Synthesis and characterization of novel nontoxic BiFe1−xAlxO3/mica-titania pigments with high NIR reflectance

A series of novel nontoxic near-infrared (NIR) reflective pigments based on Al-doped BiFeO₃ coated mica-titania were synthesized by precipitation combined with sol-gel method. The pigments of the formula BiFe_1−xAl_xO₃/mica-titania (x = 0, 0.1, 0.2, 0.3, 0.4) were characterized by XRD, FE-SEM, TG-DTA, UV–vis–NIR spectrophotometer and CIE L^* a^* b^* color scales. The results illustrate that the BiFeO₃ nanoparticles are coated on the surface of mica-titania uniformly, and the doped BiFe_1−xAl_xO₃/mica-titania is similar to BiFeO₃/mica-titania composite in morphology. Furthermore, the absorption edge of composite pigments shift to shorter wavelength (533–495 nm) can be attributed to O_2p-Fe_3d charge transfer transitions and change the color of the pigments from brown to orange. Additionally, the NIR solar reflectance of the powdered pigments and pigmented coatings were measured. The results reveal that with the increase of progressive doping of Al³⁺ for Fe³⁺, the NIR solar reflectance of the pigments increase gradually and exhibit higher NIR solar reflectance (R* ≥ 47.8%) than the conventional pigment of similar color. Moreover, we also evaluated the thermal and chemical stability of the pigments. In conclusion, the pigments have the potential to be applied as “cool pigments”.     

A novel rare-earth high-entropy RE6MoO12 with high near-infrared reflectance as a promising inorganic “cool pigment”

Inorganic “cool pigments” exhibit excellent application potential in double-carbon strategies and energy savings. High-entropy RE₆MoO₁₂ inorganic “cool pigments” with a disordered defect-fluorite-type structure namely, (La_0.25Y_0.25Er_0.25Ho_0.25)₆MoO₁₂, (Nd_0.25Y_0.25Er_0.25Ho_0.25)₆MoO₁₂ and (Tb_0.25Y_0.25Er_0.25Gd_0.25)₆MoO₁₂, were prepared through a solid-state reaction for the first time. The optical properties, color performance and thermal insulation of these materials were characterized. These pigments exhibited a high near-infrared (NIR) reflectance of 81–98%. The average NIR reflectance of the (La_0.25Y_0.25Er_0.25Ho_0.25)₆MoO₁₂ (97.31%) and (Nd_0.25Y_0.25Er_0.25Ho_0.25)₆MoO₁₂ (92.50%) pigments were greater than 90%. The high-entropy RE₆MoO₁₂ pigments possessed better chemical stabilities in acid-alkali tests than single components. In addition, the thermal conductivity of the fully dense HE-RE₆MoO₁₂ pigments was 1.05–1.16 W m^?1 K^?1 at room temperature, which is approximately 40–50% lower than that of RE₆MoO₁₂. The designed HE-RE₆MoO₁₂ pigments showed three colors: yellow, green and brownish red. In conclusion, the multicolored high-entropy RE₆MoO₁₂ pigments possessed good potential for increasing NIR solar energy reflection, which can meet the needs of “cool pigments” performance upgrades.     

Influence of crystallite size on color properties and NIR reflectance of TiO2@NiTiO3 inorganic pigments

Crystallite size may significantly impact optical properties of inorganic pigments. However, limited studies have so far been reported in this area. In this work, TiO₂@NiTiO₃ complex pigments were synthesized by precipitation-calcination method. Results showed that the increase in calcination temperature led to the formation of TiO₂@NiTiO₃ pigments with crystallite sizes from 29 to 82.6 nm but similar morphologies and aggregate particle sizes (around 1 μm). The yellow component (b*) significantly increased by 7 with crystallite size, but the integrated NIR reflectance decreased slightly (4.02%). Also, the characteristic absorption of NiTiO₃ pigments in NIR region declined the integrated NIR reflectance values.     

Facile fabrication of cool yellow pigment with enhanced NIR reflectance by tailoring oxygen defects and its application in energy-saving building

Intensity of absorption tail at long wavelength side of absorption edge is affected by concentration of oxygen vacancy (O_v), which determines chromaticity, near-infrared (NIR) reflectance and application value of cool pigments. In this work, a feasible strategy is proposed to restrain the generation of O_v by lattice distortion to enhance color and NIR reflectance. Compression lattice is formed by introducing smaller ions of Ti⁴⁺ or Zr⁴⁺ into Tb site in SrTbO₃ host. This results in significant reduction of concentration of O_v. Compared to SrTbO₃, color component L* of SrTb_0.6Zr_0.4O₃ increases from 69.09 to 87.30. Moreover, NIR and solar reflectance are remarkably enhanced, reaching 18.3% and 19.3%, respectively. In addition, 11.6 °C and 5.6 °C decreases in temperature were observed for inner surface of roof and indoor room of simulation house. The strategy proposed in this work will contribute to developing color-cool pigments with suitable properties and high solar regulation ability.     

Electrospinning and characterization of magnetoelectric NdFeO3–PbZr0.52Ti0.48O3 Core–Shell nanofibers

A core–shell nanofiber with a neodymium orthoferrite (NdFeO₃) core and lead zirconium titanate (PbZr_0.52Ti_0.48O₃) shell was prepared in this study using the sol-gel electrospinning method. Structural properties of the nanofiber were analysed using the X-ray diffraction (XRD) method, which revealed that a perovskite structure was formed. The strain was calculated using Williamson-Hall (W–H) plot. Functional groups of the nanofiber were studied using Fourier transform infrared (FTIR) spectroscopy. Morphological studies revealed the core diameter of the nanofiber to be 65 nm and its shell diameter to be 128 nm. The elemental analysis of core-shell nanofiber was made using Energy Dispersive X-ray Spectroscopy (EDS) which proved the formation of NdFeO₃ and PbZr_0.52Ti_0.48O₃ composite in the stoichiometric ratio. Topography analysis using atomic force microscopy found the average fibre diameter to be 135 nm. The nanofiber exhibited antiferromagnetic behaviour, with a saturation magnetization of 0.48 emu/g. Dynamic contact electrostatic force microscopy (DC-EFM) studies revealed that the nanofiber showed domain-switching behaviour. The ferroelectric hysteresis plots showed that the nanofiber exhibited a maximum polarization of 5.45 μC/cm² at 20 kV/cm. Also, its dielectric constant was 268 at 100 Hz. The leakage current study revealed a butterfly-shaped J-E loop, which further proved the ferroelectric behaviour of the nanofiber. The mechanism behind the leakage current was identified to be the Schottky emission. The P-E loops recorded under external magnetic fields of different strengths exhibited variations in the polarization, indicating the presence of cross-coupling between electric and magnetic order parameters. Because of the high dielectric constant displayed by the magnetoelectrically active NdFeO₃–PbZr_0.52Ti_0.48O₃ core–shell nanofiber, it can be a promising candidate for a number of applications, such as data storage devices, multimedia devices, spintronics and magnetic field sensors.     

Theoretical analysis and synthesis of Al4O4C and Al2CO phase in the resin bonded Al-Al2O3 refractory in N2-flowing

In flowing nitrogen, Al₄O₄C and Al₂CO bonded Al₂O₃-based composite was successfully prepared by a gaseous phase mass transfer pathway at 1600 °C for 3 h after an Al-AlN core-shell structure was formed in the resin bonded Al-Al₂O₃ refractory at 580 °C for 8 h. The formation mechanism of Al₄O₄C and Al₂CO phase is as follows. An Al-AlN core–shell structure is built at 580 °C for 8 h and broken at higher temperatures, and then, Al(g) reacts with C from the resin and N₂ to form Al₄C₃ and AlN, respectively. Owing to the exothermic reaction of the Al₄C₃ and AlN formation, the reaction temperature in the resin bonded Al-Al₂O₃ refractory is above the practical environmental temperature; for instance, the reaction temperature is above 1715 °C at 1600 °C in this work. Therefore, Al₄C₃ reacts with Al₂O₃ to generate Al₄O₄C and then Al₄O₄C is transformed into Al₂OC by the reaction ${\mathrm{Al}}_4{\mathrm{O}}_{\mathrm{4}}{C(s)+\text{Al}}_4{\mathrm{C}}_{\mathrm{3}}(s)\to {\mathrm{4Al}}_{\mathrm{2}}\text{OC}(s)$ at elevated temperatures. Al₂OC solid solution is finally formed through the dissolution of AlN into Al₂OC.     

Synthesis of high near infrared reflection wurtzite structure green pigments using Co-doped ZnO by combustion method

A high near-infrared reflective green pigment with a low cobalt content, Zn_0.96Co_0.04O, was prepared by solution combustion synthesis. The pigment was characterized by XRD, SEM, TG-DSC, UV–vis and CIE L*a*b*C*h* colorimetric. The resulting green pigment showed that the chromaticity performance is better. The doping Co did not affect the main crystalline structure, all samples were retained ZnO wurtzite structure. The better green hue is a* = ?15.35 and achieved a near-infrared reflectivity up to 40%, when CoO content was x?=?0.04, combustion agent was glycine, calcination temperature was 1000?°C. The synthesized pigments have a better thermal stability, chemical stability and a small amount of cobalt oxide (2.8?wt%), and the preparation process is simple. Therefore, the green pigment of ZnO wurtzite structure has great potential in serving as cool pigments for building coatings.     

Constructing ZnCo2O4@LDH Core–Shell hierarchical structure for high performance supercapacitor electrodes

In this article, ZnCo₂O₄ nanowires deposited with two kinds of typical layered double hydroxides (Ni–Al,Co–Al LDH) are developed via scalable method. Two materials all display core–shell hierarchical structure. High specific capacitance of 2041 F g⁻¹ and 1586 F g⁻¹ are obtained for ZnCo₂O₄@Co–Al LDH and ZnCo₂O₄@Ni–Al LDH,respectively. Combining with active surface and synergistic effect, the role of hierarchical structure in enhancing performance is revealed. Moreover, two all solid state supercapacitors based on fabricated materials as positive electrodes, activated carbon as negative electrodes and PVA–KOH as polymer electrolyte are assembled. The maximum power and energy densities of ZnCo₂O₄@Co–Al LDH//AC are 6200 W kg⁻¹ and 50.1 Wh kg⁻¹, respectively. While the power and energy densities of ZnCo₂O₄@Ni–Al LDH//AC are 3400 W kg⁻¹ and 27.8 Wh kg⁻¹. At last, an energy storage–conversion system, based on solar cell as input device and assembled asymmetric supercapacitor ZnCo₂O₄@Co–Al LDH//AC as output device, is integrated as a self–sustaining power device, indicating its potential in practical applications.     

A novel SiCN@TiO2 core–shell ceramic microspheres derived from a polymeric precursor

A novel core–shell ceramic microspheres, composed of a SiCN inner core and TiO₂ nanoparticles outer shell, were prepared via emulsion technique and polymer-derived ceramics (PDCs) method. The forming process of SiCN@TiO₂ core–shell ceramic microspheres were controlled by adjusting the ratio of raw material, curing temperature and pyrolysis temperature. The morphology, chemical composition and phase transformation were characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). PVSZ@TiO₂ microspheres with good spherical structure and uniform-dispersed TiO₂ surface were fabricated at 200 °C with raw material ratio of 25%. After pyrolyzed at 1400 °C, the obtained SiCN@TiO₂ core–shell ceramic microspheres retained spherical structure. The XRD showed that the products were mainly composed of rutile TiO₂, SiC and Si₃N₄ crystalline phase, which were generated by polyvinylsilazane.     

Partial wet route for YAG powders synthesis leading to transparent ceramic: A core–shell solid-state reaction process

Synthesis of Y₃Al₅O₁₂ (YAG) powders respectively presents morphology control and chemical stoichiometry problems when employing the solid-state reaction or the wet-chemical route. YAG powder retaining the morphology of Al₂O₃ powder was designed and synthesized via a partial wet-chemical process with yttrium ions precipitating on the Al₂O₃ particles. The formation process of the Y-compound/Al₂O₃ core–shell structure is discussed on the basis of zeta-potential measurements and HRTEM results. Two stages, including direct precipitation at the surface of the Al₂O₃ particles and the assembly of the yttrium precipitate from explosive nucleation onto the yttrium compound-coated Al₂O₃ particles, are proposed. A spherical surface reaction process is illustrated. A pure YAG phase can be realized at a temperature about 300 °C lower than that of the traditional solid-state reaction process.     

Silicone-acrylic hybrid aqueous dispersions of core–shell particle structure and corresponding silicone-acrylic nanopowders designed for modification of powder coatings and plastics. Part III: Effect of modification with selected silicone-acrylic nanopowders on properties of polyurethane powder coatings

Polyurethane powder coating systems consisting of polyester resin, blocked polyisocyanate and two types of “nanopowders” containing core–shell nanoparticles where the core was silicone resin of very low glass transition temperature and the shell was poly(methyl methacrylate) were examined. The blocked polyisocyanate was synthesized using biuretpolyisocyanate obtained from ureapolyisocyanate as starting material capable for blocking and ɛ-caprolactam as blocking agent. The surface properties of cured powder coatings were investigated using scanning electron microscopy (SEM) combined with energy dispersive spectrometry (EDS), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The surface structure was correlated with the chemical structure of the coatings and macroscopic surface behavior: contact angle, surface free energy, gloss, abrasion resistance, hardness and adhesion to the steel surface.     

Preparation of core–shell structural surface molecular imprinting microspheres and recognition of l-Asparagine based on [N1111]Asn ionic liquid as template

Core–shell structural surface imprinting microspheres were prepared by a simple and effective method. This method combined reversible addition–fragmentation chain transfer (RAFT) with distillation precipitation polymerization RAFT reagent-containing microspheres on the surface. Tetramethylammonium asparagine ([N₁₁₁₁]Asn) ionic liquid or l-Asn, 4-vinylpyridine (4-VP), ethylene glycol dimethacrylate (EGDMA), and RAFT reagent-containing microspheres on the surface were used as template, functional monomer, cross-linker, and chain transfer agent (CTA), respectively. Two kinds of imprinted polymer were obtained, namely, AsnIL-MIPs and Asn-MIPs. The morphology and structure of the polymers were characterized by scanning electron microscopy and Fourier-transform infrared spectroscopy. The binding and selective recognition properties of l-Asn and its analogs were investigated in aqueous solution. Compared with l-Asn as template molecule, AsnIL-MIPs showed faster binding speed and better selective recognition. The binding reached saturation after 1 h, and the selective recognition factor (α) reached 5.28 and 4.26 for the template against l-Asp and l-Arg, respectively. AsnIL-MIPs showed an improved binding rate, binding affinity, and significantly increased recognition.     

Preparation and characterization of novel polyethylene/carbon nanotubes nanocomposites with core–shell structure

Preparation of novel polyethylene/carbon nanotubes (CNTs) nanocomposites with core–shell structure was presented. The method involved in situ ethylene polymerization in which nanotube surface was treated with Grignard Agent, followed by reacting with active transition metal compound, TiCl₄. The multiwalled carbon nanotubes (MWCNTs) supported catalysts polymerize ethylene to form polymer nanocomposite. MWCNTs were homogeneously dispersed within polymer matrix, and as expected, the resultant nanocomposites featured core–shell structure which was confirmed by HRTEM. For the nanocomposite, the microscopic examination of the cryogenically fractured surface not only ensured a good distribution of carbon nano-particles in the PE matrix but also revealed the ductile-like fracture. The Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were employed for the study of covalent sidewall functionalization and chemical bonding environment of MWCNTs, also indicated effective immobilization of titanium catalyst on the MWCNTs surface. The crystalline properties, dielectric property and thermal stability of the nanocomposites were determined by WAXD, impedance analyzer and TGA. The dielectric result showed a slight decline of the dielectric constant of the nanocomposites with increase of the polymerization time, and lower dielectric loss was also observed.     

Characterization and in vitro drug release properties of core–shell hydrogel prepared by gamma irradiation

A hydrogel system was prepared based on core–shell approach for the delivery of trifluoperazine. Acrylonitrile (AN) core and methacrylic acid (MAA) shell copolymer were performed using gamma irradiation. The resulted system has been characterized by FTIR, TGA, TEM, and SEM techniques. The in vitro release study showed that the maximum drug released was 6.11?mg?g^?1 for AN–MAA copolymer through 120?min and 22.34?mg?g^?1 for AN-core–MAAc shell through 240?min. The results demonstrated that AN-core–MAAc had better properties than AN–MAA copolymer which means the preparation technique highly affects the properties of the system.     

ZnO-capped nanorod gas sensors

This paper reports on the synthesis of pristine α-Fe₂O₃ nanorods and Fe₂O₃–ZnO core–shell nanorods using a combination of thermal oxidation and atomic layer deposition (ALD) techniques; the completed nanorods were then used for ethanol sensing studies. The crystal structure and morphology of the synthesized nanostructures were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The sensing properties of the pristine and core–shell nanorods for gas-phase ethanol were examined using different concentrations of ethanol (5–200 ppm) at different temperatures (150–250 °C). The XRD and SEM revealed the excellent crystallinity of the Fe₂O₃–ZnO core–shell nanorods, as well as their uniformity in terms of shape and size. The Fe₂O₃–ZnO core–shell nanorod sensor showed a stronger response to ethanol than the pristine Fe₂O₃ nanorod sensor. The response (i.e., the relative change in electrical resistance R_a/R_g) of the core–shell nanorod sensor was 22.75 for 100 ppm ethanol at 200 °C whereas that of the pristine nanorod sensor was only 3.85 under the same conditions. Furthermore, under these conditions, the response time of the Fe₂O₃–ZnO core–shell nanorods was 15.96 s, which was shorter than that of the pristine nanorod sensor (22.73 s). The core–shell nanorod sensor showed excellent selectivity to ethanol over other VOC gases. The improved sensing response characteristics of the Fe₂O₃–ZnO core–shell nanorod sensor were attributed to modulation of the conduction channel width and the potential barrier height at the Fe₂O₃–ZnO interface accompanying the adsorption and desorption of ethanol gas as well as to preferential adsorption and diffusion of oxygen and ethanol molecules at the Fe₂O₃–ZnO interface.     

The formation of Y5V-type fine-grained ceramics based on spherical submicron BaZr0.1Ti0.9O3@Al2O3 particles

To improve multilayer ceramic capacitors (MLCCs), thinner dielectric layers are necessary. To achieve this goal, both grain size and uniformity of the MLCC particles must be controlled effectively. In this study, the core-shell structure of submicron-sized multi-function ceramic capacitors powder was synthesized using a novel precipitation route, which controls both dispersion and particle size of BaZr_0.1Ti_0.9O₃ and BaZr_0.1Ti_0.9O₃@Al₂O₃ particles. In this paper, we investigate the effect of Al₂O₃ coating on the microstructure and the dielectric properties of BaZr_0.1Ti_0.9O₃. We found that both average grain size and maximum dielectric constant (ε_max) of the ceramics decrease with increasing concentration of Al₂O₃. Our results demonstrate that fine-grained ceramic materials can meet the specifications of the Electronic Industries Alliance Y5V with a concentration of Al₂O₃-coated of 0.25 mol percent, a permittivity of 3393 at room temperature, and an average particle size of about 400 nm.     

Water as Blowing Agent: Preparation of Environmental Thermally Expandable Microspheres via Inverse Suspension Polymerization

Water-encapsulated environment-friendly core–shell thermally expandable microspheres (TEMs) were prepared via inverse suspension polymerization under atmospheric pressure. Acrylonitrile (AN), methyl methacrylic acid (MMA), and methacrylate (MA) were used as monomers, and water was used as the core material. The influences of dispersants, monomer feed ratio, and cross-linking agent on the TEMs were systematically investigated. The water could disperse well in the continuous oil phase employing both 6?g spand 80 and 0.2?g calcium stearate as dispersants. When the feed ratio of AN/MMA/MA was set at 1:2:2 and 1,4-butanediol dimethacrylate was used as cross-linking agent, TEMs possessed excellent properties. The properties of melamine resin foamed by TEMs-encapsulated water were better than that of n-octane and TEMs-encapsulated n-octane.     

Temperature-controlled conversion from Fe–Si particles to integrated Fe–Si/SiO2 core–shell structure particles during fluidised bed chemical vapour deposition

In the synthesis of ferromagnetic/SiO₂ core–shell structures, the minimum formation conditions and evolution mechanism are worth investigating. In the present study, to determine the minimum formation temperature of an integrated Fe–Si/SiO₂ core–shell structure during chemical vapour deposition in a fluidised bed, the effects of deposition temperature on the structural and magnetic performances of SiO₂ insulation coatings on Fe–Si particles were investigated. Thermodynamic calculations and differential scanning calorimetry were used to understand the thermal decomposition of C₈H₂₀O₄Si. The results of the theoretical and structural studies showed that the minimum deposition temperature of the amorphous SiO₂ insulation coating on the Fe–Si particle surface was ~880 K and that the Fe–Si/SiO₂ composite structure started to convert into an integrated Fe–Si/SiO₂ core–shell structure after the deposition temperature was raised above 920 K. The increase in the thickness of the SiO₂ insulation layer due to the increased deposition temperature was studied using X-ray diffraction and scanning electron microscope analyses. The results of X-ray photoelectron spectroscopy showed that four and five types of electronic structures existed in the SiO₂ insulation shell for silicon and oxygen, respectively, and that only 32.74 at.% of the oxygen from the Si(OSi)₃(OH) group interacted with the Fe–Si alloy surface. The results of the performance test indicated that the integrated Fe–Si/SiO₂ core–shell structure led to a substantial enhancement in the electrical resistivity of the particles and reduction in their saturation magnetisation, but hardly affected the coercive force.