First-principles study of the nanotubes from the TiO<Subscript>2</Subscript> hexagonal sheet

Using the method based on the density functional theory, the geometric and electronic properties of the TiO₂ single-wall nanotubes, constructed by rolling the most stable nanosheet along the (n, 0) and (n, n) directions, have been investigated systematically. The nanotubes with size from n?=?6 up to n?=?20 have been modeled and studied. The strain energies of the nanotubes decrease monotonically as the radii of the nanotubes increase, regardless of the rolling direction. The band gaps of the nanotubes are increasing with the increase of the n value, approaching the value of the nanosheet. However, there is one nanotube significantly different from the others, i.e., the (6, 0) nanotube. The substantial structural change of (6, 0) nanotube causes a reduction of the band gap. Then, the isovalent sulfur (S) substitution and adsorption with the (6, 0) nanotube have been studied. Energetically, S adsorption at the inner surface is preferred. Electronically, the band gaps are further reduced by 35% for S substitution of oxygen and 22% for S adsorption, respectively, making the nanotube visible light-sensitive.     

Investigation of Size and Shape Dependencies of Phase Diagrams of the Ising Nanofilms and Nanotubes on the Honeycomb Lattice Using Cellular Automata Simulation Approach

Size and shape dependencies of phase diagrams of the Ising nanofilms and nanotubes on the honeycomb lattice are investigated by means of probabilistic cellular automata simulation based on Glauber algorithm. The values of reduced critical temperature, K _c = k _B T _c/J (where k _B and J are the Boltzmann constant and nearest-neighbor coupling, respectively), for both nanofilms and nanotubes, are obtained at the different sizes of the lattices and the dependency of K _c to the number of layers is studied. By increasing the number of layers K _c increases but for number of layer more than 8, the critical temperature increases very slowly. We have shown that between two isotropic nanotubes with the same number of spins, the ones with greater diameter (more spins on the edge) have larger critical temperature. For equal size of lattices, the obtained values of K _c for nanotube are greater than the nanofilm, but for large sizes, this difference disappears.     

Synthesis and Properties of Ceramics Based on a Layered Bismuth Calcium Cobaltite

Bi₂Ca₂Co _x O _y (x = 0.5, 1.7, 2.8) ceramics have been prepared by solid-state reactions and their thermophysical, electrical-transport, and thermoelectric (functional) properties have been studied. The results demonstrate that increasing the cobalt oxide concentration in the ceramics leads to an increase in their thermal conductivity, electrical conductivity, and thermal diffusivity and a reduction in their apparent density. The largest Seebeck coefficient is offered by a single-phase ceramic with the composition Bi2Ca2Co1.7Oy, which in addition has the highest power factor (P₃₀₀ = 26.0 μW/(m K²)) and thermoelectric figure of merit (ZT₁₀₀₀ = 0.019) and the smallest linear thermal expansion coefficient (α = 9.72 × 10^–6 K^–1).     

Fabrication and characterization of thermo-responsive GO nanosheets with controllable grafting of poly(hexadecyl acrylate) chains

A series of novel poly(hexadecyl acrylate)-grafted-graphene oxides (PHDA-g-GOs) were fabricated as thermo-responsive GO nanosheets via diazonium addition and surface-initiated atom transfer radical polymerization (SI-ATRP). Various spectroscopic and microscopic evidences confirm the successful fabrication of the thermo-responsive GO nanosheets. The thermo-responsive property and thermal stability of the PHDA-g-GOs were determined by DSC and TGA. Furthermore, we have demonstrated the ability to systematically tune the chain length of polymer molecules covalently bonded to GO nanosheets by SI-ATRP. Comparing the thermo-responsive GO samples, the ?H _m and ?H _c increased as the molar ratio of monomer to initiator increased. Moreover, the T _mo, T _co, ?H _m and ?H _c values of the PHDA-g-GO3 (with a molar ratio of monomer to initiator as 1000:1) are 31.2, 31.4 °C, 79 and 76 J/g, respectively. Meanwhile, the thermo-responsive GO nanosheets have good thermal stability and shape stability. Therefore, the thermo-responsive GO nanosheet is a very promising functional material and can be used in more areas, such as the fabrication of temperature-sensitive drugs, reagents, fibers and textiles, solar energy storage and temperature sensor.     

Methods of Extracting Current Density Dependence of the Effective Activation Energy <Emphasis Type="Italic">U</Emphasis><Subscript>eff</Subscript>(J) in High <Emphasis Type="Italic">T</Emphasis><Subscript>c</Subscript> Superconductors

We have reviewed the methods of extracting current density dependence of the effective activation energy U_eff(J) from experimental data, including transport measurements and magnetic relaxations. Then we applied the method proposed by Maley etc. on our single-phase HgBaCaCuO-1223 sample to obtain the effective activation energy. The effective activation energy U_eff(J, H = 1~T) is extracted from the magnetization relaxation data. On the other hand, U_eff(J) can be theoretically estimated for the model of a sinusoidal washboard potential in superconductors. By comparing the two results we believe that the single curve obtained in the former way can be seen as real current density dependence of effective activation energy U_eff(J). In addition, we have analyzed the reasons why the magnetic decay data at various temperatures can be scaled onto a single curve. The pinning mechanism in the measured temperature range does not change, and the activation energy depends separately on the three variables: T, B, and J are thought as two important factors for this. In the temperature close to zero and near T_c, thermally assisted flux motion would no longer valid since other processes predominate.     

Monte Carlo Study of Magnetic and Thermal Phase Transitions of a Diluted Magnetic Nanosystem

Monte Carlo (MC) simulation method with the Metropolis algorithm is used to study the magnetic and thermal phase transition properties of a spherical nanoparticle. The system consists of two concentric spheres of rays R _C and R _S, respectively (R _c < R _s). For r < R _c, the spin is σ = ±3 /2 and ±1 /2, and for R _C < r ≤ R _S, the spin is S = ±7 /2, + 5/2, ±3 /2, and ±1 /2 with antiferromagnetic interface coupling. Between R _C and R _S, the sites are populated with the probability (p). We present a detailed discussion on the magnetic and thermal phase transition characteristics of the system under consideration. Our investigations show that this system can be used as a magnetic nanostructure possessing potential applications in magnetism.     

Ultralow thermal conductivity of cerium-doped Nd<Subscript>2</Subscript>Zr<Subscript>2</Subscript>O<Subscript>7</Subscript> over a wide doping range

In this paper, we report an ultralow thermal conductivity and a high-temperature phase stability of the (Nd_1?x Ce _x )₂Zr₂O_7+x system over the temperature range from room temperature to 1600 °C and over a wide composition range (0.2 ≤ x ≤ 0.8), and the (Nd_1?x Ce _x )₂Zr₂O_7+x system is therefore considered a strong candidate material for the fabrication of next-generation high-temperature thermal barrier coatings. The observed thermal conductivities (0.65–1.0 W/mK) are about 60–40% lower than those of undoped Nd₂Zr₂O₇ over the same temperature range (100–700 °C) and indicate a glass-like behavior. For comparison, the variation in the thermal conductivity with the temperature of the (Gd_1?x Ce _x )₂Zr₂O_7+x system with similar point defects was also measured, and the observed behavior was almost the same as that of undoped Gd₂Zr₂O₇ and was mostly determined by phonon–phonon scattering (λ ∝ 1/T). The effect of point defect scattering and strong phonon scattering sources (rattlers) on the thermal conductivity is also discussed in this paper. The results of this study suggest that the ultralow thermal conductivity of (Nd_1?x Ce _x )₂Zr₂O_7+x can be attributed to the presence of rattlers because of the large difference between the ionic radii of the Nd³⁺ and Ce⁴⁺ ions.     

Effect of restricted geometry and external pressure on the phase transitions in ammonium hydrogen sulfate confined in a nanoporous glass matrix

A study of heat capacity, thermal dilatation, susceptibility to hydrostatic pressure, permittivity and polarization loops was carried out on NH₄HSO₄–porous glass nanocomposites (AHS?+?PG) as well as empty glass matrices. The formation of dendrite clusters of AHS with a size, d_cryst, exceeding the pore size was found. An insignificant anisotropy of thermal expansion of AHS?+?PG showing statistically uniform distribution of AHS with random orientations of nanocrystallites over the matrix was observed. The effect of internal and external pressures on thermal properties and permittivity was studied. At the phase transition P-1???Pc, a strongly nonlinear decrease in the entropy ΔS₂ and volume strain (ΔV/V)_T2 was observed with decreasing d_cryst. The linear change in temperatures of both phase transitions P-1???Pc???P2₁/c under hydrostatic pressure is accompanied by the expansion of the temperature range of existence of the ferroelectric phase Pc, while this interval narrows as d_cryst decreases.     

Magnetic Studies in Sputtered Ni/Ti Multilayers

Magnetic properties of Ni/Ti multilayers, prepared by the DC triode sputtering method, have been studied by magnetic measurements. Both metal layers are crystalline with a (111) fiber structure when they are thicker than 20 Å. The magnetization decreases with a decrease in Ni layer thickness t _Ni and the analysis of the results at 5 K indicates the presence of a dead Ni layer about 13 Å thick. The effective anisotropy K _eff of Ni/Ti multilayers is obtained using a torque magnetometer. Spin-wave theory has been used to explain the temperature dependence of the magnetization. Approximate values for bulk exchange interaction J _b, surface exchange interaction J _S and interlayer coupling strength J _I for various Ni layer thicknesses have been obtained.     

Dielectric properties of nanosilica filled epoxy nanocomposites

This paper presents the development of epoxy-silica nanocomposites and characterized for dielectric properties. The effect of nanosilica loading (0–20 wt%), frequency, temperature and sea water aging on these properties was studied. Transmission electron microscopy (TEM) analysis of the samples showed an excellent dispersion. However, at higher silica loading TEM showed inter-contactity of the particles. The dielectric constant (ε′) increased with silica loading and reached an optimum at about 10 wt%. The ε′ of the nanocomposites showed linear decrease with frequency whereas AC conductivity (σ _ac) increases. The σ _ac and ε′ increased marginally with temperature and sea water aging.     

Thermoelectric performance of <Emphasis Type="Italic">n-type</Emphasis> (PbTe)<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>(CoTe)<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> composite prepared by high pressure sintering method

Composites of nominal composition (PbTe)_1?x(CoTe) _x (x?=?0–0.18) were fabricated by high pressure (6 GPa) sintering (773 K) method. The thermoelectric performances were investigated in the temperature range of 293–773 K. The experimental results show that CoTe utilized as the secondary phase can remarkably enhance the TE properties of PbTe, of which the highest ZT value reaches 0.88 at 473 K when x?=?0.14. The enhancement of TE performance owes much to its high electric conductivity of CoTe. Meanwhile, the high pressure sintering (HPS) samples consist of nanoparticle, which significantly enhances the boundary scattering on carriers, decreases thermal conductivity, and increases Seebeck coefficient. All the results indicate that HPS method and the addition of CoTe-composite are effective methods to enhance the thermoelectric performance of PbTe as a potential TE material.     

Phase Distribution and Magnetic Properties of Mechanically Alloyed Hard/Soft Ferrite Nanocomposites

Improvement in the magnetic properties of hard/ soft ferrite nanocomposites was studied by varying the composition of the soft phase in SrFe₁₂O₁₉/Ni_0.5Zn_0.5Fe₂O₄ nanocomposites. The SrFe₁₂O₁₉/Ni_0.5Zn_0.5Fe₂O₄ nanocomposites were prepared using the mechanical alloying method. The samples were prepared by varying the amount of the soft phase from 10 to 50 wt% while the amount of the hard phase remained 100 wt% in the ferrite nanocomposites. X-ray diffraction (XRD), a vibrating sample magnetometer (VSM), and a transmission electron microscope (TEM) were used to characterize the samples. From the result, it was found that the nanocomposite magnet with 10 wt% of soft phase content had the highest remanence ratio, M _r / M _s , which was 0.61, while the values of the coercivity, H _c , and magnetization, M _s , measured were 4482.4 G and 9.71 emu/g, respectively, and the average particle size of the ferrite nanocomposites was < 50 nm for all the samples. It was also shown that H _c decreased as the weight percent of the soft ferrite increased, which resulted from the dipolar interaction that occurred in the ferrite nanocomposites, showing the effect of phase distribution on the magnetic properties.     

Temperature-Dependent Thermal Conductivity of High Strength Lightweight Raw Perlite Aggregate Concrete

Twenty-four types of high strength lightweight concrete have been designed with raw perlite aggregate (PA) from the Erzincan Mollaköy region as new low-temperature insulation material. The effects of the water/cement ratio, the amount of raw PA, and the temperature on high strength lightweight raw perlite aggregate concrete (HSLWPAC) have been investigated. Three empirical equations were derived to correlate the thermal conductivity of HSLWPAC as a function of PA percentage and temperature depending on the water/cement ratio. Experimentally observed thermal conductivities of concrete samples were predicted 92 % of the time for each set of concrete matrices within 97 % accuracy and over the range from 1.457 W · m^?1 · K^?1 to 1.777 W · m^?1 · K^?1. The experimental investigation revealed that the usage of raw PA from the Erzincan Mollaköy region in concrete production reduces the concrete unit mass, increases the concrete strength, and furthermore, the thermal conductivity of the concrete has been improved. The proposed empirical correlations of thermal conductivity were considered to be applicable within the range of temperatures 203.15 K ≤ T ≤ 303.15 K in the form of λ = a(PAP ^b ) + c(T ^d ).     

Radar absorbing properties of carbon nanotubes/polymer composites in the V-band

This research is devoted to the study of radar absorbing properties of the composites, based on the epoxy binder and carbon nanotubes (CNT) in the frequency range of 52–73 GHz. Three species of unmodified multi-walled CNT differing in length and diameter were investigated as fillers. The reflection coefficients (K _refl) at the radar absorbing material (RAM)–air interface and the electro-magnetic radiation (EMR) absorption coefficients (K _abs) in the materials with the different content of nanotubes were measured (K _refl and K _abs were calculated using the highest (the worst) value of the voltage standing-wave ratio (VSWR) in the frequency range of 52–73 GHz). It was established that the increase in nanotubes aspect ratio (a ratio of CNT length to its diameter) leads to K _abs rising for polymer composites. Also, CNT diameter decrease leads to K _refl reduction. CNT of 8–15 nm in diameter and more than 2 μm in length are the most effective from all investigated fillers. The reflection loss values were calculated and CNT optimal concentrations were obtained at different thickness of RAMs.     

Effect of the Mn/Fe Ratio on the Microstructure and Magnetic Properties in the Powder Form (Fe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)<Subscript>2</Subscript>P System

The structure, morphology, and magnetic properties of the mechanically alloyed iron manganese phosphides (Fe_1?x Mn _x )₂P with 0.15 ≤ x ≤ 0.75 (Mn/Fe ratio = 0.17, 0.33, 0.66, and 3) have been studied by means of X-ray diffraction, scanning electron microscopy coupled with energy-dispersive X-ray spectrometry, and BS1 and BS2 magnetometry. The powder form (Fe_1?x Mn _x )₂P compounds exhibit multiphase structures that contain Fe(Mn)-type solid solution and Fe₂P-type, Mn₂P-type, Fe₃P-type, and MnP/FeP-type phosphides. The magnetization versus temperature reveals the existence of multiple magnetic phase transitions. The saturation magnetization, coercivity, and squarness M _r/M _s ratio values are discussed as a function of both the Mn content and the temperature. From the approach to saturation magnetization studies, several fundamental magnetic parameters were extracted. The local magnetic anisotropy constant K ₁ was determined.     

Facile synthesis of magnetic–plasmonic nanocomposites as <Emphasis Type="Italic">T</Emphasis><Subscript>1</Subscript> MRI contrast enhancing and photothermal therapeutic agents

Nanocomposites combining magnetic and plasmonic components have received widespread attention in recent years due to their potential applications in biomedical research. Herein, we describe a facile method for growing small iron oxide nanoparticles on various plasmonic core materials with different shapes and surfaces by utilizing a polypyrrole interlayer. By focusing on Au nanorod@polypyrrole@iron oxide (Au NR@PPy@Fe _x O) nanocomposites, we show that these systems exhibit a low r ₂/r ₁ ratio of 4.8, making them efficient T ₁ positive contrast-enhancing agents for magnetic resonance imaging (MRI). Moreover, we show that the nanocomposites are excellent photothermal agents in the second near infrared region, with high photothermal conversion efficiency, reaching up to 46%. In addition, the Au NR@PPy@Fe _x O nanocomposites show very low cytotoxicity. In summary, the present results highlight the great potential of the synthetic method and the nanocomposites developed in this study for T ₁ MRI and/or infrared thermal imaging-guided photothermal cancer therapeutic applications.

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Sorption of radioactive iodine from aqueous medium at 25°C on granulated sorbents containing nitrates of <Emphasis Type="Italic">d</Emphasis> elements

Sorption of various species of radioactive iodine from aqueous phase at 25°C with granulated sorbents based on silica gel of the MSKG type, containing nitrates of d elements, was studied. Sorbents containing Zn, Ni, Cu, and Co, both nonmodified and modified, have low distribution coefficients K _d for ¹³¹I^? and ¹³¹IO ₃ ^? (at V/m = 1000, K _d < 120 ml g^?1). Whereas nonmodified sorbents do not noticeably sorb I₂ from the aqueous phase (at V/m = 1000, K _d < 10 ml g^?1), their modified analogs adsorb molecular iodine species and have K _d ～ 170–250 ml g^?1 at V/m = 1000. The study of sorption of radioactive iodine species with granulated sorbents containing silver nitrate showed that nonmodified sorbents have relatively low distribution coefficients K _d for all species of radioactive iodine (at V/m = 1000, K _d < 100 ml g^?1). At the same time, the modified sorbents containing Ni and Ag sorb not only I₂ (at V/m = 1000, K _d ～ 270 ml g^?1) but also ¹³¹I^? and ¹³¹IO ₃ ^? ions from aqueous solutions (at V/m = 1000, K _d ～ 3100 and 1500 ml g^?1, respectively).     

Hybrid Intercalative Nanocomposites

This review focuses on organic-inorganic hybrid nanocomposites, a research area that has made rapid progress in recent years. Inorganic components (hosts) include both natural materials (clays, silicates, smectites, layered phosphates, and others) and compounds prepared by different synthetic techniques. Into their interlayer spaces, various organic guests—solvents, monomers, and polymers—can be intercalated. Among the hybrid nanocomposites analyzed in detail are those based on polyconjugated electrically conducting polymers, such as poly(aniline) and poly(pyrrole), and various mineral matrices. Particular attention is paid to polymer-metal chalcogenide nanocomposites and their applications as semiconducting materials. One of the most common and practically important intracrystalline processes in the fabrication of hybrid nanocomposites is the incorporation of monomer molecules into pores of the host, followed by controlled internal transformations into polymer, oligomer, or hybrid-sandwich products (in situ postintercalative transformations). This approach is often called “ship-in-the-bottle” polymerization. Another widely used approach is the incorporation of macromolecules into layered host lattices from solutions or melts. This process offers the possibility of producing graphite intercalation compounds and inorganic-organic multilayer composites, including self-assembled nanocomposites in the form of (P/M) _n multilayers, where M and P are oppositely charged inorganic and polymer nanolayers.     

Sorption of Molybdenum onto Titanium Hydroxide

Three types of ionic groups with different pK_i values were revealed for T-5 sorbent by potentiometric titration: for acid groups, pK₁ = 7.5 ± 0.5, pK₂ = 10.2 ± 0.5, and pK₃ = 11.0 ± 0.2; for base groups, pK₄ = 6.5 ± 0.2, pK₅ = 4.5 ± 0.2, and pK₆ = 2.7 ± 0.2. Thus, titanium hydroxide is an amphoteric ion exchanger. Each exchange group of T-5 sorbent, characterized by its definite pK_i value, was assigned to a definite hydroxy group. T-5 and T-52 sorbents exhibit high specificity to Mo in acid and neutral solutions. All the isotherms logC_S–logC_L are described by the Langmuir equation for the polyfunctional sorbent for at least two exchange sites in both nitric and sulfuric acid solutions, irrespective of the Mo speciation. Two groups of values were obtained and confirmed for T-5 and T-52 sorbents depending on the Mo concentration: k_d ≈ 10⁴ mL g^–1 at concentrations lower than 10^–5 M and k_d = 1000–2000 mL g^–1 at a concentration of 10^–5 M. The exchangeable hydroxy groups in T-5 sorbent exhibit high heat resistance, and even the sorbent calcined at 900°C preserves certain reliably measurable capacity for Mo. For T-5, the capacity for Mo only slightly depends on the solution acidity and composition and is about ~1 mmol g^–1.     

Aqueous and mechanical exfoliation,unique properties,and theoretical understanding of MoO<Subscript>3</Subscript> nanosheets made from free-standing α-MoO<Subscript>3</Subscript> crystals: Raman mode softening and absorption edge blue shift

Crystalline α-MoO₃ belts consisting of nanosheets stacked along their [010] axes were synthesized via thermal vapor transport of MoO₃ powders at elevated temperatures. The MoO₃ belts were millimeters in length along their [001] axes and tens to hundreds of micrometers in width along their [100] axes. Mechanical and aqueous exfoliations of the belts to form two-dimensional (2D) nanosheets were processed via the scotch-tape and bovine serum albumin (BSA) assisted methods, respectively. Upon scotch-tape exfoliation, the Raman features of MoO₃ exhibited monotonic decreases in intensity as the thickness was gradually fell to approach that of a 2D nanosheet. Most Raman features eventually disappeared when a monolayer nanosheet was produced, except for the Mo–O–Mo stretching mode (Ag) at ~818 cm^?1, which was accompanied by mode-softening of up to 5 cm^?1. This mode softening, hitherto not reported for 2D α-MoO₃ nanosheets, can be attributed to lattice relaxations that are validated here via theoretical density functional perturbation theory calculations. The BSA-assisted exfoliation products exhibited a blueshift in the α-MoO₃ nanosheet absorption edge; they also revealed an absorption peak at 3.98 eV that can be attributed to their intrinsic exciton absorptions. These observations, together with the facile synthesis of high-purity α-MoO₃ crystals, illuminate the possibility of further 2D α-MoO₃ nanosheet production and lattice dynamic studies.

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