Chemical synthesis and characterization of magnesium substituted amorphous calcium phosphate (MG-ACP)

Amorphous calcium phosphate (ACP) was synthesized by a simple aqueous precipitation using CaCl₂ and Na₃PO₄ in the presence of MgCl₂ to ensure the formation of the ACP phase at room temperature. Magnesium substituted ACP phases corresponding to two different compositions representing the two most prominent calcium phosphate phases (hydroxyapatite: Ca + Mg/P = 1.67 and tricalcium phosphate: Ca + Mg/P = 1.5) were synthesized by this simple approach. Both compositions of ACP phases resulted in their transformation into β-tricalcium phosphate upon heat treatment in air at 600 °C. X-ray diffraction (XRD), heat treatment, scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) and Brunauer-Emmett-Teller (BET) analyses were used to characterize the phase, thermal stability, surface area, and morphology of the synthesized ACP powders corresponding to the two different nominal Ca/P compositions. Although it is known that α-TCP is the phase that appears upon heat treatment at 600 °C unsubstituted ACP, substitution of magnesium ion in ACP (both TCP and HA composition) stabilized the structure of β-TCMP phase at 600 °C. Moreover, FT-IR analysis revealed that the ACP phase regardless of the composition, exhibited characteristic bands corresponding to that of HA, with the exception of the ACP corresponding to HA composition which exhibited a prominent OH vibrational mode.     

Synthesis of Ti(IV)-substituted calcium hydroxyapatite microparticles by hydrolysis of phenyl phosphates

Ti(IV)-substituted calcium hydroxyapatite (Ti-CaHap) microparticles were synthesized by hydrolyzing the phenyl phosphate (C₆H₅PO₄H₂) in a mixture of aqueous Ca(OH)₂ and Ti(SO₄)₂ solutions at pH = 8 and 85 °C. Then, the atomic ratio Ti/(Ca + Ti) in the starting solution was ranged from 0 to 0.20. The XRD pattern of the product formed at Ti/(Ca + Ti) = 0 was identified as CaHap. On increasing Ti/(Ca + Ti) ratio, the diffraction intensity of the CaHap peaks weakened and the unit-cell dimension c of the material was reduced. The Ti content in the particles was increased by raising Ti/(Ca + Ti) ratio and the Ti(IV) was more easily incorporated in the particles than Ca(II). All the phenyl phosphates were hydrolyzed during preparation of the particles. The CaHap formed at Ti/(Ca + Ti) = 0 was needle-like particles with the size of ca. 3.2 μm in length and ca. 0.3 μm in width. The size of Ti-CaHap particles was essentially unchanged on increasing Ti/(Ca + Ti) ratio up to 0.05. At Ti/(Ca + Ti) ? 0.10, the amorphous TiO₂ particles with a size of ca. 90 nm were generated and the size of Ti-CaHap particles was decreased, leading to the steep increase of specific surface area. It can be, therefore, presumed that the Ti(IV) is substituted with Ca(II) in CaHap crystal to form Ti-CaHap microparticles at Ti/(Ca + Ti) = 0–0.05, though the incorporation of Ti(IV) in the materials impedes the crystallization and growth of Ti-CaHap particles and accelerates the formation of amorphous TiO₂ particles at Ti/(Ca + Ti) = 0.10–0.20. Diffuse reflectance UV measurements indicated that the Ti-CaHap microparticles possess a UV absorption property and the ability is enhanced on increasing Ti/(Ca + Ti) ratio. The Beer’s plot revealed that the UV absorption ability of the synthetic Ti-CaHap microparticles is higher than that of amorphous TiO₂ ones.     

Strontium doped hydroxyapatite film formed by micro-arc oxidation

A porous strontium-doped hydroxyapatite (Sr-HA) film was prepared on titanium substrates by an electrochemical oxidation method, i.e. micro-arc oxidation (MAO). The reaction was processed using a pulse power supply with titanium substrate acted as the anode in electrolytic solution containing calcium acetate, strontium acetate and β-glycerol phosphate disodium salt pentahydrate (β-GP). The thickness, phase, composition and morphology of the coatings were investigated with X-ray diffraction (XRD), electron probe microanalysis (EPMA) and scanning electron microscopy (SEM) with energy dispersive X-ray spectrometer (EDS). The thickness of the film was about 20 µm with the porous and uneven surfaces. XRD showed that the film was mainly made up of hydroxyapatite doped with strontium and the (Sr/(Sr + Ca) ratios ranged from 0–100%, which could be expressed as the general formula of Ca_10 ? XSr_X(PO₄)₆(OH)₂, 0 ≤ X ≤ 10). Such films are expected to have significant medical applications as dental implants and artificial bone joints.     

Preparation and structure of carbonated calcium hydroxyapatite substituted with heavy rare earth ions

Calcium hydroxyapatite (CaHap) particles substituted five types of heavy rare earth ions (Ln: Y³⁺, Gd³⁺, Dy³⁺, Er³⁺ and Yb³⁺) were synthesized using a precipitation method and characterized using various means. These Ln ions strongly affected the crystal phases and the structures of the products. With increasing Ln/(Ln + Ca) in the starting solution ([X_Ln]), the length and the crystallinity of the particles first increased and then decreased. The rare earth metal-calcium hydroxyapatite (LnCaHap) solid solution particles were obtained at [X_Y] ≤ 0.10 for substituting Y system and at [X_Ln] ≤ 0.01–0.03 for substituting the other Ln systems. LnPO₄ was mixed with LnCaHap at higher [X_Ln] for all Ln systems. A series of yttrium-calcium hydroxyapatite (YCaHap) solid solutions with [X_Y] = 0–0.10 were investigated using XRD, TEM, ICP-AES, IR and TG–DTA in detail.     

Preparation and characterization of selenite substituted hydroxyapatite

Selenite-substituted hydroxyapatite (Se-HA) with different Se/P ratios was synthesized by a co-precipitation method, using sodium selenite (Na₂SeO₃) as a Se source. Selenium has been incorporated into the hydroxyapatite lattice by partially replacing phosphate (PO₄^3 ?) groups with selenite (SeO₃^2 ?) groups. X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM) techniques reveal that substitutions of phosphate groups by selenite groups cause lower carbonate groups occupying at phosphate sites and change the lattice parameters of hydroxyapatite. The powders obtained are nano-crystalline hydroxyapatite when the Se/P ratios are not more than 0.1. The particle shape of Se-HA has not been altered compared with selenite-free hydroxyapatite but Se-incorporation reduces the crystallite size. The crystallinity was reduced as the Se/P ratios increased until amorphous phase (Se/P = 0.3) appeared in the Se-HA powder obtained, and then another crystal phase presented as calcium selenite hydrate (Se/P = 10). In addition, the sintering tests show that the Se-HA powders with the Se/P ratio of 0.1 have thermal stability at 900 °C for 2 h; hence they have great potential in the fabrication of bone repair scaffolds.     

Physical and optical properties of Co2+, Ni2+ doped 20ZnO + xLi2O + (30 − x)K2O + 50B2O3 (5 ≤ x ≤ 25) glasses: Observation of mixed alkali effect

Co²⁺ and Ni²⁺ ions doped 20ZnO + xLi₂O + (30 ? x) K₂O + 50B₂O₃ (5 ≤ x ≤ 25) mol% glasses are prepared using melt quenching technique. Structural changes of the prepared glasses by addition of transition metal oxides, CoO and NiO are investigated by UV–vis–NIR, FT-IR spectroscopy and XRD. The XRD pattern indicates the amorphous nature of prepared glasses. FT-IR measurements of the all glasses revealed that the network structure of the glasses are mainly based on BO₃ and BO₄ units placed in different structural groups in which the BO₃ units being dominant. The optical absorption spectra suggest the site symmetry of Co²⁺ and Ni²⁺ ions in the glasses are near octahedral. Crystal field and inter-electronic repulsion parameters are also evaluated. The optical band gap and Urbach energies exhibited the mixed alkali effect. Various physical parameters such as density, refractive index, optical dielectric constant, polaron radius, electronic polarizability and inter-ionic distance are also determined.     

Influence of temperature, [Ca2+], Ca/P ratio and ultrasonic power on the crystallinity and morphology of hydroxyapatite nanoparticles prepared with a novel ultrasonic precipitation method

Nanocrystalline hydroxyapatite was prepared by a precipitation method with the aid of ultrasonic irradiation using Ca(NO₃)₂ and NH₄H₂PO₄ as source material and carbamide (NH₂CONH₂) as precipitator. The influence of Ca/P molar ratio, precipitation temperature, concentration of Ca²⁺ ([Ca²⁺]) and ultrasonic power on the crystallinity of the nanopowder were systematically investigated by XRD analysis. The size of the as-prepared particles was analyzed using TEM and XRD methods. The results revealed that the monophase hydroxyapatite could be obtained at the following technological conditions: [Ca²⁺] = 0.01–0.1 mol/L, ultrasonic power = 300 W, Ca/P (mol) = 1.2–2.5 and T = 313–353 K. In addition, the acicular and spherical particles could be prepared at different ultrasonic powers of 300 and 200 W, respectively.     

In vitro evaluation of osteoconductivity and cellular response of zirconia and alumina based ceramics

Developed ceria/yttria stabilized zirconia and ceria/yttria stabilized zirconia toughened alumina supported formation of apatite layer when immersed in simulated body fluid without any prior surface treatment. The formed mineral layer was confirmed as hydroxyapatite through X-ray diffraction patterns. The calcium/phosphate atomic ratio obtained from energy dispersive X-ray spectroscopy was found to be little less (Ca/P = 1.5) than that of pure hydroxyapatite (Ca/P = 1.7) which indicates the probability of mixed type calcium-phosphate compound formation. The achieved thickness of apatite layer was estimated through a surface profilometer and as high as ~ 17 μm thickness was found after 28 days of soaking. The biocompatibility of the developed materials was ensured through in vitro human osteoblast like cell (MG63) culture on ceramic discs. The morphology of attached cells was characterized through scanning electron microscopy and fluorescent microscopy which show multilayered interconnected cell growth within 8 days of culture period. Moreover, differentiation of MG63 cells was evaluated through MTT assay, total protein content and alkaline phosphatase activity.     

Synthesis of partial stabilized cement–gypsum as new dental retrograde filling material

The study describes the sol–gel synthesis of a new dental retrograde filling material partial stabilized cement (PSC)–gypsum by adding different weight percentage of gypsum (25% PSC + 75% gypsum, 50% PSC + 50% gypsum and 75% PSC + 25% gypsum) to the PSC. The crystalline phase and hydration products of PSC–gypsum were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis. The handling properties such as setting time, viscosity, tensile strength, porosity and pH, were also studied. The XRD and microstructure analysis demonstrated the formation of hydroxyapatite and removal of calcium dihydrate during its immersion in simulated body fluid (SBF) on day 10 for 75% PSC + 25% gypsum. The developed PSC–gypsum not only improved the setting time but also greatly reduced the viscosity, which is very essential for endodontic surgery. The cytotoxic and cell proliferation studies indicated that the synthesized material is highly biocompatible. The increased alkaline pH of the PSC–gypsum also had a remarkable antibacterial activity.     

Synthesis,optical and thermal characterization of novel thiazolyl heterocyclic azo dye

Thiazolyl heterocyclic azo dye and its metal (Ni²⁺, Co²⁺)–azo complexes were synthesized. Their structures were confirmed by elemental analysis, UV–VIS absorption spectra, FT-IR, ¹H NMR and MALDI-MS. The thermal properties of metal complexes were studied by DSC–TGA. The optical constants (complex refractive index N = n + ik) and thickness of the complex thin films on polished single-crystal silicon substrates were investigated on a scanning ellipsometer. Results indicate that thiazolyl metal–azo complexes possess good optical and thermal properties. They would be a promising recording medium candidate for NVD with the Super-resolution near field structure (Super-RENS) technology.     

XANES analysis of calcium and sodium phosphates and silicates and hydroxyapatite–Bioglass®45S5 co-sintered bioceramics

Bioglass®45S5 was co-sintered with hydroxyapatite at 1200 °C. When small amounts (< 5 wt.%) of Bioglass®45S5 was added it behaved as a sintering aid and also enhanced the decomposition of hydroxyapatite to β-tricalcium phosphate. However when 10 wt.% and 25 wt.% Bioglass®45S5 was used it resulted in the formation of Ca₅(PO₄)₂SiO₄ and Na₃Ca₆(PO₄)₅ in an amorphous silicate matrix respectively. These chemistries show improved bioactivity compared to hydroxyapatite and are the subject of this study. The structure of several crystalline calcium and sodium phosphates and silicates as well as the co-sintered hydroxyapatite–Bioglass®45S5 bioceramics were examined using XANES spectroscopy. The nature of the crystalline and amorphous phases were studied using silicon (Si) and phosphorus (P) K- and L_2,3-edge and calcium (Ca) K-edge XANES.Si L_2,3-edge spectra of sintered bioceramic compositions indicates that the primary silicates present in these compositions are sodium silicates in the amorphous state. From Si K-edge spectra, it is shown that the silicates are in a similar structural environment in all the sintered bioceramic compositions with 4-fold coordination.Using P L_2,3-edge it is clearly shown that there is no evidence of sodium phosphate present in the sintered bioceramic compositions. In the P K-edge spectra, the post-edge shoulder peak at around 2155 eV indicates that this shoulder to be more defined for calcium phosphate compounds with decreasing solubility and increasing thermodynamic stability. This shoulder peak is more noticeable in hydroxyapatite and β-TCP indicating greater stability of the phosphate phase. The only spectra that does not show a noticeable peak is the composition with Na₃Ca₆(PO₄)₅ in a silicate matrix indicating that it is more soluble compared to the other compositions.     

Study of optical properties of GeO2 nanocrystals as synthesized by hydrothermal technique

The GeO₂ nanocrystals (α-quartz type structure) with β-phase are synthesized at relatively lower temperature by hydrothermal route using autoclave. All samples are characterized by XRD, FESEM, EDS, TEM, photoluminescence (PL) and UV–vis absorption spectroscopy techniques. Synthesized nanocrystals have uniform shape and uniform size distribution for a particular synthesis condition, which is about 30–300 nm depending on synthesis conditions. The XRD results indicate that grown GeO₂ crystals only shows peak related to α-quartz structure with lattice parameters a = 4.985 Å and c = 5.648 Å. UV–vis absorption spectroscopy measurements reveal the bandgap energies corresponding to the GeO₂ α-quartz structure. Synthesized nanocrystals are capable to emit strong blue light around 425–435 nm under excitation of 300 nm and 325 nm and consequently the as synthesized material can be used in integrated optical devices.     

Hydrothermal synthesis and 121Sb Mössbauer characterization of perovskite-type oxides: Ba2SbLnO6 (Ln = Pr,Nd, Sm,Eu)

A mild hydrothermal process to prepare Ba₂SbLnO₆ (Ln = Pr, Nd, Sm, Eu) perovskite-type oxides are presented. These perovskites were characterized on the basis of X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), inductively-coupled plasma spectra (ICP) techniques. Primary structure was confirmed using Rietveld method based on XRD data shows that the likely space groups of Ba₂SbLnO₆ are R-3 for Ln = Pr and Nd and F_m-3_m for Ln = Sm and Eu, respectively. The measurement of Mössbauer effect of the 37.2 keV γ transition of ¹²¹Sb indicates that the isomer shift of these perovskites falls in the region of the Sb⁵⁺ and reflects some hybridized-orbital behavior in Sb–O bonds.     

Effects of Si addition on microstructure and mechanical properties of Mg–8Gd–4Y–Nd–Zr alloy

Effects of Si addition (1.0 wt.%) on microstructure and mechanical properties of Mg–8Gd–4Y–Nd–Zr alloy have been investigated using scanning electron microscopy (SEM) equipped with energy dispersive spectrum (EDS), X-ray diffraction (XRD), hardness measurements and tensile testing. The results indicated that the addition of Si led to the formation of Mg₂Si and (RE + Si)-rich particles, which enhanced the Young’s modulus of the alloy by 7 GPa while decreased the yield strength and ultimate strength by 10 MPa and 31 MPa, respectively. The tensile properties of the Mg–8Gd–4Y–Nd–Zr–Si alloy are as follows: Young’s modulus E = 51 GPa, yield strength σ_0.2 = 347 MPa, ultimate strength σ_b = 392 MPa and elongation δ = 2.7%. The increase in Young’s modulus was attributed to the formation of particles with high Young’s modulus, while the decrease in strength was ascribed to the decrease in volume fraction of metastable β′ precipitates caused by the consumption of rare earth atoms due to the formation of the rare earth containing particles.     

Green synthesis of biocompatible carbon dots using aqueous extract of Trapa bispinosa peel

We are reporting highly economical plant based method for the production of luminescent water soluble carbon dots (C-dot) using Indian water plant Trapa bispinosa peel extract without adding any external oxidizing agent at 90 °C. C-dots ranging from 5 to 10 nm were found in the solution with a prominent green fluorescence under UV-light (λ_ex = 365 nm). UV–vis spectra recorded at different time intervals (30–120 min) displayed signature absorption of C-dots between 400 and 600 nm. Fluorescence spectra of the dispersion after 120 min of synthesis exhibited characteristic emission peaks of C-dots when excited at 350, 400, 450 and 500 nm. C-dots were further analyzed using X-ray diffraction (XRD), Raman Spectroscopy and Thermo-Gravimetric Analysis (TGA). Structure of the C-dots was found to be turbostratic when studied using XRD. C-dots synthesized by our method were found to be exceptionally biocompatible against MDCK cells.     

X-ray powder diffraction,vibration and thermal studies of [A0.92(NH4)0.08]2TeCl4Br2 with A = Cs,Rb: Influence of mixed cationic and anionic substitutions

The crystal structures of [A_0.92(NH₄)_0.08]₂TeCl₄Br₂ with A = Cs, Rb have been determined using X-ray powder diffraction techniques. The two compounds crystallize in the tetragonal space group P4/mnc, with the unit cell parameters: a = 7.452(1) Å, c = 10.544(3) Å, Z = 2 and a = 7.315(2) Å, c = 10.354(4) Å, Z = 2 in the presence of Cs and Rb, respectively. These two compounds have an antifluorite-type arrangement of NH₄⁺/Rb⁺/Cs⁺ and octahedral TeCl₄Br₂^2? anions. The stability of these structure is by ionic and hydrogen bonding contacts: A?Cl, A?Br and N–H?Cl, N–H?Br. The different vibrational modes of these powders were analysed by FTIR and Raman spectroscopic studies. A DTA/TGA experiment reveals one endothermic peak at 780 K implicating the decomposition of the sample. At low temperature, one endothermic peak in thermal behavior is detected at around 213 K by DSC experiment. This transition was confirmed by dielectric measurements.     

Effects of β-alanine on morphology and optical properties of CoAl2O4 nanopowders as a blue pigment

In this paper, we have synthesized cobalt aluminate (CoAl₂O₄), nanopowders as blue pigments by the combustion method, which metal nitrates were used as precursor materials and mixture of urea and glycine as fuel. The effect of β-alanine weight percentage as a novel excess fuel on some physical characteristics (e.g. crystallite size and color) of powders has been investigated. The synthesized powders were characterized by means of X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM), Transmission electron microscope (TEM), Fourier transform infrared (FT-IR) and Ultraviolet–visible (UV–Vis) spectroscopies. XRD patterns and FT-IR spectra confirmed the formation of pure nanocrystalline CoAl₂O₄ powders after calcination of the metal-fuel gel precursors at 600 °C for 2 h. Optical band gap of 2.3 eV observed for the prepared powders. The crystallite sizes were estimated of 20–30 nm by means of TEM images and Williamson–Hall method. UV–Vis spectra of the blue metal oxides were characteristics of Co²⁺ metal ions located in tetrahedral sites. CIE L¹a¹b¹ chromatic coordinates indicated that the bluest color was obtained for β-alanine = 5.5 and 35.6 wt.%.     

Preparation and characterization of nanosized silver phosphate loaded hydroxyapatite by single step co-conversion process

The preparation and characterization of silver phosphate nanoparticles loaded hydroxyapatite aiming to enhance the bactericidal performance by a single step co-conversion technique using low temperature phosphorization in the presence of various silver nitrate concentration (AgNO₃, ranging 0.001–0.1 M) was performed. Characterization by using X-ray diffraction, infrared spectroscopy and transmission electron microscopy showed that hydroxyapatite and silver phosphate were the main phases in all converted samples and the microstructure comprised the distribution of spherical-shaped silver phosphate nanoparticles within the cluster of hydroxyapatite nanocrystals. Total silver content (ranging 0.09–5.6%) in the converted samples was found to increase with increasing silver nitrate content. Flexural modulus and strength of converted samples remained unchanged for samples using silver nitrate between 0.001 and 0.01 M, but decreased at greater silver nitrate concentration. Antibacterial activity of two selected samples (0.001 and 0.005 M AgNO₃) against two bacterial strains (Pseudomonas aeruginosa and Staphylococcus aureus) was observed since 100% reduction of viable cells after 24 h contact was detected. Cytotoxic potential by MTT assay of sample using 0.001 M AgNO₃ was only observed at 24 h extraction, but was seen at all extraction periods (24–72 h) for sample using 0.005 M AgNO₃.     

Aluminum-free glass-ionomer bone cements with enhanced bioactivity and biodegradability

Al-free glasses of general composition 0.340SiO₂:0.300ZnO:(0.250-a-b)CaO:aSrO:bMgO:0.050Na₂O:0.060P₂O₅ (a, b = 0.000 or 0.125) were synthesized by melt quenching and their ability to form glass-ionomer cements was evaluated using poly(acrylic acid) and water. We evaluated the influence of the poly(acrylic acid) molecular weight and glass particle size in the cement mechanical performance. Higher compressive strength (25 ± 5 MPa) and higher compressive elastic modulus (492 ± 17 MPa) were achieved with a poly(acrylic acid) of 50 kDa and glass particle sizes between 63 and 125 μm. Cements prepared with glass formulation a = 0.125 and b = 0.000 were analyzed after immersion in simulated body fluid; they presented a surface morphology consistent with a calcium phosphate coating and a Ca/P ratio of 1.55 (similar to calcium-deficient hydroxyapatite). Addition of starch to the cement formulation induced partial degradability after 8 weeks of immersion in phosphate buffer saline containing α-amylase. Micro-computed tomography analysis revealed that the inclusion of starch increased the cement porosity from 35% to 42%. We were able to produce partially degradable Al-free glass-ionomer bone cements with mechanical performance, bioactivity and biodegradability suitable to be applied on non-load bearing sites and with the appropriate physical characteristics for osteointegration upon partial degradation. Zn release studies (concentrations between 413 μM and 887 μM) evidenced the necessity to tune the cement formulations to reduce the Zn concentration in the surrounding environment.     

Ferrocene adsorbed into the porous octakis(hydridodimethylsiloxy)silsesquioxane after thermolysis in tetrahydrofuran media: An applied surface for ascorbic acid determination

Octakis(hydridodimethylsiloxi)silsesquioxane (Q₈M₈^H) was synthesized and Ferrocene was adsorbed in a polymeric net through electrostatic interactions, with anion forming after the cleavage of any siloxy groups (ESFc). The nanostructured materials (Q₈M₈^H and EsFc) were characterized by Fourier transform infrared spectra (FT-IR), nuclear magnetic resonance (NMR), X-ray diffraction (XRD), Thermogravimetric analyses and Voltammetric technique The cyclic voltammograms of the graphite paste electrode modified with ESFc showed one redox couple with E⁰′ = 0.320 V (1.0 mol L^?1 NaCl, v = 50 mV s^?1), with a diffusion-controlled process and the redox process shows electrocatalytic activity for the oxidation of ascorbic acid.