The removal of aniline blue dye from aqueous solutions using the A-site doped perovskite Ce 1-xBi xCrO 3 (x = 0, 0.5, 1) was investigated. The perovskite oxides were synthesised using Sol-Gel method and characterised by conventional powder X-ray diffraction technique. The X-ray diffraction measurements suggested that doping with Bismuth Ion influences both the crystal structure and the particle size of the oxides, and consequently affects the adsorption properties. It was found that both CeCrO 3 and Ce 0.5Bi 0.5CrO 3 compounds are orthorhombic and have approximate particle size of 87 and 36 nm respectively, whereas BiCrO 3 oxide has rhombohedral space group symmetry and the particle sizes are less than 49 nm. The batch mode study demonstrated that the removal capacities of Aniline Blue at 150 min and pH = 4.3 for Ce 0.5Bi 0.5CrO 3, CeCrO 3 and BiCrO 3 are 779.67, 705.45 and 440.18 mg/g respectively. The results reflect the influence of the A site doping on the adsorption properties of the oxides. The removal of Aniline Blue was found to be negatively correlated with temperature and pH.
The residual dyes from textile and printing industries are considered a wide variety of organic pollutants introduced into the water resources. There are ten thousand types of textile dyes with an estimated annual production of seven hundred thousand metric tonnes commercially available worldwide. Thirty percent of these dyes are used more than one thousand tonnes per year, and ninety percent of the textile products are used at the level of one hundred tonnes per year approximately. About 10% - 25% of textile dyes are lost during the dyeing process whilst 2% - 20% of them are directly discharged as aqueous effluents in different environmental components [
The discharge of dye-containing effluents into the wastewater system is undesirable since many of these are toxic, mutagenic and/or carcinogenic to living beings [
Adsorption is found to be superior compared to the other methods in term of initial cost, simplicity of construction and insensitivity of toxics. Thus, a wide variety of natural and synthetic materials such as activated carbon, peat, various silica, activated clay, banana pith, natural manganese mineral, oil ash, goat hair, alum sludge, natural zeolite, mixtures of flash, soil and semiconducting oxides have been investigated as dye adsorbents. Among semiconducting oxides, Perovskite type oxides have been proven to be interest due to their efficiency in adsorbing and degrading recalcitrant organic compounds [
Perovskite type oxides with the general formula ABO3 have been the focus of numerous studies. The major interest in such materials typically stems from their potential applications in the modern chemical industry such as catalysts, sensors and optical devices [
This work investigates the removal of Aniline blue (AB) from aqueous solutions using the A-site doped perovskite Ce1−xBixCrO3 (x = 0, 0.5, 1). The impact of the replacing of Ce3+(4f1) with Bi3+(6s2) has been addressed to establish the role of the A-site cation in controlling the adsorption properties of the oxides. The incorporation of a cation with a stereo chemically active lone pair of electrons onto the A-site is known to have a significant effect on the structure and properties of perovskite. This has been explored in the double perovskite Bi2FeMoO6. It is postulated that the 6s2 electrons from the Bi3+ ions influences the structure and properties [
Aniline Blue is typically organic soluble compound utilized in textile industry for dyeing of nylon, wool, silk and cotton. It belongs to triphenyl methane class of dyeing which a central carbon atom is bonded to two benzene rings and one p-quinoid group. Aniline Blue is acidic dye and has long residence time in water [
To prepare the samples studied in this work the Sol-Gel method was utilized. Appropriate amounts of Ce(NO3)3∙6H2O (99.9%, BDH), Cr(NO3)3∙6H2O (99.9%, MERCK) and Bi(NO3)3 (99.9%, MERCK) were mixed and dissolved in 25 ml of 0.1 M nitric acid (65%, CODEX). The mixture was then added to a citric acid solution (99.7%, BDH) in the mole ratio 1:2 (oxide/acid) and heated on a hotplate at 200˚C until the gel turned ashes. The final products were ground using a mortar and pestle techniques and heated in an alumina crucible within a commercial furnace at 250˚C for 12 hrs and then reground and heated in stages at 400˚C for 12 hrs and 800˚C for 48 hrs.
The phase composition and purity of the samples was determined from X-ray diffraction. The X-ray diffractometer used was Philips PW 1800 X-Ray generator located at the Libyan Oil institution, Tripoli, Libya with a copper tube (Cu-Kα1 radiation), having a wavelength of 1.5406 Å. The operating voltage was 40 kV and the current was 30 mA. The samples were measured in flat plate mode at room temperature with a scan range of 10˚ < 2θ < 80˚ and a scan length of 10 mins were used. Diffraction patterns obtained from the Inorganic Crystal Structure Database (ICSD) were used for the comparison with obtained products.
The absorbance of solutions was determined using ultraviolet visible spectrophotometer (UV/V is, model Spect-21D) and (190 - 900 Perkin-Elmer) at maximum wavelength of absorbance (580 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 50 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 heating regime described above produced crystalline, green coloured samples. X-ray diffraction measurements showed the Ce0.5Bi0.5CrO3 oxide was isostructural with undoped CeCrO3 and have an orthorhombic (Pnma) structure whereas the BiCrO3 oxide has defected rhombohedra perovskite-type structure in space group R3C.
Oxide | λ (Å) | θ (˚) | β | Dp (nm) | Lattice strain |
---|---|---|---|---|---|
CeCrO3 | 1.54056 | 29.023 | 0.0984 | 87.14 | 0.0017 |
Ce0.5Bi0.5CrO3 | 1.54056 | 28.559 | 0.2362 | 36.26 | 0.0040 |
BiCrO3 | 1.54056 | 28.537 | 0.1771 | 48.36 | 0.0030 |
The crystallite size can be calculated using sheerer formula [
D p = 0.94 λ / ( β 1 / 2 cos θ )
Unexpectedly, Ce0.5Bi0.5CrO3 displayed the lowest crystallite size, whereas the CeCrO3 had the highest crystallite size in the series. The decrease in crystallite size of Ce0.5Bi0.5CrO3 and BiCrO3 is inconsistent with the relative ionic size of the Bi3+ (8 coordinate ionic radius, 1.17 Å) and Ce3+ (1.14 Å) cations [
The removal percentage of dyes over the adsorbents can be calculated as:
R % = [ ( C i − C t ) / C i ] × 100
where R% is the removal percentage, Ci = 50 ppm is initial concentration of dye solutions, Ct is the concentration of dye at contact time estimated from the concentration dependence of absorbance fit. The effect of contact time on the AB removal was observed at the range of (0 - 150 min).
The amount of the dye adsorbed by one gram of the oxides (Q) was calculated as following:
Q ( mg / g ) = [ ( C i − C t ) × V ] / W
where t = 150 min is the contact time, V = 50 ml is the volume of AB solution and W is the mass of oxides. As shown in
To study the effect of pH, experiments were carried out at various pH values, ranging from 2 to 6 for constant dye concentration (50 ppm) and adsorbent mass (0.1 g).
Ce0.5Bi0.5CrO3 and BiCrO3 are found to be 87.36%, 86.00%, 81.28% respectively at pH = 2. The oxides displayed almost an equal efficiency of removal (~53%) at pH = 6. BiCrO3 exhibited lower percentages of removal compare to the two other oxides. The interpretation of pH effects on the efficiency of the adsorption process is a very difficult task, because of its multiple roles. It is related to the acid base property of both the metal oxide and the organic dye. The adsorption of water molecules at metal sites is followed by the dissociation of OH− groups, leading to coverage with chemically equivalent metal hydroxyl groups (M-OH). Due to amphoteric behaviour of both the metal oxide and the organic dye, the equilibrium reactions below are considered. The electrostatic interactions between the positive catalyst surface and dye anions leading to strong adsorption of the last on the oxide support.
1) M − OH + H + ↔ M − OH 2 +
2) M − OH ↔ M − O − + H +
3) Dye − OH + H + ↔ Dye + + H 2 O
4) H − Dye + OH − ↔ Dye − + H 2 O
Temperature has an important impact on the adsorption process. An increase in temperature helps the reaction to compete more efficiently with e-/H+ recombination. The removal of AB was investigated at 25˚C, 40˚C, 60˚C and 100˚C. The obtained results are illustrated below in
active sites of adsorbents and the surface area is decreased by increase the temperature.
The energy of activation (Ea), was calculated from the Arrhenius plot of lnR vs 1000/T (
The removal of Aniline blue from aqueous solution by the mixed metal perovskite Ce1−xBixCrO3 has been studied. In general, the amount of AB adsorbed by Ce0.5Bi0.5CrO3 is higher than those adsorbed by CeCrO3 and BiCrO3. The study showed no finite time for the AB removal up to 150 min. The AB removal increases as the mass of the oxides increases. The adsorption of AB was
temperature and pH dependent. The three oxides showed maximum removal efficiency of AB at 25˚C and pH = 2.0. The adsorption capacity of AB from water was 779.67, 705.45 and 440.18 mg/g using Ce0.5Bi0.5CrO3, CeCrO3 and BiCrO3 respectively. The study indicated that doping with Bismuth ions into CeCrO3 can successfully enhance the adsorption properties of the oxide.
Authors thank the Libyan Oil institution for the XRD measurements. Many thanks for Prof. Abd El-Salam. M. Elmehob for the paper proofreading.
Awin, L.A., El-Rais, M.A., Etorki, A.M., Mohamed, N.A. and Makhlof, W.A. (2018) Removal of Aniline Blue from Aqueous Solutions Using Ce1−xBixCrO3 (x = 0, 0.5, 1). Open Journal of Inorganic Non-metallic Materials, 8, 1-10. https://doi.org/10.4236/ojinm.2018.81001