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Separation Science and Technology
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Removal of ciprofloxacin from aqueous solution
using wheat bran as adsorbent
Tahira Sarwar Khokhar, Fakhar N. Memon, Ayaz Ali Memon, Fatih Durmaz,
Shahabuddin Memon, Qadeer Khan Panhwar & Saba Muneer
To cite this article: Tahira Sarwar Khokhar, Fakhar N. Memon, Ayaz Ali Memon, Fatih Durmaz, Shahabuddin Memon, Qadeer Khan Panhwar & Saba Muneer (2019) Removal of ciprofloxacin from aqueous solution using wheat bran as adsorbent, Separation Science and Technology, 54:8, 1278-1288, DOI: 10.1080/01496395.2018.1536150
To link to this article: https://doi.org/10.1080/01496395.2018.1536150
Published online: 25 Oct 2018.
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Removal of ciprofloxacin from aqueous solution using wheat bran as adsorbent
Tahira Sarwar Khokhara, Fakhar N. Memonb, Ayaz Ali Memona, Fatih Durmazc, Shahabuddin Memona,
Qadeer Khan Panhward, and Saba Muneera
aNational Centre of Excellence in Analytical Chemistry, University of Sindh, Jamshoro, Pakistan;bDepartment of Chemistry, University of Karachi, Karachi, Pakistan;cDepartment of Chemistry, Selçuk University, Konya, Turkey;dDr. M. A. Kazi Institute of Chemistry, University of Sindh, Jamshoro, Pakistan
ABSTRACT
Current study describes sorption of antibiotic drug (ciprofloxacin) by using nontoxic and biocom-patible carrier,i.e., wheat bran (WB). For sorption study, various parameters were optimized and Freundlich, Dubinin–Radushkevich, Langmuir, and Temkin isotherm models were applied to demonstrate the mechanism of sorption, while kinetics study for sorption was evaluated using diffusion models, pseudo-first-order kinetic (Langergren) and pseudo-second-order (Ho and McKay) kinetic models. In addition, thermodynamics study was also carried out. However, sorption of ciprofloxacin was pH depended and it showed 75% drug release in alkaline medium (at pH = 1.5) indicating the good release ability of WB for ciprofloxacin.
ARTICLE HISTORY Received 24 May 2018 Accepted 11 October 2018 KEYWORDS
Drug sorption; wheat bran; ciprofloxacin; kinetics; drug release
Introduction
The pharmaceutical occurrence in wastewater unfortu-nately causes adverse effects in the marine environ-ment. However, most of the wastewater treatment technologies are not designed to particularly treat such contaminants of emerging concern. Specifically, among the other pharmaceuticals, antibiotics have become a major environmental risk.[1,2] The misuse and less absorption of antibiotics lead to high water solubility and persistent behavior that represents the worldwide environmental pollution, which in turn causes serious health problems.[3]
Ciprofloxacin (C17H18FN3O3, MW = 331.4 g/mol) is
a broad spectrum fluoroquinolone synthetic che-motherapeutic antibiotic drug (Fig. 1) that is worldwide used to treat several bacterial infections by blocking bacterial DNA replication. It binds itself with an enzyme called DNA gyrase to prevent its ability of untwisting the DNA double helix required for DNA replication.[4,5] Ciprofloxacin is beneficial in the treat-ment of gastrointestinal anthrax and well regarded as the first line for the treatment of Crohn’s disease.[6,7]
The adsorptive removal of ciprofloxacin has become progressively an indispensable and more important task. For this, numerous conventional methods such as ozonation, oxidation, photocatalytic and photolytic treatments, electrochemical and peroxone processes have been explored. However, because of economic
consideration, the use of these methods is often limited.[8–10]
Owing to hundreds of applications in every field of science, sorption is considered an efficient treatment method for adsorptive removal of antibiotics.[11] Sorption process is a highly economical and valuable alternative of primary treatment, but for organic mat-ter, it is quite slow and rarely attains the equilibrium. Many researchers have proposed several nonconven-tional as well as low-cost sorbents including waste materials from industry, agricultural biosorbents and natural materials that can be potentially act as inexpen-sive sorbents.[12] Consequently, literature reports for such materials as sorbents include banana pith, rice ban, peanut shells, pine park, wood, peat, etc. They show either direct use or may be activated during sorption process.[13] Besides these, natural fibers show additional advantage over other materials due to their high biodegradable nature; environment friendly, abun-dantly available, cheap, and renewable nature contri-butes greatly to healthier ecosystem.[14] Recently, these natural polymers derived from plants have attracted the great interest of researchers due to their pharmaceutical applications in tablets as binders, diluents, and thick-eners in oral liquid and disintegrates.[15]In this regard, significant work has been carried out; for example, tea leaves were explored as pharmaceutical adsorbents by Seedher and Sidhu.[16] Chitosan/Graphene oxide was CONTACTFakhar N. Memon fakhar_memon2@yahoo.com Department of Chemistry, University of Karachi, Karachi, 75270, Pakistan
Color versions of one or more of the figures in the article can be found online atwww.tandfonline.com/lsst. 2019, VOL. 54, NO. 8, 1278–1288
https://doi.org/10.1080/01496395.2018.1536150
studied as a pharmaceutical carrier of low-cost green adsorbent by Chen et al.[17] Rem at el. have reported the sorption and desorption of trimethoprin antibiotic on cellulose acetate polymer and Attapuligate clay from aqueous solution.[18]
Keeping in view above examples, we have selected wheat bran (WB) for sorption of ciprofloxacin and its subsequent release at different pH values. The bran is commonly pealed out in the grinding of wheat into flour. WB and other correlated grain products are renowned to be nutritious foods, rich in iron, vita-min B, complex carbohydrates, fiber, and lots of other nutrients essential for healthy diet. Recently, WB apart from its nutritional aspects is highly apciated as an anticarcinogenic agent specially in pre-venting colon cancer.[19]
Current study presents the behavior of WB for the sorption and release of ciprofloxacin at different pH. This study is one of the possible applications for WB to be a potential candidate for pH-dependent drug deliv-ery application.
Material and methods
Chemicals
Ciprofloxacin used in this study was procured from commercially available source. WB was collected from a local market (Hyderabad, Sindh, Pakistan). NaOH and HCl were used to adjust the pH of solutions to the required value before mixing with the WB. Deionized water was used throughout the study. Instruments
Finest test (electrical) sieves with perforated plate (Octagon digital Lombard Road London SW19 3TZ, England) of 400, 300, 212, and 180 µm sizes were used. Fourier transforms infrared (FT-IR) spectro-photometer (Thermo Nicollet AVATAR 5700) was also used in the range 400–4000 cm−1 by applying
KBr pellet method. Perkin Elmer (Shelton, CT06484, USA) Lambda-35 double beam spectrophotometer
was used for UV–vis analysis and standard 1.00 cm quartz cells were used. Scanning electron microscopic (SEM) studies were performed using JSM-6490LV instrument (Joel, Tokyo, Japan) to get images. The pH was measured using Inolab pH meter 720 (Germany) containing glass electrode and internal reference electrode. A Gallenkamp thermostat auto-matic mechanical shaker (model BKS 305-101, UK) was used for batch sorption study.
Preparation of sorbent material
Adsorbent material was prepared by Achak et al. method.[11]Here, WB was obtained from local market. The collected material was washed several times to get rid of all dirt particles and any flour if present followed by drying in a hot oven at 50°C, for 12 h. The material was ground to 400, 300, 212, and 180 µm sizes after passing the milled material from standard steel sieves (electrical sieves) and was used without further treatment.
Sorption experiments
The batch sorption experiments were carried out by shaking known amount of the sorbent with aqueous solution of ciprofloxacin drug of desired concentra-tion on a mechanical shaker equipped with a ther-mostatic water bath having 120 rpm in a 100-mL capped flask. Initially, a known amount of sorbent was added to 10 mL of sorbate solutions with initial
concentration of 8 × 10−5 M and shaken for 1 h
allowing enough time for sorption equilibrium. Then, the mixtures were filtered through filter paper and concentration of drug was determined in the solution using spectrophotometer. The effect of various parameters on sorption was investigated by varying contact time t (5, 10, 15, 30, 45, 60 min), initial concentration of drug solution Co in the range
of 9 × 10−5–2 × 10−5 M, adsorbent dose 0.02, 0.04, 0.06, 0.08, 0.1, 0.15, 0.2 g/10 mL, and initial pH of the drug solution from 1.2, 2, 3 to 8 was used and adjusted with 0.1 M NaOH and HCl. The percentage of drug sorption was calculated by taking the differ-ence of initial and final concentration using the fol-lowing equation:
Adsorption Yieldð Þ ¼% ðCo CtÞ Co
100 (1)
where Coand Ctare the initial and at time (t)
concen-trations (mmol/L) and V is the volume of drug solution. O COOH F N HN N
Results and discussion
Characterization FT-IR study
WB posses wealth of minerals, fat, protein, carbohydrates, vitamins, and bioactive compounds as well as numerous other compounds including phenolic acids, flavonoids, tochopherols, phytosterols, lignans, carotenoids, and phy-tic acid with uneven distribution in various WB
tissues.-[20,21]Hence, the FT-IR spectrum for WB is composite of
all these components in a kernel tissue with distinct peaks indicating major kernel components. Therefore, in order to assess the interaction of WB and ciprofloxacin, FT-IR technique was employed to get functional group informa-tion of WB surface, which may be helpful in characteriz-ing the absorption bands before and after the sorption of drug.Figure 2(a,b) represents the FT-IR spectra of WB (Fig. 2a) showing the presence a peak at 3421 cm−1 for OH− groups of carbohydrates; however, after sorption (Fig. 2b) of ciprofloxacin, it is shifted to 3375 cm−1. Besides this, a peak at 1646 cm−1shows the characteristic absorption for carbonyl of carboxyl group, which is rela-tively shifted to 1651 cm−1. Another peak observed at 1039 cm−1 represents the C–O stretching vibration in anhydroglucose ring shifted to 1042 cm−1. Peak at 570 cm−1has also been shifted to 615 cm−1(Fig. 2(a,b)). Moreover, a new peak seen at 1534 cm−1 represents the stretching frequency of NH-amide group of ciprofloxacin which suggests that proteins of WB are also involved in
sorption process. Thus, proteins and polysaccharides are acting as good platforms for physical sorption of drug on WB surface. This spectral information is piece of evidence for physical sorption of drug molecules on WB surface. SEM study
As an advanced surface characterization tool, SEM pro-vides very useful information regarding characteristics topology of a material and surface morphology for differ-ent surfaces. Hence in presdiffer-ent study, morphological changes on the surface caused by sorption of ciproflox-acin on WB (pure as well as adsorbed) are studied by SEM. Through this technique, it can be seen that the surface is covered with drug molecules which can be observed by the formation of white layer on the surface of WB (Fig. 3a). However, no such findings can be seen on the surface of pure silica (Fig. 3b).
Effect of pH
In sorption process, pH of the sorbate has an important role because it affects the charge on the functional groups of biosorbent as well as their dissociation on active sites. It also influences on the sorbate solubility as well as its degree of ionization.[22] The sorption of drug on WB was studied at 1–8 pH with difference of single unit value, while all other parameters remain constant. The solutions were filtered, absorbance was determined by spectrophotometer, and % sorption was
615 1042 1534 1651 3375 570 1039 1646 3421 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 500 1000 1500 2000 2500 3000 3500 4000
A
B
Wavenumbers (cm-1) %Tcalculated. The graph was plotted between different pH values and % sorption to determine maximum sorp-tion.Figure 4ashows that the sorption of drug on WB increases with rising pH from 1 and attains to max-imum at 3 followed by decreases to pH 8. At this observed maximum pH, WB surface and drug mole-cules show definite and significantly strong attraction relative to solvent–solute causing an increased sorption (Fig. 4b). Greater sorption at pH 3 may be due to the increased positive charges on the surface of adsorbent WB, while drug has been negatively charged due to ionization/deprotonation.[23,24]
Effect of sorbent dose
The adsorbent dosage effect has been explored in the range 0.02, 0.04, 006, 0.08, 0.1, 0.15, 0.2 g/10 mL and other parameters remain constant. The result can be visualized fromFig. 5 where plot is drawn in % sorp-tion versus different amount of adsorbent. It indicates increased sorption with increasing adsorbent dose
because of the availability of many active sites. Thus, initially, the increase in sorption is observed with increased dose which becomes constant at higher values. Therefore, 0.1-g WB dose was optimized as a more suitable for further sorption studies. In fact, it is due to unsaturation of sorption sites at the time of sorption reaction.[24]
Effect of sorbate concentration
The effect of initial drug concentration on the
sorp-tion of drug was investigated from 2 × 10−5 to
9 × 10−5M range as shown inFig. 6. The equilibrium uptake values increased with increasing initial drug concentration and the value reaches to its maximum at 8 × 10−5M. This trend can be revealed by the fact that initially there are enough active sites of adsor-bent available to overcome the increased concentra-tion and at 8 × 10−5 M, the adsorbent gets saturated i.e. no more active sites available to accommodate
A B
Figure 3.Scanning electron microscopic images of (a) pure WB and (b) WB adsorbed with ciprofloxacin.
more concentration, as a result % sorption remains constant above this concentration.[25]
Temperature effect
The sorption of drug onto WB was analyzed at three different temperatures (25, 37, and 45°C) keeping all the other parameters constant. As shown inFig. 7, the sorption extent of drug has no significant differences at these three temperatures. Hence, drug sorption has not
been significantly influenced by varying temperature in the studied range. That can be explained on the basis of WB properties and the nature of adsorbate indicating the possibility of formation of strong interactive forces between the adsorbent and the adsorbate.[23]
Sorption isotherms
For the design of sorption systems, the sorption isotherm models are very important.[25] This tool provides useful Figure 4b.Proposed mechanism for effect of pH on the adsorption of WB.
information regarding maximum sorption capacity and the expected interactions between adsorbate and adsorbents. Here, four isotherm models, i.e., Langmuir, Freundlich, Dubinin–Radushkevich (D–R), and Temkin, have been applied to evaluate equilibrium experimental data.
Langmuir isotherm tells the formation of monolayer sorption of molecules due to all the binding sites show-ing equal affinity for sorbate molecules. Equation 2 represents the linear form for Langmuir isotherm.
Ce Cads¼ 1 Qb þ Ce Q (2)
where Ce is the concentration of drug at equilibrium
(mol/L), Cadsis concentration adsorbed (mol/g), Q and
b become Langmuir isotherm constants.
Separation factor (RL) is a dimensionless equilibrium
parameter which may be used to calculate favorability of sorption process from the expression (3).
RL¼ 1 1þ bCi (3) (1) RL = 0 is irreversible isotherm. (2) RL = 1 is linear isotherm. (3) RL > 1 is unfavorable isotherm. (4) 0 < RL< 1 is favorable isotherm.[26]
The heterogeneous surfaces sorption is mainly deter-mined from Freundlich isotherm which tells about the sorption sites of different attraction. Its parameters such as qe, Ce, Kf, nf, qm, b, Ks, Cads, and βs report
about the attraction of adsorbent at specific tempera-ture, pH and explain the surface properties.[27] Using linear form Eq. (4), this isotherm could be assessed as Figure 6.Effect of sorbate concentration on the adsorption.
Figure 7.(a) Shows the effect of temperature on % adsorption and (b) shows the plot of lnKc versus 1/T for ciprofloxacin sorption by WB at 6 mg/10 mL.
log Ce ¼ log A þ 1 n
log Ce (4)
where Ce is concentration at equilibrium (mol/L), A
denotes multilayer sorption capacity, (1/n) is intensity of sorption.
Dubinin–Radushkevich (D–R) (Eq. 5) is known to be more generalized than Langmuir isotherm; it easily differentiates physicochemical sorption process because it is not dependent on ideal assumptions, e.g., absence of steric hindrances between adsorbed and incoming particles, surface homogeneity on microscopic level, and equipotential of sorption sites.[28,29]
ln Cads¼ ln Xm βε2 (5)
ε ¼ RT ln 1 þ 1
Ce
(6) The difference between saturated liquid phase and fre-quently adsorbed phase is known as sorption potential. It was proposed by Polanyi. Total specific micropore volume of the adsorbent is represented by Xm
(satura-tion limit). Equa(satura-tion 7 is applied to calculate the mean free energy E (kJ/mol).
E¼ ffiffiffiffiffiffiffiffiffi1 2β
p (7)
Relationship of sorbent–sorbate interactions on sur-faces and heat of sorption is well described by Temkin equation. It suggests that heat of sorption of all molecules decreases linearly with completion of sorption sites in adsorbent.[30] Equation 8 is Temkin isotherm which is given below.
qe¼ B ln A þ B ln Ce (8)
B¼RT
b (9)
Table 1 shows values of sorption constants of all the models which give an idea concerning the favorability and unfavorability of the process. The plot of Ce/Cads
versus Ce gives a straight line indicating that
experi-mental data tabulated in Table 1 seem to follow the Langmuir isotherm. Moreover, the calculated values of RL are <1 which also represent favorable sorption of drug onto the WB.
Freundlich isotherm equation was applied to validate the sorption of drug; as a result, a linear plot was obtained. The calculated values of sorption intensity
(1/n) are greater than 0 and less than 1 which indicates the favorability of the sorption. The regression coeffi-cient R2 = 0.98 gave validation of experimental data. The sorption intensity of the Freundlich constant (n) was found to be 0.27; n value does not lie in 1–10 range which indicates the unfavorable sorption.
A plot of lnCads versusε2gives a straight line, from
the slope and intercept, β and Xm values were
calcu-lated, respectively (Table 1). The magnitude of free energy (E) plays an important role for evaluating the kind of sorption. Hence, in this case, the value of E is 1.17 kJ/mol pertaining the applicability of experimental data for the D–R isotherm as well as describe that the process was physio-sorption in nature.
Furthermore, Table 1also shows the comparison of R2 of all the isotherms. The favorability order on the basis of regression coefficients is as follows: Freundlich
(R2 = 0.98), D–R (R2 = 0.99) > Langmuir
(R2 = 0.86) > Temkin (R2 = 0.82). Therefore, each isotherm has appropriate merits in describing the potential of WB for the sorption of drug. The values of correlation coefficient indicate that sorption process is compatible, feasible and experimental data follow the D–R and Freundlich isotherm models.
The maximum adsorption capacity of other types of reported adsorbents for different antibiotics is com-pared inTable 2. It is interesting to see that the current adsorbent shows comparable performance to preciously reported methods.[31–37]
Kinetic study
The kinetic study for the sorption of ciprofloxacin on to the WB was carried out at a fixed initial concentration to investigate the controlling mechanism as a function of different temperatures, i.e., 298–318 K. This
para-meter is important for evaluating sorption
Table 1.Data of the various isotherms tabulated with various parameters.
Drug Langmuir Freundlich D–R Temkin
Ciprofloxacin Qe(mg/g) B (L/mol) RL R2 A (mol/g) n 1/n R2 E (kJ/mol) Xm (mol/g) R2 B (J/mol) A (mol/g) R2
159 0.28 0.99 0.86 2.88 0.27 3.7 0.98 1.17 6.78 0.99 57 11 0.82
Table 2.Comparison of adsorption capacity of different adsor-bents for the removal of antibiotics from aqueous media.
S. No. Adsorbent Antibiotic Qe(mg/g) Reference
1 Cu–chitosan/Al2O3 Cefixime 30.5
[31]
2 CuO nanoparticles Ciprofloxacin 105 [31]
3 Lemna minor Penicillin G 26.17 [32]
4 Organobentonite Amoxicillin 30.12 [33]
5 Walnut shell Cephalexin 233.1 [34]
6 CdS–MWCNT Cefotaxime 40 [35]
7 Maize stalks Tetracycline 36.5 [36]
phenomenon followed by sorbate molecules to attach on the sorbent surface. In order to evaluate the sorption kinetics, the effect of agitation time was observed from 5 to 120 min. In kinetic study, the rate of sorption of drug onto WB was determined by using different kinetic models[38–40]such as pseudo-first-order kinetic (Langergren)[41], pseudo-second-order kinetic (Ho and McKay)[42] and diffusion models, the Morris–Weber (intraparticle diffusion),[43,44] and Reichenberg. [45] The pseudo-first-order and second-order kinetic equa-tions are given as Eqs. (10) and (11), respectively.
ln qð e qtÞ ¼ ln qe K1t Lagergren model (10) t qt ¼ t k2q2e þ 1 qe
Ho and McKay model (11)
In Eq. (10), qt (mol/g) is the amount of sorbent adsorbed at time t, while in Eq. (11), qe (mol/g) is the amount of sorbent adsorbed at equilibrium and K1 (min−1) and K2 (g/mol/min) are the sorption rate constants. qe, K1, and K2 were obtained from the slope and intercept of linear plots of qð e qtÞ versus t and t=qt
versus t. Kinetic parameters accompany-ing correlation coefficients of kinetic models are given in Table 3. It is noted that R2 values of pseudo-first-order kinetic model at different tem-peratures such as 293, 303, and 313 K may not well explain the kinetics of sorption whereas pseudo-sec-ond-order model R2 values better explain the sorp-tion manner relative to former one. The later one describes the rate-limiting step as physical sorption based on physical interaction of adsorbate–adsorbent molecules. Moreover, pseudo-second-order kinetic model describes the sorption as purely physical in nature as supported by physical interaction between drug and WB. Both the kinetic models do not recog-nize the diffusion mechanism; hence, kinetic results
were evaluated with diffusion models. Here,
Reichenberg Eq. (12) was employed for identifying whether the sorption process takes place by intrapar-ticle interaction or film diffusion.
Q¼ 1 6e Bt
π2 (12)
By rearranging Eq. 12 in linear form gives expres-sion (13):
Bt ¼ 0:4977 ln 1 Qð Þ (13)
Linear plot of Bt versus time t clearly defines that lines are linear but not passing from origin suggesting the sorption process is film diffusion implicated from rate limiting process.
Kinetic sorption process was also evaluated using Morris–Weber Eq. (14).
qt ¼ Rd ffiffi t p
(14)
qt is the adsorbed concentration at time t, while Rd is known as intra-particle diffusion rate constant. From the linear plot of qt versus
ffiffi t p
, it was observed that lines do not pass from origin, which suggests that for adsorption of ciprofloxacin onto WB, the intra-particle diffusion is not only the rate-limiting step and some degree of boundary layer also controls the process.
Rate constant values of intra-particle transport (Rd) were estimated as 0.09, 0.08, and 0.11 mol/g/min hav-ing R2 (correlation coefficients) values 0.98, 0.92, and 0.98, respectively.
Thermodynamic parameters
Thermodynamic parameters (ΔH, ΔS, ΔG) express the spontaneity, nature, and the randomness of sorption process.[46] Thermodynamic parameters are estimated from Eq. (15) and (16):
ln Kc¼ ΔH
RT þ
ΔS
R (15)
ΔG ¼ RT ln Kc (16)
Where Kc, R and T are designated for: the
equili-brium constant, ideal gas constant (8.314 KJ/mol/K) and temperature (in Kelvin), respectively. Hence, tempera-ture effect at 298, 308 and 318 ± 1 K values was explored for drug sorption onto WB at optimal conditions. By slope and intercept of a plot (ln Kc vs. 1/T),
thermody-namic parameters were calculated. From (Fig. 7a), it has been concluded that by increasing temperature the sorp-tion increases. The plot of ln Kc vs. 1/T gives a straight Table 3.Comparisons of pseudo-first-order and pseudo-second-order kinetic models.
Pseudo-first-order kinetic model Pseudo-second-order kinetic model Intraparticle diffusion
T (°C) K1(1/min) qe(mol/g) R2 K2(1/min) qe(mol/g) R2 Rd C R2
20 0.12 0.042 0.98 0.00498 2.36 × 10−6 0.99 0.09 0.75 0.98
37 0.04 0.015 0.93 0.00496 2.46 × 10−6 0.99 0.08 0.85 0.92
line as shown in(Fig. 7b) with correlation coefficient (R2) 0.94. The values of these parameters are provided in
Table 4. All the three parameters likeΔG, ΔH and ΔS provide valuable information about the sorption process. The -veΔG° values demonstrate the viability and spon-taneity in process. It is also noted that by increasing temperature sorption process is promoted. ΔH shows the route of energy in the system. The positive value of ΔH° indicates that the sorption process is endothermic in nature. The positive value ofΔS° suggests the prob-ability of a favorable sorption with increase in the dis-orderness of the system[47,48].
Drug release
Figure 8shows the in vitro drug release profile of cipro-floxacin from the WB up to 120 min. The release per-centage of ciprofloxacin was studied at three different pH values, i.e., 1.5, 7.0, and 8.5. It has been observed that the fastest release rate of ciprofloxacin drug from WB was assimilated from 0 to 50 min; later on, the rate goes to steady at each pH; however, at pH 1.5, the maximum percent release (sharp initial release about 75%) was observed as compare to 7.0 and 8.5. This study indicated that WB with higher ciprofloxacin content has good release capability and van der Waals forces of attraction (individuality of adsorbent and adsorbate is preserved)
between the surface of WB and ciprofloxacin molecules, where the physically adsorbed molecule is removed unchanged. However, the release behavior of drug which is in fact the pH-dependent for total release amount is affected by acidic and basic pH. The max-imum drug release rate was observed at pH 1.5 (more than 70% within 50 min) which decreased in neutral and basic medium at pH.
At acidic pH, the behavior of drug functionalities with positive charges on the surface of WB occurs which enhance the repulsion between adsorbate and adsorbent, while, in basic medium, the deprotonation takes place on ciprofloxacin drug and negative charges appear on external surface of WB which eventually facilitate to release the adsorbate from WB. Here, it is important that structure and properties of drug play important role in release, and possible contrary effects of drug are minimized by efficiently delivering method. This may be initiated by swallowing properties and drug accommodation on the external surface of WB.
Conclusions
Present study highlights the appreciable sorption behavior of WB for ciprofloxacin drug. Study was carried out on three different temperatures at constant parameters such as pH 3, shaking time 1 h, and concentration of 8 × 10−5M. It was noted that at various temperatures, the extent of sorp-tion of drug may not vary significantly. Besides, the data were evaluated by using Langmuir, Freundlich, D–R, and Temkin models. The values of correlation coefficient indi-cate that sorption process is compatible, feasible and experimental data follow the D–R and Freundlich isotherm models. The kinetic study suggested the pseudo-second-Figure 8.% Release profile of ciprofloxacin drug from WB surface.
Table 4.Thermodynamic parameters for sorption of ciprofloxa-cin on WB.
ΔH (J/mol) ΔS (J/mol/K) ΔG (J/mol/K)
9.5 32.3 298 K 310 K 318 K
0 −0.41 −0.85
order and film diffusion nature of the process while ther-modynamic parameters depicted the endothermic and spontaneous nature of the sorption process. Furthermore, drug release study reveals that WB and ciprofloxacin inter-action is of physical nature; hence, WB surface shows good release abilities for drug molecules with fast and maximum release of about 75% at pH 1.2 within first burst of 50 min. The study can be useful to tackle the large-scale plants for remediation of drugs by the use of green sorbent that is highly efficient, regenerable and can be reused. Furthermore, this study is also one of the possible applica-tions for WB to be a potential candidate for pH-dependent drug delivery application.
Acknowledgements
Authors thank National Centre of Excellence in Analytical Chemistry, University of Sindh, Jamshoro, Pakistan, for facil-itating this work.
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