Template synthesis of novel porous carbons using various types of zeolites

As previously reported, high surface area microporous carbons with long-range order can be synthesized by using zeolite Y as a template. In this work, an attempt is made to synthesize porous carbon using several other types of zeolites (zeolite β, ZSM-5, mordenite and zeolite L). Special attention is paid to whether the structural regularity of each zeolite can be transferred to the carbon structure as well as with the case of zeolite Y. The carbon filling method was then examined to see which gives the highest regularity to the carbon structure. It has been found that the optimum carbon filling method for zeolite Y is not an optimum one for the other zeolites and the degree of the regularity of long-range ordering in the carbons strongly depends on zeolite type. The order of the regularity in the resultant carbons is zeolite β>>zeolite L>mordenite>ZSM-5. The effect of zeolite type on the regularity is discussed in relation to the size and the shape of the zeolite channels.     

Carbon coating of anatase-type TiO2 through their precipitation in PVA aqueous solution

Fine particles of photocatalytic anatase-type TiO₂ prepared through hydrolysis of titanium-tetraisopropoxide were coated by carbon through their precipitation in poly(vinyl alcohol) (PVA) aqueous solution, followed by heat treatment at high temperatures of 400-1000 °C in a flow of high purity Ar. Without carbon coating, the phase transformation from anatase to rutile started above 600 °C, but it was suppressed up to 800 °C with carbon coating. Suppression of the phase transformation depended on the amount of carbon coated, apparent suppression being observed with carbon content above 5 mass%. The amount of carbon coated on anatase was controlled by changing the concentration of PVA in the solution. In order to have a carbon content of about 5 mass%, a PVA solution with more than 2 mass% had to be used.     

Mechanochemical synthesis and cold sintering of mussel shell-derived hydroxyapatite nano-powders for bone tissue regeneration

According to the circular economy principles, processing routes aiming at reducing the natural resources consumption and the energy demand can be addressed as ‘green’. In this framework, mussel shells, a natural feedstock of calcium carbonate, were successfully transformed into nano-crystalline hydroxyapatite by mechanochemical synthesis at room temperature after mixing with a phosphoric acid solution. The as-synthesized powder was then consolidated up to 82 % relative density by cold sintering (600 MPa, 200 °C). The materials were fully investigated by physical, chemical and thermal characterization techniques. Cold-sintered samples were also subjected to biaxial flexural strength test, showing a flexural resistance of 23 MPa. Cell viability assessment revealed that cold sintered hydroxyapatite derived from mussel shells promotes faster adhesion and spreading of human bone marrow-derived mesenchymal stem cells, in comparison to a commercial hydroxyapatite sintered at 1050 °C. Therefore, cold-sintered mussel shells-derived hydroxyapatite can be a promising future candidate scaffold for bone tissue regeneration.     

Cactus-inspired GO/ZnO sensors for fast and robust acetone sensing properties

Fabrication of fast, high-selectivity and reliable gas sensors for real-time monitoring of acetone in exhaled gases remains a key challenge for the development of accurate diabetes diagnosis systems. Inspired by the cactus, in this paper, acetone gas sensor using graphene oxide (GO) with porous zinc oxide (ZnO) nanotube clusters was introduced by room temperature liquid phase method. Porous ZnO nanotubes with lengths of 1～2 μm formed nanoclusters and were uniformly dispersed on the GO sheets, presenting a specific “cactus-like” three-dimensional structure, which supplied more channels and active sites for the diffuse and adsorption of acetone molecules. The cactus-like GO/ZnO sensor exhibits a high response value of 54.3 (5.9-fold improvement compared to ZnO), fast response/recovery time of 3.8/2.9 s (15.7/19.8 s for ZnO), and robust stability to 50 ppm acetone at 180 °C. Special, the sensor can detect even acetone down to 0.1 ppm with a remarkable response (2.1). Moreover, the adsorption energies of different gases were calculated by density functional theory, which further confirmed the good acetone selectivity of the cactus-like GO/ZnO sensor. The appreciable gas sensing performances are mainly attributed to the unique cactus-like nanostructure with abundant holes and high specific surface area, as well as the heterojunctions between GO and ZnO. This unique biomimetic structure provides a promising strategy for designing acetone gas sensors with high practicality.     

Micromechanical properties of hydroxyapatite nanocomposites reinforced with CNTs and ZrO2

This study examined the mechanical properties, wettability, and tribology of hydroxyapatite (HA)–zirconia (ZrO₂)–carbon nanotube (CNTs) ceramic nanocomposites (with various CNT ratios (x): 1, 5, and 10 wt%). HA–ZrO₂–CNT-x powders were hydrothermally synthesized. Hot isostatic pressing (HIP) and cold isostatic pressing were used to manufacture solid and dense tablets; consolidation was performed by sintering the nanocomposites under Ar gas at 1150 °C during HIP. The microstructure and morphology of the nanocomposites were characterized via transmission electron microscopy, energy-dispersive X-ray spectroscopy, powder X-ray diffractometry, Fourier transform infrared (FTIR), and scanning electron microscopy. The effects of ZrO₂ and CNTs on the mechanical characteristics of the nanocomposites were examined via nanoindentation, reciprocating wear, and Vickers hardness tests. The microhardness of HA–ZrO₂–CNT-1% and HA–ZrO₂–CNT-5% increased by 36.8% and 66.67%, respectively, compared with that of pure HA. The nanohardness of the HA–ZrO₂–CNT-1%, HA–ZrO₂–CNT-5%, and HA–ZrO₂–CNT-10% samples was 8.3, 9.65, and 8.02 Gpa, and the corresponding elastic modulus was 83.72, 114.34, and 89.27 GPa, respectively. Both of these parameters were higher than those of pure HA. However, in the nanocomposite reinforced with 10% CNT, as opposed to those with lower CNT ratios, their values were lower. Additionally, HA–ZrO₂–CNT-10% was the most hydrophilic nanocomposite synthesized in this study with a contact angle of 48.8°.     

Influence of ceramic phosphate powders on the physicochemical and biological properties of poly(l-lactide)

In the present work, the attention is focused on cannulated, biodegradable olives made of poly(l-lactide) (PLLA) and PLLA with the addition of phosphate ceramics. The olive is an element expanding the intramedullary nail intended to be implantation the humerus bone. During degradation, the olive reduces the diameter of the nail, while ensuring the best conditions for the growth of bone tissue. The article examines the effect of the addition of tricalcium phosphate (β-TCP) and hydroxyapatite (HAp) on morphology, chemical structure, physicochemical and biological properties of PLLA during storage in a degradation medium imitating the natural environment of the human body. The introduction of β-TCP+HAp into PLLA led to significant changes in both surface morphology, chemical structure and physicochemical properties, which contributed to the faster course of the biodegradation of the orthopedic implant. Due to this process, it was found that the PLLA composite with phosphate ceramics can be successfully used in this application. Clinical studies have shown that the implantation of olive made of PLLA+β-TCP+HAp does not cause any negative systemic reactions. The orthopedic implant was biodegradable and significantly contributes to bone union.     

Slag resistance mechanism of MgO–Mg2SiO4–SiC–C refractories containing porous multiphase aggregates

The slag resistance of MgO–SiC–C (MSC) refractories should be improved because of the mismatch in the thermal expansion coefficient between the aggregates and matrix, as well as the defects caused by the affinity between periclase and slag. In this study, MgO–Mg₂SiO₄–SiC–C (MMSC) refractories were prepared using porous multiphase MgO–Mg₂SiO₄ (M-M₂S) aggregates to replace dense fused magnesia aggregates. Compared to MSC, the slag penetration index of MMSC decreased by 43.5%. The structure of the porous aggregates increased the surface roughness, and the multiphase composition of the aggregates decreased the mismatch of the thermal expansion coefficient with the matrix, thus reducing debonding between the aggregates and matrix. The aggregates and matrix in the MMSC formed an interlocking structure, which bound them more tightly to improve the slag resistance. The slag viscosity at different depths from the initial slag/refractory interface was calculated using the Ribond model. The M-M₂S aggregates increased Si_xO_y^z− in the slag, which increased the slag polymerization and slag viscosity. The aggregates and matrix in the MMSC reacted with the slag to form high melting point phases, which reduced the channel of the slag. In addition, the penetration depth and velocity derived from the Washburn Equation were modified for the CaO–SiO₂–Al₂O₃–MgO–FeO slag and magnesia based refractory to accurately evaluate slag penetration.     

The effect of chemical composition and morphology on the drug delivery properties of hydroxyapatite-based biomaterials

In the case of orthopedic and dental interventions, local antibiotic therapy reduces significantly the risk associated with the intervention. The aim of this study was the preparation and characterization of pure hydroxyapatite (HA), Si- and Mg-doped HA, which ensures the sustained release of doxycycline, and the investigation of the parameters, which were crucial for the drug release. The carriers were synthesized using the precipitation method. In order to achieve different morphologies, traditional drying and spray drying methods were used: Si-doped HA was prepared using two different sources of Si, Na₂SiO₃ and Ludox AS-40, while (Mg(NO₃)₂)*6H₂O was used for substitution with Mg. The carriers were characterized by XRD, SEM, EDX and TG/DTA methods, and the ion incorporation was also confirmed by lattice parameters calculations. Doxy was bound on the carriers by physical adsorption, the adsorption capacity increased proportionally by increasing the concentration of the initial Doxy solutions (10, 15, 20, 25 g/L). The investigated systems showed different releases with the change of the dissolution medium (in the case of HA microspheres, the release in PBS was twice as high as in SBF), chemical composition and morphology of the carriers. The retard effect of the carriers was improved by the spherical morphology, and the reduced release by ion substitution in both SBF and PBS increased as follows: HA < HASi1<HAMg < HASi2. The release mechanism of Doxy was discussed through five different release kinetics models.     

Preparation and characterization of hydroxyapatite coating by magnetron sputtering on Mg–Zn–Ag alloys for orthopaedic trauma implants

The aim of the present paper was to evaluate the effect of hydroxyapatite coatings on the two types of Mg–Zn–Ag alloys as a possible solution to control magnesium alloy degradation. The coatings were prepared by the radio frequency magnetron sputtering method at a deposition temperature of 300 °C. To perform this evaluation, the coated alloys were immersed in a simulated body fluid solution at body temperature (37 ± 0.5 °C) to determine the corrosion resistance through electrochemical and immersion tests. Moreover, the investigation also consisted of the evaluation of microchemical, mechanical, and morphological properties. The deposition temperature of 300 °C was enough to obtain a crystalline hydroxyapatite structure with a Ca/P ratio close to the stochiometric one. The adhesion of coatings was not influenced by the nature of Mg–Zn–Ag alloys, so similar values for both coated alloys were found. The results showed that the coating was homogonous deposited on the Mg–Zn–Ag alloys and the corrosion resistance of uncoated magnesium alloys was improved.