Broccoli–like Iron Oxide Nanoparticles Synthesis in Presence of Surfactants and Using Them in the Removal of Water-Colored Contamination

INTRODUCTION                                               
Iron oxides are among the most important transition metal oxides in terms of technological significance. To date, sixteen pure phases of iron oxides, i.e. Oxides, hydroxides, or oxy-hydroxides, have been discovered. These are Fe (OH)3, Fe(OH)2, Fe5(OH)8.4H2O, metal-Fe2O4, FeO. The trivalent state of these oxide compounds is one of their most distinguishing features like normal metal ferrite (M-Fe2O4). Iron, low solubility, and brilliant colors[1]. Except for iron oxide, all of the iron oxides are crystalline. The schwertmannite and the ferrihydrite are poorly-crystalline. These  oxides  can  be  created  using  any  known  wet  chemical  process.  Iron  oxide nanoparticles (IONPS)  are  made  up  of  magnetite  (Fe3O4) particles with  diameters  ranging from 1  to  100 nanometers, and are used in magnets. These nanoparticles are applied in magnetic data storage, bio sensing, drug delivery, and other applications [2]. Approximately 16 different phases of iron oxide have been reported [3], with the exception of schwertmannite and ferri-hydrite, which be crystalline [4], metallic nanoparticle production and use for super paramagnetic properties are common in therapeutic and diagnostic applications such as magnetic resonance imaging (MRI)  [5]. These  iron oxides are  also  used  as  catalysts,  sorbents,  pigments,  flocculants, coatings, gas sensors, wastewater treatment [6] and lubricants [7], based on their superior magnetic properties, these  nano  particles can also  be used  in various advanced  processes to  form nano  reactors,  added to polymer films,  and  other  products  [8].  Magnetite has an inverse spinel structure with alternating octahedral and tetrahedral-octahedral layers [9]. Magnetite, which contains both ferrous (reduced) and ferric (oxidized) iron species, is also known as iron II, III [10]. Due to higher ferrous crystal field stabilization energy (CFSE), ferrous species are observed to occupy half of the octahedral lattice sites. On the other hand, ferric species, occupy the other octahedral lattice [11]. Additionally, magnetite unit cells adhere to the face centred cubic pattern crystal lattice parameter, a = 0.8396[10]. These applications produce magnetite as super magnetic nanoparticles of iron oxide, and there is a need for the development and modification of low-cost synthesis processes. 
This study includes preparation of magnetite NPS using a novel method in aqueous solutions without and with using surfactants such as  cetrimide (CT), cetrimonium bromide (CTAB) as positive surfactants, sodium dodecyl sulphate (SDS) as a negative surfactant and triton x100 as a non-ionic surfactant. The characterizations of prepared magnetite NPS were investigated using FTIR, XRD, SEM. Based on the addition of surfactants as templates during magnetite NPS, the facial mechanism of ordering nanoparticles as broccoli shape was suggested. The removal process of water colored-contamination was compared without and with using surfactants via prepared of magnetite NPS and study the thermodynamics functions.

MATERIALS AND METHODS
Materials
All chemicals used in this study such as Ferric sulfate FeSO4 .7H2O, Sodium nitrate NaNO3, Sodium hydroxideNaOH  were  provided  by BDH. The surfactants such as cetramide (CT),  sodium dodecyl sulfate (SDS), cetrimonium bromide  (CTAB),  triton  x100  were  supplied  from  Qualikems,  DIDACTIC,  Interchimiques  SA  and Sigma-Aldrich companies respectively.   The  Eosin yellow dye (C20H6Br4Na2O5) has molar mass   691.9g/mole, dye class   (Xanthene dye), color  (Pink powder and slightly yellowish cast in aqueous solution), and wavelength  (516 nm) [12] was equipped  by CDH.

Synthesis of Spinel Fe3O4 nano crystals
Into a 400 mL beaker, 2.0 g of FeSO4•7H2O was dissolved in 150 mL of water. Into a 100 mL beaker, 50 mg of NaNO3 and 0.56 g of NaOH were mixed and dissolved in 60 mL of water. Both solutions were heated to 75 ºC separately, and then mixed together using a stirring rod, not a magnetic stirrer bar, for 10 minutes. The later mixture was transferred from the magnetic stirrer using a tong, and a green suspension was produced, and rapidly turned to black color. The black color suspension was continuously heated to 90 ºC for 10 min, then cooled to 20 ºC and the acidify of the mixture was increased by adding 3 M HCl. This black suspension was filtered using a Buchner funnel. The produced black precipitation was washed twice with 50 mL of water to remove all salts, and then dried in an oven at 100 ºC at 60 min. The black powder was scraped of the filter paper as shown in Fig. 1.
The chemical reactions of spinel Fe3O4 formed without and with surfactant were suggested using the following chemical reactions.

12 FeSO4.7H2O + 23NaOH + NaNO3→ 4Fe3O4 + 12Na2SO4 + NH3↑ +94H2O         
                                       
12 FeSO4.7H2O + 23NaOH + NaNO3 +surfactant→ 4Fe3O4 + 12Na2SO4 + NH3↑ + 94H2O +surfactant         

Application the Spinel Fe3O4 in removal of Eosin yellow dye
A 0.05 g from several samples of prepared Fe3O4 without and with of surfactants was added to 100 mL of eosin yellow dye solution in a beaker and shaking using a shakier for 10-60 minutes at 50 rpm and 22 oC. After adsorption of the dye on the Fe3O4 surface, both were uptake    by the magnet.
 The residue dye concentration after adsorption was measured in solution using UV-visible spectrophotometer at 516 nm, then the amount of adsorption Cr  will be calculated. Equations 1 and 2 were used to calculate the dye removal efficiency E% [13-14] and quantity of absorption (q %) [14-15] with different types of synthesized nanoparticles, Co is the initial concentration of dye.

RESULTS AND DISCUSSION
Synthesis of Iron oxide NPS
The main objective of this study was to synthesize magnetic iron oxide without and with surfactants (CT, CTAB, SDS, and Triton X-100) through the use of hydrated iron sulfate, where some Fe(II) is converted to Fe(III) by partial oxidation  using sodium  nitrate and  in  the presence  of the NaOH . The general mechanism of ordering the prepared Fe3O4 NPs in presence of surfactants as templates was investigated to give reasonable growth. As displayed in Fig. 2.

Characterization of the prepared Fe3O4 nanoparticles
FT-IR Analysis
FTIR spectra are appeared for all magnets prepared in Fig. 3, the broad peak at 3163.36 cm-1 assigned to the O - H group, in addition to the peak at 1100 cm-1 which is assigned to the O-Fe-O as a octahedron bending. Fe-O bond is located between 640 and 598 cm-1 which presents to the tetrahedral curvature, Fig. 3, curve B shows the broad peak at 3340 cm-1 beyond to the O–H stretching of the iron oxide and another peak at 3028 cm-1 is assigned to the N–H bending. In addition to the peaks between 2924 and 2850 cm-1 assigned to the stretching of C-H. The peak at 1207 cm-1 explains the O–H bending. The more intense bands between 744 and 598 cm-1 are represent to the Fe-O octahedral and tetrahedral bending [17]. 
The same applies to the spectrum of c, d, and e where the same peaks appear in the spectrum of magnetic iron oxide, with the presence of some distinctive peaks which belong to the active groups in the surfactant molecule. The same applies to the spectrum of c, d, and e the same peaks appear in the spectrum of magnetic iron oxide, with the presence of some distinctive peaks that belong to the active groups in the surfactant molecule, such as the peak at 3159 cm-1 indicates to the N–H bending, peak at 1111 cm-1 demonstrates the O-Fe-O the octahedron bending in fig c and the absorption at 1739 cm-1 was caused by C=O stretching in Fig. 3E.

Structure Properties 
X-ray  diffraction  (XRD)  measurements  were  used  to  obtain  the  crystal  structure  of  magnetic  Fe3O4 NP prepared in the without and with of surfactants. Fig. 4 shows that the XRD measurements for all the prepared compounds. In Fig. 4-a, the XRD measurement of the magnetic Fe3O4 Np without and with Using any surfactants was observed. The appearance of diffraction peaks at 2θ values of 18.96°(111), 30.4° (220), 35.64° (311), 43.4° (400), 53.16 degrees (422), 57.32 degrees (511), 63.12 degrees (440), and 73.12 degrees (553) are consistent with the standard XRD data of the structure of spinel Fe3O4. It was also observed that some peaks disappeared and their relative intensity changed when adding surfactants. 
the peak at 2θ values of 18.96 degrees at(111) disappeared when using Triton X100, CT, and CTAB, but the addition of surfactants leads to increase in the  relative  strength of the peaks at 2 that a  35.64 o (311),   43.4o (400),  53.16o (422),  57.32o (511), 63.12o (440), and 73.12 o (553) The prepared nanoparticles in the case of using both CT and CTAB. The Fe3O4 nanoparticles for all shapes in Fig. 3 (a) to (e)  are well crystalline and the position and the relative intensity of the diffraction peaks match well with the standard phase magnetite NPs diffraction pattern of the International Centre of Diffraction Data card (JCPDS No. 19-0629) [18].
Based on data in Table 1, the mean crystal sizes of the synthesized magnetite nanoparticles without and with addition of surfactants were calculated using Debye-Scherer formula [19-26].

Where D = the mean diameter of nanoparticles, β is the full width at half-maximum value of XRD diffraction lines,  = the wavelength of X-ray radiation source 0.15405 nm.  = the half diffraction angle –Bragg angle and k = the Scherer constant with value from 0.84 to 0.94. 
The mean crystal size of Fe3O4 NP was 8.5 nm that regarded as a quantum dote nanoparticle because its size value is less than 10 nm. This same crystal size has been observed in other studies that have reported in references [27-29]. However, after adding the surfactants during Fe3O4 NP preparation, the mean crystal size increases due to behaviour of surfactants as a template. The surfactants are surrounds of Fe3O4 NP, so, the hydrophobic terminals are being around the crystal of Fe3O4 NP, but the hydrophilic terminals are being far toward a solution, that attitude to dissolve the surfactants in the aqueous solutions then it leads to increase the value of mean crystal size of Fe3O4 NP. Furthermore, addition of the surfactant protects the Fe3O4 NP from the agglomeration before adding the surfactants because their small size and magnetic properties.
SEM analysis
Scanning Electron Microscope (SEM) is one of the most important techniques for studying various surfaces and the changes that occur on them. In this study, the SEM micrograph of the adsorbent shows morphological characteristics that are favourable for metal adsorption. 
From Fig. 5 (a-e), the small  Fe3O4 NP are agglomerated and are like-broccoli with large size, and the particle size of Fe3O4 NP without and with addition of surfactants  found  the  values  increase  with  the  following  sequences:  (20-30 nm),  (41-50 nm), (43-5 nm),(42-50 nm),and  (42-50 nm)  for  Fe3O4 NP, and with SDS, triton X100, CTAB and CT, respectively. This behaviour refers to all prepared NP as poly-crystals, these results are in agreement with the other results that have been reported in [30-33].

Application of magnetic nanoparticles for removal of Eosin yellow dye
The synthesized nanoparticles were used in the removal of eosin yellow dye as a water contamination. Fig. 6 illustrates the E removal % for using Fe3O4 raises after using surfactants at the different of dye concentrations 10 and 25 ppm. The removal of the high concentration of dye (25 ppm) was faster than the removal of low concentration of dye 10 ppm, that attitude is due to the increment in the number of collisions of the dye ions with the catalyst surface (Fe3O4 NPs) during adsorption process [34]. The best E removal  % is found after using Fe3O4  + CT as a surfactant equal to 94.7 % at 25 ppm dye and 0.05 g of NP, and equal to 94.6 % at 10 ppm dye with 0.05 g NP. Also, In Fig. 7, the adsorption capacity (q) for using Fe3O4 raises after using CT  as a surfactant  and the q maximum was 2.37 mg/g when using 25 ppm with 0.05 g of then nanoparticle, and 0.95 mg/g when using 10 ppm with 0.05 g. The using of CT as a positive surfactant gives the best removal results which is due to the acidity the dye so the attractive forces will increase on Fe3O4 NP, that was prepared in presence of a CT, the role of using CT via Fe3O4 NP preparation can be displayed in Fig. 8, that based on the hydrophobic part of this surfactant is binding with the  surface  of  Fe3O4 because  it surface is  neutral,  while the  dye  attractive  with  the  hydrophilic  part of surfactant that have a positive charge in aqueous solution [11]. The negative parts in dye will attract with the positive charge of surfactant and enhanced the removal of dye from aqueous solution.
The nanoparticles that synthesized magnetite with CT had the highest q.
    
The effectiveness of nanoparticles synthesized with the cetramide surfactant
Because  of adsorption  of eosin  yellow dye  by Fe3O4  NP  which are  synthesized  by presence  of  the surfactant. That can be behaved as reverse process and it is adsorption process will decrease with reuse for several times. This observation can be obtained during the saturated process of the active site of the synthesized nanoparticles which will be occupied by the particles of the dye. The removed eosin yellow dye from aqueous solutions decreases from 94.48% in the first stage to 75.61 % (Fig. 9), when the repeating five times this regards a good percentage, also the amount of adsorption of the dye decreases from 4.72 mg/g to 3.75 mg/g and this indicates that 0.01 g from the nanoparticles has the ability to be reused several times, but the activity of nanoparticles decreases in small amounts when the repeating for many times as shown in the Fig. 10.

Effect of temperature on removal of dye
Temperature is one of the factors affecting the removal of the dye by magnetite nanoparticles and it also affects the structure of the dye sometimes. The effect of temperature from (5 to 50) °C were studied on both the adsorption capacity of dye and the E removal % from (10-60) minutes of incubation time. The results in figure 13 were observed that the removal values increase with increasing the temperature from 5 oC to 30 oC. This behave demonstrates that the increased in the temperature will raise    the mobility and the kinetic energy of dyes’molecul in the solution, to reach easy for the active sites surface  that increase the dye affinity for adsorbed on catalyst surface [34,35]. On the other hand, the E removal % decreases at high temperatures such as 40°C and 50°C. The reason is related to the increase of the concentration of the dye with increasing in the temperature (40-50) oC which is lead to increase in the vaporization of the aqueous solutions. As shown in Fig. 11.
The thermodynamics parameters are vital parameters in the investigation the type of the adsorption process that happened on any solid surface. In outset, sorption distribution coefficient (kd) [13,35] was found using equation 4,  when  Cads.  is  the  amount  of  adsorbate  (dye)  on  the  solid  surface of the Fe3O4 NPs CT at equilibrium (mg/L). Ce is a residual dye (mg/L) in a solution at equilibrium. The standard Gibbs free energy (ΔGo) was calculated [15,36] using equation 5 (Gibbs equation), when R is universal gas constant (J/mol K) and T is the absolute temperature in Kelvin.

The change in the standard enthalpy ΔHo and change in standard entropy ΔS o were measured [37,38] using the Van’t Hoff equation (equation 6).
 

 On the other hand, the activation energy was calculated using equation 7 [15, 38].

                                                     
 Based on the results in Fig. 12 and Table 2, the positive magnitude of ΔHo value for the adsorption process of eosin yellow dye on Fe3O4 NP /CT surface is found to be endothermic nature and equal to (36.729 kJ mol-1).  This value reveals the adsorption process is chemisorption because it has the value which is a more than 20 kJ mol-1[37]. Moreover, the ΔSo magnitudes is small and positive (0.14467 kJ mol-1) that implied the randomness on the solid/solution interface raises, hence the mechanism of adsorption take place as an associative mechanism with change in the internal structure [37]. In Table 2, the positive values of activation energies increase with increasing the temperature within the range of (39.040 - 39.248) kJ mol-1 that proved the process is chemisorption. This observation is based on the calculated that Ea was between 8.4 kJ mol-1 and 83.7 kJ mol-1[37], which is given chemisorption.
 In Fig. 13, the increased in temperature caused depress in a negative ΔGo magnitudes within the range of (-7.122 mol-1 to -3.273) kJ mol-1 that indicates to this reaction is favour, spontaneous and not required to energy from an external source to convert reactants into products [37]. The thermodynamics results are in agreement with the similar results that had been reported previously [33].

CONCLUSION
During this study, magnetic iron oxide nanoparticles were prepared in the presence and absence of surfactants in their aqueous solutions. It was observed that the size of the magnetic iron oxide nano- crystals increases in presence of surfactants.  XRD  data  indicated  that the preparation of  Fe3O4 NPs  in  small  nano-size  as  quantum  dots nanoparticle, and raised the nano-size after using various surfactants. The SEM analysis was found that all samples are nanoparticle and can be agglomerated to give like-broccoli shapes.  FT-IR analysis occurred that the magnetic iron oxide nanoparticle is spinel based on positions of octahedron (Fe-O) site and tetrahedral (Fe-O) site peaks. The possibility of using the prepared magnetic nanoparticles as magnetic adsorbents in removing the eosin yellow dye from aqueous solutions was estimated. The best E removal % was found after using iron oxide NP equal to 94.48 % that prepared in the presence of CT at 25 ppm dye, 0.01 g catalyst, pH 7, 30 oC and 1 hour of the shaking process. The study also dealt with the possibility of using the prepared iron oxide more than once to remove eosin yellow dye, and it was found that nanoparticles maintain their adsorption efficiency when used several times with a small decrease in the extraction efficiency. It also dealt with the effect of temperature in the adsorption process and its impact on the efficiency of the removed dye, when it was noted that 30 oC is the best degree for dye removal. The adsorption process for eosin yellow dye on Fe3O4 prepared in presence of CT found as chemisorption in nature, with positive enthalpy and entropy.

ACKNOWLEDGMENTS
The Authors would like to thank all personnel who support this manuscript in the University of Kerbala’s faculty.

CONFLICT OF INTEREST
The authors declare that there is no conflict of interests regarding the publication of this manuscript.