Green-synthesis of superparamagnetic Fe3O4/alginate bio-nanocomposites for heavy metal contamination removal from industrial wastewater

doi:10.21203/rs.3.rs-1336564/v1

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Research Article

Green-synthesis of superparamagnetic Fe₃O₄/alginate bio-nanocomposites for heavy metal contamination removal from industrial wastewater

https://doi.org/10.21203/rs.3.rs-1336564/v1

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Version 1

posted 02 Mar, 2022

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In present study, an efficient superparamagnetic Fe₃O₄/alginate nanocomposite material (SPFe₃O₄/alg-NCM) was green-synthesized and used as nanosorbent to remove some heavy metals from industrial wastewater. Green-synthesized SPFe₃O₄/alg-NCM was characterized by using fourier transform infrared spectroscopy (FT-IR) with attenuated total reflection (ATR) unit, UV-Vis spectrophotometer, scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX), thermogravimetric analysis (TGA) and differential thermal analysis (DTA) techniques. For determination the experimental conditions to ensure maximum adsorption capacity and to find the effects of various variables including initial heavy metal concentration and flow rate on the adsorption efficiency in column system central compoiste design (CCD) was used. To predict of responses and ANOVA a regression model were derived from CCD. The adsorption efficiencies and capacities of SPFe₃O₄/alg-NCM were calculated as 31.93 mg g^-1 for Cd²⁺ and 58.8 mg g^-1 for Co²⁺. The obtained results have proven that nanosorbent can be used successfully and effectively to remove metals from industrial wastewaters. In addition, being reusable and inexpensive are other important advantages of nanosorbent.

Superparamagnetic

nano-composite material

characterization

experimental design

desirability function

industrial wastewater

Heavy metals get around to the environment, naturally (erosion of rocks, geological weathering, corrosion of metals, volcanic activities etc.) and anthropogenically especially by the increasing the development of industry (metallurgy, mining operations, fertilizer, paint, and textile industries etc.) (Foroutan et al. 2018; Briffa et al. 2020; Kumar et al. 2021). In addition to being toxic, these metals are not biodegradable and accumulate in the food chain. Heavy metals mixed up in water start with affecting aquatic organisms and affect all living things by passing through the food chain (Foroutan et al. 2018; Kataria and Garg 2018). Investigations about heavy metals are one of the most popular subjects due to the many negative effects on the environment and therefore on humans. It has also led to the development of new methods for heavy metal removal including cadmium and cobalt due to the increasing heavy metal pollution in the environment and water.

Cadmium and cobalt are classified also among the toxic heavy metals by World Health Organization (WHO) and International Programon Chemical Safety (IPCS) that harm the environment (Shafiee et al. 2019). These, like many others, are widely used in many industries. Therefore, they are found as pollutants in wastewater. Limit values for cadmium and cobalt in water have been determined by many international organizations. In drinking water, maximum permissible limits for cadmium is 3 µg L^− 1 for cobalt 1 mg L^− 1 (Zhang et al. 2018; Zharkova and Bobkova 2019).

Cadmium can cause many disorders in human bodies as diarrhea, erythrocyte destruction, skeletal deformity, trichiniasis, renal demage, respiratory problems, skeletal deformity, behavior disorders and cognitive impairment (Kataria and Garg 2018; Shim et al. 2019).

Cobalt is essential for living beings at low concentrations because it is vital cofactor in vitamin B12. In spite of that when it was taken in excess of the required amount it can be causes some injuries in the body (Awual et al. 2020; Chen et al. 2021). Many diseases such as genetic mutations in living cells, inflammations in respiratory tract, nausea and vomit, paralysis, contact allergy, eczema etc., also occur as a result of exposure to cobalt in various ways (Wahlqvist et al. 2020; Awual et al. 2020; Dehghani et al. 2020).

Due to all these negative effects, it is vital to determine and remove all heavy metals such as cobalt and cadmium by effective methods. Although there are many methods, the most preferred method for the separation and determination of elements from past to present is the adsorption method. Among the advantages of the adsorption method, it can be counted that it is economical, effective and easy (Ince et al. 2017; Foroutan et al. 2018). It is also important that many different adsorbents can be used in this method. In literature different low-cost adsorbents, black tea and sage residue (Ziarati et al. 2020), forest biowastes (Pyrzynska 2019), peanut shells (Villar da Gama et al. 2018), greenhouse crop residue (Iáñez-Rodríguez et al. 2020), bacterial strain Rhodococcus opacus and Rhodococcus rhodochrous (Dobrowolski et al. 2017), lantana camara (Robert et al. 2018) and mussel shells (Van et al. 2019) were carried out for removing Cd and Co.

Recently, with the development of nanotechnology, nano adsorbents with large surface area, high magnetic properties, high adsorption capacity and easily separable from aqueous solutions, are used in heavy metal removal (Kataria and Garg 2018; Sun et al. 2018).

In this study Amanita vaginata mushroom was utilized for obtain Fe₃O₄ superparamagnetic nanoparticles. Than these nanoparticles were coated with alginate that is a natural biopolymer. Since alginate contains a large number of carboxylate groups, it is easy to chelate metal ions (Liu et al. 2020). For this reason, alginate was used as the coating material in the study and it was successfully applied to remove Cd and Co from industrial wastewater samples.

Instruments

Characterization was performed FTIR with ATR unit (67000, Japan), TGA-DTA (DTG-60, Shimadzu, Japan), UV-Vis spectrophotometer (UV-Vis1801, Shimadzu, Japan), SEM-EDS (Hitachi SU3500, Japan) and XRD (Rigaku MiniFlex-600, Japan). Devices were utilized of SPFe₃O₄/alg-NCM and element loaded SPFe₃O₄/alg-NCM. Flame atomic absorption spectrometer (FAAS) (AAnalyst™ 800, PerkinElmer, Inc., Shelton, CT, USA) were used to determine the elements concentrations. Peristaltic pump (Shenchen, Wertheim-Germany) was used to provide solution flow from the column at a certain speed. Ultrapure water was derived from ultrapure water system (ELGA LabWater/VWS; UK) and a digital pH-meter (EZDO PL-700PV BenchTop, Taiwan) was used pH measurements.

Green-syntesis of SPFe₃O₄-NP and preparation process of nanocomposite material (SPFe₃O₄/alg-NCM)

The superparamagnetic bio-nanocomposite beads were prepared by a two steps procedure. In the first step SPFe₃O₄-NP were synthesized by green-synthesis from the Amanita vaginata extract based on Kaplan Ince et al. (2021) method. The obtained SPFe₃O₄-NP dried and used in the second step. At the second step, 100 mL of 1% (w/v) alginic acid sodium salt solution was mixed until it became homogeneous under continuous stirring at room temperature for 3 hours. Then, 1 g of SPFe₃O₄-NP that obtained in the first step was added and mixed by ultrasonic bath for 1 hour. The homogeneous mixture was added dropwise into 1% (w/v) 300 mL CaCl₂ solution with the aid of a pump, causing the rapid creation of spherical beads due to electrostatic interactions between Ca²⁺ ions and guluronate blocks (Kondaveeti et al. 2016). Obtained beads were kept in the CaCl₂ solution for 30 minutes after gelation. A plastic sieve was used to remove the beads from the CaCl₂ solution and then washed with ultrapure water.

Fixed column preparation and adsorption-desorption studies

Approximately 10 mg SPFe₃O₄/alg-NCM were used to stuff the polyethylene columns for solid phase exraction. The column was washed with ultrapure water before passing the solution through the column. Then the experimental conditions pH (1–9 for Cd²⁺ and Co²⁺), flow rate (4–12 mL min^− 1 for Cd²⁺, 2–10 mL min^− 1 for Co²⁺) and initial concentration (10–30 mg L^− 1 for Cd²⁺, 15–75 mg L^− 1 for Co²⁺) determined by CCD were applied. Peristaltic pump was used to pass through the solution into the column. The adsorbed Cd²⁺ and Co²⁺ were desorbed by 1 mL 0.1 M of HCl acid and Cd²⁺ and Co²⁺ ions concentrations were determined by using FAAS.

Analytical Method

An experiment process that is ecofriendly, ultra-fast and highly efficient was carried out to remove Cd²⁺ and Co²⁺ ions from various industrial wastewaters. For determination the concentrations of Cd²⁺ and Co²⁺ ions in real samples, a calibration curve was constituted by using standard solutions with known concentrations range from 0.1 mg L^− 1 to 2 mg L^− 1. For Cd²⁺ ions, while about 10 mg SPFe₃O₄/alg-NCM was filled the column and 15 mL of Cd²⁺ solutions pH range from 3 to 7 was adjusted with HCl (0.01–0.1 N) and NaOH (0.01–0.1 N). Solution flow rate (range from 6 mL min^− 1 to 10 mL min^− 1) and Cd²⁺ ions initial concentrations (15–25 mg L^− 1) were adjusted and applied to column. For Co²⁺, about 10 mg SPFe₃O₄/alg-NCM was filled the column and 15 mL of Co²⁺ solutions pH (range from 3 to 7) was adjusted using HCl and NaOH reagents. Co²⁺ solution flow rate (range from 4 mL min^− 1 to 8 mL min^− 1) and Co²⁺ ions initial concentrations (range from 30 mg L^− 1 to 60 mg L^− 1) were adjusted and applied to column. Both Cd²⁺ ions and Co²⁺ ions solutions were passed the column using a peristaltic pump. After the column loading process, the column filling material (SPFe₃O₄/alg-NCM) was desorbed by using 0.1 M HCl (1 mL) and Cd²⁺ ions and Co²⁺ ions were measured using a FAAS. The amount of Cd²⁺ and Co²⁺ adsorbed by the unit mass of SPFe₃O₄/alg-NCM were calculated based on following equation (Eq. 1):

$$q=\frac{\left(Co-Ce\right) V}{m}$$

where q (mg g^− 1), C_e and C₀ represent amount adsorbed per gram of SPFe₃O₄/alg-NCM, equilibrium concentrations and initial concentration of metal solution (Cd²⁺ and Co²⁺, mg L^− 1), respectively. Similarly, m (mg) represents used SPFe₃O₄/alg-NCM mass and V (L) refers to the volume of metal solution.

Experimental design for process variables’ optimization

To optimize process conditions, the CCD combined with RSM is an effective method. It is useful technique to analyze the independent variables effects on the response along with a collection of statistical data besides mathematical data. Also, CCD technique is provided various estimation and tests such as model underfitting test, regression equation estimation and testing, factors effect test, regression parameters estimation and test along with model determination coefficient calculation. The CCD is known as regression analysis because it is often preferred for estimating parameters as well as establishing relationships between test indexes and continuous variables. Experimental design approach is especially suitable for optimizing complex synergies or antagonistic effects among variables situations (Kaplan Ince and Ince 2019; Ince and Kaplan Ince 2019a, b; Alam et al. 2021). Since it has wide application areas, RSM has been used in many studies (Kaplan Ince et al. 2018; Pala et al. 2019; Serdar et al. 2019).

In this study, to study and optimize the influence of process variables, three-factors with five-levels CCD was selected. To measure the influence of each independent variables including pH (X₁), flow rate (X₂) and initial concentration (X₃) on Cd²⁺ and Co²⁺ adsorption by SPFe₃O₄/alg-NCM a CCD experimental design (Table 1) was chosen. The level of variables was coded as -1, 0 and + 1, respectively. Furthemore, the star points of + 2 and − 2 were defined corresponding to α and -α, respectively, for each set of experiments. The main, interaction and quadratic variables effects are modeled by using CCD. An experimental design based on controllable factors was performed for minimizing the effects of uncontrolled parameters. In addition, optimizing process parameters and monitoring their interactions with a minimum number of experiments is only possible using a design such as a CCD.

Table 1

Experimental parameters for Cd and Co and their levels in the CCD
Run	pH	Flow rate (mL min^− 1)	Cd initial concentration (mg L^− 1)	mg Cd/g Ads	Run			Co initial concentration (mg L^− 1)	mg Co/g Ads
1	5	8	20	12.75	1	3	8	30	8.35
2	5	8	20	9.9	2	3	4	60	7.7
3	5	4	20	12.9	3	3	8	60	22.6
4	7	10	25	26.3	4	5	6	75	58.8
5	5	8	20	11.4	5	5	6	45	3.3
6	9	8	20	27.3	6	7	8	60	44.4
7	5	12	20	10.5	7	7	4	30	12.3
8	7	6	15	13.2	8	5	6	15	18.3
9	1	8	20	12.7	9	7	8	30	9.75
10	5	8	20	11.4	10	5	6	45	4.5
11	5	8	20	10.4	11	5	6	45	4.25
12	5	8	10	13.4	12	7	4	60	40.3
13	3	10	25	13.7	13	5	2	45	6.3
14	5	8	20	11.6	14	5	6	45	3.3
15	7	10	15	10.2	15	9	6	45	34.4
16	3	10	15	13.6	16	5	10	45	17.1
17	3	6	25	14.9	17	5	6	45	3.6
18	3	6	15	8.4	18	5	6	45	4.45
19	5	8	30	30.3	19	3	4	30	3.1
20	7	6	25	32.4	20	1	6	45	1.75

Lately in studies nanoparticles whose surfaces were modified and in the way the adsorption capacity was increased are used. For these studies, SPFe₃O₄-NP were coated with iron phosphate (Zhang et al. 2018), Fe₃O₄ nanoparticles were encapsulated into calcium alginate coated chitosan hydrochloride hydrogel beads (Yi et al. 2018), graphene [email protected]₃O₄ magnetic beads were compounded with carboxymethyl chitosan and sodium alginate (Wu et al. 2019), Fe₃O₄/layered double hydroxides were trapped into calcium alginate (Sun et al. 2018), Fe₃O₄ nanoparticles were coated with sodium alginate (Serunting et al. 2018), the mixture of titanium oxide and maghemite nanoparticles immersed in polyvinyl alcohol-alginate beads (Majidnia and Idris 2015) can be given.

El-Shamy et al. (2019) used magnetite-alginate nanoparticles for Co ions adsorption from wastewaters. Co ions concentrations were determined by AAS. The adsorption efficiency and absorption capacity were calculated as 95.01% and 33.557 mg g^− 1, respectively.

In a study bionanocomposite were produced and used for copper and nickel removal. The bionanocomposite adsorption capacity was evaluated 88.49 mg g^− 1 for copper and 86.95 mg g^− 1 for nickel (Foroutan et al. 2018).

Hosseinzadeh et al. (2016) obtained nanocrystalline magnetite from hematite and used for Cd²⁺ removal in aqueous solutions. In order for cadmium not to precipitate as hydroxides, it has not been studied greater than 7 pHs’. It was stated that pH is the most effective parameter among the experimental parameters for metal removal, such as initial concentration, contact time and temperature.

In a batch system, biochar produced from greenhouse crop residue was used as adsorbent for Co removal. For adsorbent activation different materials were applied. The adsoption capacity was calculated as 30.98 mg g^− 1 (Iáñez-Rodríguez et al. 2020).

Kataria and Garg (2018) synthesized two different iron oxide nanoparticles and used these nanoparticles metal removal from ground water by batch technique. They studies effects of pH, adsorbent dose, temperature, contact time on adsorption and reusability of adsorbents. Adsorption capacities of nanoparticles were found 51 mg g^− 1 and 63.3 mg g^− 1.

In a study magnetite − manganese oxide nanoparticles immobilized by alginate. Optimum conditions for Cd²⁺ removal were selected 6 for pH, 30°C for temperature, 120 min for contact time and 10 mg for the adsorbent amount (Kumar et al. 2021).

In this study nanoparticles coated with alginate and the adsorbent adsorption capacity found high for Cd²⁺ (31.93 mg g^− 1) and Co²⁺ (58.8 mg g^− 1) ions. Because alginate molecules are occurred from carboxyl, carbonyl, and hydroxyl other groups so the obtained nanoparticles can easily adsorb the Cd²⁺ and Co²⁺ (Cheng et al. 2019).

Characterization of SPFe₃O₄/alg-NCM

Spectra of the pretreated alginate, SPFe₃O₄/alg-NCM and Cd²⁺/Co²⁺ ions loaded SPFe₃O₄/alg-NCM were compared by using FTIR-ATR. FTIR-ATR analyses were used to characterize the changes of functional groups before and after Cd²⁺/Co²⁺ biosorption. The same characteristic bands were seen in the FTIR spectra (Fig. 1) for the alginate coated beads, SPFe₃O₄/alg-NCM and Cd²⁺/Co²⁺ ions loaded SPFe₃O₄/alg-NCM: a wide band between 3400 and 3000 cm^− 1 corresponds to the OH stretch vibration. Weak peaks at 2921, 2936, 2936 and 2923 cm^− 1 in the spectrum of alginate, SPFe₃O₄/alg-NCM and SPFe₃O₄/alg-NCM loaded with Cd²⁺/Co²⁺ ions, respectively, and C–H belongs to asymmetric stretching vibration, alginate macromolecule and “egg-box” structures formed by calcium ion limit CH stretching (He et al. 2012). Metal complexes occur in different types; it can coordinate in an ionic or uncoordinated form, via non-identical coordination, via bidentate chelation coordination, and through bicognate bridging coordination. In studies of acetate carboxyl groups, there is a clear relationship between the ν_asym(COO⁻) ve ν_sym(COO⁻) bands of the FTIR spectrum and the metal coordination type, so the separation of bands (i.e. Δν = CO_asym-CO_sym) is also indicative of a specific carboxylate structure. In this study, COO-stretching (asymmetric) spectrum peaks were observed at 1593, 1592, 1601 and 1618 cm^− 1, respectively. In addition, COO-stretching (symmetrical) spectrum peaks are also seen at 1404, 1416, 1346 and 1345 cm^− 1. Therefore, Δν(COO⁻)_complex values were found to be 189, 176, 255 and 273, respectively, and SPFe₃O₄/alg-NCM is associated with bidentate bridging coordination and SPFe₃O₄/alg-NCM loaded with Cd²⁺/Co²⁺ ions is associated with undefined coordination. Metal–carboxylate interactions in metal–alginate complexes studied with FTIR spectroscopy. Differently, another important band was detected at 541 cm^− 1 which corresponds to the stress vibration of Fe-O bonds in SPFe₃O₄-NP of SPFe₃O₄/alg-NCM (Huber 2005). In Cd²⁺/Co²⁺ ions loaded SPFe₃O₄/alg-NCM, this peak shift is seen in 561 and 557cm^− 1 and there is no peak in pure alginate.

Thermogravimetric analysis of alginate, SPFe₃O₄/alg-NCM and Cd²⁺/Co²⁺ loaded SPFe₃O₄/alg-NCM were recorded in the temperature range of 30°C − 600°C (Fig. 2a). Alginate, SPFe₃O₄/alg-NCM, and Cd²⁺/Co²⁺ ions loaded SPFe₃O₄/alg-NCM exhibited similar behavior, showing the formation of magnetic particles in alginate did not change the original structure of alginate and interactions between alginate chains and magnetite or Cd²⁺/Co²⁺ ions are not strong enough to change their thermal stability. Mass losses in alginate, SPFe₃O₄/alg-NCM and Cd²⁺/ Co²⁺ ions loaded SPFe₃O₄/alg-NCM were observed in three stages.

(i) mass losses of 25% from 35°C to 300°C based upon the release of water and CO₂ molecules; (ii) losses from 300°C to 450°C were 80%, 40%, 35% and 39% were attributed to alginate decomposition products, and (iii) losses were 88%, 44%, 44% and 45%, respectively, up to 600°C and decomposition was complete. TGA analyses showed that Cd2+/Co2 + ions loaded SPFe3O4/alg-NCM have a high thermal stability. Also based on TGA-DTA analysis it is very evident that no significant change was observed in the decomposition temperature of SPFe₃O₄/alg-NCM and Cd²⁺/Co²⁺ ions loaded SPFe₃O₄/alg-NCM.

The peaks obtained from the DTA plot of alginate, SPFe₃O₄/alg NCM and Cd²⁺/Co²⁺ loaded SPFe₃O₄/alg NCM (Fig. 2b) allowed us to obtain more detailed information about thermal degradation. The decomposition of alginate is endothermic, which appears to provide complete degradation at 435°C, and the SPFe₃O₄/alg-NCM degradation is exothermic and appears to provide complete degradation at 300°C, which is evidence of the presence of Fe₃O₄ in it. Cd²⁺ loaded SPFe₃O₄/alg-NCM degradation is also exothermic and it can be seen from the peaks at 250°C and 315°C, which are determined to be in two stages, in the same way, the degradation of Cd²⁺ loaded SPFe₃O₄/alg-NCM is also exothermic, and it is determined to occur in two stages at 250°C and 290°C it can be seen from the peaks at 250°C and 290°C. These results show that Fe₃O₄ is loaded and Cd²⁺/Co²⁺ were absorbed.

From UV-Vis spectrophotometer analysis it was observed that the color will change from yellow to black immediately when the biomass extract was added to the FeCl₃ and FeCl₂ solutions and adjust the pH. In addition, the UV-Vis spectra of SPFe₃O₄-NP have shown in Fig. 3. In this figure it can be seen a broad absorption around 550 to 750 nm after reaction, indicating the production of SPFe₃O₄-NP. Both color change and UV-Vis absorption around 400–580 showed that SPFe₃O₄-NPs were successfully synthesized (Huber 2005). Formation of iron oxide nanoparticles is proven with peaks at 298–301 nm (Pattanayak and Nayak 2013).

Samples were analyzed at positions between the angle of 0°-80° 2θ. The 2θ characteristic reflection peaks in the XRD spectrum (Fig. 4) were observed at 29°, 31°, 35°, 38°, 47°, 57° and 62°. From XRD patterns it can be seen sharp peaks. These sharp peaks indicate that the Cd²⁺ and Co²⁺ loaded SPFe₃O₄/alg-NCM have high crystallinity structure. Peaks at 35.34°, 35.43° and 35.57° shows us the presence of iron. The most severe peaks were observed to be 29°.

As it can be seen EDS graph in Fig. 5, the amounts of O, Fe, Na are higher than the other elements. The excess of O and Fe is due to Fe₃O₄, and the excess of Na is due to sodium alginate. It is also seen that Cd²⁺ and Co²⁺ are loaded into the SPFe₃O₄/alg-NCM.

Shape and size distribution of the nanoparticles were investigated using SEM analysis for distinguishing morphological properties and presented in Fig. 6. SEM visual micrograph of SPFe₃O₄/alg-NCM represents the nanoparticles spherical and uniform distribution of on the alginate surface. As can be observed that after interaction by Cd²⁺ and Co²⁺ ions, the nanoparticles still retain their spherical morphology.

RSM statistical analysis and model fitting

The CCD combined with RSM was selected and performed to optimize of crucial variables and explain the response surface nature. Regression coefficients and ANOVA results reveal that quadratic model (p < 0.0001) nature very important both for Cd²⁺ and Co²⁺ ions. While Table 2 presents CCD programme, Table 3 presents ANOVA test results that contain suggested second-order equation coefficients and model terms for Cd²⁺ and Co²⁺ ions adsorption on SPFe₃O₄/alg-NCM. Suggested model variables were tested using Fisher's test. Because with this test, it shows that larger “F values” and smaller “p values” are more meaningful than the proposed model terms. In this study; while p value of less than 0.05 indicated significance at the 95% confidence level, F value of 95.55 represented that the model is important. The "Probe > F" values are a measure of whether the model terms are statistically significant. If the "Probe > F" value is less than 0.05, it means that the term is statistically significant for the model, and a value greater than 0.05 indicates that that term is statistically insignificant for the model. In this case, both Cd²⁺ and Co²⁺ all model terms including X₁, X_2, X_3, X₁X_2, X₁X_3, X₂X_3, X₁², X₂² and X₃² values are significant model terms (Tables 2 and 3).

Table 2

Analysis of variance (ANOVA) of the Cd²⁺ quadratic model
	Sum of			Mean			F		p-value
Source	Squares	df		Square			Value		Prob > F
Model			997.50		9	110.83		97.03		< 0.0001	Significant
X₁-pH			230.28		1	230.28		201.60		< 0.0001
X₂-Flow rate			6.13		1	6.13		5.36		< 0.0001
X₃-Cd initial concent.			358.16		1	358.16		313.55		< 0.0001
X₁ X₂			21.45		1	21.45		18.78		< 0.0001
X₁ X₃			102.96		1	102.96		90.14		< 0.0001
X₂ X₃			11.28		1	11.28		9.88		< 0.0001
X₁²			124.47		1	124.47		108.97		< 0.0001
X₃²			0.57		1	0.57		0.50		< 0.0001
X₃²			181.60		1	181.60		158.98		< 0.0001
Residual			11.42		10	1.14
Lack of Fit			6.46		5	1.29		1.30		0.3896	Not significant
Pure Error			4.96		5	0.99
Cor Total			1008.92		19
R²	0.9887
R²_Adj	0.9785
R²_Pred	0.9417
Adeq Precision	30.037
*p < 0.01 highly significant; 0.01 < p < 0.05 significant; p > 0.05 not significant.

Table 3

Analysis of variance (ANOVA) of the Co²⁺ quadratic model
	Sum of			Mean			F		p-value
Source	Squares	df		Square			Value		Prob > F
Model			5130.88		9	570.10		1476.85		< 0.0001	Significant
X₁-pH			1061.13		1	1061.13		2748.88		< 0.0001
X₂-Flow rate			117.18		1	117.18		303.56		< 0.0001
X₃-Co initial concentc			1650.39		1	1650.39		4275.37		< 0.0001
X₁ X₂			43.24		1	43.24		112.03		< 0.0001
X₁ X₃			239.80		1	239.80		621.22		< 0.0001
X₂ X₃			33.21		1	33.21		86.03		< 0.0001
X₁²			324.00		1	324.00		839.34		< 0.0001
X₃²			100.17		1	100.17		259.50		< 0.0001
X₃²			1906.79		1	1906.79		4939.59		< 0.0001
Residual			3.86		10	0.39
Lack of Fit			2.27		5	0.45		1.42		0.3548	Not significant
Pure Error			1.59		5	0.32
Cor Total			5134.74		19
R²	0.9992
R²_Adj	0.9986
R²_Pred	0.9963
Adeq Precision	129.914
*p < 0.01 highly significant; 0.01 < p < 0.05 significant; p > 0.05 not significant.

Furthermore, the data variation around the model that fits the experimental data is expressed as the model's lack of fit (LOF). The LOF p-values measure the fitness of the model and imply the LOF is not significant relating to the pure error. The LOF value, which is conclusive evidence for the adequacy of the model fit, provides information about the model fit without the effects of additional higher order terms. Based on Tables 2 and 3 LOF p-values of Cd²⁺ and Co²⁺ are 0.3896 and 0.3548, respectively. These p-values of LOF confirm the suitable applicability for well-fitting of the reaction. Also, the number of experiments performed was found to be sufficient, for determining the independent variables' effects for Cd²⁺ and Co²⁺ ions adsorption on SPFe₃O₄/alg-NCM. Polynomial models validity was assessed by determining the determination coefficients (R²) and determination adjusted coefficients (R²_adj). Because R² and R²_adj are defined the percentage of variability in the response. Moreover, it is desirable to have a proposed model high R² along with for validity of the model, value of R² should be greater than 0.75 (Ince and Kaplan Ince 2017). Obtained R² and R²_adj values for the previously mentioned Cd²⁺ and Co²⁺ models were satisfactory. Because R² of the models were obtained for Cd²⁺ as 0.9887 for Co²⁺ as 0.9992, it can be said that 98.87% and 99.92% of the model-predicted values matched the experimental adsorbed for Cd²⁺ and Co²⁺ values on SPFe₃O₄/alg-NCM. In addition, adequate precision (AP) measures the signal to noise ratio (S/N) and this ratio greater than 4 is desirable. The S/N should be greater than four and it is measure by AP. These values obtained as 30.037 for Cd model and 129.914 for Co model. It can be stated that is indicating an adequate signal both model. In lights of preliminary experiment studies, three critical parameters affecting Cd²⁺ and Co²⁺ adsorption were selected as independent variables. On the other hand, Cd²⁺ and Co²⁺ ions adsorption on SPFe₃O₄/alg-NCM (Y) were considered as the dependent variable. In addition, to express the relationship between independent variables and responses, experimental data were fitted to two second-order polynomial mathematical equation (Eqs. 2 and 3) presented as below for Cd²⁺ and Co²⁺:

$$Y \left(mg Cd /g {Fe}_{3}{O}_{4}/alg NCM \right)=+45.18-7.57{X}_{1}+3.51{X}_{2}-4.20{X}_{3}-0.41{X}_{1}{X}_{2}+0.36{X}_{1}{X}_{3}-0.12{X}_{2}{X}_{3}-0.56{{X}_{1}^{2}}^{ }+0.04{X}_{2}^{2}+0.11{X}_{3}^{2}$$

$$Y \left(mg Co /g {Fe}_{3}{O}_{4}/alg NCM \right)=+105.78-9.63{X}_{1}-4.78{X}_{2}-4.12{X}_{3}-0.58{X}_{1}{X}_{2}+0.18{X}_{1}{X}_{3}+0.07{X}_{2}{X}_{3}+0.90{{X}_{1}^{2}}^{ }+0.50{X}_{2}^{2}+0.04{X}_{3}^{2}$$

For determining the optimum point and achieving the highest treatment performance the best method is layout of the surface plot in the Cd²⁺ and Co²⁺ ions adsorption on SPFe₃O₄/alg-NCM process. The affect of each parameter on Cd²⁺ and Co²⁺ ions adsorption on SPFe₃O₄/alg-NCM and their interaction were given in Figs. 7 and 8. Three-dimensional (3D) response surface graphs are useful to determine response maximum, middle and minimum points and they were obtained from quadratic model. Figures 7a and 8a present 3D response surface plots of the influence of pH-flow rate on the adsorption efficiency of Cd²⁺ and Co²⁺ ions on SPFe₃O₄/alg-NCM. Both Cd²⁺ and Co²⁺ ions adsorption amount increased when pH increases from 3 to 7 (p < 0.01), after which an increase in metal uptake were observed. Although the decrease in the flow rate has a serious effect on the adsorption of Cd²⁺ ions, however, it was observed that Co²⁺ ions adsorption did not show a statistically significant increase or decrease tendency with flow rate change.

A magnetic Fe₃O₄/graphene oxide nanocomposite material was synthzed and used for Pb²⁺ removal from water samples by Thy et al. (2020). The optimum Pb²⁺ ions adsorption onto nanocomposite material conditions were performed by RSM combined with Box-Behnken design approach. In mentioned study, the critical variables such as pH and initial concentration on the adsorption the interactive effects of these parameters were examinated. For determining the model suitability and reliability statistical parameters from quadratic model were analysed using ANOVA. By using the comparison and evaluation with the "p-values" the variables and their interactions effect on the responses were investigated. It was stated that pH "p value" is smaller than 0.0001, thus this factor is highly significant factor for Pb²⁺ removal from water.

On the other hand, it is clear that the amount of adsorbed both Cd²⁺ and Co²⁺ ions were increased when both Cd²⁺ and Co²⁺ ions initial concentration (p < 0.0001) were increased (Figs. 7b and 8b). Also, when both Cd²⁺ and Co²⁺ ions solutions' pH increases from 3 to 7 (p < 0.01) amount of adsorbed metals were increased. According to ANOVA table, it was confirmed that these two variables had a significant effect on both Cd²⁺ and Co²⁺ ions adsorption. Moreover, it was observed that these two variables interaction was statistically significant (p < 0.05).

An investigation was carried out by Rasoulzadeh et al. (2020) for the Pb²⁺ ions adsorption onto Fe₃O₄ nanoparticles and chitosan-coated Fe₃O₄ particles using RSM. According to applied approach model, the optimum conditions were found to be as 0.1 g L^− 1 for Pb (II) concentration, 10.95 for pH and 5.5 mg L^− 1 for adsorbent dosage. Also, maximum removal efficiency of Pb²⁺ ions was calculated as 93.6%. It was reported that Pb²⁺ ions initial concentration directly affects the uptake capacity of the Fe₃O₄ nanoparticles and chitosan-coated Fe₃O₄ particles.

Figures 7c and 8c represents combined effect of flow rate-initial concentration of Cd²⁺ and Co²⁺ ions removal at constant pH. While the adsorption for both Cd²⁺ and Co²⁺ ions increased with the increase in the initial concentration, it was observed that the change of flow rate had a partial effect on the metal adsorption on SPFe₃O₄/alg-NCM.

As shown in Figs. 7 and 8, factors including pH and initial concentration were found to be very critical with respect to their centre points. Also, it was used for a combined effect of all the factors on a process besides to analyze variation of the factors. Mentioned factors indicate that Cd²⁺ and Co²⁺ ions removal was highly affected by these variables.

All diagnostic plots for Cd²⁺ and Co²⁺ optimization process by using CCD approach were shown in Fig. 9. For comparing all factors effect on optimum conditions for Cd²⁺ and Co²⁺ ions adsorption on SPFe₃O₄/alg-NCM a perturbation plot was carried out (Fig. 10). All parameters especially initial concentrations and pH indicates that Cd²⁺ and Co²⁺ ions removal was highly affected by these variables. Additionally, to check the lambda (λ) value a Box-Cox plot was selected for two metals. For predicting any necessary transformation this plot is often used to enhance the significance of model. No transformation was needed, based on λ values obtained from the plots.

The efficiency of the regression model for both elements and the characteristic charts for evaluation are presented in Fig. 9. Although it is clearly observed that there is a high correlation between the estimated and experimental removal values, the residuals show a normal distribution and this distribution supports the model sufficiently in the real system.

The most important statistical metrics such as lowest p-value and LOF value and along with highest F-value and R² were examinated to found maximum desirability function (DF) and select the optimal model. The models desirability values were obtained to be 0.98 and 0.75 for Cd²⁺ and Co²⁺, respectively (Fig. 11).

The optimum values of the variables used for optimization and the highest desirability values obtained depending on these values are presented in Fig. 12 for both Cd²⁺ and Co²⁺.

Desorption procedure and SPFe₃O₄/alg-NCM reusability studies

Reusability and regeneration, desorption studies were investigated for SPFe₃O₄/alg-NCM performans. For this reason, through conducting ten consecutive adsorption-desorption cycles were performed and result were given on Fig. 13. During desorption and reuse process, bio-nano materials can be damaged because of their sensitive structure. For clarifying the adsorption process nature, desorption and reuse studies are useful. In the desorption examination choosing proper eluent is very important. Therefore, various desorption reagents including H₂SO₄, HCl, HNO₃, and CH₃COOH desorption efficiency (Fig. 14) were investigated, and the best desorption eulent was obtained as 0.5 M HCl. Under optimal condition, several experimental studies for reusability were performed using HCl (0.5 M) to test SPFe3O4/alg-NCM, for understanding whether desorption process is damaging. Then, by using the best efficient eluent (0.5 M HCl) adsorbed elements onto nano-biocomposite separated from the column were desorbed and supernatant’s Cd²⁺ and Co²⁺ ions concentration were measured using ETAAS. Regenerated SPFe₃O₄/alg-NCM were washed at least five times using ultrapure water to reach neutral pH and it was stored for the next adsorption-desorption cycle. Reusability investigations proved that the SPFe3O4/alg-NCM exhibited excellent renewability and reusability up to at least ten cycles. Furthermore, for Cd²⁺ and Co²⁺ ions removal from industrial wastewater, it has been understood that it has significant potential in practical application. The obtained data are compatible with the data in the literature (Ciesielski et al. 2012; Davodi et al. 2020; Hu et al. 2020; Cheraghipour and Pakshir 2020).

Application to real samples

The developed method was carried out to industrial wastewater samples (IW) at optimum conditions (Table 4). Again, in these conditions standard addition method was applied to real samples. Cd²⁺ and Co²⁺ ion standards of 20 µg L^− 1 and 40 µg L^− 1 were added wastewater samples and the results were given in Table 4. For wastewater samples, contamination factors (CF) were calculated and CF was found in the range of 0.64–1.38 for Cd and 0.36–0.54 for Co. The level of metal pollution is expressed in 4 levels. For low contamination, CF is lower than 1; for moderate contamination, CF is in the range of 1 and 3; for considerable contamination, CF is in the range of and for very high contamination, CF is higher than 6 (Barakat et al. 2019). According to results generally wastewater samples CF is lower than 1.

Table 4

Cd²⁺ and Co²⁺ contents of industrial wastewater
Industrial wastewater (IW)	Cd²⁺ (µg L^− 1)				Co²⁺ (µg L^− 1)
Industrial wastewater (IW)	SA	Found	Removal (%)	CF	Found	Removal (%)	CF
IW 1	0.0	6.6 ± 0.3		1.32	25 ± 2		0.5
	20	27.1 ± 1.1	100		46 ± 3	100
	40	47.3 ± 3.2	100		64 ± 4	100
IW 2	0.0	6.9 ± 0.2		1.38	24 ± 2		0.48
	20	26.5 ± 2.2	99		45 ± 2	100
	40	47.7 ± 3.1	100		63 ± 3	99
IW 3	0.0	5.4 ± 0.2		1.08	27 ± 3		0.54
	20	26.4 ± 1.8	100		48 ± 4	100
	40	45.5 ± 2.0	98		68 ± 3	100
IW 4	0.0	3.2 ± 0.2		0.64	18 ± 1		0.36
	20	24.4 ± 1.5	100		36 ± 3	98
	40	43.8 ± 3.3	100		56 ± 2	99
IW 5	0.0	5.6 ± 0.2		1.12	21 ± 1		0.42
	20	27.0 ± 2.5	100		42 ± 3	100
	40	46.2 ± 3.6	100		60 ± 5	98
IW 6	0.0	4.8 ± 0.1		0.96	25 ± 2		0.5
	20	24.9 ± 2.2	100		46 ± 4	100
	40	43.3 ± 1.9	99		66 ± 4	100
*SA: Standard Addition

In order to protect the environment, heavy metals, which are one of the most important factors causing pollution, must be removed. For this purpose, in this study, a column system was created to remove Cd²⁺ and Co²⁺ from industrial wastewater samples and a superparamagnetic nanomaterial was obtained from a natural product used as column filler. The obtained supermagnetic nanoparticles were coated with alginate and their characterizations were made using various methods. In order to save many parameters such as the chemical to be used and the time to be spent, the central composite design method has been applied. From the CCD results the parameters, pH and initial element concentrations, have an important effect on adsorption. Superparamagnetic nanoparticles have been used to remove Cd²⁺ and Co²⁺ from wastewater of various factories. The adsorption capacity of SPFe₃O₄/alg-NCM for Cd²⁺ and Co²⁺ was calculated as 31.93 mg g^− 1 and 58.8 mg g^− 1, respectively. It has also been found that the material can be used at least ten times for element removal, which indicates good reusability potential. Its high adsorption potential can be a guide for testing its usage for removal of other elements. Co²⁺ CF results are lower than Cd²⁺ CF results. For both elements, generally, CF value is found low and water samples low contaminationed with these elements.

A just few samples moderate contaminated with Cd²⁺.

Ethical approval All authors declare that the manuscript has not been published previously.

Consent to participate All authors voluntarily to participate in this research study.

Consent to publish All authors consent to the publication of the manuscript.

Authors Contributions

Muharrem Ince: Supervision, Methodology, Writing- Reviewing and Editing,

Olcay Kaplan Ince: Investigation, Validation, Writing- Original draft preparation.

Burcu Aydogdu: Methodology, Investigation, Writing- Reviewing and Editing.

Hevidar Alp: Formal analysis, Investigation, Writing- Reviewing and Editing.

Funding This study was a part of the project supported by Munzur University Scientific Investigations Project Unit (MUNIBAP- GPMUB021-01).

Competing interests All authors declare that they have no competing interests.

Availability of data and materials All data generated or analyzed during this study are included in this published article.

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Green-synthesis of superparamagnetic Fe₃O₄/alginate bio-nanocomposites for heavy metal contamination removal from industrial wastewater

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Version 1

Abstract

Figures

Introduction

Experimental

Instruments

Green-syntesis of SPFe₃O₄-NP and preparation process of nanocomposite material (SPFe₃O₄/alg-NCM)

Fixed column preparation and adsorption-desorption studies

Analytical Method

Experimental design for process variables’ optimization

Results And Discussion

Conclusion

Declarations

References

Status:

Version 1

Green-synthesis of superparamagnetic Fe3O4/alginate bio-nanocomposites for heavy metal contamination removal from industrial wastewater

Status:

Version 1

Abstract

Figures

Introduction

Experimental

Instruments

Green-syntesis of SPFe3O4-NP and preparation process of nanocomposite material (SPFe3O4/alg-NCM)

Fixed column preparation and adsorption-desorption studies

Analytical Method

Experimental design for process variables’ optimization

Results And Discussion

Conclusion

Declarations

References

Status:

Version 1

Green-synthesis of superparamagnetic Fe₃O₄/alginate bio-nanocomposites for heavy metal contamination removal from industrial wastewater

Green-syntesis of SPFe₃O₄-NP and preparation process of nanocomposite material (SPFe₃O₄/alg-NCM)