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Synthesis of Fe3O4 Magnetic Nanoparticles and Investigation of Removal Capacity.

Byline: Ozlem Demir

Summary: The synthesis of nanoparticles and to examine magnetic properties of them offers a new research field. Magnetic Fe3O4 nanoparticles have more use in the environmental field. Fe3O4 is a magnetic material used in the storage media, solar energy change and electronics. Hydrothermal synthesis, micro emulsion, chemical precipitation, H2O2 oxidation of Fe(OH)2, X-ray and microwave applications can be used for Fe3O4 synthesis. In this study, the magnetic Fe3O4 nanoparticles were synthesized by the co-precipitation method and the effects of Fe3O4 nanoparticles on the removal of dye, chemical oxygen demand and chromium were investigated. The contact time, adsorbent dose and pH were considered as variables and optimized. The structure and magnetic properties of Fe3O4 were characterized by X-Ray Diffraction (XRD) Analysis. The synthesized Fe3O4 nanoparticles were used for treating the synthetic wastewater contaminated with saccharides, chromium and dye.

The various factors affecting removal efficiencies of chromium, color and chemical oxygen demand such as pH, dose of Fe3O4 and contact time were considered for optimizing the operational conditions. The results of XRD characterization showed that the product was Fe3O4 with nanoparticle magnetic properties. The optimum dye removal efficiency was achieved at 72,68 % using 1,4 g/L of Fe3O4 with the contact time of 15 minutes at pH of 5 and the optimum chromium removal efficiency of 20 % was obtained with a dose of 0,6 g/L Fe3O4 and contact time of 15 minutes at pH of 7. Besides, there was no significant removal of chemical oxygen demand. It can be concluded that, Fe3O4 can be easily synthesized and used for dye removal and chromium removal as an adsorbent.

Keywords: Magnetic nanoparticles; Fe3O4; Co-precipitation; Dye removal; Chromium removal; Chemical oxygen demand removal.

Introduction

Discharge of wastewater containing heavy metal ions and organic dyes in natural environment is a global environmental problem [1]. Industries such as leather, food and cosmetics, textiles, paper and plastics widely use dyes [2]. Dye wastes are the most common pollutants in wastewater since they are effective even at low concentrations [3] Dyes and heavy metals are toxic and carcinogenic. It is difficult to decompose in the natural environment. They can easily be accumulated in living organisms [4]. In addition, trace dyes can cause allergic dermatitis or skin irritation and are resistant to degradation by microorganisms. Azo dyes are characterized by the presence of one or more azo group. Because azo dyes have chemical stability, they are resistant to biological and chemical dewatering processes and therefore cause disposal problems in dye industries [3]. Moreover, discharging wastewater containing azo dye creates aesthetic problems and adversely affects the aquatic ecosystem.

Many studies have reported that the majority of azo dyes are toxic and/or carcinogenic. Therefore, treating wastewater containing azo dye is important [3,5]. It is possible to remove organic dyes from waste water by many physical, chemical and biological methods [6]. Coagulation-flocculation, biodegradation, ion-exchange, chemical oxidation, nanofiltration and adsorption are the treatment methods developed to remove dyes from aqueous solutions [1].

Similar to dyes, at the point of increasing pollution of the world because of rapid industrialization, heavy metal pollution poses a serious threat to the environment. Toxic metals originating from the industry are released into the environment, which is harmful to human health. These are used in industries such as chromium, wood protection, leather tanning, steel manufacturing and metal coating [7]. Chromium contamination is also an increasing problem in various industries such as chromium plating, paints, batteries and leather tanning. Chromium is a more toxic form of hexavalent Cr (VI). So, Cr (VI) must be efficiently removed from the industrial wastes before the earth and water are drained so ground waters are not polluted [8]. Chromium is in the form of Cr (III) and Cr (VI). Cr (III) is only dangerous in high concentrations, while Cr (VI) is toxic even at low concentrations. Cr (VI) in wastewater can be removed [7,9,10].

Many methods such as ion exchange, reverse osmosis, precipitation, evaporation, membrane separation are frequently used up to now for metallic removal from wastewater. Most of these methods have limits such as high investment and operating cost, removal of residual metal sludge [11]. Adsorption for removal of chromium (VI) from wastewater is effective for other classical methods [7,9,10]. Adsorbents have a large internal surface area, allowing adsorption. [12]. The choice of the adsorbents for treating wastewater is very important [1]. Activated carbon, peanut shells, mesoporous silica, polyaniline nanofibers, gelatin, kaolinite can be used as adsorbent [13]. However, having low adsorption capacities and low separation efficiencies of these adsorbents can adversely affect their application areas. [5]. Therefore, most studies have focused on developing low-cost materials that can remove contaminants from aqueous solutions. Recent studies on nanotechnology serve this field.

Nanoparticles are attracting more and more attention because of their specificity and widespread use [11].

In recent years, it has become important to adsorb pollutants from aqueous media with new nano-adsorbents. To investigate the synthesis and magnetic properties of nano-sized magnetic materials creates a new research area of technological and environmental aspects. Magnetic nanoparticles are a topic that has recently come to the fore with its magnetic resonance image in the health sector and with many uses in the environmental field [14]. Magnetic nanoparticles attract more interest than other adsorbents with their high affinity, such as low toxicity, wide surface area, rapid reactivity, and easy surface modification. [5,12]. The Fe3O4 nanoparticles have efficient, high adsorption capacity [5]. Magnetic nanoparticles are important because they have physical and chemical properties such as super magnetism, high surface area, strong adsorption capacity [9].

Magnetic Fe3O4 nanoparticles are nanoparticles that have more use in the environmental field. Fe3O4 is a magnetic material used in storage media, solar energy conversion, electronics, iron fluids and catalysts [11]. Fe3O4 has a very important role in many fields such as chemistry, physics and material science [14]. Magnetic particles provide a high adsorption capacity with their ability to be easily separated from water using an external magnetic field. With these advantages, efficient, economical, scalable, non-toxic Fe3O4 nanoparticle synthesis can be preferred in potential applications and major research areas [11]. Besides, magnetic nanoparticles are prone to aggregate due to the high magnetic attraction between the particles thus, their application is limited. So, it is necessary to modify the surface of the magnetic nanoparticles to change these particles [9].

When the nanomaterials are used as adsorbents, the mass transport resistance is greatly reduced depending on the size of the adsorbents [7]. Nanotechnology has been given great importance in developing new adsorbents with high absorptive capacity and low cost. Because nanomaterials have large surface areas that will adsorb much dye molecules on their surface [6]. Chromium removal from natural water and wastewater is a very important issue. Magnetite (Fe3O4) is a naturally occurring inorganic mineral with the property of removing aqueous Cr (VI) by electron transfer from Fe (II). Many articles have shown that magnetic Fe3O4 can be used in wastewater treatment, such as arsenic, chromium, cadmium, nickel adsorption. For example, studies on the removal of chromium-synthesized magnetic nanoparticles (Fe3O4) have shown that the adsorption capacity of magnetic particles in the nanostructure will be preferred over active carbon and clay [15].

Fe3O4 can also be used for alkalinity and hardness removal, for salinity removal, for color removal in paper industry wastewater, and for removal of natural organic matter.

Many methods such as hydrothermal synthesis, microemulsion, chemical precipitation, Fe(OH)2 oxidation with H2O2, X-ray and microwave applications are used for Fe3O4 synthesis. Co-precipitation is the simplest and cheapest method [16]. This method is a Fe3O4 synthesis method applied with a success rate of 96-99.9% [14]. In this study, the magnetic Fe3O4 nanoparticles were also synthesized by the co-precipitation method and characterized. Fe3O4 was used to adsorb Acid Blue 264 azo dyes. Besides, the chemical oxygen demand (COD) and chromium removal capacity of Fe3O4 was investigated. The effects of contact time, adsorbent dose and pH on removal capacity were evaluated.

Experimental

Synthesis of Fe3O4 Nanoparticles

Precipitation of magnetic nanoparticles can be achieved by co-precipitation of ferric ions into the sodium hydroxide solution. Electrons can move between Fe2 + and Fe3+ ions at room temperature. These nanoparticles, after surface coating, can be dispersed in certain solvents and form Ferro fluids [17].

FeCl3.6H2O (1,62 g), and FeSO4.7H2O (1,39 g) were taken in the marked quantities, dissolved in 40 mL of water. Then, 5 mL of 1 N NaOH was added at 70 Adeg C for 30 min. Black particles were formed in the medium. After this step was finished, 5 ml of 3 N NaOH was added. After the settling was complete, the particles were washed 5 times with water. They were separated by a magnet. Finally, the particles were allowed to dry under vacuum [18].

Identification of Synthesized Magnetic Nanoparticles and Determination of Magnetic Properties

Major Oxidation and X-Ray Diffraction Analysis (XRD) was performed using D8 ADVANCE BRUKER-XRD to find out the content of the product obtained and the magnetic properties after the synthesis.

Dye Removal Studies

The studies of dye adsorption were performed by batch adsorption method. The adsorption experiments were conducted by fixed concentration (40 mg/L) of dye Acid Blue 264 azo dyes. pH solution was adjusted over the range pH 5-10 using HCl and NaOH of 1 M, dosages of Fe3O4 were 0,4; 0,6; 0,8; 1; 1,2 and 1,6 g/L and contact times were 15, 30, 45, 60 and 75 minutes. Adsorption experiments were carried out with a Jar test at 150 rpm. The conditions of the experimental setup for the optimization of dye removal were given in Table 1.

Table-1: The conditions of the experimental setup for optimizing dye removal.

Experimental Set up###Dye###pH###Fe3O4###Contact Time

###Concentration###(g/L)###(min)

###(mg/L)

1.Set: Optimization###15-75

###40###7###0,8

of the Contact Time

2.Set: Optimization

###40###7###0,4-1,6###15

of Fe3O4 dose

3.Set:Optimization###4-10

###40###1,4###15

of pH

COD Removal Studies

The studies of COD removal were also performed by batch adsorption method. COD concentration was adjusted to 500 mg/L. pH solution was also adjusted over the range pH 5-10 using HCl and NaOH 1 M, dosages of Fe3O4 were 0,4; 0,6; 0,8; 1; 1,2 and 1,6 g/L and contact times were 15, 30, 45, 60 and 75 minutes. Adsorption experiments were carried out with a Jar test at 150 rpm. The conditions of the experimental setup for the optimization of COD removal were given in Table 2.

Table-2: The conditions of the experimental setup for optimizing the COD removal.

Experimental Set up###COD Concentration###pH###Fe3O4###Contact Time

###(mg/L)###(g/L)###(min)

1.Set: Optimization of Contact###15-75

###500###7###0,8

Time

2.Set: Optimization of Fe3O4 dose###500###7###0,4-1,6###15

###4-10

3.Set:Optimization of pH###500###1,4###15

Chromium Removal Studies

The contact time is one of the critical parameters effecting bio sorption and metal ion capacity. Different time intervals are selected to examine the effect of contact time at an optimum pH value of each metal ion [19].

The sorption experiments were carried out in a flask containing 0,15 g/L of chromium ion solutions with Jar test at 150 rpm for 1 h. The Cr (VI) ions sorption onto the Fe3O4 nanofibers was carried out as functions of contact time (14, 30,45, 60 and 75 min), pH (5-10) and Fe3O4 dose (0,4; 0,6; 0,8; 1; 1,2 and 1,6 g/L) in a batch system. The conditions of the experimental setup for optimizing chromium removal were given in Table 3.

Table-3: The conditions of the experimental setup for optimizing the chromium removal.

Experimental Set up###Chromium Concentration###pH###Fe3O4###Contact Time

###(g/L)###(g/L)###(min)

###15-75

1.Set: Optimization of the Contact Time###0,15###7###0,8

2.Set: Optimization of Fe3O4 dose###0,15###7###0,4-1,6###15

###15

3.Set:Optimization of pH###0,15###4-10###0,6

Results and Discussion

Fe3O4 XRD Analysis Results

Synthesized magnetic Fe3O4 was illustrated in Fig1a. XRD analysis is a technique used to find out the crystal structure and size of prepared nanoparticles [6].

The results of the major oxidation analysis on the obtained product after synthesis are shown in Table 4. According to these results, there are 93,73 % Fe, 1,12 % Si and 0,42 ppm Mn in the sample.

Table-4: Elemental analysis major oxide analysis.

###Element###Si###Fe###Mn

###Unit###%###%###ppm

###1,12###93,72###0,4

Table-5: XRD Analysis.

%###Ref. Code###Score###Compound Name###Displacement [Adeg2Th.]###Chemical Formula

100###01-075-1609###68###Magnetite low###0.080###Fe3 O4

Pos. [Adeg2Th.]###Height [cts]###FWHM [Adeg2Th.]###d-spacing [A]###Rel. int. [%]

2.0528###35244.11###0.1368###43.00158###100.00

3.7111###5536.54###0.3192###23.78924###15.71

30.2430###451.64###0.5472###2.95285###1.28

35.6341###1310.98###0.3648###2.51749###3.72

43.2634###269.23###0.5472###2.08958###0.76

57.1854###263.30###0.5472###1.60955###0.75

62.8184###341.41###0.2736###1.47808###0.97

According to XRD analysis results as given in Table 5 and Fig. 1b, it was confirmed that the chemical formula of the synthesized product was Fe3O4 and had magnetic property.

Fig. 1 shows XRD patterns of the Fe3O4. Six characteristic peaks at 23,78924; 2,95285; 2,51749; 2,08958, 1,60955 and 1,47808. The peaks showing that Fe3O4 with a spinal structure and no characteristic peak of impurities are detected in the XRD pattern.

Effects of Fe3O4 on Dye Removal

Effects of Time on Dye Removal

If a low cost adsorbent is to be used in the treatment, contact between the nanoparticles and the dye should be considered. The high removal rate of dye during short contact suggests that it is a reaction step controlling film diffusion. However, high adsorption at long time intervals indicates that it contributes to the removal of intraparticle diffusion [6].

The effect of contact time on the adsorption properties is shown in Fig. 2a. Since the mixing for 15, 30, 45, 60, 75 minutes, the optimum contact time by dye removal was observed for 15 minutes with 29 % of color removal efficiency as shown in Fig. 2a. After the 15th minute, removal efficiency was dropped.

According to the results of the study by Hariani et al., (2013), color removal increased with increasing contact time. After 30 min contact time, the color removal has become stable. The optimum color removal was 24,40 % [14]. The study by Salem et al. (2016) is concerned with the removal of amaranth foodstuff dye with magnetic Fe3O4/MgO nanoparticles synthesized by simple sol-gel method. Adsorption results show that amaranth dye is adsorbed about 90 % and reaches 96 % after 60 minutes. Rapid removal of amaranth dye at short contact times proves to be a dominant step in the dye removal of film diffusion [6]. In the study by Dalvand et al. (2016), response surface methodology was used to determine the effect of different operating conditions on dye removal with Fe3O4 and Fe3O4 @ L-arginine from textile wastewater. The results show that Fe3O4 @ L-arginine is much more effective than Fe3O4 for azo dye removal of RB19.

According to the results obtained, the adsorbent dose, pH and initial dye concentration have a significant effect on dye removal. Optimum pH conditions for dye removal by Fe3O4 @ L-arginine, 3 pH, 0,74 g/L adsorbent dose and 50 mg / L initial dye concentration were found. Under these conditions, maximum paint removal of 96,34% was achieved [12].

Cai et al., (2017) synthesized Phytic acid (PA) modified magnetic CoFe2O4 (PA/CFO) composites by a facile one-pot microwave hydrothermal method. This study proved selective adsorption of cationic methylene blue (MB) and anionic Congo red (CR) in PA / CFO nanocomposites [13].

Zhao et al., (2014) synthesized the nanoparticles of CoFe2-xGdxO4 by an improved hydrothermal method. The results showed that the synthesized nanoparticles have adsorption properties of Congo Red (CR). Substitution of Gd3+ ions increased the removal ability for CR from 131,1 to 161,1 mg/g. The absorption kinetics fitted the pseudo-second-order model. The maximum adsorption capability of CR dye onto CoFe2-xGdxO4 is up to 263,2 mg/g [20].

Chen et al., (2014) synthesized the magnetic nanoparticles CoxNi1-x Fe2O4 (x = 0, 0.3, 0.7, 0.9, 1.0) (Co-Ni) using the colloid mill and hydrothermal technique. The results suggested that adsorption capability of Co-Ni ferrite could remove Congo red dye from aqueous solution [1].

Effects of Fe3O4 dose on dye removal

Fig. 2b shows the effect of contact time to adsorb dye using Fe3O4. According to the results, the adsorption capacity increased with increasing adsorbent dosage. As the adsorbent dose increased, there was more surface area for the adsorption due to the increase in the active surface area of the Fe3O4, thus allowing the adsorbent to penetrate the adsorption more easily. The optimum dose was determined as 1,4 g/L with 16 % of removal efficiency as shown in Fig. 2b. Hariani et al., (2013) obtained close dye removal efficiency with 25 % using 0,8 g/L of Fe3O4 [14].

The study by Tan et al. (2012) showed that percentage of removal of dye concentration increased from 57,79 % to 99,89% with an increase in adsorbent dosage from 0,2 to 1,0 g/100 mL. As the dosage of the adsorbent increases, the surface area of the adsorbent will increase. As the dosage of the adsorbent increases, the duration of the equilibrium is shortened [21]. In the study of Salem et al (2016), the amount of solid catalyst can be used to determine the maximum adsorption capacity of the adsorbent. In a short time, the removal of pollutants quickly and reaching equilibrium shows the efficiency of the solid material in removing various organic pollutants. At the removal of amaranth dye, the effect of the catalyst dose was investigated at constant pH = 9 and fixed dye amount and contact time = 60 minutes at 0,1-0,4 g. Adsorption results showed that 91-95% of the dye were removed when the weight of the catalyst increased from 0,1 to 0,4 g [6].

Effects of pH on dye removal

The pH of the dye solution plays an important role in all adsorption studies and especially in the decolorization process. The maximum color removal was 72,68 % at 5 pH solution as shown Fig 2c. While the pH was close to 5 and 7, the removal rate was high. A decrease in pH was observed after 7. In similar, the results of the study by Hariani et al., (2013) confirmed that the most color removal was 25,19 % of pH solution [14]. The dye with two sulfonic groups became an easily soluble anion dye in the acidic environment. Anionic coatings and neutral solutions were easily adsorbed to Fe3O4 with positive surface charge. All adsorption depends pH.

Tan et al., (2012) conducted experiments with a 0,4 g magnetic particles at room temperature and an initial dye concentration of 250 mg / L at pH ranging from 3 to 8 to study the effect of pH on methylene blue adsorption with Fe3O4-MCP. It was observed that the dye removal efficiency, increased when pH was increased from pH 6 to pH 5. No significant dye removal was observed above pH. The results show that the cationic dye adsorbed on Fe3O4-MCP increases with pH, which is negatively charged Fe3O4-MCP And the electrostatic positive charge is attributed to the attraction between the cationic dye and the highest dye removal is 93,11% at pH 6 [21]. The aqueous solution biodegradation of heavy metals is largely dependent on the pH value of the reaction mixture to the number of metal binding sites on the biosorbent surface. At low pH (pH 5, the formation of soluble hydroxylated complexes of metal ions may compete for binding to the active sites of S. aurous and n-Fe3O4-Phth-S. Aurous biosorbents and this can be attributed to the decrease in metal bio sorption capacity values [19].

The optimum conditions for dye removal were given in Table 6.

Table-6: The Optimum Conditions for dye removal.

Adsorbent###Initial Dye###pH###Fe3O4###Contact###Removal

###Name###Concentration###(g/L)###Time###Efficiency

###(mg/L)###(min)###(%)

Fe3O4###40 mg/L###5###1,4###15###72,68

The comparison of previous study results for dye removal was given in Table 7.

Table-7: Comparison of previous studies for dye removal.

###Adsorbent###Initial Dye Concentration###pH###Dose of Adsorbent (g/L)###Contact Time (min)###Dye Removal Efficiency (%)###References

###(mg/L)

###Fe3O4###100###6###0,8###30###24,4###[14]

Fe3O4 modified L-

###50###3###0,74###-###96,34###[12]

###arginite

###Fe3O4###250###6###0,4###30###93,11###[21]

###Fe3O4###10###3###0,3###10###95###[5]

###Fe3O4###40###5###1,4###15###72,68###Presented study

Effects of Fe3O4 on COD Removal

Effects of time on color removal

It has been observed that the result is not very effective in the COD removal using Fe3O4. COD removal was illustrated in Fig. 3. The highest COD removal in the first 15 minutes in the chart was at a very low 1.98% as given in Fig.3a.

Effects of dose on COD removal

Changing the dosage in Fig. 3b. has not seemed to be effective at the removal. The highest removal efficiency was 1,9 % in 1,4 g of Fe3O4 and was at a very low level

Effects of pH on COD removal

COD removal efficiency was also not affected by pH changes. The highest removal efficiency was 1,7 % at 6 of pH.

The optimum conditions for COD removal were given in Table 8.

Table-8: The Optimum Conditions for COD removal.

Adsorbent Name###Initial COD###pH###Fe3O4###Contact Time###Removal Efficiency

###Concentration###(g/L)###(min)###(%)

###(mg/L)

###Fe3O4###500mg/L###6###1,4###15###1,7

Effects of Fe3O4 on Chromium Removal

Effects of time on Chromium removal

The bio sorption capacity values for the removal of chromium were illustrated in Fig. 4a. as a function of contact time. The experiments were carried out at an initial chromium concentration of 0,15 g/L pH 7, Fe3O4 = 0,8 g/L. As you can see, the adsorption of Cr reached its highest level in 15 minutes. The highest Cr (VI) removal was obtained at 12,5 % for 15 minutes.The highest biosorption capacity values were found in contact time up of 15 min. The fast initial metal biosorption rates at 1-15 min were attributed to the ease in surface binding based on the determined capacity values of Cr. The following slower biosorption process at time >15 min was mainly attributed to the complete saturation of the surface with the target adsorbed metal ions. Based on the outlined data in this experiment, 15 min can be listed as the optimum contact time for biosorption of the Cr ions to ensure that equilibrium conditions are attained.

Beheshti et al.,2016 investigated the influence of MWCNT/Fe3O4 concentration on the Cr (VI) ion sorption by the chitosan/MWCNT/Fe3O4 nanofibers in the initial Cr (VI) concentration of 60 mg/L, pH of 2, an adsorbent dosage of 0,5 g/L and temperatures of 25 AdegC by increasing the MWCNT/Fe3O4 concentration up to 2 wt.%. Further increase in MWCNT/Fe3O4 content led to the decrease in adsorption capacity of the chitosan/MWCNT/ Fe3O4 nanofibers for Cr (VI) ions sorption [22]. In a study by Padmavathy et al. (2016), laboratory-synthesized magnetite nanoparticles were used to remove Hexavalent chromium (Cr (VI)) from synthetically prepared waste water. The batch adsorption experiments were carried out to investigate the effects of pH, magnetite dosage, time and initial concentration on Cr (VI) removal. When the adsorption time was changed from 20 to 120 minutes, chromium removal first fell from 72 % to 69 %, then to 72 %, and then no change was observed.

As time progressed, the surface coverage of the adsorbent increased and no more adsorption occurred [7]. In a study by Rajput et al. (2016), when the pH effect on adsorption of Cr and Pb on magnetic nanoparticles was examined, it was observed that the maximum chromium removal occurred at pH 2.0 and decreased rapidly from pH 2 to 4. pH was increased from 4 to 10, and the removal was seen to be between 10-15%. High Cr6+ adsorption occurs in acidic medium with low pH. At low pH, different Cr anionic species coexist in water. Increased pH causes a Cr6+ reduction. Since the surface FeOH2+ areas are increasingly converted to Fe-O-, electrostatic charges drop to the anionic chromium species and the repulsion increases [23].

Effects of Fe3O4 dose on chromium removal

As long as all parameters are kept at a constant value, as the adsorbent dosage increases, the adsorption first increases, reaches the maximum, and then decrease. As the dosage of the adsorbent increases, chromium uptake decreases, as shown in Figure 4a. At a lower adsorbent concentration number of active sites is higher. With the increase in adsorbent dosage aggregation of particles takes place, as a result efficiency and Cr uptake decreases [7].

The effects of Fe3O4 concentration on the Cr (VI) ion sorption by the Fe3O4 nanoparticles in the initial Cr (VI) concentration of 0,15 g/L, pH of 7, contact time of 15 min were investigated. The result is illustrated in Fig. 4b. The optimum dose of Fe3O4 was determined to as 0,6 g/L, with 21 % of Cr (IV) removal efficiency. The excessive increase of Fe3O4 content led to a decrease in the adsorption capacity of Fe3O4 nanoparticles for absorption of Cr (VI) ions. Increasing the adsorption capacity by increasing Fe3O4 content can be attributed to the number of active sites of adsorbed nanoparticles. Reduction of the Cr (VI) ion uptake at higher concentrations of Fe3O4 can be attributed to the composite agglomeration of Fe3O4, which leads to reduced active areas available in the adsorption process.

In study by Beheshti et al. (2016), the efficiency of removal of chitosan / MWCNTs / Fe3O4 nanofiber adsorbent to remove Cr (VI) from aqueous solutions was investigated and the maximum absorption of Cr (VI) ions was measured at equilibrium for 30 min, pH 2 and temperature 45 AdegC [22].

Effects of pH dose on chromium removal

The effect of pH on the Cr (VI) sorption using Fe3O4 nanoparticles is investigated in the pH range of 5-10 for the initial concentration of 0,15 g/L, adsorbent dosage (Fe3O4) of 0,6 g/L 15 min of contact time. The result is illustrated in Fig 4c.. As shown, the Cr (VI) sorption capacity decreased by increasing pH amounts. A decrease in pH from pH 5 to pH 7 was observed and a slight increase between pH 7 and pH 8 was observed, followed by a decrease. The optimum pH for chromium removal was determined as 5 as shown in Fig. 4c.

The optimum conditions for chromium removal were given in Table-9.

In a study by Padmavathy et al. (2016), the batch adsorption studies were carried out to investigate the effect of pH, magnetite dosage, time and initial concentration on Cr (VI) removal. The maximum removal rate of alkali chromium is higher at lower pH. The efficiency decreased when the pH was increased from 3 to 10. As pH increases, the magnetite surface becomes more negatively charged. This causes increased impetus between Cr (VI) and magnetite nanoparticles. For this reason, as the pH increases, the elimination rate decreases. The optimum pH value of that study was found to be 3 [7].

Wang et al., (2017) synthesized a novel poly(m-phenylenediamine)/reduced graphene oxide/nickel ferrite (PmPD/rGO/NFO) nanocomposite by a facile hydrothermal method and in situ oxidative polymerization. The results confirm the formation of PmPD/rGO/NFO nanocomposite. The adsorption properties of NFO, rGO/NFO, PmPD/NFO and PmPD/rGO/NFO were evaluated. Herein, the PmPD/rGO/NFO composite shows highest adsorption capacity for Congo Red (CR), methyl orange (MO), methyl blue (MB) and toxic heavy metal ion Cr(VI). The highest adsorption for Cr (VI) as 502,5 mg/g was obtained at pH=3 [4].

The comparison of previous study results for dye removal was given in Table 10.

Table-9: The Optimum Conditions for Chromium removal.

###Initial Chromium Concentration###Contact Time###Removal Efficiency

Adsorbent Name###pH###Fe3O4 (g/L)

###(g/L)###(min)###(%)

###20

###Fe3O4###0,15###5###0,6###15

Table-10: Comparison of previous studies for chromium removal.

###Methods of adsorbent

###Adsorbent###Method of synthesis###Isotherm###Adsorption Capacity###References

###characterization

###Fabricated by

chitosan/MWC###Increased by increasing the

###Electro spinning###XRD,FTIR,SEM,TEM###Langmuir###[22]

###NT/Fe3O4###flow rate up to 4 mL/min

###process

###XRD, X-Ray photoelectron

###Max adsorption occurred at

###Nanoscale###spectroscopy (XPS),

###Freundlich###pH=2,5 and adsorption reached###[15]

###meghemite###Raman spectroscopic

###equilibrium with 15 min.

###techniques

###Reducing potential Fe3O4

###X-Ray Absorption###activates the precipitation of Cr

###Fe3O4###Co-precipitation###-###[10]

###Spectroscopies###(VI) in the form of insoluble

###and non-toxic Cr (III)

###Efficient Cr (VI) removal

###Mossbauer spectroscopy

###Fe3O4-FeB###Co-precipitation###-###under a wide range of pH###[24]

###analysis, XPS analysis

###values

###Magnetic

###Co-precipitation###-###Langmuir###At pH=3, 55,8 mg/g###[25]

###chitosan

###Fourier transform

###infrared spectroscopy (FT-

###Magnetic###IR), X-ray diffraction

Fe3O4@C@M###(XRD), thermal gravity-

###The maximum absorption

gAl-layered###The chemical self-###differential thermal

###-###amount of Cr(VI) was 152.0###[26]

###double-###assembly methods###gravity (TG-DTG),

###mg/g at 40 8C and pH 6.0.

###hydroxide###scanning electron

###(LDH)###microscopy (SEM), and

###transmission electron

###microscopy (TEM).

###n-situ growing Fe3O4###Anilino-methyl-triethoxysilane

###Silane-

###nanoparticles on###(KH-42) modified HNTs/Fe3O4

###modified

###halloysite nan- otubes###TEM, XRD, TGA, ATR-###composite exhibits the high- est

halloysite/Fe3O

###(HNTs) followed by###FTIR, BET, and Zeta###-###capacity for single adsorption###[27]

###4

###subsequent###potential.###of Cr(VI) and simultaneously

nanocomposite

###modification with###adsorption of Cr(VI) and

###s:

###silane coupling agents.###Sb(V). Moreover,

###Initial Chromium

###Concentration=0,15 g/L

###Presented

###Fe3O4###Co-precipitation###XRD###-###pH=5###Fe3O4=0,6 g/L

###study

###Contact Time=15 min

###Removal Efficiency=20 %

Conclusion

Fe3O4 has a very important role in many fields such as chemistry, physics and material science. Fe3O4 is a commercial magnetic material used in magnetic storage media, solar energy conversion, electronics, iron fluids and catalysts, and is a magnetic nanoparticle. Magnetic Fe3O4 nanoparticles are nanoparticles that have more applications in the environment. Fe3O4 also has alkalinity and hardness, the paper industry can be used for color removal and natural organic matter removal in wastewater.

In this study, the magnetic Fe3O4 nanoparticles were synthesized by co-precipitation method and the effects of this magnetic nanoparticle on dye, COD and chromium removal were investigated. As a result of the study, optimum conditions for dye removal were determined as a pH of 5, a dose of 1.4 g/L Fe3O4 and 15 min of contact time. According to the COD removal results, the highest COD removal efficiency by 1,7 % was obtained at pH=6 using 1,4 g / L Fe3O4 for 15 minutes. The effect of Fe3O4 on COD removal was observed to be very low. It was observed that the most efficient chromium removal as with 21 % was for 15 minutes of contact time using 0,6 g/L Fe3O4 dose at pH 5.

Acknowledgement

The author thanks to the members of Environmental Engineering Department of Harran University for their support during the laboratory studies.

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Publication:Journal of the Chemical Society of Pakistan
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Date:Feb 28, 2018
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