The purpose of this study was to prepare nano-titanium tannate complex (TTC) and to investigate its adsorption capacity for removal of cationic dyes such as crystal violet (CV) dye. The morphology and the main elements of TTC adsorbent were characterized by scanning electron microscopy (SEM-EDS), while its crystal structure was characterized by X-ray diffraction (XRD). Also, FT-IR spectroscopy study structural aspects of TTC. A “cotton-ball”-like and porous surface structure of titanium tannate complex (TTC) with nanoparticle size of 16.18 nm show high capability for absorbing crystal violet dye. The effect of several parameters such as contact time, initial concentrations of CV, solution pH and the amount of TTC was investigated. Three different kinetic equations such as pseudo-first order, pseudo-second order and intraparticle diffusion were used to study the order and the mechanism of the adsorption process. The adsorption of CV dye followed pseudo- second order equation. Moreover, equilibrium data were tested with four adsorption isotherm models namely, Langmuir, Freundlich, Temkin and Dubinin-Radushkevich (D-R). Langmuir was the best fit for the data with maximum capacity as 58.8 mg/g. The results of Separation factor, Surface coverage and standard free energy (ΔG°) indicated that adsorption of CV onto TTC was favorable with fast rate and spontaneous physical adsorption process.
Due to the rapid growth of the need for water in different industries, huge number of different pollutants accumulated in water. In many cases, these pollutants make water unsuitable to be reused and become wastewater [
Analytical-grad that chemicals were used in this work without further purification. Crystal violet, a type of triphenylmethane dyes with molecular formula (C25H30ClN3), (aq. solubility 16 g/l; purity 80%) as shown in
A Beaker with an amount of 50 ml (4%:1.0%, ethanol: water) of tannic acid (0.1 M) was placed in ultrasonic bath and sonicated for few minutes. Then a cretin volume of TiCl3 was added drop wise with continuous sonication for 8.0 minutes. The molar ratio of tannic acid to titanium(III) chloride was chosen to be 1:20 according to R. Zhang et al., [
To study the surface morphology and main elements present in the complex of titanium tannate, scanning electron microscopy (SEM) using SEM model Quanta 250 FEG attached with an energy dispersive X-ray spectroscopy (EDS) unit with accelerating voltage 30 K.V., magnification14x up to 1000,000 and resolution for Gun.1n was used. The crystal structure of titanium tannate was analyzed by X-ray diffraction (XRD) in scan mode with Cu-Ka radiation (l = 0.01542 nm) in the 2q range of 10˚ to 80˚. The functional group in the synthesized complex was analyzed through the analysis of Fourier transform infrared spectrometry (FTIR) using KBr pellet in the range of 400 to 4000 cm−1.
To evaluate the significant of titanium(III) tannate complex (TTC) as an adsorbent, CV dye solution was used in this study as an environmental pollutants. Stock solutions (1000 mg/L) of CV was prepared in distilled water and further diluted to the required concentration to perform the calibration curves and adsorption experiments. Serial dilutions (1.0 to 6.0 mg/L) of CV stock solutions were used to prepare the calibration curves. Batch adsorption experiments were performed by introducing known amounts of TTC into several glass tubes, each containing 5.0 mL (to minimize the waste) of CV solution with an initial concentration ranging from 40 to 150 mg/L. Tubes were agitated at 120 rpm using an electric shaker at room temperature. To ensure performing the adsorption experiments at known pH value, the pH was adjusted before starting the experiment using solution of either NaOH or HCl. At interval times, CV solutions were withdrawn and introduced into a centrifuge to separate TTC powder from samples. CV solutions of 50 mg/L with different amount of TTC powder (0.5 to 2.5 g/L) were used to study the effect of adsorbent dose on the adsorption process. The effect of pH was studied by performing similar experiments with 2.0 g/L of TTC powder at different pHs from 2.75 to 10. A known amount of TTC powder (2.0 g/L) were added to 5.0 mL of CV solution with different concentrations (40 to 150 mg/L) at room temperature to calculate the adsorption isotherm.
UV-vis spectrophotometer (Perkin Elmer) was used to determine the concentrations of CV solution before and after the adsorption experiments. Calibration curves were obtained and used to calculate dye concentrations during adsorption experiments at any time (
The amount of CV dye sorbed onto TTC powder at any time,
At equilibrium,
where
Kinetic Study will allow the determination of the rate of CV uptake by TTC adsorbent which in turn led to measuring the efficiency of the adsorption process. Three different kinetic models namely a pseudo-first order [
where
While, the linear form of pseudo second-order developed by Ho [
where
Also, intraparticle diffusion equation can be described by the following equation:
where,
The equilibrium state between the amount of adsorbed onto the adsorbent surface (
SEM images of the morphology of the synthesized titanium tannate complex (TTC) is shown in
The results in
A known amount of ttc powder 0.010 g (2.0 g/L) was added to 0.005 L of different concentrations of CV (from 40 - 150 mg/L). For a total period of 120 min at a temperature of 298 K, experiments were performed to evaluate the effect of contact time (0 - 120 min) and different initial concentrations (40, 50, 70, 90 and 150 mg/L) of CV dye on the adsorption process as shown in
16.85 mg/g, which represented about 78.11%, comparing to 19.91 mg/g (92.3%) at 120 min. Then, the adsorption of CV dye increased gradually during the following 40 min until reached equilibrium at about 120 min. Furthermore, the sorbed amount of CV dye was also increased from 16.85 to 42.10 mg/g by increasing the initial concentrations from 40 to 150 mg/L respectively. The results showed that the uptake of CV dye by TTC powder depends on the contact time and the initial concentration. This may be due to the time required for the CV dye to encounter the boundary layer effect, then diffuse to the surface of TTC powder and finally diffuse to the porous structure [
Adsorption rate can be affected by the degree of ionization of adsorbate and the surface charge of adsorbent [
To investigate the effect of adsorbent dosage on the adsorption of CV, different tubes filled with a specific volume of CV dye solution with [CV]0 (50 mg/L) at different amounts of TTC powder (0.25 to 2.5 g/L) at room temperature.
Determining the kinetic parameter (such as the rate constant) and predicting information about adsorbent/adsorbate interaction it is significant for any adsorption experiments. As discussed above, three different models were used to study the kinetic of adsorption of CV onto TTC powder.
Equation (4) expressed the linear form of Langergren pseudo first-order for the adsorption process of CV dye onto TTC adsorbent. Different concentrations of CV dye (40 - 150 mg/L) were used to calculate
The kinetic data of the adsorption of CV onto TTC were further analyzed by the linear form of pseudo-second
order model (Equation (5)). The slope and the intercept of the plot of
First-order kinetic model | Second-order kinetic model | ||||||
---|---|---|---|---|---|---|---|
[CV]0 (mg/L) | qe, exp (mg/g) | qe, cal (mg/g) | k1 (min−1) | R2 | qe, cal (mg/g) | k2 (g/mg∙min−1) | R2 |
40 | 20.060 | 5.370 | 0.035 | 0.807 | 20.41 | 0.040 | 0.999 |
50 | 23.417 | 4.498 | 0.025 | 0.974 | 23.81 | 0.025 | 0.999 |
70 | 30.671 | 11.117 | 0.012 | 0.947 | 28.57 | 0.010 | 0.997 |
90 | 36.922 | 10.188 | 0.009 | 0.934 | 32.26 | 0.011 | 0.998 |
100 | 51.502 | 0.012 | 0.012 | 0.988 | 50.00 | 0.010 | 0.998 |
of both
It is proposed that the uptake of the adsorbate (such as CV dye) by the adsorbent (such as TTC) varies almost proportionately with the square root of the contact time (t1/2) according to the Equation (6) [
The affinity of TTC adsorbent for the adsorption of CV dye was evaluated by using different adsorption isotherms such as Langmuir, Freundlich, Temkin and Dubinin-Radushkevich (D-R).
The Langmuir isotherm model assumes that a monolayer of adsorbed material (in liquid, such as CV is adsorbed over a uniform adsorbent surface such as TTC. The Langmuir-I equation is derived by some mathematical manipulation as:
where
Langmuir constants | Freundlich constants | ||||||
---|---|---|---|---|---|---|---|
58.8 | 0.156 | 0.999 | 14.99 | 3.125 | 0.895 | ||
Temkin constants | Dubinin-Radushkevich (D - R) constants | ||||||
0.236 | 2.24 | 0.962 | 44.345 | 2.220 | 0.953 | ||
Adsorbent | Reference | |
---|---|---|
Bottom ash | 12.10 | [ |
TS, NaOH-TS | 118, 195 | [ |
Ananas comosus (pineapple) leaf powder (PLP) | 158.73 | [ |
Phosphoric acid activated carbons (PAAC) | 60.42 | [ |
Sulphuric acid activated carbons (SAAC) | 85.84 | [ |
Cocoa (theobroma cacao) shell (CSAC) | 43.50 | [ |
Activated carbon | 15.7 - 19.8 | [ |
ZFA | 19.6 | [ |
ZBA | 17.6 | [ |
Different natural materials | 60.8 - 65.8 | [ |
TTC | 58.8 | present study |
Separation Factor and Surface Coverage (θ)
There are two factors such separation factor (
where
In addition, the surface coverage (θ) of the adsorbent (TTC) is related to the initial concentration of CV dye - (
where
The adsorption process takes place on a heterogeneous surface when the resulted data followed Freundlich isotherm model. Freundlich equations (linear and nonlinear) can be expressed as:
where
indicates both the relative distribution of energy and the heterogeneity of the adsorbent sites. Plot of
versus
determined from the intercept and the slope respectively. Although, the value of
Recent reports for the adsorption of crystal violet dye onto different adsorbents found similar trends indicating that the equilibrium data were described well by Langmuir model and did not fit well with Freundlich model [
Equation (14) represented the linear form of Temkin isotherm model which can be used to test the adsorption potential of adsorbent to adsorbate. This equation supposes that increasing the coverage layer of adsorbate onto the surface of adsorbent makes the heat of adsorption (
where, R is common gas constant (0.008314 kJ/mol K), T is the absolute temperature (K),
culated from the liner plots of
The adsorption data of CV dye onto TTC were also tested by Dubinin-Raduskevich (D-R) isotherm model in order to investigate the characteristic porosity and the apparent free energy of adsorption. Isotherm model of D-R (Equation (15)) does not assume constant adsorption potential or homogeneous surface for the adsorbent [
where,
where R is common gas constant (8.314 J/mol K) and T(K) is the absolute temperature.
The results in
The degree of spontaneity of the adsorption process is mainly determined from standard Gibbs free energy (DG˚) equation. Increase the negative value of DG˚ represents the increase in the spontaneity and the favorability of the adsorption [
where; T is the temperature (K), R is gas constant (kJ/mol・K) and
The main conclusions of this investigation indicated that Ti-tannate complex (TTC) could be used as an effective adsorbent for the removal of CV dye from aqueous solution. Also, the adsorption of CV dye onto TTC powder was found to depend on the contact time and the initial concentration in addition to the dosage of TTC. Furthermore, the electrostatic interactions between CV and TTC surface controlled by the value of pH and the maximum removal were observed at pH 7. Kinetic study of adsorption process showed that pseudo-second order was the best model to describe the rate of removal of CV dye with the correlation coefficient (
Author appreciated the great help and valuable discussion from Mr. Mohamed Hammad and Mr. Mahmoud Baseem, Al-Azhar University, Cairo, Egypt. Also, the author would like to thank Dr. El-Sayed Abd El-Monem Waly, Atomic Energy Authority, Egypt for great help in sample analysis.
Taha M.Elmorsi, (2015) Synthesis of Nano-Titanium Tannate as an Adsorbent for Crystal Violet Dye, Kinetic and Equilibrium Isotherm Studies. Journal of Environmental Protection,06,1454-1471. doi: 10.4236/jep.2015.612126