RESUMO
Spinel Co(x)Zn1âxAl2O4 (0 ≤ x ≤ 1) nano-catalysts were synthesized by a simple Aloe vera plant extracted green synthesis route. Powder XRD patterns and Rietveld analysis confirmed the formation of single phase, cubic spinel gahnite structure without other impurities. The lattice parameter increased from 8.089 to 8.125 A with increasing CO²âº content. The average crystallite sizes were estimated using Scherrer's method, and it was found to be in the range of 15.72 nm to 26.53 nm. FT-IR spectra showed vibrational stretching frequencies corresponding to the spinel structure. HR-SEM and HR-TEM images showed the features of well particle shaped crystals with nano-sized grains. The elemental compositions of Co, Zn, Al and O were quantitatively obtained from EDX analysis. The band gap energy estimated using Kubelka-Munk method by UV-Visible DRS method, and the values are decreased with increasing the Co²âº content (4.12 eV to 3.67 eV), due to the formation of sub bands in between the energy gap. PL spectra showed emission bands in UV as well as in the visible regions for ZnAl2O4 and Co-doped ZnAl2O4, due to the defect centers acting as the trap levels. VSM measurements revealed that pure ZnAl2O4 has diamagnetic, while Co doped ZnAl2O4 samples (x = 0.2 to 0.8) have superparamagnetism, whereas the sample CoAl2O4 has ferromagnetic in nature. Catalytic oxidation of benzyl alcohol to benzaldehyde was found that the sample Co0.6Zn0.4Al2O4 showed 93.25% conversion with 99.56% selectivity, whereas for pure ZnAl2O4, the conversion was only 86.31% with 92.85% selectivity.
RESUMO
Spine Mn(x)Co1âxAl2O4 (x = 0, 0.3 and 0.5) nanoparticles were synthesized using Sesamum indicum (S. indicum) plant extracted microwave-assisted combustion method. S. indicum plant extract simplifies the process, provides an alternative process for a simple, economical and environment friendly synthesis. The absence of surfactant/catalysts has led to a simple, cheap and fast method of synthesis of spinel nanoparticles. The as-synthesized spinel nanoparticles were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, high resolution scanning electron microscopy (HR-SEM), high resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray analysis (EDX), Brunauer Emmett Teller (BET) surface area analysis, UV-Visible diffuse reflectance spectroscopy (DRS), Photoluminescence (PL) spectroscopy, and vibrating sample magnetometer. The formation of spinel nanoparticles was confirmed by HR-SEM and HR-TEM and their possible formation mechanisms were also proposed. Powder XRD, FT-IR, SAED and EDX results confirmed the formation of pure and single cubic phase CoAl2O4 with well-defined crystalline. The optical property was determined by DRS and PL spectra. VSM measurements revealed that pure and Mn-doped CoAl2O4 samples have weak ferromagnetic behavior and the magnetization values increases with increasing the concentration of Mn²âº ions in the CoAl2O4 lattice. The sample Mn0.5Co0.5Al2O4 possessed higher surface area and smaller crystallite size than other samples, which led to enhance the performance toward the selective oxidation of benzyl alcohol into benzaldehyde.
