
==== Front
Heliyon
Heliyon
Heliyon
2405-8440
Elsevier

S2405-8440(24)13066-6
10.1016/j.heliyon.2024.e37035
e37035
Research Article
Antibiotics pollutants in agricultural soil: Kinetic, sorption, and thermodynamic of ciprofloxacin
Sharifmand Mahrokh a
Sepehr Ebrahim e.sepehr@urmia.ac.ir
a⁎
Rasouli-Sadaghiani MirHassan a
Asri-Rezaei Siamak b
Rengel Zed cd
a Department of Soil Science, Faculty of Agriculture, Urmia University, Urmia, 57135-165, Iran
b Department of Clinical Sciences, Faculty of Veterinary Medicine, Urmia University, Urmia, Iran
c Soil Science and Plant Nutrition, WA School of Agriculture and Environment, The University of Western Australia, 35 Stirling Highway, PERTH, WA, 6009, Australia
d Institute for Adriatic Crops and Karst Reclamation, 21000, Split, Croatia
⁎ Corresponding author. e.sepehr@urmia.ac.ir
30 8 2024
30 9 2024
30 8 2024
10 18 e3703511 5 2024
5 8 2024
26 8 2024
© 2024 Published by Elsevier Ltd.
2024

https://creativecommons.org/licenses/by-nc-nd/4.0/ This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
The entry of antibiotics, as pollutants, into the environment has created great concerns. Environmental dynamics of antibiotics based on soil chemical properties need to be a better understanding of their chemical behavior. This research is focused on studying the adsorption behavior and kinetic mechanisms of ciprofloxacin (CIP) in an agricultural soil. For this purpose, a batch experiment was conducted at different times (5 min–24 h), and using initial concentrations of CIP (0–1 mmol L−1) in the soil. The adsorption processes as affected by pH and ionic strength were assessed based on the modeling with response surface methodology (RSM). According to the results, the sorption equilibrium was found within 240 min, and the pseudo second-order model was the best for describing the data. Increasing the initial CIP concentration increased CIP adsorption, but increases in ionic strength and pH had an inverse effect. Based on RSM modeling, the CIP adsorption was 7.31 and 7.03 (mg g−1) in the presence of NaCl and CaCl2 electrolytes, respectively, in the optimized conditions (pH 6.5 and ionic strength 0.01 mol L−1). The spontaneous nature of CIP adsorption was determined based on thermodynamic calculations (ΔG° = −10.8 to −12.4 kJ mol−1). The interaction of pH and ionic strength was described with the quadratic model. The obtained results contribute to understanding the CIP fate in the soil environment and facilitate decisions regarding entry and controlling soil contamination due to this antibiotic.

Graphical abstract

Image 1

Highlights

• The CIP sorption was modeled in agricultural soil by response surface method (RSM).

• The experimental data were fitted well to the pseudo-second order kinetic model.

• Increasing of initial concentration caused to increase of CIP adsorption.

• The interaction of pH and ionic strength was described with the quadratic model.

• Thermodynamic analysis suggested the CIP adsorption was spontaneous and exothermic.

Keywords

Ciprofloxacin
Isotherm
RSM
Soil contamination
==== Body
pmc1 Introduction

Antibiotics have been used in human medicine and animal husbandry for many years [1]. As a consequence, antibiotics are found in different environments, such as surface and groundwater, and soil [2,3]. There are several environmental problems caused by antibiotics, even in low concentrations, including risk to human health through alteration of the natural microbial system, development of antibiotic-resistant bacteria (ARB), and antibiotic resistance [4]. Removal of antibiotics as an emerging environmental pollutant has attracted increasing attention. Some examples of materials that are effective in removing pharmaceuticals products are Moringa oleifera (MO) seeds that contain a large amount of protein (20–50 %) [5], and nano-silica produced from rice husks were used for the adsorption of pharmaceutical contaminants [6]. Alameri et al. [7] used ACAF/Fe3O4/ZnO adsorbent to remove ciprofloxacin (CIP) antibiotic from the aqueous media. This adsorbent, an environmentally friendly compound, was prepared from activated carbon of Azolla filiculoides (AFAC), magnetized using Fe3O4, and stabilized using ZnO nanoparticles [8]. There are many studies on the adsorption of antibiotics from aqueous media [9,10], but few data could be found on removal of this pollutant from soil.

Although there are different methods for removal of antibiotics from the environment, the importance of adsorption methods is well recognized. The studies on ecotoxicology, transport, and degradation of different antibiotics in soil are essential [11]. Based on previous research [12,13], soil physical and chemical properties, especially co-existing ions, strongly influence antibiotic adsorption in soil. In addition, the molecular structure of the antibiotics can affect their sorption [14].

Ciprofloxacin is one of the most widely used antibiotics, which belongs to the family of fluoroquinolones [15], in medicine and animal husbandry [16]. Consequently, fluoroquinolones are present in relatively high concentrations in sewage sludge, manure, and soil [17]. Therefore, CIP concentration detected in the soil is from 0.32 μg kg−1 to 84.85 μg kg−1 [18]. The possibility for polluting or entering of this antibiotic into water bodies, crops, and as a result the food chain transfers is affected by the adsorption process [19]. Since the CIP is present in different ionic forms depending on pH [20], the adsorption of these forms in soil is influenced by the co-existing ions such as Na+ and K+ due to competition with CIP for sorption sites. However, there is a lack of knowledge on CIP sorption, especially in calcareous soil systems. This paucity of information on CIP strongly contrasts with the other common antibiotics, such as sulfonamides and macrolides [14,21].

Although there are many studies on the CIP antibiotic removal from contaminated water through the adsorption process [22,23], and some research has been done on the adsorption of CIP soils derived from volcanic materials [24], sediments [25], and quartz sand [26], but no comparable information exists on CIP adsorption in calcareous agricultural soil, with a particular focus on the modeling and optimization of effective conditions using response surface methodology based on central composite design (RSM-CCD). Therefore, this study was aimed to characterizing the kinetics of adsorption of CIP as affected by pH (4–9) and ionic strength (0.01–0.1 mol L−1) by using RSM in the presence of NaCl and CaCl2 electrolytes. In addition, thermodynamic parameters were calculated for CIP adsorption. This research provides a theoretical basis for the removal potential, adsorption behavior, and fate of CIP in contaminated soils, especially calcareous soils.

2 Material and methods

2.1 Chemicals

The CIP (purity >98 %) was purchased from Sigma–Aldrich (Munich, Germany). A stock solution was prepared using 0.5 g of CIP in 1000 mL of deionized water. The appropriate concentrations (1, 10, 20, 30, 40, 50, and 100 mg L−1) were diluted with deionized water. The CIP speciation has been reported [27] (Fig. 1).Fig. 1 (A) The CIP speciation and the cation, zwitterion, and anion forms as a function of pH [27], (B) chemical structure of CIP (1-cyclopropyl-6-fluoro-4-oxo-7-piperazin-1-yl-quinoline-3-carboxylic acid; C17H18FN3O3·HCl; purity >98 %, molecular weight 331.34 g mol−1; pKa1 = 6.18 and pKa2 = 8.76) [24].

Fig. 1

2.2 Soil sampling

A soil sample was collected from the depth of 0–20 cm of an agricultural field of West Azerbaijan province, Iran. Then it was air-dried, and sieved (<2 mm) to determine some physicochemical properties of the soil. The soil sample was analyzed based on standard methods: soil pH and electrical conductivity (EC) were determined at 1:5 w/v soil: deionized water ratio [28]. Soil calcium carbonate [29], and organic matter (OM) [30] were measured using the standard methods. Soil texture was determined based on the hydrometer method [29].

2.3 Kinetic experiment

The kinetic experiment at different periods (5, 15, and 30 min and 1, 2, 4, 8, 12, and 24 h) was carried out by mixing a 20 mL solution containing 0.3 mmol L−1 (100 mg L−1) CIP and 0.01 mol L−1 CaCl2 (background electrolyte) with 1 g soil at 25 ± 1 °C. The suspensions were shaken (150 g force) on a reciprocating shaker during 5, 15, and 30 min and 1, 2, 4, 8, 12, and 24 h, centrifuged at 4000 g force for 10 min, and filtered through a 0.22 μm syringe filter before HPLC analysis. The amount of antibiotic adsorbed on the soil (qe, mg g−1) was calculated by the following equation [14]:(1) qe=(Ci−Ce)×v/m

where Ci and Ce are the initial and equilibrium concentrations of CIP (mg L−1) in the aqueous phase, respectively. The volume of the aqueous solution and the soil mass used in the experiment are represented by V and m, respectively.

High-performance liquid chromatography (HPLC) with fluorescence detector (Knauer model) was used to measure the CIP concentration. The injection volume was 20 μL at 35 °C.

Common kinetic equations such as pseudo-first order, pseudo-second order, Elovich, parabolic, and exponential function kinetic equations were fitted to the experimental data [31]:(2) Ln(qe−qt)=Lnqe−K1t

(3) tqt=1qe2k2+tqt

(4) qt=A+(1/β)Lnt

(5) qt=a+bt1/2

(6) Lnqt=Lna+bLnt

The adsorption rate constant was represented by K1 (g mg−1 min−1) and K2 (g mg−1 min−1) parameters. The adsorption capacity at equilibrium time and t time were shown as qe and qt (mg g−1), respectively. The Elovich equation coefficients are β (g mg−1) and A (mg g−1 min−1), and the parabolic and the exponential function constants were represented by a and b.

2.4 Sorption experiment

To perform the sorption experiment, 0.01 mol L−1 CaCl2 was added to the soil sample (20:1 solution-to-soil ratio) into the 50 mL glass centrifuge tube and then spiked with CIP at seven initial concentrations (0, 0.1, 0.2, 0.4, 0.6, 0.8, and 1 mmol L−1). The samples were shaken at 25 ± 1 °C for 4 h. The suspensions were analyzed by HPLC after centrifuging at 4000 g force for 10 min and filtering the solution with syringe filter (0.22 μm) [32]. All experiments were carried out in triplicate. The linear forms of the common isotherm models, such as Temkin and Dubinin-Radushkevich and the linear model of Henry's law, were fitted to the experimental data [33]:(7) qe=BLnKT+BLnCe

(8) Lnqe=Lnqm−βεDR2

(9) Ɛ=RTLn(1+1/Ce)

(10) E=1/−2βDR

(11) qe=KdCe

The adsorbed CIP (mg g−1) and residual concentration in solution (mg L−1) were represented by qe and Ce, respectively. The adsorption capacity and intensity were shown by B and KT in the Temkin isotherm equation. The maximum sorption capacity (qm) is calculated based on the Dubinin-Radushkevich equation, E (kJ mol−1), and β (mol2 kJ−2) are the adsorption energy and Polanyi potential in the Dubinin–Radushkevich equation, respectively. R (kJ K−1 mol−1) is gas constant, T (°K) is temperature, and Kd (L g−1) is the sorption coefficient of Henry's law.

The percentages of cationic, neutral, and anionic species of CIP are expressed as a function of its pKa and pH of the soil [34]:(12) %cationicspecies=1001+10(pH−pKa1)+10(2pH−pKa1−pKa2)

(13) %neutralspecies=1001+10(pKa1−pH)+10(pH−pKa2)

(14) %anionicspecies=1001+10(pKa2−pH)+10(pKa1+pKa2−2pH)

2.5 Modeling of pH and ionic strength

Different pH values (4–9), ionic strength (0.01–0.1 mol L−1), and background electrolyte types (NaCl and CaCl2) were used as input parameters to the RSM technique (Table 1) to test their effects on CIP adsorption. The RSM is a set of mathematical techniques for a better understanding of the effects of independent variables on adsorption processes [35]. In this study, a central composite (a randomized RSM design) was used to assess the mathematical response. A central composite for two variables (pH and ionic strength) at two levels (the minimum and maximum values) was used as an experimental design model.Table 1 Summary of the factors in the CCD method.

Table 1Factor	Name	Minimum	Maximum	Coded Law (−1)	Coded Law (+1)	Mean	Std. Dev.	
A	pH	4.00	9.00	4.73	8.27	6.50	1.44	
B	Ionic strength	0.01	0.10	0.02	0.09	0.05	0.02	

2.6 Thermodynamics

The thermodynamic studies of CIP adsorption were conducted after adding 0.01 mol L−1 CaCl2 (1:20 soil-to-solution ratio) at 0.8 mmol L−1 (300 mg L−1) initial CIP concentration. The suspension was shaken in an incubator shaker at 283, 293, 303, and 313 K for 4 h (equilibrium time) at 180 g force, and centrifuged at 10000 g force. Analyses of the CIP were performed by HPLC. Thermodynamic parameters were calculated as follows [36]:(15) Kd=1000(qe/Ce)

(16) Ln(Kd)=ΔSR−ΔHRT

The sorption capacity and equilibrium constant are denoted by qe (mg g−1) and Kd (mL g−1), respectively. R is the gas constant (8.314 J mol−1 K−1).

The Gibbs free energy (ΔG0) was calculated as [36]:(17) ΔG=−RTLn(qe/Ce)

2.7 Statistics

To evaluate the goodness of fit, the root means square error (RMSE), and the coefficient of determination (R2) were calculated. The RMSE is expressed as:(18) RMSE=∑i=1n(Pi−Oi)2/n

The measured and predicted adsorbate values are represented by Oi and Pi, respectively, and n is the number of the initial adsorbate concentrations [37].(19) R2=∑(qmod−qexp‾)2∑(qmod−qexp‾)2+∑(qexp−qmod)2

where qmod and qexp are the constant value and equilibrium capacity, respectively, and n is the number of concentrations tested. The higher R2 and lower RMSE values indicate the improved goodness of fit to the obtained data. The Design-Expert (version 13) program was used for the regression analysis.

3 Results and discussion

3.1 Soil properties

Soil had about neutral value at pHwater 7.98, and ECs was 0.89 dS m−1. Soil calcium carbonate equivalent (CCE) was 22 %. The soil was classified as non-sodic (ESP <15 %), calcareous (CCE >5 %), and non-saline according to the Keys to Soil Taxonomy classification (USDA) [38]. Soil organic carbon was 6.5 g kg−1, and the soil texture was silt loam.

3.2 Contact time

The adsorbent capacity is affected by the contact time between adsorbent and adsorbate. According to the results (Fig. 2), the adsorption rate reached 96 % during the initial 240 min, then stayed steady. The maximum adsorption capacity was obtained to be 1.93 mg g−1. Table 2 and Fig. 3 summarize the kinetic model parameters. The statistical analysis demonstrated that pseudo-second model described the data well. According to Canales et al. [24], the CIP adsorption data in Ultisol and Andisol soils best fitted to the pseudo-second order kinetic model. Identical results were reported by previous studies for CIP adsorption (the contact time of 4 h) in sediment [25]. Previous research [39] demonstrated that the slowest stage could control the CIP adsorption. The adsorption of the CIP on activated carbon extracted from Azolla filiculoides in aqueous media, increased from 37.1 % to 94.25 % during a contact period from 10 to 60 min. At first, adsorption was fast because many sites were vacant and available [8]. Then, the adsorption rate decreases, probably due to the lack of vacant sites [40].Fig. 2 Adsorption kinetics of CIP on the studied soil.

Fig. 2

Table 2 The adsorption kinetic model parameters for CIP absorption.

Table 2Kinetic models	Coefficients	Values	
Pseudo-first order	K1 (g.mg−1 min−1)	0.00	
qe (mg g−1)	0.22	
R2	0.26	
RMSE	0.26	
Pseudo-second order	K2 (g.mg−1 min−1)	5.26	
qe (mg g−1)	1.92	
R2	1.00	
RMSE	0.02	
Elovich	A (mg g−1 min−1)	1.90	
1/β (mg g−1)	0.00	
R2	0.83	
RMSE	0.02	
Parabolic	a	1.91	
b	0.00	
R2	0.52	
RMSE	0.03	
Exponential function	a	1.902	
b	0.002	
R2	0.833	
RMSE	0.020	

Fig. 3 Different kinetic models fitted to the experimental data.

Fig. 3

3.3 Adsorption isotherms

The results of CIP adsorption are represented in Fig. 4, and the adsorption parameters are given in Table 3. Based on the results, the linear isotherm of the Dubinin-Radushkevich (R2 = 0.996 and RMSE = 0.028) and Henry model (R2 = 0.991 and RMSE = 0.233) described the data well.Fig. 4 Adsorption isotherms for CIP as affected by different initial concentrations.

Fig. 4

Table 3 The isotherm parameters of CIP adsorption in calcareous soil.

Table 3Models	Temkin	Dubinin-Radushkevich	Henry's law	
Parameters	B (J mol−1)	KT (L g−1)	R2	RMSE	qm (mmol g−1)	B (mol2 KJ−2)	R2	RMSE	Kd (L g−1)	R2	RMSE	
Adsorption	1.97	1.33	0.85	0.96	0.07	0.01	0.99	0.02	0.53	0.99	0.23	

The linear model divides the antibiotic between the soil solids and the solution phase [14]. Like other fluoroquinolones, CIP interacts strongly with the binding sites of the soil surface because the Kd value is high (533.93 mL g−1), indicating that CIP has a high capacity to be adsorbed on the soil solid phase [15].

The E parameter in the Dubinin–Radushkevich isotherm equation represents the type of sorption processes. The physical and chemical adsorption processes are characterized by E < 8 kJ mol−1 and E > 16 kJ mol−1, respectively [41]. The ion exchange processes have E values between 8 and 16 kJ mol−1. Based on our results (E = 5.02 kJ mol−1), the sorption of CIP on calcareous soil was physical. Identical results were reported by previous studies for the type of CIP adsorption processes (E < 8 kJ mol−1) in soils derived from volcanic materials [24]. The retention of CIP by soil colloids and ion exchange with soil natural cations could be the possible reasons of high adsorption capacity of this antibiotic on the solid phase of the soil.

The amphoteric nature of CIP leads to its ionization under soil-relevant pH conditions. At the pH studied, the CIP exists primarily (>84 %) in the neutral form, with small percentages in the anionic and cationic forms (14 % and <2 %, respectively). Therefore, the CIP is adsorbed strongly by electrostatic interactions. Given the calcareous conditions of the studied soil, calcium ions play an important role in binding functional groups of CIP with negatively charged sites. It has been reported that surface complexation was the main mechanism for CIP adsorption in soil systems [24]. However, the cation bridging and cation exchange processes are expected [35]. The Coulombian attraction could occur via cation bridging on aluminosilicate edges. Carrasquillo et al. [42] reported that the sorption of CIP in the zwitterion form to aluminosilicates is due to the greater distance between the anionic and cationic groups, which maximizes the Coulombic attraction.

3.4 Modeling of pH and ionic strength

The RSM-CCD was employed for statistical modeling and optimization of CIP adsorption by determining the optimal conditions, including pH and ionic strength (Table 4). The optimized conditions (pH 6.5 and ionic strength 0.01 mol L−1) revealed CIP adsorption of 7.31 and 7.03 (mg g−1) in the presence of NaCl and CaCl2, respectively.Table 4 Central composite design, optimal points, and response (CIP adsorption).

Table 4Runs	Factors	Response (mg g−1)	
(A = pH)	(B= Ionic strength)	(NaCl)	(CaCl2)	
1	9.00	0.055	7.27	6.31	
2	6.50	0.055	7.30	6.63	
3	4.73	0.087	7.28	6.53	
4	4.73	0.023	7.33	6.86	
5	6.50	0.055	7.30	6.63	
6	6.50	0.055	7.30	6.62	
7	6.50	0.010	7.31	7.03	
8	6.50	0.100	7.27	6.38	
9	4.00	0.055	7.28	6.56	
10	6.50	0.055	7.30	6.63	
11	6.50	0.055	7.30	6.64	
12	8.27	0.087	7.26	6.27	
13	8.27	0.023	7.30	6.66	

It is known that pH has a main role in the adsorption processes [43], which also occurred in the present study (Fig. 5). Decreasing pH caused an increase in CIP adsorption, and a similar effect was found for ionic strength. The same results were found for sulfadiazine (SDZ) and sulfamethoxazole (SMX) sorption on soils [14]. Cations such as Ca2+ in calcareous soils compete with CIP adsorption, especially by substituting the hydrogen ions of acidic groups such as COOH or OH groups [44]. The sorption coefficients of monovalent cations are distinctly larger than those of divalent cations (Kd (NaCl) > Kd (CaCl2)). This can be due to the increase in ionic strength and the competitive effect between soluble ions and CIP in the presence of CaCl2 compared with NaCl.Fig. 5 Counter plots of the effect of the pH and the ionic strength (IS) in background solutions NaCl (A) and CaCl2 (B) on adsorption CIP (Qe).

Fig. 5

Results show that the sorption decreased as the ionic strength increased in the presence of both electrolytes. A possible interpretation is that with increasing ion concentration in the solution phase, the antibiotic and background cations compete for adsorption at surface sites. Because low-energy sorption sites are occupied sooner than high-energy sites, competitive adsorption would occur when sorption sites with lower energy are fully occupied [14].

Based on CIP pKa and speciation, the maximum adsorption values appeared around pH = 6 (Fig. 5). The CIP was recognized as CIPH+ form (protonation of the amine groups) when pH was less than pKa1, which increased the CIP adsorption on negatively charged surface sites [26]. In the present study, when the pH value was between 6.18 and 8.76 (pka1 < pH < pka2), the CIP molecule behaved like a zwitterion, and carboxyl and amine groups predominated. Hence, in addition to the electrostatic interactions, the cation exchange was an adsorption mechanism in the soil. At pH higher than pKa2, carboxyl groups would be deprotonated (CIPOH−), and the CIP was adsorbed only through the cationic bridge. In general, sorption–desorption of antibiotics is influenced by soil pH [45].

In investigating the effect of independent variables on the CIP adsorption based on the central compound method, the adsorption rate was considered a response, and the regression equations were used between the independent variables and the response based on the quadratic models. Different regression models are given in Table 5, Table 6. Significant values (P-value <0.0001) were found for the CIP adsorption (F value was 2.2). The results showed that the presented equations predicted the CIP adsorption well because of high R2 (R2 adj and R2 non-adjusted) values.Y NaCl = +7227.1 + 37.3 A −805.2 B + 43.4 AB -3.3 A2

Y CaCl2 = +7828.1–374.7 A -4798.2 B −1955.3 AB +35.4 A2 +16485.3 B2

where Y is the response (sorption of CIP on calcareous soil), A and B are pH and ionic strength, respectively.Table 5 Analysis of variance (ANOVA) values for CIP sorption by calcareous soil in the presence of NaCl.

Table 5Source	Sum of squares	Df	Mean Square	F value	p-value prob > F	
Model	3512.1	4	878.0	13.7	0.001	
A = pH	478.2	1	478.2	7.4	0.025	
B= IS	2215.5	1	2215.5	34.7	0.000	
AB	23.8	1	23.8	0.3	0.557	
A2	794.5	1	794.5	12.4	0.007	
Residual	510.5	8	63.8			
Lack of Fit	510.1	4	127.5	1244.6	<0.0001	
Pure Error	0.4	4	0.1			
Cor Total	4022.7	12				
Std. Dev.	7.9	PRESS	2534.1	R2	0.99	
Adj R2	0.99	Pred-R2	0.99	Adeq Precision	11.3	

Table 6 Analysis of variance (ANOVA) values for CIP sorption by calcareous soil in the presence of CaCl2.

Table 6Source	Sum of squares	Df	Mean Square	F value	p-value prob > F	
Model	3.130E+05	5	62591.9	2.2	0.009	
A = pH	11513.2	1	11513.2	0.4	0.039	
B= IS	3168.6	1	3168.6	0.1	0.017	
AB	48392.3	1	48392.3	1.7	0.008	
A2	85381.8	1	85381.8	3.0	0.014	
B2	1.938E+05	1	1.938E+05	6.8	0.007	
Residual	1.991E+05	7	28448.8			
Lack of Fit	1.032E+05	3	34415.4	1.4	<0.0001	
Pure Error	95895.8	4	23973.9			
Cor Total	5.121E+05	12				
Std. Dev	8.6	PRESS	88403.3	R2	0.99	
Adj- R2	0.99	Pred-R2	0.99	Adeq Precision	3.8	

3.5 Thermodynamics

The calculated thermodynamic parameters are useful for a better understanding of CIP adsorption (Fig. 6). The results indicated that the CIP adsorption process was temperature-dependent and decreased with increasing temperature. Adsorptive forces between the active sites of the sorbent and the sorbate (CIP) are weakened with increasing temperature [25]; as a result, the CIP passage through the outer boundary of the adsorbent was diminished. Table 7 summarizes Gibbs's free energy (ΔG◦) at different temperatures based on the thermodynamic relationship (P = 101.3 kpa). The spontaneous nature of the adsorption processes was demonstrated with the negative ΔG◦ values. In addition, the exothermic nature was suggested by the negative enthalpy change values (ΔH°). The negative ΔS° value demonstrated that the process was entropy-decreasing. The ΔS° lesser than zero indicates decreased disorderliness at the solid-liquid interface [46].Fig. 6 Adsorption of CIP on the soil at different temperatures.

Fig. 6

Table 7 Thermodynamic parameters for the sorption of CIP onto soil at different temperatures.

Table 7Antibiotic	ΔH°
(J mol−1)	ΔS°
(J mol−1 K−1)	ΔG° (kJ mol−1)	
283 K	293 K	303 K	313 K	
CIP	−419.39	−0.84	−12.40	−12.45	−11.38	−10.80	

4 Conclusion

In conclusion, the experimental data were fitted well to the pseudo-second order kinetic model. More than 96 % of the CIP was adsorbed during the first 240 min. Both the Dubinin-Radushkevich and Henry models described the equilibrium data well. Dubinin–Radushkevich free energy parameter of sorption (E = 5.02 kJ mol−1) indicated that the CIP sorption process in the calcareous soil was physical and electrostatic interactions and the cation bridging were the dominant processes. The CIP adsorption was decreased by increasing ionic strength and pH. The CIP adsorption in the presence of NaCl was greater than that in the presence of CaCl2. The negative ΔG◦ and ΔH◦ values indicated the spontaneous and exothermic adsorption of CIP, respectively. The experimental results obtained in this study indicate mechanisms of the CIP adsorption as well as high retention of this compound in calcareous soil systems. Nonetheless, further studies are needed to evaluate the impact of other soil factors, such as organic matter and moisture content, on CIP sorption, uptake by plants, and biodegradation.

Funding

The authors gratefully acknowledge the Office of Vice Chancellor for Research and Technology, 10.13039/501100007298 Urmia University , Iran, for providing financial support and laboratory equipment for this study.

Ethical approval

This study does not involve human and/or animal content and has no ethical standards implications.

Data availability statement

Data will be made available on request.

Conflict of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

CRediT authorship contribution statement

Mahrokh Sharifmand: Writing – original draft. Ebrahim Sepehr: Writing – original draft. MirHassan Rasouli-Sadaghiani: Writing – review & editing, Methodology. Siamak Asri-Rezaei: Writing – review & editing. Zed Rengel: Writing – review & editing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Appendix A Supplementary data

The following is the supplementary data to this article:Multimedia component 1

Multimedia component 1

Acknowledgments

The authors are thankful to the Office of Vice Chancellor for Research and Technology, Urmia University.

Appendix A Supplementary data to this article can be found online at https://doi.org/10.1016/j.heliyon.2024.e37035.
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