Synthesis and physicochemical characterization of nanocomposites of calcium hydroxylapatite-chitosan-multiwall carbon nanotubes

The synthesis and physicochemical characterization of nanocomposites of calcium hydroxylapatite-chitosan-multiwall carbon nanotubes (CNTs) was performed. The CaCl₂-(NH₄)₂HPO₄-(C₆H₁₁NO₄) _n -CNT-NH₃-H₂O system was studied by the solubility (Tananaev’s residual concentration) method and pH measurements at 25°C. Conditions for the joint precipitation of nanocrystalline calcium hydroxylapatite, chitosan, and multiwall CNTs were found. Nanocomposites with the general formula Ca₁₀(PO₄)₆(OH)₂ · x(C₆H₁₁NO₄) · yCNT · zH₂O, where x = 0.1, 0.2, and 0.5; y = 0.5, 2.0, 4.0, and 5.0; and z = 5.9–7.9. The solid phases were characterized by chemical, thermogravimetric, and X-ray diffraction analysis and IR spectroscopy.     

Nanocrystalline Calcium Carbonate Hydroxyapatites Containing Multiwall Carbon Nanotubes: Synthesis and Physicochemical Characterization

Nanocomposites (NCs) based on carbonated calcium hydroxyapatite (CHA) (bioapatite, an analogue of the inorganic component of mammalian bone tissue), carbonate apatite (Ca₁₀(PO₄)₆CO₃, CA), and multiwall carbon nanotubes (CNTs) are prepared in the system CaCl₂–(NH₄)₂HPO₄–NH₄HCO₃–NH₃–CNT–H₂O (25°C) by coprecipitation of calcium and phosphorus salts with CNTs from aqueous solutions. The physicochemical properties of nanocomposites are studied as dependent on their formation conditions and composition using the solubility (residual concentrations) method and pH measurements. The composition, crystal structure, morphology, spectroscopic and thermal characteristics of the synthesized CHA/CNT and CA/CNT NCs are determined using chemical analysis, X-ray powder diffraction, thermal analysis, and IR spectroscopy. Either CHA/CNT NCs of composition Ca₁₀(PO₄)₆(CO₃)_x(OH)_2–2х · yCNT · zH₂O, where х = 0.2; 0.5; 0.8; y = 1, 2, 3; z = 6.8–10.8, or (when х = 1) CA/CNT NCs of composition Ca₁₀(PO₄)₆CO₃ · yCNT · zH₂O, where y = 1–3; z = 6.9–10.8, are formed as the carbonate and CNT contents of the NC increase. Our results favor the understanding of the effect of carbonization and CNTs on the metabolic formation of native bone tissue apatite and can be used for the design of efficient ceramics for bone implants.     

Synthesis and physicochemical properties of calcium hydroxylapatite/multi-walled carbon nanotubes nanocomposites

Calcium hydroxylapatite/carbon nanotubes (HA/CNT) composites with various CNT contents have been synthesized by coprecipitation from aqueous solutions in the CaCl₂-(NH₄)₂HPO₄-NH₃-CNT-H₂O system (25°C) under conditions modeling the interaction between HA (Ca₁₀(PO₄)₆(OH)₂), which is an inorganic component of osseous tissue, and multi-walled CNTs. The empirical formula of the composites is Ca₁₀(PO₄)₆(OH)₂ · nCNT · 6H₂O, where n = 0.2?C5.0. The synthesis products have been identified by the solubility (Tananaev??s residual concentration) method, pH measurements, chemical analysis, X-ray diffraction, IR spectroscopy, electron spectroscopy for chemical analysis, and scanning and transmission electron microscopy. The effect of the CNT concentration in aqueous solution on the composition of the HA/CNT composites and on the crystallographic and morphological characteristics of HA nanocrystals in HA/CNT has been investigated.     

Synthesis and Physicochemical Study of Chitosan-Containing Calcium Hydroxylapatites

The CaCl₂-(NH₄)₂HPO₄-(C₆H₁₁NO₄)_n-NH₃-H₂O system at 25°C was studied by the solubility (Tananaev’s residual concentrations) technique and pH measurements. The parameters providing for the coprecipitation of nanocrystalline (12.5–18.7 nm) calcium and chitosan hydroxylapatites were found. Calcium-deficient chitosan hydroxylapatites Ca_9.8(PO₄)₆(OH)_1.6 · xC₆H₁₁NO₄ · yH₂O, where x = 0.075 or 0.37 and y = 5.8 or 6.2, and stoichiometric calcium hydroxylapatites Ca₁₀(PO₄)₆(OH)₂ · xC₆H₁₁NO₄ · yH₂O, where x = 0.075, 0.1, 0.2, 0.37, 0.5, or 0.75 and y = 5.7–7.5, were synthesized. Solid phases were characterized by chemical analysis, X-ray powder diffraction, thermogravimetric analysis, and IR spectroscopy.     

Lysine-containing calcium hydroxylapatite: Synthesis and physicochemical characterization

The CaCl₂-(NH₄)₂HPO₄-NH₂(CH₂)₄NH₂CHCOOH-NH₃-H₂O system at 25°C is studied using Tananaev’s solubility (residual concentrations) method and pH measurements. Lysine-containing calcium hydroxylapatite Ca₁₀(PO₄)₆(OH)_1.9[NH₂(CH₂)₄NH₂CHCOO]_0.1 · 6H₂O is identified using chemical analysis, thermogravimetry, powder X-ray diffraction, and IR spectroscopy.     

Synthesis and physicochemical characterization of carboxymethylcellulose-containing calcium hydroxylapatite

The CaCl₂-(NH₄)₂HPO₄-C₈H₁₁O₇Na-NH₃-H₂O system was studied at 25°C using the solubility method (Tananaev’s residual concentration method) and pH measurements. The solid phases isolated from the system were characterized using chemical analysis, X-ray powder diffraction, IR spectroscopy, and thermogravimetry. Nanocrystalline carboxymethylcellulose-containing calcium hydroxylapatites Ca₁₀(PO₄)₆(OH)₂ · xH₂O · yC₈H₁₁O₇Na with x = 6–12 and y = 0.1–0.5 were found as a result of the characterization.     

Synthesis and physicochemical study of nanocrystalline magnesium-containing calcium hydroxylapatites and chitosan

The interaction in the CaCl₂-MgCl₂-(NH₄)₂HPO₄-NH₃-H₂O and CaCl₂-MgCl₂-(NH₄)₂HPO₄-(C₆H₁₁NO₄) _n -NH₃-H₂O systems at 25°C has been investigated by the solubility (Tananaev’s residual concentration) method and by pH measurements. Magnesium-containing calcium hydroxylapatites with the general formula Mg _x Ca_{10 − x} (PO₄)₆(OH)₂ · nH₂O (x = 0.05, 0.1, 0.2, 0.3; n = 6–7.3) and magnesium- and chitosan-containing calcium hydroxylapatites with the general formula Mg _x Ca_{10 − x} (PO₄)₆(OH)₂ · y(C₆H₁₁NO₄) · nH₂O (x = 0.05, 0.1, 0.2, 0.3; y = 0.1, 0.3, 0.46; n = 6–8.3) have been isolated in the nanocrystalline state. The solids have been characterized by chemical and thermogravimetric analyses, X-ray diffraction, and IR spectroscopy.     

Structure and spectral characteristics of (NH4)2[Re2(HPO4)4 · 2H2O]

The compound (NH₄)₂[Re₂(HPO₄)₄ · 2H₂O] has been synthesized and characterized by electronic and vibrational spectroscopy. The molecular structure has been determined by X-ray diffraction (MoK _α radiation, λ = 0.71073 Å). The (NH₄)₂[Re₂(HPO₄)₄ · 2H₂O] coordination units form centrosymmetrical binuclear ordering with each metal atom being coordinated in a distorted octahedron incorporating one rhenium atom, one oxygen atom of the water molecule, and four phosphate oxygen atoms in the equatorial plane. The rhenium-rhenium bond length (2.2207 Å) corresponds to a quadruple bond between the atoms. The [Re₂(HPO₄)₄ · 2H₂O]^2- complex anions in the crystal are associated through strong hydrogen bonds formed by the phosphate O-H···O groups. The stability of dirhenium(III) tetra-μ-phosphates in aqueous solutions is considered.     

Physicochemical Principles of Synthesis of Liquid Fertilizers Based on Potassium Hydrophosphate

Technological prerequisites for obtaining special liquid fertilizers with potassium and ammonia hydrophosphates as components were studied. The solubility in the multicomponent (NH₄)₂HPO₄-K₂HPO₄-NH₄NO₃-H₂O and (NH₄)₂HPO₄-K₂HPO₄-CO(NH₂)₂-H₂O systems was studied. The chemical composition of the liquid compound fertilizers obtained was determined.     

Thermodynamic properties on quaternary aqueous solutions of chlorides charge-type 1-1*2-1*2-1: XCl + MgCl2 + CaCl2 + H2O with (X ≡ Na; NH4)

In this investigation, the quaternary aqueous solutions of chlorides charge-type 1-1*2-1*2-1 with a cation (Na⁺; NH₄⁺; Mg²⁺; Ca²⁺) have been studied using the hygrometric method at 298.15 K. The water activities of the systems NH₄Cl + MgCl₂ + CaCl₂ + H₂O and NaCl + MgCl₂ + CaCl₂ + H₂O are measured at total molalities from 0.60 mol kg⁻¹ to saturation for different ionic-strength fractions NH₄Cl or NaCl, y = 0.20, 0.50, 0.80, and z ratio ionic-strength for other solutes, with z = 0.20, 0.50 and 0.80 for each y. The obtained data allow the deduction of osmotic coefficients.     

A novel functional material based on carbon nanotubes modified by copper nanoparticles

A novel functional material is obtained on the basis of multiwall carbon nanotubes (CNT) modified by copper nanoparticles, which are distributed in the interlayer space and inside the CNT channel. Transformations induced by IR heating in a Cu(OOCH₃)₂ · H₂O-CNT system are studied by powder X-ray diffraction analysis and transmission electron microscopy. The CuO, Cu₂O, and Cu nanparticles penetrate into graphite-like layers of the CNT and form intercalated CNT. The intercalation of the CNT by Cu(OOCCH₃)₂ · H₂O can be used for their purification from impurity nanoparticles of amorphous carbon and polyaromatic compounds.     

Coprecipitation of calcium hydroxyapatite,graphene oxide,and chitosan from aqueous solutions

We determined the character of interactions between calcium hydroxyapatite Са₁₀(РO₄)₆(ОН)₂ (HA), graphene oxide (GO), and chitosan (С₆Н₁₁NO₄) _n (CHT) to yield HA/CHT/GO nanocomposites (NCs) in the СаС1₂–(NH₄)₂НРО₄–NH₃–Н₂О–(С₆Н₁₁NO₄) _n –GO system (25°С). A set of physicochemical methods helped us to elucidate composition–synthesis parameters–structure–particle size–properties correlations for the prepared NCs and to prove the feasibility to manufacture NCs with tailored HA, CHT, and GO contents, described by the bulk formula Са₁₀(РО₄)₆(ОН)₂ · х(С₆Н₁₁NO₄) _n · yGO · zН₂О, where х = 0.1, 0.2, 0.3; y = 0.6, 1.2, 2.4; and z = 6.0–7.4.     

Calcium phosphate powders synthesized from solutions with [Ca2+]/[PO 4 3− ]=1 for bioresorbable ceramics

Calcium phosphate powders for manufacturing bioceramics were synthesized via precipitation from stock solutions of (NH₄)₂HPO₄ and Ca(NO₃)₂, or CaCl₂ or Ca(CH₃COO)₂ with [Ca²⁺]/[PO₄³⁻] = 1, without pH regulation. Properties of powdered samples, including density and microstructure of ceramics sintered at 900, 1000, 1100°C, were studied. The following pairs of precursors such as Ca(NO₃)₂/(NH₄)₂HPO₄, CaCl₂/(NH₄)₂HPO₄, Ca(CH₃COO)₂/(NH₄)₂HPO₄ gave both insoluble calcium phosphates and the corresponding by-products of synthesis — NH₄NO₃, NH₄Cl, NH₄CH₃COO. These by-products were released from the calcium phosphate precipitates in the course of heating to the temperature of sintering. Owing to specific buffer properties of the solutions being formed during synthesis, the pH value varied in a wide range during the precipitation process leading to different final values of pH and, thus, to different target phase(s) after annealing at 900–1100°C. After sintering, the samples based on the powders synthesized from Ca(NO₃)₂/(NH₄)₂HPO₄ consisted of β-Ca₂P₂O₇, whereas the samples based on the powders derived from CaCl₂/(NH₄)₂HPO₄ were composed of β-Ca₂P₂O₇ and β-Ca₃(PO₄)₂, and the samples based on the powders synthesized from Ca(CH₃COO)₂/(NH₄)₂HPO₄ contained only β-Ca₃(PO₄)₂. All the powders can be considered as the precursors for fabrication of bioceramics with enhanced resorption.      

New three-dimensional (3,4)-net zincophosphites templated by linear diammonium cations: H3N(CH2)5NH3·Zn3(HPO3)4 and β-H3N(CH2)6NH3·Zn3(HPO3)4

The mild-condition syntheses, single-crystal structures and properties of H₃N(CH₂)₅NH₃·Zn₃(HPO₃)₄ and β-H₃N(CH₂)₆NH₃·Zn₃(HPO₃)₄ are reported. Both are constructed from (3,4)-nets of ZnO₄ tetrahedra and HPO₃ pyramids, sharing vertices to result in three-dimensional anionic open-frameworks. In both materials, the organic species interacts with the framework by way of N–H⋯O bonds. Crystal data: H₃N(CH₂)₅NH₃·Zn₃(HPO₃)₄, M_r = 620.22, orthorhombic, Pccn (No. 56), a = 9.5364 (9) Å, b = 21.8015 (19) Å, c = 9.1118 (7) Å, V = 1894.4 (3) Å³, Z = 4, R(F) = 0.044, wR(F²) = 0.111. β-H₃N(CH₂)₆NH₃·Zn₃(HPO₃)₄, M_r = 634.25, monoclinic, P2₁/n (No. 14), a = 8.7627 (1) Å, b = 13.8117 (2) Å, c = 16.6187 (3) Å, β = 92.680 (1)°, V = 2009.12 (5) Å³, Z = 4, R(F) = 0.072, wR(F²) = 0.187.     

Electrochemical application of titanium dioxide nanoparticle/gold nanoparticle/multiwalled carbon nanotube nanocomposites for nonenzymatic detection of ascorbic acid

Titanium dioxide nanoparticle/gold nanoparticle/carbon nanotube (TiO₂/Au/CNT) nanocomposites were synthesized, and then characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDX). A TiO₂/Au/CNT nanocomposite-modified glassy carbon (GC) electrode was prepared using the drop coating method and was investigated using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), differential pulse voltammetry (DPV), and amperometric current–time response (I-T). The modified material is redox-active. The nonenzymatically detected amount of ascorbic acid (AA) on the TiO₂/Au/CNT electrode showed a linear relationship with the AA concentration, for concentrations from 0.01 to 0.08 μM; the sensitivity was 117,776.36 μA?·?cm^?2?·?(mM)^?1, and the detection limit was 0.01 μM (S/N?=?3). The results indicated that the TiO₂/Au/CNT nanocomposite-modified GC electrode exhibited high electrocatalytic activity toward AA. This paper describes materials consisting of a network of TiO₂, Au, and MWCNTs, and the investigation of their synergistic effects in the detection of AA.     

DTA-TG and XRD study on the reaction between ZrOCl2·8H2O and (NH4)2HPO4 for synthesis of ZrP2O7

In this paper, we report results of thermoanalytical investigation on the reaction between ZrOCl₂·8H₂O and (NH₄)₂HPO₄ in molar ratio 1:2. Differential thermal-thermogravimetric and X-ray diffraction analyses were performed in order to reveal the chemical transformations, which took place during heating of the individual compounds ZrOCl₂·8H₂O, (NH₄)₂HPO₄ and the mixture ZrOCl₂·8H₂O:2(NH₄)₂HPO₄. It was shown that the transformations in the mixture below 160 °C were connected with dehydration of ZrOCl₂·8H₂O and interaction between the components of the mixture, which resulted in the formation of NH₄Cl, NH₄H₂PO₄ and a mainly amorphous zirconium phase, most likely t-ZrO₂. The zirconium component subsequently reacted with ammonium dihydrophosphate (below 200 °C) or with dehydrated phosphate derivatives (above 200 °C), which in both cases yielded an amorphous product. The interaction between the components of the mixture resulting in the formation of ZrP₂O₇ was completed by its crystallisation at 610 °C. Our study indicates an alternative low-temperature approach for the synthesis of the technologically important ZrP₂O₇ material.     

ZrONO3)2-H3PO4-KF(HF)-H2O system at molar ratios of PO 43? /Zr = 0.5?1.6 as the basis for phase formation

The system ZrO(NO₃)₂-H₃PO₄-KF(HF)-H₂O was studied at ∼20°C along sections at molar ratios of PO₄³⁻ = 0.5, 1.0, and 1.6; KF: Zr = 1−5; and HF: Zr = 2−6. Phases in precipitates were identified by X-ray powder diffraction; IR spectroscopy; and crystal-optical, chemical, X-ray fluorescence and thermal analyses. The following crystalline phases were isolated: potassium fluorozirconates K₃ZrF₇, K₂ZrF₆, δ-KZrF₅, and KZrF₅ · H₂O; zirconium hydrophosphate Zr(HPO₄)₂ · 0.5H₂O; and potassium fluorophosphate zirconate K₃Zr₃F₃(HPO₄)₃(PO₄)₂. The following amorphous basic oxo(hydroxo)fluorohydrophosphate nitrates were isolated: K₄Zr₄O_2.5F₈(HPO₄)₂(NO₃)₃ · 6H₂O, K₂Zr₃O₃F₂(HPO₄)₂(NO₃)₂ · H₂O, and KZr₃O_1.5F₃(HPO₄)₂(NO₃)₃ · 2H₂O. Fields of solid phases were constructed, and the roles of anions and cations in the phase formation were considered.     

Non-isothermal kinetics of thermal decomposition of NH<Subscript>4</Subscript>ZrH(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>·H<Subscript>2</Subscript>O

Nanocrystalline NH₄ZrH(PO₄)₂·H₂O was synthesized by solid-state reaction at low heat using ZrOCl₂·8H₂O and (NH₄)₂HPO₄ as raw materials. X-ray powder diffraction analysis showed that NH₄ZrH(PO₄)₂·H₂O was a layered compound with an interlayer distance of 1.148 nm. The thermal decomposition of NH₄ZrH(PO₄)₂·H₂O experienced four steps, which involves the dehydration of the crystal water molecule, deamination, intramolecular dehydration of the protonated phosphate groups, and the formation of orthorhombic ZrP₂O₇. In the DTA curve, the three endothermic peaks and an exothermic peak, respectively, corresponding to the first three steps' mass losses of NH₄ZrH(PO₄)₂·H₂O and crystallization of ZrP₂O₇ were observed. Based on Flynn–Wall–Ozawa equation and Kissinger equation, the average values of the activation energies associated with the NH₄ZrH(PO₄)₂·H₂O thermal decomposition and crystallization of ZrP₂O₇ were determined to be 56.720 ± 13.1, 106.55 ± 6.28, 129.25 ± 4.32, and 521.90 kJ mol⁻¹, respectively. Dehydration of the crystal water of NH₄ZrH(PO₄)₂·H₂O could be due to multi-step reaction mechanisms: deamination of NH₄ZrH(PO₄)₂ and intramolecular dehydration of the protonated phosphate groups from Zr(HPO₄)₂ are simple reaction mechanisms.     

Synthesis and physicochemical characterization of nanocrystalline chitosan-containing calcium carbonate apatites

The CaCl₂-(NH₄)₂HPO₄-NH₄HCO₃-(C₆H₁₁NO₄) _n -H₂O system at 25°C has been investigated by the solubility (Tananaev’s residual concentration) method and pH measurements. Coprecipitation conditions have been determined for nanocrystalline type A and B calcium carbonate apatites. Type A: Ca₁₀(PO₄)₆(CO₃) _x (OH)_{2 − 2x} · yC₆H₁₁NO₄ · zH₂O (x = 0.2, 0.5, 1.0; y = 0.1, 0.3, 0.5; z = 5.3−6.7); type B: Ca₁₀[(PO₄)_5.7(CO₃)_0.45]CO₃ · 0.3C₆H₁₁NO₄ · 9H₂O, and Ca₁₀[(PO₄)_5.55(CO₃)_0.675]CO₃ · 0.3C₆H₁₁NO₄ · 9.2H₂O. The solid phases have been characterized by chemical analysis, X-ray diffraction, thermogravimetric analysis, and IR spectroscopy.     

A re-interpretation of the crystal structure of ‘(NH4)2(NH3)[Ni(NH3)2Cl4]’ in terms of (NH4)2−2z[Ni(NH3)2]z[Ni(NH3)2Cl4]

A re-interpretation and re-evaluation of single-crystal X-ray diffraction data of a previously reported ‘(NH₄)₂(NH₃)[Ni(NH₃)₂Cl₄]’ (J. Solid State Chem. 162 (2001) 254) give a new formula (NH₄)_2−2z[Ni(NH₃)₂]_z[Ni(NH₃)₂Cl₄] with z=0.152. This new formula results from defects in an idealized ‘(NH₄)₂[Ni(NH₃)₂Cl₄]’ basic structure, where two adjacent NH₄⁺ cations are replaced by one Ni(NH₃)₂²⁺ unit. Cl⁻ anions from the basic structure complete the coordination sphere of the new Ni²⁺ to [Ni(NH₃)₂Cl₄]²⁻.