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Cu0.5Mn0.5Fe2O4 nano spinels as potential sorbent for adsorption of brilliant green
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JIEC-2242; No. of Pages 7 Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx
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Cu0.5Mn0.5Fe2O4 nano spinels as potential sorbent for adsorption of brilliant green Saeedeh Hashemian *, Atena Dehghanpor, Mahnaz Moghahed Islamic Azad University, Yazd Branch, Chemistry Department, Yazd, Iran
A R T I C L E I N F O
Article history: Received 3 December 2013 Received in revised form 24 September 2014 Accepted 2 October 2014 Available online xxx Keywords: Adsorption Nano spinel, CuxMn1xFe2O4, Brilliant green
A B S T R A C T
Nano spinels of CuxMn1xFe2O4 (x = 0.0, 0.2, 0.4, 0.5, 0.8 and 1) have been synthesized. Nano-particles of CuxMn1xFe2O4 were characterized by FTIR, XRD and SEM. The adsorption of brilliant green (BG) by nano particles of CuxMn1xFe2O4 was studied. Results showed that adsorption activity of nano particles are as followed: MnFe2O4 < CuFe2O4 < Mn0.2Cu0.8Fe2O4 < Mn0.8Cu0.2Fe2O4 < Mn0.4Cu0.6Fe2O4 < Mn0.5Cu0.5Fe2O4. The adsorption of BG followed pseudo-second-order kinetic model. Thermodynamic results revealed that the adsorption of BG onto Mn0.5Cu0.5Fe2O4 particles is endothermic and spontaneously process. The adsorption equilibrium was best described by the Langmuir model. The nano particles of Mn0.5Cu0.5Fe2O4 can be conveniently regenerated by chemical and physical methods after adsorption. ß 2014 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
Introduction Dyes and pigments are widely used in the textiles, paper, plastics, leather, food and cosmetic industry to color products. Most of dyes are toxic and must be removed before discharge into receiving streams. The release of colored wastewater from these industries may present an eco toxic hazard. Because of potential toxicity of dyes and their visibility in surface waters, removal and degradation of organic dyes have been a matter of considerable interest. Triphenylmethane dyes are one of the most common organic water pollutants and they are used extensively in the textile industry for dyeing nylon, wool, cotton, and silk, as well as for coloring of oil, fats, waxes, varnish, and plastics. Cationic triphenylmethane dyes have widespread use as colorants in industry and as antimicrobial agents. Brilliant green (BG) is a basic triphenylmethane-type cationic dye and is used in dilute solution as a topical antiseptic. Brilliant green is effective against gram-positive microorganisms. Basic dyes usually used for staining solutions in medicine and biology and as a photochromophore to sensitize gelatinous films [1,2]. Several treatment methods including coagulation, chemical oxidation, membrane separation, electrochemical processes, and adsorption techniques have been proposed for treatment of dye wastewaters. Considerable amounts of the literature reports the adsorption of dyes on various adsorbent surfaces especially nanomaterials [3–10].
* Corresponding author. Tel.:+988117572; fax: +987266065. E-mail address: [email protected] (S. Hashemian).
Composite oxides with spinel structures (AB2O4) are important inorganic metalloid materials and are widely used in different fields [11]. Spinels are attractive subjects for continuous scientific interest and have been deeply investigated in material science because of their physico-chemical properties. Among spinel compounds, spinel ferrites (MFe2O4, M = Ni, Mn, Fe and Cu) have received much research attention owing to both broad practical applications in several important technological fields such as ferrofluids, magneticdrug delivery, magnetic high-density information storages [11– 18], and degradation of organic pollutants such as dyes and halogenated derivatives in wastewater treatments [19] and Catalyst [20]. Magnetic separation technology combined with the adsorption process has been widely used in environmental purification applications. The adsorption of dyes and pollutants with different magnetic spinels was investigated [21–26]. In this paper, CuxMn1xFe2O4 (x = 0.0, 0.2, 0.4, 0.5, 0.8 and 1) spinels were prepared via chemical co precipitation method. Adsorption of brilliant green dye by nano spinels was investigated.
Experimental Materials and methods The all of chemicals were purchased from Merck chemical co. All of compounds were analytical grade and were used as received without any purification.
http://dx.doi.org/10.1016/j.jiec.2014.10.001 1226-086X/ß 2014 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
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Brilliant green (4-((4-(diethyl amino)-alpha-phenyl benzylidene)-2, 5-cyclohexadien-1-ylidene) diethyl ammonium sulfate), CI number 42040 and chemical formula of C27H34N2O4S as a sample of pollutant was purchased from BDH. Chemical structure of brilliant green (BG) is shown in Fig. 1. It has molecular weight of 482.63 g mol1. The standard solution of 1000 mg L1 BG was prepared and subsequently whenever necessary diluted. UV-Vis spectrophotometer 160A Shimadzu was used for determination of concentration of BG. IR measurements were performed by FTIR tensor-27 of Burker Co., using the KBr pellet between the ranges 400 to 4000 cm1. The powder X–ray diffraction studies were made on a Philips PW1840 diffractometer using Ni-filtered Cu ka radiation and wavelength 1.548A. The average particle size and morphology of samples were observed by SEM using a Hitachi S3500 Scanning Electron Microscope. All pH measurements were carried out with an ISTEK- 720P pH meter. Preparation of nano particles of CuxMn1xFe2O4 The ferrites CuxMn1xFe2O4 (x = 0.0, 0.2, 0.4, 0.5, 0.8 and 1) were synthesized using chemical co-precipitation method. Copper (II) chloride (CuCl2. 6H2O,1 mol) and ferric chloride (FeCl3. 6H2O, 2 mol) were dissolved in the distilled water and then titrated drop wise by 1 M NH3 till the pH was 9 under fast magnetic stirring at 60 (C. The prepared sample of CuFe2O4 was filtered off, washed with distilled water and then dried in a furnace at 300 (C for 3 h [5]. For preparation of CuxMn1xFe2O4, different ratio moles of Cu:Mn (x = 0.0-1) was used. For pattern, 0.5 mol CuCl2. 6H2O, 0.5 mol MnCl2. 6H2O and 2 mol FeCl3. 6H2O were used for preparation of Cu0.5Mn0.5Fe2O4. The preparation method was as the same. The samples were heated and dry in the oven of 300 (C for 3 h [27]. Adsorption studies Adsorption experiments were performed at 25 (C in an open borosilicate glass reactor of 250 ml capacity whose temperature was regulated by thermostat. The initial dye concentration of sample was 100 mg L1. 0.1 g of CuxMn1xFe2O4 (x = 0.0, 0.2, 0.4, 0.5, 0.8 and 1) was added in 30 ml of BG on rotary shaker at a constant speed of 300 rpm. Samples were withdrawn at appropriate time intervals and centrifuged at 1000 rpm for 5 min. Different parameters like; contact time and pH on the sorption capacity of BG have been studied. pH of the dye solutions were adjusted in the range of 2–12 with 0.1 M NaOH or HCl solutions. To evaluate the adsorption thermodynamic parameters, the effect of temperature on adsorption were carried out. To determine the effects of dye concentration, the dye concentrations 50–300 mg L1 of BG were used. To determine the effect of adsorbent dosage, the adsorbent concentrations of 0.05–2 g were used. To examine the effect of temperature, temperatures of 15– 60 (C were used. After the equilibrium, suspensions were filtered off and analyzed for dye concentration. Each experiment was
N
O NH2+ -
repeated five times, and the results are given averages. Relative standard deviation (% RSD) was determined between 1.7–3.0% for each point at all of experiments. The percent removal of BG by the hereby adsorbent is given by [27]:
% adsorption ¼ ½ðC 0 C e Þ=C 0 100 Where C0, Ce is denoted the initial and equilibrium concentration of BG mg L1, respectively. Result and discussion Characterization of spinel particles FTIR characterization The nano spinel particles of MnFe2O4, CuFe2O4 and Mn0.5Cu0.5Fe2O4 were also characterized by FTIR spectroscopy. The FTIR spectra of MnFe2O4, CuFe2O4 and Mn0.5Cu0.5Fe2O4 nano particles are shown in Fig. 2a–c. The absorption broad band at 3400– 3500 cm1 represented the stretching mode of H2O molecules and OH groups. The absorption band at 1600 cm1 on spectrum referred to the vibration of remainder H2O in the sample [28]. The spectrum of the nano powder in Fig. 2 shows that there are two absorption bands at 692–705 and 450–455 cm1 (M–O, M5 5Cu, Mn and Fe). The higher frequency band y1 (692–705 cm1) and lower frequency band y2 (450–455) are assigned to the tetrahedral and octahedral complexes [10]. It explains that the normal mode of vibration of tetrahedral cluster is higher than that the octahedral cluster. It should be attributed to the shorted bond of octahedral cluster [29]. SEM The morphologies of the ferrite spinel particles were studied by SEM. Fig. 3 shows the SEM images of a—MnFe2O4, b—CuFe2O4, c— Mn0.5Cu0.5Fe2O4 and d—Mn0.5Cu0.5Fe2O4 adsorbed BG. The micrographs obtained for these particles present a detail of the composite showing the two materials with complete different textures. According to SEM image of Mn0.5Cu0.5Fe2O4, the morphology of nano particles is homogeneous and the spinel nano particles consist of uniform spherical crystallites particle size with an average size of 20 nm. This value is in agreement with the XRD results. Therefore, it has better catalytic adsorptive property. XRD study XRD patterns of MnFe2O4, CuFe2O4 and Mn0.5Cu0.5Fe2O4 are shown in Fig. 4. The existence of a peak around the diffraction angle 35o corresponding to d = 2.51 (311) confirms the formation of spinel
OH S
O
Fig. 1. Chemical structure of brilliant green (BG).
O Fig. 2. FTIR of a—MnFe2O4, b—CuFe2O4, c—Mn0.5Cu0.5Fe2O4.
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Fig. 3. SEM micrograph of magnetic nano particles a—MnFe2O4 b—CuFe2O4 c—Mn0.5Cu0.5Fe2O4 and d—Mn0.5Cu0.5Fe2O4 adsorbed BG.
ferrites. As shown in Fig. 4, except some Cu impurity peaks, all peaks were indexed to be CuFe2O4 (JCPDS 77-0010). The values of lattice constant are determined for these materials. The manganese ferrite has tetragonal structure and a = b = 8.5900, c = 8.5400, a = b = g = 90, but Cu doped MnFe2O4 is cubic with a = b = c = 8.39600 and a = b = g = 908. The analysis of the diffraction pattern using 2u=308 (220), 358 (311), 448 (222), 578 (511) and 638 (440) reflection planes also confirms the formation of cubic spinel structure of the Mn0.5Cu0.5Fe2O4 [3,30]. The results showed doping of Cu on the manganese ferrite change the unite cell from tetragonal to cubic form [31]. The peak can be indexed to face center cubic structure of Jacob site ferrite (JCPDS No. 10-0319) and (JCPDS No. 73-1964). The crystallite sizes were calculated using the XRD peak broadening of the (311)peak using the Scherer’s formula: Dh k l ¼ 0:9l=ðbcos uh k l Þ where Dh k l is the particle size perpendicular to the normal line of (h k l) plane, h k l is the full width at half maximum, uh k l is the
Fig. 4. Powder XRD for a—MnFe2O4, b—Mn0.5Cu0.5Fe2O4.
Bragg angle of (h k l) peak, and l is the wavelength of X-ray. The average crystallite size of nano particles from bond width at 2u = 358 is about 20–35 nm. Adsorption study Effect of contact time Effect of contact time on the adsorption of BG onto CuxMn1xFe2O4 (x = 1, 0.8, 0.5, 0.2, 0) nano particles was investigated. 50 mL of 100 mg L1 of BG, 0.2 g of each ferrite with 300 rpm were contacted. After different agitation times, absorbance of filtrated dye determined. The difference of absorbance before and after adsorption onto ferrites showed the percent of BG removal. The percent of adsorption of BG as a function of time is shown in Fig. 5a. The BG removal increases by time till a maximum value and then become constant. MnFe2O4 sample shows lower response towards BG adsorption (60% at 120 min). To clarify the effect of Cu+2 concentration on the efficiency of catalytic adsorption different Cu+2 contents (x = 0.0, 0.2, 0.5, 0.6, 0.8 and 1) were tested. The maximum BG adsorption efficiency was observed for spinel ferrite samples which equal amount of Cu+2 and Mn+2 (Mn0.5Cu0.5Fe2O4). The efficiency of activity of ferrite at different Cu+2 concentrations reflects the effect of structure changes of ferrites. The variation of catalytic activity of ferrite spinels are as follow: MnFe2O4 < CuFe2O4 < Mn0.2Cu0.8Fe2O4 < Mn0.8Cu0.2Fe2O4 < Mn0.4Cu0.6Fe2Fe2O4 < Mn0.5Cu0.5Fe2O4.This is attributed to the different ionic radius of Mn and Cu and of more catalytic activity of copper ferrite [30]. Fig. 5 also indicates that the adsorption of BG is fast at the initial 10 min stage, and then, it becomes slower near the equilibrium. It would be for that a large number of vacant surface sites are available for adsorption during the initial stage of the treatment time, and after a lapse of time, the remaining vacant surface sites are difficult to be occupied due to repulsive forces between BG adsorbed on the surface of CuxMn1xFe2O4 ferrites and solution phase.
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particles depends strongly on pH. The acidic medium is favorable for the adsorption process of BG. With increasing pH, deprotonation takes place, which decreases the diffusion and adsorption [32]. This provides more active surface of the adsorbents and as result into more adsorption at their surfaces. Effect of adsorbent dosage The effect of the adsorbent dose on the removal of the BG was studied by varying amount of adsorbent from 0.05–2 g. It was observed that the amount of dye adsorbed varied with varying adsorbent mass and increased with increasing adsorbent mass. It is evident from the Fig. 7 that as the mass of the adsorbent dosage increases, the percentage of dye removal also increases (to 0.5 g). An increase in the adsorption with adsorbent dosage can be attributed to the availability for more adsorption sites and greater surface area for contact. The removal between 0.5 and 1.0 g of adsorbent dosage is only marginal. At adsorbent more than 1.0 g, the incremental BG removal is very small, because particle–particle interaction such as aggregation at higher mass of sorbent leads to a decrease in the availability of total surface area of the sorbent [33].
Fig. 5. Effect of contact time for adsorption of BG (100 mg L1) by 0.1 g of CuxMn1xFe2O4 (a—MnFe2O4, b—CuFe2O4, c—Mn0.2Cu0.8Fe2O4, d—Mn0.8Cu0.2Fe2O4, e—Mn0.4Cu0.6Fe2O4, f—Mn0.5Cu0.5Fe2O4. (b) Vis electronic spectra of BG before and after adsorption at different time: a—BG, b—after 15 min, c—after 30 min, d—after 45 min and f—after 60 min of contact time with Mn0.5Cu0.5Fe2O4
The visible spectra of BG and BG loaded Mn0.5Cu0.5Fe2O4 was studied. The spectrum is show in Fig. 5b. Spectrum around 435 nm and 620 nm are due to BG. These absorbance peaks are decreased in intensity as the treatment time increased, and after treatment for 60 min, this peak almost disappeared, which indicates the BG diminish after adsorption and adsorbed onto surface of Mn0.5Cu0.5Fe2O4.
Effect of temperature The removal of BG by MnFe2O4, CuFe2O4 and Mn0.5Cu0.5Fe2O4 nano particles was carried out at 10–60 (C. Increasing temperature from10 (C to 40 (C leads to increase in the percentage of removal rate. Hence, the adsorption of BG by spinel nanoparticles is a kinetically controlled process (Fig. 8). Fig. 8 Effect of temperature on the adsorption of BG onto a— CuFe2O4, b—MnFe2O4 and c—Mn0.5Cu0.5Fe2O4 (30 mL of initial dye concentration 100 mg L1 and 0.5 g sorbent). Adsorption kinetics Several models are available to investigate the adsorption kinetics. To find a suitable adsorption model for describing the
100
100
80
80 % Adsorption
% Adsorption
Effect of pH The influence of pH on the removal of BG dye by nano spinels (MnFe2O4, CuFe2O4 and Mn0.5Cu0.5Fe2O4) was studied to gain farther insight into the adsorption process. To determine the optimum pH, the pH value was changed from 2 to 12 with fixed initial concentration of 100 mg L1 of BG and contact time 30 min [31]. Fig. 6 shows the percentage removal of BG by nano spinel
Effect of concentration of BG dye Effect of the concentration of BG was investigated by repeating experiments with different initial concentrations (50, 100, 150, 200 and 300 BG mg L1). The results showed that, when the initial concentration of BG varied from 50 to 100 mg L1, the adsorption capacity of Mn0.5Cu0.5Fe2O4 increased from 79 to 92%. It is clear that the adsorption process is highly dependent on initial concentration of solution. With increasing the concentration of BG from 100 to 300 mg L1 the adsorption removal decreased from 92 to 53%. The maximum adsorption of dye occurred at low concentrations about 100 mg L1. This indicates that the initial dye concentrations played an important role in the adsorption removal of BG on the Mn0.5Cu0.5Fe2O4 particles.
60 40 a
20
c
b
60 40
b
c
a
20 0
0 0
2
4
6 pH
8
10
12
Fig. 6. Effect of pH on the adsorption of BG onto a—MnFe2O4, b—CuFe2O4 and c— Mn0.5Cu0.5Fe2O4 (30 mL of initial dye concentration 100 BG mg L1, temperature 25 (C and 0.2 g sorbent).
0
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 mass of sorbent (g)
2
Fig. 7. Effect of adsorbent dosage of BG adsorption onto a—MnFe2O4, b—CuFe2O4 and c—Mn0.5Cu0.5Fe2O4 (30 mL of initial BG concentration 100 mg L1, temperature 25 (C and pH 2).
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absolute temperature (K), and A is the pre-exponential factor (g mg1 min1). A plot of ln k versus the reciprocal of the absolute temperature should be a straight line if the reaction follows Arrhenius behavior [28]. The slope and the intercept of the line give the activation energy and the pre-exponential factor, respectively. Activation energy of adsorption of BG was calculated from pseudo second order model for two temperatures (25 (C and 35 (C) for MnFe2O4, CuFe2O4 and Mn0.5Cu0.5Fe2O4. The results are shown in Table 1.
% Adsorption
80 60 40 20
a
c
30 T (°C)
40
b
0 0
10
20
50
60
Adsorption isotherms
Fig. 8. Effect of temperature on the adsorption of BG onto a—CuFe2O4, b—MnFe2O4 and c—Mn0.5Cu0.5Fe2O4(30 mL of initial dye concentration 100 mg L1 and 0.5 g sorbent).
experimental kinetic data, the data were fitted into the first and second-order models: The pseudo-first order model assumes that the rate of change of solute uptake with time is directly proportional to difference in saturation concentration and amount of solid uptake with time [34]: log ðqe qt Þ ¼ logqe k1 t
(1)
Where qe and qt are the amounts of dye adsorbed per unite mass of the adsorbent (mg g1) at equilibrium and time t, respectively and k1 is the rate constant of adsorption (min1). When log(qe – qt) was plotted against time, a straight line should be obtained with a slope of k1, if the first order kinetics is valid. The pseudo-second order model as developed by Ho and McKay [35] has the following form: t t ¼ þ 1=ðk2 q2e Þ qt qe
(2)
Where qe and qt represent the amount of dye adsorbed (mg g1) at equilibrium and at any time. k2 in the rate constant of the pseudo-second order equation (g mg1 min1). A plot of t/qt versus time (t) would yield a line with a slope of 1/qe and an intercept of 1/ (k2 qe2), if the second order model is a suitable expression. The plot between log (qe–qt) versus time t shows the pseudo first order model and the plot of t/qt versus time t shows the pseudo second order model, respectively (Table 1). The kinetic model with a higher correlation coefficient R2 was selected as the most suitable one (Table 1). The results show that adsorption kinetics of BG fitted well the pseudo-second-order kinetic model. As the removal of dye kinetics was monitored at different temperatures, the rate constants were calculated in order to find out whether the reaction follows Arrhenius behavior. According to the Arrhenius, the relationship between the rate constant of the reaction and the absolute temperature can be written as: ln k ¼ Ea=ðR TÞ þ ln A
(3)
Where k is the rate constant (g mg1 min1), Ea is the activation energy (J mol1), R is the gas constant (8.314 J K1 mol1), T is the Table 1 Kinetic parameters for adsorption of BG by MnFe2O4, CuFe2O4 and Mn0.5Cu0.5Fe2O4. Sorbents
MnFe2O4 CuFe2O4 Mn0.5Cu0.5Fe2O4
5
Ea (kJ mol1)
First order
Second order
R2
K1 (min1)
R2
K2 (g mg1)
2.2 106 0.65 106 1.43 106
0.798 0.826 0.862
0.253 0.227 0.29
0.950 0.9556 0.992
3.6 102 4.2 102 4.9 102
The quantity of the dye that could be adsorbed over the nano spinels surface is a function of concentration and may be explained by adsorption isotherm. The Freundlich and Langmuir isotherm models were applied to the adsorption data. The Langmuir adsorption model is given as: C e =qe ¼ 1=K L qm þ ð1=K L ÞC e
(4)
Where qe is the solid phase equilibrium concentration (mg g1); Ce is the liquid equilibrium concentration of dye in solution (mg L1); KL is the equilibrium adsorption constant related to the affinity of binding sites (L mg1); and qm is the maximum amount of dye per unit weight of adsorbent for complete monolayer coverage (mg g1). The Freundlich adsorption isotherm model, which is an empirical equation used to describe heterogeneous adsorption systems, can be represented as follows: qe ¼ K F C e 1=n
(5)
Where qe and Ce are defined as above, KF is the Freundlich constant representing the adsorption capacity (mg g1), and n is the heterogeneity factor depicting the adsorption intensity. In most references, Freundlich adsorption may also be expressed as the following equation: Log qe ¼ Log K F þ 1=n Log C e
(6)
The isotherm parameters of Langmuir and Freundlich for adsorption of BG onto Mn0.5Cu0.5Fe2O4 are listed in Table 2. By comparing the values obtained R2 charts, which was intended adsorption process by adsorbing of BG by Mn0.5Cu0.5Fe2O4. The results showed that the equilibrium data were better represented by Langmuir isotherm equation than done by the Freundlich equation (Figs. 9 and 10). Comparison of isotherm and kinetic models of brilliant green adsorption with different sorbents The isotherm and kinetic models of brilliant green adsorption was compared with several low cost adsorbents and they are reported in Table 3. The results of Table also show, kinetic and isotherm models of ferrite spinel of Mn0.5Cu0.5Fe2O4, CuFe2O4 and MnFe2O4 were similar to other carbon and fibrous sorbents. Table 2 Langmuir and Freundlich constants for the adsorption of BG by MnFe2O4, CuFe2O4 and Mn0.5Cu0.5Fe2O4. Sorbent
Freundlich KF
Langmuir
n
R2
qm mg g1
KL L mg1
R2
0.543 0.43 0.45
0.927 0.933 0.955
0. 82 0.775 0.86
16.4 18.5 16.13
0.968 0.975 0.986
mg g1 MnFe2O4 CuFe2O4 Mn0.5Cu0.5Fe2O4
0.176 0.07 0.027
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Ce/qe
6
0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
Table 3 Comparison of Isotherm and kinetic models of brilliant green with different sorbents.. Isotherm model
Adsorbent
4.37 3.35 3.3 3.2 2.4 2.4 2.2 1.9 1.85 Ce Fig. 9. Langmuir isotherm for adsorption of BG using MnFe2O4, CuFe2O4 and Mn0.5Cu0.5Fe2O4.
Thermodynamic studies The amount of BG adsorbed at equilibrium at different temperatures 20–60 (C, have been examined to obtain thermodynamic parameters for the adsorption system. The thermodynamic parameters, change in the standard free energy (DG0), enthalpy (DH0) and entropy (DS0) associated with the adsorption process and these were determined using the following equations [33]:
DG0 ¼ RT ln K C
(7)
Where, DG0 is the standard free energy change, T the absolute temperature, R the universal gas constant (8.314 J mol1 K1) and KC the equilibrium constant. The apparent equilibrium constant of the sorption, KC, is obtained from: K C ¼ C A =C S
(8)
Where KC is the equilibrium constant, CA is the amount of CR adsorbed on the adsorbent of solution at equilibrium (mg L1); CS is the equilibrium concentration of BG in the solution (mg L1). KC values calculated at different temperature to allow the determination of the thermodynamic equilibrium constant (KC) [33]. The free energy changes are also calculated by using the following equations: lnK c ¼ DG0 =RT ¼ DH0 =RT þ DS0 =R
(9)
DH0 and DS0 were calculated the slope and intercept of van,t Hoff plots of ln KC versus 1/T. The results of thermodynamic parameters of BG adsorption onto Mn0.5Cu0.5Fe2O4 are given in Table 4. The overall standard free energy change during the adsorption process was negative for the experimental range of temperatures and the system did not gain energy from an external source. It becomes more favorable when temperature increased [33].
Kinetic Ref model
Polyaniline/multiwalled carbon nanotubes Langmuir White rice husk ash Langmuir Chitosan Langmuir Rice husk ash Langmuir Luffa cylindrical sponge Langmuir Agricultural waste Red clay Langmuir, Freundlich Langmuir Neem leaf powder Kaolin Langmuir Raw Bagasse Freundlich Chemically activated raw Freundlich baggase Langmuir Diatomite–attapulgite MnFe2O4 Langmuir CuFe2O4 Langmuir Mn0.5Cu0.5Fe2O4 Langmuir
28 28 28 2 28 18 28
[36] [37] [38] [39] [40] [41] [42]
28 28 – –
[43] [44] [45] [5]
– 28 28 28
[46] In this study In this study In this study
Photocatalytic activity Since some dyes are degraded by direct UV irradiation [31], it should be examined to what extent BG is photolyzed if no nanospinels were used. The photocatalytic activity of Mn0.5Cu0.5Fe2O4 nanoparticles for the degradation of BG was evaluated. In a typical experiment, 30 ml of dye solution 100 mg L1 and 0.5 g of nanoparticle was mixed using a magnetic stirrer. After a period of time in the dark, the solution was irradiated. The light source was Hg lamp (300 W, lmax = 365 nm). The samples from the reaction mixture were taken from the reactor at appropriate time intervals in order to monitor the dye concentration in the solution. The solution was analyzed by the UV–vis method using 160 A Shimadzu spectrometer. The concentration of BG in the samples was calculated using the calibration curve. Two experiments were carried out under the same conditions, one in the presence of nanoparticles and UV irradiation and the second without UV irradiation. The simultaneous utilization of UV irradiation and nanoparticles increase the degradation rate of BG so that 90% of BG is removed within 1 min. In the presence of nanospinel without UV irradiation, the concentration of dye decreases quickly at the beginning, and then reaches to a saturation value as a result of adsorption of dye molecules on the nanospinel was done. Hence, the new nanospinels cannot act as photocatalysts for the degradation of BG in an aqueous solution. The degradation is just an adsorption process. Desorption studies Desorption studies can help to further studying the mechanism of adsorption and the feasibility of regenerating the adsorbents.
2.2 2 Table 4 Thermodynamic parameters for adsorption of BG by adsorption onto Mn0.5Cu0.5Fe2O4.
logq e
1.8 1.6 1.4
CuFe2O4 MnFe2O4 Mn0.5Cu0.5Fe2O4
1.2 1 0.2
0.3
0.4
0.5
0.6
0.7
log Ce Fig. 10. Freudlich isotherm for adsorption of BG using MnFe2O4, CuFe2O4 and Mn0.5Cu0.5Fe2O4.
Temperature (8C)
KC
15 20 25 30 35 45 55
1.09 1.11 1.24 1.57 1.86 3.25 4.6
DG0
D H0
(KJ mol1)
(KJ mol
0.19 0.24 0.51 1.09 1.56 3.06 4.1
24.7
DS0 (J mol1 k1) 1
) 88
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The reversibility of adsorption for Mn0.5Cu0.5Fe2O4 was investigated by desorption experiments. For the desorption study, 0.5 g Mn0.5Cu0.5Fe2O4 adsorbent was added to 50 mL of BG solutions (100 mg L1, pH 2.0), once equilibrium reached, the BG-adsorbed nano particles adsorbent was separated and stirred in 50 mL of 0.1 M HCl, HNO3, NaCl, NaOH and H2SO4 solution for 1 h, and then the concentration of BG was measured. The desorption percentages of Mn0.5Cu0.5Fe2O4 by H2SO4 was found to be about 85%. The capacity of Mn0.5Cu0.5Fe2O4 for adsorption of BG after five-cycle regeneration was as followed:
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12]
H2SO4 > HCl > HNO3 > NaCl > NaOH:
[13]
The Mn0.5Cu0.5Fe2O4 is simple to thermally regenerate and regeneration temperature is commonly at or beyond 300 8C. The good regeneration result and relatively low regeneration temperature demonstrated that the Mn0.5Cu0.5Fe2O4 could offer high adsorptive activity. The adsorption capacity of the Mn0.5Cu0.5Fe2O4 for dye after its regeneration has also been studied. The regenerated samples of Mn0.5Cu0.5Fe2O4 were again saturated with BG with the same initial concentration of 100 mg L1, determining their new adsorption capacity. Generally, the adsorption capacity of the Mn0.5Cu0.5Fe2O4 decreases as the number of regeneration cycle increased. Further, our experiment also display that the adsorption capacity could maintain above 90% of its initial capability for BG after three cycles and above 80% of its initial capability for five cycles and 75% for BG after eight cycles. The result here illustrates that Mn0.5Cu0.5Fe2O4 can be employed repeatedly for the removal of dyes.
[14] [15]
Conclusion The nano ferrites of CuxMn1xFe2O4 (x = 0.0, 0.2, 0.4, 0.5, 0.8 and 1) were prepared. The nano particles were characterized by FTIR, XRD and SEM. The nano particles of spinel type were test for degradation of BG dye from aqueous solutions. Effect of contact time, pH and mass of sorbent and initial concentration of BG on adsorption of BG onto CuxMn1xFe2O4 were investigated. The results showed that the maximum adsorption capacity of BG was observed for Mn0.5Cu0.5Fe2O4. Kinetic data follows pseudo secondorder kinetic model. Adsorption behavior is better described by Langmuir type isotherm model. The negative values of DG0 indicated that the adsorption process of dye onto Mn0.5Cu0.5Fe2O4 is spontaneous. The nano spinels could be conveniently regenerated after adsorption by chemical and physical methods. The Mn0.5Cu0.5Fe2O4 new nanospinels are promising candidates for the adsorption of cationic triphenylmethane dyes from wastewaters.
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Cu0.5Mn0.5Fe2O4 nano spinels as potential sorbent for adsorption of brilliant green Saeedeh Hashemian *, Atena Dehghanpor, Mahnaz Moghahed Islamic Azad University, Yazd Branch, Chemistry Department, Yazd, Iran
A R T I C L E I N F O
Article history: Received 3 December 2013 Received in revised form 24 September 2014 Accepted 2 October 2014 Available online xxx Keywords: Adsorption Nano spinel, CuxMn1xFe2O4, Brilliant green
A B S T R A C T
Nano spinels of CuxMn1xFe2O4 (x = 0.0, 0.2, 0.4, 0.5, 0.8 and 1) have been synthesized. Nano-particles of CuxMn1xFe2O4 were characterized by FTIR, XRD and SEM. The adsorption of brilliant green (BG) by nano particles of CuxMn1xFe2O4 was studied. Results showed that adsorption activity of nano particles are as followed: MnFe2O4 < CuFe2O4 < Mn0.2Cu0.8Fe2O4 < Mn0.8Cu0.2Fe2O4 < Mn0.4Cu0.6Fe2O4 < Mn0.5Cu0.5Fe2O4. The adsorption of BG followed pseudo-second-order kinetic model. Thermodynamic results revealed that the adsorption of BG onto Mn0.5Cu0.5Fe2O4 particles is endothermic and spontaneously process. The adsorption equilibrium was best described by the Langmuir model. The nano particles of Mn0.5Cu0.5Fe2O4 can be conveniently regenerated by chemical and physical methods after adsorption. ß 2014 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
Introduction Dyes and pigments are widely used in the textiles, paper, plastics, leather, food and cosmetic industry to color products. Most of dyes are toxic and must be removed before discharge into receiving streams. The release of colored wastewater from these industries may present an eco toxic hazard. Because of potential toxicity of dyes and their visibility in surface waters, removal and degradation of organic dyes have been a matter of considerable interest. Triphenylmethane dyes are one of the most common organic water pollutants and they are used extensively in the textile industry for dyeing nylon, wool, cotton, and silk, as well as for coloring of oil, fats, waxes, varnish, and plastics. Cationic triphenylmethane dyes have widespread use as colorants in industry and as antimicrobial agents. Brilliant green (BG) is a basic triphenylmethane-type cationic dye and is used in dilute solution as a topical antiseptic. Brilliant green is effective against gram-positive microorganisms. Basic dyes usually used for staining solutions in medicine and biology and as a photochromophore to sensitize gelatinous films [1,2]. Several treatment methods including coagulation, chemical oxidation, membrane separation, electrochemical processes, and adsorption techniques have been proposed for treatment of dye wastewaters. Considerable amounts of the literature reports the adsorption of dyes on various adsorbent surfaces especially nanomaterials [3–10].
* Corresponding author. Tel.:+988117572; fax: +987266065. E-mail address: [email protected] (S. Hashemian).
Composite oxides with spinel structures (AB2O4) are important inorganic metalloid materials and are widely used in different fields [11]. Spinels are attractive subjects for continuous scientific interest and have been deeply investigated in material science because of their physico-chemical properties. Among spinel compounds, spinel ferrites (MFe2O4, M = Ni, Mn, Fe and Cu) have received much research attention owing to both broad practical applications in several important technological fields such as ferrofluids, magneticdrug delivery, magnetic high-density information storages [11– 18], and degradation of organic pollutants such as dyes and halogenated derivatives in wastewater treatments [19] and Catalyst [20]. Magnetic separation technology combined with the adsorption process has been widely used in environmental purification applications. The adsorption of dyes and pollutants with different magnetic spinels was investigated [21–26]. In this paper, CuxMn1xFe2O4 (x = 0.0, 0.2, 0.4, 0.5, 0.8 and 1) spinels were prepared via chemical co precipitation method. Adsorption of brilliant green dye by nano spinels was investigated.
Experimental Materials and methods The all of chemicals were purchased from Merck chemical co. All of compounds were analytical grade and were used as received without any purification.
http://dx.doi.org/10.1016/j.jiec.2014.10.001 1226-086X/ß 2014 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
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Brilliant green (4-((4-(diethyl amino)-alpha-phenyl benzylidene)-2, 5-cyclohexadien-1-ylidene) diethyl ammonium sulfate), CI number 42040 and chemical formula of C27H34N2O4S as a sample of pollutant was purchased from BDH. Chemical structure of brilliant green (BG) is shown in Fig. 1. It has molecular weight of 482.63 g mol1. The standard solution of 1000 mg L1 BG was prepared and subsequently whenever necessary diluted. UV-Vis spectrophotometer 160A Shimadzu was used for determination of concentration of BG. IR measurements were performed by FTIR tensor-27 of Burker Co., using the KBr pellet between the ranges 400 to 4000 cm1. The powder X–ray diffraction studies were made on a Philips PW1840 diffractometer using Ni-filtered Cu ka radiation and wavelength 1.548A. The average particle size and morphology of samples were observed by SEM using a Hitachi S3500 Scanning Electron Microscope. All pH measurements were carried out with an ISTEK- 720P pH meter. Preparation of nano particles of CuxMn1xFe2O4 The ferrites CuxMn1xFe2O4 (x = 0.0, 0.2, 0.4, 0.5, 0.8 and 1) were synthesized using chemical co-precipitation method. Copper (II) chloride (CuCl2. 6H2O,1 mol) and ferric chloride (FeCl3. 6H2O, 2 mol) were dissolved in the distilled water and then titrated drop wise by 1 M NH3 till the pH was 9 under fast magnetic stirring at 60 (C. The prepared sample of CuFe2O4 was filtered off, washed with distilled water and then dried in a furnace at 300 (C for 3 h [5]. For preparation of CuxMn1xFe2O4, different ratio moles of Cu:Mn (x = 0.0-1) was used. For pattern, 0.5 mol CuCl2. 6H2O, 0.5 mol MnCl2. 6H2O and 2 mol FeCl3. 6H2O were used for preparation of Cu0.5Mn0.5Fe2O4. The preparation method was as the same. The samples were heated and dry in the oven of 300 (C for 3 h [27]. Adsorption studies Adsorption experiments were performed at 25 (C in an open borosilicate glass reactor of 250 ml capacity whose temperature was regulated by thermostat. The initial dye concentration of sample was 100 mg L1. 0.1 g of CuxMn1xFe2O4 (x = 0.0, 0.2, 0.4, 0.5, 0.8 and 1) was added in 30 ml of BG on rotary shaker at a constant speed of 300 rpm. Samples were withdrawn at appropriate time intervals and centrifuged at 1000 rpm for 5 min. Different parameters like; contact time and pH on the sorption capacity of BG have been studied. pH of the dye solutions were adjusted in the range of 2–12 with 0.1 M NaOH or HCl solutions. To evaluate the adsorption thermodynamic parameters, the effect of temperature on adsorption were carried out. To determine the effects of dye concentration, the dye concentrations 50–300 mg L1 of BG were used. To determine the effect of adsorbent dosage, the adsorbent concentrations of 0.05–2 g were used. To examine the effect of temperature, temperatures of 15– 60 (C were used. After the equilibrium, suspensions were filtered off and analyzed for dye concentration. Each experiment was
N
O NH2+ -
repeated five times, and the results are given averages. Relative standard deviation (% RSD) was determined between 1.7–3.0% for each point at all of experiments. The percent removal of BG by the hereby adsorbent is given by [27]:
% adsorption ¼ ½ðC 0 C e Þ=C 0 100 Where C0, Ce is denoted the initial and equilibrium concentration of BG mg L1, respectively. Result and discussion Characterization of spinel particles FTIR characterization The nano spinel particles of MnFe2O4, CuFe2O4 and Mn0.5Cu0.5Fe2O4 were also characterized by FTIR spectroscopy. The FTIR spectra of MnFe2O4, CuFe2O4 and Mn0.5Cu0.5Fe2O4 nano particles are shown in Fig. 2a–c. The absorption broad band at 3400– 3500 cm1 represented the stretching mode of H2O molecules and OH groups. The absorption band at 1600 cm1 on spectrum referred to the vibration of remainder H2O in the sample [28]. The spectrum of the nano powder in Fig. 2 shows that there are two absorption bands at 692–705 and 450–455 cm1 (M–O, M5 5Cu, Mn and Fe). The higher frequency band y1 (692–705 cm1) and lower frequency band y2 (450–455) are assigned to the tetrahedral and octahedral complexes [10]. It explains that the normal mode of vibration of tetrahedral cluster is higher than that the octahedral cluster. It should be attributed to the shorted bond of octahedral cluster [29]. SEM The morphologies of the ferrite spinel particles were studied by SEM. Fig. 3 shows the SEM images of a—MnFe2O4, b—CuFe2O4, c— Mn0.5Cu0.5Fe2O4 and d—Mn0.5Cu0.5Fe2O4 adsorbed BG. The micrographs obtained for these particles present a detail of the composite showing the two materials with complete different textures. According to SEM image of Mn0.5Cu0.5Fe2O4, the morphology of nano particles is homogeneous and the spinel nano particles consist of uniform spherical crystallites particle size with an average size of 20 nm. This value is in agreement with the XRD results. Therefore, it has better catalytic adsorptive property. XRD study XRD patterns of MnFe2O4, CuFe2O4 and Mn0.5Cu0.5Fe2O4 are shown in Fig. 4. The existence of a peak around the diffraction angle 35o corresponding to d = 2.51 (311) confirms the formation of spinel
OH S
O
Fig. 1. Chemical structure of brilliant green (BG).
O Fig. 2. FTIR of a—MnFe2O4, b—CuFe2O4, c—Mn0.5Cu0.5Fe2O4.
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Fig. 3. SEM micrograph of magnetic nano particles a—MnFe2O4 b—CuFe2O4 c—Mn0.5Cu0.5Fe2O4 and d—Mn0.5Cu0.5Fe2O4 adsorbed BG.
ferrites. As shown in Fig. 4, except some Cu impurity peaks, all peaks were indexed to be CuFe2O4 (JCPDS 77-0010). The values of lattice constant are determined for these materials. The manganese ferrite has tetragonal structure and a = b = 8.5900, c = 8.5400, a = b = g = 90, but Cu doped MnFe2O4 is cubic with a = b = c = 8.39600 and a = b = g = 908. The analysis of the diffraction pattern using 2u=308 (220), 358 (311), 448 (222), 578 (511) and 638 (440) reflection planes also confirms the formation of cubic spinel structure of the Mn0.5Cu0.5Fe2O4 [3,30]. The results showed doping of Cu on the manganese ferrite change the unite cell from tetragonal to cubic form [31]. The peak can be indexed to face center cubic structure of Jacob site ferrite (JCPDS No. 10-0319) and (JCPDS No. 73-1964). The crystallite sizes were calculated using the XRD peak broadening of the (311)peak using the Scherer’s formula: Dh k l ¼ 0:9l=ðbcos uh k l Þ where Dh k l is the particle size perpendicular to the normal line of (h k l) plane, h k l is the full width at half maximum, uh k l is the
Fig. 4. Powder XRD for a—MnFe2O4, b—Mn0.5Cu0.5Fe2O4.
Bragg angle of (h k l) peak, and l is the wavelength of X-ray. The average crystallite size of nano particles from bond width at 2u = 358 is about 20–35 nm. Adsorption study Effect of contact time Effect of contact time on the adsorption of BG onto CuxMn1xFe2O4 (x = 1, 0.8, 0.5, 0.2, 0) nano particles was investigated. 50 mL of 100 mg L1 of BG, 0.2 g of each ferrite with 300 rpm were contacted. After different agitation times, absorbance of filtrated dye determined. The difference of absorbance before and after adsorption onto ferrites showed the percent of BG removal. The percent of adsorption of BG as a function of time is shown in Fig. 5a. The BG removal increases by time till a maximum value and then become constant. MnFe2O4 sample shows lower response towards BG adsorption (60% at 120 min). To clarify the effect of Cu+2 concentration on the efficiency of catalytic adsorption different Cu+2 contents (x = 0.0, 0.2, 0.5, 0.6, 0.8 and 1) were tested. The maximum BG adsorption efficiency was observed for spinel ferrite samples which equal amount of Cu+2 and Mn+2 (Mn0.5Cu0.5Fe2O4). The efficiency of activity of ferrite at different Cu+2 concentrations reflects the effect of structure changes of ferrites. The variation of catalytic activity of ferrite spinels are as follow: MnFe2O4 < CuFe2O4 < Mn0.2Cu0.8Fe2O4 < Mn0.8Cu0.2Fe2O4 < Mn0.4Cu0.6Fe2Fe2O4 < Mn0.5Cu0.5Fe2O4.This is attributed to the different ionic radius of Mn and Cu and of more catalytic activity of copper ferrite [30]. Fig. 5 also indicates that the adsorption of BG is fast at the initial 10 min stage, and then, it becomes slower near the equilibrium. It would be for that a large number of vacant surface sites are available for adsorption during the initial stage of the treatment time, and after a lapse of time, the remaining vacant surface sites are difficult to be occupied due to repulsive forces between BG adsorbed on the surface of CuxMn1xFe2O4 ferrites and solution phase.
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particles depends strongly on pH. The acidic medium is favorable for the adsorption process of BG. With increasing pH, deprotonation takes place, which decreases the diffusion and adsorption [32]. This provides more active surface of the adsorbents and as result into more adsorption at their surfaces. Effect of adsorbent dosage The effect of the adsorbent dose on the removal of the BG was studied by varying amount of adsorbent from 0.05–2 g. It was observed that the amount of dye adsorbed varied with varying adsorbent mass and increased with increasing adsorbent mass. It is evident from the Fig. 7 that as the mass of the adsorbent dosage increases, the percentage of dye removal also increases (to 0.5 g). An increase in the adsorption with adsorbent dosage can be attributed to the availability for more adsorption sites and greater surface area for contact. The removal between 0.5 and 1.0 g of adsorbent dosage is only marginal. At adsorbent more than 1.0 g, the incremental BG removal is very small, because particle–particle interaction such as aggregation at higher mass of sorbent leads to a decrease in the availability of total surface area of the sorbent [33].
Fig. 5. Effect of contact time for adsorption of BG (100 mg L1) by 0.1 g of CuxMn1xFe2O4 (a—MnFe2O4, b—CuFe2O4, c—Mn0.2Cu0.8Fe2O4, d—Mn0.8Cu0.2Fe2O4, e—Mn0.4Cu0.6Fe2O4, f—Mn0.5Cu0.5Fe2O4. (b) Vis electronic spectra of BG before and after adsorption at different time: a—BG, b—after 15 min, c—after 30 min, d—after 45 min and f—after 60 min of contact time with Mn0.5Cu0.5Fe2O4
The visible spectra of BG and BG loaded Mn0.5Cu0.5Fe2O4 was studied. The spectrum is show in Fig. 5b. Spectrum around 435 nm and 620 nm are due to BG. These absorbance peaks are decreased in intensity as the treatment time increased, and after treatment for 60 min, this peak almost disappeared, which indicates the BG diminish after adsorption and adsorbed onto surface of Mn0.5Cu0.5Fe2O4.
Effect of temperature The removal of BG by MnFe2O4, CuFe2O4 and Mn0.5Cu0.5Fe2O4 nano particles was carried out at 10–60 (C. Increasing temperature from10 (C to 40 (C leads to increase in the percentage of removal rate. Hence, the adsorption of BG by spinel nanoparticles is a kinetically controlled process (Fig. 8). Fig. 8 Effect of temperature on the adsorption of BG onto a— CuFe2O4, b—MnFe2O4 and c—Mn0.5Cu0.5Fe2O4 (30 mL of initial dye concentration 100 mg L1 and 0.5 g sorbent). Adsorption kinetics Several models are available to investigate the adsorption kinetics. To find a suitable adsorption model for describing the
100
100
80
80 % Adsorption
% Adsorption
Effect of pH The influence of pH on the removal of BG dye by nano spinels (MnFe2O4, CuFe2O4 and Mn0.5Cu0.5Fe2O4) was studied to gain farther insight into the adsorption process. To determine the optimum pH, the pH value was changed from 2 to 12 with fixed initial concentration of 100 mg L1 of BG and contact time 30 min [31]. Fig. 6 shows the percentage removal of BG by nano spinel
Effect of concentration of BG dye Effect of the concentration of BG was investigated by repeating experiments with different initial concentrations (50, 100, 150, 200 and 300 BG mg L1). The results showed that, when the initial concentration of BG varied from 50 to 100 mg L1, the adsorption capacity of Mn0.5Cu0.5Fe2O4 increased from 79 to 92%. It is clear that the adsorption process is highly dependent on initial concentration of solution. With increasing the concentration of BG from 100 to 300 mg L1 the adsorption removal decreased from 92 to 53%. The maximum adsorption of dye occurred at low concentrations about 100 mg L1. This indicates that the initial dye concentrations played an important role in the adsorption removal of BG on the Mn0.5Cu0.5Fe2O4 particles.
60 40 a
20
c
b
60 40
b
c
a
20 0
0 0
2
4
6 pH
8
10
12
Fig. 6. Effect of pH on the adsorption of BG onto a—MnFe2O4, b—CuFe2O4 and c— Mn0.5Cu0.5Fe2O4 (30 mL of initial dye concentration 100 BG mg L1, temperature 25 (C and 0.2 g sorbent).
0
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 mass of sorbent (g)
2
Fig. 7. Effect of adsorbent dosage of BG adsorption onto a—MnFe2O4, b—CuFe2O4 and c—Mn0.5Cu0.5Fe2O4 (30 mL of initial BG concentration 100 mg L1, temperature 25 (C and pH 2).
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absolute temperature (K), and A is the pre-exponential factor (g mg1 min1). A plot of ln k versus the reciprocal of the absolute temperature should be a straight line if the reaction follows Arrhenius behavior [28]. The slope and the intercept of the line give the activation energy and the pre-exponential factor, respectively. Activation energy of adsorption of BG was calculated from pseudo second order model for two temperatures (25 (C and 35 (C) for MnFe2O4, CuFe2O4 and Mn0.5Cu0.5Fe2O4. The results are shown in Table 1.
% Adsorption
80 60 40 20
a
c
30 T (°C)
40
b
0 0
10
20
50
60
Adsorption isotherms
Fig. 8. Effect of temperature on the adsorption of BG onto a—CuFe2O4, b—MnFe2O4 and c—Mn0.5Cu0.5Fe2O4(30 mL of initial dye concentration 100 mg L1 and 0.5 g sorbent).
experimental kinetic data, the data were fitted into the first and second-order models: The pseudo-first order model assumes that the rate of change of solute uptake with time is directly proportional to difference in saturation concentration and amount of solid uptake with time [34]: log ðqe qt Þ ¼ logqe k1 t
(1)
Where qe and qt are the amounts of dye adsorbed per unite mass of the adsorbent (mg g1) at equilibrium and time t, respectively and k1 is the rate constant of adsorption (min1). When log(qe – qt) was plotted against time, a straight line should be obtained with a slope of k1, if the first order kinetics is valid. The pseudo-second order model as developed by Ho and McKay [35] has the following form: t t ¼ þ 1=ðk2 q2e Þ qt qe
(2)
Where qe and qt represent the amount of dye adsorbed (mg g1) at equilibrium and at any time. k2 in the rate constant of the pseudo-second order equation (g mg1 min1). A plot of t/qt versus time (t) would yield a line with a slope of 1/qe and an intercept of 1/ (k2 qe2), if the second order model is a suitable expression. The plot between log (qe–qt) versus time t shows the pseudo first order model and the plot of t/qt versus time t shows the pseudo second order model, respectively (Table 1). The kinetic model with a higher correlation coefficient R2 was selected as the most suitable one (Table 1). The results show that adsorption kinetics of BG fitted well the pseudo-second-order kinetic model. As the removal of dye kinetics was monitored at different temperatures, the rate constants were calculated in order to find out whether the reaction follows Arrhenius behavior. According to the Arrhenius, the relationship between the rate constant of the reaction and the absolute temperature can be written as: ln k ¼ Ea=ðR TÞ þ ln A
(3)
Where k is the rate constant (g mg1 min1), Ea is the activation energy (J mol1), R is the gas constant (8.314 J K1 mol1), T is the Table 1 Kinetic parameters for adsorption of BG by MnFe2O4, CuFe2O4 and Mn0.5Cu0.5Fe2O4. Sorbents
MnFe2O4 CuFe2O4 Mn0.5Cu0.5Fe2O4
5
Ea (kJ mol1)
First order
Second order
R2
K1 (min1)
R2
K2 (g mg1)
2.2 106 0.65 106 1.43 106
0.798 0.826 0.862
0.253 0.227 0.29
0.950 0.9556 0.992
3.6 102 4.2 102 4.9 102
The quantity of the dye that could be adsorbed over the nano spinels surface is a function of concentration and may be explained by adsorption isotherm. The Freundlich and Langmuir isotherm models were applied to the adsorption data. The Langmuir adsorption model is given as: C e =qe ¼ 1=K L qm þ ð1=K L ÞC e
(4)
Where qe is the solid phase equilibrium concentration (mg g1); Ce is the liquid equilibrium concentration of dye in solution (mg L1); KL is the equilibrium adsorption constant related to the affinity of binding sites (L mg1); and qm is the maximum amount of dye per unit weight of adsorbent for complete monolayer coverage (mg g1). The Freundlich adsorption isotherm model, which is an empirical equation used to describe heterogeneous adsorption systems, can be represented as follows: qe ¼ K F C e 1=n
(5)
Where qe and Ce are defined as above, KF is the Freundlich constant representing the adsorption capacity (mg g1), and n is the heterogeneity factor depicting the adsorption intensity. In most references, Freundlich adsorption may also be expressed as the following equation: Log qe ¼ Log K F þ 1=n Log C e
(6)
The isotherm parameters of Langmuir and Freundlich for adsorption of BG onto Mn0.5Cu0.5Fe2O4 are listed in Table 2. By comparing the values obtained R2 charts, which was intended adsorption process by adsorbing of BG by Mn0.5Cu0.5Fe2O4. The results showed that the equilibrium data were better represented by Langmuir isotherm equation than done by the Freundlich equation (Figs. 9 and 10). Comparison of isotherm and kinetic models of brilliant green adsorption with different sorbents The isotherm and kinetic models of brilliant green adsorption was compared with several low cost adsorbents and they are reported in Table 3. The results of Table also show, kinetic and isotherm models of ferrite spinel of Mn0.5Cu0.5Fe2O4, CuFe2O4 and MnFe2O4 were similar to other carbon and fibrous sorbents. Table 2 Langmuir and Freundlich constants for the adsorption of BG by MnFe2O4, CuFe2O4 and Mn0.5Cu0.5Fe2O4. Sorbent
Freundlich KF
Langmuir
n
R2
qm mg g1
KL L mg1
R2
0.543 0.43 0.45
0.927 0.933 0.955
0. 82 0.775 0.86
16.4 18.5 16.13
0.968 0.975 0.986
mg g1 MnFe2O4 CuFe2O4 Mn0.5Cu0.5Fe2O4
0.176 0.07 0.027
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Ce/qe
6
0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
Table 3 Comparison of Isotherm and kinetic models of brilliant green with different sorbents.. Isotherm model
Adsorbent
4.37 3.35 3.3 3.2 2.4 2.4 2.2 1.9 1.85 Ce Fig. 9. Langmuir isotherm for adsorption of BG using MnFe2O4, CuFe2O4 and Mn0.5Cu0.5Fe2O4.
Thermodynamic studies The amount of BG adsorbed at equilibrium at different temperatures 20–60 (C, have been examined to obtain thermodynamic parameters for the adsorption system. The thermodynamic parameters, change in the standard free energy (DG0), enthalpy (DH0) and entropy (DS0) associated with the adsorption process and these were determined using the following equations [33]:
DG0 ¼ RT ln K C
(7)
Where, DG0 is the standard free energy change, T the absolute temperature, R the universal gas constant (8.314 J mol1 K1) and KC the equilibrium constant. The apparent equilibrium constant of the sorption, KC, is obtained from: K C ¼ C A =C S
(8)
Where KC is the equilibrium constant, CA is the amount of CR adsorbed on the adsorbent of solution at equilibrium (mg L1); CS is the equilibrium concentration of BG in the solution (mg L1). KC values calculated at different temperature to allow the determination of the thermodynamic equilibrium constant (KC) [33]. The free energy changes are also calculated by using the following equations: lnK c ¼ DG0 =RT ¼ DH0 =RT þ DS0 =R
(9)
DH0 and DS0 were calculated the slope and intercept of van,t Hoff plots of ln KC versus 1/T. The results of thermodynamic parameters of BG adsorption onto Mn0.5Cu0.5Fe2O4 are given in Table 4. The overall standard free energy change during the adsorption process was negative for the experimental range of temperatures and the system did not gain energy from an external source. It becomes more favorable when temperature increased [33].
Kinetic Ref model
Polyaniline/multiwalled carbon nanotubes Langmuir White rice husk ash Langmuir Chitosan Langmuir Rice husk ash Langmuir Luffa cylindrical sponge Langmuir Agricultural waste Red clay Langmuir, Freundlich Langmuir Neem leaf powder Kaolin Langmuir Raw Bagasse Freundlich Chemically activated raw Freundlich baggase Langmuir Diatomite–attapulgite MnFe2O4 Langmuir CuFe2O4 Langmuir Mn0.5Cu0.5Fe2O4 Langmuir
28 28 28 2 28 18 28
[36] [37] [38] [39] [40] [41] [42]
28 28 – –
[43] [44] [45] [5]
– 28 28 28
[46] In this study In this study In this study
Photocatalytic activity Since some dyes are degraded by direct UV irradiation [31], it should be examined to what extent BG is photolyzed if no nanospinels were used. The photocatalytic activity of Mn0.5Cu0.5Fe2O4 nanoparticles for the degradation of BG was evaluated. In a typical experiment, 30 ml of dye solution 100 mg L1 and 0.5 g of nanoparticle was mixed using a magnetic stirrer. After a period of time in the dark, the solution was irradiated. The light source was Hg lamp (300 W, lmax = 365 nm). The samples from the reaction mixture were taken from the reactor at appropriate time intervals in order to monitor the dye concentration in the solution. The solution was analyzed by the UV–vis method using 160 A Shimadzu spectrometer. The concentration of BG in the samples was calculated using the calibration curve. Two experiments were carried out under the same conditions, one in the presence of nanoparticles and UV irradiation and the second without UV irradiation. The simultaneous utilization of UV irradiation and nanoparticles increase the degradation rate of BG so that 90% of BG is removed within 1 min. In the presence of nanospinel without UV irradiation, the concentration of dye decreases quickly at the beginning, and then reaches to a saturation value as a result of adsorption of dye molecules on the nanospinel was done. Hence, the new nanospinels cannot act as photocatalysts for the degradation of BG in an aqueous solution. The degradation is just an adsorption process. Desorption studies Desorption studies can help to further studying the mechanism of adsorption and the feasibility of regenerating the adsorbents.
2.2 2 Table 4 Thermodynamic parameters for adsorption of BG by adsorption onto Mn0.5Cu0.5Fe2O4.
logq e
1.8 1.6 1.4
CuFe2O4 MnFe2O4 Mn0.5Cu0.5Fe2O4
1.2 1 0.2
0.3
0.4
0.5
0.6
0.7
log Ce Fig. 10. Freudlich isotherm for adsorption of BG using MnFe2O4, CuFe2O4 and Mn0.5Cu0.5Fe2O4.
Temperature (8C)
KC
15 20 25 30 35 45 55
1.09 1.11 1.24 1.57 1.86 3.25 4.6
DG0
D H0
(KJ mol1)
(KJ mol
0.19 0.24 0.51 1.09 1.56 3.06 4.1
24.7
DS0 (J mol1 k1) 1
) 88
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The reversibility of adsorption for Mn0.5Cu0.5Fe2O4 was investigated by desorption experiments. For the desorption study, 0.5 g Mn0.5Cu0.5Fe2O4 adsorbent was added to 50 mL of BG solutions (100 mg L1, pH 2.0), once equilibrium reached, the BG-adsorbed nano particles adsorbent was separated and stirred in 50 mL of 0.1 M HCl, HNO3, NaCl, NaOH and H2SO4 solution for 1 h, and then the concentration of BG was measured. The desorption percentages of Mn0.5Cu0.5Fe2O4 by H2SO4 was found to be about 85%. The capacity of Mn0.5Cu0.5Fe2O4 for adsorption of BG after five-cycle regeneration was as followed:
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12]
H2SO4 > HCl > HNO3 > NaCl > NaOH:
[13]
The Mn0.5Cu0.5Fe2O4 is simple to thermally regenerate and regeneration temperature is commonly at or beyond 300 8C. The good regeneration result and relatively low regeneration temperature demonstrated that the Mn0.5Cu0.5Fe2O4 could offer high adsorptive activity. The adsorption capacity of the Mn0.5Cu0.5Fe2O4 for dye after its regeneration has also been studied. The regenerated samples of Mn0.5Cu0.5Fe2O4 were again saturated with BG with the same initial concentration of 100 mg L1, determining their new adsorption capacity. Generally, the adsorption capacity of the Mn0.5Cu0.5Fe2O4 decreases as the number of regeneration cycle increased. Further, our experiment also display that the adsorption capacity could maintain above 90% of its initial capability for BG after three cycles and above 80% of its initial capability for five cycles and 75% for BG after eight cycles. The result here illustrates that Mn0.5Cu0.5Fe2O4 can be employed repeatedly for the removal of dyes.
[14] [15]
Conclusion The nano ferrites of CuxMn1xFe2O4 (x = 0.0, 0.2, 0.4, 0.5, 0.8 and 1) were prepared. The nano particles were characterized by FTIR, XRD and SEM. The nano particles of spinel type were test for degradation of BG dye from aqueous solutions. Effect of contact time, pH and mass of sorbent and initial concentration of BG on adsorption of BG onto CuxMn1xFe2O4 were investigated. The results showed that the maximum adsorption capacity of BG was observed for Mn0.5Cu0.5Fe2O4. Kinetic data follows pseudo secondorder kinetic model. Adsorption behavior is better described by Langmuir type isotherm model. The negative values of DG0 indicated that the adsorption process of dye onto Mn0.5Cu0.5Fe2O4 is spontaneous. The nano spinels could be conveniently regenerated after adsorption by chemical and physical methods. The Mn0.5Cu0.5Fe2O4 new nanospinels are promising candidates for the adsorption of cationic triphenylmethane dyes from wastewaters.
7
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