Enhancement of glass-ceramic performance by TiO2 doping: In vitro cell viability,proliferation, and differentiation

A new TiO₂-containing bioactive glass and glass-ceramics based on 50SiO₂-(45-X)CaO-(XTiO₂)-5P₂O₅ system was designed using a sol–gel technique (where X = 5, 7.5 and 10 wt %). The roles of the crystallization behavior and physicochemical characteristics of the designed glass and glass-ceramics which were played in the introduction of TiO₂ substitutions were investigated. Moreover, cell proliferation and differentiation were evaluated against human osteosarcoma cells (Saos-2). The TiO₂/CaO replacements led to the formation of a stronger glass structure and thus increased thermal parameters and the chemical stabilization of the designed materials. The FTIR data confirmed the existence of Ti within the glass and glass-ceramics samples, and no remarkable effect on their chemical integrity was observed. The XRD patterns indicated that calcium-containing minerals, including Ca₂SiO₄,Ca₃(PO₄)₂, Ca(Ti,Si)O₅, CaTiSiO₅, and Ca₁₅(PO₄)₂·(SiO₄)₆ phases were developed as a role of structure/texture under the applied heat-treatment. The results of the cytotoxicity test proved that a safe sample dose is 12–50 μg/ml, at which cell viability is ≥ 85%. The cell differentiation determined by ALP test proved the superiority of glass-ceramics compared with their native glasses. Therefore, the obtained materials could be safely used as novel biocompatible materials for the regeneration of bone tissue.     

3D CaP porous scaffolds with grooved surface topography obtained by the sol-gel method

The influence of surface topography on cellular behaviour and its importance for the development of three-dimensional scaffolds for bone tissue engineering are a topic of growing interest. To date, the introduction of topographical patterns into the surface of 3D porous ceramic scaffolds has proven difficult, due partly to the brittle nature of ceramic materials as well as the currently available fabrication technologies. In this study, a grooved pattern was introduced into the surface of 3D multilayer porous ceramic scaffolds by the chemical etching technique. The patterned scaffolds were characterised by X-Ray Diffraction (XRD), Scanning Electron Microscopy with Energy Dispersive X-Ray Spectroscopy (SEM-EDX) and Digital Holographic Microscopy (DHM). Their bioactivity was also evaluated in vitro by immersion in simulated body fluid (SBF) for 12 h, 1, 7, 14 and 21 days. Scaffolds were constituted mainly with a mixture of the calcium pyrophosphate (Ca₂O₇P₂) and β-tricalcium phosphate (Ca?(PO?)?) phases. The pyrophosphate on the external layer was dissolved as a result of the etching process, leaving grooves on the surface. Ridges and grooves were nano-/micrometric, with dimensions of around 900 nm–1.5 μm in width and 200 nm–300 nm in depth. Moreover, the mechanical properties and bioactive capacity of the patterned scaffolds were not affected by chemical etching, making them suitable to be used in bone tissue engineering.     

Characteristics and gas sensor applications of ZnO-Perovskite heterostructure

In this study, zinc oxide (ZnO) nanofibers were prepared using the electrospinning method, and the effects of different spinning voltages and annealing temperatures on the fiber structure were tested. La_0.8Sr_0.2FeO₃ (LSFO) perovskite film was prepared by a sol-gel method. Then we dip LSFO on ZnO nanofiber and grow it on the interdigital gold electrode substrate for gas sensors. The results show that the ZnO/LSFO heterostructure gas sensor has a good sensing response to H₂S gas and exhibits good gas selectivity. The best gas response is 52.17% under 4 ppm H₂S and work temperature 200°C, which has good recovery and reproducibility.     

Fabrication of Si3N4–SiC/SiO2 composites using 3D printing and infiltration processing

Si₃N₄–SiC/SiO₂ composites were prepared by employing three-dimensional (3D) printing using selective laser sintering (SLS) and infiltration processing. The process was based on the infiltration of silica sol into porous SLS parts, and silicon carbide and silicon nitride particles were bonded by melted nano-sized silica particles. To optimize the manufacturing process, the phase compositions, microstructures, porosities, and flexural strengths of the Si₃N₄–SiC/SiO₂ composites prepared at different heat-treatment temperatures and infiltration times were compared. Furthermore, the effects of the SiC mass fraction and the addition of Al₂O₃ and mullite fibers on the properties of the Si₃N₄–SiC/SiO₂ composites were investigated. After repeated infiltration and heat treatment, the flexural strength of the 3D-printed Si₃N₄–SiC/SiO₂ composite increased significantly to 76.48 MPa. Thus, a Si₃N₄–SiC/SiO₂ composite part with a complex structure was successfully manufactured by SLS and infiltration processes.     

SiC/SiC mini-composites with multilayer ZrSiO4 interphase: Room-temperature properties and toughening mechanism

SiC/SiC mini-composites reinforced with SiC fibers coated with different numbers of ZrSiO₄ sublayers prepared via a non-hydrolytic sol-gel process were fabricated. The tensile strength and work of fracture of the prepared SiC/SiC mini-composites were determined, and the relationship between their mechanical properties and fracture morphologies was discussed. The toughening mechanism and the variation tendency of their mechanical properties were further elaborated by analyzing the interfacial debonding morphologies of the SiC/SiC mini-composites with 1 and 4 layers of ZrSiO₄ interphase as well as the results of prior studies. A relatively rare phenomenon—the delamination of the multilayer ZrSiO₄ interphase in the SiC/SiC mini-composites but not on the SiC fibers—was observed, which clearly demonstrated the weak bonding between the ZrSiO₄ sublayers in the SiC/SiC mini-composites. The ZrSiO₄ sublayer delamination mechanism was then explained based on the high-magnification morphologies found in and beside the ZrSiO₄ interphase.     

Weatherability of hybrid organic–inorganic silica protective coatings on glass

Currently, there is a growing interest in the application of silicon-based technologies for the development of advanced hybrid organic–inorganic coatings with strong weatherability. In this study, the sol–gel process is used to prepare such coatings on glass and their resistance to weathering effects is assessed afterwards. Various sols were prepared by mixing a silica-based inorganic matrix (tetraethyl orthosilicate) with different quantities of silica alkoxides functionalised with various organic groups. Subsequently, the sols were dip-coated onto glass samples at low temperatures without any heat treatment. The coatings prepared were analysed before and after three model ageing tests simulating various weathering parameters. After ageing, the best performing coatings showed good overall homogeneity and transparency (optical microscopy, SEM), improved water repellency and adhesion to the glass substrate (static contact angle measurements, cross-cut tape tests) and no colour or chemical composition changes (UV–VIS, FTIR). Compared with commercial hybrid silica products, the alkyl- and methacryloxy-functionalised silica coatings particularly displayed improved homogeneity, elasticity and barrier properties. Thus, these low temperature coatings, easily applicable to thin films, appear to fulfil the main requirements for the protection of the glass exposed to weathering phenomena.     

Facile deposition of ZnO:Cu films: Structural and optical characterization

Sol–gel technology has been applied for preparation of ZnO:Cu films. The proposed facile approach allows obtaining a wide variety of copper doped zinc oxide systems, revealing different structural and optical behaviors. The work presents structural and optical studies depending on Cu concentration and thermal treatments in the range of 500–800 °C. The structural analysis is performed by X-Ray diffraction (XRD). It reveals that small Cu addition enhances the film crystallization. Increasing copper concentration results in deterioration of ZnO:Cu crystallization. XRD study manifests no Cu oxide phases in ZnO:Cu film structure for lower Cu additions. For a specific higher copper concentration, an appearance of a small fraction of copper oxide is detected. Vibrational properties have been characterized by FTIR spectroscopy. The effect of the copper introduction into ZnO reveals a slight change of optical properties compared to ZnO films for certain Cu ratios. ZnO:Cu films with higher copper contents manifest different optical behaviors with very high transparency in spectral visible range.     

Boosted hydrogen evolution activity from Sr doped ZnO/CNTs nanocomposite as visible light driven photocatalyst

CNTs were decorated onto Sr doped ZnO nanoparticles to construct an efficient photocatalyst via a facile sol-gel method. The as-fabricated Sr doped ZnO/CNTs with recyclability exhibits Sr and CNTs content dependent hydrogen evolution activit under visible light illumination. The Sr doped ZnO/CNTs photocatalyst shows the highest hydrogen evolution rate of 2732.2 μmolh^?1g^?1, which is 33.7 and 2.83 times higher than pure ZnO and Sr doped ZnO photocatalysts, respectively. The improved hydrogen evolution activity of Sr doped ZnO/CNTs is primarily assigned to high surface area, Sr doping and construction of heterojunction, which can extend the light absorption, decrease the optical band gap and improve the charge separation. Moreover, the underlying photocatalytic mechanism is proposed on the basis of Mott-Schottky study and explains the interfacial charge transfer process from ZnO to CNTs and Sr. This work open new strategies to synthesize CNTs based nanocomposite for hydrogen evolution.     

Efficient dye-sensitized solar cells based on CNTs and Zr-doped TiO2 nanoparticles

The light scattering, harvesting and adsorption effects in dye-sensitized solar cells (DSSCs) are studied by preparation of coated carbon nanotubes (CNTs) with TiO₂ and Zr-doped TiO₂ nanoparticles in the forms of mono- and double-layer cells. X-ray diffraction (XRD) analysis reveals that the phase composition of Zr-doped TiO₂ electrode is a mixture of anatase and rutile phases with major rutile content, whereas it is the same mixture with major anatase content for coated CNTs with TiO₂. Furthermore, the average crystallite size of Zr-doped TiO₂ electrode is slightly decreased with Zr introduction. Field emission scanning electron microscope (FE-SEM) images show that the porosity of Zr-doped TiO₂ electrodes is higher than that of undoped electrode, enhancing dye adsorption. UV–visible spectroscopy analysis reveals that the absorption onset of Zr-doped TiO₂ electrodes is slightly shifted to longer wavelength (the red-shift) in comparison with that of undoped TiO₂ electrode. Moreover, the band gap energy of TiO₂ nanoparticles is decreased by Zr introduction, enhancing light absorption. It is found that electron injection of monolayer TiO₂ electrode is improved by introduction of 0.025 mol% Zr, resulted in enhancement of its power conversion efficiency (PCE) up to 6.81% compared with 6.17% for pure TiO₂ electrode. Moreover, electron transport and light scattering are enhanced by incorporation of 0.025 wt% coated CNTs with TiO₂ in the over-layer of double layer electrode. Therefore, double layer solar cell composed of 0.025 mol% Zr-doped TiO₂ nanoparticles as the under-layer and mixtures of these nanoparticles and 0.025 wt% coated CNTs with TiO₂ as the over-layer shows the highest PCE of 8.19%.     

Comparison of structural,spectral and magnetic properties of NiO nanofibers obtained by sol–gel electrospinning from two different polymeric binders

NiO is a p-type semiconductor with wide band gap energy. In this study, nickel oxide nanofibers were fabricated by sol–gel electrospinning followed by high temperature calcination, using two sacrificial polymeric binders. Poly(2-ethyl-2-oxazoline) (PEtOx) in water and styrene-acrylonitrile random copolymer (SAN) in N,N- dimethylformamide (DMF) along with nickel (II) acetate tetrahydrate (NATH), as metal oxide precursor, were the two distinct polymeric systems used in this study. The morphological and structural properties of NiO fibers obtained from the aforementioned systems were compared with each other. The degradation behavior of the sacrificial polymeric binder imparted a significant effect on the properties of the obtained NiO fibers. The grain sizes and the activation energies for grain growth of NiO fibers from two systems were different. The non-stoichiometric NiO fibers obtained from the SAN/NATH system had a better ferromagnetic behavior as compared with that produced from the PEtOx/NATH system. This non-stoichiometry made a difference also in the optical band gap energies of the NiO nanofibers.