Fe3O4 magnetic nanoparticles with diameters varying from 10 to 426 nm were synthesized and characterized.Heating effects of Fe3O4 magnetic nanoparticles under radiofrequency capacitive field(RCF) with frequency of 27....Fe3O4 magnetic nanoparticles with diameters varying from 10 to 426 nm were synthesized and characterized.Heating effects of Fe3O4 magnetic nanoparticles under radiofrequency capacitive field(RCF) with frequency of 27.12 MHz and power of 60-150 W were investigated.When the power of RCF is lower than 90 W,temperatures of Fe3O4 magnetic nanoparticles(75-150 mg/mL) can be raised and maximal temperatures are all lower than 50 ℃.When the power of RCF is 90-150 W,temperatures of Fe3O4 magnetic nanoparticles can be quickly raised and are all obviously higher than those of normal saline and distilled water under the same conditions.Temperature of Fe3O4 magnetic nanoparticles can even reach 70.2 ℃ under 150 W RCF.Heating effects of Fe3O4 magnetic nanoparticles are related to RCF power,particle size and particle concentration.展开更多
Maghemite (γ-Fe<sub>2</sub>O<sub>3</sub>) nanoparticles have been synthesized using chemical co-precipitation at a different temperature. Characterizations of the sample were performed by X-ra...Maghemite (γ-Fe<sub>2</sub>O<sub>3</sub>) nanoparticles have been synthesized using chemical co-precipitation at a different temperature. Characterizations of the sample were performed by X-ray diffraction (XRD), transmission electron microscopy (TEM), alternating gradient magnetometry (AGM) and thermogravimetryanalysis (TGA). The stability of the maghemite nanoparticles suspension was studied at different pH and time of storage by dynamic light scattering (DLS) and zeta potential measurements. The XRD patterns confirmed that the particles were maghemite. TEM observation showed that the particles have spherical morphology with narrow particle size distribution. The particles showed superparamagnetic behavior with good thermal stability. The increasing of temperature in the synthesis of maghemite nanoparticles produced smaller size particles, lower magnetization, better thermal stability and more stable maghemite nanoparticle suspension.展开更多
Magnetic nanoparticles（Fe3O4） were synthesized by co-precipitating Fe^2＋ and Fe^3＋ ions in an ammonia solution and treating under hydrothermal conditions.Cellulase was immobilized onto Fe3O4 magnetic nanoparticles...Magnetic nanoparticles（Fe3O4） were synthesized by co-precipitating Fe^2＋ and Fe^3＋ ions in an ammonia solution and treating under hydrothermal conditions.Cellulase was immobilized onto Fe3O4 magnetic nanoparticles via glutaraldehyde activation.Using response surface methodology and Box-Behnken design,the variables such as magnetic nanoparticle concentration,glutaraldehyde concentration,enzyme concentration,and cross linking time were optimized.The Box-Behnken design analysis showed a reasonable adjustment of the quadratic model with the experimental data.Statistical contour plots were generated to evaluate the changes in the response surface and to understand the relationship between the nanoparticles and the enzyme activity.Scanning electron microscopy,X-ray diffraction analysis,and Fourier transform infrared spectroscopy were studied to characterize size,structure,morphology,and binding of enzyme onto the nanoparticles.The stability and activity of the bound cellulase was analyzed using various parameters including pH,temperature,reusability,and storage stability.The immobilized cellulase was compared with free cellulase and it shows enhanced stability and activity.展开更多
The mechanisms and effects about the interaction between serum albumins and silver nanoparticles have been intensively studied by means of transmission electron microscopy (TEM), circular dichroism (CD) and ultraviole...The mechanisms and effects about the interaction between serum albumins and silver nanoparticles have been intensively studied by means of transmission electron microscopy (TEM), circular dichroism (CD) and ultraviolet-visible (UV-Vis) spectroscopy. The adsorption of serum al-bumins on the surface of silver nanoparticles is observed by TEM. The studies with the surface plasmon bands indicate that the electrostatic and hydrophilic interactions are the major forces be-tween serum albumins and silver nanoparticles; the number of adsorbed monolayer serum albu-min molecules to a silver nanoparticle with the size of 60 nm is about 6.7×105. The far-UV CD spectra provide the evidence that the secondary structure of adsorbed serum albumins adopt a looser and more extended conformation, in which the content of -helix decreases, whereas the content of -sheet, turn and unordered coil increases. Using time-scanning UV-Vis spectra to monitor the interacting process, the particular twofold hysteresis effects are significantly found with the coverage of aggregated silver nanoparticles and the conformational transition of serum albumins, respectively. The rate constants and the thermodynamics parameters about the hysteretic processes are also calculated.展开更多
Despite considerable advances in synthesizing high-quality core/shell upconversion(UC)nanocrystals(NC;UCNC)and UCNC photophysics,the application of near-infrared(NIR)-excitable lanthanide-doped UCNC in the life and ma...Despite considerable advances in synthesizing high-quality core/shell upconversion(UC)nanocrystals(NC;UCNC)and UCNC photophysics,the application of near-infrared(NIR)-excitable lanthanide-doped UCNC in the life and material sciences is still hampered by the relatively low upconversion luminescence(UCL)of UCNC of small size or thin protecting shell.To obtain deeper insights into energy transfer and surface quenching processes involving Yb^(3+) and Er^(3+) ions,we examined energy loss processes in differently sized solid core NaYF_(4) nanocrystals doped with either Yb^(3+)(YbNC;20%Yb^(3+))or Er^(3+)(ErNC;2%Er^(3+))and co-doped with Yb^(3+) and Er^(3+)(YbErNC;20%Yb^(3+) and 2%Er^(3+))without a surface protection shell and coated with a thin and a thick NaYF_(4) shell in comparison to single and co-doped bulk materials.Luminescence studies at 375 nm excitation demonstrate back-energy transfer(BET)from the ^(4)G_(11/2) state of Er^(3+) to the ^(2)F_(5/2) state of Yb^(3+),through which the red Er^(3+) ^(4)F_(9/2) state is efficiently populated.Excitation power density(P)-dependent steady state and time-resolved photoluminescence measurements at different excitation and emission wavelengths enable to separate surface-related and volume-related effects for two-photonic and three-photonic processes involved in UCL and indicate a different influence of surface passivation on the green and red Er3+emission.The intensity and lifetime of the latter respond particularly to an increase in volume of the active UCNC core.We provide a three-dimensional random walk model to describe these effects that can be used in the future to predict the UCL behavior of UCNC.展开更多
Fe5O7(OH)4H2O ferrihydrite is a low-crystallinity antiferromagnetic material.c-Fe2O3(maghemite)magnetic nanoparticles were prepared from a ferrihydrite precursor,by chemically induced transformation in FeCl2/NaOH solu...Fe5O7(OH)4H2O ferrihydrite is a low-crystallinity antiferromagnetic material.c-Fe2O3(maghemite)magnetic nanoparticles were prepared from a ferrihydrite precursor,by chemically induced transformation in FeCl2/NaOH solution.The magnetization,morphology,crystal structure and chemical composition of the products were determined by vibrating sample magnetometry,transmission electron microscopy,X-ray diffraction(XRD),energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy(XPS).Ferrihydrite underwent aggregation growth and transformed into a-FeO(OH)(goethite)particles,which subsequently transformed into c-Fe2O3nanoparticles,that became coated with NaCl.The c-Fe2O3particles had a flake-like morphology,when prepared from 0.01 mol/L FeCl2and a FeCl2:NaOH molar ratio of 0.4.The c-Fe2O3particles were more spherical,when prepared from a FeCl2:NaOH molar ratio of 0.6.The Fe content of the flake-like particles was lower than that of the spherical particles.Their magnetizations were similar,and the coercivity of the flake-like particles was larger.The differences in morphology and magnetization were attributed to the surface effect,and the difference in coercivity to the shape effect.展开更多
基金Projects(30571779,10775085) supported by the National Natural Science Foundation of ChinaProject(Z07000200540704) supported by Beijing Municipal Science and Technology Commission,China
文摘Fe3O4 magnetic nanoparticles with diameters varying from 10 to 426 nm were synthesized and characterized.Heating effects of Fe3O4 magnetic nanoparticles under radiofrequency capacitive field(RCF) with frequency of 27.12 MHz and power of 60-150 W were investigated.When the power of RCF is lower than 90 W,temperatures of Fe3O4 magnetic nanoparticles(75-150 mg/mL) can be raised and maximal temperatures are all lower than 50 ℃.When the power of RCF is 90-150 W,temperatures of Fe3O4 magnetic nanoparticles can be quickly raised and are all obviously higher than those of normal saline and distilled water under the same conditions.Temperature of Fe3O4 magnetic nanoparticles can even reach 70.2 ℃ under 150 W RCF.Heating effects of Fe3O4 magnetic nanoparticles are related to RCF power,particle size and particle concentration.
文摘Maghemite (γ-Fe<sub>2</sub>O<sub>3</sub>) nanoparticles have been synthesized using chemical co-precipitation at a different temperature. Characterizations of the sample were performed by X-ray diffraction (XRD), transmission electron microscopy (TEM), alternating gradient magnetometry (AGM) and thermogravimetryanalysis (TGA). The stability of the maghemite nanoparticles suspension was studied at different pH and time of storage by dynamic light scattering (DLS) and zeta potential measurements. The XRD patterns confirmed that the particles were maghemite. TEM observation showed that the particles have spherical morphology with narrow particle size distribution. The particles showed superparamagnetic behavior with good thermal stability. The increasing of temperature in the synthesis of maghemite nanoparticles produced smaller size particles, lower magnetization, better thermal stability and more stable maghemite nanoparticle suspension.
文摘Magnetic nanoparticles（Fe3O4） were synthesized by co-precipitating Fe^2＋ and Fe^3＋ ions in an ammonia solution and treating under hydrothermal conditions.Cellulase was immobilized onto Fe3O4 magnetic nanoparticles via glutaraldehyde activation.Using response surface methodology and Box-Behnken design,the variables such as magnetic nanoparticle concentration,glutaraldehyde concentration,enzyme concentration,and cross linking time were optimized.The Box-Behnken design analysis showed a reasonable adjustment of the quadratic model with the experimental data.Statistical contour plots were generated to evaluate the changes in the response surface and to understand the relationship between the nanoparticles and the enzyme activity.Scanning electron microscopy,X-ray diffraction analysis,and Fourier transform infrared spectroscopy were studied to characterize size,structure,morphology,and binding of enzyme onto the nanoparticles.The stability and activity of the bound cellulase was analyzed using various parameters including pH,temperature,reusability,and storage stability.The immobilized cellulase was compared with free cellulase and it shows enhanced stability and activity.
基金This work was supported by the National Natural Science Foundation of China(Grant No.20261001)CEMFoundation for N&T Joint Academythe Science Foundation of Guangxi Zhuang Autonomous Region.
文摘The mechanisms and effects about the interaction between serum albumins and silver nanoparticles have been intensively studied by means of transmission electron microscopy (TEM), circular dichroism (CD) and ultraviolet-visible (UV-Vis) spectroscopy. The adsorption of serum al-bumins on the surface of silver nanoparticles is observed by TEM. The studies with the surface plasmon bands indicate that the electrostatic and hydrophilic interactions are the major forces be-tween serum albumins and silver nanoparticles; the number of adsorbed monolayer serum albu-min molecules to a silver nanoparticle with the size of 60 nm is about 6.7×105. The far-UV CD spectra provide the evidence that the secondary structure of adsorbed serum albumins adopt a looser and more extended conformation, in which the content of -helix decreases, whereas the content of -sheet, turn and unordered coil increases. Using time-scanning UV-Vis spectra to monitor the interacting process, the particular twofold hysteresis effects are significantly found with the coverage of aggregated silver nanoparticles and the conformational transition of serum albumins, respectively. The rate constants and the thermodynamics parameters about the hysteretic processes are also calculated.
基金from the German Science Foundation(DFG,Nos.RE 1203/18-1 and HA 1649/7-1)。
文摘Despite considerable advances in synthesizing high-quality core/shell upconversion(UC)nanocrystals(NC;UCNC)and UCNC photophysics,the application of near-infrared(NIR)-excitable lanthanide-doped UCNC in the life and material sciences is still hampered by the relatively low upconversion luminescence(UCL)of UCNC of small size or thin protecting shell.To obtain deeper insights into energy transfer and surface quenching processes involving Yb^(3+) and Er^(3+) ions,we examined energy loss processes in differently sized solid core NaYF_(4) nanocrystals doped with either Yb^(3+)(YbNC;20%Yb^(3+))or Er^(3+)(ErNC;2%Er^(3+))and co-doped with Yb^(3+) and Er^(3+)(YbErNC;20%Yb^(3+) and 2%Er^(3+))without a surface protection shell and coated with a thin and a thick NaYF_(4) shell in comparison to single and co-doped bulk materials.Luminescence studies at 375 nm excitation demonstrate back-energy transfer(BET)from the ^(4)G_(11/2) state of Er^(3+) to the ^(2)F_(5/2) state of Yb^(3+),through which the red Er^(3+) ^(4)F_(9/2) state is efficiently populated.Excitation power density(P)-dependent steady state and time-resolved photoluminescence measurements at different excitation and emission wavelengths enable to separate surface-related and volume-related effects for two-photonic and three-photonic processes involved in UCL and indicate a different influence of surface passivation on the green and red Er3+emission.The intensity and lifetime of the latter respond particularly to an increase in volume of the active UCNC core.We provide a three-dimensional random walk model to describe these effects that can be used in the future to predict the UCL behavior of UCNC.
基金supported by the National Natural Science Foundation of China (51375039 and 11074205)
文摘Fe5O7(OH)4H2O ferrihydrite is a low-crystallinity antiferromagnetic material.c-Fe2O3(maghemite)magnetic nanoparticles were prepared from a ferrihydrite precursor,by chemically induced transformation in FeCl2/NaOH solution.The magnetization,morphology,crystal structure and chemical composition of the products were determined by vibrating sample magnetometry,transmission electron microscopy,X-ray diffraction(XRD),energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy(XPS).Ferrihydrite underwent aggregation growth and transformed into a-FeO(OH)(goethite)particles,which subsequently transformed into c-Fe2O3nanoparticles,that became coated with NaCl.The c-Fe2O3particles had a flake-like morphology,when prepared from 0.01 mol/L FeCl2and a FeCl2:NaOH molar ratio of 0.4.The c-Fe2O3particles were more spherical,when prepared from a FeCl2:NaOH molar ratio of 0.6.The Fe content of the flake-like particles was lower than that of the spherical particles.Their magnetizations were similar,and the coercivity of the flake-like particles was larger.The differences in morphology and magnetization were attributed to the surface effect,and the difference in coercivity to the shape effect.
