查看更多>>摘要：Due to the unique physical and chemical properties,rare earth elements(REEs)play a significant role in the high-tech field.In the past few decades,the rare earth reserve in China has been gradually decreasing and more pressure has been exerted on the global rare earth supply for the increasing demand of REEs,which indicates that it is essential to recycle secondary resources to meet the rare earth demand.As for rare earth molten salt electrolytic slag(REMES),although its high rare earth content has potential huge economic value,its high fluorine content of approximately 10 wt％-20 wt％can pollute the environ-ment.Three methods are used to treat REMES.Hydrometallurgical and pyro-hydrometallurgical methods have gotten a big success for solving most of the hydrometallurgical problems,while some problems,like long route and waste water,need to be solved.Vacuum distillation is a new and promising method with a short process due to its harmlessness and high efficiency,but has shortcomings such as high energy consumption and material adaptability.This review presents these above three treatment methods,and the challenges and chances of using the recovery technique of REMES in an environmentally friendly way.
查看更多>>摘要：ZnS and ZnS:3.125％Ce3+(ZSC)quantum dots(QDs)were synthesized by a low-temperature solid-phase method.The crystal structure,photoluminescence(PL)properties of ZSC QDs,and their effects on the growth and kojic acid production of Aspergillus oryzae(A.oryzae)were investigated.It is found that both QDs have a cubic blend structure with the average particle size ranging of 2.75-6.14 nm.Ce3+doping not only increases the band gap of ZnS QDs from 3.43 to 3.48 eV,but also increases the PL intensity by about 2.23 times,which is due to the fact that the electron carrier concentration is improved,and then the rate of radiative recombination is increased.The integral emission intensity,biomass,extracellular proteins yield,and kojic acid production of A.oryzae cultured with ZSC(ZnS)QDs are about 4.31(3.23),1.61(1.20),1.12(1.09),and 2.99(1.68)times higher than that of medium without QDs,respectively.
查看更多>>摘要：Förster resonance energy transfer(FRET)is a widely used spectroscopic technique.The development of donor-acceptor combinations is essential to advance this technique.To make the energy transfer effi-ciency independent of the external environment,we explored the potential of constructing donor-acceptor combinations with lanthanide ion-doped nanoparticles(LNPs),in which the 4f electrons of the lanthanide ions are shielded by the 5s and 6p electrons.Non-radiative energy transfer between LNPs was demonstrated in self-assembled nanostructures and core-shell structure of LNPs was used to control the distance between donor and acceptor in self-assembled nanostructures.The emission in-tensity ratio of donor and acceptor illustrates that the energy transfer efficiency decreases significantly with increasing distance and the effective energy transfer distance is 8.5 nm,showing the potential of using LNPs as donor-acceptor pairs in the construction of distance-dependent energy transfer system.
查看更多>>摘要：At present,with the increasing application needs of phosphor-converted white light-emitting diode(w-LED),the synthetic efficiency and thermal stability of phosphor become urgent problems.Herein,this research reports a microwave-assisted fast synthesis approach to obtain a Sm3+-activated borotellurate Na2Y2TeO4(BO3)2(NYTB)red phosphor with high crystallinity,excellent thermostability,and low chro-maticity shift.For the NYTB-based phosphor,in contrast to the conventional solid-state synthesis,the microwave-assisted synthesis method involves lower synthesis temperature and shorter processing time.Additionally,the concentration quenching mechanism was determined.The w-LED device pack-aged with the studied phosphor exhibits a near-standard white light with proper CCT and high Ra parameters.
查看更多>>摘要：A series of orange-red light emitting Ca2MgSi2O7∶Sm3+nanopowders were fabricated via low-cost eco-friendly green combustion technique using Aloe vera gel as fuel.The phase purity of the samples were confirmed by the powder X-ray diffraction(PXRD)technique.Pure single-phase tetragonal structure is observed from the PXRD results with no additional impurity peaks.The band gap energy of the fabricated powders was estimated by diffuse reflectance spectra(DRS)and is found to be in the range of 4.01-5.98 eV.A high resolution scanning electron microscope(SEM)was used to study the morpho-logical behaviour of the samples.Honeycomb-like structures are observed from the SEM results.The particle size was evaluated by transmission electron microscopy(TEM)and is found to be～50 nm.The interplanar distance is found to be 0.53 nm.Photoluminescence properties were systematically studied in detail.The phosphors are successfully excited at 403 nm NUV light,producing reddish-orange char-acteristic emission.The emission peaks are centered at 558(4G5/2 → 6H5/2),607(4G5/2 → 6H7/2)and 645 nm(4G5/2 → 6H9/2),respectively.Among the observed peaks the red emanation(4G5/2 → 6H7/2)is stronger than the orange emission(4G5/2 →6H5/2)in the current investigation.The photoluminescent concentration quenching is noticed above 5 mol％Sm3+ion doping content.The dipole-dipole inter-action resulting in cross relaxation is found to be the principal cause of concentration quenching mechanism.The color features such as Commission Internationale de l'Eclairage(CIE)and correlated color temperature(CCT)were studied in detail.The optimized chromaticity coordinates were estimated to be(0.6363,0.3632),which fall in the reddish-orange region.The average CCT value obtained is 3362 K.The average color purity is found to be～82％.Sm3+incorporated Ca2MgSi2O7 samples are possible contender for single white light generation commercial candidates owing to their strong hypersensitivity of Sm3+ions through host,least possibility for re-absorption of blue-green emission owing to poor direct f-f excitation of Sm3+ions,and high color purity(reddish-orange emission).The prepared powders exhibit excellent electrochemical redox properties and CPE modified optimized powders show outstanding sensitive response which indicates its use in the potential electrochemical sensor materials for drug sensing studies.
查看更多>>摘要：Sulfate adsorption is one of the factors that cause the poisoning of catalyst in the low-temperature NH3 selective catalytic reduction reaction(NH3-SCR).In this paper,by controlling the co-adsorption time of SO2 and O2 at 150 ℃,a range of sulfated MnCeOx catalysts with different contents of metal sulfate species were prepared to reveal the influence of metal sulfate species content on the catalytic performances and reaction mechanisms at low temperature.The catalytic activity below 250 ℃ rapidly decreases with increasing metal sulfate species content.The results of characterizations shed light on the reduction of specific surface area,Mn4+and Ce3+content,and redox ability of MnCeOx owing to the formation of metal sulfate species.Further experiments reveal that metal sulfate species preferentially absorb on MnOx domains rather than on CeO2 domains,and the adsorbed metal sulfate species can suppress the Eley-Rideal and the Langmuir-Hinshelwood reaction mechanisms over the sulfated MnCeOx.All the above results are detrimental to the activity of sulfated MnCeOx in the low-temperature NH3-SCR reaction.
查看更多>>摘要：CeO2-based catalysts are widely investigated for selective catalytic reduction(SCR)of NO with NH3.Interaction of NO/O2 with CeO2 generally produces two surface species,i.e.,nitrates and nitrites.How-ever,the explicit quantification of these two species is still unresolved.Herein,we reported that spec-trophotometry characterization was effective in determining surface adsorbed NOx species on CeO2 by measuring the corresponding ions(NO2 and NO3)dissolved in aqueous solution.Experimental results show that both nitrate(-NO3)and nitrite(-NO2)species can be quantitatively evaluated and the ac-curacy is verified by calibrating with NOx-TPD result.Exclusive transfer of adsorbed NOx from catalyst surface to aqueous solution is confirmed and the dissolution process can be accelerated by ultrasonic treatment.Moreover,useful information related to evolution of surface NOx species under various conditions(O2 treatment,different adsorption temperature and duration)and over different catalysts(Fe2O3,MnO2 and MnOx-CeO2)are provided.The result of present study demonstrates the potential of spectrophotometry for quantitative discrimination of surface NOx species on CeO2 and other oxide-based materials,which is conducive to mechanism analysis of SCR reaction.
查看更多>>摘要：LaFe11.8Si1.2/10 wt％Ce60Co40 composites were prepared by spark plasma sintering and subsequent diffusion annealing.A novel core-shell structure is observed with the LaFe11.8Si1.2 particles as the core and the(La,Ce)2(Fe,Co,Si)17(2:17)phase as the shell.As diffusion annealing time(ta)increases,this core-shell structure is replaced by the formation of the(La,Ce)1(Fe,Co,Si)13 phase.Annealing at 1323 K for 12 h results in samples with(-△SM)max of 9.30 J/(kg.K)(△μ0H=2 T),good mechanical properties((σbc)max=402 MPa,ε=4.21％)and thermal conductivity of 8.7 W/(m·K).Thus,bulk composites with excellent comprehensive properties for magnetic refrigeration are obtained in this work.
查看更多>>摘要：We synthesized a potassium gadolinium phosphate K3Gd(PO4)2 with monoclinic structure(P21/m)by the high-temperature solid-state reaction method.Its lattice constants obtained by Rietveld refinements of XRD curve are a=0.7411 nm,b=0.5624 nm,and c=0.9433 nm.Magnetic and magnetocaloric properties of K3Gd(PO4)2 were investigated in detail.The magnetic phase transition temperature of K3Gd(PO4)2 was determined by ultra-low temperature testing to be 0.58 K.K3Gd(PO4)2 exhibits large magnetic entropy changes(-△SM).The maximum-△SM are 20.2 and 29.4 J/(kg·K)in the magnetic field variation(△H)of 1 and 2 T,respectively,which are larger than that of the commercial Gd3Ga5O12(GGG).The maximum adiabatic temperature change(△Tad)reaches 5.91 K under a magnetic field change(△H)of 1 T.K3Gd(PO4)2 is a potential magnetic refrigeration material for obtaining sub-Kelvin temperatures.
查看更多>>摘要：The present study reported the influence of heavy rare-earth elements(Gd and/or Dy)on Sm-Co-based melt-spun ribbons.Microstructure and magnetic properties of Sm-Co-based(Sm1-xRExCo5)ternary and quaternary systems were investigated.The X-ray diffraction,Auger spectroscopy,scanning electron microscopy(SEM)and transmission electron microscopy(TEM)analyses reveal the presence of the 1:5H and 2:17R phases in the as-spun ribbons.A high-temperature magnetic measurement reports a Curie temperature(Tc)at～825 and～869 K in Sm0.6Gd0.4Co5(ribbon A)and Sm0.6Gd0.3Dy0.1Co5(ribbon B),respectively.A low-temperature magnetic measurement on Sm0.6Gd0.3Dy0.1Co5 ribbons exhibits a type-2 SR(spin reorientation)behaviour at～72 K,which arises due to the presence of the DyCo5 phase.Room temperature magnetic measurements reveal that overall magnetic measurement(OMP)is about 24 and 29.9 for ribbons A and B,respectively.Consequently,the comparative investigations profess that ribbon B shows better magnetic performance due to Dy addition with reduced grain size.This observation in-dicates that the Gd and Dy substituted Sm-Co magnet can be a potential magnet for high-temperature applications.
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