Abstract Scallop shell-Fe3O4 nanoparticles were syn- thesized by co-precipitation and hydrothermal methods. The removal efficiency of RB5 was studied as a ...
Water Air Soil Pollut (2015) 226:321 DOI 10.1007/s11270-015-2539-7
Application of Scallop shell-Fe3O4 Nano-Composite for the Removal Azo Dye from Aqueous Solutions Azita Mohagheghian & Robabeh Vahidi-Kolur & Melina Pourmohseni & Jae-Kyu Yang & Mehdi Shirzad-Siboni
Received: 14 May 2015 / Accepted: 7 July 2015 # Springer International Publishing Switzerland 2015
Abstract Scallop shell-Fe3O4 nanoparticles were synthesized by co-precipitation and hydrothermal methods. The removal efficiency of RB5 was studied as a function of pH, adsorbent dosage, initial RB5 concentration, ionic strength, and temperature. Coating of Fe3O4 nanoparticles onto Scallop shell was identified by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and energy dispersive X-ray (EDX) analysis. Maximum adsorption was obtained at pH 3. The removal efficiency of RB5 was increased with increasing adsorbent dosage. However, it was decreased with increasing initial RB5 concentration, temperature and in the presence of any anions. Adsorption kinetic study revealed that the pseudo-second order model better described the removal rate than the pseudo-first order model and intra-particle diffusion model. Adsorption isotherm was analyzed by both Langmuir and Freundlich equation. Experimental result was well described by the Langmuir equation. Maximum adsorption capacity was estimated to be 1111.11 mg/g. A. Mohagheghian : R. Vahidi-Kolur : M. Pourmohseni Department of Environmental Health Engineering, School of Health, Guilan University of Medical Sciences, Rasht, Iran J.2). Since the most effective removal of RB5 was observed with pH equals to 3, the other experiments were performed at this pH. 3.2.2 The Effect of Adsorbent Dosage and Contact Time
Fig. 5 VSM image of samples
The influence of adsorbent dosage on the removal efficiency for RB5 was investigated at various amounts of
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Scallop shell-Fe3O4 nanoparticles in the range of 0.1– 0.4 g/L at pH 3 with variation of reaction time (Fig. 7). Indeed, the removal efficiency increased from 44.73 to 99.99 % by increasing the adsorbent dosage from 0.1 to 0.4 g/L over the entire reaction time (2–120 min). This trend can be explained by the increased active sites for the removal of contaminants along with the increase of the adsorbent dosage. As shown in Fig. 7, the removal rate of RB5 at all dosages was rapid in the first stages of contact time (30 min) and then it was gradually slowed until reactions reach a near equilibrium after 120 min. The rapid adsorption at initial reaction time may be attributed to the abundance of free active sites on the surface of Scallop shell-Fe3O4 nanoparticles and easy availability of them for RB5 molecules (Heibati et al., 2014; Karadag et al., 2007). As the active sites are occupied by RB5, adsorption rates are decreased due to having little available active sites on the adsorbents. Since the removal efficiency of RB5 was not much different between dosage 0.24 and 0.4 g/L (almost 14 %), further experiments were performed at 0.24 g/L. Indeed, the removal efficiency enhanced from 42.25 to 85.43 % by increasing the contact time from 2 to 120 min at pH 3 and adsorbent dosage equal to 0.24 g/L.
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concentration (10, 20, 30, 60, 90, 120 mg/L) at constant adsorbent dosage (0.24 g/L) and at pH 3 (Fig. 8). When the initial RB5 concentration was increased from 10 to 120 mg/L, the RB5 removal efficiency was decreased from 99.67 to 45.59 %. The reason for this result can be explained with the fact that the adsorbent has a limited number of active sites, which would become saturated above a certain RB5 concentration (Zhu et al., 2010). Similar observations were also reported for the removal of dyes (Karadag et al., 2007; Vimonses et al., 2009; Xue et al., 2009). 3.2.4 Effect of Ionic Strength
Effect of initial RB5 concentration on the removal efficiency of RB5 was studied by varying the initial RB5
To assess the effect of different type of background electrolytes such as Cl−, CO23 −,HCO−3 , and SO24 − on the removal efficiency of RB5, constant amounts of NaCl, Na2CO3, NaHCO3, and Na2SO4 (30 mg/L) were added to the batch system before beginning the adsorption at constant concentration of RB5 (30 mg/L) and adsorbent dosage (0.24 g/L) at pH 3. Figure 9 shows that removal efficiency of RB5 decreased in the presence of any anions. The order of removal efficiency was as follows: control > sodium sulfate > sodium bicarbonate > sodium chloride > sodium carbonate. This removal trend can be explained by that Cl−, CO23 −,HCO−3 , and SO24 − may interfere or compete the electrostatic attraction between SO−3 ions in RB5 species and surface of Scallop shell-Fe3O4 nanoparticles (Farrokhi et al., 2014).
Fig. 7 The effect of adsorbent dose on the removal of RB5 dye by Scallop shell coated with Fe3O4 nanoparticles in different time interval (initial dye concentration=30 mg/L, pH=3, 298 K)
Fig. 8 The effect of initial RB5 dye concentration on the removal of RB5 dye by Scallop shell coated with Fe3O4 nanoparticles in different time interval (pH=3, adsorbent dose=0.24 g/L, 298 K)
3.2.3 The Effect of Initial RB5 Concentration
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Fig. 9 The effect of ionic strength on the removal of RB5 dye by Scallop shell coated with Fe3O4 nanoparticles in different time interval (pH=3, initial dye concentration=30 mg/L, adsorbent dose=0.24 g/L, 298 K)
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shows that removal efficiency for each process was 34.4, 56.02, and 85.43 %. These experiments demonstrate that both Scallop shell and Fe3O4 nanoparticles are needed for the effective removal of RB5. The changes in the absorption spectra of RB5 solutions at different time interval are shown in Fig. 11. The spectrum of RB5 in the visible region exhibits a main band with a maximum at 597 nm. The decrease of absorption peak of RB5 at 597 nm indicates a rapid removal of the azo dye. Complete removal of the dye solution was observed at 2 h in the optimized conditions. Reusability of adsorbent is an important factor for the application of developed adsorbent in the treatment of wastewater. Hence, the adsorption of RB5 was performed by Scallop shellFe3O4 nanoparticles for six repeated runs. As can be seen in Fig. 12, adsorption capacity of RB5 by Scallop shellFe3O4 nanoparticles was maintained up to six consecutive runs, suggesting a plausible adsorbent in the treatment of organic dyes.
3.2.5 Comparison of Each Process, Spectral Changes, and Reusability
3.3 Kinetic, Equilibrium, and Thermodynamic Studies
To evaluate effect of various processes on the removal efficiency of RB5, removal efficiency of RB5 by Scallop shell, Fe3O4, and Scallop shell-Fe3O4 nanoparticles were compared at the initial RB5 concentration (30 mg/L), adsorbent dosage (0.24 g/L), and at pH 3. Figure 10
Adsorption kinetic experiments were performed at different RB5 concentration (10, 20, 30, 60, 90, 120 mg/L), at constant adsorbent dosage (0.24 g/L), and at pH 3. The pseudo-first-order, pseudo-second-order, and intraparticle-diffusion model models were applied in order to
Fig. 10 The contribution of each process involved on the RB5 dye by Scallop shell coated with Fe3O4 nanoparticles in different time interval (pH=3, initial dye concentration=30 mg/L, adsorbent dose=0.24 g/L, 298 K)
Fig. 11 Spectral changes of RB5 dye solution by Scallop shell coated with Fe3O4 nanoparticles in different time interval (pH=3, initial dye concentration=30 mg/L, adsorbent dose=0.24 g/L, 298 K)
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Fig. 12 The results of reusability test for the removal of RB5 dye by Scallop shell coated with Fe3O4 nanoparticles in different time interval (pH=3, initial dye concentration=30 mg/L, adsorbent dose=0.24 g/L, 298 K)
find an efficient model for the description of adsorption. The relevant equations for the kinetic, equilibrium, and thermodynamic studies are shown in Table 2 (Azizian, 2004; Liu and Liu, 2008; Sadaf and Bhatti, 2014; Samarghandi et al., 2011; Shaker, 2015; ShirzadSiboni et al., 2014c; Shirzad-Siboni et al., 2011a). To obtain kinetic data for the removal of RB5, ln qt 1−qe versus t; qt versus t and qt versus t0.5 was plot2
ted for the pseudo-first-order, pseudo-second-order and intra-particle-diffusion models, respectively. The kinetic parameters for the removal RB5 at different initial RB5 concentrations by pseudo-first-order, pseudo-second-order, and intra-particle-diffusion models are summarized in Table 3. The kinetic data for RB5 adsorption showed the best fitting (R 2 = 0.997) with the pseudo-second-order model. Moreover, when the initial RB5 concentration increased from 10 to 120 mg/L, the value of k2 (g/mg-min) and R2 for the pseudo-second-order model were decreased from 0.14 to 0.0008 g/mg-min and 0.999 to 0.994, respectively. Also, qe (mg/g) increased from 41.7 to 227.3 mg/g. This result indicated that adsorption data were in agreement with this model. In addition, the suitability of data deducted from
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the pseudo-second-order confirms that the ratelimiting step in adsorption of RB5 by Scallop shell-Fe3O4 nanoparticles might be coming from electrostatic attraction phenomenon. The value of C was measured as 61.4 mg/g, indicating that intra-particle diffusion is not the only controlling step for RB5 adsorption, and the process is controlled by boundary layer diffusion to some degree. Also, the kinetic data were fitted with the linear regression statistics method. The estimated P values for RB5 have been summarized in Table 3. From these results, kinetic data for RB5 adsorption was fitted well with the pseudo-second-order model (P
