Preparation Of Iron Oxide Nanoparticle

Published Date: 02 Nov 2017

Abstract

The present study evaluated the adsorptive removal of methylene blue from aqueous solution by iron oxide nanoparticles (NPs). Iron oxide nanoparticles are synthesized by chemical precipitation method and characterized by XRD, TEM, particle size analyzer and zeta potential measurement. The results showed that adsorption isothermal data were fitted well to Langmuir isotherm then Fraundlich isotherm. Adsorption kinetics of methylene blue was carried out with pseudo-first order and pseudo-second order kinetics but adsorption follow pseudo-second order kinetic model. Maximum pH 5 and high salt concentration is needed for adsorption of methylene blue by iron oxide NPs. It is a simple and economic methodology, has been developed to efficiently eliminate the dye by adsorptive reduction process using iron oxide nanoparticle. The present study may be considered for large scale applications for the efficient removal of dyes from textile effluents.

Keywords: Iron oxide NPs; Adsorptive dye removal; Methylene blue; Isotherm model

1. Introduction

Textile industries produce large amount of effluents which contain dyes and these dyes are important source of water pollution. Dyes are coloured substance which undergo biological and chemical changes and are hazardous for environment [1]. Dyes are toxic in nature and some are carcinogenic [2-3]. Dyes in waste water affect aquatic life; hence it is very necessary to treat the dyes bearing effluents before its discharge into the environment. Adsorption is a physical method and efficiently used to remove dyes from solutions [4-5]. Various adsorbents were developed and have been commercialized to treat polluted waters [4-5]. These adsorbents are highly porous particles and have high surface area for adsorption. Among different types of adsorbents, nano-sized iron oxide has great application in biosorption; bio application and waste water treatment [6-7]. Iron oxide nanoparticles posses low toxicity and have capacity to uptake heavy metal in waste water treatment [8].

Iron oxide nanoparticle has super paramagnetic property, as they are attracted to magnetic field but after removal of magnetic field no residual magnetism they retain. This property makes iron oxide nanoparticle suitable for removal of pollutants as compared to nonmagnetic nanoparticle [9]. In present work, we studied the adsorptive removal of methylene blue from aqueous solution by using iron oxide nanoparticles. The effect of pH and saline concentration for the adsorptive removal was also evaluated.

2. Materials and Method

2.1. Materials

Methylene blue was obtained from Otto kemi Industries, Mumbai. Ferric Chloride (FeCl3.6H2O), Ferrous Chloride (FeCl2.4H2O), Ammonia and Tri sodium citrate were purchased from Merck (Darmstadt, Germany).

2.2. Preparation of iron oxide nanoparticle

Chemical co-precipitation method was used for synthesis of iron oxide nanoparticles as per the methodology described by Ichiyanagi et al. [10] . Ferrous chloride and ferric chloride were dissolved separately in 100 mL deionised water to prepare a stock solution. Then, ferric chloride and ferrous chloride were mixed in the molar ratio of 2:1. After mixing, the solution was kept for1 h stirring at 80 á´¼C, after that temperature was raised to 90 á´¼C and ammonia was added. Tri sodium citrate (0.3 M) was prepared in 50 mL of deionised water and was added to the above prepared solution at the same temperature and left the solution for 1 h in stirrer. Then the precipitate was washed twice with deionised water and lyophilized.

2.3. Characterization of nanoparticle

The size and morphology of iron oxide nanoparticle were observed by transmission electron microscopy (Jeol JEM-2100F, Japan). Further the particles were subjected to particle size analysis (Malvern instruments, U.K.) and zeta potential measurement (Malvern instruments, U.K.). The particles were also subjected to X-Ray diffraction analysis using a Bruker AXS, difractometer D8, Germany. The target was Cu Kα (λ=1.54A˚). The generator was operated as 45 kV and with a 30 mA current. The scanning range (2θ) was selected from 10̊ to 100̊.

2.4. Adsorption Studies

Isothermal studies were carried out with different concentration of methylene blue with 5 mg of nanoparticle for 4 h shaking. Langmuir and Freundlich models were used to analyze the equilibrium adsorption data. Langmuir’s isotherm states the monolayer adsorption and the Freundlich’s model considers multilayer adsorption. Equilibrium adsorption was calculated by using following equation.

Where C0 (mg/L) is the initial dye concentration, Ce (mg/L) is the amount of dye left after the interaction, qe is the amount of dye adsorbed at equilibrium, V is the volume in L and W (mg) is weight of the nanoparticle used for adsorption.

2.5. Effect of pH on Adsorption

The effect of pH on the adsorption of methylene blue on nanoparticles was studied at different pH (4-9). The pH was adjusted using 0.1 N HCL and 0.1 N NaOH. Methylene blue concentration 10 mg/L was interacted with iron oxide nanoparticle (5 mg) for 4 h in an orbital shaker at 150 rpm. The samples were centrifuged at 10, 000 x g for 30 min and amount of dye left in supernatant was calculated using visible spectrophotometer (Equiptronics, Mumbai, India) by measuring the absorbance at 665 nm.

2.6. Effect of NaCl concentration on adsorption

The effect of NaCl concentration on adsorption of methylene blue on nanoparticles was studied at different NaCl concentration (0.01 mM - 1 M). Dye and nanoparticles were interacted for 4 h in an orbital shaker at 150 rpm. Thereafter, the samples were centrifuged and amount of dyes left in supernatant was calculated.

2.7. Effect of Different Adsorbent dosage on Adsorption

The effect of different dosage of adsorbents on adsorption was evaluated by interacting different amount of NPs (1-10 mg) with 100 mg/L of dyes solution for 4 h in an orbital shaker at 150 rpm. The sample was centrifuged and amount of dye left in supernatant was calculated.

2.8. Adsorption kinetics

Adsorption kinetics was carried out by interacting 5 mg of NPs with an initial concentration of 250 mg/L dye up to 96 h. At various time intervals the interaction mixture was centrifuge at 10,000 x g for 20 min. The supernatant were collected and amount of dye left in supernatant was determined by visible spectrophotometer by measuring absorbance at 665 nm. The amount of adsorption was calculated at time t, qt (mg/mg) by following equation:

Where C0 (mg/L) is the initial dye concentration, Ct (mg/L) is the amount of dye left at time t, qt is the amount of dye adsorbed at equilibrium at time t, V is the volume of solution in L and W (mg) is weight of nanoparticles used.

3. Results and discussion

3.1. Effect of pH on adsorptive removal

The study of pH for adsorptive removal of dye is an important parameter which affects color, solubility and adsorption capacity of dye solution. The effect of pH on adsorption of methylene blue on iron oxide nanoparticle was determined at different pH (4-9). The results showed that maximum adsorption observed at pH 5 (Fig. 1). Mark and Chen [11] studied the adsorptive removal of methylene blue using PAA-bound iron oxide NPs. They found that the adsorption capacity increased with increasing the solution pH. In this study we found that the adsorption capacity of iron oxide NPs decreased with increasing solution pH and at pH 9 the adsorption was negligible. The difference in adsorption may be due to the difference in capping agent used to stabilize the NPs.

Fig.3.2. Effect of NaCl concentration on adsorptive removal

It is important to investigate the adsorption of dye in the presence of NaCl because wastewater has high level of salt concentration. The results show that the adsorption remained constant for all the salt concentrations tested (Fig. 2). Mark and Chen [11] reported that adsorption of methylene blue on iron oxide NPs was constant with the increase of salt concentration. In another study the adsorption of methylene blue decreased with increasing salt concentration [12]. Adsorption of dyes depends upon properties of dyes and surface chemistry of the adsorbent used.

3.3. Effect of various adsorbent doses on adsorption

The effect of initial adsorbent dosage on adsorptive removal of methylene blue by iron oxide nanoparticle was evaluated by interacting different concentration of NPs (1 mg-10 mg/L) with 250 mg/L of dye. The percentage removal of dye was increased with increase in amount of NPs (Fig. 3). Nanoparticles have higher surface to volume ratio; therefore, by increasing the amount of adsorbent, more amount of dye could be removed [12].

3.3. Adsorption isothermal experiments

Adsorption capacity of iron oxide nanoparticle can be explained by adsorption isotherm studies. The adsorption process can be explained by Langmuir and Freundlich models. The Langmuir adsorption isotherm perform monolayer adsorption process in that once a molecule occupies a site no further adsorption can take place. In our experiment, data fitted well with Langmuir model suggesting that monolayer adsorption of methylene blue on the surface of iron oxide nanoparticle. The high R2 value (regression coefficients) showed that Langmuir model predict good adsorption behavior of methylene blue on the surface of iron oxide nanoparticle. Fig 4 shows the plot of Ce/qe verses Ce. The Langmuir equation is expressed as follows:

(1)

Where Ce is the amount of dye left in supernatant (mg/L), qe is amount of dye adsorbed at equilibrium, qmax is maximum amount of dye on nanoparticle to form monolayer and Ka is adsorption constant (L/mg). The linear form of Langmuir equation is:

(2)

The constants qmax and Ka were calculated from intercepts and linear plot slops of Ce/qe verses Ce. The Freundlich model assumes multilayer adsorption. The Frundlich equation can be expressed as follows:

(3)

Where Ce is concentration of dye left in supernatant after interaction with nanoparticle (mg/L), qe is the amount of dye adsorbed at equilibrium, kF is Frundlich constant. The linear form of Frundlich equation can be expressed as:

(4)

Fig. 5 shows that plot of log qe versus log Ce, constant kF and exponent 1/n to be determined. The less value of regression coefficient (R2) indicates that the Freundlich experimental model did not fit for methylene blue adsorption on the surface of iron oxide NPs. Langmuir model states that maximum adsorption capacity consists of monolayer adsorption, accompanied between adsorbed molecules [12].

3.4. Adsorption kinetics

The adsorption kinetics predicts the rate of adsorption of dye on the surface of nanoparticle and provides data for adsorption reactions. There are two kinetic models viz. the pseudo-first-order [13] and pseudo-second-order [14] equations were used. Fig. 6 shows that adsorption kinetics of methylene blue on the surface of NPs. The adsorption kinetics was carried out at 250 mg/L of initial dye concentration. Pseudo-first-order kinetic equation can be expressed as:

(5)

Where qe is amount of dye adsorbed at equilibrium, qt is amount of dye adsorbed at time t, and k1 is rate constant which can be calculated from straight line plot of log (qe-qt) verses time (h). The R2 values are relatively small and the experimental qe value do not agree with calculated values (Fig. 6).

Pseudo-second-order kinetic equation is expressed as:

(6)

The second order rate constant k2 and qe values were determined from the slopes and intercepts. R2 value indicates the linear relation of t/qt verses time (h) shown in Fig. 7. The correlation coefficients (R2) of pseudo first order model was 0.930 and for second order model was 0.994. The calculated values of qe from pseudo first order reaction do not give reasonable value and are too low as compared to pseudo-second order reaction.

4. Conclusion

Here we have studied the adsorptive removal of dye using iron oxide NPs. The effect of pH, NaCl and different adsorbent doses were evaluated. The adsorption isotherm fitted well to Langmuir isotherm. Kinetics of adsorption was studied and adsorption proceeds according to pseudo-second-order model which provides good correlation of data. Thus the present study shows that effective removal of methylene blue by using iron oxide NPs and can be applied for large scale removal of dyes using nanoparticles.