In this study, the magnetically recyclable Fe3O4@C/BiOBr heterojunction with enhanced visible light-driven photocatalytic ability was obtained by two-step solvothermal method. The phase, morphology, and structure of the samples were investigated by XRD, FESEM, HRTEM, and XPS. The Fe3O4@C/BiOBr heterojunction was composed of Fe3O4@C sphere and BiOBr microsphere with diameters of 200 nm and 1000 nm, respectively. The photocatalytic performance of Fe3O4@C/BiOBr composite for RhB was examined under visible light irradiation. The photocatalytic activity of Fe3O4@C/BiOBr composite was much higher than that of pure BiOBr and Fe3O4@C. After 35 min of irradiation, 97% of RhB could be removed with the Fe3O4@C/BiOBr photocatalyst. Based on radical trapping experiments of active species, the mechanism of enhanced photocatalytic performance was proposed. In addition, the superparamagnetic property of the photocatalyst not only allows its easy recyclability by an external magnetic field but also maintains high photocatalytic activity after five cyclic experiments.
Small core-shell Fe3O4@Pd superparamagnetic nanoparticles (MNPs) were obtained with good control in size and shape distribution by metal-complex thermal decomposition in organic media. The role of the stabilizer in the synthesis of MNPs was studied, employing oleylamine (OA), triphenylphosphine (TPP) and triphenylamine (TPA). The results revealed that, among the stabilizer investigated, the presence of oleylamine in the reaction media is crucial in order to obtain an uniform shell of Pd(0) in Fe3O4@Pd MNPs of 7?±?1 nm. The synthesized core-shell MNPs were tested in Pd-catalyzed Heck-Mizoroki and Suzuki-Miyaura coupling reactions and p-chloronitrobenzene hydrogenation. High conversion, good reaction yields, and good TOF values were achieved in the three reaction systems with this nanocatalyst. The core-shell nanoparticle was easily recovered by a simple magnetic separation using a neodymium commercial magnet, which allowed performing up to four cycles of reuse.
Nano-octahedra of cobalt ferrite CoxFe3???xO4 (1?≤?x?<?2), with a broad size distribution around 15–20 nm, were synthesized by a hydrothermal method using nitrates as precursors. For the first time, single-phased nano-octahedra of cobalt-rich ferrite CoxFe3???xO4 (x?=?1.5) were synthesized. The nano-octahedra are crystallized in a normal spinel structure, with tetrahedral sites occupied by Co2+. This specific octahedral shape was obtained with anionic, cationic, and nonionic surfactants. The nature of the surfactant influenced the chemical composition of the powder and the size of the nano-octahedra. The {100} truncation of the octahedra is more pronounced for the small particles. For the first time, single-phased nanoparticles with as much as x?=?1.8 cobalt were synthesized with ethylene glycol as solvent. These nanoparticles, around 8 nm in size, have no specific shape and possess a lacunar spinel structure similar to maghemite. The samples were characterized by X-ray diffraction, transmission electron microscopy, and energy-dispersive spectroscopy.
CeO2 and Fe2O3 co-modified titanate nanosheet (Fe2O3/CeO2@TNS) was prepared by one-pot hydrothermal method; the photocatalyst exhibited large surface area with CeO2 and Fe2O3 particles well dispersed on the surface. The results of XRD, BET, and Raman proved that the CeO2 and Fe2O3 introduced in the TNS influenced its structure evolution from 3D to 2D. The modification resulted in a shift of the absorption edge toward a longer wavelength and the band gap reduced to 2.87 eV. The three-component systems performed excellent photocatalytic activity and cycle stability on phenol and methyl blue (MB) solution under sunlight; nearly total phenol and MB were degraded in dozens of minutes. And the reaction rate constant (K) of Fe2O3/CeO2@TNS on phenol degradation was 1.77, 3.25, 4.88, and 13-fold of Fe2O3@TNS, CeO2@TNS, bare TNS, and P25, respectively. The enhanced photocatalytic activity could be ascribed to the efficient separation of photogenerated pairs through the formation of tandem n-n-n heterojunction among the three-component systems. This work will be useful for the design of other tandem n-n-n heterojunction photocatalytic systems for application in energy conversion and environmental remediation.
Spinel ferrites can be used in magnetic targeting and microwave heating and can therefore be used for targeted and controllable drug delivery. We used the cetyltrimethylammonium bromide-assisted solvothermal method to synthesize a series of spinel ferrites (MxFe3-xO4, M=Mg, Mn, Fe, Co, Ni, Cu, Zn) with a mesoporous or hollow-mesoporous structure suitable for direct drug loading and the particle diameters ranging from 200 to 350 nm. We investigated the effects of M2+ cation on the morphology and properties of these products by analyzing their transmission electron microscopy images, mesoporous properties, magnetic properties, and microwave responses. We chose hollow-mesoporous MxFe3-xO4 (M=Fe, Co, Zn) nanoparticles, which had better overall properties, for the drug VP16 (etoposide) loading and microwave-controlled release. The CoxFe3-xO4 and Fe3O4 particles trapped 61.5 and 64.8%, respectively, of the VP16, which were higher than that (60.4%) of ZnxFe3-xO4. Controllable drug release by these simple magnetic nanocarriers can be achieved by microwave irradiation, and VP16-loaded CoxFe3-xO4 released the most VP16 molecules (more than 50% after 1 h and 69.1% after 6 h) under microwave irradiation. Our results confirm the favorable drug loading and microwave-controlled delivery by these ferrites, and lay a theoretical foundation to promote clinical application of the targeted controllable drug delivery system.
Graphical abstract In the present study, we prepared mesoporous or hollow-mesoporous spinel ferrites (MxFe3-xO4, M=Mg, Mn, Fe, Co, Ni, Cu, Zn) by CTAB-assisted solvothermal method and solved the problem of Cu and Ni impurities in CuxFe3-xO4 and NixFe3-xO4 products by means of magnetic separation and additional redox reactions, respectively. We investigated the effects of the M2+ cation on the morphology, mesoporous properties, magnetic properties, and microwave responses of these ferrites. Then, the drug loading and microwave-controlled drug release of hollow-mesoporous MxFe3-xO4 (M?=?Fe, Co, Zn) nanoparticles with better overall properties were also studied. CoxFe3-xO4 has the best overall performances for microwave-controlled drug release.
Metal nanoparticles have been combined with magnet metal–organic frameworks (MOFs) to afford new materials that demonstrate an efficient catalytic degradation, high stability, and excellent reusability in areas of catalysis because of their exceptionally high surface areas and structural diversity. Magnetic MxOy@N-C (M = Fe, Co, Mn) nanocrystals were formed on nitrogen-doped carbon surface by using 8-hydroxyquinoline as a C/N precursor. The Co@N-C, MnO@N-C, and Fe/Fe2O3@N-C catalysts were characterized by X-ray diffraction (XRD), Raman, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), N2 adsorption/desorption, and X-ray photoelectron spectroscopy (XPS). The catalytic performances of catalysts were thoroughly investigated in the oxidation of aniline solution based on sulfate radicals (SO4?.) toward Fenton-like reaction. Magnetic MxOy@N-C exhibits an unexpectedly high catalytic activity in the degradation of aniline in water. A high magnetic MxOy@N-C catalytic activity was observed after the evaluation by aniline degradation in water. Aniline degradation was found to follow the first-order kinetics, and as a result, various metals significantly affected the structures and performances of the catalysts, and their catalytic activity followed the order of Co > Mn > Fe. The nanoparticles displayed good magnetic separation under the magnetic field.
Minimizing of the boundary friction coefficient is critical for engine efficiency improvement. It is known that the tribological behavior has a major role in controlling the performance of automotive engines in terms of the fuel consumption. The purpose of this research is an experimental study to minimize the boundary friction coefficient via nano-lubricant additives. The tribological characteristics of Al2O3 and TiO2 nano-lubricants were evaluated under reciprocating test conditions to simulate a piston ring/cylinder liner interface in automotive engines. The nanoparticles were suspended in a commercially available lubricant in a concentration of 0.25 wt.% to formulate the nano-lubricants. The Al2O3 and TiO2 nanoparticles had sizes of 8–12 and 10 nm, respectively. The experimental results have shown that the boundary friction coefficient reduced by 35–51% near the top and bottom dead center of the stroke (TDC and BDC) for the Al2O3 and TiO2 nano-lubricants, respectively. The anti-wear mechanism was generated via the formation of protective films on the worn surfaces of the ring and liner. These results will be a promising approach for improving fuel economy in automotive.
The paper presents the synthesis, characterization, and in vitro cytotoxicity tests of Fe3O4 magnetic nanoclusters coated with ethylenediaminetetraacetic acid disodium salt (EDTA). Electron microscopy analysis (SEM) evidences that magnetite nanoparticles are closely packed into the clusters stabilized with EDTA with well-defined near spherical shapes and sizes in the range 100–200 nm. From XRD measurements, we determined the mean size of the crystallites inside the magnetic cluster about 36 nm. The saturation magnetization determined for the magnetic clusters stabilized with EDTA has high value, about 81.7 emu/g at 300 K. X-ray photoelectron spectroscopy has been used to determine both the elemental and chemical structure of the magnetic cluster surface. In vitro studies have shown that the magnetic clusters at low doses did not induce toxicity on human umbilical vein endothelial cells or lesions of the cell membrane. In contrast, at high doses, the magnetic clusters increased the lipid peroxidation and reduced the leakage of a cytoplasmic enzyme, lactate dehydrogenase (LDH), in parallel with increasing the antioxidant defense.
In flame spray pyrolysis (FSP), the generation of uniform nanoparticles can be quite challenging due to difficulties in controlling droplet sizes during liquid spraying and uneven flame temperature. Here, we report a method to produce relatively uniform nanocrystals of a Tb3+ doped Y2O3 phosphor. In ethanol, metal nitrate precursors were simply mixed with organic surfactants to form a homogeneous solution which was then subjected to FSP. Depending on relative concentrations of the surfactant (oleic acid) to the metal precursors (yttrium and terbium nitrates), different sizes and morphologies of Y2O3:Tb3+ particles were obtained. By adjusting the surfactant concentration, Y2O3:Tb3+ crystals as small as 20~25 nm were acquired. X-ray diffraction and transmittance electron microscopy were used to prove that as-synthesized nanoparticles were highly crystalline due to the high temperature of FSP. X-ray photoelectron spectroscopy revealed that terbium dopants were well distributed throughout Y2O3 particles and a small portion of carbonate impurities were remained on the surface of particles, presumably originated from incomplete combustion of the organic surfactants. Photoluminescence (PL) spectra of Y2O3:Tb3+ nanocrystals exhibited a green light emission ensuring that the terbium doping was successfully occurred. However, when post-annealing was performed on the nanocrystals, their PL was dramatically enhanced indicating that quenching centers such as carbonate impurities and surface defects may have been removed by the annealing process. Owing to the continuous processability of FSP, this current method can be a practical way to produce nanoparticles in a large quantity. The obtained Y2O3:Tb3+ nanocrystals were used to fabricate a transparent film with poly-ethylene-co-vinyl acetate (poly-EVA) polymer, which was suitable for a spectral converting layer for a solar cell.
In this paper, the green synthesis of fluorescent carbon dots (CDs) via one-step hydrothermal treatment of cornstalk was investigated. This approach is facile, economical, and effective. The obtained CDs with an average diameter of 5.2 nm possess many excellent properties such as emitting blue fluorescence under UV light (365 nm), high monodispersity, good stability, excellent water dispersibility, and absolute quantum yield of 7.6%. Then, these CDs were used as sensing probes for the detection of Fe2+ and H2O2 with detection limits as low as 0.18 and 0.21 μM, respectively. This sensing platform shows advantages such as high selectivity, good precision, rapid operation, and avoiding the precipitation of iron oxyhydroxides.
BaWO4 nanoparticles were successfully used as the photocatalysts in the degradation of methylthioninium chloride (MTC) dye at different pH levels of aqueous solution. Pure phase of barium tungstate (BaWO4) nanoparticles was synthesized by modified molten salt process at 500 °C for 6 h. Structural and morphological characterizations of BaWO4 nanoparticles (average particle size of ~40 nm) were studied in details using powder x-ray diffraction (XRD), FTIR, Raman, energy-dispersive, electron microscopic, and x-ray photoelectron spectroscopy (XPS) techniques. Direct band gap energy of BaWO4 nanoparticles was found to be ~3.06 eV from the UV–visible absorption spectroscopy followed by Tauc’s model. Photocatalytic properties of the nanoparticles were also investigated systematically for the degradation of MTC dye solution in various mediums. BaWO4 nanoparticles claim the significant enhancement of the photocatalytic degradation of aqueous MTC dye to non-hazardous inorganic constitutes under alkaline, neutral, and acidic mediums.
Water dispersible boron nanoparticles have great potential as materials for boron neutron capture therapy of cancer and magnetic resonance imaging, if they are prepared on a large scale with uniform size and shape and hydrophilic modifiable surface. We report the first method to prepare spherical, monodisperse, water dispersible boron core silica shell nanoparticles (B@SiO2 NPs) suitable for aforementioned biomedical applications. In this method, 40 nm elemental boron nanoparticles, easily prepared by mechanical milling and carrying 10-undecenoic acid surface ligands, are hydrosilylated using triethoxysilane, followed by base-catalyzed hydrolysis of tetraethoxysilane, which forms a 10-nm silica shell around the boron core. This simple two-step process converts irregularly shaped hydrophobic boron particles into the spherically shaped uniform nanoparticles. The B@SiO2 NPs are dispersible in water and the silica shell surface can be modified with primary amines that allow for the attachment of a fluorophore and, potentially, of targeting moieties.
A facile and efficient one-pot method for the synthesis of well-dispersed hollow CuFe2O4 nanoparticles (H-CuFe2O4 NPs) in the presence of cellulose nanocrystals (CNC) as the support was described. Based on the one-pot solvothermal condition control, magnetic H-CuFe2O4 NPs were in-situ grown on the CNC surface uniformly. TEM images indicated good dispersity of H-CuFe2O4 NPs with uniform size of 300 nm. The catalytic activity of H-CuFe2O4/CNC was tested in the catalytic reduction of 4-nitrophenol (4-NP) in aqueous solution. Compared with most CNC-based ferrite catalysts, H-CuFe2O4/CNC catalyst exhibited an excellent catalytic activity toward the reduction of 4-NP. The catalytic performance of H-CuFe2O4/CNC catalyst was remarkably enhanced with the rate constant of 3.24 s?1 g?1, which was higher than H-CuFe2O4 NPs (0.50 s?1 g?1). The high catalytic activity was attributed to the introduction of CNC and the special hollow mesostructure of H-CuFe2O4 NPs. In addition, the H-CuFe2O4/CNC catalyst promised good conversion efficiency without significant decrease even after 10 cycles, confirming relatively high stability. Because of its environmental sustainability and magnetic separability, H-CuFe2O4/CNC catalyst was shown to indicate that the ferrite nanoparticles supported on CNC were acted as a promising catalyst and exhibited potential applications in numerous ferrite based catalytic reactions.
The delta phase of bismuth oxide (δ-Bi2O3) is an important metal oxide due to its highest conductivity of any oxide material. However, it is only stable over a narrow high temperature range, and thus, incorporation of small, high-valence cation is a prerequisite for stabilizing its cubic structure to room temperature. The δ-Bi2O3 is also known to have low photocatalytic activity because of its low conduction band edge. As a consequence, the conduction band electrons cannot be consumed by the dissolved oxygen to produce superoxide radicals. Herein, for the first time, the δ-Bi2O3 has been successfully synthesized through a facile hydrothermal route without addition of any dopant. The as-synthesized δ-Bi2O3 shows ultrahigh photocatalytic activity for cylindrospermopsin decomposition. Within only 20 min of UV irradiation, the degradation efficiency for cylindrospermopsin by 0.5 g/L of the δ-Bi2O3 with a cylindrospermopsin concentration of 5 mg/L reaches 98%. Restricted charge carrier recombination and effective consumption of the conduction band electrons are behind such an unprecedented high photocatalytic activity of the δ-Bi2O3.
In this paper, single-crystalline hexahedron hematite is successfully obtained by a simple hydrothermal approach with assistance of PVP as surfactant. SEM and XRD results show that the as-obtained α-Fe2O3 has a nanohexahedron shape with high uniformity and high crystallinity. The effects of a few factors influencing the morphology of α-Fe2O3, such as PVP amount, reaction temperature, etc., are investigated carefully. More importantly, time-dependent experiments are carried out to have in-depth insight into the formation of the single-crystalline α-Fe2O3 nanohexahedron. Based on the full characterization of as-obtained α-Fe2O3, it is concluded that PVP as surfactant plays an important role in the formation of the hexahedron shape of α-Fe2O3. Besides, the proposed formation mechanism of α-Fe2O3 nanohexahedron is that the shape of α-Fe2O3 evolves from the nuclei, needle-like shapes, and urchin-like aggregates to the hexahedron shape, driven by minimization of surface energy and Ostwald ripening. When used as an anode material for lithium-ion batteries, nanohexahedron α-Fe2O3 shows a high rate capability. Moreover, after 150 cycles, the storage capacity of α-Fe2O3 is still up to 680 mAh g?1 and almost remains unchanged, suggesting high cyclability.
Electrochemical reduction of carbon dioxide is one of the methods which have the capability to recycle CO2 into valuable products for energy and industrial applications. This research article describes about a new electrocatalyst “reduced graphene oxide supported gold nanoparticles” for selective electrochemical conversion of carbon dioxide to carbon monoxide. The main aim for conversion of CO2 to CO lies in the fact that the latter is an important component of syn gas (a mixture of hydrogen and carbon monoxide), which is then converted into liquid fuel via well-known industrial process called Fischer-Tropsch process. In this work, we have synthesized different composites of the gold nanoparticles supported on defective reduced graphene oxide to evaluate the catalytic activity of reduced graphene oxide (RGO)-supported gold nanoparticles and the role of defective RGO support towards the electrochemical reduction of CO2. Electrochemical and impedance measurements demonstrate that higher concentration of gold nanoparticles on the graphene support led to remarkable decrease in the onset potential of 240 mV and increase in the current density for CO2 reduction. Lower impedance and Tafel slope values also clearly support our findings for the better performance of RGOAu than bare Au for CO2 reduction.
This work reported a novel kind of CdTe quantum dot (QD) decorated mesoporous SiO2 (m-SiO2/QD) hybrid hollow nanoparticles for carrying photodynamic therapy (PDT) reagent. Both rod-like and spherical nanoparticles were prepared by using different shaped templates. Due to the porous shell and hollow interior, the hybrid m-SiO2/QD hollow nanorod with 360 nm long and 120 nm in diameter was selected for carrying zinc(II) phthalocyanine (ZnPc) photosensitizing molecules (61 mg/g) since the generated reactive 1O2 could be easily delivered out of the hollow particles through the porous shell (BET area 251 cm2/g). It was found that the m-SiO2/QD-ZnPc hollow nanorods exhibited a good PDT activity and showed effective photocytotoxicity for the cancer cells. Because of the porous nature, fluorescence characteristic, and excellent storage ability, the m-SiO2/QD hybrid hollow particles possessed broad potential in the fluorescent labeled PDT.
Graphic abstract m-SiO2/QD hybrid hollow particles with different morphologies could be successfully synthesized by using the templating method and they could be used as carriers for photodynamic therapy reagents.
Surface-enhanced Raman scattering (SERS) is greatly structure-dependent on the absorbed nanoparticles. Nanostructures with different novel morphologies show different Raman enhancement factor orders of magnitude. Herein, a unique nanostructure with fruitful SERS-active sites, composed of hollow interiors and thorns which named as hollow sea-urchin gold nanoparticles (HSU-GNPs), was synthesized by using a one-pot galvanic replacement method. And the corresponding morphologies and optical properties were characterized by TEM images and absorption spectra. Importantly, the synthetic parameters of HSU-GNPs were optimized to obtain a superior SERS performance by analyzing the formation mechanism and the SERS spectra of R6G-labeled HSU-GNPs which obtained at different concentrations of AgNO3. Furthermore, the SERS-based application of HSU-GNPs was performed on the dose-response detection of thiram. The experimental result shows this detection strategy is available for thiram with decent sensitivity and reproducibility, which suggests that it is an excellent candidate for the detection of pesticides.
Graphical abstract This study reports a low-cost and easy-operated pesticide residues detection method based on hollow sea-urchin gold nanoparticles using SERS.
In the past decade, a variety of drug carriers based on mesoporous silica nanoparticles has been extensively reported. However, their biocompatibility still remains debatable, which motivated us to explore the porous nanostructures of other metal oxides, for example titanium dioxide (TiO2), as potential drug delivery vehicles. Herein, we report the in vitro hemolysis, cytotoxicity, and protein binding of TiO2 nanoparticles, synthesized by a sol–gel method. The surface of the TiO2 nanoparticles was modified with hydroxyl, amine, or thiol containing moieties to examine the influence of surface functional groups on the toxicity and protein binding aspects of the nanoparticles. Our study revealed the superior hemocompatibility of pristine, as well as functionalized TiO2 nanoparticles, compared to that of mesoporous silica, the present gold standard. Among the functional groups studied, aminosilane moieties on the TiO2 surface substantially reduced the degree of hemolysis (down to 5%). Further, cytotoxicity studies by MTT assay suggested that surface functional moieties play a crucial role in determining the biocompatibility of the nanoparticles. The presence of NH2– functional groups on the TiO2 nanoparticle surface enhanced the cell viability by almost 28% as compared to its native counterpart (at 100 μg/ml), which was in agreement with the hemolysis assay. Finally, nonspecific protein adsorption on functionalized TiO2 surfaces was examined using human serum albumin and it was found that negatively charged surface moieties, like –OH and –SH, could mitigate protein adsorption to a significant extent.
Barium titanate (BT) nanoparticles are coated by titania and modified by fluoroalkylsilane. The BT nanoparticles are incorporated into polyvinylidene fluoride (PVDF) films to obtain highly dielectric and transparent nanocomposite films at low filler loadings. Incorporation of BT nanoparticles having average sizes of 12 and 22 nm is performed. Incorporation of BT nanoparticles enhances the permittivity of PVDF films. Higher transparency of nanocomposite films is achieved by incorporating 12-nm nanoparticles compared to that by 22-nm nanoparticles. The polarisation mechanism in the nanocomposite films is examined using the Vo–Shi model. The result indicates that even a slight increase in the thickness of titania-coating layer on the BT nanoparticles increase the permittivity of the nanocomposite films. Comparison of the measured and calculated permittivities showed that the incorporation of BT nanoparticles coated with titania provides a practical approach to create transparent nanocomposite films having high permittivity.
