Simple inorganic routes for the synthesis of WO3 nanostructures with variable crystal phases, WO3·(H2O)0.5 and (NH4)0.33WO3, and their self-assembled structures as nanoplates and nanospheres, respectively, were reported. The morphologies and formation of nanoplates and nanospheres were controlled by changing the solvent amount (H2O/n-propanol) in the solvothermal reactions without any stabilizing agent or surfactant. The adsorption properties of the WO3 nanostructures were studied, and it was found that nanospheres show remarkably higher and ultrafast adsorption of methylene blue (MB) in comparison to nanoplates and commercial WO3. The adsorption isotherms, kinetics, mechanism, and reusability of (NH4)0.33WO3 nanospheres were systematically studied. The nanospheres exhibited an exceptionally high adsorption rate K 2 of 17.24 g·mg–1·min–1 and the maximum adsorption capacity of 116 mg·g–1 for MB. The adsorption cycle of nanospheres was examined, and the removal efficiency of MB remained at ∼98–99% even after three regeneration cycles. In addition, (NH4)0.33WO3 nanospheres exhibited excellent selective adsorption performance toward several cationic dyes, including MB, malachite green (MG), safranin O (SO), crystal violet (CV), and separate MO, a negatively charged dye, with a separation efficiency of 99.93 and 77.31% from binary and pentanary dye mixture solutions, respectively, at neutral pH.

Superparamagnetic cobalt ferrite (CFO) nanocrystals (NCs) with sizes ∼ 6 nm and ∼ 4 nm were synthesized using a facile solvothermal method using fatty acids, lauric acid and stearic acid, as the capping agents. The synthesized nanocrystals were well characterized by XRD, FT-IR, XPS, SEM and TEM. The formation mechanism was explored and it was shown that the fatty acid was actually chemisorbed as a carboxylate onto the surface of CFO NCs. The experimental results specify that the size and size distribution of the CFO NCs were highly dependent on the length of fatty acid hydrophobic chain. Corresponding changes of the magnetic properties were investigated by measuring magnetization as a function of field and temper-ature, which suggest that the CFO NCs were superparamagnetic in nature. The catalytic properties for the oxidation of styrene in organic medium were examined by using the synthesized CFO NCs with sizes ∼ 6 nm and ∼ 4 nm. The synthesized CFO NCs, well dispersible in organic media, were demonstrated to be highly catalytically active, reached 100% conversion of styrene in 12 h with ∼ 77% and ∼ 82% selectivity for styrene oxide respectively. The magnetic CFO nanocatalysts were easily separated and recovered from the reaction medium by an external magnet, and reused for several cycles without losing catalytic selectivity for styrene oxide.[a] V.

No abstract