Study of the dc resistivity and thermoelectric power in Mn-substituted Ni–Zn ferrites

The electrical resistivity and thermoelectric power as a function of temperature and Mn concentration for Ni_0.6-t Mn _t Zn_0.4Fe₂O₄ (t = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) have been studied. It was observed that temperature variation of resistivity exhibits two breaks. Each break is associated with a change in activation energy. The activation energy in the paramagnetic region is found to be greater than that in the ferrimagnetic one. Moreover, it was found that the resistivity increases with increasing Mn content. The sign of thermoelectric power measurements revealed n-type conduction for all investigated samples. The results are explained according to the spin polaron model.     

Single-Atom Gd Nanoprobes for Self-Confirmative MRI with Robust Stability

Gadolinium (Gd)-based complexes are extensively utilized as contrast agents (CAs) in magnetic resonance imaging (MRI), yet, suffer from potential safety concerns and poor tumor targeting. Herein, as a mimic of Gd complex, single-atom Gd nanoprobes with r₁ and r₂ values of 34.2 and 80.1 mM⁻¹ s⁻¹ (far higher than that of commercial Gd CAs) at 3 T are constructed, which possessed T₁/T₂ dual-mode MRI with excellent stability and good tumor targeting ability. Specifically, single-atom Gd is anchored on nitrogen-doped carbon matrix (Gd-N_xC) through spatial-confinement method, which is further subjected to controllable chemical etching to afford fully etched bowl-shape Gd-N_xC (feGd-N_xC) with hydrophilic properties and defined coordination structure, similar to commercial Gd complex. Such nanostructures not only maximized the Gd³⁺ site exposure, but also are suitable for self-confirmative diagnosis through one probe with dual-mode MRI. Moreover, the strong electron localization and interaction between Gd and N atoms afforded feGd-N_xC excellent kinetic inertness and thermal stability (no significant Gd³⁺ leaching is observed even incubated with Cu²⁺ and Zn²⁺ for two months), providing a creative design protocol for MRI CAs.     

EPMA,EPR, electronic and vibrational spectral studies on natural aurichalcite

The electron probe micro analysis (EPMA), electron paramagnetic resonance (EPR), electronic and vibrational spectral studies on a natural mineral, aurichalcite were studied at room temperature. The EPMA analysis revealed the concentration of copper in the mineral to be 2·6 wt% and zinc as 24·5 wt%. The optical spectra revealed the presence of copper inD _4h symmetry with crystal field (Dq) and tetragonal field (Ds andDt) parameters as 1250, 1600 and 520 cm⁻¹ respectively. This further confirmed the presence of Cu(II) ion in an elongated tetragonal site. The EPR studies indicated the presence of Cu(II) ion, but hyperfine lines could not be resolved due to the high concentration of the paramagnetic impurity in the mineral. The IR spectrum confirmed the presence of water and carbonate ion.     

Ten‐Gram‐Scale Facile Synthesis of Organogadolinium Complex Nanoparticles for Tumor Diagnosis

The market of available contrast agents for clinical magnetic resonance imaging (MRI) has been dominated by gadolinium (Gd) chelates based T₁ contrast agents for decades. However, there are growing concerns about their safety because they are retained in the body and are nephrotoxic, which necessitated a warning by the U.S. Food and Drug Administration against the use of such contrast agents. To ameliorate these problems, it is necessary to improve the MRI efficiency of such contrast agents to allow the administration of much reduced dosages. In this study, a ten‐gram‐scale facile method is developed to synthesize organogadolinium complex nanoparticles (i.e., reductive bovine serum albumin stabilized Gd‐salicylate nanoparticles, GdSalNPs‐rBSA) with high r₁ value of 19.51 mm ^?1 s^?1 and very low r₂/r₁ ratio of 1.21 (B₀ = 1.5 T) for high‐contrast T₁‐weighted MRI of tumors. The GdSalNPs‐rBSA nanoparticles possess more advantages including low synthesis cost (≈0.54 USD per g), long in vivo circulation time (t_1/2 = 6.13 h), almost no Gd³⁺ release, and excellent biosafety. Moreover, the GdSalNPs‐rBSA nanoparticles demonstrate excellent in vivo MRI contrast enhancement (signal‐to‐noise ratio (ΔSNR) ≈ 220%) for tumor diagnosis.     

Synthesis of poly(3-hexylthiophene)-graft-poly(t-butyl acrylate-co-acrylic acid) and its role of compatibilizer for enhancement of mechanical and electrical properties of Nylon 66/multi-walled carbon nanotube composites

A compatibilizer, poly(3-hexylthiophene)-graft-poly(t-butyl acrylate-co-acrylic acid) was synthesized, where the acrylic aid was formed by hydrolysis of t-butyl acrylate unit. It has been identified that poly(3-hexylthiophene) backbone of the compatibilizer interacts with multi-walled carbon nanotubes (MWCNTs) via π–π interaction and the acrylic acid unit of the graft chain interacts with Nylon 66 (N66) matrix via hydrogen bonding. When a small amount of compatibilizer was added to N66/MWCNT composites, MWCNTs were more homogeneously dispersed in N66 matrix than the case without compatibilizer. As a consequence, mechanical and electrical properties of the composites with compatibilizer were largely improved as compared with those of composites without compatibilizer.     

Preparation of water dispersible,fluorescent Ag–PAA–PVP hybrid nanogels and their optical properties

A simple method of synthesizing hybrid silver–polyacrylic acid–poly(N-vinylpyrrolidone) (Ag–PAA–PVP) nanogels was demonstrated through in situ reducing Ag⁺ inside PAA–PVP nanogels, which were formed by polymerization of acrylic acid in the PVP solution. Due to the ion exchange between Ag⁺ and acid protons of PAA, stable Ag⁺ clusters were formed inside the PAA–PVP nanogels, and hybrid nanogels were obtained by reducing Ag⁺ by ascorbic acid. Transmission electronic microscopic (TEM) images clearly showed the existence of silver nanoparticles inside the Ag–PAA–PVP nanogels. These hybrid nanogels showed typical surface plasma resonance absorption peak around 420 nm, and the size of the silver nanoparticles inside the Ag–PAA–PVP nanogels could be controlled from 9.5 ± 1.6 nm to 1.9 ± 0.4 nm by increasing the feeding amount of Ag⁺. In addition, these hybrid nanogels showed photoluminescent properties in fluorescent spectra. Considering the pH sensitive property of these hybrid nanogels, they will have potential application in drug delivery and biomedical imaging systems.     

Microstructural thermostability of high nitrogen austenitic stainless steel

A high nitrogen austenitic stainless steel, Fe–24Mn–18Cr–3Ni–0.62N, was isothermally annealed from 750 to 900 °C for different times to investigate the thermostability of its microstructures. Results show that the precipitates were Cr₂N and initially formed along the grain boundary. The time–temperature–precipitation diagram was established, according to which the critical cooling rate of this material with less than 0.1–0.5 vol.% of precipitated Cr₂N was specified as 30 °C/min. The microhardness of the matrix in samples annealed at different temperatures decreased with the diffusion of nitrogen from the matrix to grain boundaries.     

Cloud point extraction and flame atomic absorption spectrometry combination for copper(II) ion in environmental and biological samples

A cloud point extraction procedure was presented for the preconcentration of copper(II) ion in various samples. After complexation by 4-(phenyl diazenyl) benzene-1,3-diamine (PDBDM) (chrysoidine), copper(II) ions were quantitatively recovered in Triton X-114 after centrifugation. 0.5 ml of methanol acidified with 1.0 mol L⁻¹ HNO₃ was added to the surfactant-rich phase prior to its analysis by flame atomic absorption spectrometry (FAAS). The influence of analytical parameters including ligand, Triton X-114 and HNO₃ concentrations, bath temperature, heating time, centrifuge rate and time were optimized. The effect of the matrix ions on the recovery of copper(II) ions was investigated. The detection limit (3S.D._b/m, n = 10) of 0.6 ng mL⁻¹ along with preconcentration factor of 30 and enrichment factor of 41.1 with R.S.D. of 1.0% for Cu was achieved. The proposed procedure was applied to the analysis of various environmental and biological samples.     

Adsorption of platinum(IV) and palladium(II) from aqueous solution by thiourea-modified chitosan microspheres

The chitosan microparticles were prepared using the inverse phase emulsion dispersion method and modified with thiourea (TCS). TCS was characterized by scanning electron microscope (SEM), the Fourier transform infrared (FT-IR) spectra, sulfur elemental analysis, specific surface area and pore diameter. The effects of various parameters, such as pH, contact time, initial concentration and temperature, on the adsorption of Pt(IV) and Pd(II) by TCS were investigated. The results showed that the maximum adsorption capacity was found at pH 2.0 for both Pt(IV) and Pd(II). TCS can selectively adsorb Pt(IV) and Pd(II) from binary mixtures with Cu(II), Pb(II), Cd(II), Zn(II), Ca(II), and Mg(II). The adsorption reaction followed the pseudo-second-order kinetics, indicating the main adsorption mechanism of chemical adsorption. The isotherm adsorption equilibrium was well described by Langmuir isotherms with the maximum adsorption capacity of 129.9 mg/g for Pt(IV) and 112.4 mg/g for Pd(II). The adsorption capacity of both Pt(IV) and Pd(II) decreased with temperature increasing. The negative values of enthalpy (ΔH°) and Gibbs free energy (ΔG°) indicate that the adsorption process is exothermic and spontaneous in nature. The adsorbent was stable without loss of the adsorption capacity up to at least 5 cycles and the desorption efficiencies were above 95% when 0.5 M EDTA–0.5 M H₂SO₄ eluent was used. The results also showed that the preconcentration factor for Pt(IV) and Pd(II) was 196 and 172, respectively, and the recovery was found to be more than 97% for both precious metal ions.     

Synthesis and Characterization of Some Transition Metal Chelates of 5-(1-Hydroxy-6-Naphthylazo-3-Sodium Sulphonate) Thiobarbituric (L1) and Barbituric (L2) Acids

1.IntroductionThereisaconsiderableinterestinthechemistryofbarbituricandthiobarbituricacidderivativesbecauseoftheirabilitytofunctionaschelatingagentsutilizedfortheanalyticaldeterminationofalargenumberoftransitionmetalions[1~6].Theaimofthepresentstudyistoprepareandelucidatethestructureofthemetalchelatesformedbycombinationof5-(1-hydroxy-6-naphthylazo-3-sodiumsulphonate)thiobarbituricandbarbituricacidswithsometransitionmetalions(VO'+,Mn'+,Fe3+lCos+)Niz+andCu:+).2.ExperimentalAllthechemicalsused…     

Interpolymer complexation between copovidone and carbopol and its effect on drug release from matrix tablets

The interaction between copovidone and Carbopol 907 is pH dependent. When the pH of an aqueous solution fell below pH 4.5, a water-insoluble complex began to form and precipitate. This complex resulted from a hydrogen-bond-induced interaction between the carboxylic groups in Carbopol 907 and the carbonyl groups of N-vinylpyrrolidone repeat units in copovidone. Consisting of these two polymers at an approximate 1:1 weight ratio, the complex was an amorphous material with a glass transition temperature of 157?°C. The interpolymer complexation in situ was applied to modify drug release properties of Carbopol 907-based theophylline matrix tablets. The effect of copovidone on drug release was dependent on the pH of the dissolution medium. In a 0.1 N hydrochloride acid solution at pH 1.2 and 50?mM acetate buffer at pH 4.0, an insoluble tablet matrix was formed as a result of the in situ interpolymer complexation, and theophylline was released therefore via Fickian diffusion. In a 50?mM phosphate buffer at pH 6.8, drug release from the matrix tablets was still impacted by the in situ interpolymer complexation because of the low-pH microenvironment induced by Carbopol 907. As a result, drug release rate of the matrix tablet containing both polymers at pH 6.8 was slower than that of the matrix tablets containing individual polymers. We observed similar drug release rates at both pH 1.2 and pH 6.8 between tablets containing the physical blend of these two polymers and tablets containing preformed interpolymer complexes.     

Impact of the transition metal ion-doped on the electrical and magnetic properties of La0.67Ca0.33MnO3Ag0.15-based polycrystalline ceramics

In this work, high-quality La_0.67Ca_0.33MnO₃:Ag_0.15 and La_0.67Ca_0.33Mn_0.98B_0.02O₃:Ag_0.15 (B = Fe, Co, Ni) ceramics were prepared by the sol–gel route. The slight substitution of the Mn sites has significantly affected the metal–insulator transition and the ferromagnetic–paramagnetic transition. The Mn site doping leads also to a decrease in the temperature of the metal–insulator transition, an enhancement in resistivity, and a reduction in the saturation magnetization. More specifically, the Fe doping approach can significantly increase the peak temperature coefficient of resistance (TCR_peak), since the TCR_peak increases from 62.5%·K^?1 to 75.4%·K^?1. In addition, Fe, Co, and Ni doping can effectively elevate the peak magnetoresistance (MR_peak), of which the modification induced by Fe is the most significant since it enhances from 71.5% to 87.0%. Both the TCR_peak and MR_peak obtained are the highest in the current study, which can greatly promote the application of the manganate materials in the field of infrared detection and magnetic sensitivity.     

Applicability of the polymeric precursor method to the synthesis of nanometric single- and multi-layers of Zn1?xMnxO (x?=?0–0.3)

Polymeric precursor method (Pechini) was employed to fabricate single- and multilayers of Zn_1−x Mn _x O (x = 0–0.3) on glass substrates. X-ray diffraction measurements revealed that crystal structure of Zn_1−x Mn _x O multilayers is the typical hexagonal würzite structure of pristine ZnO. A reduced peak intensity and widened full width half maximum (FWHM) value of prominent peaks suggested that the Mn²⁺ ions have substituted the Zn²⁺ ion without changing the würzite structure of pristine ZnO up to Mn concentrations x ≤ 0.2. A distinct redshift of the absorption edge was observed as the Mn concentration x was increased. Additionally, the absorption edge was less sharp due, probably, to s–d and p–d interactions, which give rise to band gap bowing. Nevertheless, amorphous states appearing in the band gap as a consequence of reduced crystallinity may also be responsible for the shrinking of the band gap in this material. Interestingly, the field dependence of the magnetization showed typical paramagnetic behavior for all the chosen Mn concentrations with no evidence of ferromagnetic ordering. Probably, the absence of ferromagnetism in the studied Zn_1−x Mn _x O films is strongly related to defects (say Mn impurities at the interface between nano-crystallites) in ZnO due to partial substitution of host Zn ions by Mn ions.     

Electrochemical preparation of Fe-Mn alloy film in organic bath

Fe-Mn alloy films have been prepared by electrodeposition in an organic bath containing FeCl₂ + MnCl₂ in dimethyl formamide. The electroreduction of Mn(II) was irreversible and the diffusion coefficient of Mn(II) was calculated to be 8.0 × 10^− 11 m² s^− 1 at 298 K. An amorphous film of Fe-Mn was obtained by potentiostatic electrolysis. The Mn content varied from 4.8 at.% to 72.3 at.% with increase in the applied cathodic potential. Scanning electron microscope investigation showed that the deposited film was homogeneous and consisted of spherical particles. Nano-sized pores were observed in the surface of these particles. After heat treatment at 773 K, large crystal grains formed and X-ray diffraction patterns indicate that solid solution of Mn in γ-Fe occurred. The alloying temperature of the Fe-Mn film was determined to be 1013 K using differential thermal analysis.     

Control of Swelling of Responsive Nanogels by Nanoconfinement

The volume phase transition (VPT) behavior and the swelling properties of individual thermoresponsive poly(N‐isopropylacrylamide) (PNIPAM)‐based nanogels are investigated by in situ atomic force microscopy (AFM). Using a template‐based synthesis method, cylindrical nanogels are synthesized for different polymerization times within nanopores (80 nm) of poly(ethylene terephthalate) (PET) track‐etched membranes. The confinement conditions, characterized by the ratio Φ between the average chain length and the pore diameter, are varied between 0.35 and 0.8. After dissolving the membranes, the volume of individual nanogels composed of PNIPAM‐g‐PET diblock copolymers is numerically extracted from AFM images while varying the water temperature from 28 to 44 °C. From the measured volumes, the swelling of nanogels is investigated as a function of both the water temperature and the confinement conditions imposed during the synthesis. Contrary to the VPT, the maximum swelling of the nanogels is strongly affected by these confinement conditions. The volume of nanogels in the swollen state can reach 1.1 to 2.1 times their volume in the collapsed state for a ratio Φ of 0.8 and 0.5, respectively. These results open a new way to tune the swelling of nanogels, simply by adjusting the degree of confinement imposed during their synthesis within nanopores, which is particularly interesting for biomedical applications requiring a high degree of control over swelling properties, such as drug‐delivery nanotools.     

Precipitation during aging in N-containing austenitic stainless steels

Two different N-containing austenitic stainless steels were aged at temperatures from 600 to 800 °C for 10 to 1000 min in order to study the precipitation kinetics. In general, the fastest precipitation occurred in the aged steel with higher content of interstitial solutes, named 24Cr–15Ni–4Mn–0.32N–0.04C steel. Time-temperature-precipitation, TTP, diagrams showed that the intergranular precipitation of M₂₃C₆ and M₂N preceded to the intragranular precipitation of M₂N and M₂N and η phase in the aged 24Cr–15Ni–4Mn–0.32N–0.04C and 12Cr–12Ni–10Mn–5Mo–0.24N–0.02C steels, respectively. Besides, the presence of cellular precipitation of austenite and M₂N was observed to occur in the aged 24Cr–15Ni–4Mn–0.32N–0.04C steel.     

Spectroscopic investigations on hybrid nanocomposites: CdS : Mn nanocrystals in a conjugated polymer

We have used electron paramagnetic resonance (EPR) spectroscopy for investigating the properties of spins, such as those carried by polarons which carry both spin and charge in poly (meta/para phenylene) PMPP: CdS doped Mn based nanocomposites. To identify the nature of paramagnetic species in PMPP matrix, we have studied the effect of different physical parameters. It was found that we are in presence of trapped polarons and localized spins which concentration has been estimated. Moreover, spin–spin and spin–lattice relaxation rates have been calculated. Then, we discussed the results of optical and EPR study on the hybrid nanocomposite (CdS nanostructures, doped with manganese (II) ions, incorporated in PMPP conjugated polymer matrix). The optical spectra of these nanocomposites were compared to the existing models of energy levels in quantum dots. Moreover, by the use of electronic paramagnetic resonance, conclusions about the location and the symmetry of Mn²⁺ ions have been drawn. The nanocomposite energy gap is in the 3.2–3.3 eV range. The size of the nanoparticle is about 3.3 nm and Mn²⁺ ions are located at or near the nanoparticle surface.     

Thermophysical and Magnetic Properties of Carbon Beads Containing Nickel Nanocrystallites

Ferromagnetic and superparamagnetic nickel nanocrystallites, stabilized in a carbon matrix, were prepared by a three-step procedure including formation of a Ni acrylamide complex, followed by frontal polymerization and pyrolysis of the polymer at various temperatures. It was found that the procedure applied enables fabrication of magnetic beads containing metallic nanocrystallites embedded in a carbon matrix. The size of the crystallites, their morphology, volume fraction, and magnetic properties can be tailored by the pyrolysis temperature. The size of the crystallites affects their behavior in an external magnetic field, i.e., a heating process is the most effective for a sample pyrolyzed at 873 K. The revealed H ⁿ-type dependence of the temperature increase rate, (dT/dt) _t=0, on the amplitude of the magnetic field indicates the presence of both superparamagnetic and ferromagnetic particles in all the samples studied since n > 2. For the superparamagnetic particles, the heating mechanism is associated with Néel relaxation. For the lower values of the magnetic field amplitude, H <  H ₀, the relaxation losses dominate whereas for the opposite case, H >  H ₀, the magnetic hysteresis is the main source of thermal energy losses. The composites containing magnetic Ni nanocrystallites entrapped in a carbon matrix can be potentially applied for hyperthermia treatment.     

A Magnetofluorescent Carbon Dot Assembly as an Acidic H2O2‐Driven Oxygenerator to Regulate Tumor Hypoxia for Simultaneous Bimodal Imaging and Enhanced Photodynamic Therapy

Recent studies indicate that carbon dots (CDs) can efficiently generate singlet oxygen (¹O₂) for photodynamic therapy (PDT) of cancer. However, the hypoxic tumor microenvironment and rapid consumption of oxygen in the PDT process will severely limit therapeutic effects of CDs due to the oxygen‐dependent PDT. Thus, it is becoming particularly important to develop a novel CD as an in situ tumor oxygenerator for overcoming hypoxia and substantially enhancing the PDT efficacy. Herein, for the first time, magnetofluorescent Mn‐CDs are successfully prepared using manganese(II) phthalocyanine as a precursor. After cooperative self‐assembly with DSPE‐PEG, the obtained Mn‐CD assembly can be applied as a smart contrast agent for both near‐infrared fluorescence (FL) (maximum peak at 745 nm) and T₁‐weighted magnetic resonance (MR) (relaxivity value of 6.97 mM^?1 s^?1) imaging. More interestingly, the Mn‐CD assembly can not only effectively produce ¹O₂ (quantum yield of 0.40) but also highly catalyze H₂O₂ to generate oxygen. These collective properties of the Mn‐CD assembly enable it to be utilized as an acidic H₂O₂‐driven oxygenerator to increase the oxygen concentration in hypoxic solid tumors for simultaneous bimodal FL/MR imaging and enhanced PDT. This work explores a new biomedical use of CDs and provides a versatile carbon nanomaterial candidate for multifunctional nanotheranostic applications.     

Coarsening of δ-Ni<Subscript>2</Subscript>Si precipitates in a Cu–Ni–Si alloy

The coarsening behavior of rod-shaped and spherical δ-Ni₂Si precipitates in a Cu–1.86 wt% Ni–0.45 wt% Si alloy during aging at 823–948 K has been investigated by measuring both precipitate size by transmission electron microscopy (TEM) and solute concentration in the Cu matrix by electrical resistivity. The rod-shaped δ precipitates have an elongated shape along 〈[`5] 5 8 \overline{5} 5 8 〉_m and a {110}_m habit-plane facet. The coarsening theory of a spherical precipitate in a ternary alloy developed by Kuehmann and Voorhees (KV) has been modified to a case of rod-shaped precipitates. The coarsening kinetics of average size of the rod-shaped and spherical δ precipitates with aging time t obey the t ^1/3 time law, as predicted by the modified KV theory. The kinetics of depletion of the supersaturation with t are coincident with the predicted t ^−1/3 time law. Application of the modified KV theory has enabled calculation of the energies of sphere, {110}_m and rod-end interfaces from the data on coarsening alone. The energy of the {110}_m interface having a high degree of coherency to the Cu matrix is estimated to be 0.4 J m⁻², the incoherent sphere-interface energy 0.6 J m⁻², and the rod-end interface energy 5.2 J m⁻².