Magnetic iron oxides have been used in biomedical applications, such as contrast agents for magnetic resonance imaging, carriers for controlled drug delivery and immunoassays, or magnetic hyperthermia for the past 40 years. Our aim is to investigate the effect of pressure and temperature on the structural, thermal, and magnetic properties of iron oxides prepared by hydrothermal synthesis at temperatures of 100–200 °C and pressures of 20–1000 bar. It has been found that pressure influences the type of iron oxide crystalline phase. Thus, the results obtained by Mössbauer characterization are in excellent agreement with X-ray diffraction and optical microscopy characterization, showing that, for lower pressure values (100 bar, the major crystalline phase is goethite. In addition, thermal analysis results are consistent with particle size analysis by X-ray diffraction, confirming the crystallization of the synthesized iron oxides. One order of magnitude higher magnetization has been obtained for sample synthesized at 1000 bar. The same sample provides after annealing treatment, the highest amount of good quality magnetite leading to a magnetization at saturation of 30 emu/g and a coercive field of 1000 Oe at 10 K and 450 Oe at 300 K, convenient for various applications.

Recently, carbon nanotubes (CNTs) have been used extensively to develop new materials and devices due to their specific morphology and properties. The reinforcement of different metal oxides such as zinc oxide (ZnO) with CNT develops advanced multifunctional materials with improved properties. Our aim is to obtain ZnO-CNT nanocomposites by in situ hydrothermal method in high-pressure conditions. Various compositions were tested. The structure and morphology of ZnO-CNT nanocomposites were analyzed by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry—thermogravimetry (DSC-TG), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM). These analyses showed the formation of complex ZnO-CNT structures. FT-IR spectra suggest possible interactions between CNT and ZnO. DSC-TG analysis also reveals the formation of some physical bonds between ZnO and CNT, through the appearance of endothermic peaks which could be assigned to the decomposition of functional groups of the CNT chain and breaking of the ZnO-CNT bonds. XRD characterization demonstrated the existence of ZnO nanocrystallites with size around 60 nm. The best ZnO:CNT composition was further selected for preliminary investigations of the potential of these nanocomposite powders to be processed as pastes for extrusion-based 3D printing.

Doped nanoparticles based on titanium dioxide are of interest for their multifunctional properties and enlarged photocatalytic activity in visible domain. Silica doped titanium dioxide nanoparticles were prepared by hydrothermal method and their structural characteristics and photocatalytic activity were determined, in order to be used for leather coating as alternative to halogen based flame retardants and dry cleaning solvents. A range of concentrations from 2% to 20% silica doped titanium dioxide nanoparticles (% denotes the theoretical weight percent of Si) was synthesized and characterized by ICP-OES, FT-IR, UV-vis spectroscopy, XRD, HRTEM and DLS. Titanium dioxide network penetration was supported by Si-O-Ti and OH identification in FT-IR spectra mainly on surface of 10% and 20% silica doped titanium dioxide nanoparticles. The increase of Si-O-Ti bonds with Si dopant concentration acts as efficient barriers against sinterization and growth of TiO2 particles and explains the low particle size identified in HRTEM analyses as compared to undoped TiO2NPs. UV-vis diffuse reflectance spectra of doped titanium dioxide nanoparticles showed the shifting of absorption band to visible domain for 10% silica doped titanium dioxide nanoparticles. The crystallite sizes were calculated from XRD spectra, ranging between 16.2 and 18.1nm. HRTEM measurement of hydrothermally synthesized titanium dioxide nanoparticles showed anatase crystallites in the range of 8.8–27nm, while in the 20% silica doped titanium dioxide nanoparticle sample smaller crystallite with sizes between 2.7nm and 3.5nm was identified due to the constraints of the SiO2-based amorphous matrix. Nano sizes of 64nm and 72nm were found in water dispersions of 10% and 20% silica doped titanium dioxide nanoparticles and the Zeta potentials were of −53.6mV and −52.9mV, which indicate very good stabilities. The leather surface treated with composites of film forming polymers and 10% silica doped titanium dioxide nanoparticles displayed photocatalytic properties against methylene blue dye under UV and visible light exposure, attributed to reactive species generation with effect on surface hydrophilicity increase. The activation energies for decomposition of leathers treated with 10% and 20% silica doped titanium dioxide nanoparticles were 2.083×104J/mol and 2.36×104J/mol respectively, as compared to 6.576×103J/mol for untreated leathers, showing increased thermal stability according to DSC measurements. The hydrothermal route for silica doped nanoparticle preparation proved advantages in enhancing photocatalytic properties in the visible domain and thermal resistance, with prospect for multifunctional applications

Core–shell nanoparticles are functional materials with tailored properties, able to improve the requirements of various applications. Both core and shell components can be inorganic or organic, and there are numerous studies in this field regarding their synthesis methods, properties, and applications. This review aims to study core–shell nanostructures with Fe₃O₄ cores and different shell types, observing their antibacterial and anticancer properties. By the type of coating, Fe₃O₄ core–shell nanoparticles (NPs) are classified into four categories: metal-coated NPs, metal-organic framework (MOF) coated NPs, metal oxide coated NPs, and polymer-coated NPs. Each category is briefly presented, emphasizing anticancer or antibacterial properties and specific applications (cancer diagnosis or therapy, drug carrier). Moreover, synthesis methods and particle size for both core and shell nanostructures, as well as the magnetic properties of the final core–shell material, are summarized in this review. Most of the consulted papers discussed sphere-like core–shell nanoparticles obtained by chemical methods such as coprecipitation, hydrothermal, and green synthesis methods using plant extract. These types of core–shell nanoparticles could be used as drug nanocarriers for tumor-targeted drug delivery, hyperthermia treatment, or contrast agents. Further work needs to be conducted to understand nanoparticles’ interaction with living cells and their traceability in the human body.