Effects of different reaction parameters in the hydrothermal synthesis of molybdenum oxides (MoO3) were investigated and monoclinic (β-) MoO3 was prepared hydrothermally for the first time. Various temperatures (90/210 °C, and as a novelty 240 °C) and durations (3/6 h) were used. At 240 °C, cetyltrimethylammonium bromide (CTAB) and CrCl3 additives were also tested. Both the reaction temperatures and durations played a significant role in the formation of the products. At 90 °C, h-MoO3 was obtained, while at 240 °C the orthorhombic (α-) MoO3 formed with hexagonal rod-like and nanofibrous morphology, respectively. The phase transformation between these two phases was observed at 210 °C. At this temperature, the 3 h reaction time resulted in the mixture of h- and α-MoO3, but 6 h led to pure α-MoO3. With CTAB the product was bare o-MoO3, however, when CrCl3 was applied, pure metastable m-MoO3 formed with the well-crystallized nanosheet morphology. The gas sensing of the MoO3 polymorphs was tested to H2, which was the first such gas sensing study in the case of m-WO3. Monoclinic MoO3 was found to be more sensitive in H2 sensing than o-MoO3. This initial gas sensing study indicates that m-MoO3 has promising gas sensing properties and this MoO3 polymorph is promising to be studied in detail in the future.

This study presents the preparation of pure, Sr and Mg-doped hydroxyapatite (HAP) by precipitation. Sr-doped HAPs (SrHAPs) and Mg-doped HAPs (MgHAPs) were fabricated with Sr molar ratio of 2, 4, 6, 8, 12 % and Mg molar ratio of 2, 4 %, respectively. Ca(NO3)2, Sr(NO3)2, Mg(NO3)2, (NH4)2HPO4 were used as starting materials, the Ca/P molar ratio was kept 1.67 during every synthesis and a 900 °C heat treatment was conducted to enhance the crystallinity. All of the products were analyzed by XRD, SEM and EDX, moreover lattice parameters and crystallite size calculations were performed to prove the ion incorporation into the crystal structure. The HAP structure was maintained when 2 and 4 Sr and 2 Mg % were applied and EDX confirmed the Sr and Mg content in these samples. In all other cases, various Sr and Mg-containing phases (Sr0.13Ca2.87(PO4)2, Ca2P2O7, Mg0.29Ca2.71(PO4)2) were identified while the HAP structure disappeared. It was shown that lattice parameters and the unit cell volume of Sr-doped HAPs increased slightly compared to pure HAP due to the bigger radius of Sr 2+ than Ca 2+. As the ionic radius of Mg 2+ is smaller than Ca 2+ , we demonstrated the distortion in the unit cell. Crystallite sizes increased as the amount of Sr and Mg raised. SEM experiments demonstrated that ion incorporation had little influence on the morphology, i.e. pure, Sr or Mg-doped HAPs were mostly homogenous, constituted of strongly sintered nanometer sized grains. Antimicrobial tests indicated that SrHAP with 4 Sr % and MgHAP with 2 % Mg had positive effect on cell viability.

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In this study, Bi2WO6 was prepared by the hydrothermal method. The effects of reaction temperature (150/170/200 °C) and reaction time (6/12/24 h) were investigated. The role of strongly acidic pH (1 >) and the full range between 0.3 and 13.5 were studied first. Every sample was studied by XRD and SEM; furthermore, the Bi2WO6 samples prepared at different temperatures were examined in detail by EDX and TEM, as well as FT-IR, Raman and UV-vis spectroscopies. It was found that changing the temperature and time slightly influenced the crystallinity and morphology of the products. The most crystallized product formed at 200 °C, 24 h. The pure, sheet-like Bi2WO6, prepared at 200 °C, 24 h, and 0.3 pH, gradually transformed into a mixture of Bi2WO6 and Bi3.84W0.16O6.24 with increasing pH. The nanosheets turned into a morphology of mixed shapes in the acidic range (fibers, sheets, irregular forms), and became homogenous cube- and octahedral-like shapes in the alkaline range. Their band gaps were calculated and were found to vary between 2.66 and 2.59 eV as the temperature increased. The specific surface area measurements revealed that reducing the temperature favors the formation of a larger surface area (35.8/26/21.6 m2/g belonging to 150/170/200 °C, respectively).