Bioactivity and mechanical properties of polydimethylsiloxane (PDMS)–CaO–SiO2 hybrids with different calcium contents

Polydimethylsiloxane (PDMS)–CaO–SiO₂ hybrids with starting compositions containing PDMS/(Si(OC₂H₅)₄+PDMS) weight ratio=0.30, H₂O/Si(OC₂H₅)₄ molar ratio=2, and Ca(NO₃)₂/Si(OC₂H₅)₄ molar ratios=0–0.2, were prepared by the sol–gel method. The apatite-forming ability of the hybrids increased with increasing calcium content in the Ca(NO₃)₂/Si(OC₂H₅)₄ molar ratio range 0–0.1. The hybrids with a Ca(NO₃)₂/Si(OC₂H₅)₄ molar ratio range 0.1–0.2 formed apatite on their surfaces in a simulated body fluid (SBF) within 12 h. The hybrid with a Ca(NO₃)₂/Si(OC₂H₅)₄ molar ratio of 0.10 showed an excellent apatite-forming ability in SBF with a low release of silicon into SBF. It also showed mechanical properties analogous to those of human cancellous bones. This hybrid is expected to be useful as a new type of bioactive material.     

Solubility and coprecipitation of barium and strontium nitrates in HNO<Subscript>3</Subscript> solutions and multicomponent systems

The solubility of Ba(NO₃)₂ and Sr(NO₃)₂ in HNO₃ solutions at 25–95°C is characterized by the power dependence on the total concentration of the nitrate ion with the exponent for Ba(NO₃)₂ equal to −2 in ∼9 M HNO₃ and −6 in more concentrated acid solutions. The latter exponent is also characteristic of the more soluble Sr(NO₃)₂ throughout the examined range of HNO₃ concentrations. In strongly acidic solutions, Ba(NO₃)₂ coprecipitates with Sr(NO₃)₂. The solubility curve for Ba(NO₃)₂ in NH₄(Na)NO₃ solutions suggests formation of a double salt, whereas in UO₂(NO₃)₂ solutions the dependence is the same as in HNO₃ solutions.     

Fabrication of spherical CaO–SrO–ZnO–SiO2 particles by sol–gel processing

This study was concerned with the fabrication of ceramic CaO–SrO–ZnO–SiO₂ spherical particles, which are novel candidates for the glass phase in glass polyalkenoate cements (GPCs). GPCs made from these glasses have potential as bone cements because, unlike conventional GPCs, they do not contain aluminum ions, which inhibit the calcification of hydroxyapatite in the body. The glass phase of GPCs require a controllable glass morphology and particle size distribution. Sol–gel processing can potentially be used to fabricate homogenous ceramic particles with controlled morphology. However, a thorough study on preparation conditions of spherical CaO–SrO–ZnO–SiO₂ particles by sol–gel processing has, to date, not been reported. In this study, gels were prepared by hydrolysis and polycondensation of tetraethoxysilane (TEOS) in an aqueous solution containing polyethylene glycol and nitrates of calcium, strontium and zinc. It was possible to control the morphology and size of the gels by varying the H₂O/TEOS molar ratio and the metal ion content in the starting compositions. An aliquot of 3–5 μm homogenous spherical particles were obtained at a H₂O/TEOS molar ratio of 42.6 when the starting composition molar ratios were Sr(NO₃):Ca(NO₃)₂:Zn(NO₃)₂:Si(OC₂H₅)₄ = x:0.12:(0.40 − x):0.48 (0 ≤ x ≤ 0.8). Starting composition limitations are caused by the low solubility of strontium ions in the minimal amount of water used and the acceleration of hydrolysis as well as polycondensation at higher water content.     

Selective growth of ZnO nanorods for gas sensors using ink-jet printing and hydrothermal processes

Selective growth of ZnO nanorod arrays with well-defined areas was developed to fabricate the NO₂ gas sensor. The seed solution was ink-jet printed on the interdigitated electrodes. Then, vertically aligned ZnO nanorods were grown on the patterned seed layer by the hydrothermal approach. The influences of seed-solution properties and the ink-jet printing parameters on the printing performance and the morphology of the nanorods were studied. Round micropattern (diameter: 650 μm) of ZnO nanorod arrays is demonstrated. The dimensions and positions of the nanorod arrays can be controlled by changing the printed seed pattern. The effects of nanorod structure and nanorod size on the gas-sensing capability of ZnO nanorod gas sensors were demonstrated. Due to the high surface-to-volume ratios of the nanorod-array structure, the ZnO nanorod gas sensor can respond to 750 ppb NO₂ at 100 °C. The sensors without baking treatment exhibit the typical response of a p-type semiconductor. However, only the response of n-type semiconductor oxides was observed after the annealing treatment at 150 °C for 2 h.     

Characterization of zirconium, lanthanum and lead oxide deposits prepared by cathodic electrosynthesis

Cathodic electrosynthesis of zirconium, lanthanum and lead oxides was performed from aqueous solutions of ZrOCl₂ · 8H₂O, La(NO₃)₃ · 6H₂O and Pb(NO₃)₂, respectively. The deposits were characterized by X-ray diffraction, thermogravimetric and differential thermal analyses. Crystallite sizes of zirconia were derived at different temperatures from X-ray broadening data. The influence of hydrogen peroxide on the electrosynthesis process, crystallization and phase evolution of deposits has been studied. A possible mechanism of electrosynthesis and the role of hydrogen peroxide are discussed.     

Solution‐Processed Wide‐Bandgap Organic Semiconductor Nanostructures Arrays for Nonvolatile Organic Field‐Effect Transistor Memory

In this paper, the development of organic field‐effect transistor (OFET) memory device based on isolated and ordered nanostructures (NSs) arrays of wide‐bandgap (WBG) small‐molecule organic semiconductor material [2‐(9‐(4‐(octyloxy)phenyl)‐9H‐fluoren‐2‐yl)thiophene]3 (WG₃) is reported. The WG₃ NSs are prepared from phase separation by spin‐coating blend solutions of WG₃/trimethylolpropane (TMP), and then introduced as charge storage elements for nonvolatile OFET memory devices. Compared to the OFET memory device with smooth WG₃ film, the device based on WG₃ NSs arrays exhibits significant improvements in memory performance including larger memory window (≈45 V), faster switching speed (≈1 s), stable retention capability (>10⁴ s), and reliable switching properties. A quantitative study of the WG₃ NSs morphology reveals that enhanced memory performance is attributed to the improved charge trapping/charge‐exciton annihilation efficiency induced by increased contact area between the WG₃ NSs and pentacene layer. This versatile solution‐processing approach to preparing WG₃ NSs arrays as charge trapping sites allows for fabrication of high‐performance nonvolatile OFET memory devices, which could be applicable to a wide range of WBG organic semiconductor materials.     

Self-Supported Pd Nanorod Arrays for High-Efficient Nitrate Electroreduction to Ammonia

Electrochemical nitrate (NO₃⁻) reduction to ammonia (NH₃) offers a promising pathway to recover NO₃⁻ pollutants from industrial wastewater that can balance the nitrogen cycle and sustainable green NH₃ production. However, the efficiency of electrocatalytic NO₃⁻ reduction to NH₃ synthesis remains low for most of electrocatalysts due to complex reaction processes and severe hydrogen precipitation reaction. Herein, high performance of nitrate reduction reaction (NO₃⁻RR) is demonstrated on self-supported Pd nanorod arrays in porous nickel framework foam (Pd/NF). It provides a lot of active sites for H* adsorption and NO₃⁻ activation leading to a remarkable NH₃ yield rate of 1.52 mmol cm⁻² h⁻¹ and a Faradaic efficiency of 78% at −1.4 V versus RHE. Notably, it maintains a high NH₃ yield rate over 50 cycles in 25 h showing good stability. Remarkably, large-area Pd/NF electrode (25 cm²) shows a NH₃ yield of 174.25 mg h⁻¹, be promising candidate for large-area device for industrial application. In situ FTIR spectroscopy and density functional theory calculations analysis confirm that the enrichment effect of Pd nanorods encourages the adsorption of H species for ammonia synthesis following a hydrogenation mechanism. This work brings a useful strategy for designing NO₃⁻RR catalysts of nanorod arrays with customizable compositions.     

ZrO<Subscript>2</Subscript> thin films on Si substrate

In the advancement of metal–oxide–semiconductor technology, Si-based semiconductor, with SiO₂ as outstanding dielectric, has been dominating microelectronic industry for decades. However, the drastic down-scaling in ultra-large-scale integrated circuitry has made ultrathin SiO₂ (~1.2 nm) unacceptable for many practical reasons. Introduction of ZrO₂ as high-κ dielectrics replacing SiO₂ is undeniably a potential yet formidable solution for the aforementioned problem. The objective of this review is to present the current knowledge of ZrO₂ thin film as gate dielectric on Si, in terms of its material and electrical properties produced by various deposition techniques. One of the techniques being focused is thermal oxidation of sputtered Zr and the mechanisms of transforming the metal into oxide has been extensively reviewed.     

Controlled synthesis of ZnO branched nanorod arrays by hierarchical solution growth and application in dye-sensitized solar cells

We demonstrate the controlled synthesis of ZnO branched nanorod arrays on fluorine-doped SnO₂-coated glass substrates by the hierarchical solution growth method. In the secondary growth, the concentration of Zn(NO₃)₂/hexamethylenetetramine plays an important role in controlling the morphology of the branched nanorod arrays, besides that of diaminopropane used as a structure-directing agent to induce the growth of branches. The population density and morphology of the branched nanorod arrays depend on those of the nanorod arrays obtained from the primary growth, which can be modulated though the concentration of Zn(NO₃)₂/hexamethylenetetramine in the primary growth solution. The dye-sensitized ZnO branched nanorod arrays exhibit much stronger optical absorption as compared with its corresponding primary nanorod arrays, suggesting that the addition of the branches improves light harvesting. The dye-sensitized solar cell based on the optimized ZnO branched nanorod array reaches a conversion efficiency of 1.66% under the light radiation of 1000 W/m². The branched nanorod arrays can also be applied in other application fields of ZnO.     

Synthesis of γ-MnOOH nanorods and their isomorphous transformation into β-MnO<Subscript>2</Subscript> and α-Mn<Subscript>2</Subscript>O<Subscript>3</Subscript> nanorods

γ-MnOOH nanorods with different diameters were synthesized by a simple one-step polymer-assisted hydrothermal method using 50% (wt.%) Mn(NO₃)₂ solution and PEG-10000 as reagents. The diameters of as-synthesized γ-MnOOH nanorods were well controlled by simply varying the volume of the 50% Mn(NO₃)₂ solution. The calcination behavior of the as-synthesized γ-MnOOH nanorods was studied. Nanorods of β-MnO₂ and α-Mn₂O₃ were synthesized by calcination at 350 and 600 °C for 1 h respectively.     

Reaction of Cd(NO3)2·4H2O with 4,4'–bipyridine (bpy) in MeOH solvent: synthesis and characterization of T-shaped [Cd(bpy)1.5(NO3)2]·3H2O,square grid [Cd(bpy)2(H2O)2](NO3)2·4H2O and linear polymeric [Cd(bpy)(H2O)2(NO3)2]

The influence of concentration of water and metal salt in the reaction between Cd(NO₃)₂·4H₂O and 4,4′–bipyridine in MeOH has been studied and three compounds namely, T-shaped [Cd(bpy)_1.5(NO₃)₂]·3H₂O, 1 square grid [Cd(bpy)₂(H₂O)₂](NO₃)₂ 4H₂O, 2 and one dimensional linear polymer, [Cd(bpy)(H₂O)₂(NO₃)₂], 3 were isolated quantitatively in this process. Compound 1 forms in MeOH at high dilution of the metal salt (5.0 mg/mL or less) and for the metal-to-ligand ratio 1:(1.5–2.0). Compound 2 forms exclusively in the concentration range, 17–33% for water in MeOH by volume and 12–28 mg/mL for the metal salt of the solution. Outside these limits, mixtures of 2 and 3 were isolated. For 1:1 ratio of metal salt to bpy, the linear polymer, 3 was obtained in major quantity and its formation was found to be independent of concentration of water or the metal salt. Compounds 1 and 2 have been characterized by X-ray crystallography. On heating all the compounds decompose through a common intermediate [Cd(bpy)(NO₃)₂] and finally to CdO as monitored by TG.     

Synthesis and crystal structure CoNi<Subscript>2</Subscript>(BO<Subscript>3</Subscript>)<Subscript>2</Subscript>

A new metal orthoborate compound, cobalt dinickel orthoborate, CoNi₂(BO₃)₂ has been successfully synthesized for the first time. The title compound was synthesized by thermally-induced solid-state chemical reaction at 900°C between the initial reagents of Co(NO₃)₂ · 6H₂O, Ni(NO₃)₂ · 6H₂O and H₃BO₃ which were mixed with the mol ratio of 1: 2: 2 respectively. The obtained product was structurally characterized by X-ray powder diffraction technique. It has been found that the CoNi₂(BO₃)₂ crystallizes in the kotoite type and isostructural with the compounds having the chemical formula M₃(BO₃)₂ where M—Mg, Co and Ni. The synthesized compound belongs to the orthorhombic crystal system with the refined unit cell parameters of a = 5.419(9) Å, b = 8.352(0) Å, c = 4.478(8) Å and Z = 2. The space group was determined as Pnmn. Further characterizations by FTIR, elemental analysis and thermal analysis were also performed.     

Sintering of Mullite–Zirconia Composite Powder Prepared by Ultrasonic Spray Pyrolysis Technique

Sinterabilities of mullite (3Al₂O₃·2SiO₂–zirconia (ZrO₂)composite powders prepared by ultrasonic spray pyrolysis techniques (USPTs) were examined. Starting mullite powders containing 18.5 mol% (15.0 vol%) of zirconia (ZrO₂) were prepared by single-nozzle (SN) and double-nozzle (DN) USPT. In SN-USPT, the composite powder was prepared by spray pyrolysis of a water–ethanol solution in an Al(NO₃)₃–Si(OC₂H₅)₄–ZrOCl₂–YCl₃ system at 900°C, using one ultrasonic vibrator. In DN-USPT, the composite powder was prepared by simultaneous spray pyrolyses of a water–ethanol solution in an Al(NO₃)₃–Si(OC₂H₅)₄ system and one in a ZrOCl₂–YCl₃ system at 900°C, using two ultrasonic vibrators. When these composite compacts were fired at a temperature between 1400 and 1700°C for 5 h, the relative densities attained maxima, i.e., 87.2% (SN-USPT) and 95.5% (DN-USPT), at the firing temperature of 1500°C. Densification of the DN-USPT-derived powder compact proceeded more markedly than that of the SN-USPT-derived powder compact.     

Si-substituted hydroxyapatite nanopowders: Synthesis, thermal stability and sinterability

Synthetic hydroxyapatites incorporating small amounts of Si have shown improved biological performances in terms of enhanced bone apposition, bone in-growth and cell-mediated degradation.This paper reports a systematic investigation on Si-substituted hydroxyapatite (Si 1.40 wt%) nanopowders produced following two different conventional wet methodologies: (a) precipitation of Ca(NO₃)₂·4H₂O and (b) titration of Ca(OH)₂. The influence of the synthesis process on composition, thermal behaviour and sinterability of the resulting nanopowders is studied.Samples were characterised by electron microscopy, induced coupled plasma atomic emission spectroscopy, thermal analysis, infrared spectroscopy, N₂ adsorption measurements, X-ray diffraction and dilatometry. Semicrystalline Si-substituted hydroxyapatite powders made up of needle-like nanoparticles were obtained, the specific surface area ranged between 84 and 110 m²/g. Pure and Si-substituted hydroxyapatite nanopowders derived from Ca(NO₃)₂·4H₂O decomposed around 1000 °C. Si-substituted hydroxyapatite nanopowders obtained from Ca(OH)₂ were thermally stable up to 1200 °C and showed a distinct decreased thermal stability with respect to the homologous pure sample. Si-substituted hydroxyapatites exhibited higher sintering temperature and increased total shrinkage with respect to pure powders. Nanostructured dense ceramics were obtained by sintering at 1100 °C Si-substituted hydroxyapatites derived from Ca(OH)₂.     

Solid-state sensors for in-line monitoring of NO2 in automobile exhaust emission

Three types of planar solid-state sensors for measuring NO₂ in a gas mixture has been designed and tested in the laboratory under controlled atmosphere between 573–723 K. The concentration of NO₂ in the gas mixture was in the range of 0–500 ppm with the balance gas consisting of air. The three types of NO₂ gas sensors that have been tested in this investigation can be schematically represented as follows:Pt, NO₂ + air, NaNO₃ + Ba(NO₃)₂ | NASICON disk | Porous YSZ disk | NO₂ + air, Pt (I)Pt, NO₂ + air, NaNO₃ + Ba(NO₃)₂ | NASICON disk | YSZ thin film | NO₂ + air, Pt (II)Pt, NO₂ + air, Pt | YSZ disk | Au – Pd, NO₂ + air, Pt (III)In sensor (I) the two solid electrolyte disks were attached by diffusion bonding at elevated temperature whereas in sensor (II) the (8 mol% Y₂O₃–ZrO₂) YSZ thin film was deposited on (Na₃Zr₂Si₂PO₁₂) NASICON disk by radio frequency (RF) magnetron sputtering technique. The measured open circuit electromotive force (Emf) of each sensor was found to attain stable value at all the concentrations of NO₂ in the gas mixture and also varied linearly as a function of the logarithm of the partial pressure of NO₂ in the gas mixture. The time required to reach 90% of the stable emf at a fixed concentration of NO₂ and at a constant temperature was found to be 30–40 min for sensor (I) and approximately 2–3 min for sensor (II) and (III).     

Self‐Formed Channel Devices Based on Vertically Grown 2D Materials with Large‐Surface‐Area and Their Potential for Chemical Sensor Applications

2D layered materials with sensitive surfaces are promising materials for use in chemical sensing devices, owing to their extremely large surface‐to‐volume ratios. However, most chemical sensors based on 2D materials are used in the form of laterally defined active channels, in which the active area is limited to the actual device dimensions. Therefore, a novel approach for fabricating self‐formed active‐channel devices is proposed based on 2D semiconductor materials with very large surface areas, and their potential gas sensing ability is examined. First, the vertical growth phenomenon of SnS₂ nanocrystals is investigated with large surface area via metal‐assisted growth using prepatterned metal electrodes, and then self‐formed active‐channel devices are suggested without additional pattering through the selective synthesis of SnS₂ nanosheets on prepatterned metal electrodes. The self‐formed active‐channel device exhibits extremely high response values (>2000% at 10 ppm) for NO₂ along with excellent NO₂ selectivity. Moreover, the NO₂ gas response of the gas sensing device with vertically self‐formed SnS₂ nanosheets is more than two orders of magnitude higher than that of a similar exfoliated SnS₂‐based device. These results indicate that the facile device fabrication method would be applicable to various systems in which surface area plays an important role.     

Surfactant-assisted hydrothermal preparation of submicrometer-sized two-dimensional BiFeO<Subscript>3</Subscript> plates and their photocatalytic activity

2-Dimensional bismuth ferrite (BiFeO₃) plates were hydrothermally synthesized starting from Bi(NO₃)₃ and Fe(NO₃)₃ in the presence of cetyltrimethylammonium bromide (CTAB) as a morphology directing template. The amount of CTAB was altered to study their effects on the final results. The average diameter and thickness of BiFeO₃ plates were about 1.3–2 μm and 200–300 nm. X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–visible diffuse reflection spectrum (UV–vis DRS) were used to investigate the samples’ crystallinity, purity, morphology, spectral features. Furthermore, the effect of the morphology on photocatalysis was also evaluated by photodecolorization of orange II under a blended-light mercury fluorescent lamp (λ ≥ 410 nm). As a result, BiFeO₃ plates showed a much higher photocatalytic activity than bulk BiFeO₃ for photodecolorization of orange II, suggesting potential application in photocatalysis.     

Synthesis of perovskite-type (La1−xCax)FeO3 (0 ≤ x ≤ 0.2) at low temperature

Gel formation was realized by adding citric acid to a solution of La(NO₃)₃·5H₂O, Ca(NO₃)₂·4H₂O, and Fe(NO₃)₂·9H₂O. Perovskite-type (La_1−xCa_x)FeO₃ (0 ≤ x ≤ 0.2) was synthesized by firing the gel at 500 °C in air for 1 h. The crystallite size (D_1 2 1) decreased with increasing x, while the specific surface area was 6.8-9.4 m²/g and independent of x. The XPS measurement of the (La_1−xCa_x)FeO₃ surface indicated that the Ca²⁺ ion content increased with increasing x, while the Fe ion content was independent of x. Catalytic activity for CO oxidation increased with increasing x.     

UV–Ozone Interfacial Modification in Organic Transistors for High‐Sensitivity NO2 Detection

A new type of nitrogen dioxide (NO₂) gas sensor based on copper phthalocyanine (CuPc) thin film transistors (TFTs) with a simple, low‐cost UV–ozone (UVO)‐treated polymeric gate dielectric is reported here. The NO₂ sensitivity of these TFTs with the dielectric surface UVO treatment is ≈400× greater for [NO₂] = 30 ppm than for those without UVO treatment. Importantly, the sensitivity is ≈50× greater for [NO₂] = 1 ppm with the UVO‐treated TFTs, and a limit of detection of ≈400 ppb is achieved with this sensing platform. The morphology, microstructure, and chemical composition of the gate dielectric and CuPc films are analyzed by atomic force microscopy, grazing incident X‐ray diffraction, X‐ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy, revealing that the enhanced sensing performance originates from UVO‐derived hydroxylated species on the dielectric surface and not from chemical reactions between NO₂ and the dielectric/semiconductor components. This work demonstrates that dielectric/semiconductor interface engineering is essential for readily manufacturable high‐performance TFT‐based gas sensors.     

Mesogenic lanthanoid metal complexes of a non-mesogenic Schiff-base, N,N′-di-(4-hexadecyloxysalicylidene)-l′,8′-diamino-3′,6′-dioxaoctane

A non-mesogenic Schiff-base, N,N′-di-(4-hexadecyloxysalicylidene)-l′,8′-diamino-3′,6′-dioxaoctane, H₂dhdsdd (H₂L²), was synthesized, structure studied by elemental analyses and mass, NMR and IR spectra and ligated to some Ln^III metal ions that yielded mesogenic (SmA/N) Ln^III complexes of the general composition, [Ln₂(L²H₂)₃(NO₃)₄](NO₃)₂, where Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy and Ho. IR and NMR spectral data imply a bi-dentate bonding of the Schiff-base in its zwitterionic form (as L²H₂) to the Ln^III ions through two phenolate oxygens, rendering the overall geometry around Ln^III to distorted mono-capped octahedron.