Direct dyes removal using modified magnetic ferrite nanoparticle
© Mahmoodi et al.; licensee BioMed Central Ltd. 2014
Received: 28 July 2013
Accepted: 28 May 2014
Published: 11 June 2014
The magnetic adsorbent nanoparticle was modified using cationic surface active agent. Zinc ferrite nanoparticle and cetyl trimethylammonium bromide were used as an adsorbent and a surface active agent, respectively. Dye removal ability of the surface modified nanoparticle as an adsorbent was investigated. Direct Green 6 (DG6), Direct Red 31 (DR31) and Direct Red 23 (DR23) were used. The characteristics of the adsorbent were studied using Fourier transform infrared (FTIR), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The effect of adsorbent dosage, initial dye concentration and salt was evaluated. In ternary system, dye removal of the adsorbent at 90, 120, 150 and 200 mg/L dye concentration was 63, 45, 30 and 23% for DR23, 97, 90, 78 and 45% for DR31 and 51, 48, 42 and 37% for DG6, respectively. It was found that dye adsorption onto the adsorbent followed Langmuir isotherm. The adsorption kinetic of dyes was found to conform to pseudo-second order kinetics.
Removal of dye from colored wastewater using adsorbent is interested because specific substances are transferred from liquid onto solid surface. The traditional adsorbents have some disadvantages such as relatively limited pollutant removal capacity and poor separation ability [1–4].
The pollutant removal using magnetic nanoparticle as adsorbents is an emerging field of water and wastewater treatment [5, 6]. The magnetic adsorbents could be separated based on their nanostructures because the ease of direction of magnetization would vary depending on the ordering of atoms in the magnetic structure [5, 7]. The use of a magnetic field induces the magnetization of the nanoparticle and thus makes the use of a magnetic force possible, but when the magnetic field is cut of, the magnetization immediately decreases to zero. It is important for the release of nanoparticles after adsorption process [6, 8].
Several magnetic materials have been used to remove dyes from aqueous solution [9–12]. Nanoparticles have low adsorption capacity of anionic dyes due to repulsion of the negative charge of nanoparticle surface and anionic dyes. Thus, they should be modified. Liu et al. prepared and characterized ammonium-functionalized silica nanoparticle as a new adsorbent to remove methyl orange from aqueous solution . Absalan et al. modified Fe3O4 magnetic nanoparticles using ionic liquid and used to remove of reactive red-120 and 4-(2-pyridylazo) resorcinol from aqueous samples . A literature review showed that surface modified zinc ferrite nanoparticle by cetyl trimethylammonium bromide (CTAB) was not used to remove dyes. ZFN was synthesized in previous study and used for photo catalytic degradation of dyes . In this paper, zinc ferrite nanoparticle (ZFN) was synthesized and its surface was modified using CTAB. Dyes were removed using ZFN-CTAB and magnetic ferrite nanoparticle (ZFN). Three direct dyes (Direct Red 23 (DR23), Direct Red 31 (DR31) and Direct Green 6 (DG6)) were used as model compounds. The present work aims to study an appropriate and economic procedure for removal of dyes from water by adsorption on ZFN-CTAB as a magnetic adsorbent. The dye adsorption isotherm and kinetic and effect of operational parameters such as adsorbent dosage, initial dye concentration and salt on dye removal was evaluated in details.
Synthesis and characterization of ZFN-CTAB
ZFN (≤80 nm) was synthesized in our laboratory. 4.90 g zinc nitrate (297 g/mol) and 13.4 g iron nitrate (404 g/mol) was dissolved in 50 mL distilled water and added to aqueous mixed solution 4.2 g NaOH in 70 mL distilled water and 3 mL ethylene diamine (ED). This solution was heated at 90°C for 1 h to achieve complete chelation. The powder was calcined on alumina crucible at 500°C for 1 h, with a heating rate of 10°C/min .
CTAB (0.4 g) was added to solution containing 10 mL acetone, 125 mL distilled water and 1 g ZFN. The mixture was stirred in a mixer for 1 h. The organo-modified ZFN was separated from the mixture by magnetic force and then was washed with distilled water until free of salts.
Fourier transform infrared (FTIR), scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to characterize ZFN and ZFN-CTAB. FTIR spectrum (Perkin-Elmer Spectrophotometer Spectrum One) in the range 4000–450 cm−1 was studied. The morphological structure of the ZFN-CTAB was examined by SEM using LEO 1455VP scanning microscope. Crystallization behavior was identified by XRD model Siemens D-5000 diffractometer with Cu Kα radiation (λ = 1.5406 A°) at room temperature.
Batch adsorption procedure
The dye adsorption was done by mixing of adsorbent in 250 mL of a dye solution (50 mg/L) for 60 min. The solution samples were taken at certain time intervals (0, 2.5, 5, 7.5, 10, 15, 20, 30, 40, 50 and 60 min.) and adsorbent particles were separated by magnetic force. The change on the absorbance of all solution samples were monitored and determined at certain time intervals during the adsorption process. At the end of the adsorption experiments, the dye concentration was determined.
UV–vis Perkin-Elmer Lambda 25 spectrophotometer was employed for absorbance measurements of samples. The maximum wavelength (λmax) used for determination of residual concentration of DG6, DR23 and DR31 in supernatant solution using UV–VIS spectrophotometer were 623, 500 and 523 nm, respectively. The solution pH was adjusted by adding H2SO4 or NaOH.
The isotherm and kinetics of dye adsorption on ZFN-CTAB was studied by contacting 250 mL of dye solution with initial dye concentration of 50 mg/L at room temperature (25°C) for 60 min at different ZFN-CTAB dosages (0.4-2 g/L).
The effect of operational parameters such as adsorbent dosage (0.4-2 g/L), initial dye concentration (50–200 mg/L), pH (2–11) and salt (0.02 M of NaHCO3, Na2CO3 and Na2SO4) on dye removal was investigated.
Results and discussion
Characterization of ZFN-CTAB
Effect of operational parameter on dye removal
Effect of adsorbent dosage
The increase in dye adsorption with adsorbent dosage is due to the increasing of adsorbent surface and availability of more adsorption sites. However, if the adsorption capacity was expressed in mg adsorbed per gram of material, the capacity decreased with the increasing amount of adsorbent. It can be attributed to overlapping or aggregation of adsorption sites resulting in a decrease in total adsorbent surface area available to the dye and an increase in diffusion path length . The results showed that ZFN-CTAB has higher dye removal efficiency in compare with unmodified ZFN. Thus for further study, optimum amount 0.4 g of ZFN-CTAB was used.
Effect of dye concentration
The amount of the dye adsorbed onto ZFN-CTAB increases with an increase in the initial dye concentration of solution if the amount of adsorbent is kept unchanged. It can be attributed to the increase in the driving force of the concentration gradient with the higher initial dye concentration. The adsorption of dye by ZFN-CTAB is very intense and reaches equilibrium very quickly at low initial concentration. At a fixed ZFN-CTAB dosage, the percentage of adsorption decreased. In other words, the residual dye concentration will be higher for higher initial dye concentrations. In the case of lower concentrations, the ratio of initial number of dye moles to the available adsorption sites is low and subsequently the fractional adsorption becomes independent of initial concentration .
Effect of pH
Effect of salt
The inorganic anions exist in colored industrial wastewater . These substances may compete for the active sites on the adsorbent surface or deactivate the adsorbent. Thus, dye adsorption efficiency decreases.
Comparison of single and ternary systems
The results obviously showed that DR31 was removed more than other dyes in ternary system for all effects. The study of dyes adsorption demonstrated that the percentage of adsorption decreased in ternary system (150 ppm) in compare with single system (50 ppm) for each dyes; because some of adsorption sites occupies with other dyes. Investigating of other effect showed that adsorption of dyes had same procedure in both single and ternary systems.
The adsorption isotherm is important to design of adsorption systems. The mechanism of dye removal was studied by isotherm models. The relation between the mass of the dye adsorbed at a particular temperature, the pH, particle size and liquid phase of the dye concentration is discussed by the adsorption isotherms. The current research presents a method of direct comparison of the isotherm fit of several models to enable the best-fit and best isotherm parameters to be obtained [20–22]. Several isotherms such as Langmuir, Freundlich and Tempkin models were studied in details [23–25].
where q e , C e , K L and Q 0 are the amount of dye adsorbed at equilibrium (mg/g), the equilibrium concentration of dye in solution (mg/L), Langmuir constant (L/g) and the maximum adsorption capacity (mg/g), respectively.
The Freundlich isotherm was developed mainly to allow for an empirical account of the variation in adsorption heat with concentration of an adsorbate (vapor or solute) on an energetically heterogeneous surface.
where K F is adsorption capacity at unit concentration and 1/n is adsorption intensity.
K T is the equilibrium binding constant (L/mg) corresponding to the maximum binding energy and constant B 1 is related to the heat of adsorption.
Linearized isotherm coefficients for dye adsorption onto ZFN-CTAB (Q 0 : mg/g; K L : L/mg; K F : L/g; K T : mg/L and B 1 : mg.g −1 )
The R 2 values show that the dye adsorption isotherm using ZFN-CTAB does not follow the Freundlich and Tempkin isotherms (Table 2). The linear fit between the C e /q e versus C e and the calculated R 2 values for Langmuir isotherm model show that the dyes adsorption isotherm can be approximated as Langmuir model (Table 2). This means that the adsorption of dyes takes place at specific homogeneous sites and a one layer adsorption onto ZFN-CTAB surface. The maximum adsorption capacity (Q0) was 26.1, 55.5 and 64.1 mg/g for DR23, DR31 and DG6, respectively.
The dye removal ability of different magnetic adsorbents
Q 0 (mg/g)
Magnetic alginate bead
Magnetic multi-wall carbon nanotube nanocomposite
Brilliant cresyl blue
Multi-walled carbon nanotube filled with Fe2O3
Direct Red 23
Direct Red 31
Direct Green 6
The adsorption rate of dyes onto adsorbent was investigated by adsorption kinetics. Adsorption kinetic using pseudo-first order equation, pseudo-second order equation and intraparticle diffusion model were determined in order to investigate the mechanism of dye adsorption onto different adsorbents [31, 32].
where q e , q t and k 1 are the amount of dye adsorbed at equilibrium (mg/g), the amount of dye adsorbed at time t (mg/g) and the equilibrium rate constant of pseudo-first order kinetics (1/min), respectively. The linear fit between the log (q e –q t ) and contact time (t) can be approximated as pseudo-first order kinetics.
where k 2 is the equilibrium rate constant of pseudo-second order (g/mg min).
where k p and I are the intraparticle diffusion rate constant and intercept, respectively.
Linearized kinetic coefficients for dye adsorption onto ZFN-CTAB (Adsorbent: g; (q e ) Exp : mg/g; (q e ) Cal. : mg/g; k 1 : 1/min; k 2 : g/mg min and k p : mg/g min 1/2 )
The linearity of the plots (R 2 ) demonstrates that pseudo-first order and intraparticle diffusion kinetic models do not play a significant role in the uptake of the dye by ZFN-CTAB (Table 4). The linear fit between the t/q t versus contact time (t) and the calculated R 2 values for pseudo-second order kinetics model show that the dye removal kinetic can be approximated as pseudo-second order kinetics (Table 4). In addition, the experimental q e ((q e ) Exp .) values agree with the calculated ones ((q e ) Cal .), obtained from the linear plots of pseudo-second order kinetics (Table 4).
In this paper, ZFN-CTAB was synthesized and its dye removal ability was investigated. Direct Red 23 (DR23), Direct Red 31 (DR31) and Direct Green 6 (DG6) were used as model compounds. Adsorption kinetic of dyes was found to conform to pseudo-second order kinetics. It was found that dye adsorption onto ZFN-CTAB followed with Langmuir isotherm. It can be concluded that the ZFN-CTAB being as a magnetic adsorbent with high dye adsorption capacity might be a suitable alternative to remove dyes from colored aqueous solutions.
This work was done in Department of Environmental Research, Institute for Color Science and Technology. Dr Mahmoodi is grateful for the support from the ICST.
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