In this research, the magnetic NiFe2O4 nanocomposite was synthesized using Pulicaria gnaphalodes methanolic extract and applied to remove penicillin G from aqueous solutions. The results of field emission scanning electron microscopy, X-ray powder diffraction, Fourier transform infrared, Vibrating-Sample Magnetometer (VSM), and energy-dispersive spectroscopy-mapping analyses showed that this nanocomposite was well synthesized with a size of approximately 50–70 nm. The maximum adsorption capacity of the magnetic NiFe2O4 nanocomposite was 22.95 mg/g under optimal conditions. In addition, the experimental data of penicillin G adsorption by the magnetic NiFe2O4 nanocomposite showed that ΔH and ΔS values were positive and ΔG was negative and were following the Temkin isotherm model with R2 =  0.99 and follows the pseudo-second-order kinetic model.

  • The adsorption of penicillin G by NiFe2O4 was maximum in optimal conditions (pH = 3, nanocomposite dose: 0.3 g/L, penicillin G concentration: 30 g/L, contact time: 20 min, and time temperature: 313 K).

  • The thermodynamic study of the adsorption process showed that the values of ΔH and ΔS are positive and ΔG is negative.

  • Penicillin G adsorption by NiFe2O4 nanoparticles conforms to Temkin isotherm with R2 = 0.99.

Today, nanotechnology is one of the newest developing sciences and has wide applications in various fields such as medicine, agriculture, pharmaceuticals, aerospace, environment, and electronic industries (Naghizadeh et al. 2013a; Sinsinwar et al. 2018; Mortazavi-Derazkola et al. 2021a). Nanomaterials are very small particles that have nanodimensions from 1 to 100 nm. Since nanocomposites have a high surface-to-volume ratio, they have properties such as chemical stability, thermal conductivity, and high catalytic properties (Agarwal et al. 2017; Naghizadeh et al. 2017a). In recent years, magnetic nanomaterials, the most important of which are spinel ferrites with the general formula MFe2O4 (M = Ni, Fe, Cu, Co, Mn, etc.) due to their high removal capacity, reactivity to remove environmental pollutants, fast kinetics, efficiency isolation, and reusability, have received much attention from researchers (Teymourian et al. 2013; Zandipak & Sobhanardakani 2016). Nickel ferrite (NiFe2O4) has been widely studied as one of the most important magnetic nanocomposites due to its thermal stability and stable resistance. These magnetic nanocomposites have various applications such as gas sensors, catalysts, magnetic storage systems, photomagnetic materials, transformers, microwave devices, and magnetic temperature converters (Sivakumar et al. 2011a; Abu-Dief et al. 2016). Various physical and chemical methods, such as sol–gel processes (Fardood et al. 2017), hydrothermal (Li et al. 2010), co-precipitation (Sivakumar et al. 2011b), microemulsion (Hirai et al. 1999), and microwave synthesis (Bousquet-Berthelin et al. 2008), have been used for the synthesis of the nickel ferrite magnetic nanocomposite. In general, nanocomposite synthesis methods include physical, chemical, and biological methods (biosynthesis), of which biosynthesis of the metal nanocomposite is a possible alternative method for physical and chemical methods due to its compatibility with the environment, not use of toxic chemicals, cost-effectiveness, and less energy consumption (Iravani 2011; Hussain et al. 2016; Roy et al. 2017). Biosynthesis refers to the synthesis of nanocomposites through biological pathways such as plant extracts, enzymes, fungi, and bacteria. The use of plant extracts for the green synthesis of nanocomposites has received much attention from researchers due to their biological safety and cheapness (Rana et al. 2020; Derakhshani et al. 2023b). In recent years, the use of these nanocomposites in the removal of environmental pollutants, including antibiotics, is considered one of the newest methods of removing pollutants in the world. Penicillin G is one of the antibiotics that is widely used.

Today, large amounts of antibiotics have been identified that enter the human environment through pharmaceutical industry wastewater, hospital, and urban wastewater. An antibiotic is a substance that can kill microorganisms or inhibit their growth or metabolic activity (Dehghani et al. 2014; Choudhary et al. 2021). Antibiotics have been detected in very low concentrations (ppt) in surface and underground water sources and high concentrations (ppm) in hospital wastewater, and usually their concentration (ppb) in municipal wastewater is between these two ranges (Kümmerer 2009). Antibiotics are grouped into two categories: non-beta-lactam and beta-lactam, based on having a beta-lactam ring in their structure. Beta-lactam antibiotics are a large group of antibiotics that include penicillins, cephalosporins, monobactams, and carbapenems. Most beta-lactam antibiotics act by affecting the cell walls of bacteria and are active against many anaerobic, Gram-positive and Gram-negative organisms (Kamranifar et al. 2019a, 2019b). Penicillin G, which is produced from a fungus called Penicillium chrysogenum, is classified as an antibiotic with a beta-lactam ring. Due to its high production and its wide use in the treatment of syphilis, staphylococcal, and streptococcal infections, this drug is of great interest to health officials (Mohammadi & Sardar 2013). Antibiotics are lipophilic and stable compounds and can remain in the environment for a long time, so their presence is dangerous even in low concentrations. These compounds are very resistant to biological degradation and cause bacterial resistance; therefore, they are considered a threat to human health (Bound & Voulvoulis 2006; Xu et al. 2007). Common processes used in water and wastewater treatment are usually not capable of removing or destroying antibiotics, which is why researchers use physical treatment, chemical oxidation, and biological degradation to remove these contaminants from aquatic environments (Klavarioti et al. 2009; Le-Minh et al. 2010; El-Shafey et al. 2012). Among these methods, we can mention nanofiltration (Yang et al. 2018), photo-Fenton (Chaudhuri & Elmolla 2008), surface adsorption (Peng et al. 2019), photocatalytic destruction (Gad-Allah et al. 2011; Xekoukoulotakis et al. 2011), and coagulation (Choi et al. 2008). Some of these methods, despite having advantages, also have disadvantages that limit their use. For example, the advanced oxidation process is very expensive and complex and may produce undesirable oxidation by-products (Githinji et al. 2011; Wang et al. 2017). The use of membrane separation technologies such as nanofiltration may be problematic due to membrane fouling (Wang et al. 2017). Among these methods, adsorption is an effective method to remove various pollutants, that is simple, practical, and low-cost, and does not produce toxic by-products (Han et al. 2008). In the process of surface adsorption in aqueous solutions, the adsorbed materials that are in solution form accumulate on the surface of the absorbent solid material. In recent years, much attention has been paid to the synthesis of nanocomposites as adsorbents in water and wastewater treatment (Akbari et al. 2019). In this research, the NiFe2O4 magnetic nanocomposite was used to remove penicillin G from aqueous solutions, and the effects of various parameters such as pH, penicillin G concentration, adsorbent dose, contact time, temperature and thermodynamic process, isotherm, and kinetics of the absorption process were investigated.

Chemicals and reagents

In the present study, chemical materials such as iron(III) nitrate [Fe(NO3)3‧9H2O], nickel nitrate [NiCl2‧6H2O], sodium hydroxide [NaOH], sodium dodecyl sulfate surfactant (SDS), hydrochloric acid [HCl], ethylene glycol [C2H6O2], and sodium thiosulfate [Na2S2O3] were obtained from Merck Company. Penicillin G was obtained from the Sigma Aldrich Company. It should be noted that all solutions were prepared freshly before the experiments.

Preparation of Pulicaria gnaphalodes extract

Pulicaria gnaphalodes plants were collected from all over South Khorasan, Birjand, Iran. First, fresh P. gnaphalodes was washed three times with water and then three times with deionized water. Then, the amount of dried powder was extracted with a methanol solution (percolation process; percolation is the process of slowly passing a liquid through a filter). The solvent was removed using a rotary vacuum evaporator (Hei zbad WB eoc, Germany).

Biosynthesis of the NiFe2O4 magnetic nanocomposite

The magnetic NiFe2O4 nanocomposite was prepared according to Shirzadi-Ahodashti et al.’s (2020) research. In a typical procedure, 5 g of iron nitrate hexahydrate (Fe(NO3)3‧9H2O) was dissolved in 70 mL of deionized water under nitrogen gas conditions for 1 h. In a separate container, the SDS surfactant (with a molar ratio of 1:1 to iron salt) was dissolved in 30 mL of distilled water and with P. gnaphalodes extract added to iron salt. The reaction continued for 30 min under vigorous stirring at room temperature. Then, 1.47 g of nickel chloride salt (NiCl2‧6H2O) was added to the reaction solution. Finally, the pH of the reaction reached 12 by adding 2 M sodium hydroxide. After 2 h, the sediments obtained were washed and dried after centrifugation at room temperature for 24 h. The magnetic NiFe2O4 nanocomposite was obtained by calcination of the precipitations obtained at 600 °C for 3 h. The schematic of methanolic extraction and biosynthesis of magnetic NiFe2O4 nanocomposite is shown in Figure 1.
Figure 1

Schematic of methanolic extraction and biosynthesis of the magnetic NiFe2O4 nanocomposite.

Figure 1

Schematic of methanolic extraction and biosynthesis of the magnetic NiFe2O4 nanocomposite.

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Characterization and analytical methods

X-ray powder diffraction (XRD) analysis was performed by using a Philips PW1800 X-ray diffractometer using nickel-filtered CuKα radiation (λ = 0.154 nm) at two angles from 10° to 80°. Field emission scanning electron microscopy (FESEM) spectra were done by using the TESCAN MIRAIII model, energy-dispersive X-ray spectroscopy (EDX) (TESCAN, MIRA III, Czech Republic), and Raman spectroscopy (Micro Raman Spectrometer, Avantes, Netherland). A Perkin–Elmer spectrum 100 Fourier transform infrared (FTIR) spectrometer was used for FTIR measurements.

Experimental setup

In this study, the effects of various parameters such as pH, dosage of magnetic NiFe2O4 nanocomposite, initial concentrations of penicillin G, contact times, and temperature on the removal rate of penicillin G from aqueous solutions were investigated. The methods of evaluating the effect of these variables are summarized in the below sections.

Determination of pHzpc

To determine the pHzpc, first, the pH of the initial solution was adjusted between 2 and 12 by 1 M NaOH and HCl solutions. Then 0.25 g of the magnetic NiFe2O4 nanocomposite was added to Erlenmeyer flasks containing 50 mL of distilled water. After 24 h, the samples were taken from the shaker, and their pH was measured again. The graph of the initial pH was plotted against the final pH. The intersection point of the two curves was introduced as pHzpc.

Adsorption experiments

In this study, all chemicals were obtained from Merck, Germany. Penicillin G powder was purchased from Sigma Aldrich and used to prepare a stock solution of 500 mg/L. The other concentrations of penicillin G were prepared by diluting the stock solution. In this research, the effects of parameters such as pH (3, 5, 7, 9, 11), magnetic NiFe2O4 nanocomposite dosages (0.03, 0.5, 1, 1.5, and 2 g/L), initial concentration of penicillin G (2, 5, 10, 15, 20, and 30 mg/L), contact time (5, 15, 20, 40, 60, 90 min), and temperature (283–313 K) were evaluated on penicillin G adsorption by the NiFe2O4 magnetic nanocomposite. HCl and NaOH solutions were used to adjust the pH. A shaker (Multi shaker, NB-101MT, Korea) was used to mix the sample. Then, the nanocomposite was separated by an external magnet and centrifuged after passing through a 0.45-μm Whatman filter paper (Sigma-301, Germany). Next, the concentration of penicillin G residue was determined by a UV-Visible spectrophotometer (UV/Vis Spectrophotometer T80+, instrument) at a wavelength of 290 nm (Kamranifar et al. 2019a). Then, the adsorption capacity, kinetics, isotherms, and thermodynamics of the penicillin G adsorption process on the magnetic nanocomposite NiFe2O4 were determined. The amount of penicillin G adsorbed on the magnetic NiFe2O4 nanocomposite was calculated using the following equation:
formula
(1)
where q is the amount of penicillin G adsorbed by NiFe2O4 (mg/g); C0 is the initial penicillin G concentration (mg/L); Ce is the equilibrium concentration of penicillin G (mg/L); V is the initial solution volume (L); and m is the magnetic NiFe2O4 nanocomposite dosage (Naghizadeh et al. 2013b).

Characteristics of adsorbent

XRD analysis

The purity and phase of the as-fabricated samples were characterized by XRD. Prepared magnetic NiFe2O4 nanocomposites were subjected to XRD and as can be seen in Figure 2, the considered diffraction peaks with 2θ values of 30.43°, 36.12°, 37.19°, 43.27°, 54.63°, 57.18°, and 63.84° are related to the planes (2 2 0), (3 1 1), (2 2 2), (4 0 0), (4 2 2), (5 1 1), and (4 4 0) of crystalline nickel ferrite, respectively. No additional phases were identified. Planes of the cubic spinel ferrite are matched with JCPDS Card No. 01-074-2081. The crystalline phase and diffraction information of the synthesized magnetic NiFe2O4 nanocomposite were consistent with previous studies (Sivakumar et al. 2012).
Figure 2

XRD pattern of the NiFe2O4 nanocomposite.

Figure 2

XRD pattern of the NiFe2O4 nanocomposite.

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FESEM and energy-dispersive spectroscopy (EDS)-mapping analyses

To investigate the morphology and particle size of the magnetic magnetic NiFe2O4 nanocomposite, FESEM measurements were performed. The scanning electron micrograph of the synthesized magnetic NiFe2O4 nanocomposite with the elemental mapping using EDS is shown in Figure 3. As can be seen, the particle size is regular and the larger particles may be owing to the agglomeration of small magnetic particles. By carefully examining Figure 3, it can be seen that the magnetic NiFe2O4 nanocomposite is spherical-like in morphology with a size of approximately 50–70 nm. EDS-mapping spectra of the magnetic NiFe2O4 nanocomposite are shown in Figures 4 and 5. As can be seen, the EDS spectrum and elemental mappings of the magnetic NiFe2O4 nanocomposite illustrate the presence and the uniform distribution of nickel (Ni), iron (Fe), and oxygen (O) elements, which confirm the synthesis of magnetic NiFe2O4 nanocomposite. The results of this analysis agreed with the results reported by Vivekanandhan et al. (2013).
Figure 3

FESEM spectra images of the NiFe2O4 nanocomposite.

Figure 3

FESEM spectra images of the NiFe2O4 nanocomposite.

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Figure 4

EDX curve of the magnetic NiFe2O4 nanocomposite.

Figure 4

EDX curve of the magnetic NiFe2O4 nanocomposite.

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Figure 5

Mapping spectra of the magnetic NiFe2O4 nanocomposite.

Figure 5

Mapping spectra of the magnetic NiFe2O4 nanocomposite.

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FTIR analysis

FTIR was used for the identification of functional group presence in the samples. Structural coordination of the magnetic NiFe2O4 nanocomposite was studied using FTIR analysis, and the recorded spectrum is shown in Figure 6. By examining the UV spectrum, two bands at 3,458 and 1,643 cm−1 were assigned to the typical stretching modes of absorbed water (H2O). There are two significant peaks in the area below 1,000 cm−1. The peaks at 496 and 674 cm−1 are related to the octahedral (Fe3+-O) and tetrahedral (Ni2+/Fe3+-O) frameworks of Fe or Ni ions, respectively (Shirzadi-Ahodashti et al. 2020). Therefore, this FTIR spectrum proves that a magnetic NiFe2O4 nanocomposite was formed.
Figure 6

FTIR analysis of the magnetic NiFe2O4 nanocomposite.

Figure 6

FTIR analysis of the magnetic NiFe2O4 nanocomposite.

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VSM analysis

VSM analysis is the main method to study the magnetic properties of materials. The result of this analysis is to obtain the hysteresis curve or the hysteresis loop of the material, and using it, data such as saturation magnetization, inhibition, and magnetic permeability can be calculated. The results of VSM analysis of magnetic NiFe2O4 nanocomposite are shown in Figure 7. As can be seen in the graph, the magnetic property of these nanoparticles is about 25 emu/g, which shows that the nanoparticles have magnetic properties and are easily separated and recovered by an external magnet.
Figure 7

VSM analysis of the magnetic NiFe2O4 nanocomposite.

Figure 7

VSM analysis of the magnetic NiFe2O4 nanocomposite.

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UV–Vis absorption spectra of penicillin G

UV–Vis spectroscopic analysis is a basic test for measuring absorption wavelengths, identifying compounds, measuring band gaps, and monitoring reaction progress (Mortazavi-Derazkola et al. 2021a,  2021b). In this study, the optimal wavelength for measuring different concentrations of penicillin G was obtained using the UV–Vis spectrum. According to Figure 8, the intensity of: Intense Surface Plasmon Resonance (SPR) bands increased with increasing the concentration of penicillin G in the solution. The absorbance of the samples was read in the range of 200–400 nm with a spectrophotometer and it was observed that the maximum absorption of penicillin G in all studied concentrations was at the wavelength of 290 nm.
Figure 8

UV–Vis absorption spectra of penicillin G at room temperature and different penicillin G concentrations.

Figure 8

UV–Vis absorption spectra of penicillin G at room temperature and different penicillin G concentrations.

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pHzpc determination

pHzpc is the point where the positive and negative electric charges on the surface of the adsorbent reach equilibrium and the surface charge of the adsorbent is neutral (Derakhshani et al. 2023a). Figure 9 shows that the pHzpc of the magnetic NiFe2O4 nanocomposite is about 6.9. Therefore, at a pH higher than 6.9, the adsorbent surface has a negative charge, and at a pH lower than 6.8, the adsorbent surface has a positive charge.
Figure 9

pHzpc of magnetic NiF2O4 nanocomposite.

Figure 9

pHzpc of magnetic NiF2O4 nanocomposite.

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Influence of solution pH

In this study, the effect of solution pH with values of 3, 5, 7, 9, and 11 on the adsorption of penicillin G by the magnetic NiFe2O4 nanocomposite was investigated and the results are shown in Figure 10. The results of this diagram show that the highest adsorption percentage of penicillin G by the nanocomposite occurred at pH 9.
Figure 10

Influence of pH for the adsorption of penicillin G by the magnetic NiFe2O4 nanocomposite.

Figure 10

Influence of pH for the adsorption of penicillin G by the magnetic NiFe2O4 nanocomposite.

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As pH increased from 3 to 9, the adsorption capacity of penicillin G increased from 2.93 to 12.40 mg/g. The pH of the solution is one of the important parameters in the process of penicillin G surface adsorption on the adsorbent because it has a great effect on the efficiency of the adsorption process and changes in the pH of the solution cause a change in the surface charge of the adsorbent (Samarghandi et al. 2015; Mousavi et al. 2021). The increase in the adsorption of penicillin G in the alkaline solution pH (pH > pHpzc) can be related to the negative charge on the surface of NiFe2O4 nanocomposite and the activation of electrostatic attraction between penicillin G and the nanocomposite for adsorption. The decrease in the adsorption of penicillin G at acidic pH is due to the increase in the repulsive force between penicillin G and the adsorbent. In the study conducted in 2019 by Nourmradi et al., the removal of penicillin G by modified cationic surfactant montmorillonite was investigated and similar results were obtained. Their findings showed that for the removal of penicillin G, the adsorption capacity of the modified clay was 88.5 mg/g at a contact time of 60 min at pH 9 (Nourmoradi et al. 2019).

Influence of adsorbent dosage

In this study, the effect of adsorbent dose (0.3, 0.5, 1, 1.5, and 2 g/L) on the adsorption of penicillin G by the magnetic NiFe2O4 nanocomposite was investigated, and the results are shown in Figure 11.
Figure 11

Influence of adsorbent dosage for the adsorption of penicillin G by the magnetic NiFe2O4 nanocomposite.

Figure 11

Influence of adsorbent dosage for the adsorption of penicillin G by the magnetic NiFe2O4 nanocomposite.

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As it is clear from Figure 11, with the increase in adsorbent dosage, the percentage of adsorption increases somewhat. By increasing the amount of adsorbent, the surface area and the number of accessible places for surface adsorption of the pollutant also increase (Ahmadian 2013). However, with a further increase in the adsorbent dose, the number of active sites of adsorbent becomes much higher than the threshold points. Therefore, only a part of the active sites of adsorbent is occupied by penicillin G, and as a result, the adsorption capacity decreases (Wu et al. 2013a). On the other hand, according to the q = ((C0Ce) v)/m formula, the denominator of the fraction increases with the increase in the adsorbent dose, but the rest of the parameters are constant; therefore, the adsorption capacity of penicillin G decreases.

Influence of contact time and initial concentration of penicillin G

The initial concentration of penicillin G is one of the most important parameters that affect its adsorption by the magnetic NiFe2O4 nanocomposite. In this study, the effect of contact time (10–90 min) and initial concentration of penicillin G (2, 5, 10, 15, 20, and 30 mg/L) on its adsorption by the adsorbent nanocomposite were investigated, and the results are shown in Figure 12.
Figure 12

Influence of contact time and initial concentration for the adsorption of penicillin G by the magnetic NiFe2O4 nanocomposite.

Figure 12

Influence of contact time and initial concentration for the adsorption of penicillin G by the magnetic NiFe2O4 nanocomposite.

Close modal

As can be seen from Figure 12, as the concentration of penicillin G increases, the adsorption capacity increases and the maximum adsorption capacity occurs in 20 min. The reason is that in the initial stage, a large number of active sites on the adsorbent are available and the high driving force causes the rapid transfer of penicillin G molecules to the surface of absorbent nanoparticles. After that, the adsorption capacity gradually decreases and then reaches equilibrium. The decrease in the adsorption rate is due to the decrease in the number of active sites remaining on the adsorbent (Naghizadeh et al. 2013b; Wu et al. 2013b; Mohammadi et al. 2022). The reason for increasing the adsorption capacity by increasing the concentration of penicillin G is that increasing the initial concentration leads to an increase in the probability of contact between the pollutant and the adsorbent, and finally, the active sites of adsorption are used to the maximum (Balarak et al. 2017; Akbari et al. 2019).

Influence of the temperature and the thermodynamic process

To determine the effect of temperature on the adsorption process of penicillin G by NiFe2O4 magnetic nanoparticles, temperatures of 283, 293, 303, and 313 K were selected. The adsorption process was carried out at pH 9, a nanoparticle dose of 0.3 g/L, and the penicillin G concentration of 15 mg/L for 20 min. As can be seen from Figure 13, the adsorption capacity of magnetic nanoparticles increases with increasing temperature, and this may be because the inactive sites on the surface of the adsorbent become active with increasing temperature (Gerçel & Gerçel 2007; Hossein Panahi et al. 2020). All the thermodynamic parameters were determined from the following equations (Naghizadeh et al. 2017b):
formula
(2)
formula
(3)
formula
(4)
where Kc is the equilibrium constant, CAd is the concentration of penicillin G adsorbed on NiFe2O4 at equilibrium (mg/L), Ce is the equilibrium concentration of penicillin G in the solution (mg/L), R is the gas constant (8.314 J/(K·mol)), and T is the temperature in Kelvin. The values of ΔH° and ΔS° can be obtained from the slope and intercept of the Van't Hoff plot of ln Kc versus 1/T.
Figure 13

Influence of temperature for the adsorption of penicillin G by the magnetic NiFe2O4 nanocomposite.

Figure 13

Influence of temperature for the adsorption of penicillin G by the magnetic NiFe2O4 nanocomposite.

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Table 1 shows the thermodynamic parameters of the adsorption process including enthalpy changes (ΔH), entropy changes (ΔS), and Gibbs free-energy changes (ΔG). In this table, it is shown that ΔH and ΔS are positive and ΔG is negative. The positive value of ΔH indicates that the adsorption process of penicillin G by nanoparticles is naturally endothermic and the adsorption capacity of the adsorbent increases with increasing temperature. According to the results of Table 2, ΔG has negative values, and this indicates the possibility of the spontaneous adsorption process. That is, the adsorption process can be done without the need to add energy from the outside.

Table 1

Thermodynamics parameters of penicillin G adsorption by the magnetic NiFe2O4 nanocomposite

AdsorbentT (K)qe (mg/g)Thermodynamics parameters
ΔG (kJ/mol)ΔH (kJ/mol)ΔS (J/mol K)
NiFe2O4 283 8.85 −0.17 28.14 99.81 
293 11.1 −0.87 
303 16.85 −2.35 
313 19.4 −3.00 
AdsorbentT (K)qe (mg/g)Thermodynamics parameters
ΔG (kJ/mol)ΔH (kJ/mol)ΔS (J/mol K)
NiFe2O4 283 8.85 −0.17 28.14 99.81 
293 11.1 −0.87 
303 16.85 −2.35 
313 19.4 −3.00 
Table 2

Kinetics constant calculations for the adsorption of penicillin G by the magnetic NiFe2O4 nanocomposite

AdsorbentC0 (mg/L)Pseudo-first-order
Pseudo-second-order
qe, exp (mg/g)
K1 (min−1)qe, cal (mg/g)R2K2 (g/mg min)qe, cal (mg/g)R2
NiFe2O4 2.00 0.025 1.34 0.88 0.05 2.06 0.964 2.10 
5.00 0.034 3.36 0.78 0.02 8.00 0.991 7.75 
10.00 0.036 5.14 0.65 0.01 15.97 0.994 15.65 
15.00 0.033 5.31 0.58 0.01 18.50 0.994 18.50 
20.00 0.036 4.80 0.68 0.02 20.42 0.998 20.20 
30.00 0.035 5.63 0.60 0.01 23.22 0.996 22.95 
AdsorbentC0 (mg/L)Pseudo-first-order
Pseudo-second-order
qe, exp (mg/g)
K1 (min−1)qe, cal (mg/g)R2K2 (g/mg min)qe, cal (mg/g)R2
NiFe2O4 2.00 0.025 1.34 0.88 0.05 2.06 0.964 2.10 
5.00 0.034 3.36 0.78 0.02 8.00 0.991 7.75 
10.00 0.036 5.14 0.65 0.01 15.97 0.994 15.65 
15.00 0.033 5.31 0.58 0.01 18.50 0.994 18.50 
20.00 0.036 4.80 0.68 0.02 20.42 0.998 20.20 
30.00 0.035 5.63 0.60 0.01 23.22 0.996 22.95 

Determination of adsorption kinetics

Reaction kinetics is used to predict the adsorption rate of the pollutants. In this study, pseudo-first-order and pseudo-second-order kinetic models were evaluated for penicillin G adsorption on the magnetic NiFe2O4 nanocomposite, and the results are shown in Figure 14 and Table 2.
Figure 14

Pseudo-first-order kinetics and pseudo-second-order kinetics of penicillin G adsorption by the magnetic NiFe2O4 nanocomposite.

Figure 14

Pseudo-first-order kinetics and pseudo-second-order kinetics of penicillin G adsorption by the magnetic NiFe2O4 nanocomposite.

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By investigating the correlation coefficient obtained for the pseudo-first-order and pseudo-second-order kinetic models, it was found that the adsorption data in this research follow the pseudo-second-order kinetic model. By examining and comparing the value of qe in experimental and kinetic models, we conclude that the experimental data are much closer to the pseudo-second-order model data than to the pseudo-first-order model.

Study of adsorption isotherm models

Five models, namely Langmuir, Freundlich, Brunauer -Emmett -Teller (BET), Temkin, and Dubinin-Radushkevich, were used to investigate the adsorption isotherms of penicillin G by NiFe2O4 magnetic nanoparticles, and their data are presented in Table 3.

Table 3

Isotherm and constant calculations for the adsorption of penicillin G by the magnetic NiFe2O4 nanocomposite

IsothermsConstantsValues
Langmuir qmax (mg/g) 13.92 
KL (L/mg) 0.05 
RL 0.33 
R2 0.96 
Freundlich kf (mg/g) 0.94 
1/n 1.12 
N 0.89 
R2 0.94 
BET 1/AXm 26.87 
(A − 1)/(AXm34.84 
A 937.04 
Xm 26.90 
R2 0.57 
Temkin AT, L/mg 0.65 
bT 345.30 
B 7.18 
R2 0.99 
Dubinin-Radushkevich β, mol2/kJ2 0.00 
E, kJ/mol 0.51 
qm, mg/g 14.64 
R2 0.96 
IsothermsConstantsValues
Langmuir qmax (mg/g) 13.92 
KL (L/mg) 0.05 
RL 0.33 
R2 0.96 
Freundlich kf (mg/g) 0.94 
1/n 1.12 
N 0.89 
R2 0.94 
BET 1/AXm 26.87 
(A − 1)/(AXm34.84 
A 937.04 
Xm 26.90 
R2 0.57 
Temkin AT, L/mg 0.65 
bT 345.30 
B 7.18 
R2 0.99 
Dubinin-Radushkevich β, mol2/kJ2 0.00 
E, kJ/mol 0.51 
qm, mg/g 14.64 
R2 0.96 

The comparison of correlation coefficients in Table 3 revealed that the adsorption of penicillin G by the magnetic NiFe2O4 nanocomposite follows the Temkin isotherm with R2 = 0.99. Adsorption isotherm is one of the most important parameters in the design of pollutant adsorption systems from aqueous solutions, which expresses the interaction between the adsorbent and the adsorbed material. For this reason, it is very important to investigate the adsorption isotherms to optimize the consumption of an adsorbent material and determine its capacity (Piccin et al. 2011). As we have seen in this study, the adsorption process of penicillin G follows the Temkin isotherm. In this isotherm, the amount of adsorbed substance is proportional to the logarithm of the adsorbed pressure. This model assumes that the heat of adsorption of all molecules reduces linearly instead of logarithmically with an increasing surface coverage of the adsorbent (Khaled et al. 2009; Piccin et al. 2011). The Temkin isotherm is obtained by the following equations:
formula
(5)
formula
(6)
formula
(7)
where qe is the adsorption capacity in equilibrium (mg/g); R is theuniversal gas constant (8.314 J/K mol); T is the temperature (K); bT is the constant related to heat of sorption (J/mol); AT is the Temkin isotherm equilibrium binding constant (L/mg); and Ce is the concentration of the solute at equilibrium (mg/L).

The values of AT, bT, and B are given in Table 3.

In the study of Kamranifar et al. (2019a), who investigated the adsorption of penicillin G by magnetic nanocomposites, they concluded that the adsorption of penicillin G had better compatibility with the Langmuir model and then with Temkin, Freundlich, and Dubinin–Radushkevich models.

This study was conducted to evaluate the effect of magnetic nanoparticles NiFe2O4 as an adsorbent in the removal of penicillin G from aqueous solutions. In this research, the results of the analyses performed (FESEM, XRD, FTIR, VSM, and EDS-mapping) showed that the synthesis of the magnetic NiFe2O4 nanocomposite was successful. The size of the magnetic NiFe2O4 nanocomposite was determined to be 50–70 nm based on FESEM analysis. The results obtained from this study showed that the NiFe2O4 magnetic nanocomposite could absorb penicillin G with a high maximum adsorption capacity in the following optimal conditions: pH = 9, nanocomposite dose: 0.3 g/L, penicillin G concentration: 30 g/L, contact time: 20 min, and time temperature: 313 K. Additionally, the results of the thermodynamic study of the adsorption process showed that the values of ΔH and ΔS are positive and ΔG is negative. According to the results of isotherm studies, the experimental data of penicillin G adsorption by the magnetic NiFe2O4 nanocomposite follow the Temkin model with R2 = 0.99 and pseudo-second-order kinetics with R2 = 0.99. In general, the findings obtained from this study showed that the magnetic NiFe2O4 nanocomposite has a high efficiency as an adsorbent for the adsorption of penicillin G.

We gratefully acknowledge the Research Council of Birjand University of Medical Sciences (Grant Number: 456905) for the financial support.

This paper was approved as the Ph.D. thesis on the BUMS ethical committee with code IR.BUMS.REC.1401.004.

All authors contributed to the study's conception and design. Material preparation, data collection, and analysis were performed by E.D., A.N., and S.M-D. The first draft of the manuscript was written by E.D. and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

This research project was funded by the Birjand University of Medical Sciences (Grant Number: 456905).

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.

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