Environ Monit Assess (2015) 187:412 DOI 10.1007/s10661-015-4635-y

2,4-Dinitrophenylhydrazine functionalized sodium dodecyl sulfate-coated magnetite nanoparticles for effective removal of Cd(II) and Ni(II) ions from water samples Soheil Sobhanardakani & Raziyeh Zandipak

Received: 10 January 2015 / Accepted: 21 May 2015 # Springer International Publishing Switzerland 2015

Abstract 2,4-Dinitrophenylhydrazine immobilized on sodium dodecyl sulfate (SDS)-coated magnetite and was used for removal of Cd(II) and Ni(II) ions from aqueous solution. The prepared product was characterized by X-ray diffraction (XRD) analysis, Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). The size of the nanoparticles according to SEM was obtained around 20–35 nm. In batch tests, the effects of pH, contact time, initial metal concentration, and temperature were studied. The kinetic and equilibrium data were modeled with recently developed models. The adsorption kinetics and isotherms were well fitted by the fractal-like pseudosecond-order model and Langmuir–Freundlich model, respectively. Maximum adsorption capacity by this adsorbent is 255.1 mg g−1 for Cd(II) ion and 319.6 mg g−1 for Ni(II) ion at pH 7.0 and 25 °C. The method was successfully applied to the removal of metal cations in real samples (tap water, river water, and petrochemical wastewater).

Keywords Adsorption efficiency . Isotherm . Kinetic . Real sample S. Sobhanardakani (*) Department of the Environment, College of Basic Sciences, Hamedan Branch, Islamic Azad University, Hamedan, Iran e-mail: [email protected] R. Zandipak Young Researchers & Elite Club, Hamedan Branch, Islamic Azad University, Hamedan, Iran

Introduction Nowadays, release of pollutants such as heavy metal ions to the environment becomes one of the most important problems for soil, air, and water. The presence and accumulation of heavy metals in industrial wastewaters have a toxic or carcinogenic effect on living species (Wong et al. 2003; Wang et al. 2011). These include metals such as Pb, Ag, Cu, Cd, Ni, Cr, Zn, and Hg (Ali Fil et al. 2012a; Sobhanardakani et al. 2013a; Li et al. 2014). Excess heavy metals are discharged into the aqueous environment through various sources including metal smelters, effluents from plastics, mining operations, microelectronics, paper industries, usage of fertilizers, and pesticides (Yang et al. 2009; Li et al. 2014). Cd and Ni are two of the most significant heavy metals often found in different effluents and travel through the food chain via bioaccumulation (Ali Fil et al. 2012b). World Health Organization (WHO) has set that the maximum amounts of Cd and Ni in drinking water are 0.003 and 0.1 mg L−1, respectively (Boparai et al. 2011; Sun et al. 2014). Human exposure to nickel ions at higher doses is associated with serious health effects like dermatitis, nausea, coughing, chronic bronchitis, gastrointestinal distress, reduced lung function, and lung cancer. Cadmium exposure may cause nausea, salivation, muscular cramps, and anemia (Ruparelia et al. 2008; Gupta et al. 2014). Currently, numerous techniques have been adopted to remove heavy metals from wastewater, including adsorption, chemical precipitation, electrochemical treatment, ion exchange, membrane separation, and

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reverse osmosis (Zhu et al. 2012; Zhang et al. 2013a, b). Among these methods, adsorption is considered to be the most effective technique for water and wastewater treatment, due to its simplicity, low cost, ease of operation, and high efficiency (Kaprara et al. 2013; Sobhanardakani et al. 2013b; Hong et al. 2014). Nano-scale material is widely used to the effective adsorption of different chemical species from water samples. Magnetic nanoparticles (MNPs) such as magnetite (Fe3O4) and maghemite (γ-Fe2O3), new kinds of nano-scale material, are used in the fields of biotechnology and biomedicine and as an efficient adsorbent. Due to their dual properties of high surface area and magnetic response, fast adsorption kinetics and the ease of magnetically assisted separation from water are expected (Türk and Alp 2014; Wang et al. 2011). The use of synthetic iron oxides is much more economical than the use of commercial highly efficient activated carbon, in a 30:1 relative ratio depending on the particular kind of activated carbon. But separation of these particles from aqueous medium is difficult because of very small dimension and high dispersion. The magnetic separation provides suitable route for online separation, where particles with affinity to target species are mixed with the heterogeneous solution. Upon mixing with the solution, the particles tag the target species. External magnetic fields are then applied to separate the tagged particles from the solution (Afkhami et al. 2010; Bagheri et al. 2012; Zhang et al. 2013a, b). However, the basic disadvantages of this solid adsorbent are the low metal adsorption capacity and the lack of selectivity in removal of metal ions, which leads to other species interfering with the target metal ions. To overcome this problem, chemical or physical modification of the adsorbent surface with some organic compounds, especially chelating ones, is usually used to load the surface with some donor atoms such as oxygen, sulfur, nitrogen, and phosphorus (Afkhami et al. 2010; Tombácz et al. 2013). These donor atoms are capable of selective binding with certain metal ions. When a modifier is immobilized at the surface of the adsorbent, the target metals are not only removed by adsorption on the surface of the metal oxide but could be removed by a surface attraction/chemical bonding phenomenon on the newly added chemicals (Zhang et al. 2009; Ye et al. 2014). In this study, we used sodium dodecyl sulfate (SDS), which is an anionic surfactant and tends to interact with surface of magnetite nanoparticles and coats them. The concentration of SDS was fixed at 5×10−3 M, which is

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below the critical micellization concentration (c.m.c.) of SDS (8×10−3 M). Above the c.m.c., the excess of SDS would form micelles in the aqueous solution, which does not become adsorbed on the magnetite surface. The SDS can form hemi-micelles or ad-micelles on the magnetite by strong adsorption (Afkhami and Moosavi 2010). Afterwards, SDS-coated magnetite nanoparticles were synthesized by a simple method, modified with 2,4-dinitrophenylhydrazine (2,4-DNPH is an important reagent which can act as electron pair donors reacting with most of hard and intermediate cations), and used for removal of metal ions from water samples. The effects of pH and temperature on the adsorption efficiency were studied. Finally, kinetic and isotherm of adsorption were evaluated.

Materials and methods Apparatus and reagents The concentration of metal ions was determined by inductively coupled plasma optical emission spectrometry (ICP-OES) (JY138 Ultrace, France). All pH measurements were made with a 780-pH meter (Metrohm, Switzerland) combined with a glace-calomel electrode. The crystal structure of synthesized materials was determined by an XRD (38066 Riva, d/G.Via M. Misone, 11/ D (TN) Italy) at ambient temperature. The structure of the nanoparticles was characterized by a scanning electron microscope (SEM-EDX, XL30 and Philips Netherland). FT-IR spectra (4000–400 cm−1) in KBr were recorded on PerkinElmer, spectrum 100, FT-IR spectrometer. Specific surface area and porosity were defined by N2 adsorption–desorption porosimetry (77 K) using a porosimeter (Bel Japan, Inc.). All chemicals were of analytical reagent grade or the highest purity available from Merck (Merck, Darmstadt, Germany). Double-distilled water was used throughout the study. Stock solutions of Cd(II) and Ni(II) (1000 mg L−1) were prepared by dissolving appropriate amount of Ni(NO3)2·6H2O and Cd(NO3)2·4H2O in double-distilled water. Metal solutions of different initial concentrations were prepared by dilution of 1000 mg L−1. Preparation of magnetite nanoparticles The magnetite nanoparticles were prepared by the conventional co-precipitation method with minor

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modifications. FeCl3·6H2O (11.68 g) and FeCl2·4H2O (4.30 g) were dissolved in 200 mL double-distilled water under nitrogen gas atmosphere with vigorous stirring at 85 °C, which led to smaller and more homogenized particles. Then, 20 mL of 30 % NH3 was added to the solution. After the addition of NH3 to the solution, the color of bulk solution was changed from orange to black immediately. The magnetite precipitates were washed twice with double-distilled water and once with 0.02 mol L−1 sodium chloride and were separated from solution with a magnet (Bagheri et al. 2012).

qe (mg g−1) were computed using the following equation:

Preparation of the magnetite modified with 2,4-dinitrophenylhydrazine Two-gram sample of magnetite nanoparticles was suspended in 50 mL of water and mixed with 100 mg of SDS. Then, 20 mL of the solution of 2,4dinitrophenylhydrazine (0.90 g 2,4-DNPH in concentrated HCl+acetonitrile) was added. The suspension was stirred at 60 °C for 3 h. The mixture was followed by evaporation of the solvent, washing, air-drying, and storing in a closed bottle for subsequent use.

The adsorption kinetic experiments were carried out at three different initial concentrations of (30, 60, 100 mg L−1) Cd(II) and Ni(II). In each concentration, 15 mL of metal solution was added to 0.03 g of adsorbent and was shaken at 150 rpm at temperature 25 °C. Then, samples were withdrawn at different time intervals, and the residual concentration of Cd(II) and Ni(II) ions was determined by the ICP-OES method. The amount of pollutant adsorbed at each time interval per unit mass of the adsorbent qt (mg g−1), was computed by following equation:

Point of zero charge pH

qe ¼

The point of zero charge pH (pHpzc) for the adsorbent was determined by introducing 0.03 g of adsorbent into eight 100 mL Erlenmeyer flasks containing 0.01 mol L−1 NaNO3 solutions. The pH values of the solutions were adjusted to 2, 3, 4, 5, 6, 7, 8, and 9 using solutions of HNO3 and NaOH. The solution mixtures were allowed to equilibrate in an isothermal shaker (25 °C) for 24 h. The final pH was measured after 24 h. The pHpzc is the point where the pHinitial =pHfinal.

where C0 and Ct (mg L−1) are the liquid phase concentrations of Cd(II) and Ni(II) ions at initial and any time t, respectively.

Equilibrium adsorption studies Adsorption equilibrium experiments were carried out by adding 15 mL of different initial concentration of Cd(II) (30–400 mg L−1) and Ni(II) (30– 450 mg L−1) solution to 0.03 g of adsorbent at temperature 25 °C. The samples were shaken in a shaker for 24 h. Then, metal-loaded magnetite nanoparticles were separated with magnetic decantation, and the residual concentration of Cd(II) and Ni(II) in the bulk (Ce) was determined using an ICP-OES analysis. The amount of adsorbed Cd(II) and Ni(II) per unit mass of adsorbent at equilibrium

qe ¼

ðC 0 −C e ÞV W

ð1Þ

where C0 and Ce (mg L−1) are the initial and equilibrium concentrations, respectively, V (L) is the volume of the solution, and W (g) is the mass of adsorbent used. Kinetic adsorption studies

ðC 0 −C t ÞV W

ð2Þ

Preparation of real samples In order to demonstrate the applicability and reliability of the method for real samples, three samples, including tap water, river water, and petrochemical wastewater were prepared and analyzed. Tap water samples were taken from our research laboratory (Islamic Azad University, Hamedan, Iran), river water and petrochemical wastewater were collected in a 2.0-L PTFE bottle. All samples filtered through a filter paper (Whatman No. 40) to remove suspended particulate matter.

Results and discussion Characterization of modified magnetite nanoparticles The X-ray diffraction pattern of magnetite nanoparticles is shown in Fig. 1. Furthermore, it can be seen that all

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Fig. 1 XRD patterns of magnetite nanoparticles

the diffraction peaks are consistent with the six diffraction peaks at (220), (311), (400), (422), (511), and (440) by comparison with Joint Committee on Powder Diffraction Standards (JCPDS card, file No. 79–0418), which are indexed to the cubic spinel phase of Fe3O4. Therefore, the obtained XRD pattern indicates that the prepared nanoparticles are Fe3O4. The average crystallite size (D in nm) of Fe3O4 was determined from XRD pattern according to the Scherrer equation. D¼

Κλ β cosθ

ð3Þ

where λ is the wavelength of the X-ray radiation (1.5406 Å), Κ is a constant taken as 0.89, θ is the diffraction angle, and β is the full width at half maximum (FWHM). The average size of the Fe3O4 was calculated as around 22 nm. The SEM image of the particles, as shown in Fig. 2, revealed that the average diameter for SDS-coated magnetite nanoparticles modified with 2,4-DNPH was around 20–35 nm with a spherical shape. Specific surface areas are commonly reported as BET surface areas obtained by applying the theory of Brunauer, Emmett, and Teller (BET) to nitrogen adsorption/desorption isotherms measured at 77 K. This is a standard procedure for the determination of the specific surface area of sample. The specific surface area of the sample is determined by physical adsorption of a gas on the surface of the solid and by measuring the amount of adsorbed gas corresponding to a monomolecular layer on the surface. The data are treated according to the BET theory (Brunauer et al. 1938; Walton and Snurr 2007). The results of the BET method showed that the average specific surface areas of magnetite nanoparticles and SDS-coated magnetite nanoparticles modified

Fig. 2 SEM image of SDS-coated magnetite nanoparticles modified with 2,4-DNPH

with 2,4-DNPH were 99.3 and 75.5 m2 g−1, respectively. It can be concluded from these values that the synthesized nanoparticles have relatively large specific surface areas. This decrease in surface area of SDS-coated magnetite nanoparticles modified with 2,4-DNPH as compared to magnetite nanoparticles is possibly due to aggregation after surface modification. The FT-IR spectra of 2,4-DNPH (a), magnetite nanoparticles (b), and modified magnetite nanoparticles (c) are shown in Fig. 3. As shown in Fig. 3b, the peak at 580 cm−1 corresponds to Fe–O bond in Fe3O4. After modification of the magnetite with 2,4-DNPH, modified magnetite nanoparticles, it shows a visible broad band in the 3200– 3500 cm−1 region which is due to stretching vibrations of OH or N–H groups with varying degrees of H bonding. The absorption spectrum showed that the absorption bands at 1345, 1532, and 1598 cm−1 are corresponding to the bending vibration of N–H group (Fig. 3c). A comparison of these characteristic spectral bands indicated that the surface-modified magnetite nanoparticles contained –NH–functional group as a result of the immobilization procedure.

Adsorption isotherms modeling The effect of initial metal concentration on its removal percentage and the amount of adsorbed Cd(II) and Ni(II) were investigated in the initial concentration range of 30 to 400 and 30 to 450 mg L−1, respectively. The results

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Fig. 3 FT-IR spectrum of the 2,4DNPH (a), magnetite nanoparticles (b), and SDScoated magnetite nanoparticles modified with 2,4-DNPH (c)

indicate that adsorption percentage is high at lower metal concentration and decreases gradually with increasing metal concentration. At lower Cd(II) and Ni(II) concentration, high surface area concerns to the available vacant sites of adsorbent that is attributed to increase in the concentration gradient and rate of Cd(II) and Ni(II) diffusion to adsorbent. At high concentration of Cd(II) and Ni(II), the available sites of adsorbent become fewer; hence, the removal percentage of these metals depends on the initial metal concentration. The analysis of the adsorption isotherms by fitting the adsorption data into different isotherm models is an important step to find the suitable model that can be used for design process. In this study, the Langmuir (L), Freundlich (F), Temkin (T), Redlich–Peterson (R–P), Langmuir–Freundlich (L–F), and Brouers–Sotolongo (B–S) models are adopted to describe the adsorption behaviors of Cd(II) and Ni(II) ions. Langmuir isotherm is often used to describe adsorption of solute from liquid solutions, and this model assumes monolayer adsorption onto a homogeneous surface with finite number of identical sites (Langmuir 1918). The non-linear form of Langmuir isotherm model is given as follows: qe ¼

qm K L C e 1 þ K LCe

ð4Þ

where qm (mg g−1) and KL (L mg−1) are known as Langmuir constants and referred to maximum adsorption capacity and affinity of adsorption, respectively. In order to predict the favorability of the adsorption

process, the essential characteristic of Langmuir equation can be described using the dimensionless separation factor RL, which can be defined as follows: RL ¼

1 1 þ Κ L C0

ð5Þ

where C0 is the maximal initial concentration of metal ion (mg L−1). RL indicates the nature of the adsorption process. If RL >1, the isotherm is unfavorable, RL =1, the isotherm is linear, 0

2,4-Dinitrophenylhydrazine functionalized sodium dodecyl sulfate-coated magnetite nanoparticles for effective removal of Cd(II) and Ni(II) ions from water samples.

2,4-Dinitrophenylhydrazine immobilized on sodium dodecyl sulfate (SDS)-coated magnetite and was used for removal of Cd(II) and Ni(II) ions from aqueou...
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