Search Results (11)

In the present study, we synthesized fluorocarbon-coated cobalt ferrite (CoFe₂O₄) magnetic nanoparticles using alkoxysilanes such as trimethoxy(3,3,3-trifluoropropyl)silane (TFPTMS), trimethoxy(1H,1H,2H,2H-nonafluorohexyl)silane (NFHTMS), and triethoxy(1H,1H,2H,2H-perfluorodecyl)silane (PFDTES). The synthesized nanoparticles were characterized by various techniques, including X-ray diffractometry (XRD), transmission electron microscopy (TEM/HRTEM/EDXS), Fourier transform infrared spectroscopy (FTIR), specific surface area measurements (BET), and magnetometry (VSM). To understand their surface characteristics, contact angle (CA) measurements were carried out, providing valuable insights into their hydrophobic properties. Among the samples of CoFe₂O₄ coated with fluoroalkoxysilanes, those with PFDTES surface coating had the highest water contact angle of 159.2°, indicating their superhydrophobic character. The potential of the prepared fluoroalkoxysilane-coated CoFe₂O₄ nanoparticles for the removal of waste low-SAPS synthetic engine oil from a model aqueous solution was evaluated based on three key parameters: adsorption efficiency (%), adsorption capacity (mg/g), and desorption efficiency (%). All synthesized CoFe₂O₄ samples coated with fluoroalkoxysilane showed high oil adsorption efficiency, ranging from 87% to 98%. The average oil adsorption capacity for the samples was as follows: F₃-SiO₂@CoFe₂O₄ (3.1 g of oil/g of adsorbent) > F₉-SiO₂@CoFe₂O₄ (2.7 g of oil/g of adsorbent) > F₁₇-SiO₂@CoFe₂O₄ (1.5 g of oil/g of adsorbent) as a result of increasing oleophobicity with increasing fluorocarbon chain length. The desorption results, which showed 77–97% oil recovery, highlighted the possibility of reusing the adsorbents in multiple adsorption/desorption cycles. Full article

Carbonic anhydrase (CA)-based biological CO₂ capture is emerging as a prominent carbon capture and storage (CCS) technology. We developed a tagged CA–Ferritin chimera, resulting in a high-purity, high-activity, micrometer-sized CA aggregate, SazF, with a yield of 576.6 mg/L (protein/medium). SazF has an optimum temperature of 50 °C and demonstrates thermal stability between 40 and 60 °C. It operates efficiently in Tris–HCl buffer (pH = 8–9), making it compatible with ship exhaust conditions. For enhanced stability and reusability, SazF was encapsulated in SiO₂ and integrated into an epoxy resin to produce a corrosion-active coating. This coating, applied to foam metal fillers, showed less than 3% protein leakage after ten days and retained over 70% activity after a month at 60 °C. This simple preparation method and the cost-effective production of these biomaterials that can continuously and efficiently absorb CO₂ in high-temperature environments are suitable for most CO₂ capture devices. They have a broad application prospect in the field of industrial carbon capture. Full article

The addition of CaF₂@SiO₂ and SiC whiskers to ceramic tools can improve their flexural strength and fracture toughness, reduce surface damage, and improve their cutting performance. The cutting experiments showed that under the same cutting conditions, the surface roughness of the workpiece processed with the Al₂O₃/TiC/SiC/CaF₂@SiO₂ (ATSC10) tool was significantly lower than that of the workpiece processed with the Al₂O₃/TiC/ SiC (ATS) tool. Additionally, the main cutting force and cutting temperature when cutting with the ATSC10 tool were lower by 30 and 31.7%, respectively. These results were attributed to the precipitation of CaF₂ from the nanocoated particles during cutting and the formation of a uniform and continuous lubricating film on the surface of the tool. The wear on the front surface of the ATS tool was mainly adhesive, and that on the back tool surface was mainly abrasive. For ATSC10, the main forms of wear on the tool front surface were adhesive and abrasive, whereas the main form of wear on the tool back surface was abrasive with slight adhesive wear. The addition of nano-coated particles and whiskers improved the mechanical properties of the cutting tool while maintaining good cutting performance. Full article

In recent years, perovskite solar cells (PSCs), often referred to as the third generation, have rapidly proliferated. Their most prominent deficiencies are their low efficiency and poor stability. To enhance their productivity, a combination of silicon and perovskite is employed. Here, we present a 3D simulation analysis of various electrical and optical properties of PSCs using the SILVACO simulation software. Using the inverted planar method with inorganic transport materials and the proper selection of anti-reflective coatings with a back contact layer increases the efficiency of PSCs to 28.064%, and enhances their stability without using silicone composites. Several materials, including CaF₂, SiO₂, and Al₂O₃, with various thicknesses have been employed to investigate the effect of anti-reflective coatings, and to improve the efficiency of the simulated PSC. The best thickness of the absorbent layer is 500 nm, using a CaF₂ anti-reflective coating with an optimal thickness of 110 nm. A polymer composition of Spiro-OMeTAD and inorganic materials Cu₂O and NiOx was used as the hole transport material (HTM) and inorganic ZnO was employed as the electron transport material (ETM) to optimize the solar cell efficiency, and an optimized thickness was considered for these materials. Yields of 29.261, 28.064 and 27.325% were obtained for Spiro-OMeTAD/ZnO, Cu₂O/ZnO and NiOx/ZnO, respectively. Thus, Spiro-OMeTAD yields the highest efficiency. This material is highly expensive with a complex synthesis and high degradability. We proposed to employ Cu₂O to alleviate these problems; however, this reduces the efficiency by 1.197%. As a graphene connector has high flexibility, reduces cell weight, and is cheaper and more accessible compared to other metals, it was regarded as an optimal alternative. The simulation results indicate that using the inverted planar method with inorganic transport materials for graphene-based PSCs is highly promising. Full article

Magnesium alloys are actively researched for biodegradable implants in order to avoid an implant-removal surgery after the healing process. However, the high degradation rate of Mg leads to hydrogen evolution and may increase the pH of the environment, causing an inflammatory response. In the present work, bioactive plasma electrolytic oxidation (PEO) coatings on three MgxZnyCa alloys (two cast alloys and one extruded; x = 1, 3 or 0.5; y = 1 or 0.3), manufactured by Helmholtz-Zentrum Hereon, Geesthacht, were generated in order to enhance the corrosion resistance, bioactivity and cytocompatibility of the alloys. AC PEO process was carried out in two environmentally friendly alkaline electrolytes containing Ca, P and Si as bioactive elements. The electrolytes were a true solution and a particle suspension. F-free electrolyte design was employed to ensure cytocompatibility of the coatings with different types of cells. The materials were characterized by SEM, EDS, XRD and optical profilometry. The corrosion behavior was evaluated by EIS and hydrogen evolution measurements during 5 days of immersion in 0.9% NaCl and α-MEM solutions, a complete one and an inorganic part only, at 37 °C. PEO coatings (7–13 µm-thick, Sa = 1.85–4.19 µm) were constituted by MgO, Ca₃(PO4)₂, Ca₅(PO₄)₃(OH) and Mg₂SiO₄ phases. Both PEO coatings decreased the degradation rate of Mg alloys; corrosion resistance of coated samples in inorganic α-MEM increased by more than an order of magnitude (|Z|10 mHz, Ω·cm²): MgZnCa = 746, MgZnCa/PEO = 8544…28,277). All materials exhibited considerably greater corrosion rates in 0.9% NaCl than in α-MEM, where phosphate-based additives acted as corrosion inhibitors. Corrosion rates were slightly greater in complete α-MEM than in inorganic α-MEM due to the presence of complexing aminoacids. The developed coatings are considered suitable candidates for the subsequent development of hybrid hierarchical ceramic/biodegradable polymer systems. Full article

The aim of this work was to characterize the structure and corrosion properties of the MgCa_4.5(Gd_0.5) alloys surface treated by the micro-arc oxidation (MAO) process. The MgCa_4.5 and MgCa_4.5Gd_0.5 alloy samples were processed by MAO in an electrolyte composed of NaOH (10 g/dm³), NaF (10 g/dm³), NaH₂PO₄ (5 g/dm³), Na₂SiO₂·5H₂O (10 g/dm³) and water. Two different voltages (120 V and 140 V) were used in the MAO process. The alloys protected by an oxide layer formed in the MAO were then the subject of corrosion resistance tests in an environment simulating the human body (Ringer’s solution). After the experiments, the resulting samples were investigated using SEM, XPS and EDS techniques. The addition of Gd affected the fragmentation of the coating structure, thereby increasing the specific surface; higher voltages during the MAO process increased the number and size of surface pores. Corrosion tests showed that the MgCa_4.5Gd_0.5 alloys were characterized by low polarization resistances and high corrosion current densities. The studies indicated the disadvantageous influence of gadolinium on the corrosion resistance of MgCa_4.5 alloys. The immersion tests confirmed lower corrosion resistance of MgCa_4.5Gd_0.5 alloys compared to the referenced MgCa_4.5 ones. The MgCa_4.5 alloy with the MAO coating established at voltage 140 V demonstrated the best anticorrosion properties. Full article

Silica-based bioactive glasses (SBG) hold great promise as bio-functional coatings of metallic endo-osseous implants, due to their osteoproductive potential, and, in the case of designed formulations, suitable mechanical properties and antibacterial efficacy. In the framework of this study, the FastOs^®BG alkali-free SBG system (mol%: SiO₂—38.49, CaO—36.07, P₂O₅—5.61, MgO—19.24, CaF₂—0.59), with CuO (2 mol%) and Ga₂O₃ (3 mol%) antimicrobial agents, partially substituting in the parent system CaO and MgO, respectively, was used as source material for the fabrication of intentionally silica-enriched implant-type thin coatings (~600 nm) onto titanium (Ti) substrates by radio-frequency magnetron sputtering. The physico-chemical and mechanical characteristics, as well as the in vitro preliminary cytocompatibility and antibacterial performance of an alkali-free silica-rich bio-active glass coating designs was further explored. The films were smooth (R_RMS < 1 nm) and hydrophilic (water contact angle of ~65°). The SBG coatings deposited from alkali-free copper-gallium co-doped FastOs^®BG-derived exhibited improved wear performance, with the coatings eliciting a bonding strength value of ~53 MPa, Lc3 critical load value of ~4.9 N, hardness of ~6.1 GPa and an elastic modulus of ~127 GPa. The Cu and Ga co-doped SBG layers had excellent cytocompatibility, while reducing after 24 h the Staphylococcus aureus bacterial development with 4 orders of magnitude with respect to the control situations (i.e., nutritive broth and Ti substrate). Thereby, such SBG constructs could pave the road towards high-performance bio-functional coatings with excellent mechanical properties and enhanced biological features (e.g., by coupling cytocompatibility with antimicrobial properties), which are in great demand nowadays. Full article

Bioactive glass F18 (BGF18), a glass containing SiO₂–Na₂O–K₂O–MgO–CaO–P₂O₅, is highly effective as an osseointegration buster agent when applied as a coating in titanium implants. Biocompatibility tests using this biomaterial exhibited positive results; however, its antimicrobial activity is still under investigation. In this study we evaluated biofilm formation and expression of virulence-factor-related genes in Candida albicans, Staphylococcus epidermidis, and Pseudomonas aeruginosa grown on surfaces of titanium and titanium coated with BGF18. C. albicans, S. epidermidis, and P. aeruginosa biofilms were grown on specimens for 8, 24, and 48 h. After each interval, the pH was measured and the colony-forming units were counted for the biofilm recovery rates. In parallel, quantitative real-time polymerase chain reactions were carried out to verify the expression of virulence-factor-related genes. Our results showed that pH changes of the culture in contact with the bioactive glass were merely observed. Reduction in biofilm formation was not observed at any of the studied time. However, changes in the expression level of genes related to virulence factors were observed after 8 and 48 h of culture in BGF18. BGF18 coating did not have a clear inhibitory effect on biofilm growth but promoted the modulation of virulence factors. Full article

In order to reduce the influence of CaF₂ addition on the mechanical properties of self-lubricating ceramic tools, we applied a silicon dioxide (SiO₂) coating on calcium fluoride (CaF₂) nanoparticles through hydrolysis and condensation reactions using the tetraethoxysilane (TEOS) method. The powder was dried by the azeotropic method, so that it acquired a better dispersibility. The resulting composite powders were characterized using XRD (X-ray diffraction) and TEM (transmission electron microscopy), showing that the surface of CaF₂ was coated with a layer of uniform and compact SiO₂. SiO₂ shells with different thicknesses could be obtained by changing the amount of TEOS added, and the thickness of the SiO₂ shells could be controlled between 1.5 and 15 nm. At the same time, a ceramic material containing CaF₂ nanoparticles and CaF₂@SiO₂-coated nanoparticles was prepared. It had the best mechanical properties when CaF₂@SiO₂-coated nanoparticles were added; its flexural strength, fracture toughness, and hardness were 562 ± 28 MPa, 5.51 ± 0.26 MPa·m^1/2, and 15.26 ± 0.16 GPa, respectively. Compared with the ceramic tool containing CaF₂ nanoparticles, these mechanical properties were increased by 17.57%, 12.67%, and 4.88%, respectively. The addition of CaF₂@SiO₂-coated nanoparticles greatly improved the antifriction and wear resistance of the ceramic material, and the antifriction and wear resistance were balanced. Full article

Within the field of tissue engineering, thin films have been studied to improve implant fixation of metallic or ceramic materials in bone, connective tissue, oral mucosa or skin. In this context, to enhance their suitability as implantable devices, titanium-based substrates received a superficial vitroceramic coating by means of laser ablation. Further, this study describes the details of fabrication and corresponding tests in order to demonstrate the bioactivity and biocompatibility of the newly engineered surfaces. Thus, the metallic supports were covered with a complex material composed of SiO₂, P₂O₅, CaO, MgO, ZnO and CaF₂, in the form of thin layers via a physical deposition techniques, namely pulsed laser deposition. The resulting products were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning and transmission electron microscopy coupled with energy dispersive X-ray spectroscopy, selected area electron diffraction, and electron energy loss spectroscopy. It was found that a higher substrate temperature and a lower working pressure lead to the highest quality film. Finally, the samples biocompatibility was assessed and they were found to be bioactive after simulated body fluid soaking and biocompatible through the MTT cell viability test. Full article

The role of post-magmatic processes in the composition of chromitites hosted in ophiolite complexes, the origin of super-reduced phases, and factors controlling the carbon recycling in a supra-subduction zone environment are still unclear. The present contribution compiles the first scanning electron microscope/energy-dispersive (SEM/EDS) data on graphite-like amorphous carbon, with geochemical and mineral chemistry data, from chromitites of the Skyros, Othrys, Pindos, and Veria ophiolites (Greece). The aim of this study was the delineation of potential relationships between the modified composition of chromite and the role of redox conditions, during the long-term evolution of chromitites in a supra-subduction zone environment. Chromitites are characterized by a strong brittle (cataclastic) texture and the presence of phases indicative of super-reducing phases, such as Fe–Ni–Cr-alloys, awaruite (Ni₃Fe), and heazlewoodite (Ni₃S₂). Carbon-bearing assemblages are better revealed on Au-coated unpolished sections. Graphite occurs in association with hydrous silicates (chlorite, serpentine) and Fe²⁺-chromite, as inclusions in chromite, filling cracks within chromite, or as nodule-like graphite aggregates. X-ray spectra of graphite–silicate aggregates showed the presence of C, Si, Mg, Al, O in variable proportions, and occasionally K and Ca. The extremely low fO₂ during serpentinization facilitated the occurrence of methane in microfractures of chromitites, the precipitation of super-reducing phases (metal alloys, awaruite, heazlewoodite), and graphite. In addition, although the origin of Fe–Cu–Ni-sulfides in ultramafic parts of ophiolite complexes is still unclear, in the case of the Othrys chromitites, potential reduction-induced sulfide and/or carbon saturation may drive formation of sulfide ores and graphite-bearing chromitites. The presented data on chromitites covering a wide range in platinum-group element (PGE) content, from less than 100 ppb in the Othrys to 25 ppm ΣPGE in the Veria ores, showed similarity in the abundance of graphite-like carbon. The lack of any relationship between graphite (and probably methane) and the PGE content may be related to the occurrence of the (Ru–Os–Ir) minerals in chromitites, which occur mostly as oxides/hydroxides, and to lesser amounts of laurite, with pure Ru instead activating the stable CO₂ molecule and reducing it to methane (experimental data from literature). Full article