NiFe_(2)O_(4) nanoparticles(<10 nm)embedded in a NiO matrix have been fabricated by calcining the corresponding Ni^(Ⅱ)Fe^(Ⅲ)-layered double hydroxide(LDH)precursors at high temperature(500℃).Compared with the NiFe_(2)O_(4)/NiO nanocomposite obtained by calcination of a precursor prepared by a traditional chemical coprecipitation method,those derived from NiFe-LDH precursors show much higher blocking temperatures(TB)(~380 K).The enhanced magnetic stability can be ascribed to the much stronger interfacial interaction between NiFe_(2)O_(4) and NiO phases due to the topotactic nature of the transformation of the LDH precursor to the NiFe_(2)O_(4)/NiO composite material.Through tuning the Ni^(Ⅱ)/Fe^(Ⅲ) molar ratio of the NiFe-LDH precursor,the NiFe_(2)O_(4) concentration can be precisely controlled,and the TB value as well as the magnetic properties of the final material can also be regulated.This work represents a successful example of the fabrication of ferro(ferri)magnetic(FM)/antiferrimagnetic(AFM)systems with high magnetic stability from LDH precursors.This method is general and may be readily extended to other FM/AFM systems due to the wide range of available LDH precursors.
Two kinds of optically transparent thin films with photochromic properties have been fabricated based on co-intercalation of 4-(4-anilinophenylazo)benzenesulfonate(AO5)and sodium dodecylbenzene sulfonate(SDS)into the galleries of a ZnAl layered double hydroxide(LDH)by two synthetic methods:solvent evaporation and in situ crystallization.The two films possess LDH crystallites in different orientations relative to the substrates depending on their fabrication method:horizontal and vertical.The relationship between the photochromic behavior of the interlayer chromophore and the orientation of the LDH crystallites is studied thoroughly.The orientation of the LDH crystallite influences the photochromic behavior of the films.The films exhibited different absorption and wettability characteristics,providing the potential for application of dye-LDH films as photochromic materials and light sensitive switches.
Quantum dots(QDs)luminescent films are extensively applied to optoelectronics and optical devices.However,QDs aggregation results in the quenching of their fluorescence property which limits their practical applications to a greater extent.In order to resolve this issue,3-mercaptopropionic acid(3-MPA)functionalized Cadmium Tellurium(CdTe)QDs were stabilized by silk fibroin(SB)and coassembled with layered doubled hydroxide(LDH)to form(QDs@SF/LDH)_(n)ultrathin films(UTFs)via the layer-by-layer(LBL)technique.UV-Vis absorption and fluorescence spectroscopy showed a stepwise and normal growth of the films upon increasing the number of deposition cycles.XRD and AFM studies confirmed the formation of a periodic layered structure and regular surface morphology of the thin films.As compared to(CdTe QDs/LDH)_(n)UTFs,the(CdTe QDs@SF/LDH)_(n)UTFs displayed fluorescence enhancement and longer fluorescent lifetime,both in solid states and aqueous solutions.Furthermore compared with the solution state,the fluorescence enhancement of SF-RC and SF-β are,respectively,7 times and 17 times in the(CdTe QDs@SF/LDH)_(n)UTFs,indicating that the LDH nanosheets favor the fluorescence enhancement effect on the CdTe QDs@SF.The fabricated materials displayed fluorescence response to a biological molecule such as immune globulin,lgG.Thus,the(CdTe QDs@SF/LDH)_(n)UTFs has a potential to be used as biosensor.
Muhammad Sohail HarooneLing LiAftab AhmadYaping HuangRuili MaPing ZhangYuehua HuQari Muhammad KaleemJun Lu
Ammonia is important for industrial development and human life.The traditional Haber Bosch method converts nitrogen into ammonia gas at high temperatures and pressures,causing serious pollution and greenhouse gas emissions.These problems prompt the nitrogen fixation method to proceed in a sustainable way.Ultrathin Ni/V-layered double hydroxides(Ni/V-LDHs)nanosheets with different proportions were prepared successfully for photocatalystic reduction of nitrogen to ammonia,through aqueous miscible organic solvent method(AMO)to achieve the higher surface area and rich oxygen vacancies,containing more carriers and active sites to enhance nitrogen reduction.And the optimal catalyst of Ni/V-LDHs 11 AMO possesses the highest photocatalytic efficiency(176μmol·g^(-1)·h^(-1)),indicating its potential application prospects in catalyst fields.Consequently,this work achieves an environmentally friendly,low-cost and efficient conversion method for nitrogen reduction to ammonia through solar energy.
Cobalt ferrite CoxNi1-xFe2O4 （x = 0, 0.5, 1 ） particles with controllable magnetic properties have been prepared by calcination of co-substituted NiFe^2＋Fe^3＋ -layered double hydroxide （NiFe^2＋Fe^3＋-LDH） precursors prepared via a scalable method involving separate nucleation and aging steps （SNAS）. Their structural and magnetic characteristics were investigated by powder X-ray diffraction （XRD）, scanning electron microscopy （SEM） and vibrating sample magnetometry （VSM）. Measurements of magnetic properties show that the saturation magnetization （Ms） and coercivity （He） of the calcined products increased with increasing cobalt content. The LDH precursor-based product obtained by calcination of a mixture of CoFe^2＋Fe3^＋-LDH and NiFe^2＋Fe^3＋ -LDH powders with a Co/Ni molar ratio of 1：1, exhibits a moderate value of Ms and an increased value of He compared to the corresponding values for an Ni0.5Co0.5Fe2O4 material prepared by calcination of a Co0.5Ni0.5Fe^2＋Fe^3＋-LDH precursor, and a physical mixture of CoFe2O4 and NiFe2O4 with a Co/Ni molar ratio of 1 ： 1. These results may provide a way to regulate magnetic anisotropy of ferrite spinels by varying the composition of the LDH precursors.
