Continuous microwave assisted flow synthesis and characterization of calcium deficient hydroxyapatite nanorods

Synthetic calcium deficient hydroxyapatite (CDHA) nanorods (<100?nm) were rapidly prepared with the help of a new continuous microwave assisted flow synthesis (CMFS) reactor in 5?min only from aqueous solution of calcium hydroxide and orthophosphoric acid at pH 8.5. The effect of various reaction parameters like, pH, concentration, temperature, residence time, degree of crystallinity and particle surface area were studied in detail. The phase purity, particle size and morphology of the powder samples were characterised by techniques such as X-ray diffraction analysis, transmission electron microscopy, scanning electron microscopy and FTIR and Raman spectroscopy. With the help of X-ray photoelectron spectroscopy, the chemical analysis was completed. Measurements were taken into account to estimate the particle size following the dynamic light scattering. The results showed that the employed synthesis procedure offered an efficient and economical route to achieve high quality nano-sized products with suitable size and low level of impurities.     

Fabrication of mesoporous carbonated hydroxyapatite/carbon nanotube composite coatings by microwave irradiation method

Carbonated hydroxyapatite/carbon nanotube composite coatings (MHCs) with mesoporous structures were fabricated by electrophoretic deposition of nacre powders and carbon nanotubes on Ti6Al4V substrates followed by treatment with a phosphate buffer solution (PBS) by microwave irradiation method. The carbon nanotubes are dispersed uniformly on the whole MHCs. The conversion mechanism of the crack-free nacre/carbonate nanotube composite coatings (NCCs) to MHCs is a dissolution-precipitation reaction. After soaking in PBS, calcium ions are released from the nacre powders and react with phosphate ions to form carbonated hydroxyapatite nanoparticles. These nanoparticles aggregate to form mesopores with the pore sizes of ~ 3.9 nm among them. Simulated body fluid (SBF) immersion tests reveal that MHCs have a good in vitro bioactivity.     

Microwave rapid heating for the synthesis of gold nanorods

A microwave heating system with a sealed reaction chamber and a precise temperature-controlled module was employed to assess the synthesis of tetradecylammonium bromide (TOAB) cation surfactant-stabilized gold nanorods. Scanning electron microscopy (SEM) was employed to characterize the size and the shape of particles. It was found that both TOAB concentrations and reaction temperature programs played an important role in the formation of gold nanorods. By using higher TOAB concentration and faster rising reaction temperature, gold nanorods with higher aspect ratio could be produced. This finding demonstrated the combination of TOAB surfactant and microwave system to be a useful approach for the preparation of gold nanorods.     

Amino acid-assisted synthesis of strontium hydroxyapatite bone cement by a soft solution freezing method

Among many cations that can substitute for calcium in the structure of hydroxyapatite, strontium provokes an increasing interest because of its beneficial effect on bone formation and prevention of bone resorption. Strontium-incorporated calcium phosphates show potential in biomedical application, particularly the doped strontium may help in new bone formation. We have synthesized strontium hydroxyapatite powders at 2 °C by a soft solution freezing method using glycine as the template. The structural and morphological characterizations were carried out on the as obtained powders using Fourier transform infrared spectroscopy, X-ray diffraction analysis and scanning electron microscopy techniques. Strontium was quantitatively incorporated into hydroxyapatite where its substitution for calcium provoked a linear shift of the infrared absorption bands of the hydroxyl and phosphate groups. The strontium substituted bone cement has potential for use in orthopaedic surgeries. The present study shows that the addition of glycine plays an important role in reducing the particle size of strontium hydroxyapatite which could be used for biomedical applications.     

Size-controlled synthesis of hydroxyapatite nanorods by chemical precipitation in the presence of organic modifiers

Size-controlled synthesis of hydroxyapatite nanorods was carried out by chemical precipitation method using citric acid, sodium dodecyl sulphate, and sodium dodecylbenzene sulphonate as organic modifiers and starting from calcium nitrate, phosphoric acid, and ammonia solution. The crystallinity of the resultant hydroxyapatite increased with increasing the autoclaving temperature. The particle sizes of the resultant HAP nanorods varied with the presence of the different structured organic modifiers and the synthetic temperature. The interaction between the anions of the modifiers and the hydroxyapatite crystallites controlled the crystal growth.     

Size-controlled synthesis of hydroxyapatite nanorods in the presence of organic modifiers

Size-controlled synthesis of hydroxyapatite nanorods was carried out by chemical precipitation followed by hydrothermal treatment using trisodium citrate, Tween 20, and polyethylene glycol (MW 600) as organic modifiers and starting from calcium nitrate and phosphoric acid. The particle sizes of the resultant hydroxyapatite nanorods varied with the chemical structures of the present organic modifiers and the crystallinity of the hydroxyapatite increased with an increasing autoclaving temperature.     

Hydrothermal synthesis of calcium hydroxyapatite nanorods in the presence of PVP

Calcium hydroxyphosphate (Ca₁₀(PO₄)₆(OH)₂, HAP) nanorods have been successfully synthesized by a simple and mild hydrothermal treatment in the presence of polyvinylpyrrolidone (PVP). A complex of calcium nitrate (Ca(NO₃)₂) and Na₂HPO₄ was used to supply the calcium and phosphate ions during the reactions. The synthesis of pure HAP nanorods was under near neutral condition. The morphology and structure of the samples were characterized by transmission electron microscope (TEM), scanning electron microscope (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FT-IR) spectroscopy analysis. The nanorods were uniform with diameter of 20–25 nm and length ranging from several hundreds of nanometers to several micrometers. The influence of different experiment conditions, i.e., the PVP concentration, molar ratio of Ca²⁺ to HPO₄ ²⁻, reaction time, and temperature, on the morphology of the nanorods was investigated. The formation mechanism of rod-like HAP and effects of PVP on the crystal nucleation and growth have also been discussed.     

Preparation and thermal stability analysis of hydroxyapatite derived from the precipitation process and microwave irradiation method

Thermally stable hydroxyapatite (HAP) polycrystals were prepared using H₃PO₄, glucose and Ca(NO₃)₂·4H₂O, as starting materials with microwave irradiation method and coprecipitation method, respectively. The crystal structure was monitored by XRD. The calcium/phosphorous molar ratio of the different as-precipitated hydroxyapatite was determined by ICP. The results show that various parameters such as aging time, microwave irradiation power and time have significant effects on thermal stability of hydroxyapatite. The thermal stability of HAP increases with protraction of aging time, microwave irradiation time and power, respectively. Aging time reached to 24 h; HAP made by precipitation can exist stably at calcination of 1200 °C. Microwave time and power was 1 h or 700 W, respectively; the sample quenched from 1200 °C is still HAP.     

Structural and magnetic properties of Zn1-xcoxO nanorods prepared by microwave irradiation technique

We have successfully synthesized large-scale aggregative flowerlike Zn1-xCo(x)O (0.0 < or = x < or = 0.07) nanostructures, consisting of many branches of nanorods at different orientations with diameter within 100-150 nm (tip diameter approximately 50 nm) and length of approximately 1 microm. The rods were prepared using Zinc nitrate, cobalt nitrate and KOH in 180 Watt microwave radiation for short time interval. The synthesized nanorods were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), field emission transmission electron microscopy (FETEM) and DC magnetization measurements. XRD and TEM results indicate that the novel flowerlike nanostructures are hexagonal with wurtzite structure and Co ions were successfully incorporated into the lattice position of Zn ions in ZnO matrix. The selected area electron diffraction (SAED) pattern reveals that the nanorods are single crystal in nature and preferentially grow along [0 0 1] direction. Magnetic studies show that Zn1-xCo(x)O nanorods exhibit room temperature ferromagnetism. This novel nanostructure could be a promising candidate for a variety of future spintronic applications.     

Controlled hydrothermal synthesis of strontium-substituted hydroxyapatite nanorods and their application as a drug carrier for proteins

Without the addition of any organic additives, both undoped hydroxyapatite (HAp) and different strontium (Sr)-substituted hydroxyapatite (SrHAp) samples with amounts from 1 to 20?mol.% were synthesized via hydrothermal route. The crystal texture, chemical functional group and microstructure were well characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and inductively coupled plasma (ICP), respectively. And the protein adsorption and release properties of bovine serum albumin (BSA) and lysozyme (LYS) were investigated on the samples to search for a well protein drug delivery vehicle. The results revealed that the pure HAp consisted of uniform nanobelts and all SrHAp samples had a rod-like morphology. The lattice parameters of SrHAp were larger than HAp, while they had similar crystal structure. The protein adsorption and release tests indicated that the incorporation of Sr into HAp lattice could increase the amounts of BSA and LYS adsorption. The BSA adsorption capacity of 1SrHAp was found to be 55.52?mg/g, which was about 14.64% higher than that of HAp. The 15SrHAp possessed the highest LYS loading amount of 90.54?mg/g, which was about three times that of HAp. And SrHAp exhibited sustained protein release capability.     

表面活性剂辅助室温液相合成BaCO3纳米棒

用阳离子表面活性剂十六烷基三甲基溴化铵(CTAB)为形貌控制剂,通过室温液相反应成功制备出BaCO3纳米棒.纳米棒的直径为60～250nm、长度达几微米.用X射线粉末衍射和透射显微镜技术对所制备纳米晶的成分、形状和尺寸进行了表征分析.研究结果表明,表面活性剂对BaCO~纳米棒的形成起着关键的作用.对BaCO~纳米棒的形成机理作了深入的讨论,提出了BaCO3纳米棒的表面活性剂软模板诱导自组装生长机理.     

A simple method for the synthesis of silicon carbide nanorods

SiC nanorods were synthesized by a reaction at a temperature of 1200 degrees C, under an argon gas atmosphere, from silicon and amorphous carbon powders mixed by ball milling. The reaction product, which contain SiC nanorods and nanoparticles, has been characterized by high-resolution transmission electron microscopy, X-ray diffraction, and micro-Raman spectroscopy. The synthesized nanorods are more than 1 micron long with a mean diameter of about 10-30 nm. The nanorods possess a well-defined crystalline structure with a thin layer of amorphous SiO2 on the surface. Raman shifts of SiC nanorods and the role of structural defects are discussed.     

Synthesis of mesoporous hydroxyapatite nanoparticles using a template-free sonochemistry-assisted microwave method

A facile template-free sonochemistry-assisted microwave method was successfully developed for the synthesis of mesoporous hydroxyapatite nanoparticles (MHN) in a short time. The prepared MHN were characterized by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and N₂ adsorption–desorption isotherms. TEM images showed a clear rod-like morphology with length of 50–100 nm and width of about 20 nm. XRD and FTIR indicated a typical hydroxyapatite phase with high crystallinity. N₂ adsorption–desorption isotherms revealed an irregular mesoporous structure. Judging from the values calculated from N₂ isotherms, the specific surface area and pore volume obviously decreased after the sintering process. In a typical example, the specific surface area, pore volume, and pore size of MHN before and after calcination were 79.74 m²/g, 0.46 cm³/g, 2.7 nm and 45.41 m²/g, 0.22 cm³/g, 2.8 nm, respectively. In addition, MHN could be synthesized in a period of time as short as 10 min. Further investigation indicated that microwave radiation played a dominant role in the emergence of mesoporous structure, while ultrasound irradiation acted as a supporting role. Based on the above results, a possible mechanism of formation of mesoporous hydroxyapatite has been proposed.     

Low-temperature synthesis of CuS nanorods by simple wet chemical method

CuS nanorods of length 60–100 nm and 15 nm in diameter have been synthesized by simple wet chemical method at 105 °C using CuCl₂·2H₂O as Cu-precursor, CS₂ as S-source and ethylenediamine as the attacking reagent. The plausible reaction mechanism has been proposed and the effect of reaction temperature on morphology has been discussed. X-ray diffraction (XRD) pattern suggests the formation of hexagonal phase CuS. The morphology of the products has been studied by transmission electron microscope (TEM) analysis. A detailed optical study has also been done.     

机械化学法合成羟基磷灰石过程中的"爆炸式"反应

应用机械化学原理,研究了在振动磨样机中由磷酸二氢钙(MCPM)和氢氧化钙合成羟基磷灰石(HAP)过程的动力学机制,并建立了相应的动力学模型.结果表明,合成过程为生成中间产物二水磷酸氢钙(DCPD)的两步式反应,其中第二步反应在第一步反应结束后才开始,并且在很短的时间内(＜30s)迅速完成,即发生了"爆炸式"反应,反应过程可用类Avrami方程进行表征.探讨了发生"爆炸式"反应的可能机理.     

Efficient one pot synthesis of chitosan-induced gold nanoparticles by microwave irradiation

An efficient and rapid method for the preparation of gold nanoparticles (AuNPs) within a few minutes has been developed by direct microwave irradiation of HAuCl₄ and chitosan mixed solution in one pot. Herein, chitosan molecules acted as both the reducing and stabilizing agent for the preparation of AuNPs. The obtained AuNPs have different shapes, such as the spherical nanoparticles, triangular nanoplates and nanorods, which were characterized by ultraviolet-visible (UV-Vis) spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and fourier transform infrared spectroscopy (FTIR). Additionally, the results showed that microwave power could affect the required time for preparing the AuNPs arising from the distinction of heating rate, and long irradiation time was favorable for complete reduction of HAuCl₄ when a low microwave power was applied.     

Rational synthesis of a nanocrystalline calcium phosphate cement exhibiting rapid conversion to hydroxyapatite

The rational synthesis, comprehensive characterization, and mechanical and micromechanical properties of a calcium phosphate cement are presented. Hydroxyapatite cement biomaterial was synthesized from reactive sub-micrometer-sized dicalcium phosphate dihydrate and tetracalcium phosphate via a dissolution-precipitation reaction using water as the liquid phase. As a result nanostructured, Ca-deficient and carbonated B-type hydroxyapatite is formed. The cement shows good processibility, sets in 22 ± 2 min and entirely transforms to the end product after 6 h of setting reaction, one of the highest conversion rates among previously reported for calcium phosphate cements based on dicalcium and tetracalcium phosphates. The combination of all elucidated physical-chemical traits leads to an essential bioactivity and biocompatibility of the cement, as revealed by in vitro acellular simulated body fluid and cell culture studies.The compressive strength of the produced cement biomaterial was established to be 25 ± 3 MPa. Furthermore, nanoindentation tests were performed directly on the cement to probe its local elasticity and plasticity at sub-micrometer/micrometer level. The measured elastic modulus and hardness were established to be E_s = 23 ± 3.5 and H = 0.7 ± 0.2 GPa, respectively. These values are in close agreement with those reported in literature for trabecular and cortical bones, reflecting good elastic and plastic coherence between synthesized cement biomaterial and human bones.     

Investigation on the rapid degradation of congo red catalyzed by activated carbon powder under microwave irradiation

Azo dyestuff-congo red in aqueous solution can be degraded rapidly under microwave irradiation in the presence of activated carbon powder. The results showed that the degradation ratio could reach 87.79% for 25 mL total volume with 50mg/L congo red and 2.0 g/L activated carbon powder under 1.5 min microwave irradiation. Furthermore, within the same irradiation time, congo red could be degraded fully by increasing addition amount (e.g. 3.6g/L) of activated carbon powder and the degradation ratio was up to 96.49%. Otherwise, with the same addition amount, congo red also could be degraded completely by prolonging irradiation time (e.g. 2.5 min) and the degradation ratio was up to 97.88%. In addition, the influences of microwave irradiation time, initial concentration of congo red, addition amount and used times of activated carbon powder as well as solution acidity on the degradation were discussed in details adopting UV-vis spectra, FT-IR spectra, ion chromatography, high phase liquid chromatography (HPLC) and TOC analysis technologies. Here, the method using activated carbon powder as catalyst under microwave irradiation shows many advantages including high degradation ratios, short reaction time, low costs, no intermediates and no secondary pollution. Therefore, it may be fit for dealing with various azo dyestuff wastewaters on a large scale.