Removal of crystal violet from water by magnetically modified activated carbon and nanomagnetic iron oxide
© Hamidzadeh et al.; licensee BioMed Central. 2015
Received: 9 July 2014
Accepted: 6 January 2015
Published: 31 January 2015
Magnetically modified activated carbon, which synthesized by nanomagnetic iron oxide, was used for fast and effective removal of Crystal Violet from aqueous solutions. The scanning electron microscopy (SEM) images of nano-adsorbent showed that the average sizes of adsorbent are less than 100 nm. The various parameters, affecting on adsorption process, were examined including pH and temperature of dye solution, dose of adsorbent, and contact time. Then, thermodynamic parameters of sorption were calculated. Langmuir and Freundlich isotherms were used to fit the resulting data. Adsorption kinetics was consistent with a pseudo second order equation. Thermodynamic parameters of adsorption, ∆H0, and ∆S0 were calculated. Also, for further investigations, nano magnetic iron oxides was synthesized and used as adsorbent. Sorption capacities were depending on the temperature varied from 44.7 to 67.1 mg/g and from 12.7 to 16.5 mg/g for magnetically modified activated carbon and nanomagnetic iron oxide, respectively.
Large amounts of dyes are produced and applied in various industries. Small amounts of dyes (less than 1 ppm for some dyes) are visible in water [1,2]. As the most of the dyes in wastewater are stable to light and oxidation and also resistant to aerobic digestion, they damage to the aquatic life .
Crystal Violet (CV) is a synthetic basic cationic dye used for various purposes including biological stain, dermatological agent, veterinary medicine, additive to poultry feed to inhibit propagation of mold, intestinal parasites, and textile dyeing industries etc. [4,5]. It is a mutagen, mitotic poison, and also proven potent carcinogen [6,7].
Various processes were developed for the dye removal from the wastewater including adsorption and biosorption [8-10], chemical and electrochemical oxidation [11-13], membrane separation process , photodegradation , etc.
Magnetic separation techniques have found important applications in environmental technology. In adsorption processes, the magnetic adsorbent can be easily separated from solution after adsorption process . The magnetizations of adsorbents such as peanut husks , sawdust , baker's yeast cells , activated coconut shell carbon  etc. were investigated for removal dyes and other concomitances. Since Activated carbon is one of most useful adsorbent for removal of dye, in this study, it was modified by nanomagnetic iron oxide for fast and effective removal of Crystal Violet. The SEM images indicated the sizes of adsorbent particles are in nano scales. Adsorbent efficiency in removal Crystal Violet was studied. The affecting parameters on adsorption process were examined. The thermodynamic and kinetic adsorption parameters of Crystal violet onto magnetically modified activated carbon were obtained while; they have not been reported in previous studies. In order to comparative studies, nanomagnetic iron oxide (that used for magnetization of activated carbon) were synthesized and used as adsorbent.
Materials and methods
Activated charcoal was purchased from BDH Ltd Poole England. Crystal Violet dye was from Merck Darmstadt Germany. All other chemicals used in this study were of high purity and used without further purification. Double distilled water was used for all experiments.
Batch adsorption experiments with 10 ml of Crystal Violet solution (5 mg/l) were done for 1–10 mg of adsorbent, 1 to 10 min contact times, 3–9 pHs, and at 20, 30 and 40°C.
pHs of solutions were adjusted by expected values of nitric acid and sodium hydroxide solutions. Analysis of dye concentration was carried out by UV–vis spectrophotometer in 593 nm wavelength.
Where qe is adsorption capacity (mg of adsorbed dye per g of adsorbent), Ce is equilibrium concentration of dye (mg/l), v is the volume of the solution (l) and w is the mass of adsorbent (g).
Where k2 is the second order reaction rate equilibrium constant (g mg−1 min−1).
Result and discussion
The adsorbent dosage
The contact time
pH of Crystal Violet solution
Temperature of dye solution
Dye removal was examined at different temperatures range started from 27°C (as ambient temperature) to 70°C. 10 ml of dye solution 5 mg/l was contacted to 0.01 g of magnetically modified activated carbon for 5 min at pH 5 at 27, 40, 50, 60, and 70°C.
The thermodynamic parameters of adsorption of Crystal Violet on magnetically modified activated carbon
∆G 0 (kJ/mol)
∆S 0 (kJ/mol.K)
∆H 0 (kJ/mol)
The rate constants and linear regressions of First order and Second order for adsorption of Crystal Violet on magnetically modified activated carbon and nanomagnetic iron oxide
k 1 (min −1 )
k 2 (g mg −1 min −1 )
Magnetically modified activated carbon
Nanomagnetic iron oxide
1.38 × 10−2
In order to perform further investigation, nanomagnetic iron oxide was synthesized as similar as described in experimental section, without any addition of activated carbon. In the same conditions, nanomagnetic iron oxide was used as adsorbent. The kinetic results shown in Table 2 indicated that, the kinetic of adsorption was the same as magnetically modified activated carbon with lower rate constant (k2).
The parameters of Langmuir and Freundlich isotherms at different temperatures for adsorption of Crystal Violet on magnetically modified activated carbon and nanomagnetic iron oxide
Magnetically modified activated carbon
Nanomagnetic iron oxide
In the same conditions, the experiments were performed by nanomagnetic iron oxide as the adsorbent. The obtained results listed in Table 3 show that, Langmuir and Freundlich did not well describe the adsorption isotherm model. The values of qmax increased by increasing the temperature and also were less than those for magnetically modified activated carbon.
The previous studies on magnetic adsorbents to removal Crystal Violet
10 mg cm−3
Magnetically labeled Baker's yeast cells
85.9 mg g−1
magnetically modified Saccharomyces cerevisiae subsp. uvarum cells
41.7 mg g−1
Ferrofluid modified sawdust
51.16 mg g−1
magnetically modified Chlorella Vulgaris cells
42.91 mg g−1
Magnetic fluid modified peanut husks
80.9 mg g−1
Magnetically modified spent grain
40.2 mg g−1
Magnetic carbon-iron oxide nanocomposite
81.70 mg g−1
Magnetically modified spent coffee grounds
68.1 mg g−1
Magnetically modified activated car bon
67.1 mg g−1
Nanomagnetic iron oxide
16.5 mg g−1
The results indicate that magnetically modified activated carbon have considerable potential for the removal of Crystal Violet, also the magnetic adsorbent can be simply removed from solution by using magnet or appropriate magnetic separator after adsorption process. The obtained results of this investigation implicate that this adsorbent was more able to remove dye in the less time with compared to some of studies listed in Table 4. Also we investigated Thermodynamic and kinetic studies for removal process more than other pervious works.
The resulting adsorption capacities demonstrate that, although nanomagnetic iron oxide can be as an adsorbent, but its efficiency is much lower than magnetically modified activated carbon.
The authors thank the staffs of Payam Noor University of Varamin, specially Mrs. Rezaiee and Mrs. Haj Husseini.
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