1 Introduction

Medications, in general, are synthesized to maintain their physical and chemical properties for a time sufficient to serve a therapeutic purpose for some form of disease (Bila and Dezotti 2003). When administered, they can be partially metabolized and excreted in the urine and feces and, as a consequence, can enter sewage treatment plants, where traditional effluent treatment is inefficient to degrade them, thus contaminating those water resources (di Bernardo and Dantas 2005; Kolpin et al. 2002). Thus, the increased concentration of some residual drugs may cause environmental and public health impacts (Jorgensen and Halling-Sorensen 2000; Doorslaer et al. 2014). Drugs that do not undergo an effective degradation process prior to their entry with effluents into rivers and lakes generate aquatic toxicity, genotoxicity, alteration of the reproductive cycle of aquatic species, and endocrine disorders (Kümmerer et al. 2000). Among the drugs, antibiotics have the most damaging consequences, where ciprofloxacin is one example of antibiotics. These are more active in infections against gram-negative bacteria and widely used in treatments of various types of infections, such as: urinary, respiratory, gastrointestinal, cutaneous, orthopedic, and articular (Mierzwa and Hespanhol 2005). However, a major problem is the difficult removal of these when they are released into the environment (Melo et al. 2009; Prieto et al. 2011).

Some studies investigate the removal using the adsorption method because it presents some advantages like cost-benefit, flexibility, simple design, easy operation, insensitivity to toxic pollutants, and the possibility of being reused (Klavarioti et al. 2009). Adsorbents such as the carbon materials (Ji et al. 2011; Li et al. 2014), metal oxide (Ji et al. 2013), polymers (Tan et al. 2013), and zeolites (Blasioli et al. 2014; Braschi et al. 2010) were previously studied and presented limitations as limited pore sizes, since the antibiotic molecules shown are in the nanometer range, or did not show adequate functionality for the adsorption of antibiotics, since they have complex molecular formulas and different functional groups. Developing of new adsorbents and of internal adsorption mechanisms are of great interest in the research of adsorption antibiotics (Gao et al. 2015).

Previous works reported the release of drugs using drugs similar to ciprofloxacin in different structures based on functionalized silica. García-Muñoz et al. studied the influence of textural structures and properties of these materials on the controlled release of methylprednisolone hemisuccinate, where it was observed that the structures with better properties obtained higher adsorption of the drug (García-Muñoz et al. 2014). The literature reports the functionalization of structures using different functional groups and the results showed that for the functionalized structure with the higher amine content organosilane, the amounts of drugs adsorption were higher, in relation to non-functionalized samples (Ortiz-Bustos et al. 2017; Martín et al. 2018). Drug release rates in mesoporous silica materials are strongly influenced by the adsorption behavior of the species when they are close to the functional groups on the surface, which are measured by molecular interactions at specific sites (Morales et al. 2016).

We can also cite some metal oxides as good adsorbents (Pelaez et al. 2012; Danwittayakul et al. 2015), among which titanium dioxide (TiO2) and zinc oxide (ZnO) are widely used (Etacheri et al. 2015; Chang et al. 2016). This is because they exhibit a good stability in aqueous media, low cost, as well as environmentally favorable features (Akyol and Bayramoğlu 2005). Researchers reported impregnation of ZnO supported on silica structures, being the mesoporous silica structure. Because these materials have relatively large pore sizes (2–30 nm), they allow drugs with larger structures to access the mesoporous inner surfaces. In addition, both the internal mesochannel surfaces and external particle surfaces of mesoporous silicas can be functionalized with a variety of chemical structures that assist in a greater interaction with the pharmaceuticals and thus influence the adsorption and release properties of these species (Calvillo et al. 2008; Izquierdo-Barba et al. 2009; Gignone et al. 2015). Within the mesoporous silicas found in the literature, the SBA-15 becomes an excellent option, because they present good stability, as well as surface area and diameter of excellent pores (Babu et al. 2012). This combination showed the ability of the material as an adsorbent aiding in the removal in pollutants found in the aquatic environment (Popova et al. 2016).

This work was carried out with the purpose of studying the adsorption process of the antibiotic ciprofloxacin over ZnO supported on SBA-15 molecular sieve.

2 Experimental

2.1 Reagents

Zinc Acetate (Aldrich); potassium hydroxide (KCl, Vetec); isopropyl alcohol (Dynamic, 95%); 2-aminoethanol (MEA) (Aldrich); tetraethyl orthosilicate (TEOS, Aldrich, 98%); pluronic P123 (Aldrich); hydrochloric acid (HCl, Vetec, 37%); deionized water; ethyl alcohol (Dynamic, 95%); and 10−4 M ciprofloxacin solution (Aldrich, 98.9%) were used in the study.

2.2 Methods

2.2.1 Synthesis of ZnO Nanoparticles

First, 8.23 g of zinc acetate (Zn(Ac)2) in 15 mL of isopropyl alcohol was added. Under this mixture, 2.3 mL MEA with 15 mL of isopropyl alcohol was added. After preparation, all solutions were mixed slowly. The final solution was then oven dried at 100 °C for 2 h and calcined for 3 h at 600 °C with an air flow rate of 100 mL/min.

2.2.2 Synthesis of SBA-15

A typical synthesis method to obtain pure SBA-15 by the hydrothermal method is described with molar ratios: 1 TEOS:0.015 P123:2.75 HCl:166.0 H2O. Initially the pluronic P123 was dissolved in deionized water and HCl. That mixture was maintained at 40 °C for 24 h under constant stirring. The formed gel was transferred to a stainless autoclave, which was sealed in a hydrothermal system at 100 °C for 48 h. The obtained sample was washed with 50 mL of ethyl alcohol several times, vacuum filtered, and calcined at 600 °C for 4 h under refluxing air to decompose of the template (Luz Jr et al. 2010).

2.2.3 Functionalization of the SBA-15 with ZnO

The functionalization process was performed by the post-synthesis method with the addition of 0.5 g of SBA-15 in 25 mL of water, and the mixture received the nomenclature of (S1). A dispersion with the required mass of the ZnO nanocrystals was also prepared to achieve the proportion of each of the adsorbents (5, 10, and 20%) which received the (S2) nomenclature. The solutions (S1) and (S2) were mixed and subjected to constant stirring at a temperature of 80 °C until all of the liquid had evaporated. The resulting solid was collected and dried in the oven at 100 °C for 2 h and then calcined at 600 °C for 5 h with airflow rate of 100 mL/min. The same method synthesized the other samples, making the changes in the mass of the zinc oxide nanocrystals according to the mass percentage of the adsorbent.

2.3 Characterization of the Samples

For identifying the spatial arrangements of the samples, x-ray diffraction was performed in the 2θ bands of 0.5–5° and 10–80°, in low and medium angle in the Shimadzu equipment, model XRD 6000, with radiation source of CuKα (λ = 0.15406 nm), nickel filter, operating at 30 kV and 30 mA at 0.5°/min speed. The textural properties and adsorption isotherms, as well as the specific area investigation, were obtained by the Brunauer-Emmett-Teller (BET) method, using the Micromeritics ASAP-2020 equipment, with a relative pressure range (P/P0) of 0.01 to 0.99 at the temperature of the liquid nitrogen (77 K). The micropore volume (Vmic) and area (Smic) were determined by applying the t plot equation to the N2 adsorption isotherms. The software micromeritics was used to generate the non-linear density functional theory (NLDFT) pore size distribution (PSD) curves from the N2 adsorption isotherms using adsorption branch and the kernel “N2, 77K, Cylindrical Pores in an Oxide Surface” of the mentioned software. To determine the x-ray intensities and the density of the active sites of the adsorbents of the samples, FRX was performed using a ZnO-SBA-15 pellet in the different mass proportions (5, 10, 20%), using the Rigaku RIX 3100 equipment. The absorbance spectra of the solutions were obtained on the Shimadzu spectrophotometer, model UV-2600 in the range between 200 and 800 nm.

2.4 Adsorption Test

Adsorption was performed using the following procedure: 40 mg of the adsorbent, previously activated at 300 °C for 180 min, were dispersed in 100 mL of ciprofloxacin solution (10−4 mol/L). The suspension was kept under continuous agitation (without light) for 180 min at 25 °C. During that process, at certain time intervals, a 3-mL aliquot was withdrawn and the samples were centrifuged at 100 rpm using an IKA® mini G instrument for 2 min for UV-Vis analysis with 200–800 nm scanning. The process was repeated for the other adsorbents. A calibration curve was made to determine the concentration of the drug as a function of adsorption and the wavelength analyzed was 273 nm, which is the most intense band of ciprofloxacin.

The adsorbent capacity of the adsorbent, q e (mg/g), was calculated according to Eq. (1) (Peng et al. 2016a, b).

$$ {q}_e=\left( Ci- Cf\right).\frac{V}{M} $$
(1)

where q e is the adsorbed amount (mg/g), V is the volume of the solution, and M is the adsorbent mass.

The kinetic study for the adsorption of ciprofloxacin was carried out in a batch process. An amount of 100 mL of 2.5, 5, 15, and 25 mg/L concentrations of ciprofloxacin solution were placed in contact with 40 mg of the adsorbents at a temperature of 25 ± 1 °C, with the time varying from 0 to 180 min, and the saturation equilibrium was reached in the first 60 min of the test. After each period, the supernatant was separated from the adsorbent by centrifugation (at 100 rpm for 2 min). The concentration was determined by spectrophotometry in the UV-Vis region using the equation obtained by the calibration curve previously done before the tests. The results of the kinetics were adjusted to three kinetic models: pseudo-first order, pseudo-second order, and intra-particle diffusion (Ho and McKay 1998, 1999).

2.5 Adsorption Isotherms

The adsorption isotherms were performed by placing 40 mg of adsorbent in contact with 100 mL of ciprofloxacin solution in concentrations of 2.5 to 25 mg/L. The system was placed under stirring at 25 °C (298.15 K). After stirring, the supernatants were separated from the adsorbent by centrifugation (at 100 rpm for 2 min). The adsorbed amount was determined by spectrophotometry in the UV-Vis region (Eq. 1).

The models of Langmuir (Eq. 2) (Langmuir 1916), Freundlich (Eq. 3), and Temkin (Eq. 4) (Gessner and Hasan 1987).

$$ \frac{C_e}{q_e}=\frac{1}{q_{\mathrm{max}}^b}+\frac{C_e}{q_{\mathrm{max}}} $$
(2)
$$ \log {q}_e=\frac{1}{n}\log {C}_e+\log {K}_f $$
(3)
$$ {q}_e=\frac{1}{n_T}\ln {K}_T+\frac{1}{n_T}\ln {C}_e $$
(4)

2.6 Adsorption Test with Temperature Variation

The maximum adsorbed amount per 180 min of the adsorbent was analyzed. In this study, 40 mg of the ZnO-SBA-15 adsorbent (10%) was added to 100 mL of ciprofloxacin solution of 10 mg/L and stirred for 180 min at 25 ± 1 °C, 35 ± 1 °C, and 45 ± 1 °C. At the end of the estimated time for each aliquot, the material was centrifuged at 100 rpm for 2 min and the supernatant was quantified by UV-Vis spectrophotometry.

The thermodynamic parameters ΔG° (Gibbs free energy), ΔH° (enthalpy), and ΔS° (entropy) were obtained for the adsorption processes at three different temperatures, 25, 35, and 45 °C (298.15, 308.15, and 318.15 K), using Eqs. 5 and 6:

$$ \log {K}_e=\frac{{\varDelta S}^{{}^{\circ}}}{2303R}-\frac{{\varDelta H}^{{}^{\circ}}}{2303 RT} $$
(5)
$$ {\varDelta G}^{{}^{\circ}}={\varDelta H}^{{}^{\circ}}-{T\varDelta S}^{{}^{\circ}} $$
(6)

where R is the gas constant (J/mol K), T is the temperature (K), and K e is the equilibrium constant at temperature T, obtained by the Freundlich model (Gessner and Hasan 1987; Li et al. 2014).

2.7 Adsorption Test with pH Variation

The adsorption sweep of the pH values was performed with pH adjustment (in the values: 2, 5, 6, 7, 8, 9, and 12) of ciprofloxacin concentration of 10 mg/L. The pH adjustment was performed using 0.5 mol/L solutions of HCl and NaOH. Subsequently, about 100 mL of solution of each pH was added to about 40 mg of the adsorbent and placed under continuous stirring at a temperature of 25 ± 1 °C for 60 min, time required to reach equilibrium. After the shaking time was over, the samples were centrifuged at 100 rpm for 2 min and quantified by UV spectrometry.

3 Results and Discussion

3.1 X-ray Diffraction and N2 Adsorption/Desorption

X-ray patterns in low angle, shown in Fig. 1, demonstrated that all samples show five diffraction peaks indexed to planes (100), (110), (200), (210), and (300), which are characteristic of two-dimensional mesoporous materials with P6mm symmetry, like to SBA-15 molecular sieve (Zhao et al. 1998; Sanz-Pérez et al. 2017). This fact indicates that the SBA-15 hexagonal mesoporous structure was sustained after the ZnO incorporation (Zhang et al. 2000). However, with the ZnO incorporation on the SBA-15, there was a reduction in diffraction peaks intensity, indicating the impregnation promoted the increase in mesoporous arrangement (Taghavimoghaddam et al. 2012; Sareen et al. 2015). On the other hand, for the ZnO-SBA-15 sample (10%), the effect of the impregnated amount did not significantly change the order of SBA-15 when compared to the other two impregnated samples. When observed, the diffraction peaks related to the plane (100), it is observed a shift to higher 2θ values, which can indicate that there was a decrease of the mesoporous parameter due to ZnO insertion on SBA-15 structure (Jiang et al. 2006).

Fig. 1
figure 1

XRD patterns of SBA-15, ZnO-SBA-15 (5%), ZnO-SBA-15 (10%), and ZnO-SBA-15 (20%) samples in low angle

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The x-ray diffraction in a wide angle of the ZnO nanocrystals employed in this research, in which all Bragg diffraction peaks are shown in Fig. 2. All Bragg diffraction peaks are typical of hexagonal zinc oxide crystals (JCPDS: 36-1451) (Chang et al. 2016). The Sheer equation determined the size of the ZnO nanoparticles, which have an average size of 39.4 nm. The results show that the synthesized ZnO nanocrystals have a hexagonal and monophasic wurtzite structure (Mayrinck et al. 2014). N2 adsorption/desorption isotherms of all solid samples are shown in Fig. 3.

Fig. 2
figure 2

XRD patterns of ZnO-SBA-15 (5%), ZnO-SBA-15 (10%), and ZnO-SBA-15 (20%) samples in wide angle

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Fig. 3
figure 3

N2 adsorption/desorption isotherms of SBA-15, ZnO, ZnO-SBA-15 (5%), ZnO-SBA-15 (10%), and ZnO-SBA-15 (20%) samples

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The sample of ZnO nanocrystals shown above has type-III isotherm and H3 type hysteresis, which is characteristic of nonporous with the presence of adsorbed volume related to interstitial or interparticle spaces (Carraro et al. 2014; IUPAC 2015). As the nanoparticles of ZnO are not porous, the formation of interstices between the nanoparticles of ZnO can explain the phenomenon, the material presents pore volume corroborating with the values of volumes for materials found in the literature and that present the same characteristics of these nanoparticles (Lv et al. 2011; Al-Kahlout 2014).

The samples of SBA-15 incorporated with different percentages of ZnO (Fig. 4) have a type-IV (a) isotherm with type-HI hysteresis loop (Carraro et al. 2014; IUPAC 2015), which is characteristic of uniform mesoporous materials and cylindrical pore systems, as expected when one has a molecular sieve of the SBA-15 type (Moosavi et al. 2012).

Fig. 4
figure 4

Ciprofloxacin adsorption on ZnO-SBA-15 (10%)

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The textural properties of the samples were obtained from nitrogen adsorption/desorption isotherms, as well as by the x-ray diffraction results, and are shown in Table 1.

Table 1 Textural properties of the samples determined from the nitrogen adsorption/desorption isotherms at 77 K, applying the BET, t plot, and NLDFT models
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In the surface area data, calculated by the BET method, shown in Table 1, it is observed that a surface area decreases when the incorporated oxide content increases, which can mean that the oxide is incorporated on SBA-15 external surface (Bhuyan et al. 2018).

In addition, it is observed in Table 1 that mesoporous parameter (a0) is smaller in impregnated samples than SBA-15 sample, as beforehand indicated by XRD patterns (Fig. 1). This fact may be associated to decrease in average pore diameter (Dp) or in wall thickness (Mihai et al. 2010). However, until analyzing Table 1, it can see that impregnated samples have a higher average pore diameter in comparison to that of SBA-15 sample. This apparent contradiction can be explained by the higher Dp of ZnO (18.16 nm) than that of SBA-15 (5.89 nm). Thereby, the ZnO incorporation on SBA-15 surface promotes an increase in the mean of pore diameter. This explanation is corroborated by average pore diameter increasing with ZnO content increase in impregnated samples.

3.2 Adsorption Result

Table 2 shows the q e results, as well as the adsorption and kinetics study for ZnO, SBA-15, ZnO-SBA-15 (5%), ZnO-SBA-15 (10%), and ZnO-SBA-15 (20%):

Table 2 q e value of the samples of ZnO, SBA-15, ZnO-SBA-15 (5%), ZnO-SBA-15 (10%), and ZnO-SBA-15 (20%)
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From Table 2, it can be observed that the values of q e are proportional to the incorporated amount of ZnO in the SBA-15, and that the effect of the incorporation improves the adsorption, since, when comparing the mass of pure ZnO to the one of the adsorbent ZnO-SBA-15 (20%), which is 20% of the pure, the adsorption value of ciprofloxacin is very close, showing that the process becomes more effective with the incorporation of ZnO.

Figure 4 shows the adsorption of ciprofloxacin in the sample of ZnO-SBA-15 (10%) at 25 °C (Table 3). According to the results shown in Fig. 4, it is possible to observe that the adsorption equilibrium was reached with 60 min of test in all the samples, regardless of the ZnO percentage of the sample, and that the adsorbed amount is proportional to the amount of ZnO impregnated in SBA-15.

Table 3 Parameters obtained with the Langmuir, Freundlich, and Temkin isotherm models for the adsorption of ciprofloxacin in samples at 25 °C (298.15 K) and saturation time of 180 min
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The Freundlich model describes a non-ideal adsorption on heterogeneous surfaces with multiple layers of adsorption. That model assumes that the strongest binding sites are occupied first and that binding strength decreases with increasing site occupancy degree (Gessner and Hasan 1987; Peng et al. 2016a). In all cases, the R2 values of Freundlich were very close to 1, showing it is the model that best suits the case. When the values of n > 1, there is a strong indication of the presence of highly energetic sites and the greater that difference between n and 1, the greater the distribution of that binding energy on the surface of the adsorbent. Those values can also suggest the occurrence of cooperative adsorption, in which they involve strong interactions between the molecules of the adsorbate itself, values of n between 1 < n < 10 indicate favorable adsorption (Desta 2013; Jalil et al. 2015; Danalioğlu et al. 2017).

It is also possible to observe that, for the ZnO and SBA-15 samples, the value of n < 1 shows an unfavorable adsorption for the pure samples. Nevertheless, in the samples where impregnation occurred, an increased value of n occurs, showing that the impregnation improves the adsorption of ciprofloxacin in the adsorbents. There is also a decreased ZnO-SBA-15 (20%) sample, which may be because the micropores are blocked in that sample, as shown in Table 1 of textural properties. The sample with the highest qmax is ZnO-SBA-15 (10%), with 446 mg/g, and there is a reduced value of the equilibrium constant and of n, with an increased percentage of zinc oxide incorporation in SBA-15.

From the correlation factor (R2) values, it was possible to determine that the model that best suits that adsorption is of pseudo-second order, because the correlation values approach to 1. That adsorption mechanism shows that the reaction on the surface of the adsorbent is the step that controls the adsorption rate. The nature of the sorption process depends on the physical or chemical characteristics of the adsorbent system and on the conditions of the system (Peng et al. 2015, 2016a). The second-order model suggests that the adsorption process of ciprofloxacin is due to the chemisorption of that material with the adsorbent, and the ZnO-SBA-15 (10%) adsorbent has the highest correlation factor among all, R2 = 0.9999 (Azizian 2004; Yan et al. 2017).

That sample also has a higher velocity constant K2 = 0.01136, which shows us that the adsorption velocity for that sample is the largest among the others (Peng et al. 2016a). Another relevant fact to the study is that the q e values obtained in Table 2 are in tune with the theoretical q e results obtained by the pseudo-second-order model; all values are very close, which shows that the model followed by the pseudo-second order is the one closest to the adsorption of ciprofloxacin in the samples Table 4 summarizes all models.

Table 4 Kinetic adsorption models in ciprofloxacin solution 10 mg/L
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3.3 Influence of pH

Figure 5 shows the relationship between the amounts of ciprofloxacin in the ZnO-SBA-15 (10%) sample as a function of the pH of the medium. The increasing sequence of the adsorption capacity, in which increasing the hydrophobicity of mesoporous silica results in the best adsorptive property of the most hydrophilic adsorbent (Gao et al. 2015). The adsorption is proportional to the electrostatic interaction between the adsorbent and the adsorbate. The pH of the aqueous solution is an important parameter for controlling the adsorption process. In a low pH condition, the destruction of the zinc oxide structure occurs, being converted to Zn2+ ions, which inhibits the interaction between the participants, reducing the adsorption. It is observed that at values of pH < 4 and pH > 8, the sorption capacity is very low (Ghasemi and Azizi 2017). At the natural pH (near the isoelectric point of ciprofloxacin), the ciprofloxacin present in the solution in zwitterionic form increases the electrostatic interaction between it and ZnO, improving the adsorption. At high pH, the ciprofloxacin present undergoes repulsive interaction between OH− anions. For ciprofloxacin, there is protonation of the amine group at a pH below 6.1 and deprotonation of the negatively charged carboxylic group. The maximum adsorption corresponded to the zwitterionic species (Jiang et al. 2013; Ma et al. 2015; Peng et al. 2016a, b). Some studied materials reported behavior similar to that seen in the structure of ZnO (El-Kemary et al. 2010; Danalioğlu et al. 2017).

Fig. 5
figure 5

Relationship between the adsorbed amounts at equilibrium (q e ) and the pH

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3.4 Thermodynamic Parameters

The value of Gibbs free energy (ΔG°) Table 5 was calculated by the equation ΔG° = −RTlnK e , where K e can be the Freundlich equilibrium constant or the distribution constant, determined by the ratio of the amount adsorbed at equilibrium by the concentration value at equilibrium (Peng et al. 2016a). In order to determine the ΔG°, the distribution constant was used, and the calculated value by the Freundlich constant is very close to the value determined by the distribution constant. Equation 10 also determined the values of ΔH° and ΔS°.

Table 5 Thermodynamic parameters obtained for ciprofloxacin adsorption in samples at 25, 35, and 45 °C (298.15, 308.15, and 318.15 K)
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The influence of temperature is an important factor in the actual application of the antibiotic removal process. Furthermore, one may observe that an increased ciprofloxacin adsorption occurs with increasing temperature, indicating that ciprofloxacin adsorption under the material is favored at higher temperatures, which shows that the process has an endothermic nature (Miao et al. 2016; Peng et al. 2015). The enthalpy variance value shows that the nature of the interaction between the active sites of the adsorbent and the adsorbate is of physiosorption (Zhang et al. 2007). The increased amount of adsorbed ciprofloxacin with increasing temperature can be attributed to the increased mobility of the molecules in solution or also the activation of some new active sites on the SBA-15, where it is seen that after the addition of metal oxide, the negative value of ΔG increased (Wang et al. 2013; Konicki et al. 2013). By the value of ΔG obtained using the K d distribution constant, we can observe that an increased temperature also increases the spontaneity of the reaction, as shown in Table 4 (Peng et al. 2014).

4 Conclusion

The characterization results of ZnO-SBA-15 (5%), ZnO-SBA-15 (10%), and ZnO-SBA-15 (20%) adsorbents synthesized by the post-synthesis method showed that the oxide adsorption was efficient in the catalytic support and that the zinc oxide nanoparticles were efficiently synthesized by the proposed method. With the x-ray diffraction analysis, one observed that the incorporation of the zinc oxide did not damage the mesoporous structure of the SBA-15 molecular sieve. Through the N2 adsorption and desorption analysis, one observed that there was good absorption by zinc oxide nanoparticles in the SBA-15, thus causing a decrease in the specific surface area and increase in pore volume. With UV-Vis spectroscopy, it was possible to analyze the adsorption caused by the use of the adsorbent in the ciprofloxacin solution. The Langmuir, Freundlich, and Temkin models were used to describe the isotherms, and the Freundlich model was the most adequate in comparison with the Langmuir and Temkin model, indicating the process involved in the cooperative sorption. In addition, the ZnO-SBA-15 (10%) sample had higher sorption capacity and faster adsorption rates. The kinetic model of pseudo-second order better interpreted the rates of sorption of ciprofloxacin on the samples. This study also demonstrated that neutral or zwitterionic species have significant affinity for adsorption with the material.