Removal of Penicillin G from aqueous solutions by a cationic surfactant modified montmorillonite

Graphical abstract


Specifications
The effects of different parameters such as surfactant loading rate onto the clay, solution pH, contact time, adsorbate concentration and temperature were explored on the sorption of Penicillin G from aqueous phase Experimental design: The sorption process was conducted in batch mode by 100 mL of the drug solutions containing the clay adsorbent Trial registration: No applicable Ethics: No applicable Value of the Protocol HDTMA-Mt as a cost-effective and eco-friendly adsorbent was used for the removal of Penicillin G from aqueous media. Various kinetics, isotherms and also thermodynamic data obtained by this study are useful for designing and planning sorption system of Penicillin G removal by the modified clay in water and wastewater. The pseudo-second kinetic (R 2 = 0.999) and Freundlich isotherm (R 2 = 0.915) models best fitted the experimental data of Penicillin G by the adsorbent.

Description of protocol
Data Concern about water pollution by different pollutants from human activities is becoming greatly increased in many developing and developed counties [1][2][3][4]. Penicillin G or Benzylpenicillin is one of the common antibiotics, which is used successfully for prevention and treatment of many bacterial infections in humans and animals [5,6]. After use by human and animals, up to ninety percent of the antibiotics may be excreted via urine and faeces into sewage and eventually in the water bodies and environment [7,8]. Antibiotics in environment may also increase the problem of development and spread of antibiotic resistance, posing a potential threat to public health, since they can be released into the environment after their use [9,10]. Nowadays, antibiotics have been found in the effluents of many pharmaceutical industries and hospitals, sanitary sewage, surface water and groundwater [11]. Therefore, development of an effective method is greatly desired for the treatment Penicillin G from effluents in order to protect the public health in communities. Adsorption can be considered as an effective method for the uptake of many contaminants from domestic and industrial effluents [7].  Table 1 lists the main physical and chemical characteristics of Penicillin G. The experimental runs were carried out according to Table 2. The FTIR and XRD patterns of the raw and modified montmorillonite are shown in Fig. 1. The influences of different parameters including loading rate of surfactant onto the clay, solution pH, contact time, drug concentration, and temperature are presented in Figs. 2-6. For Fig. 3(b), at pH value lower than pHzpc, the adsorbent surface becomes positively charged, while at pH more than pHzpc, the adsorbent surface is negatively charged. The pHzpc value obtained for the adsorbent was 8.5, that is the pH at which the curve crosses the line pH initial = pH final . Also, Table 3 shows kinetics, isotherms and thermodynamic studies applied in this research. The values of various kinetics and isotherms models and thermodynamic are listed in Tables 4-6, respectively.

Materials
Montmorillonite clay was purchased from Laviosa Co (Italy). Penicillin G sodium salt (<96%) antibiotic and HDTMA surfactant (!99%) were provided from Sigma Aldrich Co (USA). Other chemicals including HCl and NaOH were obtained from the Merck Co (Germany). To adjust solution pH, HCl and NaOH (0.1 M) were used in the experiments. The stock solution (1 g/L) of Penicillin G was weekly made by distilled water and stored at refrigerator (4 C). The desired working solutions were prepared using dilution of the solution.        Freundlich [19,20] lnq e ¼ ln k f þ 1 n lnCe lnq e vs: lnCe 1 n ln k f Kinetics Pseudo-first order [21,22] ln q e À q t ð Þ ¼ lnq e À k 1 t ln q e À q t ð Þ vs: t k 1 lnq e Pseudo-second order [23,24] Intraparticle diffusion [8] q t ¼ K id t 1 2 þ C q t vs: t 1 2 K id C Thermodynamics [25] DG ¼ ÀRT ln k,

Modification of montmorillonite
First, 30 g of montmorillonite clay was dissolved in one liter of distilled water. The suspension was mixed at room temperature (25 C) using a mechanical stirrer (600 rpm for 24 h), and after that it was centrifuged (6000 rpm for 15 min). The above process resulted in the separation of impurities such as quartz and iron oxide in the bottom of clay. After centrifugation, the impurities were separated and the treated clay was dried (60 C for 24 h). The purified clay was finally ground and sieved to 125 mm [12].
The above purification action increased the cation exchange capacity (CEC) from 86 meq to 108 meq per 100 g of the clay. The obtained clay was finally modified by different loading rates of HDTMA and used in the experiments.

Study design
The experiments in this study were conducted in batch mode at room temperature. All the testes were carried out by 100 mL of the solution containing Penicillin G into 250 mL Erlyn myer flasks via 0.1 g of the modified clay. The suspensions were mixed by an orbital shaker (250 rpm). The concentration of the drug was measured into the clear supernatant after centrifugation (6000 rpm for 15 min) by an UV/Vis spectrophotometer at maximum absorption wavelength of 313 nm. All the experiments were respectively performed according to Table 2. Eq. (1) was used to calculate the adsorption capacity [13,14]: where q e (mg/g) is adsorption capacity of clay, C 0 and Ce (mg/L) are the initial and residual concentrations of the contaminant in the solution, respectively. V (L) is the volume of the solution and m (g) is the clay mass used [15][16][17].

Analytical methods
The FTIR spectra of the raw-Mt and HDTMA-Mt were specified by a FTIR spectrophotometer (JASCO, FT/IR-6300, Japan) in wavelengths of 400-4000 cm À1 . The crystallite structure of the adsorbents was also determined via a X-ray diffractometer (Bruker, D8ADVANCE, Germany) by Ni filtered Cu Ka radiation (1.5406A o ). The concentration of Penicillin G into the cleared solutions was determined by an UV/Vis spectrophotometer (DR5000, Hach, USA).