Hydrophilic magnetic polymer latexes. 2. Encapsulation of adsorbed iron oxide nanoparticles

The encapsulation of seed polymer particles coated by anionic iron oxide nanoparticles has been investigated using N-isopropylacrylamide as a main monomer, N,N-methylene bisacrylamide as a crosslinking agent, itaconic acid as a functional monomer and potassium persulfate as an anionic initiator. The magnetic latexes obtained have been characterized with regard to particle size, iron oxide content and electrophoretic mobility. All these properties have been examined by varying several polymerization parameters: reaction medium, monomer(s) and crosslinking agent concentrations, nature of seed latexes and type of polymerization (batch versus shot process). The magnetic content in the polymer microspheres strongly depends on the polymerization procedure (i.e., encapsulation process) and varies between 6 and 23 wt%, and monodisperse magnetic polymer particles were obtained. Received: 28 December 1999 Accepted in revised form: 15 June 1999     

Adsorption of cationic copolymer nanoparticles onto bamboo fiber surfaces measured by conductometric titration

Monosized nanoparticles of 57.3 nm were prepared by cationic emulsion polymerization using a polymerizable emulsifier DMHB. The adsorption of nanoparticles onto bamboo fibers was measured by conductometric titration. The results indicated that the adsorption capacity increased with increasing contact time until 120 min. The equilibrium data for nanoparticles adsorption onto bamboo fibers were well fitted to the Langmuir equation. Moreover, the monolayer adsorption capacity of nanoparticles in the concentration range (from 0.03 g/L to 0.6 g/L) studied, as calculated from Langmuir isotherm model at 25℃, was found to be 38.61 mg/g of fibers. The SEM images showed that the nanoparticles form a uniform monolayer on bamboo fiber surfaces.     

Adsorption studies of cationic starch onto quartz surface through an electrode-separated piezoelectric sensor

In the construction of an electrode-separated piezoelectric sensor (ESPS), the quartz surface is in direct contact with the liquid phase. The negatively charged quartz crystal surface can adsorb cationic starch. This adsorption process was in situ monitored from the frequency shift of the ESPS. It was shown that the adsorption of cationic starch onto the quartz surface is reversible with respect the dilution of the bulk phase. The adsorption behavior can be described by Langmuir model. The adsorption density and kinetics parameters were estimated from the frequency responses of the ESPS. The influence of pH and ionic strength on adsorption parameters was investigated. It was shown that the influence of pH on the adsorption rate was slight. With increasing ionic strength, the rate constants for adsorption and desorption increase, but the adsorption equilibrium constant and saturation adsorption density decrease. The adsorption equilibrium constant and adsorption density reach a maximum in buffer of pH 10.     

Semi-quantitative determination of cationic surfactants in aqueous solutions using gold nanoparticles as reporter probes

Concentrations of cationic surfactants in aqueous solutions have been estimated on the basis of changes in the color of gold nanoparticles, used as reporter probes. We have shown that the colors of gold nanoparticles with anionic protective groups on their surfaces shift from red to indigo/purple and then back to red in a range of cationic surfactant solutions in which concentrations vary from very low to above the theoretical CMCs. The color changes occur near the theoretical CMCs, presumably because the presence of surfactant micelles in the solution prevents the gold nanoparticles from aggregating. We have used gold nanoparticles as reporter probes to determine the concentrations of cationic surfactants in products such as hair conditioners, which often contain large amounts of alkyltrimethylammonium halides. Although this approach can only provide an estimate, it can be performed simply by addition of a given amount of gold nanoparticles to a series of diluted solutions, without the need for instruments or labor-intensive procedures. Figure Photographs of a series of diluted hair conditioner solutions with added gold nanoparticles

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Investigation of iron oxide nanoparticles by capillary zone electrophoresis

The electrophoretic behavior of γ-Fe₂O₃ nanoparticles was studied in aqueous solutions of Na₂SO₄-NaOH (pH 10.8) and of Na₂SO₄-Na₃cit (pH 7.1) as running electrolytes. Two electrophoretic zones (smooth and with spikes) due to colloidal and suspended particles of approximately the same size range were formed during the runs. The suspension stability and size distribution were shown to depend on the composition of electrolyte used for dispersing the solids. The effects of electric field strength, injection time, injection pressure as well as sodium citrate concentration were studied and particle electrophoretic mobilities were calculated. Electron micrographs of particles studied were obtained. Preparation of reference samples based on the colloidal γ-Fe₂O₃ has been discussed.     

Adsorption kinetics of fluoride on iron(III)-zirconium(IV) hybrid oxide

Fluoride occurs in some drinking water sources at levels that are hazardous to health. Tests were conducted to assess the ability of a mineral-based adsorbent to take-up fluoride ion. Consequently, in search of novel adsorbent media, crystalline and hydrous iron(III)-zirconium(IV) hybrid oxide (IZHO) was synthesized, and tested to determine its capacity and kinetics for fluoride adsorption. The Fourier Transform Infrared (FTIR) spectrum of IZHO indicated the presence of Fe–O–Zr linkage which showed hybrid nature of the synthetic oxide. The optimum pH range for fluoride adsorption was ranged between 4.0 and 7.0. The analyses of the isotherm equilibrium data using the Langmuir and the Redlich–Peterson model equations by linear and non-linear methods showed that the data fitted better with latter model than the former. Thermodynamic analysis showed spontaneous nature of fluoride adsorption, and that took place with the increase of entropy. The kinetic data obtained for fluoride adsorption on IZHO at pH 6.8 (±0.1) and room temperature (303±2 K) described both the pseudo-first order and the reversible first-order equations equally well (r ²= ∼0.98–0.99), and better than pseudo second order equation (r ²= ∼0.96–0.98) for higher concentrations (12.5 and 25.0 mg/dm³) of fluoride. The kinetics of fluoride adsorption on the mixed oxide took place with boundary layer diffusion. External mass transport with intra-particle diffusion phenomena governed the rate limiting process, which has been confirmed from the Boyd poor non-linear kinetic plots.     

Adsorption of As (V) on iron oxide nanoparticle films studied by in situ ATR-FTIR spectroscopy

Stabilization of arsenic contaminated soils by iron oxides has been proposed as a remediation technique to prevent leaching of arsenate into the environment. Fundamental studies are needed to establish under which conditions the complexes formed are stable. In the present work, a powerful technique, viz. ATR-FTIR spectroscopy, is adapted to the studies of adsorption of arsenate species on iron oxides. This technique facilitates acquisition of both quantitative and qualitative in situ adsorption data.In the present work, about 800 nm thick films of 6-lineferrihydrite were deposited on ZnSe ATR crystals. Arsenate adsorption on the ferrihydrite film was studied at pD values ranging from 4 to 12 and at an arsenate concentration of 0.03 mM in D₂O solution. The amount of adsorbed arsenate decreased with increasing pD as a result of the more negatively charged iron oxide surface at higher pD values. The adsorption and desorption kinetics were also studied. Arsenate showed a higher adsorption rate within the first 70 min and a much lower adsorption rate from 70 to 300 min. The low adsorption rate at longer reaction times was partly due to a low desorption rate of already adsorbed carbonate species adsorbed at the surface. The desorption of carbonate species was evidenced by the appearance of negative absorption bands. The desorption of adsorbed arsenate complexes was examined by flushing with D₂O at pD 4 and 8.5 and it was found that the complexes were very stable at pD 4 suggesting formation of mostly inner-sphere complexes whereas a fraction of the complexes at pD 8.5 were less stable than at pD 4, possibly due to the formation of outer-sphere complexes.In summary, the ATR technique was shown to provide in situ information about the adsorption rate, desorption rate and the speciation of the complexes formed within a single experiment, which is very difficult to obtain using other techniques.     

Polysaccharide-modified iron oxide nanoparticles as an effective magnetic affinity adsorbent for bovine serum albumin

The magnetic separation technique based on magnetic iron oxide nanoparticles (MNPs) has potential applications in protein adsorption and purification, enzyme immobilization, cell sorting, nucleic acid detachment, and drug release. However, the naked MNPs are often insufficient for their hydrophilicity, colloidal stability, and further functionalization. To overcome these limitations, chitosan was firstly carboxymethylated and then covalently conjugated on the surface of the MNPs ranging in size from about 5 to 15 nm, which were prepared by co-precipitating iron (II) and iron (III) in alkaline solution and then treating under hydrothermal conditions. It was found that such modification did not result in the phase change of the MNPs, and the resultant modified nanoparticles were still superparamagnetic. In particular, the colloidal stability of MNPs in aqueous suspension was improved after the surface modification. By investigating the adsorption of bovine serum albumin (BSA) on the modified MNPs, it was observed that the adsorption capacity of the BSA on the modified MNPs increased rapidly within several minutes and then reached the maximum value at about 10 min. The adsorption equilibrium isotherm could be fitted well by the Langmuir model. The medium pH affected greatly the adsorption of the BSA. The maximum adsorption of the BSA occurred at the pH value close to the isoelectric point of the BSA, with a saturation adsorption amount of 94.45 mg/g (25 °C). For the BSA feed concentration of 1.017 mg/ml, a high desorption percentage of 91.5% could be achieved under an alkaline condition (pH 9.4).     

A DFT study of the effect of copper promotion upon iron oxide surface species

Cluster models for sites on the {1 1 1} surface of Fe₃O₄ were used to study the strength of bonding of water-gas shift intermediates using density functional theory. Three site models were used, representing an unpromoted catalyst, a catalyst where copper cations substitute for iron cations below the surface and a catalyst where copper cations substitute in the surface. The strengths of bonding of oxygen, carbon dioxide, dissociated water and dissociated formic acid were all observed to decrease by less than 20 kJ mol⁻¹ when copper substituted below the surface, but they decreased by 60–80 kJ mol⁻¹ when copper substituted in the surface of the catalyst. A minimum energy structure for molecularly adsorbed water was not identified because all attempts to do so resulted in dissociation.     

Surface functionalization of polymer latex particles. III. A convenient method of producing ultrafine poly(methylstyrene) latexes with aldehyde groups on the surface

A convenient method of preparing ultrafine poly(methylstyrene) (PMS) latex particles with aldehyde groups on the surface is developed. PMS latexes in the size range 33–81 nm were prepared via microemulsion polymerization, using cetyltrimethylammonium bromide (CTAB) as surfactant. The surface of the PMS latexes was oxidized in the presence of tert-butyl hydroperoxide catalyzed by copper(II) chloride. As the degree of oxidation increased up to 6 h, the amounts of aldehyde group increased. Bigger particles were found to have a slightly higher rate of oxidation than small ones under the same oxidation conditions. The particle size underwent little change during oxidation; thus, the amounts of functional groups and the particle size could be controlled concurrently. Dialysis study of the oxidized PMS microlatexes indicated that the instability of highly oxidized PMS microlatexes was caused by the reduction of total surface charge density due to the presence of carboxylic acid groups. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2103–2109, 1998     

磁性铁氧化物纳米粒子制备及其体内应用研究

磁性铁氧化物纳米粒子由于其生物相容性和低毒性而广泛的应用于生物医学领域。本文总结了近年来制备各种磁性铁氧化物纳米粒子的方法,比较了它们在粒径、结晶度以及制备条件等方面的优缺点,概括了对其进行表面修饰改性材料的种类,阐述近年来磁性铁氧化物纳米粒子在体内应用中药物运输、磁共振成像、磁热疗方面的进展,并指出当前应用中的主要方向和亟待解决的问题。     

Optimization and ecofriendly synthesis of iron oxide nanoparticles as potential antioxidant

The present study involves the use of Box-Behnken design for optimization of the energy-efficient process variables, eco-friendly synthesis of nanoparticles of iron oxide using Coriandrum sativum L. (cilantro) leaf extract. The factors, which significantly influenced mean nanoparticle size, surface charge, and size distribution, were the volume of leaf extract, agitation speed, and temperature. The developed model using Box-Behnken design was validated by synthesizing the iron nanoparticles using optimized operational conditions i.e. 10 ml volume of leaf extract, 1500 rpm agitation speed and 30 °C temperature. This resulted in the formation of highly stable iron oxide nanoparticles with mean particle size 161.5 nm and polydispersity index 0.132 with a zeta potential of −19.5 mV. The free radical inhibitory activity of prepared iron oxide nanoparticles was found comparable to ascorbic acid. These results reveal that iron nanoparticles for a biomedical application can be prepared at ambient temperature in an eco-friendly manner.     

Synthesis, morphological-structural characterization and magnetic properties of amorphous iron (III)-oxyhydroxy-phosphate nanoparticles

The synthesis, the chemical, morphological, structural characterization and the magnetic properties of amorphous iron oxyhydroxy phosphate nanoparticles are reported. Aggregated spherical particles (diameter: 5-12 nm) are obtained showing a ferrihydrite-like behavior similar to that of the bacterial ferritin iron oxyhydroxy-phosphate core. A superparamagnetic behavior is observed with blocking temperatures ranging from ∼20 to ∼50 K depending on the iron and phosphate content.     

An amperometric biosensor based on acetylcholinesterase immobilized onto iron oxide nanoparticles/multi-walled carbon nanotubes modified gold electrode for measurement of organophosphorus insecticides

An acetylcholinesterase (AChE) purified from maize seedlings was immobilized covalently onto iron oxide nanoparticles (Fe₃O₄NP) and carboxylated multi walled carbon nanotubes (c-MWCNT) modified Au electrode. An organophosphorus (OP) biosensor was fabricated using this AChE/Fe₃O₄/c-MWCNT/Au electrode as a working electrode, Ag/AgCl as standard and Pt wire as an auxiliary electrode connected through a potentiostat. The biosensor was based on inhibition of AChE by OP compounds/insecticides. The properties of nanoparticles modified electrodes were studied by scanning electron microscopy (SEM), Fourier transform infrared (FTIR), cyclic voltammograms (CVs) and electrochemical impedance spectroscopy (EIS). The synergistic action of Fe₃O₄NP and c-MWCNT showed excellent electrocatalytic activity at low potential (+0.4 V). The optimum working conditions for the sensor were pH 7.5, 35 °C, 600 μM substrate concentration and 10 min for inhibition by pesticide. Under optimum conditions, the inhibition rates of OP pesticides were proportional to their concentrations in the range of 0.1–40 nM, 0.1–50 nM, 1–50 nM and 10–100 nM for malathion, chlorpyrifos, monocrotophos and endosulfan respectively. The detection limits were 0.1 nM for malathion and chlorpyrifos, 1 nM for monocrotophos and 10 nM for endosulfan. The biosensor exhibited good sensitivity (0.475 mA μM⁻¹), reusability (more than 50 times) and stability (2 months). The sensor was suitable for trace detection of OP pesticide residues in milk and water.     

Aromatic amine mediated ring opening of epoxides: A reaction catalyzed by biogenic iron oxide nanoparticles

An efficient green method was used for the synthesis of polyphenol capped iron oxide nanoparticles (ION) from an agro waste, peanut skin. The polyphenol capped ION was characterized by Fourier transformed infra-red (FTIR), Powder XRD and X-ray photoelectron spectroscopic (XPS) analysis. To evaluate the catalytic activities of ION, ring opening of epoxides by aromatic amines has been performed and the catalyst showed good activity with yields up to 90% of the major products using only 20 ​mg of the catalyst under solvent free neat condition at room temperature (28 ​°C) after 5 ​h. These nanoparticles can be reused for three times without significant loss in their activities.     

Solid phase extraction-spectrophotometric determination of fluoride in water samples using magnetic iron oxide nanoparticles

A new, sensitive, fast and simple method using magnetic iron oxide nanoparticles (MIONs), as an adsorbent has been developed for extraction, preconcentration and determination of traces of fluoride ions. The determination method is based on the discoloration of Fe(III)-SCN complex with extracted fluoride ions which was subsequently monitored spectrophotometrically at λ_max = 458 nm. Various parameters affecting the adsorption of fluoride by the MIONs have been investigated, such as pH of the solution, type, volume and concentration of desorbing reagent, amount of adsorbent and interference effects. A linear response for the determination of fluoride was achieved in the concentration range of 0.040-1.250 μg mL⁻¹. The limit of detection (LOD) and limit of quantification (LOQ) for fluoride based on 3 times and 10 times the standard deviation of the blank (3S_b, 10S_b) were 0.015 and 0.042 μg mL⁻¹ (n = 20) for fluoride ion, respectively. A preconcentration factor of 50 was achieved in this method. The proposed procedure has been applied for determination of fluoride concentration in various water samples. The results obtained from this method were successfully compared with those provided by standard SPADNS method.     

Synergism of Pt nanoparticles and iron oxide support for chemoselective hydrogenation of nitroarenes under mild conditions

An efficient and low-cost supported Pt catalyst for hydrogenation of niroarenes was prepared with colloid Pt precursors and α-Fe₂O₃ as a support. The catalyst with Pt content as low as 0.2 wt% exhibits high activities, chemoselectivities and stability in the hydrogenation of nitrobenzene and a variety of niroarenes. The conversion of nitrobenzene can reach 3170 mol_conv h^?1 mol_Pt^?1 under mild conditions (30 °C, 5 bar), which is much higher than that of commercial Pt/C catalyst and many reported catalysts under similar reaction conditions. The spatial separation of the active sites for H₂ dissociation and hydrogenation should be responsible for the high chemoselectivity, which decreases the contact possibility between the reducible groups of nitroarenes and Pt nanoparticles. The unique surface properties of α-Fe₂O₃ play an important role in the reaction process. It provides active sites for hydrogen spillover and reactant adsorption, and ultimately completes the hydrogenation of the nitro group on the catalyst surface.     

A layered magnetic iron/iron oxide nanoscavenger for the analytical enrichment of ng-L concentration levels of heavy metals from water

Magnetically driven separation techniques have received considerable attention in recent decade because of their great potential application. In this study, we investigate the application of an unmodified layered magnetic Fe/Fe₂O₃ nanoscavenger for the analytical enrichment and determination of sub-parts per billion concentrations of Cd(II), Pb(II), Ni(II), Cr(VI) and As(V) from water samples. The synthesized nanoscavenger was characterized by BET, TGA, XRD and IR and the parameters influencing the extraction and recovery of the preconcentration process were assessed by atomic absorption spectrometry. The possible mechanism of the enrichment of heavy metals on Fe/Fe₂O₃ was proposed, which involved the dominant adsorption and reduction. The nanoscale size offers large surface area and high reactivity of sorption and reduction reactions. The obtained limits of detection for the metals studied were in the range of 20–125 ng L⁻¹ and the applicability of the nanomaterial was verified using a real sample matrix. The method is environmentally friendly as only 15 mg of nanoscavenger are used, no organic solvent is required for the extraction and the experiment is performed without the need for filtration or preparation of packed preconcentration columns.     

Modified iron oxide nanoparticles as solid phase extractor for spectrophotometeric determination and separation of basic fuchsin

This study presents a novel separation, preconcentration and determination of basic fuchsin (BF) in an aqueous solution by sodium dodecyl sulfate (SDS)-bounded iron oxide nanoparticles (S-IONPs). It is shown that the novel magnetic nano-adsorbent is quite efficient for the adsorption and desorption of BF at 25 °C. Different parameters such as pH, temperature, ionic strength and composition of desorbent solvent were optimized. The effect of some co-existing ions on the determination was investigated. The nanoparticles were analyzed by transmission electron microscopy (TEM) and the sizes of S-IONPs were in the range of 20-100 nm. The method showed good linearity for the determination of BF in the range of 10-300 ng mL⁻¹ with a regression coefficient of 0.9989. The limit of detection (LOD) (signal-to-noise ratio of 3:1) was 0.0073 μg L⁻¹ and the relative standard deviation (RSD) for 0.03 μg mL⁻¹ and 0.2 μg mL⁻¹ of BF were 4.53% and 4.73%, respectively. The BF was determined successfully in spiked samples of Karoon River water.