Continuous preparation of Fe3O4 nanoparticles combined with surface modification by L-cysteine and their application in heavy metal adsorption

L-cysteine functionalized Fe₃O₄ magnetic nanoparticles (Cys–Fe₃O₄ MNPs) were continuously fabricated by a simple high-gravity reactive precipitation method combined with surface modification through a novel impinging stream-rotating packed bed with the assistance of sonication. The obtained Cys–Fe₃O₄ MNPs was characterized by XRD, TEM, FTIR, TGA and VSM, and further used for the removal of heavy metal ions from aqueous solution. The influence of pH values, contact time and initial metal concentration on the adsorption efficiency were investigated. The results revealed that the adsorption of Pb(II) and Cd(II) were pH dependent process, and the pH 6.0 was found to be optimum condition. Moreover, the adsorption kinetic for Cys–Fe₃O₄ MNPs followed the mechanism of the pseudo-second order kinetic model, and their equilibrium data were fitted with the Langmuir isothermal model well. The maximum adsorption capacities calculated from Langmuir equation were 183.5 and 64.35 mg g⁻¹ for Pb(II) and Cd(II) at pH 6.0, respectively. Furthermore, the adsorption and regeneration experiment showed there was about 10% loss in the adsorption capacity of the as-prepared Cys–Fe₃O₄ MNPs for heavy metal ions after 5 times reuse. All the above results provided a potential method for continuously preparing recyclable adsorbent applied in removing toxic metal ions from wastewater through the technology of process intensification.     

Synthesis and characterization of In2S3 nanostructures via ultrasonic method in the presence of thioglycolic acid

In the present study, nanocrystalline In₂S₃ with different morphologies and particle sizes were obtained via an ultrasonic method by employing InCl₃·4H₂O, thioglycolic acid (TGA) and propylene glycol as In³⁺, sulfur source and solvent agent, respectively. Besides, the effects of preparation parameters such as time and power of ultrasonic irradiation, solvent, and surfactant on the morphology and particle size of the products were studied. The synthesis procedure is simple and facile for the preparation of structures with various morphologies. The morphology, structure, and composition of the as-synthesized nanostructures have been investigated by X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Optical properties of the as-prepared sample were investigated by photoluminescence (PL) and ultraviolet–visible (UV–vis) spectroscopy.     

Polydopamine interface encapsulating graphene and immobilizing ultra-small,active Fe3O4 nanoparticles for organic dye adsorption

In this study, a combined process of bio-inspired modification and magnetic treatment is presented for the preparation of a polydopamine (Pdop)-modified graphene (Pdop-G)-based adsorbent which incorporates ultra-small, active Fe₃O₄ nanoparticles (with an average size of 6.5 nm). Not only can the nanoparticles impart superparamagnetism to the modified graphene adsorbent but also enhance the adsorption performance. The ultra-small size of Fe₃O₄ nanoparticles allows the exposure of a high proportion of low-coordinated sites such as corners and edges. Additional active sites can thus be provided to bind methylene blue molecules, in addition to the active Pdop-G surface with catechol and amine groups which induce hydrogen bonding, electrostatic attraction, and π-π stacking interactions. The Pdop interface wraps graphene and immobilizes Fe₃O₄, endowing the magnetic Pdop-G (MPG) with high adsorption capacity, easy recyclability, and excellent reusability for the organic pollutant removal. In stark contrast, the counterpart without the interfacial Pdop layer suffers from severe Fe₃O₄ aggregation, causing its adsorption performance inferior to that of MPG. The MPG-based adsorption obeys the pseudo-second-order kinetics, and the intraparticle diffusion model also indicates the complex adsorption pathway, including the external and intraparticle mass transfer. The Langmuir isotherm can better fit the experimental data than the Freundlich isotherm, with the theoretical maximum adsorption capacities estimated to be 131.6, 140.3, and 152.0 mg/g at 30, 40, and 50 °C, respectively. The adsorption is endothermic and spontaneous, along with an increase in the randomness at the solid-solution interface. The separation factor (R_L) reveals the favorable adsorption process with MPG. The superparamagnetism imparted via the Fe₃O₄ composition makes MPG easily recyclable. Furthermore, the removal rate can be maintained at about 90% after 5 runs of repeated usage of MPG. This study opens up a new avenue to the magnetization of adsorbents for enhancing adsorption performance in addition to imparting magnetism.     

Silica coating of Fe3O4 magnetic nanoparticles with PMIDA assistance to increase the surface area and enhance peptide immobilization efficiency

The high efficiency of using N-(phosphonomethyl)iminodiacetic acid (PMIDA) as a surfactant for formation of a silica coating on Fe₃O₄ magnetic nanoparticles (MNPs) with a large surface area has been demonstrated. The coating of PMIDA-stabilized MNPs with silica and their further APS-functionalization significantly increased the specific area (up to 203 m² g^?1) and the number of amino groups (up to 1.12 mmol/g) grafted on their surface compared to nanomaterials synthesized without preliminary SiO₂-coating. The comparative study of the peptide modification efficiency, using as an example pH-low insertion peptide (pHLIP), of MNPs coated with 3-aminopropylsilane (APS) or SiO₂/APS was carried out. It has been shown that silica coating of PMIDA-stabilized MNPs leads to a significant increase in the degree of immobilization of the peptide (up to 22 μmol per g of MNPs). Comprehensive characterization of the obtained materials at each stage of the synthesis was carried out using scanning electron microscopy (SEM), energy dispersive X-ray fluorescence spectroscopy (EDX), BET analysis, ATR Fourier transformed infrared spectroscopy (FTIR), termogravimetric analysis (TGA), CHN-elemental analysis, dynamic light scattering (DLS), and vibrating sample magnetometry (VSM). The proposed approach to applying SiO₂-coating of MNPs can be useful for design of new materials for biomedical and chemical purposes.     

Multifunctional Fe3O4@Ag@TiO2-xNx core-shell composite particles for dye adsorption and visible-light photocatalysis

This study prepares Fe₃O₄@Ag@TiO₂ (FAT) particles via a solvothermal route, then thermally treats the particles over a temperature range from 300 to 500 °C in flowing nitrogen atmosphere to form Fe₃O₄@Ag@TiO_2-xN_x (x = 0.056 to 0.15) (FATN) core-shell composite particles. The FATN particles comprise an outermost TiO_2-xN_x shell of about 20–50 nm in thickness, a Brunauer-Emmett-Teller surface area of 103.2–152.5 m²/g, and a Barrett-Joyner-Halenda pore size of 12.9–30.2 nm. The particles show dye adsorption and visible-light photocatalysis against a model methylene-blue (MB) dye in water. For the FATN particles being treated at 400 °C, they show a dark adsorption of 54.8% and an additional visible-light photodegradation of 25.1% when using a dyed wastewater with an initial MB concentration of 5 × 10^-6 M. This compares favorably to those being treated at other nitridation temperatures. The 500 °C-treated FATN particles yet exhibit a dark adsorption of 99.1% against the MB solution. Use of an external magnet can facilely recycle the composite particles. The recycled particles remain greater than 72% of their initial MB removal capability after use of five times. The intermediate Ag nanolayer can release Ag ions to the surrounding water medium through the mesoporous shell channel. The time-dependent Ag release appears to follow the Voigt-Maxwell model and reaches 0.764 ppm after 48 h, suggesting a long-time releasing efficacy.     

磁性Fe3O4@SiO2颗粒结构对其吸附DNA的影响

采用共沉淀法和水热法制备了不同结构的超顺磁性Fe3O4@SiO2纳米颗粒,对其进行表征,研究了其吸附DNA的性能及磁分离性能. 结果表明,20?750 nm范围内粒径较大的颗粒与DNA结合时可提供更多单位平面结合位点,使结合的稳定性和结合几率增加,DNA结合量提高. 不同核?壳结构的Fe3O4@SiO2纳米颗粒的磁分离响应时间不同,内核大小相近时,壳层厚度增加会导致颗粒在磁场中受到的磁力与阻力的比值减小,磁响应时间增加,DNA回收率降低. 粒径约为200 nm的Fe3O4@SiO2纳米颗粒用于纯化全血中DNA最好,提取率为95.2%,磁响应时间为10 s.     

Influence of Fe3O4 nanoparticles decoration on dye adsorption and magnetic separation properties of Fe3O4/rGO nanocomposites

Magnetite (Fe₃O₄) nanoparticles were prepared by solvothermal method and its composites with reduced graphene oxide namely FG1, FG2, and FG3 (changing magnetite precursor loading 0.1, 0.5, and 1 respectively) were used as adsorbents for the removal of methyl violet (MV) dye. The structural and morphological results confirm that rGO sheets were decorated with Fe₃O₄ and it ensures the variation of active sites toward dye removal property. The maximum adsorption capacity obtained for FG2 was 196 mg/g. The adsorption isotherms and kinetics better fit Langmuir and pseudo-second-order kinetic model for FG1 and FG2. Increasing of Fe₃O₄ loading on rGO reduces the dye adsorption sites and too low Fe₃O₄ loading affects the magnetic separation. The optimal loading of Fe₃O₄ on rGO is important parameter for the adsorption process and fast separation of adsorbent.     

In situ preparation of monodispersed Ag/polyaniline/Fe3O4 nanoparticles via heterogeneous nucleation

Acrylic acid and styrene were polymerized onto monodispersed Fe₃O₄ nanoparticles using a grafting copolymerization method. Aniline molecules were then bonded onto the Fe₃O₄ nanoparticles by electrostatic self-assembly and further polymerized to obtain uniform polyaniline/Fe₃O₄ (PANI/Fe₃O₄) nanoparticles (approximately 35 nm). Finally, monodispersed Ag/PANI/Fe₃O₄ nanoparticles were prepared by an in situ reduction reaction between emeraldine PANI and silver nitrate. Fourier transform infrared and UV-visible spectrometers and a transmission electron microscope were used to characterize both the chemical structure and the morphology of the resulting nanoparticles.     

Ni0.5Zn0.5Fe2O4-dispersed In2O3-spotted ZnO nanoparticles: Ammonia-source and surface and photocatalytic properties

Ammonia-source, used to attain the desired pH during synthesis, is conceived to influence the physical characteristics of ZnO-based nanomaterials, and the catalytic activity is susceptible to surface characteristics of semiconductor–photocatalyst. In this context, Ni_0.5Zn_0.5Fe₂O₄-dispersed In₂O₃-spotted ZnO nanoparticles have been obtained by using either tetramethyl ammonium hydroxide or ammonium carbonate as ammonia-source at identical pH (9) using identical quantities of the precursors following identical synthetic procedure. The nanoparticles have been characterized using energy dispersive X-ray spectroscopy, elemental mapping, selected area electron and X-ray diffractometries, transmission electron microscopy, etc. The nanoparticles obtained using ammonium carbonate possess larger (1) pore width, (2) pore volume, and (3) surface area compared with nanoparticles prepared employing tetramethyl ammonium hydroxide. Although the electrical properties of both the samples do not differ remarkably, the violet light-absorption of the sample prepared using the carbonate is slightly larger than that of the other sample. Further, the In₂O₃-spotting is slightly larger on using ammonium carbonate than using tetramethyl ammonium hydroxide. To degrade dye under visible light, the sample obtained using ammonium carbonate shows larger catalytic activity compared with nanoparticles prepared using tetramethyl ammonium hydroxide. The observed photocatalytic activities are explained based on the surface characteristics.     

Spherical porous granules in MgOFe2O3Nb2O5 system: In situ observation of formation behavior using high-temperature confocal laser-scanning microscopy

The pyrolytic reactive granulation process, yielding ceramic spherical porous granules, is simple, consisting of typical ceramic processing methods, viz., wet-ball milling of powders, vacuum drying, granulation via sieving through a screen mesh, and one-step heat treatment for local reactive sintering within each granule. Here, the microstructural development of spherical porous granules was successfully visualized by in situ high-temperature confocal laser-scanning microscopy during the heating up to 1400 °C in air. Based on the result of the in situ observation, a simple but powerful size-controlling process of spherical porous granules, viz., multiscreen sieving after the heating was demonstrated. Nearly monodispersed spherical porous granules composed of pseudobrookite-type MgFeNbO₅ were easily obtained.     

Synthesis of Fe3O4@SiO2@MPS@P4VP nanoparticles for nitrate removal from aqueous solutions

In this study, synthesis of Fe₃O₄@SiO₂@MPS@poly(4‐vinylpyridine) core‐shell‐shell structure was investigated as an efficient adsorbent for removal of nitrate ions from aqueous solutions. Fe₃O₄ nanoparticles were initially prepared by co‐precipitation method, then the surface of Fe₃O₄ was coated with SiO₂ through a modified St öber method. Finally, the Fe₃O₄@SiO₂ nanoparticles were modified by 3‐(trimethoxysilyl) propyl methacrylate followed by emulsion polymerization of 4‐vinylpyridine. The resultant material was acidified in HCl solution to be effective for nitrate removal. The synthesized sample was characterized by X‐ray diffraction, transmission electron microscopy, field‐emission scanning electron microscopy, Fourier‐transform infrared spectra, thermogravimetric analysis (TGA), and vibrating sample magnetometer. The removal efficiency was optimized for some experimental parameters such as pH, contact time, and amount of sorbent loading. The maximum predictable adsorption capacity was 80.6 (mg nitrate/g sorbent) at optimum conditions. Also, regeneration of the nitrate adsorbed particles was possible with NaOH solution. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44330.     

TEM investigations of wear mechanism of Al2O3 and Si3N4 compacts with GLPs additions

Extended lifetime of ceramic cutting plates is ever more desired. One way of approaching it entails sintering precursor materials with graphene-like nanoplatelets (GLPs) acting as solid lubricants. Therefore, Al₂O₃ and Si₃N₄ ceramic powders with addition of GLPs of grade 3 (fine) or grade 4 (coarse) were Spark Plasma Sintered. It is found that the 0.15 wt% GLPs addition of both grades allows to keep hardness practically at the same level as GLPs-free compacts (~16 GPa). Only larger GLPs additions (2 wt%) caused its evident decrease (down to 14−15 GPa). The ball-on-disc test revealed that only Al₂O₃+0.15 wt% GLPs(3) shows a 50% reduction in wear rate. The post mechanical test examination by SEM confirmed that Al₂O₃ compacts with small GLPs showed smooth wear track, as opposed to those having a Si₃N₄ matrix with large meandering cavities. TEM observations revealed that the wear damage caused by the ball was restricted to ~2 µm deep sub-surface areas, while, carbon is found to transfer from the GLPs agglomerates into tribo-film. The present experiments showed, that ceramic sinters with small addition of GLPs platelets could exhibit lower wear than GLPs-free ones and therefore show a potential for application as cutting plates.     

γ-Ray assisted synthesis of silver nanoparticles in chitosan solution and the antibacterial properties

In the present study, chitosan had been utilized as a “green” stabilizing agent for the synthesis of spherical silver nanoparticles in the range of 5–30 nm depending on the percentage of chitosan used (0.1, 0.5, 1.0 and 2.0 wt%) under γ-irradiation. X-ray diffractometer identified the nanoparticles as pure silver having face-centered cubic phase. Ultraviolet–visible spectra exhibited the influence of γ-irradiation total absorbed dose and chitosan concentration on the yield of silver nanoparticles. The antibacterial properties of the silver nanoparticles were tested against Methicillin-resistant Staphylococcus aureus (MRSA) (gram-positive) and Aeromonas hydrophila (gram-negative) bacteria. This work provides a simple and “green” method for the synthesis of highly stable silver nanoparticles in aqueous solution with good antibacterial property.     

Investigation of PEG adsorption on the surface of zinc oxide nanoparticles

The influence of polyethylene glycol (PEG) on the adsorption at zinc oxide/polymer solution interface has been determined. PEG macromolecules bond with the solid surface mainly via the -OH group of the surface of ZnO nanoparticles, which may interact with PEG through hydrogen bonding. Adsorption isotherms demonstrate the marked influence of the PEG molecular weight and the concentration of polymer solution on the extent of adsorption. The thickness of the adsorbed polymer layer on ZnO nanoparticles was calculated on the basis of measurements of their suspension viscosities in the absence and presence of adsorbed polymer. Results show that the thickness of the adsorption layer increased with increasing polymer molecular weight and the concentration of polymer solution. The main factors responsible for the changes in zeta potential were determined on the basis of the data obtained. The shift of the slippage plane away from the surface of ZnO nanoparticles plays major role below pH_iep. Above pH_iep, the blockage of the adsorption sites is the predominant factor.     

改性果胶-Fe3O4磁性微球制备及对Pb 2+吸附性能

合成了一种琥珀酸酐改性果胶-四氧化三铁（Fe₃O₄）磁性微球吸附剂,分别采用扫描电镜（SEM）、红外光谱（FT-IR）、X射线衍射（XRD）等手段对样品进行了表征,并研究了其吸附铅离子（Pb ²⁺）的性能。研究结果表明：成功制备了琥珀酸酐改性果胶-Fe₃O₄磁性微球,改性果胶包覆四氧化三铁几乎没有改变Fe₃O₄的尖晶石结构,其表面疏松多孔;改性果胶-Fe₃O₄磁性微球对铅离子的吸附符合准二级动力学方程、Langmuir等温吸附方程,吸附过程主要为化学吸附。最佳吸附条件：吸附时间为600 min,吸附温度为40 ℃,溶液pH为5,吸附剂添加量为20 mg,溶液中Pb ²⁺质量浓度为800 mg/L。改性果胶-Fe₃O₄磁性微球吸附剂用于脱除毛蚶子、扇贝酶解液中的Pb ²⁺,Pb ²⁺去除率分别为76.47%和80.34%,效果良好。     

Microwave-assisted Fe3O4 nanoparticles catalyzed synthesis of chromeno[1,6]naphthyridines in aqueous media

Fe₃O₄ nanocatalyst was prepared by co-precipitation method and characterized by XRD, FT-IR, TEM, VSM and BET analyses. The particles have an average size of 7 nm and possess highly open mesopores, moderate surface area, and uniform morphology with superparamagnetic behavior. Activity of catalyst was probed through the synthesis of chromeno[1,6]naphthyridines in water under microwave irradiation (MW) and it was about 7-fold higher as compared to conventional method. Nanocatalyst plays a dual role of catalyst as well as susceptor, and enhances the overall capacity to absorb MW. Fe₃O₄ NPs easily recovered by simple magnetic separation and recycled at least 5 times.     

Synthesis of magnetic Fe3O4@SiO2-(-NH2/-COOH) nanoparticles and their application for the removal of heavy metals from wastewater

In this work, Fe₃O₄@SiO₂-(-NH₂/-COOH) nanoparticles were synthesized for the removal of Cd²⁺, Pb²⁺ and Zn²⁺ ions from wastewater. The results of characterization showed that Fe₃O₄@SiO₂-(-NH₂/-COOH) was superparamagnetic with a core–shell structure. The surface of Fe3O4 was successfully coated with silica and modified with amino groups and carboxyl groups through the use of a silane coupling agent, polyacrylamide and polyacrylic acid. The dispersion of the particles was improved, and the surface area of the Fe3O4@SiO2-(-NH2/-COOH) nanoparticles was 67.8 m²/g. The capacity of Fe₃O₄@SiO₂-(-NH₂/-COOH) to adsorb the three heavy metals was in the order Pb²⁺ > Cd²⁺ > Zn²⁺, and the optimal adsorption conditions were an adsorption dose of 0.8 g/L, a temperature of 30°C and concentrations of Pb²⁺, Cd²⁺ and Zn²⁺ below 120, 80 and 20 mg/L, respectively. The maximum adsorption capacities for Pb²⁺, Cd²⁺ and Zn²⁺ were 166.67, 84.03 and 80.43 mg/g. The adsorption kinetics followed a pseudo-second-order model and Langmuir isotherm model adequately depicted the isotherm adsorption process. Thermodynamic analysis showed that the adsorption of the three metal ions was an endothermic process and that increasing the temperature was conducive to this adsorption.     

Al2O3/Fe2O3吸附剂脱除硫化氢的性能

采用共沉淀法制备了氧化铝改性的氧化铁吸附剂,并采用比表面积(BET)、X射线衍射(XRD)技术对吸附剂进行了表征。在固定吸附床上,考察了制备条件及吸附条件对吸附剂脱除硫化氢性能的影响。结果表明,引入氧化铝能显著提高氧化铁对硫化氢的吸附净化能力。氧化铁与氧化铝质量比为1∶0.5,造孔剂十六烷基三甲基溴化铵(CTAB)质量分数为2%,焙烧温度500℃时,采用共沉淀法的负载氧化铝吸附剂的吸附效果最好。在气速20 mL/min,吸附温度80℃时,脱硫率和穿透硫容可分别达到99.3%和105 mg/g,其穿透硫容比未经改性的活性氧化铁提高了49.8 mg/g。     

In situ synthesis of Al2O3‐supported ZnCr2O4 nanoparticles for application as an activated photocatalyst

Zincochromite nanoparticles (NPs) were precipitated on surfaces of the as‐prepared Al₂O₃ micron‐sized particles by a heterogeneous precipitation technique using urea as a homogeneous precipitation agent. This procedure leads to decrease the pore diameter and increase the pore volume and specific surface area (a_s), realizing the potential access to ZnCr₂O₄ catalytic sites. Although the obtained band gap energy (E_g) of Al₂O₃‐ZnCr₂O₄ composite is about 2.3 eV (more than ZnCr₂O₄), the absorbance is enhanced about 1.5 orders of magnitude. These characteristics make it an effective photocatalyst of inorganic dyes from an aqueous media. Dye removal performance of the nanocomposite powder is higher than that of pure ZnCr₂O₄, which is attributed to an increase in the photocatalytic sites and the absorbance intensity. It was believed that the surface area created from Al₂O₃ support realized the potential access to ZnCr₂O₄ catalytic sites. To confirm these assertions, X‐ray diffractometry (XRD), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS), and N₂ adsorption‐desorption analysis were applied.     

Embedding Gd2O3 nanoparticles hydrothermally prepared in a Fe3O4 shell and surface modification with a dextrose bio capping agent

The present work describes a multi-stage processing method for the hydrothermal synthesis of gadolinium oxide (Gd₂O₃) nanoparticles and subsequent surface modification with iron oxide (Fe₃O₄) and dextrose. To prepare gadolinium oxide nanoparticles, gadolinium chloride was reacted with sodium hydroxide, and the resulting precipitate was autoclaved. Subsequently, the product was calcined. Afterward, Gd₂O₃ nanoparticles were coated with a Fe₃O₄ nanolayer synthesized via coprecipitation, and the resulting core-shell nanocomposites were encapsulated in a dextrose capping agent for enhanced biocompatibility. The effect of various Gd₂O₃ synthesis parameters on particle size, structure, and magnetic properties was then investigated. These parameters included preliminary precipitation temperature (25, 90 °C) and stirring speed (400, 1000 rpm), hydrothermal temperature (150 and 180 °C) and pressure (5 and 10 bar), and final calcination temperature (600 and 1000 °C). For the investigation of nanocomposites, X-ray diffraction (XRD), scanning and transmission electron microscopy, dynamic laser scattering (DLS), Fourier-Transform infrared spectroscopy (FTIR), and magnetometry (VSM) techniques were used, while the viability of colloidal samples was determined using the MTT-assay method. The results indicated that increasing the steering speed and temperature of the precipitation process and raising the calcination temperature reduced the size of Gd₂O₃ nanoparticles. Autoclave dehydration had no discernible effect on Gd₂O₃ nanoparticles. TEM and SEM images confirmed the core/shell structure of Gd₂O₃/Fe₃O₄. The shell thickness of 74–95 nm core nanoparticles was in the range of 30–40 nm. With a saturation magnetization of 3.4 emu/g, the nanoparticles exhibited paramagnetic behavior. The 48-h MTT assay demonstrated excellent biocompatibility up to 285 μg solid concentrations containing 24.5 μg [Fe] and 91.2 μg [Gd], with viability remaining greater than 50% at 400 μg solid concentration.