A novel removal of Ni2+ ions from water solutions using dispersive solid-phase extraction method with nano Fe3O4/chitosan-acrylamide hydrogel

doi:10.21203/rs.3.rs-2439474/v1

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Research Article

A novel removal of Ni2+ ions from water solutions using dispersive solid-phase extraction method with nano Fe3O4/chitosan-acrylamide hydrogel

https://doi.org/10.21203/rs.3.rs-2439474/v1

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The effluent release containing heavy metals as Ni²⁺ ions has drastic risks to both the natural environment and human health. In this research, the nano Fe₃O₄/chitosan-acrylamide hydrogel was prepared as a novel nano sorbent for dispersive solid-phase extraction of Ni²⁺ ions and applyed in for the water sample solution. The pH, amount and type of elution solvent, the extraction time and etc were optimized for the improving the efficiency of proposed method. Analytical parameters such as concentration factor, the limit of detection and relative standard deviation (%) were achieved as 33.3, 1.25 µg L^− 1 and 1.8%, respectively. The capacity in equilibrium sorption was calculated 22.54 mg g^− 1. Furthermore, to estimate adsorption mode, the model of Freundlich and Langmuir was fitted to empirical isotherm data. Besides, to check the basic process of the metal adsorption mechanism pseudo-first-order and pseudo-second-order and Roginsky-Zeldovich model were investigated and the resuls were fitted with the pseudo-second-order model. Finally, the nano Fe₃O₄/chitosan-acrylamide hydrogel exhibited high performance to removal the Ni²⁺ ions from water sample solution.

Dispersive Solid Phase Extraction

Removal‏

Magnetic sorbent

Ni2+ ions

chitosan

acrylamide

At low concentrations, nickel(Ni) acts as a micronutrient and a toxin in marine systems and freshwater. At high levels of this element, it can bind to the cell membrane and prevent the transfer process through the cell wall(Izatt et al. 1985). For normal metabolism of many living organisms, required about 40ng mL^-1 of Ni(Gomes-Gomes et al. 1995, Unger 1979). Also, Ni compounds have many industrial uses and so increase the pollutants in the environment(Izatt et al. 1991). Therefore, new methods for preconcenrtation, determination and selective removal of trace amount of Ni in various samples such as industrial, medicinal and environmental water samples have been considered.

In the past years, different method similar to reverse osmosis, membrane adsorption, ion-exchange and cloud point extraction were applied to removal of heavy metals from wastewater (Fu and Wang 2011). But, these techniques have several limits and difficulties, such as low performance and Sludge production (Jiang et al. 2015). Adsorption method was often proposed to remove heavy metals from wastewater due to its simplicity, high efficiency, low cost, low toxicity and easy scale-up(Khan et al. 2011, Joshi and Srivastava 2019). By using magnetic nanomaterial particles as adsorbents in solid phase extraction (SPE), which is actually called magnetic solid phase extraction (MSPE), due to the high specific surface area of nanomaterials and the use of magnets without centrifugation or sample purification, the adsorption capacity increases and it becomes easier to separate the analyte from the sample(Wierucka and Biziuk 2014, Bagheri et al. 2011).

After cellulose, chitosan is the second natural polysaccharide obtained from deacetylation of chitin. Chitin is found in crustaceans, arthropods, molluscs and the cell wall of some fungi (Sadeghi-Kiakhani et al. 2019). Chitosan is an inexpensive biosorbent that has been effective in removal of heavy metals due to its biocompatible, biodegradable, seversl functional groups such as hydroxyl, amino and Estamido group(Rahangdalea et al. 2018). Due to the low acid stability, poor recyclability and mechanical properties of chitosan, functional group grafting is usually used to improve its stability and adsorption( Miretzky and Cirelli 2009, Varma et al. 2004, Mourya and Inamdar 2008, Salehi et al. 2021).

Recently, acrylamide grafted chitosan was used by al-Karawi et al. and the results showed that increasing the functional groups on chitosan increased the adsorption capacity of copper (II) in chitosan(Al-Karawi et al. 2011).Among different techniques, spectrometric methods especially Flame and graphite furnace atomic absorption spectrometry (AAS) is commonly used for determination of Ni(Boudreau and Cooper 1989, Kvitek et al. 1982).

The aim of the current research is to synthesize a new nanomagnetic adsorbent for the preconcentration of Ni²⁺ ions and then determine it by flame atomic absorption spectroscopy (FAAS). First, the adsorbent was synthesized by modifying chitosan with Fe₃O₄ nanoparticles and acrylamide to increase the functional groups of chitosan and improve its properties. Then, the magnetic nano sorbent was characterized by FT-IR, XRD and SEM. After optimizing the effective parameters on Ni²⁺ ions adsorption using the suggested method, the experimental data were fitted on the isotherm and adsorption kinetics models. Finally, resuls showed that this method was successfully applied in the removal of Ni²⁺ ions in water and wastewater samples.

Reagents

chitosan, acrylamide, (99% purity) and Ni(II) chloride (NiCl₂·2H₂O, 98% purity) provided by Fluka Co. Potassium chlorate (KClO_3, 99.55% purity), sulfuric acid (H₂SO₄(,with purity more than 97%, nitric acid (HNO₃), with purity more than 63%, hydrochloric acid with purity more than 37%, sodium hydroxide with purity more than 98%, ethanol (C₂H₆O(,with purity more than 99.9%) were acquired from Fluka, Germany. All other chemical agents were in analytical grade and applied without further purification. Ni(II) stock solution (1000 mg L^− 1) was prepared using deionized water.

Instruments

The infrared spectroscopy was recorded by FTIR spectrometer (FTIR, Thermo, AVATAR, Massachusetts, USA). The patterns of X-ray diffraction (XRD) obtained were performed on a Philips PW-1800 diffractometer apparatus (Cu Kα radiation). The SEM images of scanning electron microscopy were taken with the microscope of scanning electron (Philips, model EM-3200). The concentration of Ni(II) ions was analyzed by the PG-990 flame spectrophotometer and atomic absorption of graphite furnace spectrometer (PG, England). The choice of the FAAS method was due to the availability and cheapness of this method. To compare the results in real samples, we also measured the samples by the graphite furnace spectrometer. The aqueous samples were separated by centrifugation (Hettich, Universal 320). An ultrasonic apparatus (UP400S, Hielscher) was used for sonication. The pH measurements of solutions were done by a pH meter (PB-11, Sartorius).

Synthesis of nano iron oxide

Separately, 2.5 g of FeCl₂ and 5 g of FeCl₃ were dissolved in 50 mL of distilled water. A flask was used to combine the two solutions. One side of the mixture was kept continually under nitrogen gas, while the other side received 50 mL of 3 M NaOH, which was added and vigorously stirred for 1 hour at 60°C. It was then rinsed in distilled water to get the pH level down to 7, and finally, it was dried in a 70°C oven.

Hydrogel preparation

The 20 mL of distilled water was used to dissolve 5 ml of acrylic acid monomer, and then 0.1 g of chitosan is added. The mixture was then well stirred for 4 hours before being strained. A 5 g of acrylamide was dissolved in 20 mL of distilled water before adding acrylic acid/chitosan (filtered solution). The monomer solution was added to 0.1 g of nano-iron oxide dissolved in 10 mL of water in a small beaker and stirred with a glass stirrer and then 0.2 g of ammonium persulfate and 0.05 g of N,N'-methylenebisacrylamide were combined in the same beaker and placed at a temperature of 70°C under nitrogen gas, where polymerization took place. The polymer was then dried in a vacuum oven at a temperature of 60°C. Scheme 1 shows the Synthesis of chitosan-acrylamide

Removal Of Ni²⁺ Ions From Aqueous Solutions

The adsorption behavior of Fe₃O₄/chitosan-acrylamide hydrogel towards the Ni²⁺ ions was investigated in detail. In fact, the result of pH (2.0–10.0), reaction time (5–40 min), initial adsorbent amount (1.0–7.0 mg), and sample volume (50-1000 mL) on the adsorption of Ni²⁺ ions was investigated. The temperature effect on removal of Ni²⁺ ion, was investigated in the range 5–50°C. In a generic test, the 5 mg of nano Fe₃O₄/chitosan-acrylamide hydrogel and 50 mL of Ni²⁺ ions solution with 2 mgL^− 1 of concentration in the water sample was stirred at 25°C for 40 min to get equilibrium mode(Moghimi 2013). Afterward, the Ni²⁺ ions in the sample, in extraction by the Fe₃O₄/chitosan-acrylamide hydrogel were determined by flame atomic absorption spectrophotometer using a calibration curve. In the case of the presence of interference in the aqueous samples, a certain variation of over ± 5% was studied in the Ni²⁺ ions adsorption. Besides, all the model of isotherm studies were carried out at 25°C. The capacity in equilibrium sorption (${q}_{e}$ (mgg^− 1)) was obtained from the Eq. (1):

$${q}_{e}=V({C}_{0}-{C}_{e})/W$$

Where C_e and C₀ are the equilibrium and initial Ni²⁺ ions concentration (mgL^− 1) in each remaining solution, respectively. V term in Eq. 1 is the volume (L) of the Ni²⁺ ions sample and w (g) is sorbent mass (Salehi at el. 2022).

Desorption And Recovery Studies From The Adsorbent

After the adsorption study, the Fe₃O₄/chitosan-acrylamide hydrogel loaded with Ni²⁺ ions was gathered and washed with multiple elution solvents (0.1-3 mol L^− 1 of HNO₃, 0.1 mol L^− 1 of HCl and 0.1 mol L^− 1 of NaOH). Also, the volume of optimum elution solvent(100–1000 mL) was investigated for Ni²⁺ ions recovery.

Reusability study of the nano Fe₃O₄/chitosan-acrylamide hydrogel

To check the nano Fe₃O₄/chitosan-acrylamide hydrogel reusability, the sorption-desorption experiments were performed 5 cycles repeatedly through specified processes. First, 50 mL of 0.2 mg L^− 1 solution of Ni²⁺ ions prepared at pH = 6 and then 5 mg of nano Fe₃O₄/chitosan-acrylamide hydrogel was added and stirred for 15 min, then the sorbent separated with a magnet and finally eluted with HNO₃ (2 M) and then the concentration of Ni²⁺ ions in solution was analyzed by FAAS. Then the adsorbent was eluted by water and ethanol and dried and re-examined for the second time according to the said method. This experiment was performed up to 5 times.

Check The Repeatability Of The Method

To determine the repeatability of the method, first, 5 mg of nano Fe₃O₄/chitosan-acrylamide hydrogel was poured into 5 containers with 50 mL of 0.2 mg L^− 1 solution of Ni²⁺ ions and adjusted at pH = 6, then was stirred for 15 min and the sorbent was separated with a magnet and finally was eluted with 8 mL of HNO₃ (1 M). Finally, the solution was determined by flame atomic absorption spectroscopy.

Characterizations

FTIR Analysis

Figure 1(a) presents the findings of the FTIR investigation of the nano Fe₃O₄/chitosan-acrylamide hydrogel. The peak at 3442 cm^− 1 in the FTIR spectra is related to the OH. The -CH stretch bond is related to the peaks at 2927 cm^− 1 and 2855 cm^− 1 (Jiang et al. 2015, Liu et al. 2021). Additionally, the stretching C = O vibration reached its peak at 1625 cm^− 1. Bending vibration connected the Fe-O band in Fe₃O₄ to the peak at 775 cm^− 1 (Duru et al. 2016). The N-H bond peak at 1457 cm^− 1 illustrates the amidation reaction between the carboxyl groups of polyacrylic acid and the amine groups of chitosan (Xiang et al. 2017). The FTIR spectra after Ni²⁺ ions adsorption is shown in Fig. 1(b). When Ni²⁺ ions were adsorbed on the nano Fe₃O₄/chitosan-acrylamide hydrogel, the broad peak of the adsorbent that was attributed to NH or OH at 3442 cm^− 1 was altered to 3446 and 3780 cm^− 1, proving that NH or OH may interact with Ni²⁺ ions.

X-ray Diffraction Analysis

Only two significant peaks, positioned at 8° and 21°, in the nano Fe₃O₄/chitosan-acrylamide hydrogel XRD pattern demonstrate acrylamide's amorphous nature. The presence of chitosan was shown by a peak at 2θ = 10° in Fig. 2(a) (Yuan et al. 2015). Peaks at 2θ = 35.5°, 57.15°, and 62.77°, respectively, correlate to magnetic particles and support the presence of Fe₃O₄ particles (Chen et al. 2014). The peak has emerged at 2θ = 12° following the sorption of Ni²⁺ ions and may indicate the interaction between the amine group of chitosan and the Ni²⁺ ions (Fig. 2(b)).

SEM Analysis

According to the SEM findings in Fig. 3(a), the nano Fe₃O₄/chitosan-acrylamide hydrogel is made with nanometer particles that are placed on it and can be related to iron nanoparticles. Also, after the adsorption of Ni²⁺ ions by the nano Fe₃O₄/chitosan-acrylamide hydrogel, it can be seen that the morphology of the adsorbent has changed (Fig. 3b). The EDS analysis showed the constituent components of the adsorbent (Fig. 3a), and also EDS represented the Ni²⁺ ions adsorption was successfully by the nano Fe₃O₄/chitosan-acrylamide hydrogel (Fig. 3b).

Effective parameters on the adsorption of Ni²⁺ ions

pH Optimization

The pH of Ni²⁺ ions solution affect the main feature of their adsorption by Fe₃O₄/chitosan-acrylamide nano hydrogel. In fact, the Ni²⁺ ions adsorption is associated mostly with the protonation and deprotonation of binding sites from ligand posited on the surface of nano Fe₃O₄/chitosan-acrylamide hydrogel (Salehi et al. 2022).The results obtained from pH changes in Ni²⁺ ions adsorption percentage showed that with the increase of solution pH to pH = 5, the Ni²⁺ adsorption percentage reached the maximum(Figura 4). This is because at pHs below 4, nitrogen atoms of the ligand are protonated in an acidic environment and Ni²⁺ ions can be completely inhibited (Navarro et al. 2003). While at pH values above 6 Ni²⁺ ions react with hydroxide ions to produce Ni(OH)₂.

Time Effect

To know the sorption behaviors of nano Fe₃O₄/chitosan-acrylamide hydrogel towards Ni²⁺ spices, the adsorption percentage of Ni²⁺ ions at different contact times was investigated. The results of Fig. 5. showed that with the increased time to 20 min, the adsorption percentage increases because the Ni²⁺ ions in the solution have more opportunity to be adsorbed on the adsorbent functional groups.

Effect Of Adsorbent Amount

The amount of nano Fe₃O₄/chitosan-acrylamide hydrogel has a great effect on adsorption. The results of Fig. 6 showed that by increasing the amount of nano Fe₃O₄/chitosan-acrylamide to 6 mg, the adsorption percentage increased and then the changes were insignificant, so 5 mg of nano Fe₃O₄/chitosan-acrylamide was chosen as the optimal adsorbent amount.

Temperature Effect

According to the results of Fig. 7, the Ni²⁺ ions adsorption was changed in proportion to temperature, which is due to the changed diffusion rate and mobility of reactive species. The adsorption yield of Ni²⁺ ions onto nano Fe₃O₄/chitosan-acrylamide hydrogel was favorable at high temperatures because the mobility rate of reactive species was increased (Peer et al. 2018).

Sample Volume Effect

Figure 8 illustrates the effect of sample volume on Ni²⁺ ions adsorption by nano Fe₃O₄/chitosan-acrylamide hydrogel. The results were indicated the Ni²⁺ ions were adsorbed up to 200 mL of sample volume on the nano Fe₃O₄/chitosan-acrylamide hydrogel, after which the Ni²⁺ ions were appeared in the sample solution. According to the definition of limit volume, the limit volume in this experiment is 200 mL, and if the volume of the sample solution containing Ni²⁺ ions is more than 200 mL, ions are not completely adsorbed.

Effect Of Interferences

In the current research, the effect of ions interference was studied on Ni²⁺ ions adsorption by nano Fe₃O₄/chitosan-acrylamide hydrogel. According to the results showed in Table 1, the adsorption percentage of Ni²⁺ ions in the presence of foreign ions was well done and foreign ions had little effect on the determination of Ni²⁺ ions.

Table 1

The adsorption percentage of Ni²⁺ ions in the presence of foreign ions
Ions	Amount added (mg)	% Recovery of Ni²⁺ion
Na⁺	15	98.3 (1.3)^a
K⁺	15	98.2 (1.2)
Ca²⁺	15	99.8 (1.3)
Mg²⁺	15	98.6 (1.4)
Fe²⁺	10	98.8 (1.8)
Cr³⁺	10	97.9 (1.2)
Co²⁺	7	98.5 (1.8)
Cl⁻	7	96.9 1.2)
Br⁻	4.5	99.0 (1.0)
F⁻	4.5	98.8 (1.9)
Mn²⁺	6.5	99.8 (1.3)
Zn²⁺	6.0	95.7 (0.5)
^a Values in parentheses are % RSD based on three individual replicate analyses

Desorption

Effect Of Elution Solvents On The Recovery Of Ni Ions

Among the parameters affecting the recovery system, the type of elution solvent is one of the main parameters that has a great impact on the recovery system. In this research, elution solvents including HNO₃, HCl and NaOH were investigated to recover Ni²⁺ ions. Considering the maximum recovery for optimal solvent selection, the HNO₃ was selected for the extraction of Ni²⁺ ions from nano Fe₃O₄/chitosan-acrylamide hydrogel. The results reported in Fig. 9 demonstrated that in the balance created between the nano Fe₃O₄/chitosan-acrylamide hydrogel and the HNO₃ (1 M), more H⁺ is replaced Ni²⁺ on the adsorbent and as a result, the more Ni²⁺ is extracted. The decrease in recovery at higher concentration than 1 M can be due to molecular association between nitric acid molecules and a decrease in proton activity resulting in a decrease in the acidity of elution solvent. In this research, the volume of the HNO₃ (1 M) was investigated for Ni²⁺ ions recovery. Different volumes of HNO₃ (1 M) were selected for Ni²⁺ ions extraction and the optimal volume of HNO₃ (1 M) was obtained 8 mL. The results in Fig. 10 showed that from the volume of 8 ml onwards, all Ni²⁺ ions entered the solvent and the balance went slightly towards HNO₃ and recycling was complete.The concentration factor (33.3) was obtained as the ratio of the volume of the sample solution (100 mL) to the volume of the recovery solution (6 mL).

Stability And Reusability Evaluation

The cost of the adsorption system has a direct relationship with the potential for nano Fe₃O₄/chitosan-acrylamide hydrogel reusability. Therefore, the reusability and stability of the nano Fe₃O₄/chitosan-acrylamide hydrogel in the optimal condition of adsorption and desorption were investigated. The results showed that the nano Fe₃O₄/chitosan-acrylamide hydrogel can be reused more than 3 times without a profound loss of adsorption efficiency. After the first adsorbent recycling (adsorption and desorption), the nano Fe₃O₄/chitosan-acrylamide hydrogel retained about 90.2% of the adsorption efficiency retention for Ni²⁺ ions. Even after recycling the adsorbent 3 times, the adsorption efficiency of the nano Fe₃O₄/chitosan-acrylamide hydrogel was still 83.2% for Ni²⁺ ions (Fig. 11).

Adsorption isotherms

The survey of the isotherm models represents a good comprehension of the Ni²⁺ ions adsorption mechanism on nano Fe₃O₄/chitosan-acrylamide hydrogel. For this purpose, the model of Langmuir and Freundlich was used to fit the Ni²⁺ ions adsorption isotherms onto the nano Fe₃O₄/chitosan-acrylamide hydrogel. The isotherm of Langmuir is generally applied to qualify the sorption onto a uniform surface of adsorbent supposing the monotony of the sites of adsorption and not interplay among the analyte and adsorbent. The model in the linear form is expressed as (Kouotou et al. 2021):

${C}_{e}/{q}_{e}\text{=}\left(1/{K}_{L}{q}_{max}\right)+\left({C}_{e}/{q}_{max}\right)$ (2) Where, C_e (mgL^− 1) is the concentration in the equilibrium of Ni²⁺ ions, q_e (mgg^− 1) is the capacity of equilibrium adsorption and q_m (mgg^− 1) is the capacity of Langmuir monolayer saturation. The K_L (Lmg^− 1) is a Langmuir constant related to the adsorption energy. This model can be expressed in other terms called separation coefficient (R_L) which is a dimensionless constant, giving data about the feasibility of the process of adsorption (Arvand et al. 2022, Salehi et al. 2022). It can be expressed as:

$${R}_{L=}1/(1+{K}_{L}{C}_{0})$$

The Freundlich pattern is appropriate for explaining the adsorption enthalpy on an adsorbent with an uncoordinated surface, supposing the binding tendency reduces with the growth in the degree of adsorption. The linear term of this model is expressed as:

$${ln} {q}_{e}\text{=}{ln}{K}_{F} +1/n({ln}{C}_{e})$$

The K_F and n terms are Freundlich constants and indicate the adsorption of capacity and intensity, respectively. The isotherm model of Langmuir and Freundlich was applied to test the correlation among the Ni²⁺ ions sorption on nano Fe₃O₄/chitosan-acrylamide hydrogel. A parameters comparison among the two isotherms is shown in Table 2. As can be seen, the Langmuir model was displayed a preferable value of correlation (R²) and a premiere compatible with the empirical result than the model of the Freundlich, demonstrating that the Ni²⁺ ions adsorption onto nano Fe₃O₄/chitosan-acrylamide hydrogel was based on a unit layer and with chemisorption process on a monotonous surface. In addition, the R_L value was in the range of 0–1, which confirmed that the nano Fe₃O₄/chitosan-acrylamide hydrogel was the desired adsorbent of Ni²⁺ ions.

Table 2

Langmuir and Freundlich isotherm parameters for Ni²⁺ ions adsorption
Langmuir model		Freundlich model
q_m, mgg^− 1	22.69	K_F, Lg^− 1	4.48
K_L, Lmg^− 1	3.79	n	2.85
R_L	0.60	R²	0.939
R²	0.987	R²	0.939

Adsorption kinetics of the Ni²⁺ ions

The kinetic result was analyzed with three used kinetic adsorption models, including the pseudo-first, second-order, and the Roginsky-Zeldovich models (Fig. 12). The pseudo-first-order model is written as follows:

$$1/{q}_{t}=\left({K}_{1}/{q}_{e}t\right)+\left(1/{q}_{e}\right)$$

In Eq, 5 q_e and q_t terms (mgg^− 1) are the adsorption value in equilibrium and t (min), respectively; K₁ (min^− 1) is the pseudo-first-order rate constant. The linear model of the pseudo-second-order pattern could be displayed as follows :

$$t/{q}_{t}=\left(1/{K}_{2}{q}_{e}^{2}\right)+\left(t/{q}_{e}\right)$$

In Eq, 6 K₂ (g(mg min)⁻¹) is the constant of the pseudo-second-order rate.

The linear form of the Roginsky-Zeldovich model is given as:

$${q_{\text{t}}}=\frac{1}{\beta }\log (\alpha \times \beta )+\frac{1}{\beta }\log t$$

Where 𝛼 (mg(g min)^− 1) is the rate of Roginsky-Zeldovich initial sorption. (g mg⁻¹) is a constant of desorption (Kanmaz et al. 2020).

According to R² in Table 3, the pseudo-second-order model was fitted with a better kinetic result than the pseudo-first-order adsorption model. The Roginsky-Zeldovich model was vastly applied to qualify the pseudo-second-order model and was remarked that the nano Fe₃O₄/chitosan-acrylamide hydrogel surface was uncoordinated. The kinetic constant values of the Roginsky-Zeldovich equation for Ni²⁺ ions were deposited in Table 3. According to the R² value, it could be derived that the Roginsky-Zeldovich model is well adapted to explain the Ni²⁺ ions sorption onto the Nano Fe₃O₄/chitosan-acrylamide hydrogel compared with a model of the pseudo-first-order.

Table 3

Estimated parameters of adsorption kinetics for the adsorption of Ni²⁺ ions on nano Fe₃O₄/chitosan-acrylamide hydrogel.
Pseudo-first order		Pseudo-second order		Roginsky-Zeldovich
q_e (mg g^− 1)	0.68	q_e (mg g^− 1)	4.39	α (mg(g min) ⁻¹)	6.76
k₁ (min^− 1)	0.09	k₂ (g(mg min) ⁻¹)	0.003	β (g mg^− 1)	1.48
R²	0.79	R²	0.998	R²	0.88

Analytical performance

Calibration curve of Ni²⁺ ions extraction method

After optimizing all the parameters affecting the Ni²⁺ ions adsorption, the calibration curve was drawn for Ni²⁺ ions adsorption with the dispersive solid-phase extraction method by nano Fe₃O₄/chitosan-acrylamide hydrogel. For this purpose, different concentrations of Ni²⁺ ion solutions were prepared and nano Fe₃O₄/chitosan-acrylamide hydrogel was added to each of the solutions under optimal conditions.. Then the adsorption steps of Ni²⁺ ions were performed, and adsorption of these Ni²⁺ ions solutions were measured by flame atomic absorption spectrophotometer. This method provided a very good linear range between 0.5–20 mg/L and a value of correlation (R² = 0.9994) for Ni²⁺ ions.

The limit of detection (LOD) for Ni²⁺ ion adsorption by nano Fe₃O₄/chitosan-acrylamide hydrogel, achieved according to the slope of the Ni²⁺ ions concentration curve applying a signal-to-noise ratio of 3 (LOD = 1.25 µgL^− 1). The limit of quantification (LOQ) was calculated from 5.15 µgL^− 1.

Precisions Of Method

The precisions of this method was obtained from relative standard deviation (RSD) and by measuring the Ni²⁺ ions adsorption of 5 solutions in intra- and inter-day. To do this, 5 standards solutions of Ni²⁺ ions with the optimal condition were prepared (Ashrafzadeh and Qomi 2016). By obtaining the maximum adsorption of Ni²⁺ ions, the RSD based on intra-day and inter-day were achieved in 1.80% and 0.95% (n = 3), respectively.

Repeatability Of The Method

The reproducibility of each method is an important factor in determining reliability. Based on the results, 1.8% was obtained for reproducibility.

Application On Real Samples

After the dispersive extraction technique was completed with nano Fe₃O₄/chitosan-acrylamide hydrogel and optimal conditions were found for it, several real samples of water and wastewater were analyzed. The real samples included the Jajrood river water, Tehran tap water, synthetic samples, Rang Alvand factory, and Shahre Rey university effluent. These water samples were collected with 10 suitable PET bottles for each sample. The bottles were washed with plain water and a suitable detergent solution. Then they were filled with a nitric acid solution (1 M) and were lefted overnight. The bottles were then washed with plain and distilled water and after that, the bottles were completely dried and labeled. The colloidal and suspended particles were removed with filtration, then their pH was adjusted to 5 for each sample. For the first time, the water samples were injected into the device without any concentration and separation. In the second time, increasing the concentration of Ni²⁺ ions and separating them was done according to the presented method, and then water samples were injected into the device. The results of this analysis are shown in Table 4. As can be seen, there are more Ni²⁺ ions in the sample of the Charmshahr factory effluent and Varamin University effluent, respectively, but there was no Ni²⁺ ions in the tap water sample. There is also a small amount of Ni²⁺ ions in the water sample of the Varamin. The proposed method has been able to detect the trace amount of Ni²⁺ ions in the synthetic sample without observing a large difference in the amount of Ni²⁺ ions.

Table 4

Determination of Ni²⁺ ions in real samples
Samples	Added Ni (II) (µg)	Atomic absorption (flame)	Atomic absorption (furnace)
Tehran tap water	0	N.D^a	N.D
	10.00	10.07 (1.3)^b	10.06 (2.4)
Varamin Tap water	0	5.04 (1.4)	5.19 (2.3)
	10.00	15.65 (1.6)	15.46 (2.5)
Charshahr factory effluent	0	67.06 (2.0)	66.31 (2.9)
	10	77.09 (1.7)	75.89 (2.2)
Varamin university effluent	0	20.03 (1.3)	19.87 (2.5)
	10.00	30.06 (2.0)	29.90 (2.3)
synthetic samples ( Co²⁺, Pb²⁺, Na⁺, Al^{3 +}, Ba²⁺, Ca²⁺, Cu²⁺) 0.02 mg	0	N.D	N.D
	10.00	10.66 (2.1)	10.40 (1.7)
^a Not Detected
^b Values in parentheses are % RSD based on three individual replicate analyses

Paired T-test

The T test was used to compare the value obtained from the furnace atomic absorption method with graphite atomic spectroscopy. Following the values obtained for T and the test results, it was observed that with a 95% confidence interval, there is no significant difference between the values obtained by the atomic absorption method of the flame atomic absorption furnace.Therefore these two methods can be used to determination of Ni²⁺ ions in water samples.

Comparison Of The Removal Of Ni Ions By Various Adsorbents And Methods

Table 5 showed some parameters such as concentration factor, limit of detection and correlation coefficient removal of Ni²⁺ ions by for various adsorbents and methods. Results demonstrated the proposed method is more accurate, simpler, and faster because it has a lower value of detection limit and less relative standard deviation [31–35].( Anthemidis et al. 2003, Atsumi et al. 2005, Wang and Hansen 2002, Zhu et al. 2006, Fan and Zhou 2006).

Table 5

Comparison of the removal of Ni²⁺ ions by various adsorbents and methods.
Methode	Adsorbent type	Amount of adsorbent (mg)	Concentration factor	Relative standard deviation	The detection limit (µg/L)	Ref
On – line solvent extraction – GF AAS	Ammonium diethyl dithiophosphate	14/0	24.6	3.2	2.8	Anthemidis et al. 2003
CO-Precipitation-GF AAS	Ytterbium hydroxide	25.0	100	3.2	2.9	Atsumi et al. 2005
On – line SPE-GF AAS	Diethyldithiophosphate	3	59.4	1.3	1.3	Wang and Hansen 2002
CPE-GF AAS	P-octyl polyethyleneglycolphenyether	10.0	50	2.1	5.9	Zhu et al. 2006
SDME-GF AAS	Dithizone–chloroform	5.0	65	7.4	0.7	Fan and Zhou 2006
SPE	nano Fe₃O₄/chitosan-acrylamide hydrogel	5.0	33.3	1.8	1.25	This work

The current research was to promote an efficient, easy, inexpensive, and selectable method for removal of Ni²⁺ ions in several samples of water and wastewater. For the removal of Ni²⁺ ions from aqueous solutions, we have synthesized new Fe₃O₄/chitosan-acrylamide hydrogel through modification of chitosan. A multistep method was applied to Fe₃O₄/chitosan-acrylamide hydrogel surface. However, the recovery of Ni²⁺ ions was studied and it was displayed the pH of the samples, the time of contact, and the temperature notably affect its recovery. Besides, It was displayed that the nano Fe₃O₄/chitosan-acrylamide hydrogel exhibits the high ability to adsorb Ni²⁺ ions (The capacity in equilibrium sorption = 22.54 mgg^− 1) at pH = 5. Afterward, due to the adsorption isotherms, the Langmuir isotherm was the most convenient one to explain the sorption of Ni²⁺ ions by the nano Fe₃O₄/chitosan-acrylamide hydrogel. Among the different washing solvents that affect the extraction of Ni²⁺ ions, the HNO₃ (1M) demonstrated the best Ni²⁺ ions recovery from the nano Fe₃O₄/chitosan-acrylamide hydrogel. Then, considering the kinetics models of Ni²⁺ ions adsorption, the pseudo-second-order kinetic model was the most proper one to describe the adsorption of Ni²⁺ ions by the nano Fe₃O₄/chitosan-acrylamide hydrogel. Finally, the resulting dispersive solid-phase extraction based on nano Fe₃O₄/chitosan-acrylamide hydrogel adsorbent presented a high extraction efficiency of Ni²⁺ ions from various water and wastewater samples.

Author Contributions Statement:

Morteza Parsayi Arvand, performed the analysis. Ali Moghimi, supervised the analyses and he is Corresponding author. Narges Salehi, wrote the main manuscript text. All authors reviewed the manuscript.

Funding:

No funding was received to assist with the preparation of this manuscript.

Conflicts of interest:

The authors declare they have no financial interests.

Availability of data and material:

All of the data and material is owned by the authors and/or no permissions are required.

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Scheme 1 is available in the Supplementary Files section

No competing interests reported.

Scheme1.jpg
Scheme 1: Synthesis of chitosan-acrylamide

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A novel removal of Ni2+ ions from water solutions using dispersive solid-phase extraction method with nano Fe3O4/chitosan-acrylamide hydrogel

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Abstract

Figures

Introduction

Materials And Methods

Reagents

Instruments

Synthesis of nano iron oxide

Hydrogel preparation

Removal Of Ni2+ Ions From Aqueous Solutions

Desorption And Recovery Studies From The Adsorbent

Check The Repeatability Of The Method

Results And Discussion

Characterizations

FTIR Analysis

X-ray Diffraction Analysis

SEM Analysis

Effective parameters on the adsorption of Ni2+ ions

pH Optimization

Time Effect

Effect Of Adsorbent Amount

Temperature Effect

Sample Volume Effect

Effect Of Interferences

Desorption

Effect Of Elution Solvents On The Recovery Of Ni Ions

Stability And Reusability Evaluation

Adsorption isotherms

Adsorption kinetics of the Ni2+ ions

Analytical performance

Calibration curve of Ni2+ ions extraction method

Precisions Of Method

Repeatability Of The Method

Application On Real Samples

Paired T-test

Comparison Of The Removal Of Ni Ions By Various Adsorbents And Methods

Conclusion

Declarations

References

Schemes

Additional Declarations

Supplementary Files

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Removal Of Ni²⁺ Ions From Aqueous Solutions

Effective parameters on the adsorption of Ni²⁺ ions

Adsorption kinetics of the Ni²⁺ ions

Calibration curve of Ni²⁺ ions extraction method