Combining urea oxidation reaction(UOR) with hydrogen evolution reaction(HER) is an effective method for energy saving and highly efficient electrocatalytic hydrogen production. Herein, molybdenumincorporated cobalt carbonate hydroxide nanoarrays(CoxMoyCH) are designed and synthesized as a bifunctional catalyst towards UOR and HER. Benefiting from the Mo doping, the dispersed nanoarray structure and redistributed electron density, the CoxMoyCH catalyst display outstanding catalytic performance and durability for both HER and UOR, affording the overpotential of 82 m V for HER and delivering a low potential of the 1.33 V for UOR(vs. reversible hydrogen electrode, RHE) to attain a current density of 10 m A cm^(-2), respectively. Remarkably, when CoxMoyCH was applied as bifunctional catalyst in a twoelectrode electrolyzer, a working voltage of 1.40 V is needed in urea-assisted water electrolysis at10 m A cm^(-2) and without apparent decline for 40 h, outperforming the working voltage of 1.51 V in conventional water electrolysis.

Promoting surface reconstruction of NiFe layered double hydroxides via intercalating[Cr(C_(2)O_(4))_(3)]^(3-)for enhanced oxygen evolution

Rationally manipulating surface reconstruction of catalysts for water oxidation,inducing formation and dynamic accumulation of catalytically active centers still face numerous challenges.Herein,the introduction of[Cr(C_(2)O_(4))_(3)]^(3-)into NiFe LDHs by intercalation engineering to promote surface reconstruction achieves an advanced oxygen evolution reaction(OER)activity.In view of the weak electronegativity of Cr^(3+) in[Cr(C_(2)O_(4))_(3)]^(3-),the intercalation of[Cr(C_(2)O_(4))_(3)]^(3-)is expected to result in an electron-rich structure of Fe sites in NiFe LDHs,and higher valence state of Ni can be formed with the charge transfer between Fe and Ni.The optimized electronic structure of NiFe-[Cr(C_(2)O_(4))_(3)]^(3-)-LDHs with more active Ni^(3+) species and the expedited dynamic generation of Ni^(3+) (Fe)OOH phase during the OER process contributed to its excellent catalytic property,revealed by in situ X-ray absorption spectroscopy,Raman spectroscopy,and quasi-in situ X-ray photoelectron spectroscopy.With the modulated electronic structure of metal sites,NiFe-[Cr(C_(2)O_(4))_(3)]^(3-)-LDHs exhibited promoted OER property with a lower overpotential of 236 mV at the current density of 10 mA cm^(-2).This work illustrates the intercalation of conjugated anion to dynamically construct desired Ni^(3+) sites with the optimal electronic environment for improved OER electrocatalysis.

Activation of iridium site by anchoring ruthenium atoms on defects for efficient anodic catalyst in polymer electrolyte membrane water electrolyzers

1.Introduction Hydrogen is an ideal energy carrier to tackle the energy crisis and greenhouse effect,because of its high energy density and low emission.The production,storage and transportation of hydrogen are key factors to the practical application of hydrogen energy.As the scientific and technological understanding of the electrochemical devices was advancing in the past few decades,water electrolyzers based on the proton exchange membrane (PEM) have attracted much focus for its huge potential on the production of hydrogen via water splitting.PEM electrolyzers use perfluorinated sulfonic acid (PFSA) based membranes as the electrolyte.

Spinel Li Mn_(2)O_(4)integrated with coating and doping by Sn self-segregation

The development of high-performance and low-cost cathode materials is of great significance for the progress in lithium-ion batteries.The use of Co and even Ni is not conducive to the sustainable and healthy development of the power battery industry owing to their high cost and limited resources.Here,we report LiMn_(2)O_(4)integrated with coating and doping by Sn self-segregation.Auger electron energy spectrum and soft X-ray absorption spectrum show that the coating is Sn-rich LiMn_(2)O_(4),with a small Sn doping in the bulk phase.The integration strategy can not only mitigate the Jahn–Teller distortion but also effectively avoid the dissolution of manganese.The as-obtained product demonstrates superior high initial capacities of 124 mAh·g^(-1)and 120 mAh·g^(-1)with the capacity retention of 91.1%and 90.2%at 25℃and55℃after 50 cycles,respectively.This novel material-processing method highlights a new development direction for the progress of cathode materials for lithium-ion batteries.

Room-Temperature Ferromagnetism in Fe/Sn-Codoped In_(2)O_(3)Powders and Thin Films

Fe/Sn-codoped In_(2)O_(3)powders and films are prepared by a vacuum annealing process and a pulsed laser deposition technique,respectively.The structural and magnetic properties of the samples are investigated.The obvious room-temperature ferromagnetism is observed in both(In_(0.92)Fe_(0.05)Sn_(0.03))_(2)O_(3)powders and films,but their magnetic behaviors are very different.The ferromagnetism of the vacuum-annealed powders is partially due to precipitated Fe_(3)O_(4)impurity.By contrast,the ferromagnetism of the films is intrinsic and does not originate from any magnetic impurity,as confirmed by the extensive x-ray absorption spectroscopy and magnetization studies.

Activating surface atoms of high entropy oxides for enhancing oxygen evolution reaction

High entropy oxides(HEOs) have attracted extensive attention of researchers due to their remarkable properties. The electrocatalytic activity of electrocatalysts is closely related to the reactivity of their surface atoms which usually shows a positive correlation. Excellenet stability of HEOs leads to their surface atoms with relative poor reactivity, limiting the applications for electrocatalysis. Therefore, it is significant to activate surface atoms of HEOs. Constructing amorphous structure, introducing oxygen defects and leaching are very effective strategies to improve the reactivity of surface atoms. Herein, to remove chemical inert, low-crystallinity(Fe, Co, Ni, Mn, Zn)_(3)O_(4) (HEO-Origin) nanosheets with abundant oxygen vacancies was synthesized, showing an excellent catalytic activity with an overpotential of 265 mV at 10 mA/cm^(2), which outperforms as-synthesized HEO-500℃-air(335 mV). The excellent catalytic performance of HEO-Origin can be attributed to high activity surface atoms, the introduction of oxygen defects efficiently altered electron distribution on the surface of HEO-Origin. Apart from, HEO-Origin also exhibits an outstanding electrochemical stability for oxygen evolution reaction(OER).

Ni2P Nanosheets:A High Catalytic Activity Platform for Electrochemical Detection of Acetaminophen

Main observation and conclusion Accurate determination of acetaminophen concentration is essential for studying the metabolic status of acetaminophen in clinical practice.In this study,nickel phosphide was used for electrochemical detection of acetaminophen for the first time.

Fe_(2)Mn(μ_(3)-O)(COO)_(6) Cluster Based Stable MOF for Oxidative Coupling of Amines via Heterometallic Synergy

The direct catalytic oxidative coupling of amines is one of the attracting methods for the synthesis of a variety of pharmaceutical or industrial needed imines.Numerous earth-abundant manganese based salts,oxides,and complexes have been applied in this reaction.However,these compounds suffered from difficult separation,large catalyst loading,complicated reactivation or indeterminate activity.Considering the facts that metal-organic frameworks(MOFs)with crystalline structure,precise composition,and enormous surface area have superior performance in heterogeneous catalytic reactions,herein,we introduced Mn into[Fe_(3)(μ_(3)-O)(CH_(3)COO)_(6)],one of the precursors for the preparation of stable MOFs,and got[Fe_(2)Mn(μ_(3)-O)(CH_(3)COO)_(6)]cluster.After ligand replacement with biphenyl-3,4’,5-tricarboxylic acid(BPTC),heterometallic cluster-based[Fe_(2)Mn(μ_(3)-O)(BPTC)2(DMF)2(H_(2)O)](1)was obtained.As expected,1 is stable and able to catalyze the homo-or cross-coupling of amines effectively and selectively with 0.9 mol%catalyst loading at room temperature.Control experiments indicated that the catalytic activity of 1 mainly stems from Mn sites and that Fe synergistically contributes to the stability.Additionally,1 is recyclable and can be reused easily for at least 8 runs without obvious decrease in catalytic ability.To our knowledge,1 should be the first heterometallic cluster-based MOF with defined structure suitable for the synthesis of diverse imines from oxidative coupling of amines under mild conditions,which may shed light on the easy preparation of effective heterogeneous catalysts for organic synthesis.

A Two-Dimensional NiMoO_(4)Nanowire Electrode for the Sensitive Determination of Hydroquinone in Four Types of Actual Water Samples

Hydroquinone(HQ)poses immeasurable risk to human health and the natural environment on the grounds of high toxicity of organic phenolic compounds.Herein,an innovative electrochemical sensor based on two-dimensional nickel molybdate nanowires(NiMoO_(4)NWs)is constructed for the ultra-sensitive determination of HQ,which can provide useful reference for the human health and environment protection.Two-dimensional NiMoO_(4)NWs are prepared successfully through a facile hydrothermal reaction and annealing process.The obtained two-dimensional NiMoO_(4)NWs are characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),high-resolution TEM(HRTEM),energy-dispersive X-ray spectroscopy(EDS)mapping and X-ray photoelectron spectroscopy(XPS).The accurate contents of Ni and Mo have been characterized by inductively coupled plasma atomic emission spectroscopy(ICP-AES),confirming that the lower content of the nickel in NiMoO_(4)NWs possesses the higher catalytic activity of HQ.Under the optimized conditions,the constructed HQ sensor exhibits satisfactory electrocatalytic activity with a low detection limit of 0.0355μmol/L(S/N=3),a wide linear range of 0.05-4600μmol/L and sensitivity of 170.064μA/(mmol cm^(2)).The sensor has been successfully applied to the detection of HQ in rainwater,tap water,domestic sewage and drinking water samples with satisfactory recovery.At the same time,this sensor has excellent reproducibility,selectivity,and stability.The constructed sensor has potential practical application value and broad application prospect in human health and environmental monitoring.

Conversion reaction lithium metal batteries

Contemporary social problems,such as energy shortage and environmental pollution,require developing green energy storage technologies in the context of sustainable development.With the application of secondary battery technology becoming widespread,the development of traditional lithium(Li)-ion batteries,which are based on insertion/deinsertion reactions,has hit a bottleneck;instead,conversion-type lithium metal batteries(LMBs)have attracted considerable attention owing to the high theoretical capacity of Li metal anodes.In this review,Li-S,Li-O_(2),and Li-SOCl_(2)batteries are used as examples to summarize LMBs based on their conversion reactions from the perspectives of cathode material,anode material,electrolyte,separator,and current collector.Key challenges exist regarding the conversion reactions of various batteries.To achieve the optimum performance and improve the application effect,several improvement strategies have been proposed in relation to reasonable designs of next-generation high-performance rechargeable batteries.

Mn3O4 nanoparticles@reduced graphene oxide composite:An efficient electrocatalyst for artificial N2 fixation to NH3 at ambient conditions

Currently,industrial-scale NH3 production almost relies on energy-intensive Haber-Bosch process from atmospheric N2 with large amount of CO2 emission,while low-cost and high-efficient catalysts are demanded for the N2 reduction reaction (NRR).In this study,Mn3O4 nanoparticles@reduced graphene oxide (Mn3O4@rGO) composite is reported as an efficient NRR electrocatalyst with excellent selectivity for NH3 formation.In 0.1 M Na2SO4 solution,such catalyst obtains a NH3 yield of 17.4 μg·h^-1·mg^-1cat.and a Faradaic efficiency of 3.52% at-0.85 V vs.reversible hydrogen electrode.Notably,it also shows high electrochemical stability during electrolysis process.Density functional theory (DFT) calculations also demonstrate that the (112) planes of Mn3O4 possess superior NRR activity.