Synthesis and in-depth analysis of highly ordered yttrium doped hydroxyapatite nanorods prepared by hydrothermal method and its mechanical analysis

In this study, undoped and yttrium (Y) doped nanocrystalline hydroxyapatite crystals were synthesized by the hydrothermal method at 180 °C for 24 h. Highly ordered and oriented hydroxyapatite (HAp) nanorods were prepared by yttrium doping and their nanostructure and physical properties were compared with those of undoped HAp rods. FESEM images showed that the doping with Y ions reduced the diameter (from 25 nm to 15 nm) and increased the length (from 95 nm to 115 nm) of the synthesized rods. The aspect ratio of the undoped and Y-doped nanorods were calculated to be 4.303 (SD = 0.0959) and 7.61 (SD = 0.0355), respectively. Specific surface area (SSA) analysis showed that SSA also increased from 66.74 m²/g to 68.57 m²/g with the addition of yttrium. Y-doped HAp nanorod reinforced HMWPE composites displayed the better mechanical performance than those reinforced with pure HAp nanorods. The possible strengthening of nanorods and the increase of SSA due to the reduction in the size of nanorods in the presence of yttrium may have contributed to the strengthening of Y-doped HAp/HMWPE composites.     

Electrochemical synthesis and characterization of hydroxyapatite powders

Electrochemical synthesis of hydroxyapatite powders was performed galvanostatically from homogeneous solution of Na₂H₂EDTA·2H₂O, NaH₂PO₄ and CaCl₂ at a concentration relationship Ca/EDTA/PO₄³⁻ of 0.25/0.25/0.15 M at current densities of 137 and 207 mA cm⁻² and pH values of 9.0 and 12.0. The hydroxyapatite powders were characterized by X-ray diffraction, size distribution measurements, transmission electron microscopy, scanning electron microscopy and thermogravimetric and differential thermal analysis. The influence of the electrochemical synthesis parameters, e.g. applied current density and pH value, on the phase composition, crystallite size, morphology and thermal characteristics of hydroxyapatite powders were investigated.     

Controllable synthesis of hydroxyapatite nanocrystals via a dendrimer-assisted hydrothermal process

The morphology and size of hydroxyapatite Ca₁₀(PO₄)₆(OH)₂ (denoted HAP) can be controlled under hydrothermal treatment assisted with different dendrimers, such as carboxylic terminated poly(amidoamine) (PAMAM) and polyhydroxy terminated PAMAM. The structure and morphology were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR) and transmission electron microscopy (TEM). IR spectra were also used to investigate the complexation of Ca²⁺ with PAMAM. The results revealed that the inner cores of the PAMAM dendrimers are hydrophilic and potentially open to calcium ions, since interior nitrogen moieties serve as complexation sites, especially in case of the polyhydroxy terminated PAMAM. And the reasonable mechanism of crystallization was proposed that it can be attributed to the localization of nucleation site: external or interior PAMAM. Additionally, the PAMAM dendrimer with carboxylic and polyhydroxy groups has an effective influence on the size and shape of hydroxyapatite (HAP) nanostructures. Different crystal morphology was accomplished by adsorption of different dendrimers onto specific faces of growing crystals, altering the relative growth rates of the different crystallographic faces and leading to different crystal habits.     

Influence of morphology and surface characteristics on the photocatalytic activity of rutile titania nanocrystals

This article presents the synthesis of phase-pure rutile titania with different morphologies via hydrothermal method at significantly low temperatures (40-150 °C) without any additives and their application as efficient photocatalyst for environmental remediation. Phase and morphology has been determined with X-ray diffraction (XRD) and transmission electron microscopy (TEM). Ultra violet diffuse reflectance spectroscopy (UV-DRS) shows the optical band-gap in the range of ∼2.8-3.1 eV and Brunauer-Emmett-Teller specific surface area is found to be between 70 and 140 m²/g depending on the synthesis conditions. Raman spectroscopic analyses of the samples provide valuable insights into the structural and stoichiometric details. Photodegradation of the pollutant azo-dye, methyl orange (MO) in presence and absence of oxygen was performed to study the photocatalytic efficiency of the synthesized materials. Complete photodegradation of the dye is confirmed with high performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LC-MS) study. Dependence of dye photodegradation rate on morphology, specific surface area, surface nonstoichiometry and acidity were investigated in detail. Catalyst performance was compared from the rate constants obtained for each reaction using non-linear least square fitting (NLSF) to the experimental data in a concentration ratio (C₀/C_t) versus time (t) plot which shows extraordinarily high activity for all samples compared to commercial reference. Among them the catalyst synthesized at 40 °C for 16 h showed best activity. Kinetic study of the reaction matches well with simulated fit to experimental data and confirms to be pseudo-first order reaction.     

Influence of processing method on the properties of hydroxyapatite nanoparticles in the presence of different citrate ion concentrations

The objective of this study was to investigate the effect of processing methods on the formation of ultra fine hydroxyapatite (HAp) nanoparticles in the presence of citrate ions and analyze their various physical properties. The addition of the citrate ions was found to reduce the size and prevent the agglomeration of HAp particles dramatically in the high gravity (HG) method compared to precipitation method. In precipitation method, the particle size reduced from 300 ± 70 nm to 90 ± 20 nm with the addition of citrate ions. In high gravity method, the particle size decreased more significantly from 80 ± 10 nm to 13 ± 5 nm with the addition of citrate ions. Furthermore, more uniform size distribution of nanoparticles was achieved in high gravity method. X-ray diffraction of nanoparticles prepared in both method exhibited slight shift of peaks to the higher angle with the addition of citric acid, indicating the incorporation of carbonate (CO₃) content in the HAp nanoparticles irrespective of the particle size. The mechanical properties of HWMPE matrix composite reinforced with nanoparticles was examined and this nanocomposite with nanoparticles prepared in high gravity method with the addition of citrate ions showed increased mechanical strength due to the considerable reduction in the particle size and higher uniformity of the particles. In vitro cellular analyses of the nanoparticle prepared in high gravity with the addition of citrate ions also displayed the most pronounced spreading of cell growth.     

Preparation of amino-acid-regulated hydroxyapatite particles by hydrothermal method

The hydroxyapatite nanorods (about 80 nm in length and 15 nm in width) with uniform size were achieved by hydrothermal method at 100 °C and pH 10 in the presence of alanine and glutamic acid. A special instillment order was used and the prepared powders were characterized for phase composition by X-ray diffraction and Fourier Transform infrared spectroscopy. The size and morphology of HAP nanoparticles were studied by Transmission electron microscopy. The characterization showed that the amino acid could induce the synthesis of hydroxyapatite nanoparticle and control HAP crystal growth when HAP crystal was formed. An instable monetite phase (CaPO₃OH) was found in the progress of ACP transforming to HAP.     

One-pot template-free synthesis of mesoporous boehmite core-shell and hollow spheres by a simple solvothermal route

Uniform-sized and monodispersed boehmite core-shell and hollow spheres have been successfully synthesized using a template-free solvothermal route. The experimental parameters such as reaction duration, the trisodium citrate amounts and solvents are shown to play important roles in the formation of the AlOOH core-shell and hollow spheres. X-ray diffraction, Fourier transform IR, thermal gravimetric analysis, N₂ adsorption/desorption, scanning electron microscopy, transmission electron microscopy, and high-resolution TEM were used to characterize the products. The results show that the prepared polycrystalline hollow spheres are composed of well-aligned AlOOH nanowires and have an orthorhombic structure. Finally, a dissolution-renucleation mechanism was proposed for the formation of boehmite hollow structures.     

Growth and time dependent alignment of KCl crystals in Hemoglobin LB monolayer

Nature and organism often use the biomineralization technique to build up various highly regular structures such as bone, teeth, kidney stone etc., and recently this becomes the strategy to design and synthesis of novel biocomposite materials. We report here the controlled crystallization of KCl in Langmuir and Langmuir Blodgett (LB) monolayer of Hemoglobin (Hb) at ambient condition. The nucleation and growth of KCl crystals in Hb monolayer has temporal and KCl concentration dependency. The growth of KCl crystals in LB film of Hb has distinct behavior in the alignment of crystals from linear to fractal like structures depending on growth time. The crystallographic identity of the biomineralized KCl crystal is confirmed from HR-TEM, XRD, and from powder diffraction simulation. Our results substantiated that the template of Langmuir monolayer of proteins plays a crucial role in biomineralization as well as in designing and synthesizing of novel biocomposite materials.     

Selective synthesis of copper nanoplates and nanowires via a surfactant-assisted hydrothermal process

A facile solution-phase process has been demonstrated for the selective preparation of single-crystalline Cu nanoplates and nanowires by reducing Cu⁺ with ascorbic acid (VC) in the presence of cetyltrimethylammonium bromide (CTAB) or cetyltrimethylammonium chloride (CTAC). To study the formation process of nanoplates and nanowires, samples obtained at various stages of the growth process were studied by TEM and XRD. The possible mechanism was discussed to elucidate the formation of different morphologies of Cu nanostructures. UV–vis spectra of the Cu nanoplates and nanowires were recorded to investigate their optical properties, which indicated that the as-prepared Cu nanostructures exhibited morphology-dependent optical property.     

Single crystalline ZnO nanorods grown by a simple hydrothermal process

Single crystalline ZnO nanorods with wurtzite structure have been prepared by a simple hydrothermal process. The microstructure and composition of the products were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM, energy dispersive X-ray spectrum (EDS) and Raman spectrum. The nanorods have diameters ranging from 100 nm to 800 nm and length of longer than 10 µm. Raman peak at 437.8 cm^− 1 displays the characteristic peak of wurtzite ZnO. Photoluminescence (PL) spectrum shows a blue light emission at 441 nm, which is related to radiative recombination of photo-generated holes with singularly ionized oxygen vacancies.     

Micro- and nano-sized peptidic assemblies prepared via solid-vapor approach: Morphological and spectroscopic aspects

The short aromatic dipeptide l-diphenylalanine (FF) was used to build supramolecular assemblies from amorphous films that were deposited onto Si substrates using an adapted form of the solid-vapor method [Adv. Mater. 20 (2008) 3754–3758]. The morphological and spectroscopic behaviors of the resulting micro- and nano-sized 1-D arrays were investigated. The formation of the structures was examined under different preparation conditions; specifically, the nature of the solvent (water or aniline), the concentration of peptides in the precursor solution and the incubation time were varied. Our results indicate that changes in preparation have dramatic consequences on the final morphology of the assemblies. Particularly, our data suggest that the solvent vapor pressure and a reduction of the hydrophobic capabilities of the substrate play a relevant role on structuration since they presumably increase heat and mass transport, respectively. Spectroscopic data reveal that the use of different vapors promotes the emergence of new vibrational modes, which is interpreted as a change in the symmetry of the molecular arrangement that is accompanied by an increase in the number of degrees of freedom. These findings strongly indicate that different symmetries-presumably orthorhombic and hexagonal symmetries-can be obtained depending on the type of solvent used during the preparation. To assess the interaction between our structures and a functionalizing agent, aniline was polymerized onto the structured films and then their morphological and spectroscopic behaviors were also investigated.     

In vitro study of nano-sized zinc doped bioactive glass

Surface reactivity in physiological fluid has been linked to bioactivity of a material. Past research has shown that bioactive glass containing zinc has the potential in bone regeneration field due to its enhanced bioactivity. However, results from literature are always contradictory. Therefore, in this study, surface reactivity of bioactive glass containing zinc was evaluated through the study of morphology and composition of apatite layer formed after immersion in simulated body fluid (SBF). Nano-sized bioactive glass with 5 and 10 mol% zinc were synthesized through quick alkali sol–gel method. The synthesized Zn–bioglass was characterized using field emission scanning electron microscope (FESEM), energy dispersive X-ray spectrometer (EDX), X-ray diffractometer (XRD) and Fourier transform infrared spectrometer (FTIR). Samples after SBF immersion were characterized using scanning electron microscope (SEM) and EDX. Morphological study through SEM showed the formation of spherical apatite particles with Ca/P ratio closer to 1.67 on the surface of 5 mol% Zn–bioglass. Whereas, the 10 mol% Zn–bioglass samples induced the formation of flake-like structure of calcite in addition to the spherical apatite particles with much higher Ca/P ratio. Our results suggest that the higher Zn content increases the bioactivity through the formation of bone-bonding calcite as well as the spherical apatite particles.     

Influence of thermal treatment conditions on two-dimensional crystal growth of nanocrystal corundum abrasives

The effect of thermal treatment on mechanical property and microstructure evolution in two-dimension of nanocrystal corundum abrasives has been investigated. The abrasives with and without presence of bond were calcined at different thermal treatment temperatures. The results indicated that thermal treatment conditions had obvious influence on crystal size and mechanical strength of corundum abrasives. Crystal size increased with increasing of the calcining temperature, and crystal growth of sample with presence of bond was more remarkable than that without presence of bond. And it was found that 950 °C is the critical temperature of abnormal crystal growth of corundum abrasives in the heated treatment conditions. Beyond this critical temperature, crystal size evidently increased while strength and wear resistance of abrasive decreased. In this case, the degradation of the abrasive in microstructure and strength should be important considerations for the preparation of ceramic corundum abrasive grinding tool.     

Crystallization and morphology of mordenite zeolite influenced by various parameters in organic-free synthesis

A series of mordenite zeolites with different morphologies were synthesized via a facile organic-free hydrothermal route, and characterized by X-ray diffraction, scanning electron microscopy, X-ray fluorescence spectrometer and N₂ adsorption-desorption techniques. Influences of synthetic parameters, including seed crystal, silicon precursor, SiO₂/Al₂O₃, Na₂O/SiO₂ and H₂O/SiO₂, on mordenite crystallization were investigated systematically. It was found that mordenite zeolites with various morphologies, such as fiber-like, rod-like, prism-like and needle-like ones could be synthesized in control. Especially, novel nano fiber-like MOR crystals with high c/b aspect ratio were prepared from low silica concentration system, which was manipulated by using small initial SiO₂/Al₂O₃ ratio, large H₂O/SiO₂ and silicon source with slow dissolution rate. Moreover, mordenite samples with various morphologies exhibited different mesopore property and thermal stability.     

Biodegradable amylose films reinforced by graphene oxide and polyvinyl alcohol

Graphene oxide/amylose (GO/amylose) composite films with different amounts of graphene oxide (GO), glycerol and polyvinyl alcohol (PVA) were prepared by a solution casting method. The structure, morphologies, and properties of the films were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, thermal gravimetric analysis, UV–vis spectroscopy and tensile tests. The results indicated good dispersion of the GO nanosheets in the GO/amylose composite films and consequently a significant improvement in their mechanical properties. The addition of GO increased the tensile strength of the GO/amylose films, significantly. When glycerol was used as a plasticizer, the elongation at break of the films increased. When PVA was also added to the composite films, the films were mechanically strong and flexible. The incorporation of GO also decreased the moisture absorbability and UV transmittance of the films. The stability of the GO/amylose films in acidic and alkaline solutions was also studied and the films had excellent stability in both acidic and alkaline aqueous mediums.     

Influence of stirring in the synthesis of gold nanorods

Gold nanorods have been prepared by the seed-mediated growth method, in order to find the effect of stirring during the synthesis to the final shape and optical properties. The presence or absence of stirring during each step of the preparation procedure was considered a parameter to control in order to adjust the optical absorption associated with the surface plasmon resonance of the nanorods. Results show that the longitudinal surface plasmon resonance band shifts to larger wavelengths in the absence of stirring of the growth solution. Width and intensity of the absorption band associated with the longitudinal surface plasmon is reduced upon stirring during the synthesis. On the contrary, the position of the transversal surface plasmon resonance band scarcely depends upon stirring. Theoretical calculations performed using the Gans model are coherent with experimental obtained results, showing that as the aspect ratio increases, longitudinal plasmons absorption shifts toward larger wavelengths and increases both intensity and bandwidth.     

Synthesis and characterization of a lamellar hydroxyapatite/DNA nanohybrid

Two-dimensional layered materials exhibit desired functionalities when being used as gene delivery materials. In this study, a novel gene delivering vector, lamellar hydroxyapatite (HAp)/DNA nanohybrid was prepared. The structure of HAp/DNA nanohybrid was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Fourier transform infrared (FT-IR) spectroscopy analysis revealed that ion-exchange occurred during the process. Gel electrophoresis analysis confirmed that the lamellar HAp could protect DNA from degradation of DNase I and the protected DNA could be recovered readily under acid conditions. Furthermore, the integrity of released DNA was confirmed by UV–vis spectra.     

The characteristic of the ZnO nanowire morphology grown by the hydrothermal method on various surface-treated seed layers

ZnO nanowires with various density and diameters were obtained by altering the wetting properties of aluminum doped ZnO (AZO) seed layers. AZO seed layers deposited on glass substrates were treated by inductor coupled plasmas (ICP) or atmospheric pressure plasma (APP) systems in order to control wettability before ZnO nanowire growth. Morphology of ZnO nanowires grown by the hydrothermal method was influenced by wettability of AZO seed layers. Our investigation shows that the diameter of ZnO nanowire increases and the length of ZnO nanowire decreases when the contact angle on the AZO seed layer is decreased. As a result, we confirmed that the morphology of ZnO nanowires could be easily controlled by surface treatment of seed layers with the plasma system.     

Egg albumin-assisted preparation,characterization and influencing factors of Dumbbell-shaped BaCO3 superstructures

Dumbbell-shaped barium carbonate superstructures were successfully synthesized in the aqueous system containing egg albumin and ethylenediaminetetraacetate disodium (EDTA-2Na), employing BaCl₂, NaHCO₃ and NH₃·H₂O as the starting reagents. The as-prepared product was characterized by X-ray powder diffraction (XRD), energy dispersive spectrometry (EDS), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Some factors influencing the morphology of BaCO₃ crystals, such as the time, the amounts of egg albumin and EDTA-2Na, were studied. Experimental facts showed that a proper amount of egg albumin and EDTA-2Na played crucial roles in the formation of dumbbell-shaped BaCO₃ superstructures.     

Nanocrystalline zeolite beta: The effect of template agent on crystal size

Zeolite beta was hydrothermally synthesized using the method reported by Camblor et al. [M.A. Camblor, A. Corma, A. Misud, J. Perez-Pariente, S. Valencia, Stud. Surface Sci. Microporous Mater. 105 (1997) 341]. The influence of template agent, aluminum content and gel dilution on the crystalline size of zeolite beta was carefully studied. When the crystalline size reduces from 500 to 30 nm, the pore volume particularly the mesopore volume of zeolite beta significantly increased. The experimental results also evidenced that more template agent employed in the initial gel resulted in smaller crystalline sizes of zeolite beta whereas the water content has little effect on the crystalline size. This is the first work that demonstrates the important role of the template content in the initial gel in the determination of the crystalline size of nanosized zeolite beta.