Ebrahim Mostafavi | Stanford University (original) (raw)
Journal Papers by Ebrahim Mostafavi
Three-dimensional (3D) biodegradable and bio-mimetic porous scaffolds are ideal frameworks for sk... more Three-dimensional (3D) biodegradable and bio-mimetic porous scaffolds are ideal frameworks for skin tissue engineering. In this study, hybrid constructs of 3D scaffolds were successfully fabricated by the freeze-drying method from combinations of the type I collagen (Col) and synthetic poly(lactic acid) (PLLA) or polycaprolactone (PCL). Four different groups of 3D porous scaffolds including PCL, PCL− Col, PCL−PLLA, and PCL−PLLA−Col were fabricated and systematically characterized by hydrogen nuclear magnetic resonance, Fourier transform infrared spectroscopy, and scanning electron microscopy (SEM). Adipose tissue-derived mesenchymal stem cells (AT-MSCs) were seeded in all scaffolds, and the viability, proliferation, and adhesion of the cells were investigated using dimethylthiazol diphenyltetrazolium bromide assay and SEM. The results showed that scaffolds containing Col, particularly PCL−PLLA−Col scaffold, with pore sizes close to 400 nm and being sufficiently interconnected, have significantly greater potential (p < 0.01) for encouraging AT-MSCs adhesion and growth. The PCL−PLLA provided a mechanically stronger mesh support, and the type I Col microsponges encouraged excellent cell adhesion and tissue formation. The scaffold with the best properties could be an appropriate functional candidate for the preparation of artificial skin constructs.
Metal nanoparticles (MNPs) produced by green approaches have received global attention because of... more Metal nanoparticles (MNPs) produced by green approaches have received global attention because of their physicochemical characteristics and their applications in the field of biotechnology. In recent years, the development of synthesizing NPs by plant extracts has become a major focus of researchers because of these NPs have low hazardous effect in the environment and low toxicity for the human body. Synthesized NPs from plants are not only more stable in terms of size and shape, also the yield of this method is higher than the other methods. Moreover, some of these MNPs have shown antimicrobial activity which is consistently confirmed in past few years. Plant extracts have been used as reducing agent and stabilizer of NPs in which we can reduce the toxicity in the environment as well as the human body only by not using chemical agents. Furthermore, the presence of some specific materials in plant extracts could be extremely helpful and effective for the human body; for instance, polyphenol, which may have antioxidant effects has the capability for capturing free radicals before they can react with other biomolecules and cause serious damages. In this article, we focused on of the most common plants which are regularly used to synthesize MNPs along with various methods for synthesizing MNPs from plant extracts.
Magnetic nanoparticles have properties that cause to apply them in cancer therapy and vehicles fo... more Magnetic nanoparticles have properties that cause to apply them in cancer therapy and vehicles for the delivery of drugs such as 5FU, especially when they are modified with biocompatible copolymers. The aim of this study is to modify superparamagnetic iron oxide nanoparticles (SPIONPs) with PCL–PEG–PCL copolymers and then utilization of these nanoparticles for encapsulation of anticancer drug 5FU. The ring-opening polymerization (ROP) was used for the synthesis of PCL–PEG–PCL copolymer by e-caprolactone (PCL) and polyethylene glycol (PEG2000). We used the double emulsion method (water/oil/ water) to prepare 5FU-encapsulated Fe3O4 magnetic nanoparticles modified with PCL–PEG–PCL copolymer.
Chemical structure and magnetic properties of 5FU-loaded magnetic-polymer nanoparticles were
investigated systematically by employing FT-IR, XRD, VSM and SEM techniques. In vitro release profile of
5FU-loaded NPs was also determined. The results showed that the encapsulation efficiency value for
nanoparticles were 90%. Moreover, the release of 5FU is significantly higher at pH 5.8 compared to pH
7.4. Therefore, these nanoparticles have sustained release and can apply for cancer therapy.
Nanoparticles have been used for engineering 28 composite materials to improve the intrinsic prop... more Nanoparticles have been used for engineering 28 composite materials to improve the intrinsic properties and/or 29 add functionalities to pristine polymers. The majority of the 30 studies have focused on the incorporation of spherical nano-31 particles within the composite fibers. Herein, we incorporate 32 anisotropic branched-shaped zinc oxide (ZnO) nanoparticles 33 into fibrous scaffolds fabricated by electrospinning. The addition 34 of the branched particles resulted in their protrusion from fibers, 35 mimicking the architecture of a rose stem. We demonstrated 36 that the encapsulation of different shape particles significantly 37 influences the physicochemical and biological activities of the 38 resultant composite scaffolds. In particular, the branched 39 nanoparticles induced heterogeneous crystallization of the polymeric matrix as well as enhance the ultimate mechanical strain 40 and strength. Moreover, the three-dimensional (3D) nature of the branched ZnO nanoparticles enhanced adhesion properties of 41 the composite scaffolds to the tissues. In addition, the rose stem-like constructs offered excellent antibacterial activity, while 42 supporting the growth of eukaryote cells.
Advanced Materials Research, 2014
In this study, multiferroic BiFeO3 (BFO) powders were synthesized via mechanical activation of Bi... more In this study, multiferroic BiFeO3 (BFO) powders were synthesized via mechanical activation of Bi2O3 and Fe2O3 with the molar ratio of 1:1, using a planetary high energy ball mill and subsequent heat treatment. All samples were milled for 20 h and heat treated at various temperatures. XRD, FESEM, LPSA, and VSM techniques were used to evaluate the powder particle characteristics. FESEM images of 20 h milled sample indicated plate-like particles with a mean thickness of 45 nm and its LPSA results showed the mean agglomerate size of about 2.0 μm. XRD results of calcined samples showed that the BFO phase began to form at 650 °C and fully formed at 750 °C. In comparison to the conventionally processed samples, BFO phase formation temperature decreases by ∼100 °C in the samples produced by mechanical activation assisted process. VSM measurements of the sample heat treated at 750°C revealed a saturation magnetization (Ms) of 0.054 emu/g and coercivity (Hc) of 412 Oe.
In this study, Ni-CNTs nano-composite was synthesized via mechanical milling. The phase compositi... more In this study, Ni-CNTs nano-composite was synthesized via mechanical milling. The phase composition and morphology of the samples were investigated employing X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM). The effects of powder particle characteristics on the catalytic performance of the samples have also been systematically studied using various techniques such as temperature programmed reduction (TPR), N2 adsorption-desorption, and CO hydrogenation experiment, respectively. The results showed that by increasing the milling time and also CNTs content, the mean crystallite size of Ni decreases from 73nm in un-milled Ni sample to 35nm for the sample processed with 30wt% CNTs and milled for 15 hours. Moreover, addition of CNTs prevents Ni from oxidation and also agglomeration of the nano-composite particles. FESEM micrographs depicted that CNTs gradually embedded in Ni particles and dispersed more homogeneously on increasing milling time. TEM images showed that adding CNTs up to 10wt% resulted in the refinement of Ni particles to 25nm. BET results indicated that addition of CNTs up to 30wt% to Ni sample increased the surface area from 0.9 to 57 m 2 /g. Furthermore, enhancement in the reducibility of Ni by increasing CNTs was observed from TPR results. Consequently, the activity of prepared nano-composite samples as the CO hydrogenation catalyst was improved at all temperatures. Ni-10wt% CNTs as the best nano-composite sample exhibits the complete CO conversion at 340°C with the highest CH4 selectivity attributed to the smaller particle size and high surface area confirmed by TEM and BET techniques, respectively.
Nanostructured barium doped bismuth ferrite, Bi 0.8 Ba 0.2 FeO 3 porous ceramics with a relativel... more Nanostructured barium doped bismuth ferrite, Bi 0.8 Ba 0.2 FeO 3 porous ceramics with a relatively high magnetic coercivity was fabricated via sacrificial pore former method. X-ray diffraction results showed that 20 wt.% Ba doping induces a structural phase transition from rhombohedral to distorted pseudo-cubic structure in the final porous samples. Moreover, utilizing Bi 0.8 Ba 0.2 FeO 3 as the starting powder reduces the destructive interactions between the matrix phase and pore former, leading to an increase in stability of bismuth ferrite phase in the final porous ceramics. Urea-derived Bi 0.8 Ba 0.2 FeO 3 porous ceramic exhibits density of 4.74 g/cm 3 and porosity of 45 % owing the uniform distribution of interconnected pores with a mean pore size of 7.5 µm. Well defined nanostructured cell walls with a mean grain size of 90 nm were observed in the above sample, which is in a good accordance with the grain size obtained from BET measurements. Saturation magnetization decreased from 2.31 in the Bi 0.8 Ba 0.2 FeO 3 compact sample to 1.85 A·m 2 /kg in urea-derived Bi 0.8 Ba 0.2 FeO 3 porous sample; moreover, coercivity increased from 284 to 380 kA/m.
In this study the characteristics of two different kinds of La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) powder... more In this study the characteristics of two different kinds of La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) powders, one in-house powder synthesized by a co-precipitation method and another purchased from the Fuel Cell Materials Co. (FCM Co., USA) were compared. The co-precipitated powder was prepared by using ammonium carbonate as the precipitant with a NH4+/NO3- molar ratio of 2 and calcination at 1000°C for 1 h. Phase composition, morphology and particle size distribution of powders were systematically studied using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and laser particle size analysis (LPSA), respectively. The synthesized and commercial LSCF powders were overlaid on an Yttria-stabilized zirconia (YSZ) electrolyte having a gadolinium-doped ceria (GDC) interlayer. Electrochemical Impedance Spectroscopy (EIS) measurements were carried out at various operating temperatures in the range of 600-850°C. XRD and FESEM analysis revealed that single phase nano-crystalline LSCF powder with a mean crystallite size of 14 nm and mean particle size of 90 nm was obtained after calcination at 1000°C. The presence of hard agglomerated particles larger than a few microns in the commercial powder and also sub-micron agglomerates in the co-precipitated LSCF powder might be related to the final mechanical milling process and high calcination temperature of powders, respectively. LPSA results showed an identical mean particle size of about 1.5μm for both LSCF powders. EIS results revealed almost identical polarization resistance for both LSCF powders.
Nano-structured Bi1−xBaxFeO3(x = 0, 0.2) were synthesized by solid-state reaction.Ferromagnetic, ... more Nano-structured Bi1−xBaxFeO3(x = 0, 0.2) were synthesized by solid-state reaction.Ferromagnetic, ferroelectric and dielectric properties enhanced with Ba doping.The best properties obtained in calcined doped sample at 850 °C.20wt.% Ba-dopant change the structure of BFO from rhombohedral to pseudo-cubic.Bi1−xBaxFeO3(x = 0, 0.2) compounds were synthesized by conventional solid-state reaction method. Structural, morphological, magnetic and ferroelectric properties of the products were investigated systematically by employing X-ray diffraction, field emission scanning electron microscope, vibrating sample magnetometer as well as electrical evaluation techniques, respectively. The XRD results demonstrated distorted rhombohedral BiFeO3 crystal structure with the space group of R3c. However, 20wt% Ba doped sample underwent a structural phase transition from rhombohedral to distorted pseudo-cubic structure. FESEM images of the BiFeO3 sample calcined at 850 °C showed agglomerated nano-particles with a mean particle size of 60 nm, while Bi0.8Ba0.2FeO3 sample showed uniform cubic particles with a mean particle size of 220 nm. For Bi0.8Ba0.2FeO3 sample calcined at 850 °C, an anomaly in permittivity was observed in the vicinity of 370 °C which is around the Neel temperature of bismuth ferrite and is in agreement with the recent reports.
In this study, porous bismuth ferrite ceramics were synthesized by sacrificial pore former method... more In this study, porous bismuth ferrite ceramics were synthesized by sacrificial pore former method. A mixture of BiFeO3 and 20wt% of various pore formers including high density polyethylene, polyethylene glycol, polyvinyl alcohol, urea and graphite was intensively milled for 10 h in a planetary ball mill, uniaxially cold pressed and then subjected to the multi-stage heat treatment. The results revealed that urea and polyvinyl alcohol are appropriate candidates for maintaining the strength of the final porous structure. Density and porosity measurements showed that by employing 20wt% of high density polyethylene and graphite, a porous sample with a maximum porosity of nearly 40% could be obtained. Mercury porosimetry results showed that using urea as a pore former gives porous bismuth ferrite with a mean pore diameter of 7μm, uniform pore distribution as well as interconnected pores. Moreover, reactions between BiFeO3 matrix phase and thermal decomposition products of pore formers can lead to degradation of the BiFeO3 phase in the final porous samples. Analysis of X-ray diffraction patterns illustrated that in the samples processed with graphite, high density polyethylene and polyvinyl alcohol as pore former, BiFeO3 matrix phase partially or completely decomposes to intermediate phases of Bi2Fe4O9 and Bi25FeO40. While, using of urea does not damage the matrix phase and porous BiFeO3 within the original pervoskite structure could be prepared. Furthermore, thermodynamic investigation was carried out for prediction of possible interactions between matrix phase and pore former at elevated temperatures.
Advanced Materials Research, Jan 1, 2014
Nano-structured lanthanum strontium cobalt ferrite, La0.6Sr0.4Co0.2Fe0.8O3 (LSCF), was successful... more Nano-structured lanthanum strontium cobalt ferrite, La0.6Sr0.4Co0.2Fe0.8O3 (LSCF), was successfully synthesized via co-precipitation method using metal nitrates as starting materials. Effects of precipitating agent and calcination temperature on the phase composition and morphology of synthesized powders were systematically studied using X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM), respectively. XRD analysis revealed that a single phase La0.6Sr0.4Co0.2Fe0.8O3 perovskite was obtained in the processed sample using ammonium carbonate as precipitating agent with a NH4+/NO3-molar ratio of 2 after calcination at 1000C for 1 h. The phase composition of products was also affected by changing pH values. Moreover, using sodium hydroxide as a precipitant resulted in a mixture of La0.6Sr0.4Co0.2Fe0.8O3 and cobalt ferrite (CoFe2O4) phases. Careless washing of the precursors can also led to the formation of mixed phase after calcination of final powders. Mean crystallite size of the obtained powders was not noticeably affected by varying calcination temperature from 900 to 1050C and remained almost the same at 10 nm, however increasing calcination temperature to 1100C resulted in sharp structural coarsening. FESEM studies demonstrate that relatively uniform particles with mean particle size of 90 nm were obtained in the sample processed with a NH4+/NO3- molar ratio of 2 after calcination at 1000C for 1 h.
The effects of milling energy induced during intermediate mechanical activation of precursors on ... more The effects of milling energy induced during intermediate mechanical activation of precursors on the synthesis of nano-structured BiFeO3 powders have been systematically investigated. X-ray diffractometer, laser particles size analyzer, field emission scanning electron microscope, vibrating sample magnetometer and electrical evaluation techniques were used to study phase composition, particles size distribution, morphology, magnetic properties and ferroelectric properties of the products, respectively. Applying a total energy of 171.18kJ/g during milling led to formation of an amorphous structure which resulted in decreasing the formation temperature of bismuth ferrite phase by about 100˚C, although small amounts of secondary phases were detected. This sample shows the mean particles size of 170nm and the mean crystallite size of 40nm, when calcined at 750˚C. Saturation magnetization (MS) increased from 0.054 to 0.071A.m2/kg and coercive field (HC) decreased from 32.63 to 6.37kA/m by increasing the milling energy from 13.48 to 171.18kJ/g. In addition, electrical hysteresis loops demonstrated a decrease in the current leakage by increasing the milling energy and lowering the calcination temperature.
Nano-sized barium hexaferrite particles were synthesized by mechanical activation of BaCO3 and Fe... more Nano-sized barium hexaferrite particles were synthesized by mechanical activation of BaCO3 and Fe2O3 powders mixture as starting materials. The effects of mechanical milling energy on the phase composition, morphology, thermal behavior and magnetic properties of the samples were systematically investigated by employing X-ray diffractometer, field emission scanning electron microscopy, differential thermal/thermo gravimetery analysis and vibrating sample magnetometer, respectively. The milling energy was calculated at five different levels using collision model. It was found that there is an optimum milling energy value for obtaining barium hexaferrite phase. The results revealed that applying a minimum total milling energy of 93.7 kJ/g was necessary for formation of almost single barium hexaferrite at a relatively low calcination temperature of 800C. FESEM micrograph of the above sample exhibited nano-size particles with a mean particle size of 80 nm. Further increase in milling energy leads to dramatic decrease in phase purity as well as magnetic characteristics of the samples. By increasing the milling energy from 93.7 to 671.9 kJ/g, saturation magnetization (Ms) decreased from 22.5 to 0.39 emu/g, and also coercivity (Hc) decreased from 4.28 to 1.46 kOe.
Advanced Materials Research, Jan 1, 2014
Conference Presentations by Ebrahim Mostafavi
In this study the characteristics of two La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) powders, one obtained from... more In this study the characteristics of two La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) powders, one obtained from an in-house synthesized by co-precipitation method and a commercial one from Fuel Cell Materials Co. (USA), were compared. The co-precipitated powder was processed by using ammonium carbonate as precipitating agent with a NH4+/NO3- molar ratio of 2 and calcination at 1000C for 1 h. Phase composition, morphology and particle size distribution of powders were systematically studied using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and laser particle size analysis (LPSA), respectively. The synthesized and commercial LSCF powders were overlaid on Yttria-stabilized zirconia (YSZ) electrolyte having a gadolinium-doped ceria (GDC) interlayer. Electrochemical Impedance Spectroscopy (EIS) measurement was carried out at various operating temperatures in the range of 600-850C. XRD and FESEM analysis revealed that single phase nano-crystalline LSCF powder with a mean crystallite size of 14 nm and mean particle size of 90 nm is obtained after calcination at 1000C. The presence of hard agglomerated particles larger than few microns in commercial powder and also sub-micron agglomerates in co-precipitated LSCF powder can be related to the final mechanical milling process and high calcination temperature of powders, respectively. LPSA results show identical mean particle size of about 1.5μm for both LSCF powders. EIS results revealed almost identical polarization resistance for both LSCF powders.
Multiferroic bismuth ferrite, BiFeO3, was synthesized via conventional solid-state reaction metho... more Multiferroic bismuth ferrite, BiFeO3, was synthesized via conventional solid-state reaction method using Bi2O3, Fe2O3 as starting materials. Effects of Bi2O3/Fe2O3 molar ratio and calcination temperature on the phase composition, morphology and magnetic properties of produced powders were systematically studied using XRD, FESEM/EDS and VSM techniques, respectively.The results revealed that BiFeO3 phase with rhombohedral R3c structure with a mean particle size of 40 nm was formed in the sample processed with a Bi2O3/Fe2O3 molar ratio of 1:1 after calcination at 800 °C. Rietveld analysis which was applied to the x-ray diffraction data via MAUD software indicated high purity of 95%wt for the above sample. Deviation from the stoichiometric molar ratio (Bi2O3/Fe2O3: 0.9, 1.1, 1.2) yielded higher content of the intermediate phases of Bi2Fe4O9 and Bi25FeO40. FESEM studies showed that the mean particle size was increased from 40 to 62 nm by increasing calcination temperature from 800 to 850 °C. VSM results for 1:1 molar ratio samples indicated that increasing the calcination temperature from 800 to 850 °C increased saturation magnetization (Ms) from 0.087 to 0.116 emu/g and also coercive field (Hc) from 60 to 100 Oe.
In this study, multiferroic BiFeO3 (BFO) powders were synthesized via mechanical activation of Bi... more In this study, multiferroic BiFeO3 (BFO) powders were synthesized via mechanical
activation of Bi2O3 and Fe2O3 with the molar ratio of 1:1, using a planetary high energy ball mill
and subsequent heat treatment. All samples were milled for 20 h and heat treated at various
temperatures. XRD, FESEM, LPSA, and VSM techniques were used to evaluate the powder
particle characteristics. FESEM images of 20 h milled sample indicated plate-like particles with a
mean thickness of 45 nm and its LPSA results showed the mean agglomerate size of about 2.0 μm.
XRD results of calcined samples showed that the BFO phase began to form at 650 °C and fully
formed at 750 °C. In comparison to the conventionally processed samples, BFO phase formation
temperature decreases by ∼100 °C in the samples produced by mechanical activation assisted
process. VSM measurements of the sample heat treated at 750 °C revealed a saturation
magnetization (Ms) of 0.054 emu/g and coercivity (Hc) of 412 Oe.
Nano-structured manganese cobalt oxide (MnCo2O4) was successfully synthesized by co-precipitation... more Nano-structured manganese cobalt oxide (MnCo2O4) was successfully synthesized by co-precipitation method using metal nitrates as starting materials. The phase formation and morphology of the products were characterized by means of X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM), respectively. The effects of pH and calcination temperature were investigated on the characteristics of MnCo2O4 powders. The results revealed that the MnCo2O4 phase was obtained easier at relatively higher pH values. XRD results showed that at the temperature of 450˚C the phase formation was not completed, while with increasing the calcination temperature to 1000˚C the desired phase was fully achieved. Furthermore, by increasing the calcination temperature from 550 to 1000˚C, the mean crystallite size of the powders increases from 30 to 140 nm. FESEM investigation shows that in the sample processed with OH-/NO3- =1.5 and calcined at 550˚C completely uniform particles with mean size of 45nm can be obtained.
Papers by Ebrahim Mostafavi
Three-dimensional (3D) biodegradable and bio-mimetic porous scaffolds are ideal frameworks for sk... more Three-dimensional (3D) biodegradable and bio-mimetic porous scaffolds are ideal frameworks for skin tissue engineering. In this study, hybrid constructs of 3D scaffolds were successfully fabricated by the freeze-drying method from combinations of the type I collagen (Col) and synthetic poly(lactic acid) (PLLA) or polycaprolactone (PCL). Four different groups of 3D porous scaffolds including PCL, PCL− Col, PCL−PLLA, and PCL−PLLA−Col were fabricated and systematically characterized by hydrogen nuclear magnetic resonance, Fourier transform infrared spectroscopy, and scanning electron microscopy (SEM). Adipose tissue-derived mesenchymal stem cells (AT-MSCs) were seeded in all scaffolds, and the viability, proliferation, and adhesion of the cells were investigated using dimethylthiazol diphenyltetrazolium bromide assay and SEM. The results showed that scaffolds containing Col, particularly PCL−PLLA−Col scaffold, with pore sizes close to 400 nm and being sufficiently interconnected, have significantly greater potential (p < 0.01) for encouraging AT-MSCs adhesion and growth. The PCL−PLLA provided a mechanically stronger mesh support, and the type I Col microsponges encouraged excellent cell adhesion and tissue formation. The scaffold with the best properties could be an appropriate functional candidate for the preparation of artificial skin constructs.
Metal nanoparticles (MNPs) produced by green approaches have received global attention because of... more Metal nanoparticles (MNPs) produced by green approaches have received global attention because of their physicochemical characteristics and their applications in the field of biotechnology. In recent years, the development of synthesizing NPs by plant extracts has become a major focus of researchers because of these NPs have low hazardous effect in the environment and low toxicity for the human body. Synthesized NPs from plants are not only more stable in terms of size and shape, also the yield of this method is higher than the other methods. Moreover, some of these MNPs have shown antimicrobial activity which is consistently confirmed in past few years. Plant extracts have been used as reducing agent and stabilizer of NPs in which we can reduce the toxicity in the environment as well as the human body only by not using chemical agents. Furthermore, the presence of some specific materials in plant extracts could be extremely helpful and effective for the human body; for instance, polyphenol, which may have antioxidant effects has the capability for capturing free radicals before they can react with other biomolecules and cause serious damages. In this article, we focused on of the most common plants which are regularly used to synthesize MNPs along with various methods for synthesizing MNPs from plant extracts.
Magnetic nanoparticles have properties that cause to apply them in cancer therapy and vehicles fo... more Magnetic nanoparticles have properties that cause to apply them in cancer therapy and vehicles for the delivery of drugs such as 5FU, especially when they are modified with biocompatible copolymers. The aim of this study is to modify superparamagnetic iron oxide nanoparticles (SPIONPs) with PCL–PEG–PCL copolymers and then utilization of these nanoparticles for encapsulation of anticancer drug 5FU. The ring-opening polymerization (ROP) was used for the synthesis of PCL–PEG–PCL copolymer by e-caprolactone (PCL) and polyethylene glycol (PEG2000). We used the double emulsion method (water/oil/ water) to prepare 5FU-encapsulated Fe3O4 magnetic nanoparticles modified with PCL–PEG–PCL copolymer.
Chemical structure and magnetic properties of 5FU-loaded magnetic-polymer nanoparticles were
investigated systematically by employing FT-IR, XRD, VSM and SEM techniques. In vitro release profile of
5FU-loaded NPs was also determined. The results showed that the encapsulation efficiency value for
nanoparticles were 90%. Moreover, the release of 5FU is significantly higher at pH 5.8 compared to pH
7.4. Therefore, these nanoparticles have sustained release and can apply for cancer therapy.
Nanoparticles have been used for engineering 28 composite materials to improve the intrinsic prop... more Nanoparticles have been used for engineering 28 composite materials to improve the intrinsic properties and/or 29 add functionalities to pristine polymers. The majority of the 30 studies have focused on the incorporation of spherical nano-31 particles within the composite fibers. Herein, we incorporate 32 anisotropic branched-shaped zinc oxide (ZnO) nanoparticles 33 into fibrous scaffolds fabricated by electrospinning. The addition 34 of the branched particles resulted in their protrusion from fibers, 35 mimicking the architecture of a rose stem. We demonstrated 36 that the encapsulation of different shape particles significantly 37 influences the physicochemical and biological activities of the 38 resultant composite scaffolds. In particular, the branched 39 nanoparticles induced heterogeneous crystallization of the polymeric matrix as well as enhance the ultimate mechanical strain 40 and strength. Moreover, the three-dimensional (3D) nature of the branched ZnO nanoparticles enhanced adhesion properties of 41 the composite scaffolds to the tissues. In addition, the rose stem-like constructs offered excellent antibacterial activity, while 42 supporting the growth of eukaryote cells.
Advanced Materials Research, 2014
In this study, multiferroic BiFeO3 (BFO) powders were synthesized via mechanical activation of Bi... more In this study, multiferroic BiFeO3 (BFO) powders were synthesized via mechanical activation of Bi2O3 and Fe2O3 with the molar ratio of 1:1, using a planetary high energy ball mill and subsequent heat treatment. All samples were milled for 20 h and heat treated at various temperatures. XRD, FESEM, LPSA, and VSM techniques were used to evaluate the powder particle characteristics. FESEM images of 20 h milled sample indicated plate-like particles with a mean thickness of 45 nm and its LPSA results showed the mean agglomerate size of about 2.0 μm. XRD results of calcined samples showed that the BFO phase began to form at 650 °C and fully formed at 750 °C. In comparison to the conventionally processed samples, BFO phase formation temperature decreases by ∼100 °C in the samples produced by mechanical activation assisted process. VSM measurements of the sample heat treated at 750°C revealed a saturation magnetization (Ms) of 0.054 emu/g and coercivity (Hc) of 412 Oe.
In this study, Ni-CNTs nano-composite was synthesized via mechanical milling. The phase compositi... more In this study, Ni-CNTs nano-composite was synthesized via mechanical milling. The phase composition and morphology of the samples were investigated employing X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM). The effects of powder particle characteristics on the catalytic performance of the samples have also been systematically studied using various techniques such as temperature programmed reduction (TPR), N2 adsorption-desorption, and CO hydrogenation experiment, respectively. The results showed that by increasing the milling time and also CNTs content, the mean crystallite size of Ni decreases from 73nm in un-milled Ni sample to 35nm for the sample processed with 30wt% CNTs and milled for 15 hours. Moreover, addition of CNTs prevents Ni from oxidation and also agglomeration of the nano-composite particles. FESEM micrographs depicted that CNTs gradually embedded in Ni particles and dispersed more homogeneously on increasing milling time. TEM images showed that adding CNTs up to 10wt% resulted in the refinement of Ni particles to 25nm. BET results indicated that addition of CNTs up to 30wt% to Ni sample increased the surface area from 0.9 to 57 m 2 /g. Furthermore, enhancement in the reducibility of Ni by increasing CNTs was observed from TPR results. Consequently, the activity of prepared nano-composite samples as the CO hydrogenation catalyst was improved at all temperatures. Ni-10wt% CNTs as the best nano-composite sample exhibits the complete CO conversion at 340°C with the highest CH4 selectivity attributed to the smaller particle size and high surface area confirmed by TEM and BET techniques, respectively.
Nanostructured barium doped bismuth ferrite, Bi 0.8 Ba 0.2 FeO 3 porous ceramics with a relativel... more Nanostructured barium doped bismuth ferrite, Bi 0.8 Ba 0.2 FeO 3 porous ceramics with a relatively high magnetic coercivity was fabricated via sacrificial pore former method. X-ray diffraction results showed that 20 wt.% Ba doping induces a structural phase transition from rhombohedral to distorted pseudo-cubic structure in the final porous samples. Moreover, utilizing Bi 0.8 Ba 0.2 FeO 3 as the starting powder reduces the destructive interactions between the matrix phase and pore former, leading to an increase in stability of bismuth ferrite phase in the final porous ceramics. Urea-derived Bi 0.8 Ba 0.2 FeO 3 porous ceramic exhibits density of 4.74 g/cm 3 and porosity of 45 % owing the uniform distribution of interconnected pores with a mean pore size of 7.5 µm. Well defined nanostructured cell walls with a mean grain size of 90 nm were observed in the above sample, which is in a good accordance with the grain size obtained from BET measurements. Saturation magnetization decreased from 2.31 in the Bi 0.8 Ba 0.2 FeO 3 compact sample to 1.85 A·m 2 /kg in urea-derived Bi 0.8 Ba 0.2 FeO 3 porous sample; moreover, coercivity increased from 284 to 380 kA/m.
In this study the characteristics of two different kinds of La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) powder... more In this study the characteristics of two different kinds of La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) powders, one in-house powder synthesized by a co-precipitation method and another purchased from the Fuel Cell Materials Co. (FCM Co., USA) were compared. The co-precipitated powder was prepared by using ammonium carbonate as the precipitant with a NH4+/NO3- molar ratio of 2 and calcination at 1000°C for 1 h. Phase composition, morphology and particle size distribution of powders were systematically studied using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and laser particle size analysis (LPSA), respectively. The synthesized and commercial LSCF powders were overlaid on an Yttria-stabilized zirconia (YSZ) electrolyte having a gadolinium-doped ceria (GDC) interlayer. Electrochemical Impedance Spectroscopy (EIS) measurements were carried out at various operating temperatures in the range of 600-850°C. XRD and FESEM analysis revealed that single phase nano-crystalline LSCF powder with a mean crystallite size of 14 nm and mean particle size of 90 nm was obtained after calcination at 1000°C. The presence of hard agglomerated particles larger than a few microns in the commercial powder and also sub-micron agglomerates in the co-precipitated LSCF powder might be related to the final mechanical milling process and high calcination temperature of powders, respectively. LPSA results showed an identical mean particle size of about 1.5μm for both LSCF powders. EIS results revealed almost identical polarization resistance for both LSCF powders.
Nano-structured Bi1−xBaxFeO3(x = 0, 0.2) were synthesized by solid-state reaction.Ferromagnetic, ... more Nano-structured Bi1−xBaxFeO3(x = 0, 0.2) were synthesized by solid-state reaction.Ferromagnetic, ferroelectric and dielectric properties enhanced with Ba doping.The best properties obtained in calcined doped sample at 850 °C.20wt.% Ba-dopant change the structure of BFO from rhombohedral to pseudo-cubic.Bi1−xBaxFeO3(x = 0, 0.2) compounds were synthesized by conventional solid-state reaction method. Structural, morphological, magnetic and ferroelectric properties of the products were investigated systematically by employing X-ray diffraction, field emission scanning electron microscope, vibrating sample magnetometer as well as electrical evaluation techniques, respectively. The XRD results demonstrated distorted rhombohedral BiFeO3 crystal structure with the space group of R3c. However, 20wt% Ba doped sample underwent a structural phase transition from rhombohedral to distorted pseudo-cubic structure. FESEM images of the BiFeO3 sample calcined at 850 °C showed agglomerated nano-particles with a mean particle size of 60 nm, while Bi0.8Ba0.2FeO3 sample showed uniform cubic particles with a mean particle size of 220 nm. For Bi0.8Ba0.2FeO3 sample calcined at 850 °C, an anomaly in permittivity was observed in the vicinity of 370 °C which is around the Neel temperature of bismuth ferrite and is in agreement with the recent reports.
In this study, porous bismuth ferrite ceramics were synthesized by sacrificial pore former method... more In this study, porous bismuth ferrite ceramics were synthesized by sacrificial pore former method. A mixture of BiFeO3 and 20wt% of various pore formers including high density polyethylene, polyethylene glycol, polyvinyl alcohol, urea and graphite was intensively milled for 10 h in a planetary ball mill, uniaxially cold pressed and then subjected to the multi-stage heat treatment. The results revealed that urea and polyvinyl alcohol are appropriate candidates for maintaining the strength of the final porous structure. Density and porosity measurements showed that by employing 20wt% of high density polyethylene and graphite, a porous sample with a maximum porosity of nearly 40% could be obtained. Mercury porosimetry results showed that using urea as a pore former gives porous bismuth ferrite with a mean pore diameter of 7μm, uniform pore distribution as well as interconnected pores. Moreover, reactions between BiFeO3 matrix phase and thermal decomposition products of pore formers can lead to degradation of the BiFeO3 phase in the final porous samples. Analysis of X-ray diffraction patterns illustrated that in the samples processed with graphite, high density polyethylene and polyvinyl alcohol as pore former, BiFeO3 matrix phase partially or completely decomposes to intermediate phases of Bi2Fe4O9 and Bi25FeO40. While, using of urea does not damage the matrix phase and porous BiFeO3 within the original pervoskite structure could be prepared. Furthermore, thermodynamic investigation was carried out for prediction of possible interactions between matrix phase and pore former at elevated temperatures.
Advanced Materials Research, Jan 1, 2014
Nano-structured lanthanum strontium cobalt ferrite, La0.6Sr0.4Co0.2Fe0.8O3 (LSCF), was successful... more Nano-structured lanthanum strontium cobalt ferrite, La0.6Sr0.4Co0.2Fe0.8O3 (LSCF), was successfully synthesized via co-precipitation method using metal nitrates as starting materials. Effects of precipitating agent and calcination temperature on the phase composition and morphology of synthesized powders were systematically studied using X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM), respectively. XRD analysis revealed that a single phase La0.6Sr0.4Co0.2Fe0.8O3 perovskite was obtained in the processed sample using ammonium carbonate as precipitating agent with a NH4+/NO3-molar ratio of 2 after calcination at 1000C for 1 h. The phase composition of products was also affected by changing pH values. Moreover, using sodium hydroxide as a precipitant resulted in a mixture of La0.6Sr0.4Co0.2Fe0.8O3 and cobalt ferrite (CoFe2O4) phases. Careless washing of the precursors can also led to the formation of mixed phase after calcination of final powders. Mean crystallite size of the obtained powders was not noticeably affected by varying calcination temperature from 900 to 1050C and remained almost the same at 10 nm, however increasing calcination temperature to 1100C resulted in sharp structural coarsening. FESEM studies demonstrate that relatively uniform particles with mean particle size of 90 nm were obtained in the sample processed with a NH4+/NO3- molar ratio of 2 after calcination at 1000C for 1 h.
The effects of milling energy induced during intermediate mechanical activation of precursors on ... more The effects of milling energy induced during intermediate mechanical activation of precursors on the synthesis of nano-structured BiFeO3 powders have been systematically investigated. X-ray diffractometer, laser particles size analyzer, field emission scanning electron microscope, vibrating sample magnetometer and electrical evaluation techniques were used to study phase composition, particles size distribution, morphology, magnetic properties and ferroelectric properties of the products, respectively. Applying a total energy of 171.18kJ/g during milling led to formation of an amorphous structure which resulted in decreasing the formation temperature of bismuth ferrite phase by about 100˚C, although small amounts of secondary phases were detected. This sample shows the mean particles size of 170nm and the mean crystallite size of 40nm, when calcined at 750˚C. Saturation magnetization (MS) increased from 0.054 to 0.071A.m2/kg and coercive field (HC) decreased from 32.63 to 6.37kA/m by increasing the milling energy from 13.48 to 171.18kJ/g. In addition, electrical hysteresis loops demonstrated a decrease in the current leakage by increasing the milling energy and lowering the calcination temperature.
Nano-sized barium hexaferrite particles were synthesized by mechanical activation of BaCO3 and Fe... more Nano-sized barium hexaferrite particles were synthesized by mechanical activation of BaCO3 and Fe2O3 powders mixture as starting materials. The effects of mechanical milling energy on the phase composition, morphology, thermal behavior and magnetic properties of the samples were systematically investigated by employing X-ray diffractometer, field emission scanning electron microscopy, differential thermal/thermo gravimetery analysis and vibrating sample magnetometer, respectively. The milling energy was calculated at five different levels using collision model. It was found that there is an optimum milling energy value for obtaining barium hexaferrite phase. The results revealed that applying a minimum total milling energy of 93.7 kJ/g was necessary for formation of almost single barium hexaferrite at a relatively low calcination temperature of 800C. FESEM micrograph of the above sample exhibited nano-size particles with a mean particle size of 80 nm. Further increase in milling energy leads to dramatic decrease in phase purity as well as magnetic characteristics of the samples. By increasing the milling energy from 93.7 to 671.9 kJ/g, saturation magnetization (Ms) decreased from 22.5 to 0.39 emu/g, and also coercivity (Hc) decreased from 4.28 to 1.46 kOe.
Advanced Materials Research, Jan 1, 2014
In this study the characteristics of two La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) powders, one obtained from... more In this study the characteristics of two La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) powders, one obtained from an in-house synthesized by co-precipitation method and a commercial one from Fuel Cell Materials Co. (USA), were compared. The co-precipitated powder was processed by using ammonium carbonate as precipitating agent with a NH4+/NO3- molar ratio of 2 and calcination at 1000C for 1 h. Phase composition, morphology and particle size distribution of powders were systematically studied using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and laser particle size analysis (LPSA), respectively. The synthesized and commercial LSCF powders were overlaid on Yttria-stabilized zirconia (YSZ) electrolyte having a gadolinium-doped ceria (GDC) interlayer. Electrochemical Impedance Spectroscopy (EIS) measurement was carried out at various operating temperatures in the range of 600-850C. XRD and FESEM analysis revealed that single phase nano-crystalline LSCF powder with a mean crystallite size of 14 nm and mean particle size of 90 nm is obtained after calcination at 1000C. The presence of hard agglomerated particles larger than few microns in commercial powder and also sub-micron agglomerates in co-precipitated LSCF powder can be related to the final mechanical milling process and high calcination temperature of powders, respectively. LPSA results show identical mean particle size of about 1.5μm for both LSCF powders. EIS results revealed almost identical polarization resistance for both LSCF powders.
Multiferroic bismuth ferrite, BiFeO3, was synthesized via conventional solid-state reaction metho... more Multiferroic bismuth ferrite, BiFeO3, was synthesized via conventional solid-state reaction method using Bi2O3, Fe2O3 as starting materials. Effects of Bi2O3/Fe2O3 molar ratio and calcination temperature on the phase composition, morphology and magnetic properties of produced powders were systematically studied using XRD, FESEM/EDS and VSM techniques, respectively.The results revealed that BiFeO3 phase with rhombohedral R3c structure with a mean particle size of 40 nm was formed in the sample processed with a Bi2O3/Fe2O3 molar ratio of 1:1 after calcination at 800 °C. Rietveld analysis which was applied to the x-ray diffraction data via MAUD software indicated high purity of 95%wt for the above sample. Deviation from the stoichiometric molar ratio (Bi2O3/Fe2O3: 0.9, 1.1, 1.2) yielded higher content of the intermediate phases of Bi2Fe4O9 and Bi25FeO40. FESEM studies showed that the mean particle size was increased from 40 to 62 nm by increasing calcination temperature from 800 to 850 °C. VSM results for 1:1 molar ratio samples indicated that increasing the calcination temperature from 800 to 850 °C increased saturation magnetization (Ms) from 0.087 to 0.116 emu/g and also coercive field (Hc) from 60 to 100 Oe.
In this study, multiferroic BiFeO3 (BFO) powders were synthesized via mechanical activation of Bi... more In this study, multiferroic BiFeO3 (BFO) powders were synthesized via mechanical
activation of Bi2O3 and Fe2O3 with the molar ratio of 1:1, using a planetary high energy ball mill
and subsequent heat treatment. All samples were milled for 20 h and heat treated at various
temperatures. XRD, FESEM, LPSA, and VSM techniques were used to evaluate the powder
particle characteristics. FESEM images of 20 h milled sample indicated plate-like particles with a
mean thickness of 45 nm and its LPSA results showed the mean agglomerate size of about 2.0 μm.
XRD results of calcined samples showed that the BFO phase began to form at 650 °C and fully
formed at 750 °C. In comparison to the conventionally processed samples, BFO phase formation
temperature decreases by ∼100 °C in the samples produced by mechanical activation assisted
process. VSM measurements of the sample heat treated at 750 °C revealed a saturation
magnetization (Ms) of 0.054 emu/g and coercivity (Hc) of 412 Oe.
Nano-structured manganese cobalt oxide (MnCo2O4) was successfully synthesized by co-precipitation... more Nano-structured manganese cobalt oxide (MnCo2O4) was successfully synthesized by co-precipitation method using metal nitrates as starting materials. The phase formation and morphology of the products were characterized by means of X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM), respectively. The effects of pH and calcination temperature were investigated on the characteristics of MnCo2O4 powders. The results revealed that the MnCo2O4 phase was obtained easier at relatively higher pH values. XRD results showed that at the temperature of 450˚C the phase formation was not completed, while with increasing the calcination temperature to 1000˚C the desired phase was fully achieved. Furthermore, by increasing the calcination temperature from 550 to 1000˚C, the mean crystallite size of the powders increases from 30 to 140 nm. FESEM investigation shows that in the sample processed with OH-/NO3- =1.5 and calcined at 550˚C completely uniform particles with mean size of 45nm can be obtained.