Surfactant-free electrochemical synthesis of fluoridated hydroxyapatite nanorods for biomedical applications

Fluoridated hydroxyapatite (FHA) [Ca₁₀(PO₄)₆F_x(OH)_2−x, x = 0–2] is believed to be a promising calcium phosphate (CaP) to replace pure hydroxyapatite (HA) for next-generation implants, owing to its better biocompatibility, higher antibacterial activity, and lower solubility. Notably, the shape and size of the CaP crystals play key roles in their performance and can influence their applications. One-dimensional (1D) FHA nanorods are important CaP materials which have been widely used in regenerative medicine applications such as restorative dentistry. Unfortunately, the traditional synthesis methods for FHA nanorods either employ surfactants or take a relatively long time. In this study, we aimed to propose a facile synthesis route to fabricate FHA nanorods without any surfactants using an electrochemical deposition method for the first time. This study focused on preparing FHA nanorods without the assistance of any surfactant, unlike the traditional synthesis methods, to avoid chemical impurities. FHA nanorods with lengths of 124–2606 nm, diameters of 28–211 nm, and aspect ratios of 4.4–21.8 were synthesized using the electrochemical method, followed by a heat treatment. For the as-synthesized FHA nanorods, the Ca/P ratio was 1.60 and the atomic concentration of F was 2.06 at.%. An ultrastructure examination revealed that each FHA nanorod possessed long-range order, good crystallinity, and a defect-free lattice with a certain crystallographic plane orientation along the whole rod. In short, we propose a novel, surfactant-free, cost-saving, and more efficient route to synthesize FHA nanorods which can be widely applied in multiple biomedical applications, including drug delivery, bone repair, and restorative dentistry.     

Coating Y2O3 nano-particles with ZrO2-additive via precipitation method for colloidal processing of highly transparent Y2O3 ceramics

In the present work, transparent Y₂O₃ ceramics were prepared via colloidal processing method using ZrO₂-coated nano-sized Y₂O₃ powders. The chemical precipitation method was adopted for the coating of Y₂O₃ raw powder. The evolution of the coated-ZrO₂ layer upon calcination was studied. The rheological behaviors of the slurries of Y₂O₃ powders coated with different content of ZrO₂-additive were investigated. The pH_IEP of ZrO₂-coated Y₂O₃ powders shows intermediate values between that of raw Y₂O₃ and ZrO₂ powders. As the ZrO₂-coating concentration increased from 0 to 5.0 at%, the magnitude of the negative zeta potential at pH > pH_IEP shows a general trend of increment, whereas it decreased at pH < pH_IEP. The viscosity decreases pronouncedly with the increase of ZrO₂ content from 0.5 at% to 3.0 at%. The suspensions with low viscosity and high stability was achieved for a solid loading of 35.0 vol% using Y₂O₃ powders coated with 5.0 at% ZrO₂. The dispersed suspensions were consolidated by centrifugal casting method and the green bodies shown improved homogeneity. Transparent Y₂O₃ ceramics were fabricated by vacuum sintering at 1800 ℃ for 5 h. Transmittance at wavelength 800 nm (1.0 mm thick) reached 80.8%, close to the theoretical value of Y₂O₃.     

Preparation of porous SiC-Al2O3 ceramics via gelcasting utilising a shrinkable pore-forming agent and oxidised coarse-grained SiC

By utilising soaked millet as a shrinkable pore-forming agent, porous silicon carbide-alumina (SiC-Al₂O₃) ceramics were prepared via gelcasting. The fabrication of SiC-Al₂O₃ ceramics based on oxidised and unoxidised coarse-grained SiC was also studied. The water swelling, drying shrinkage, and low-temperature carbonisation of the millet were investigated. We found that the shrinkage of the soaked millet was greater than that of gel body during drying, which left large gaps that prevented shrinkage stresses from destroying the gel body. Low-temperature carbonisation of the millet should be performed slowly at 220–240?°C because its expansion rate increases to 45% at 250?°C, resulting in the cracking of samples. At a constant sintering temperature, the flexural strength of the SiC-Al₂O₃ ceramics prepared with SiC powders oxidised at 1000?°C was the highest, indicating that oxidised powders can successfully decrease the required sintering temperature and improve the flexural strength of composite ceramics. Based on our optimised process, porous SiC-Al₂O₃ ceramics were sintered at 1500?°C for 2?h. When their skeletons were fully developed, their pore sizes were in the range of 1.5–2?mm. Their porosity and flexural strength were 60.2–65.1% and 8.3–10.5?MPa, respectively.     

有机污染物的气相色谱分析

从环境样品的采样技术、样品预处理、样品的分析测试几方面简述有机污染物气相色谱分析技术,并探讨分析测试过程中的质量保证.色谱柱的效能及控制最佳操作条件是保证样品分析结果准确度的关键.     

Tunable structure and intensive upconversion photoluminescence for Ho3+-Yb3+ codoped bismuth titanate composite synthesized by sol-gel-combustion (SGC) method

Ho³⁺ and Yb³⁺ codoped bismuth titanate (BTO) composite powders with infrared to visible upconversion luminescence (UCL) function were prepared by SGC method. The effects of Ho³⁺ and Yb³⁺ doping content on the structure and property were investigated for BTO: xHo, 0.2 Yb (x = 0, 0.02, 0.04, 0.06, 0.08, 0.1) and BTO: 0.02Ho, yYb (y = 0.1, 0.2, 0.3, 0.5, 0.7, 0.9) samples. All the samples include three bismuth titanate phases (Bi₄Ti₃O₁₂, Bi₂Ti₂O₇, and Bi₂₀TiO₃₂), and the phase proportion can be tuned by changing Ho³⁺ and Yb³⁺ doping content. These powders are well crystalized with honeycomb-like microscopic structure, and with good absorption for 233 nm, 310 nm and 975 nm wavelength. The band gap can be tuned from 3.53 eV to 4.03 eV when increasing Yb³⁺ content from y = 0 to y = 0.9. A strong 530–580 nm green emission band and a relative weak 630–690 nm red one corresponding to Ho³⁺: ⁵S₂ → ⁵I₈ and ⁵F₅ → ⁵I₈ transitions appear in the UCL spectra for all the BTO: Ho, Yb samples when pumped at 980 nm. The emission intensities can well be tuned with various Ho³⁺ and Yb³⁺ content. The optimal UCL was obtained in BTO: 0.02Ho, 0.5 Yb for all the prepared samples. The energy transfer mechanism is analyzed by building a two-photon energy transfer model, which is proved by the relationship between emission intensities and pumping power measurement. The concentration quenching of Ho³⁺ is caused by cross relaxation of CR₁ and CR₂ (Ho: ⁵F₄, ⁵S₂ + ⁵I₈ → ⁵I₄ + ⁵I₇) and by CR₃ (Ho: ⁵F₄, ⁵S₂ + Yb: ²F_7/2 → Ho: ⁵I₆ + Yb: ²F_5/2) for Yb³⁺ quenching. The mean luminescence lifetime (τ_m) from Ho: ⁵S₂ decreases monotonously with the increase of Ho³⁺ and Yb³⁺ content.     

Insight into the vacancy effects on mechanical and electronic properties of Tantalum Silicide

The effects of the vacancies on the structural stability, elastic constants, elastic moduli, brittle-to-ductile transition and electronic properties of Tantalum Silicide (TaSi₂) are investigated in detail by first-principles calculations. The values of vacancy formation energy confirm that the perfect TaSi₂ and TaSi₂ with different atomic vacancies can exhibit the structural stability at ground state. It is found that Ta atom vacancies are more stable than Si atom vacancies in TaSi₂ with vacancies. The elastic constants and elastic moduli describe the mechanical behavior for TaSi₂ and TaSi₂ with vacancies. The different atomic vacancies weaken the elastic stiffness for TaSi₂. But the values of B/G confirm that the brittle-to-ductile transition occurs with different atomic vacancies for TaSi₂. Although these vacancies make the shear and volume deformation resistance of TaSi₂ weaker, they obviously improve the brittle behavior of TaSi₂. The difference charge density and electronic structures are calculated to discuss and analyze the structural stability and mechanical properties for the perfect TaSi₂ and TaSi₂ with vacancies.     

绿色合成分子筛的研究进展

分子筛由于具有规则的孔道结构、适宜的酸性、良好的热和水热稳定性等特点,广泛应用于吸附、分离、离子交换及催化等领域。传统水热法制备分子筛因需要使用大量溶剂和有机模板剂,存在合成效率低、生产成本高、污染环境等一系列问题。近年来,随着"绿色化学"理念的深入人心,开发绿色、可持续的分子筛制备路线备受关注,逐渐成为该领域的研究热点。本文主要从水热法、离子热法、干胶法以及无溶剂法等几个方面,对国内外分子筛绿色合成的最新研究进展进行综述,并归纳比较上述合成方法的优缺点。最后,提出目前绿色合成分子筛过程中存在的问题,展望其未来发展前景。     

Effect of K2O content on breakdown strength and energy-storage density in K2O-BaO-Nb2O5-SiO2 glass-ceramics

Phase evolution, dielectric properties, breakdown strength, and energy-storage performance were studied by varying K₂O content in K₂O-BaO-Nb₂O₅-SiO₂ glass-ceramics. It was found that dielectric loss with the increase of K₂O content increases owing to the un-crystallized K₂O into the glass network, while dielectric breakdown strength firstly increases and then decreases due to the competition between two physical mechanisms, i.e., interfacial polarization and bridging-oxygen bond broken by the non-bridging oxygen ions. With the increase of K₂O content, energy-storage density firstly increased up to 12.06±0.69 J/cm³ with a high breakdown strength of 1973 kV/cm, and then decreased. Also, the discharged efficiency is obtained as a high value of 92% from P-E hysteresis loops.     

Surface phase transformation of ZrO2 in VOx/ZrO2 catalysts for boosting propane nonoxidative dehydrogenation

The nanocatalysts of VO_x deposited on ZrO₂ supports with single monoclinic (ZrO₂-M), tetragonal (ZrO₂-T), and binary monoclinic-tetragonal (ZrO₂-MT) phase were synthesized. VO_x/ZrO₂-MT catalysts exhibit better performance during propane nonoxidative dehydrogenation than VO_x/ZrO₂-M and VO_x/ZrO₂-T catalysts. Among VO_x/ZrO₂-MT catalysts, the conversion and deactivation rate constant of VO_x/ZrO₂-M₃₁T₆₉ catalyst is 35.2% and 0.22 h⁻¹, respectively. The promoting role of ZrO₂-MT is revealed by experiments and theoretical calculations. The MT-mixed phase structure in VO_x/ZrO₂-MT catalyst improves the structural properties and dispersion of VO_x. The tetragonal-monoclinic transformation on the ZrO₂-MT surface facilitates VO_x reduction and produces additional V³⁺ active sites. The highly dispersed V³⁺ sites on the ZrO₂-MT surface accelerate C H bond breaking and boost the desorption of propylene, which is the key reason for enhancing activity and stability during the reaction, respectively. Insight into the role of surface phase transformation of ZrO₂-MT is expected to obtain high-efficient catalysts further.     

A nanocomposite of dual-phase Fe/TiCN wrapped in nitrogen-doped carbon with magnetic and dielectric characters for superior microwave absorption

A careful approach to the optimization of magnetic and dielectric losses in nanomaterials can improve the electromagnetic wave absorption loss performance for certain microwave absorption applications. In this study we prepared dual core (Fe/TiCN) coated with nitrogen (N) doped carbon shell nanocomposite by arc-discharge method under mix atmospheres of working gases and with varying elemental compositions. Among all nanocomposites, (Fe/TiC_0.7N_0.3)@N–C dual-core@ N- doped shell nanocomposite exhibits enhanced microwave absorption. Owing to the novel dual-core@ N-doped shell structure and numerous defects induced by doping N in carbon shells, an improved dielectric relaxation in composite is observed and the minimum reflection loss was reached −44.36 dB at 5.3 GHz for 4.8 mm thickness.