The authors have declared that no competing interests exist.
Two samples of the defectdouble perovskites with general formula Sr2CaNbO5.5 and Sr2CaTaO5.5 were synthesized and their cap abilities in the removal of neutral red dye investigated. Both samples have faced cubic perovskite-type structure in space group
Organic dyes are considered to be extremely environmental pollutants. Their effluents are, in many cases, carcinogenic and toxic
Recently, there is a growing interest in developing new adsorbent materials with diverse compositions, properties and functionalities. The physical characteristics of the adsorbents, such as surface area, porosity, size distribution, density and surface charge, all influence the adsorption process. Perovskite oxides with general formula
Nuteral Red is a eurhodin dye used for staining in histology. It is used as a counter stain in combination with other dyes, and for many staining methods. Together with Janus Green B, it is used to stain embryonal tissues and supravital staining of blood
The preparation of samples involved different stoichiometric compositions of Ta2O5 (Merck, 99.99%) and CaCO3 or SrCO3 (BDH, 99.98-99.99%). The mixtures were initially ground and preheated at 850°C for 12 h, and then reground and heated at 1100°C for 48 h.
The crystallography of the samples was examined by a PANalytical X’Pert X-ray powder diffraction using Cu Kα radiation (1.5400 Ȧ) and a PIXcel solid-state detector. the operating voltage was 40kV and the current was 30 mA. he samples were measured in lat plate mode at room temperature with a scan range of 10°<2θ<80° and a scan length of 10 mins were used. The structures were refined using the program RIETICA
The absorbance of solutions was determined using ultraviolet visible spectrophotometer (UV/Vis, model Spect-21D) and (190-900 Perkin- Elmer) at maximum wavelength of absorbance (520 nλ). The concentrations of solutions were estimated from the concentration dependence of absorbance fit. The pH measurements were carried out on a WTW720 pH meter model CT16 2AA (LTD Dover Kent, UK) and equipped with a combined glass electrode.
Batch mode removal studies were carried out by varying several parameters such as contact time, pH, temperature and mass of prepared oxide (adsorbent). Essentially, a 50 ml of dye solution with concentration of 10 ppm was taken in a 250 ml conical flask in which the initial pH was adjusted using HCl/NaOH. Optimized amount of adsorbent was added to the solution and stirred using magnetic stirrer for specific time. The oxide samples were separated from solutions using centrifuge 3500 CPM for 5 minutes.
The preparation of an extensive solid state solution allows us to study the effects of altering the chemical composition on the physical properties. The heating regime described above produced crystalline, yellowish coloured, samples. X-ray diffraction measurements (
The Average Crystallite size Dp, specific surface area S, lattice strain φ, Lattice parameter
Dp= (0.94λ)/(β1/2×cosϴ). (1)
S = 6000/ (Dp ×ρ). (2)
Both the shape and the size of particles are defined by the preparation methods; however the ratio of nucleation to growth rates of particles is also important. Each of these processes depends in turn on variations in the reaction conditions such as the temperature, the nature and concentrations of metal and ligand, and the nature of stabilizer and reducer. The differences in the crystallite size, surface area and density of the two oxides (see table) could be attributed to one of these variations.
Formula |
|
|
|
|
V (Å3) | |
Sr2CaNbO5.5 | 50.45 | 4.70 | 13.64 | 0.0015 | 8.2401(2) | 559.490(1) |
Sr2CaTaO5.5 | 43.69 | 5.67 | 24.20 | 0.0031 | 8.2300(3) | 557.670(1) |
The removal percentage of dyes over the adsorbents can be calculated as: R% = [(Ci-Ct)/Ci] × 100, where R% is the removal percentage, Ci = 10 ppm is initial concentration of dye solution, Ct is the concentration of dye at contact time estimated from the concentration dependence of absorbance fit.
The amount of the dye adsorbed by one gram of the oxides (Q) was calculated as following: Q (mg/g) = [(Ci-Ct)×V]/W, where t= 180 min is the contact time, V= 50 ml is the volume of NR solution and W is the mass of oxides. As shown in
Temperature has an important impact on the adsorption process. An increase in temperature helps the reaction to compete more efficiently with
The pH of solutions is a key parameter in dye adsorption. The magnitude of electrostatic charges which are impacted by the ionised dye molecules is controlled by the solution pH. As a result the rate of adsorption will vary with the pH of the medium used. In general, at low solution pH, the percentage of dye removal will decrease for cationic dye adsorption, while for anionic dyes the percentage of removal will increase. This is due to the increase in the positive charge on the solution interface and the adsorbent surface. In contrast, high solution pH is preferable for cationic dye adsorption but shows a lower efficiency for anionic dye adsorption. The positive charge at the solution interface will decrease while the adsorbent surface appears negatively charged
To study the effect of pH, experiments were carried out at various pH values, ranging from 2 to 10 for constant dye concentration (10 ppm) and adsorbent mass (0.1g).
The removal of Neoutral Red from aqueous solution by the nano particle oxides Sr2CaNbO5.5 and Sr2CaTaO5.5 has been reported. The oxides were synthesised by solid state reaction and characterized by XRD. Despite the differences in crystallite size, the mounts of NR adsorbed by the two oxides were similar. The replacement of Nb5+ by Ta5+ has showed no influence on the removal capacities. The maximum removal capacities of Neutral red are 190.5 mg/g for the two oxides. Such result could be attributed to the similarity in the cell volumes of the oxides. The removal of dye gradually increased as time and pH increases but decreased as temperature increased.