Phyto-assisted synthesis of magnetic NiFe₂O₄ nanocomposite using the Pulicaria gnaphalodes methanolic extract for the efficient removal of an antibiotic from the aqueous solution: a study of equilibrium, kinetics, isotherms, and thermodynamics Open Access

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.

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.

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).

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.

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.

To determine the pH_zpc, 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 pH_zpc.

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 > pH_pzc) 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).

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 = ((C₀–C_e) 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.

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).

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.

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 q_e 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.

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.

The values of A_T, b_T, 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.