Study of iron oxide nanoparticles in soil for remediation of arsenic

There is a growing interest in the use of nanoparticles for environmental applications due to their unique physical and chemical properties. One possible application is the removal of contaminants from water. In this study, the use of iron oxide nanoparticles (19.3 nm magnetite and 37.0 nm hematite) were examined to remove arsenate and arsenite through column studies. The columns contained 1.5 or 15 wt% iron oxide nanoparticles and soil. Arsenic experiments were conducted with 1.5 wt% iron oxides at 1.5 and 6 mL/h with initial arsenate and arsenite concentrations of 100 μg/L. Arsenic release occurred after 400 PV, and 100% release was reached. A long-term study was conducted with 15 wt% magnetite nanoparticles in soil at 0.3 mL/h with an initial arsenate concentration of 100 μg/L. A negligible arsenate concentration occurred for 3559.6 pore volumes (PVs) (132.1 d). Eventually, the arsenate concentration reached about 20% after 9884.1 PV (207.9 d). A retardation factor of about 6742 was calculated indicating strong adsorption of arsenic to the magnetite nanoparticles in the column. Also, increased adsorption was observed after flow interruption. Other experiments showed that arsenic and 12 other metals (V, Cr, Co, Mn, Se, Mo, Cd, Pb, Sb, Tl, Th, U) could be simultaneously removed by the iron oxide nanoparticles in soil. Effluent concentrations were less than 10% for six out of the 12 metals. Desorption experiment showed partial irreversible sorption of arsenic to the iron oxide nanoparticle surface. Strong adsorption, large retardation factor, and resistant desorption suggest that magnetite and hematite nanoparticles have the potential to be used to remove arsenic in sandy soil possibly through in situ techniques.     

Synthesis and characterization of magnetite nanopowders

We have synthesized the iron oxide nanoparticles using the newly developed mechanical ultrasonication method with the FeSO₄ · 7H₂O. We have also investigated the crystallographic structural properties, morphology, and magnetic properties of the nanopowders. According to the high resolution X-ray diffraction result, the as-synthesized iron oxide nanoparticles were magnetite (Fe₃O₄). The particle size of the magnetite nanoparticles was about 6 nm confirmed by transmission electron microscopy image. The particle shape was almost a sphere confirmed by scanning electron microscopy image. The coercivity and saturation magnetization of the as-synthesized iron oxide nanopowders were 114 Oe, and 3.7 emu/g, respectively.     

Experimental and theoretical study on the β-FeOOH nanorods: growth and conversion

This study presents an experimental and theoretical study on the growth of monodispersed akaganéite (β-FeOOH) nanorods with tunable aspect ratios (longitudinal to transversal) under mild conditions (80 °C, aqueous solution). The synthesis of β-FeOOH nanorods is highly influenced by the presence of salt ions, and thus, the effect of various anions (e.g., NO₃ ⁻, SO₄ ²⁻, F⁻, Cl⁻, and Br⁻) were investigated on the microstructure, morphology, and size of the nanoparticles. It was found that these anions could interact strongly or weakly with the FeO₆ octahedral unit in the ferric oxyhydroxides, hence greatly affect the morphology, crystallization, and structure of the iron oxide/oxyhydroxide nanoparticles under the reported conditions. Moreover, these nanorods could be converted into magnetite (Fe₃O₄) through the reduction of hydrazine, which provides a new template approach to prepare magnetite nanorods with shape and size control at ambient conditions. The microstructure, composition, and structural transformation of the as-synthesized nanoparticles were characterized by various techniques, such as transmission electron microscopy (TEM and HRTEM), X-ray diffraction (XRD), and energy dispersive spectroscopy (EDS). The possible formation and growth mechanism of akaganéite nanorods were discussed. Finally, the influence of anions on the β-FeOOH(100), (110), and (001) surfaces was further understood by theoretical simulations (e.g., molecular dynamics method).     

Controlled flame synthesis of αFe<Subscript>2</Subscript>O<Subscript>3</Subscript> and Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles: effect of flame configuration,flame temperature,and additive loading

Superparamagnetic iron oxide nanoparticles are used in diverse applications, including optical magnetic recording, catalysts, gas sensors, targeted drug delivery, magnetic resonance imaging, and hyperthermic malignant cell therapy. Combustion synthesis of nanoparticles has significant advantages, including improved nanoparticle property control and commercial production rate capability with minimal post-processing. In the current study, superparamagnetic iron oxide nanoparticles were produced by flame synthesis using a coflow flame. The effect of flame configuration (diffusion and inverse diffusion), flame temperature, and additive loading on the final iron oxide nanoparticle morphology, elemental composition, and particle size were analyzed by transmission electron microscopy (TEM), high-resolution TEM (HR-TEM), energy dispersive spectroscopy (EDS), and Raman spectroscopy. The synthesized nanoparticles were primarily composed of two well known forms of iron oxide, namely hematite αFe₂O₃ and magnetite Fe₃O₄. We found that the synthesized nanoparticles were smaller (6–12 nm) for an inverse diffusion flame as compared to a diffusion flame configuration (50–60 nm) when CH₄, O₂, Ar, and N₂ gas flow rates were kept constant. In order to investigate the effect of flame temperature, CH₄, O₂, Ar gas flow rates were kept constant, and N₂ gas was added as a coolant to the system. TEM analysis of iron oxide nanoparticles synthesized using an inverse diffusion flame configuration with N₂ cooling demonstrated that particles no larger than 50–60 nm in diameter can be grown, indicating that nanoparticles did not coalesce in the cooler flame. Raman spectroscopy showed that these nanoparticles were primarily magnetite, as opposed to the primarily hematite nanoparticles produced in the hot flame configuration. In order to understand the effect of additive loading on iron oxide nanoparticle morphology, an Ar stream carrying titanium-tetra-isopropoxide (TTIP) was flowed through the outer annulus along with the CH₄ in the inverse diffusion flame configuration. When particles were synthesized in the presence of the TTIP additive, larger monodispersed individual particles (50–90 nm) were synthesized as observed by TEM. In this article, we show that iron oxide nanoparticles of varied morphology, composition, and size can be synthesized and controlled by varying flame configuration, flame temperature, and additive loading.     

Characterization of crystalline silica nanorods synthesized via a solvothermal route using polyvinylbutyral as a template

The preparation of crystalline silica nanorods is presented. Crystalline silica nanorods were synthesized via a simple solvothermal route using polyvinylbutyral (PVB) as a template in an autoclave with ethylenediamine as a solvent at 180 °C for 25 h. Silica nanorods with diameters in the range of 50–80 nm were obtained. The solvothermal route with a PVB template played affected the crystallization process and the growth of the silica nanorods. The as-synthesized products were characterized using X-ray diffraction, energy dispersive spectrometry, scanning electron microscopy, and transmission electron microscopy.     

Electromagnetic wave absorption properties of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> octahedral nanocrystallines in gigahertz range

Large-scale octahedral Fe₃O₄ nanocrystallines with crystalline size of 100−500 nm were synthesized by a facile solvent-thermal method for electromagnetic wave application. The Fe₃O₄ nanocrystallines showed a higher saturation magnetization (M _s ) value of 86.8 emu/g and larger coercivity (H _cj ) value of 255 Oe than that of magnetite polycrystallines because of their good crystallization and dispersion. The epoxy resin composites with 40 vol% Fe₃O₄ powders provided good electromagnetic wave absorption performance (RL < −20 dB) in the range of 2.0–4.3 GHz over the absorber thicknesses of 3.5–6.8 mm. A minimum RL value of −47 dB was observed at 3.1 GHz with a thickness of 4.8 mm.     

Structure of Fe–Pt alloy included carbon nanocapsules synthesized by an electric plasma discharge in an ultrasonic cavitation field of liquid ethanol

For the first time Fe–Pt alloy included carbon nanocapsules were synthesized by an electric plasma discharge in an ultrasonic cavitation field of liquid ethanol. This contrasts the extensively used chemical synthesis methods which produce uncoated Fe–Pt alloy nanoparticles. We proposed that the as-synthesized Fe–Pt alloy included carbon nanocapsules are potentially useful in biomedical applications. Thereby an aim of this work was to coat the Fe–Pt alloy nanoparticles by graphite shells using plasma discharge in liquid ethanol and to study the structure and magnetic properties of the carbon encapsulated Fe–Pt alloy nanoparticles. The core–shell structured nanoparticles were characterized by transmission electron microscopy and X-ray diffraction. These methods revealed the presence of a disordered face-centered cubic (fcc) structure (γFe, Pt) in the cores of the as-synthesized carbon nanocapsules. The as-synthesized carbon nanocapsules showed the soft magnetic character at room temperature. These carbon nanocapsules may provide a new approach in the transport and delivery of anticancer drugs.     

Biotinylated chitosan-based SPIONs with potential in blood-contacting applications

Haemocompatible biotinylated superparamagnetic nanoparticles (size range 300–700 nm) have been obtained by coating magnetite through ionic gelation with a mixture of chitosan and sodium tripolyphosphate, followed by subsequent functionalisation with biotin. The evaluations of their magnetic properties together with haemocompatibility tests have shown that these nanoparticles exhibit the prerequisite behaviour for use in magnetic field–assisted separations within biological systems.     

Structure and optical properties of tungsten oxide nanomaterials prepared by a modified plasma arc gas condensation technique

With the use of a modified plasma arc gas condensation technique and control of the processing parameters, namely, plasma current and chamber pressure, we synthesized tungsten oxide nanomaterials with aspect ratios ranging from 1.1 (for equiaxed particles with the length and width of 48 nm and 44 nm, respectively) to 12.7 (for rods with the length and width of 266 nm and 21 nm, respectively). The plasma current and chamber pressure, respectively, ranged from 70 to 90 A and from 200 to 600 Torr. We then characterized the tungsten oxide nanomaterials by means of X-ray diffraction, high-resolution transmission electron microscope, UV–visible spectroscope, and photoluminescence (PL) spectroscope. Experimental results show that equiaxed tungsten oxide nanoparticles were produced at a relatively low plasma current of 70 A, whereas nanorods were produced when plasma currents or chamber pressures were increased. All of the as-prepared tungsten oxide nanomaterials exhibited a WO_2.8 phase. Compared to the nanoparticles, the nanorods exhibited unique properties, such as a redshift in the UV–visible spectrum, a blue emission in PL spectrum, and a good performance in field emission. With respect to the field emission, the turn-on voltage for WO_2.8 nanorods was found to be as low as 1.7 V/μm.     

Metal-on-oxide nanoparticles produced using laser ablation of microparticle aerosols

A continuous aerosol process has been studied for producing nanoparticles of oxides that were decorated with smaller metallic nanoparticles and are free of organic stabilizers. To produce the oxide carrier nanoparticles, an aerosol of 3–6 μm oxide particles was ablated using a pulsed excimer laser. The resulting oxide nanoparticle aerosol was then mixed with 1.5–2.0 μm metallic particles and this mixed aerosol was exposed to the laser for a second time. The metallic micron-sized particles were ablated during this second exposure, and the resulting nanoparticles deposited on the surface of the oxide nanoparticles producing an aerosol of 10–60 nm oxide nanoparticles that were decorated with smaller 1–5 nm metallic nanoparticles. The metal and oxide nanoparticle sizes were varied by changing the laser fluence and gas type in the aerosol. The flexibility of this approach was demonstrated by producing metal-decorated oxide nanoparticles using two oxides, SiO₂ and TiO₂, and two metals, Au and Ag.     

Temperature-resolved synchrotron X-ray diffraction of nanocrystalline titania in solvent: the effect of Cr–Sb and V–Sb doping

Nanocrystalline titania pigments were produced by high temperature-forced hydrolysis in a coordinating high-boiling solvent (and water for reference). The effect of synthesis conditions and co-doping with Cr–Sb and V–Sb on particle size and anatase-to-rutile transformation (A → R) was studied by temperature-resolved synchrotron X-ray diffraction. The experiments were performed directly on low concentration (3.5 vol.%) as-synthesized suspensions of titania nanoparticles (up to 230 °C) and on the corresponding dried powders (up to 950 °C). Crystallite size of as-synthesized nano-anatase is around 20 nm (glycol) or 70 nm (water); it exhibits a slow growth rate up to the onset temperature of the A → R. Phase composition and crystallite size are drastically influenced by both synthesis conditions and doping. Synthesis in water resulted in the simultaneous occurrence of anatase and brookite; transformation into rutile begins early but with a slower rate with respect to glycol-based samples. Doping affected the A → R, whose onset temperature in undoped titania (700 °C) was lowered to 650 °C (V–Sb) or prevented up to 950 °C (Cr–Sb). Both (V–Sb) and (Cr–Sb) dopings reduced the volume thermal expansion rate of anatase.     

Structure and magnetic properties of Zn<Subscript>0.9</Subscript>Co<Subscript>0.1</Subscript>O nanorods synthesized by a simple sol–gel method using metal acetylacetonate and poly(vinyl alcohol)

Room-temperature ferromagnetism was observed in Zn_0.9Co_0.1O nanorods with diameters and lengths of ∼100–200 nm and ∼200–1000 nm, respectively. Nanorods were synthesized by a simple sol–gel method using metal acetylacetonate powders of Zn and Co and poly(vinyl alcohol) gel. The XRD, FT-IR and SAED analyses indicated that the nanorods calcined at 873–1073 K have the pure ZnO wurtzite structure without any significant change in the structure affected by Co substitution. Optical absorption measurements showed absorption bands indicating the presence of Co²⁺ in substitution of Zn²⁺. The specific magnetization of the nanorods appeared to increase with a decrease in the lattice constant c of the wurtzite unit cell with the highest value being at 873 K calcination temperature. This magnetic behavior is similar to that of Zn_0.9Co_0.1O nanoparticles prepared by polymerizable precursor method. We suggest that this behavior might be related to hexagonal c-axis being favorable direction of magnetization in Co-doped ZnO and the 873 K (energy of 75 meV) being close to the exciton/donor binding energy of ZnO.     

Single step surface modification of highly stable magnetic nanoparticles for purification of His-tag proteins

The aim of this study was to develop a simple, cheap, and rapid method for purification of His-tag recombinant proteins with high yields. The new immobilized metal ion affinity adsorbent containing superparamagnetic nanoparticles and hydrophilic resins are proposed here to improve the purification of His-tagged recombinant proteins. In this report, we have described the preparation of nanosized superparamagnetic nanoparticles (Fe₃O₄) which were prepared by chemical precipitation method followed by surface modification using phosphonomethyl iminodiacetic acid. The stable surface functionalized nanoparticles were further linked with Ni²⁺ for purification of 6× His-tagged proteins. The phosphonate group of the N-phosphonomethyl iminodiacetic acid ligand acts as a surface anchoring agent on magnetite nanoparticles and the remaining free –COOH groups outside for binding with Ni²⁺ ions. The nanoparticles were approximately 6–8 nm in size and were stable and had negligible non-specific binding for protein. The proteins were purified within 1 h and observed on sodium dodecyl sulfate-polyacrylamide electrophoresis gel.     

Facile synthesis of additive-assisted nano goethite powder and its application for fluoride remediation

The present article describes a novel synthesis route for nano-sized goethite (α-FeOOH) using hydrazine sulphate as an additive. The X-ray diffraction (XRD) peaks of synthesized powder matched well with those of α-FeOOH. Transmission electron microscopy (TEM) showed the particles of irregular shape in the range of 1–10 nm. Batch adsorption experiments for fluoride uptake were performed to study the influence of various experimental parameters such as contact time (10 min to 7 h), initial fluoride concentration (10–150 mg L⁻¹), pH (2–11.6) and the presence of competing anions. The time data fitted well to pseudo-second-order kinetic model. The fluoride removal passed through broad maxima in pH ranges of 6–8. High adsorption capacity of 59 mg g⁻¹ goethite was obtained. The isothermic data fitted well to Freundlich model. The presence of other ions namely chloride and sulphate adversely affected fluoride removal. Fluoride from contaminated water sample could be successfully brought down from 10.25 to 0.5 mg L⁻¹.     

Facile synthesis and phase control of copper chalcogenides with different morphologies

A series of stoichiometric and nonstoichiometric copper–chalcogenide nanocrystallines with different morphologies, e.g., extremely high aspect ratio nanofibers (Cu₉S₈), tubular structure (Cu _x S (x=∼1.86–1.96), nanorods (CuS, Cu₃₁S₁₆), platelets (β-CuSe, Cu₃Se₂), rope-like Cu₃Se₂, as well as spherical nanoparticles (Cu₇Se₄, Cu_2−x Se), have been successfully synthesized in 20 vol% water and 80 vol% organic solvents mixture under mild conditions. The products were characterized by various techniques, including X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), electronic diffraction (ED), and high-resolution transmission electron microscopy (HRTEM). The studies of the optical properties revealed that the copper chalcogenides have a wide absorption in the range of about 400–700 nm, with accessional IR band. Systematic studies showed that the mixture of 20 vol% water and 80 vol% organic solvents played a key role in controlling the copper chalcogenides with different morphologies and phases.     

High quality and tuneable silica shell–magnetic core nanoparticles

Obtaining small (<50 nm), monodispersed, well-separated, single iron oxide core–silica (SiO₂) shell nanoparticles for biomedical applications is still a challenge. Preferably, they are synthesised by inverse microemulsion method. However, substantial amount of aggregated and multicore core–shell nanoparticles is the undesired outcome of the method. In this study, we report on the production of less than 50 nm overall size, monodispersed, free of necking, single core iron oxide–SiO₂ shell nanoparticles with tuneable shell thickness by a carefully optimized inverse microemulsion method. The high degree of control over the process is achieved by understanding the mechanism of core–shell nanoparticles formation. By varying the reaction time and precursor concentration, the thickness of silica layer on the core nanoparticles can be finely adjusted from 5 to 13 nm. Residual reactions during the workup were inhibited by a combination of pH control with shock freezing and ultracentrifuging. These high-quality tuneable core–shell nanocomposite particles exhibit superparamagnetic character and sufficiently high magnetization with great potential for biomedical applications (e.g. MRI, cell separation and magnetically driven drug delivery systems) either as-prepared or by additional surface modification for improved biocompatibility.     

A new one-step synthesis method for coating multi-walled carbon nanotubes with iron oxide nanorods

A facile solution-chemical method has been developed to be capable of covering a multiwalled carbon nanotube (MWNTs) with iron oxide nanorods without using any bridging species. MWNTs in this composite were decorated randomly by α-Fe₂O₃ nanorods with diameters in the range of 3–5 nm and lengths of 15–30 nm. The formation route to anchor α-Fe₂O₃ nanorods onto MWNTs was proposed as the intercalation and adsorption of iron ions onto the wall of MWNTs, followed by the nucleation and growth of α-Fe₂O₃ nanorods. α-Fe₂O₃/MWNTs nanocomposites show specific high Brunauer–Emmett–Teller surface areas. The photocatalytic activity experiment indicated that the prepared α-Fe₂O₃/MWNTs nanocomposites exhibited a higher photocatalytic activity for the photocatalytic decolorization of rhodamine B aqueous solution under the visible-light illumination than the single phase α-Fe₂O₃ samples. This methodology made the synthesis of MWNTs-nanorods composites possible and may be further extended to prepare more complicated nanocomposites based on MWNTs for technological applications.     

Silver and gold nanoparticle coated membranes applied to protein dot blots

Detection and identification of low abundance biomarker proteins is frequently based on various types of membrane-based devices. Lowering of the protein detection limits is vital in commercial applications such as lateral flow assays and in Western blots widely used in proteomics. These currently suffer from insufficient detection sensitivity and low retention for small 2–5 kDa proteins. In this study, we report the deposition of two types of metal nanoparticles: gold colloids (50–95 nm diameter) and silver fractals onto a range of commonly used types of membranes including polyvinylidene fluoride (PVDF). Due to strong affinity of proteins to noble metals, such modified membranes have the potential to effectively capture trace proteins preventing their loss. The membranes modified by metal particles were characterized optically and by SEM. The membrane performance in protein dot blots was evaluated using the protein—fluorophore conjugates Deep Purple-bovine serum albumin and fluorescein—human serum albumin. We found that the metal nanoparticles increase light extinction by metals, which is balanced by increased fluorescence, so that the effective fluorescence signal is unchanged. This feature combined with the capture of proteins by the nanoparticles embedded in the membrane increases the detection limit of membrane assays.     

Synthesis,characterization and role of zero-valent iron nanoparticle in removal of hexavalent chromium from chromium-spiked soil

Chromium is an important industrial metal used in various products/processes. Remediation of Cr contaminated sites present both technological and economic challenges, as conventional methods are often too expensive and difficult to operate. In the present investigation, Zero-valent iron (Fe⁰) nanoparticles were synthesized, characterized, and were tested for removal of Cr(VI) from the soil spiked with Cr(VI). Fe⁰ nanoparticles were synthesized by the reduction of ferric chloride with sodium borohydride and were characterized by UV–Vis (Ultra violet–Visible) and FTIR (Fourier transform infrared) spectroscopy. The UV–Vis spectrum of Fe⁰ nanoparticles suspended in 0.8% Carboxymethyl cellulose showed its absorption maxima at 235 nm. The presence of one band at 3,421 cm⁻¹ ascribed to OH stretching vibration and the second at 1,641 cm⁻¹ to OH bending vibration of surface-adsorbed water indicates the formation of ferrioxyhydroxide (FeOOH) layer on Fe⁰ nanoparticles. The mean crystalline dimension of Fe⁰ nanoparticles calculated by XRD (X-ray diffraction) using Scherer equation was 15.9 nm. Average size of Fe⁰ nanoparticles calculated from TEM (Transmission electron microscopy) images was found around 26 nm. Dynamic Light Scattering (DLS) also showed approximately the same size. Batch experiments were performed using various concentration of Fe⁰ nanoparticles for reduction of soil spiked with 100 mg kg⁻¹ Cr(VI). The reduction potential of Fe⁰ nanoparticles at a concentration of 0.27 g L⁻¹ was found to be 100% in 3 h. Reaction kinetics revealed a pseudo-first order kinetics. Factors like pH, contact time, stabilizer, and humic acid facilitates the reduction of Cr(VI).     

Synthesis and characterization of a polyaniline-modified SnO<Subscript>2</Subscript> nanocomposite

Polyaniline-modified tin oxide and tin oxide nanoparticles were synthesized using a solution route technique. The obtained pristine products were characterized with X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, and optical absorption spectroscopy. Thermogravimetric analysis results showed that the polyaniline-modified SnO₂ nanoparticles exhibit higher thermal stability than the SnO₂ nanoparticles. Scanning electron microscopy analysis on the as-synthesized powders showed spherical particle in the range of 50–100 nm.