Partial Oxidation as a Rational Approach to Kinetic Control in Bioinspired Magnetite Synthesis

Biological systems show impressive control over the shape, size and organization of mineral structures, which often leads to advanced physical properties that are tuned to the function of these materials. Such control is also found in magnetotactic bacteria, which produce—in aqueous medium and at room temperature—magnetite nanoparticles with precisely controlled morphologies and sizes that are generally only accessible in synthetic systems with the use of organic solvents and/or the use of high‐temperature methods. The synthesis of magnetite under biomimetic conditions, that is, in water and at room temperature and using polymeric additives as control agents, is of interest as a green production method for magnetic nanoparticles. Inspired by the process of magnetite biomineralization, a rational approach is taken by the use of a solid precursor for the synthesis of magnetite nanoparticles. The conversion of a ferrous hydroxide precursor, which we demonstrate with cryo‐TEM and low‐dose electron diffraction, is used to achieve control over the solution supersaturation such that crystal growth can be regulated through the interaction with poly‐(α,β)‐dl ‐aspartic acid, a soluble, negatively charged polymer. In this way, stable suspensions of nanocrystals are achieved that show remanence and coercivity at the size limit of superparamagnetism, and which are able to align their magnetic moments forming strings in solution as is demonstrated by cryo‐electron tomography.     

Fe3O4/polyethylene glycol nanocomposite as a solid‐phase microextraction fiber coating for the determination of some volatile organic compounds in water

A high‐performance metal oxide polymer magnetite/polyethylene glycol nanocomposite was prepared and coated in situ on the surface of the optical fiber by sol–gel technology. The magnetite nanoparticles as nanofillers were synthesized by a coprecipitation method and bonded with polyethylene glycol as a polymer. The chemically bonded coating was evaluated for the headspace solid–phase microextraction of some environmentally important volatile organic compounds from aqueous samples in combination with gas chromatography and mass spectrometry. The prepared fiber was characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. The mass ratio of nanofiller and polymer on the coating extraction efficiency, morphology, and stability were investigated. The parameters affecting the extraction efficiency, including the extraction time and temperature, the ionic strength, desorption temperature, and time were optimized. The sol–gelized fiber showed excellent chemical stability and longer lifespan. It also exhibited high extraction efficiency compared to the two types of commercial fibers. For volatile organic compounds analysis, the new fiber showed low detection limits (0.008–0.063 ng/L) and wide linearity (0.001–450 × 10⁴ ng/L) under the optimized conditions. The repeatability (interday and intraday) and reproducibility were 4.13–10.08 and 5.98–11.61%, and 7.35–14.79%, respectively (n = 5). For real sample analysis, three types of water samples (ground, surface, and tap water) were studied.     

Analysis of microcystins using high‐performance liquid chromatography and magnetic solid‐phase extraction with silica‐coated magnetite with cetylpyridinium chloride

Microcystins (MCs), produced by freshwater cyanobacteria, can be serious water pollutants, so it is important to monitor their concentration in drinking water. We have developed a method for rapid and accurate determination of microcystin levels in environmental water, using magnetic solid‐phase extraction and high‐performance liquid chromatography with UV detection. The magnetic composite material, which was combined with cetylpyridinium chloride, was prepared by hydrothermal synthesis. The optimal extraction of microcystins in water sample was achieved by optimizing the amount of adsorbent, time of adsorption, ratio of eluting solvent, and volume of eluent. Under the optimal conditions, the limit of detection of MC‐LR was 0.001 μg/L, and the limit of quantification was 0.0028 μg/L. The limit of detection of MC‐RR was 0.001 μg/L, and the limit of quantification was 0.003 μg/L. These values are far lower than those established by the International Health Organization for the maximum concentration of microcystins in drinking water. The magnetic solid‐phase extraction adsorbent used in this method has the advantages of simple preparation, low price, and easy solid–liquid separation, and it can be used for the rapid and sensitive monitoring of trace microcystins in environmental water samples.     

Monitoring Imidazoline Derivatives via Functionalized Nano-Potentiometric Platforms in Aqueous Humor and Dosage Forms

The determination of two imidazoline derivatives [oxymetazoline HCl (OXY) and xylometazoline HCl (XYLO)] was described using different potentiometric platforms. The first electrode type was constructed using tetraphenyl borate (TPB) as anionic exchanger with β-cyclodextrins (β-CD) as ionophore forming oxymetazoline-tetraphenyl borate (OXY-TPB) and xylometazoline-tetraphenyl borate (XYLO-TPB), respectively. The second electrode type was prepared by modification of the first type by conjugation with magnetic iron oxide nanoparticles (MNP) forming (OXY-MNP) and (XYLO-MNP). The synthesized electrodes were fully characterized. The effect of magnetic nano-sized particles as a highly dispersible material with β-CDs on the electrode characteristics was investigated and compared against the classical electrodes. The response time, working pH range and selectivity coefficients were studied. The functionalized nano-electrodes (OXY-MNP and (XYLO-MNP) were found to be more sensitive than the classical electrodes with linearity ranges (1×10⁻⁶–1×10⁻² M). The functionalized nano-electrodes were successfully applied for the in-line analysis of OXY and XYLO in pharmaceutical dosage forms and spiked rabbit aqueous humor samples with no prior extraction of treatment. This suggests the future use of these electrodes in clinical studies of both drugs of interest.     

SYNTHESIS AND CHARACTERIZATION OF SURFACE-HYPERBRANCHED MAGNETITE NANOPARTICLE FOR BOVINE SERUM ALBUMIN IMMOBILIZATION

A hyperbranched polyamidoamine polymer was synthesized on the surface of magnetite nanoparticles to enhance bovine serum albumin (BSA) immobilization efficiency. The amount of immobilized bovine serum albumin (BSA) on the surface-hyperbranched magnetite nanoparticle was up to 2.5 times as much as that of magnetite nanoparticle modified with only amino silane.     

Synthesis and characterization of the novel diamine‐functionalized Fe3O4@SiO2 nanocatalyst and its application for one‐pot three‐component synthesis of chromenes

Fe₃O₄@SiO₂@propyltriethoxysilane@o‐phenylendiamine as an environmentally‐benign functionalized silica‐coated magnetic organometallic nanomaterial has been synthesized and characterized by Fourier transforms infrared (FT‐IR) spectroscopy, scanning electron microscopy (SEM) images and energy dispersive X‐ray (EDX) and vibrating sample magnetometer (VSM) analyses. Then, its catalytic activity was investigated for the one‐pot three‐component condensation reaction between dimedone, malononitrile and various substituted aromatic aldehydes to afford the corresponding 2‐amino‐4H‐chromene derivatives under mild reaction conditions. This nanocatalyst can be easily recovered from the reaction mixture by using a magnet and reused for at least five times without significant decrease in catalytic activity.     

Advanced Sensing of Antibiotics with Magnetic Gold Nanocomposite: Electrochemical Detection of Chloramphenicol

The sensing and accurate determination of antibiotics in various environments represents a big challenge, mainly owing to their widespread use in medicine, veterinary practice, and other fields. Therefore, a new, simple electrochemical sensor for the detection of antibiotic chloramphenicol (CAP) has been developed in this work. The amplification strategy of the sensor is based on the application of magnetite nanostructures stabilized with carboxymethyl cellulose (Fe₃O₄‐CMC) and decorated with nanometer‐sized Au nanoparticles (NPs) (Fe₃O₄‐CMC@Au). In this case, CMC serves as a stabilizing agent, preventing the aggregation of Fe₃O₄ NPs, and hence, enabling the kinetic barrier for electron transport to be overcome, and the Au NPs serve as an electron‐conducting tunnel for better electron transport. As a proof of concept, the developed nanosensor is used for the detection of CAP in human urine samples, giving a recovery value of around 97 %, which indicates the high accuracy of the as‐prepared nanosensor.     

One‐Pot Synthesis of Pomegranate‐Structured Fe3O4/Carbon Nanospheres‐Doped Graphene Aerogel for High‐Rate Lithium Ion Batteries

A unique hierarchically nanostructured composite of iron oxide/carbon (Fe₃O₄/C) nanospheres‐doped three‐dimensional (3D) graphene aerogel has been fabricated by a one‐pot hydrothermal strategy. In this novel nanostructured composite aerogel, uniform Fe₃O₄ nanocrystals (5–10 nm) are individually embedded in carbon nanospheres (ca. 50 nm) forming a pomegranate‐like structure. The carbon matrix suppresses the aggregation of Fe₃O₄ nanocrystals, avoids direct exposure of the encapsulated Fe₃O₄ to the electrolyte, and buffers the volume expansion. Meanwhile, the interconnected 3D graphene aerogel further serves to reinforce the structure of the Fe₃O₄/C nanospheres and enhances the electrical conductivity of the overall electrode. Therefore, the carbon matrix and the interconnected graphene network entrap the Fe₃O₄ nanocrystals such that their electrochemical function is retained even after fracture. This novel hierarchical aerogel structure delivers a long‐term stability of 634 mA h g^?1 over 1000 cycles at a high current density of 6 A g^?1 (7 C), and an excellent rate capability of 413 mA h g^?1 at 10 A g^?1 (11 C), thus exhibiting great potential as an anode composite structure for durable high‐rate lithium‐ion batteries.     

Click functionalization of magnetite nanoparticles: A new magnetically recoverable catalyst for the selective epoxidation of olefins

A new magnetically recoverable heterogeneous molybdenum catalyst was developed by means of a click chemistry approach. First, silica‐coated magnetite nanoparticles were functionalized using a bidentate ligand via thiol–ene click reaction of mercaptopropyl‐modified magnetite nanoparticles with acrylic acid. Then, a molybdenum complex was covalently supported on the surface of the clicked silica‐coated magnetite nanoparticles. The prepared catalyst was characterized using Fourier transform infrared and inductively coupled plasma optical emission spectroscopies, X‐ray diffraction, vibrating sample magnetometry and transmission electron microscopy. The catalytic performance of the prepared heterogeneous catalyst was investigated in the epoxidation of olefins with tert‐butyl hydroperoxide as oxidant. This catalyst could be reused for five runs without significant loss of activity and selectivity.     

Heterogenized peroxopolyoxotungstate catalyst on the surface of clicked magnetite‐graphene oxide nanocomposite: Magnetically recoverable epoxidation catalyst

A new heterogeneous catalyst for the epoxidation of olefins was prepared by immobilization of peroxophosphotungstate anions on the surface of clicked magnetite‐graphene oxide as magnetically recoverable support. To prepare the heterogeneous catalyst, the clicked magnetite‐graphene oxide support was prepared by thiolene click reaction of thiol functionalized graphene oxide with vinyl modified magnetite nanoparticles. The tailored support was then modified with aminopropyl groups followed by electrostatic interaction with peroxophosphotungstate anions to achieve the desired heterogeneous catalyst. Characterization of the catalyst was performed by various physicochemical methods which confirmed the successful immobilization of peroxopolyoxotungstate species on the surface of clicked magnetite‐graphene oxide. Catalytic activity of the catalyst revealed its high catalytic activity and selectivity in the epoxidation of various olefins in the presence of H₂O₂ as green oxidant. This heterogeneous catalyst can be magnetically reused several times without significant loss of activity and selectivity.