Nh4vo3

To establish the S:L ratio at which the best recovery efficiency of vanadium (V) takes place, the amount of adsorbent material, SiO₂Fe_xO_y (0.05; 0.1; 0.2; 0.3; 0.4; and 0.5), was varied, maintaining the constant volume of solution (25 mL) of ammonium metavanadate, NH₄VO₃ (Merck, Darmstadt, Germany), containing 50 mg Vanadium (V)/L. Adsorption was accomplished in a Julabo SW23 shaker with thermostat and stirring, where the samples are kept in contact for 60 min at 298 K and 200 rpm.
Vanadium (V) analysis was performed by UV-VIS spectroscopy using the Varian Carry 50 spectrometer. Then, 2.5 mL of sample solution was added to 1 mL of H₂SO₄ 6 N (CHEMICAL Company), 1 mL of H₃PO₄ 6 N (Sigma Aldrich) and 0.5 mL of Na₂WO₄ solution (Merck) (8.25 g of Na₂WO₄ in 50 mL of water). The spectra were recorded at a wavelength of 400 nm.

CuSO₄.5H₂O, NH₄VO₃, ethylenediamine (en), propylenediamine (pn), triethylenetetramine (TETA) and tetraethylenepentamine (TEPA) were purchased from Merck Company. All of the chemicals were used as received without further purifications. For characterization of the products, X-ray diffraction (XRD) patterns were recorded by a Rigaku D-max C III, X-ray diffractometer using Ni-filtered Cu Ka radiation. Scanning electron microscopy (SEM) images were obtained on Philips XL-30ESEM. Transmission electron microscopy (TEM) image was obtained on a Philips EM208 transmission electron microscope with an accelerating voltage of 200 kV. Fourier transform infrared (FT-IR) spectra were recorded on Shimadzu Varian 4300 spectrophotometer in KBr pellets. The magnetic properties of the samples were detected at room temperature using a vibrating sample magnetometer (VSM, Meghnatis Kavir Kashan Co., Kashan, Iran). Room temperature photoluminescence (PL) was studied on a Perkin Elmer (LS 55) fluorescence spectrophotometer.

All chemicals (NH₄VO₃, Sb₂O₃, NiCl₂·6H₂O (Merck); CoCl₂·6H₂O, FeCl₂·4H₂O (Fluka); ethylenediamine (Grüssing); 1-(2-aminoethyl)piperazine (Alfa Aesar)) were purchased and used without further purification. All compounds were prepared under solvothermal conditions in DURAN® glass tubes (inner volume 11 mL) at 150 °C for 7 d using similar ratios for the reactants (see below for exact amounts used). After cooling to room temperature, the products were filtered off, washed with water and ethanol and dried in vacuo. The compounds were obtained as brown crystals. Compounds I–III could be prepared within a wide temperature range from 120–160 °C and the first crystals were observed after 3 d reaction time. Remarkably, crystals of IV were observed, when 1-(2-aminoethyl)piperazine was added to the reaction slurry and the reactant ratios were slightly altered compared to those for I–III. The role of 1-(2-aminoethyl)piperazine for product formation is not clear. In the following, the reaction conditions giving the best yields are summarised. The Ni and Co containing compounds (I and II) crystallised also applying an en : H₂O ratio of 1 : 3, while III could only be obtained for a fixed en:H₂O ratio of 1 : 5.