Although different NbO_(x) units are present in Nb_(2)O_(5)‐based catalysts,the correlations between these structures and activity remain unclear,which considerably hinders the further development of Nb_(2)O_(5) phot...Although different NbO_(x) units are present in Nb_(2)O_(5)‐based catalysts,the correlations between these structures and activity remain unclear,which considerably hinders the further development of Nb_(2)O_(5) photocatalysis.Herein,we utilized N‐hydroxyphthalimide(NHPI)as the probe molecule to distinguish the role of different NbO_(x) units in the activation of C–H bond under visible light irradia‐tion.With the addition of NHPI,Nb_(2)O_(5) catalysts with highly disordered NbO_(6) units exhibited higher activities than that with slightly disordered NbO_(6) units(419‒495 vs.82μmol·g^(-1)·h^(-1))in photocata‐lytic selective oxidation of ethylbenzene.Revealed by Raman spectra,electron paramagnetic reso‐nance spectra,and transmission‐electron‐microscopy images,highly disordered NbO_(6) units were confirmed to act as the active sites for the transfer of photogenerated electrons from NHPI,pro‐moting the generation of phthalimide‐N‐oxyl(PINO)radicals for the enhanced conversion of ethylbenzene under visible light irradiation.This study provides guidance on the role of local NbO_(x) units in Nb_(2)O_(5) photocatalysis.展开更多
A new compound Sr6Sn2Nb8O30 was found in the ternary system of SrO-SnO2-Nb2O5. The transparent colorless crystal with needle-like shape can be grown by flux method. The crystal structure of new compound was determined...A new compound Sr6Sn2Nb8O30 was found in the ternary system of SrO-SnO2-Nb2O5. The transparent colorless crystal with needle-like shape can be grown by flux method. The crystal structure of new compound was determined by X-ray diffraction, and its belongs to tungsten bronze structure. Sr6Sn2Nb8O30 crystallizes in orthorhombic system with unit cell parameters a= 17. 579 (DA,6= 17. 509(DA,c=7. 7880(5)A,Z = 4 and space group Cmm2.展开更多
采用传统的高温固相法制备一种新型的红色荧光粉Ba_(6)Gd_(2)Ti_(4)O_(17):Sm^(3+),并通过X射线衍射(X-ray diffraction,XRD)、扫描电子显微镜(scanning electron microscope,SEM)、荧光(photoluminescence,PL)光谱及色坐标表征系列样...采用传统的高温固相法制备一种新型的红色荧光粉Ba_(6)Gd_(2)Ti_(4)O_(17):Sm^(3+),并通过X射线衍射(X-ray diffraction,XRD)、扫描电子显微镜(scanning electron microscope,SEM)、荧光(photoluminescence,PL)光谱及色坐标表征系列样品的物相、形貌和发光性能.PL光谱表明该荧光粉可以被近紫外光有效激发,在407 nm近紫外光激发下,发射光谱由四个发射峰组成,最强发射峰位于616 nm处,归结为Sm^(3+)的^(4)G_(5/2)→^(6)H_(7/2)跃迁.随着Sm^(3+)掺杂量的增加,荧光粉的发光强度先增大后减小,最佳掺杂比例(物质的量分数)为3%.系列掺杂比例荧光粉的色坐标基本不变,均位于红光区.研究结果表明,该荧光粉是一种具有应用前景的新型白光发光二极管(light-emitting diode,LED)用红色荧光粉.展开更多
A novel K_(2)Nb_(2)O_(6)photocatalyst with pyrochlore structure has been synthesized via a facile one-pot hydrother-mal route with no aid of additives.The as-prepared samples were characterized by powder X-ray diffrac...A novel K_(2)Nb_(2)O_(6)photocatalyst with pyrochlore structure has been synthesized via a facile one-pot hydrother-mal route with no aid of additives.The as-prepared samples were characterized by powder X-ray diffraction,ultra-violet-visible spectroscopy and field emission scanning electron microscopy.The photocatalytic H_(2)evolution was performed in an aqueous methanol solution under UV light irradiation.The as-prepared K_(2)Nb_(2)O_(6)photocatalyst with pyrochlore structure showed higher H_(2)production activity than that of perovskite KNbO_(3)and commercial Nb2O5 powders in the absence of cocatalysts,due mainly to its unique crystal and energy band structures.The rate of H_(2)evolution can be significantly enhanced by loading of Pt nanoparticles.The highest H_(2)evolution rate of 121μmol/h was reached when 0.7 wt%Pt nanoparticles were used,which was about 20 times higher than that of pristine K_(2)Nb_(2)O_(6).展开更多
(Sr_(0.5)Ba_(0.5))Nb_(2)O_(6) ultra-fine powders were synthesized by a novel sol–gel route,and the mechanism of the reaction was discussed.SrCO_(3),BaCO_(3),oxalate niobium and citric acid were used to initiate the ...(Sr_(0.5)Ba_(0.5))Nb_(2)O_(6) ultra-fine powders were synthesized by a novel sol–gel route,and the mechanism of the reaction was discussed.SrCO_(3),BaCO_(3),oxalate niobium and citric acid were used to initiate the sol–gel process,and ethylene glycol(EG)was added to further polymerize the cross-linking structure.The evolution of the(Sr_(0.5)Ba_(0.5))Nb_(2)O_(6) phase,the reaction process and the microstructures were investigated by X-ray diffraction(XRD),Raman spectroscopy,Fourier transform infrared spectroscopy,DSC-TG and scanning electron microscopy.The synthesis temperature of the(Sr_(0.5)Ba_(0.5))Nb_(2)O_(6) powders reached as low as 1200℃,and the size and morphology of the powders were controlled by temperature.By adjusting the calcination temperature,we obtained(Sr_(0.5)Ba_(0.5))Nb_(2)O_(6) powders with uniform sizes of 20 nm to 500 nm.Then,dense(Sr_(0.5)Ba_(0.5))Nb_(2)O_(6) ceramics were successfully prepared using these ultrafine powders.Finally,an enhanced electrocaloric effect(ECE)value of 0.35℃ was obtained at 100 kV/cm.展开更多
Ferroelectric Sr_(0.6)Ba_(0.4)Nb_(2)O_(6)(SBN)shows typical unfilled tetragonal tungsten bronze structure where 1/6 A sites and all C sites are unoccupied.The presence of such structural vacancy provides the possibili...Ferroelectric Sr_(0.6)Ba_(0.4)Nb_(2)O_(6)(SBN)shows typical unfilled tetragonal tungsten bronze structure where 1/6 A sites and all C sites are unoccupied.The presence of such structural vacancy provides the possibility to further modulate the crystal structure and electrical properties.In this work,alkali ions(Li^(+),Na^(+),K^(+))doped SBN ceramics have been fabricated via solid-solution reaction method.In general,each doping promotes the crystal structure evolves from unfilled toward filled tungsten bronze.However,the different doping ion radius causes the differences in occupying initial structural vacancies,resulting in significantly different electrical properties,Li^(+)doping enhances relaxor characteristic whereas Na+and K^(+)doping lead to normal ferroelectric behavior,accompanying an increase in Curie temperature(TC)from 36℃ of SBN to 40,212,148℃ of Li^(+),Na^(+)and K^(+)doping,respectively.Benefiting from improved relaxor degree and high density,the Li^(+)doped SBN displays a good energy storage performance.Since the ratio of Sr/Ba and(Sr+Ba)/Nb has not been changed,this work presents direct evidence for the effect of structural vacancy on crystal structure and properties,as well as inspiration for further work on unfilled tungsten bronze.展开更多
文摘Although different NbO_(x) units are present in Nb_(2)O_(5)‐based catalysts,the correlations between these structures and activity remain unclear,which considerably hinders the further development of Nb_(2)O_(5) photocatalysis.Herein,we utilized N‐hydroxyphthalimide(NHPI)as the probe molecule to distinguish the role of different NbO_(x) units in the activation of C–H bond under visible light irradia‐tion.With the addition of NHPI,Nb_(2)O_(5) catalysts with highly disordered NbO_(6) units exhibited higher activities than that with slightly disordered NbO_(6) units(419‒495 vs.82μmol·g^(-1)·h^(-1))in photocata‐lytic selective oxidation of ethylbenzene.Revealed by Raman spectra,electron paramagnetic reso‐nance spectra,and transmission‐electron‐microscopy images,highly disordered NbO_(6) units were confirmed to act as the active sites for the transfer of photogenerated electrons from NHPI,pro‐moting the generation of phthalimide‐N‐oxyl(PINO)radicals for the enhanced conversion of ethylbenzene under visible light irradiation.This study provides guidance on the role of local NbO_(x) units in Nb_(2)O_(5) photocatalysis.
基金Funded by International Centre for Diffraction Data(ICDD).
文摘A new compound Sr6Sn2Nb8O30 was found in the ternary system of SrO-SnO2-Nb2O5. The transparent colorless crystal with needle-like shape can be grown by flux method. The crystal structure of new compound was determined by X-ray diffraction, and its belongs to tungsten bronze structure. Sr6Sn2Nb8O30 crystallizes in orthorhombic system with unit cell parameters a= 17. 579 (DA,6= 17. 509(DA,c=7. 7880(5)A,Z = 4 and space group Cmm2.
基金Financial support from the Ministry of Science and Technology of China(Nos.2014CB239402 and 2013CB834505)the National Natural Science Founda-tion of China(Nos.51322213,21301183,20901081,51172245,and 91127005)+2 种基金Knowledge Innovation Pro-ject of the Chinese Academy of Sciences(KGCX2-EW-311-3)the Beijing Natural Science Foundation(Nos.2112042 and 2122054)the 100 Talents Program of the Chinese Academy of Sciences,and Scientific Research Foundation for Returned Scholars of Ministry of Educa-tion of China is gratefully acknowledged.
文摘A novel K_(2)Nb_(2)O_(6)photocatalyst with pyrochlore structure has been synthesized via a facile one-pot hydrother-mal route with no aid of additives.The as-prepared samples were characterized by powder X-ray diffraction,ultra-violet-visible spectroscopy and field emission scanning electron microscopy.The photocatalytic H_(2)evolution was performed in an aqueous methanol solution under UV light irradiation.The as-prepared K_(2)Nb_(2)O_(6)photocatalyst with pyrochlore structure showed higher H_(2)production activity than that of perovskite KNbO_(3)and commercial Nb2O5 powders in the absence of cocatalysts,due mainly to its unique crystal and energy band structures.The rate of H_(2)evolution can be significantly enhanced by loading of Pt nanoparticles.The highest H_(2)evolution rate of 121μmol/h was reached when 0.7 wt%Pt nanoparticles were used,which was about 20 times higher than that of pristine K_(2)Nb_(2)O_(6).
基金National Natural Science Foundation of China under Grant No.51202215Natural Science Foundation of Zhejiang Province under Grant No.LY15E02003Chinese National Basic Research Program under Grant No.2015CB654601.
文摘(Sr_(0.5)Ba_(0.5))Nb_(2)O_(6) ultra-fine powders were synthesized by a novel sol–gel route,and the mechanism of the reaction was discussed.SrCO_(3),BaCO_(3),oxalate niobium and citric acid were used to initiate the sol–gel process,and ethylene glycol(EG)was added to further polymerize the cross-linking structure.The evolution of the(Sr_(0.5)Ba_(0.5))Nb_(2)O_(6) phase,the reaction process and the microstructures were investigated by X-ray diffraction(XRD),Raman spectroscopy,Fourier transform infrared spectroscopy,DSC-TG and scanning electron microscopy.The synthesis temperature of the(Sr_(0.5)Ba_(0.5))Nb_(2)O_(6) powders reached as low as 1200℃,and the size and morphology of the powders were controlled by temperature.By adjusting the calcination temperature,we obtained(Sr_(0.5)Ba_(0.5))Nb_(2)O_(6) powders with uniform sizes of 20 nm to 500 nm.Then,dense(Sr_(0.5)Ba_(0.5))Nb_(2)O_(6) ceramics were successfully prepared using these ultrafine powders.Finally,an enhanced electrocaloric effect(ECE)value of 0.35℃ was obtained at 100 kV/cm.
基金This work was supported by the National Natural Science Foundation of China(No.12174179)the Natural Science Foundation of Jiangsu Province(No.BK20221251)the Dengfeng B project of Nanjing University and the Postgraduate Research&Practice Innovation Program of Jiangsu Province(No.KYCX23_0149).
文摘Ferroelectric Sr_(0.6)Ba_(0.4)Nb_(2)O_(6)(SBN)shows typical unfilled tetragonal tungsten bronze structure where 1/6 A sites and all C sites are unoccupied.The presence of such structural vacancy provides the possibility to further modulate the crystal structure and electrical properties.In this work,alkali ions(Li^(+),Na^(+),K^(+))doped SBN ceramics have been fabricated via solid-solution reaction method.In general,each doping promotes the crystal structure evolves from unfilled toward filled tungsten bronze.However,the different doping ion radius causes the differences in occupying initial structural vacancies,resulting in significantly different electrical properties,Li^(+)doping enhances relaxor characteristic whereas Na+and K^(+)doping lead to normal ferroelectric behavior,accompanying an increase in Curie temperature(TC)from 36℃ of SBN to 40,212,148℃ of Li^(+),Na^(+)and K^(+)doping,respectively.Benefiting from improved relaxor degree and high density,the Li^(+)doped SBN displays a good energy storage performance.Since the ratio of Sr/Ba and(Sr+Ba)/Nb has not been changed,this work presents direct evidence for the effect of structural vacancy on crystal structure and properties,as well as inspiration for further work on unfilled tungsten bronze.
