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Efficient and recoverable magnetic AC-Fe3O4 nanocomposite for rapid removal of promazine from wastewater
Materials Chemistry and Physics 240 (2020) 122109
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Efficient and recoverable magnetic AC-Fe3O4 nanocomposite for rapid removal of promazine from wastewater Bessy D’Cruz, Metwally Madkour **, Mohamed O. Amin, Entesar Al-Hetlani * Department of Chemistry, Faculty of Science, Kuwait University, P.O. Box 5969, Safat, 13060, Kuwait
H I G H L I G H T S
G R A P H I C A L A B S T R A C T
� AC-Fe3O4 nanocomposite was used as efficient and reusable magnetic nanoadsorbent. � Antipsychotic drug, promazine pharma ceutical waste was used as the adsorbate. � The adsorption equilibrium was ach ieved after 6 min with complete removal of 99.9%.
A R T I C L E I N F O
A B S T R A C T
Keywords: Adsorption AC-Fe3O4 nanocomposite Promazine Kinetics Isotherms
Because of its high adsorption efficiency, facile magnetic separation process, and rapid adsorption kinetics, a magnetic activated carbon-Fe3O4 (AC-Fe3O4) nanocomposite was fabricated and applied as a nanoadsorbent for the effective exclusion of a pharmaceutical substance from wastewater. This nanocomposite was characterized using several analytical techniques, including X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, Raman spectroscopy, N2 sorptometry, transmission electron microscopy (TEM), magnetic property analysis, and isoelectric point (pHIEP) analysis. The efficacy of the mag netic nanocomposite adsorption was studied using a type of phenothiazine antipsychotic drug (promazine) as the adsorbate. Adsorption parameters such as the nanoadsorbent dosage, initial drug concentration, pH of the so lution, and adsorption kinetics were investigated. The results demonstrated that the adsorption equilibrium was rapidly attained after 6 min with almost complete elimination (99.97%) of the promazine. A batch system was used to determine the adsorption kinetics and isotherm of promazine onto the AC-Fe3O4 nanocomposite, and the obtained results corresponded to pseudo-second-order-kinetic and Langmuir isotherm model, respectively. The nanocomposite exhibited an adsorption capacity of 101.01 mg g 1, with a negligible loss in efficiency after five adsorption cycles. Therefore, this nanocomposite could be used as an efficient platform to remove contaminants from wastewater.
1. Introduction Pharmaceuticals are extensively used in medicine, industry,
agriculture, and people’s daily lives. The disposal of these compounds directly or indirectly in water can make them ubiquitous pollutants and a challenging environmental issue [1]. Therefore, several removal
* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (M. Madkour), [email protected] (E. Al-Hetlani). https://doi.org/10.1016/j.matchemphys.2019.122109 Received 15 May 2019; Received in revised form 2 August 2019; Accepted 30 August 2019 Available online 5 September 2019 0254-0584/© 2019 Elsevier B.V. All rights reserved.
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Materials Chemistry and Physics 240 (2020) 122109
a 1800
Intensity (a.u.)
1600 1400
b 2+
Fe 2+ Fe (724.6 eV) (725.5 eV)
Fe2p1/2 (724.6 eV)
800
2+
Fe 2+ (710.7 eV) Fe (711.9 eV)
3+
Fe (727.1 eV)
3+
Fe (713.7 eV)
1200 1000
Fe2p3/2
Fe(III)Fe2p1/2 Satellite Fe(III)Fe2p3/2 Satellite
600 400 730
725
720
715
Binding energy (eV)
710
c
d
(C) AC-Fe3O4
220
200 100 291 290 289 288 287 286 285 284 283
10
Binding energy (eV)
20
30
40
50
440
C=O (288.5 eV)
(B) AC
511
C-O (285.6 eV)
400
Intensity (a.u.)
Intensity (a.u.)
400 300
(A) Fe3O4 NPs
C-C (284.6 eV)
500
311
735
60
2-Theta (in degree)
70
80
Fig. 1. a–c XPS spectra of AC-Fe3O4 nanocomposite: (a) Fe 2p, (b) O 1s, and (c) C 1s. (d) XRD spectra of (A) Fe3O4 NPs, (B) bare AC, and (C) AC-Fe3O4 nanocomposite.
approaches have been investigated, such as adsorption, coagulation, photolysis, biological, and advanced oxidation approaches [2]. Because of its high effectiveness, speed, and lack of undesired derivatives, adsorption has been effectively exploited in the elimination of envi ronmental effluents from water sources. Owing to their large surface areas and efficiencies in both very low (~1 ppm) and very high pollutant concentration ranges (~1000 ppm), nanoadsorbents have shown rela tively large adsorption capacities [3]. Activated carbon (AC) is commonly used as a sorbent to eliminate different contaminants from aquatic environments because of its distinctive structure and high adsorption capacity [4]. AC has a large surface area and is commercially available at a low cost, which renders it ideal for adsorption applications. Furthermore, the surface of AC con tains different functional groups that aid in the adsorption process through different interaction mechanisms [5]. However, one of the major drawbacks of using AC is its isolation and removal from water after the adsorption is completed. Therefore, laborious methods such as filtration [6] and centrifugation [7] are commonly adopted. The use of magnetic nanoadsorbents for wastewater treatment has gained much attention due to their facile preparation and phase sepa ration, in addition to their potential for treating a large quantity of wastewater in a short period of time [8]. Previously, magnetic nano adsorbents such as a γ-Fe2O3@Fe3O4 composite [9] and C-dots/Fe3O4 [10] were employed as sorbents for heavy metals from contaminated water. Furthermore, the application of these nanoadsorbents was
extended to the removal of pharmaceuticals, including the use of an Fe3O4/methacrylic acid nanocomposite for the removal of carbamaze pine and diatrizoate [11], Fe3O4/pectin and Fe3O4/silica/pectin nano composites for the removal of the ciprofloxacin and moxifloxacin antibiotics [12], and an Fe3O4@GO nanocomposite for the removal of tetracyclines [13]. Therefore, in this study, an AC-Fe3O4 nanoadsorbent was success fully fabricated as a magnetic nanocomposite and utilized for the exclusion of the drug promazine from wastewater. The prepared nano composite was characterized via X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier-transform infrared (FTIR) Raman spectroscopy, transmission electron microscopy (TEM), mag netic susceptibility, and isoelectric point analysis. Several parameters that influence the adsorption efficiency were investigated, including the nanoadsorbent dosage, initial drug concentration, pH of the solution, reusability, adsorption kinetics, and isotherm. 2. Experimental 2.1. Materials and methods Ferric chloride 97% (FeCl3), ferrous chloride 98% (FeCl2), ammo nium hydroxide (NH4OH, 28–30%), activated charcoal (AC), sodium hydroxide, hydrochloric acid, and promazine hydrochloride were ob tained from Sigma Aldrich. All of these chemicals were used as received. 2
B. D’Cruz et al.
Transmittance (%)
a
98 96 94 92 90 88 90
Materials Chemistry and Physics 240 (2020) 122109
A
1577
1120
B
75
1629 1427
60 3434
45 4000 3500 3000 2500 2000 1500 1000 -1
Wavenumber(cm )
632 587
500
b
Intensity (A.U.)
12000 9000 6000 3000 0 200 150
A
1340 1600
0
concentration (1, 10, 20, 40, 80, 100, or 120 mg L 1). The solution mixture was stirred and then subjected to an external magnet to isolate the magnetic nanocomposite. The supernatant solution was filtered through membrane filters, and the filtrate was subjected to UV–vis analysis (Agilent Cary 5000 Scan UV–vis–near-infrared spectrometer) at 252 nm to evaluate the concentration of promazine remaining in the supernatant at different time periods. In the pH experiment, 0.1 mol L 1 of HCl or NaOH was used to adjust the solution pH of the promazine from 7.0 to 9.5. To assess the effect of the contact time on the promazine adsorption, experiments to determine the batch adsorption kinetics were performed with an adsorbent dosage of 10 mg and 10 mL of promazine (40 mg L 1) at pH 8.5 at different time intervals. The amount of promazine adsorbed (mg g 1) at any time (t) and the adsorption efficiency (% Removal) of the sorbent could be determined using equations (1) and (2), respectively.
B
100 50
Fig. 3. N2 adsorption isotherms of bare AC, Fe3O4 NPs, and AC-Fe3O4 nanocomposite.
681 278 346
500 1000 1500 2000 2500 3000 3500 4000 -1
Raman shift (cm )
Fig. 2. (a) FTIR and (b) Raman spectra of (A) bare AC and (B) AC-Fe3O4 nanocomposite.
qt ¼
The water used throughout the experiments was DI water from a water deionizer (Elix Milli Q).
%Removal ¼
Ct Þ
ðC0 m
(1)
V Ct Þ
ðC0 C0
� 100
(2)
where Co and Ct are the promazine concentrations at the initial time and time t (mg L 1), respectively; V is the promazine solution volume (L), and m is the mass of the magnetic adsorbent (g). On the other hand, the amount of promazine adsorbed at equilibrium (qe) is calculated using equation (1) while replacing Ct with Ce, which is the promazine equi librium concentration (mg L 1). Batch isotherms were obtained using 10 mg of the magnetic nano composite at a pH of 8.5, while investigating an initial promazine con centration range of 40–120 mg L 1. After mixing for 6 min, the magnetic nanocomposite was magnetically collected, and the resulting solution was subjected to UV–vis analysis.
2.2. Preparation of AC-Fe3O4 nanocomposite The magnetic AC-Fe3O4 nanocomposite was synthesized by sus pending 0.2 g of AC in 100 mL of DI water and sonicating for 15 min. Subsequently, 1.41 g of FeCl3 and 0.55 g of FeCl2 were added under vigorous stirring. Thereafter, an aqueous solution of NH4OH (28%) was added dropwise to adjust the pH of the mixture to ~11. The solution was stirred for 60 min. Then, the precipitate was collected using an external magnet and washed repeatedly with DI water and ethanol. Finally, the obtained nanocomposite was dried at 80 � C overnight. 2.3. Promazine removal from wastewater
2.4. Regeneration of AC-Fe3O4 nanocomposite
The removal of promazine by the AC-Fe3O4 nanocomposite was investigated and optimized in a series of experiments. The parameters investigated included the initial adsorbent dosage, initial promazine concentration, and solution pH. Generally, batch adsorption studies were conducted by mixing 10 mg of the AC-Fe3O4 nanocomposite and 10 mL of an aqueous solution of promazine with a known initial
The promazine-loaded AC-Fe3O4 nanocomposite was magnetically separated from the solution for reuse, and the supernatant was subjected to UV–vis analysis. Thereafter, the removal of the adsorbed promazine from the nanocomposite was achieved by ultrasonication with DI water for 30 min. The nanocomposite was then thoroughly washed with DI 3
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Materials Chemistry and Physics 240 (2020) 122109
Fig. 4. TEM of AC-Fe3O4 nanocomposite. The scale bar is 200 nm.
water and ethanol, followed by drying at 80 � C. Then, the reusability was tested by mixing the dried nanoadsorbent with a fresh promazine solution using the procedure described in section 2.3. Using this regeneration procedure, the magnetic nanocomposite was recycled five times and reused in adsorption experiments.
were ascribed to Fe 2p3/2 and Fe 2p1/2 of Fe3O4, and were further deconvoluted into six peaks at 711.9, 713.65, 719.2, 725.5, 727.1, and 733.2 eV. The peaks at 711.9 and 725.5 eV are ascribed to Fe2þ, and the peaks at 713.7 and 727.1 eV are related to the Fe3þ in the Fe3O4 phase. Furthermore, the satellite peaks present at 719.2 and 733.2 eV proved the existence of Fe3þ in the Fe2O3 phase, revealing that the surface of the magnetic nanocomposite was faintly oxidized in the air environment [14]. The O 1s spectrum was de-convoluted into two peaks located at 530.4 and 531.7 eV, which can be allocated to the oxygen bonds of Fe–O and H–O, respectively, as presented in Fig. 1b [15]. The C 1s XPS spectra for the AC-Fe3O4 nanocomposite (Fig. 1c) were further de-convoluted into three peaks positioned at 284.6, 285.6, and 288.5 eV, which were – O, respectively assigned to C–C, oxygen containing group C–O, and C– [14]. The XRD patterns of the Fe3O4, AC, and AC-Fe3O4 nanocomposite are shown in Fig. 1d. Several significant diffraction peaks at 2θ ¼ 30.20, 35.6, 43.4, 57.1, and 62.9 were indexed to the 220, 311, 400, 511, and 440 reflections, respectively, which confirmed the formation of pure cubic spinel Fe3O4 [16]. The same series of characteristics peaks were also obtained with the AC-Fe3O4 nanocomposite. However, the in tensities of these peaks were significantly reduced as a result of the coating of amorphous AC on the surface of the Fe3O4 NPs. FTIR spectral analysis was performed to confirm the formation of the AC-Fe3O4 nanocomposite, as shown in Fig. 2a. The peaks at 1577 and –C 1120 cm 1 and the broad peak at 3434 cm 1 correspond to C– stretching vibrations of the benzene ring skeleton, C–O stretching vi brations, and O–H stretching vibration, respectively [17]. On the other hand, in the FTIR spectrum of the AC-Fe3O4 nanocomposite, the observed peaks at 3434, 1629, and 1427 cm 1 correspond to the O–H – C stretching, and C–C bending vibrations, respectively, stretching, C– confirming the presence of AC in the magnetic nanocomposite [18]. In addition, the FTIR spectrum showed two strong, overlapped peaks at 587 and 632 cm 1 attributed to Fe–O bond stretching vibrations of Fe3O4, which confirmed the presence of iron oxide [19]. Further investigation was performed using Raman spectroscopy, as illustrated in Fig. 2b. Bands were clearly observed at 681, 346, and 278 cm 1, which corresponded to the Fe–O–Fe bond in Fe3O4. Additionally, in both spectra, the Raman peaks for the D and G bands of carbonaceous ma terials appeared at 1340 and 1600 cm 1, which confirmed the successful
2.5. Characterization of AC-Fe3O4 nanocomposite Surface elemental analysis of the magnetic nanocomposite was per formed through XPS using an ESCALAB250 xi spectrometer equipped with an Al Kα radiation source. The powder XRD patterns were obtained via a Bruker D8 advanced diffractometer with a Cu-Kα radiation source (λ ¼ 0.1542 nm). The functional groups of the nanocomposite were studied using FTIR spectroscopy with a Jasco FTIR-6300. The Raman spectra were obtained using a Renishaw inVia confocal Raman spec trometer. The 514 nm line of an argon ion laser was used for the exci tation wavelength, with an exposure time of 10 s and a 24001/mm grating linked to a CCD camera detector. The Brunauer–Emmett–Teller (BET) surface area of the nanocomposite was determined using nitrogen sorption isotherms at 195 � C (on a model Gemini VII, ASAP 2020 automatic Micromeritics sorptometer, USA). Before the analysis, the sample was degassed for 12 h at 110 � C. The morphology of the magnetic nanocomposite was analyzed using transmission electron microscopy (TEM) (model: JEOL JEM 1230 (JEOL Ltd., Japan) operating at 120 KV. The magnetic properties were determined using magnetic susceptibility balance (Sherwood Scientific, Cambridge England). A Zetasizer Nano ZS (Malvern Instruments Ltd, Malvern, UK) was employed to determine the isoelectric point (pHIEP). 3. Results and discussion 3.1. Characterization of AC-Fe3O4 nanocomposite XPS analyses were conducted to determine the composition and chemical states of the nanomagnetic AC-Fe3O4 composite. Fig. 1a–c shows the XPS spectra of the magnetic nanocomposite, which confirm the presence of iron, oxygen, and carbon. Fig. 1a displays the Fe 2p XPS spectrum showing binding energies (BEs) at 710.7 and 724.6 eV which 4
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Materials Chemistry and Physics 240 (2020) 122109
Fig. 5. Effects of AC-Fe3O4 nanocomposite dosage on (a) adsorption capacity and (b) adsorption efficiency for removal of promazine. Conditions: promazine concentration ¼ 100 mg L 1 and total volume ¼ 10 mL.
Fig. 6. Effects of initial promazine concentration on (a) adsorption capacity and (b) adsorption efficiency of AC-Fe3O4 nanocomposite. Conditions: adsor bent dosage ¼ 10 mg and total volume ¼ 10 mL.
formation of the AC-Fe3O4 nanocomposite [20]. N2 sorption measurements were conducted to evaluate the surface properties of the Fe3O4 NPs, bare AC, and AC-Fe3O4 nanocomposite, as shown in Fig. 3. The N2 isotherm obtained for all the materials can be classed as type IV, which confirmed their mesoporous nature [21]. On the other hand, the hysteresis of AC and AC-Fe3O4 can be classified as H3, while that of Fe3O4 NPs can be classified between H1 and H3 [22]. Moreover, N2 sorpometry measurements revealed that the surface area of the Fe3O4 NPs was enhanced 7.5 fold from 105.44 to 788.66 m2 g 1 with the introduction of AC. Additionally, the pore diameter (Dp) of the magnetic nanocomposite dramatically decreased from 13.5 to 3.48 nm compared to that of the Fe3O4 NPs. Consequently, the enlarged surface area of the magnetic nanocomposite could enhance and improve its adsorption performance. The morphological properties the Fe3O4-AC nanocomposite were determined using TEM (Fig. 4). TEM images of the Fe3O4-AC nano composite showed that it is almost spherical in shape and is approxi mately 20 nm in size. Mass susceptibility measurements for the prisitne Fe3O4 NPs and the Fe3O4-AC magnetic nanocomposite were 4.348 � 10 4 cm3 g 1 and 2.575 � 10 4 cm3 g 1, respectively. The low
value of the magnetic nanocomposite could be attributed to the presence of AC in the nanocomposite. 3.2. Adsorption experiments 3.2.1. Effect of AC-Fe3O4 dosage Initially, to quantify the adsorption of promazine onto glass bottles, the adsorption experiment was conducted without adsorbent, and it was noticed that no adsorption occurred during the experiment. The ability to remove large quantities of harmful materials present in water with a minimum amount of adsorbent has economic benefits. Therefore, to determine the impact of various amounts of AC-Fe3O4 on the removal of promazine, adsorbent dosages from 6 to 14 mg were used. The amount of promazine adsorbed at equilibrium (qe) at each concentration was evaluated using a modification of equation (1) and is shown in Fig. 5a. Patently, the amount of promazine adsorbed at equi librium decreased as the adsorbent dosage increased, which can be attributed to the overlapping of adsorption sites on the nanocomposite at a high adsorbent dosage. This resulted in a reduction of the sites available for adsorption [23]. However, the promazine adsorption 5
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Zeta potential(mV)
a
30 20 10 0 -10 -20 -30 20 15 10 5 0 -5
Materials Chemistry and Physics 240 (2020) 122109
(A) Promazine pH (IEP)= 6.5
(B) AC-Fe3O4
pH (IEP)= 9.35
2
3
4
5
6
pH
7
8
9
10
b Adsorption efficiency (%)
100.0 99.5 99.0 98.5 98.0 97.5 97.0 96.5 96.0 7.0
7.5
8.0
pH
8.5
9.0
9.5 Fig. 8. (a) Effect of adsorption time on amount of promazine adsorbed. (b) Pseudo-second-order plot of adsorption of promazine onto AC-Fe3O4 nano composite. Conditions: initial concentration of promazine ¼ 40 mg L 1, dosage of AC-Fe3O4 ¼ 10 mg, and pH ¼ 8.5.
Fig. 7. (a) Isoelectric points of (A) promazine and (B) AC-Fe3O4 in pH range of 1–10, with isoelectric points highlighted using green dotted lines, and (b) effect of pH on removal of promazine by magnetic AC-Fe3O4 nanocomposite. Con ditions: adsorbent dosage ¼ 10 mg, initial concentration of promazine: 40 mg L 1, and total volume ¼ 10 mL.
Table 1 Fitting parameters of pseudo-first-order (mass transfer) and pseudo-secondorder (chemical reaction) adsorption kinetic models for promazine uptake by AC-Fe3O4 nanocomposite.
efficiency increased with an increase in the adsorbent dosage in the range of 6–10 mg and then plateaued at higher concentrations (Fig. 5b). This could be ascribed to the large surface area and availability of more active sites for adsorption [24]. Above 10 mg of the AC-Fe3O4 nano composite, the adsorption equilibrium of the drug was reached, and therefore, 10 mg was used as the adsorbent dosage in further experiments.
Pseudo-first-order model
Pseudo-second-order model
k1 (min 1)
qe (mg g 1)
R2
k2 (g mg
0.402
16.80
0.9137
0.119
1
min
1
)
qe (mg g 1)
R2
40.65
0.9997
percentage was high at a lower initial drug concentration and decreased at higher concentrations [25]. Hence, 40 mg L 1 was used as the opti mum promazine concentration in further experiments.
3.2.2. Effect of initial promazine concentration Various initial concentrations of promazine ranging from 1 to 100 mg L 1 were examined to elucidate the effect of the concentration on the adsorption capacity of the AC-Fe3O4 nanocomposite, as repre sented in Fig. 6a and b. Notably, the amount of promazine adsorbed increased with the initial drug concentration. However, the percentage of promazine removed increased and then plateaued, which revealed that the promazine removal was dependent on its initial concentration. At a lower initial drug concentration, a greater number of active adsorption sites on the nanocomposite were accessible. However, at a higher drug concentration, the number of active adsorption sites could not accommodate the number of drug molecules. Thus, the drug removal
3.2.3. Effect of pH The pH of the drug solution influenced the surface charge, ionization degree, and dissociation of the functional groups present on the surface of the nanocomposite [26]. The isoelectric points (pHIEP) of the pro mazine and synthesized nanocomposite were determined using Zeta potential (ζ) measurements (pH ¼ 1 to 10) and are shown in Fig. 7a. The pHIEP values of the promazine and AC-Fe3O4 nanocomposite were ~ 6.5 and 9.35, respectively. When the pH of the solution was below 9.3, the 6
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Materials Chemistry and Physics 240 (2020) 122109
the potential with the variation of the pH. At a pH value of 7.1, the potential was þ2 mV, while it increased to þ5.5 mV at pH 8.5, sug gesting that the surface of the nanoadsorbent had a more positive charge. Hence, the removal percentage showed a slight increase with an increase in pH from 7.1 to 8.5 and almost reached 100%. 3.2.4. Kinetics of adsorption The effect of the adsorption time on the amount of promazine adsorbed (qt) by the magnetic nanocomposite is shown in Fig. 8a. Initially, the adsorption capacity and promazine removal percentage increased, it then equilibrated after 6 min with 99.3% removal. The magnetic nanocomposite acted as a fast adsorbent compared to other adsorbents, where equilibrium is reached after hours rather than mi nutes [28]. The adsorption kinetics revealed valuable data regarding the adsorption process and mechanism. Thus, two models were employed to fit the adsorption kinetic parameters using equations (3) and (4) [29], as listed in Table 1. lnðqe
qt Þ ¼ lnqe
t 1 1 ¼ tþ qt qe k2 q2e
k1 t
(3) (4)
where k1 (min 1) and k2 (g mg 1 min 1) are the equilibrium rate con stants of pseudo-firstt-order and pseudo-second-order models, respec tively; while qe and qt (mg g 1) are the adsorbed amounts of promazine at equilibrium and at any time t (min), respectively. The kinetic parameters and correlation coefficients (R2) for these models were calculated from the straight line plots of ln (qe - qt) and t/qt versus t and are given in Table 1. The adsorption kinetics data followed the pseudo-second-order model (Fig. 8b), with an R2 value of 0.999 [30]. These findings sug gested that the amount of promazine adsorbed at equilibrium was highly affected by the promazine adsorption rate. 3.2.5. Adsorption isotherms Langmuir and Freundlich models were employed to elucidate the nature of the interaction between the drug molecules and nano composite surface active sites, as well as to determine the adsorption capacity at equilibrium [34]. The Langmuir isotherm is a theoretical model that describes the formation of a monolayer of the adsorbate on a homogeneous surface without any interaction between the adsorbent and adsorbate. The Langmuir linear equation is expressed as follows [32, 35]:
Fig. 9. (a) Plot of qe versus Ce for adsorption of promazine onto AC-Fe3O4 nanocomposite. (b) Langmuir plot of promazine adsorption by AC-Fe3O4 nanocomposite. Adsorbent dosage: 10 mg and pH ¼ 8.5.
Table 2 Isotherm parameters for removal of promazine by AC-Fe3O4 nanocomposite. Langmuir isotherm model KL (mL g 0.103
1
)
Qm (mg g
101.01
Ce Ce 1 ¼ þ qe Qm Qm KL
Freundlich isotherm model 1
)
R2 0.999
KF (mL g
52.49
1
)
n
R2
4.21
0.9675
(5)
On the other hand, the Freundlich isotherm is more applicable to the adsorption over a heterogeneous surface, where strong interaction oc curs between the adsorbent and the adsorbate molecules. The linear form of the Freundlich equation is as follows [33,36]:
nanoadsorbent was positively charged, and the promazine was nega tively charged. Thus, it is theorized that the binding of the promazine onto the nanoadsorbent was governed by electrostatic interactions over the investigated pH values. A study was performed to investigate the effect of the solution pH on the promazine removal, and the results are shown in Fig. 7b. The batch experiment for the pH study was conducted in a pH range of 7–9.5 to avoid insufficient resolutions (pH < 7) and/or precipitation of the pro mazine (pH > 9) [27]. Fig. 7b shows the amount of promazine removal (percentage) in a range of pH values, and the findings confirmed that the adsorption efficiency dramatically increased and reached a maximum value of 99.7% in the range of 8.5–8.9. However, the adsorption effi ciency drastically decreased beyond a pH of 8.9. The increase in the promazine removal amount with pH can be attributed to the change in
lnqe ¼ lnKF þ
lnCe n
(6)
where Ce and qe represent the equilibrium concentration of promazine in solution (mg L 1) and the equilibrium promazine concentration adsor bed on the materials (mg g 1), respectively. In addition, Qm is the maximum adsorption capacity of promazine, KL (mL g 1) is the Lang muir constant concerning the affinity of the adsorption sites, and KF (mL g 1) and n are constants correlated to the adsorption capacity and adsorption intensity, respectively. Plots of Ce/qe versus Ce and lnqe versus lnCe were employed to determine the Langmuir and Freundlich constants, respectively. The equilibrium adsorption of promazine onto the AC-Fe3O4 nanocomposite is presented in Fig. 9a, and the equilibrium adsorption data were fitted 7
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Materials Chemistry and Physics 240 (2020) 122109
Table 3 Removal of different contaminants using AC-iron oxide magnetic nanocomposite. Compound
Concentration
Equilibrium adsorption (min)
Percentage of removal (%)
Equilibrium isotherm model
Kinetic model
Maximum adsorption capacity (mg g 1)
Ref
Promazine
1–100 ppm
6
99.97
Langmuir
101.01
100
–
Langmuir
270–324
This work [4]
120
85.20
393.7
[37]
300
76.4
Langmuir and Temkin Freundlich
90.91
[38]
90
44.22–95.26
142.85
[39]
– 180
– 99.2–99.8
Freundlich and Langmuir Langmuir Langmuir
321 2.41
[40] [41]
2880 (48 h)
97
Sips and Langmuir
Pseudo-secondorder Pseudo-secondorder pseudo-secondorder Pseudo-secondorder Pseudo-secondorder – Pseudo-secondorder pseudo-1st and -second-order
327.85
[42]
MO
a
600 mg L
Isonicotinic acid Aniline
1
1.23–6.6 g L
1
50–300 ppm 1
Amoxicillin
50–300 mg L
MBb MO MB
– 0.2–2.0 mmol L
Trinitrophenol
23–228 ppm
a b
1
MO ¼ Methyl orange. MB ¼ Methylene blue.
with high efficiency. 4. Conclusion
Adsorption Efficiency (%)
100
A magnetic AC-Fe3O4 nanocomposite was successfully synthesized for the efficient adsorptive removal of the widely used antipsychotic drug promazine from an aqueous solution and was effectively charac terized by several analytical techniques. Batch adsorption studies were conducted and indicated that the adsorption efficiency of the nano composite is dependent on various conditions. The obtained kinetic data followed the pseudo-second-order model, while the Langmuir model showed a good fit with the obtained equilibrium data, with a maximum monolayer adsorption capacity of 101.01 mg g 1. Additionally, the repeated use of the magnetic nanocomposite over five consecutive cy cles showed an adsorption efficiency decrease of less than 1%. There fore, the synthesized magnetic nanocomposite has remarkable potential as an effective adsorbent for the removal of contaminants such as drugs in wastewater. More interestingly, the resulting AC-Fe3O4 nano composite exhibited a strong response to the external magnetic field, thus adding the advantage of a facile and efficient method for separating the nanocomposite from an aqueous solution.
98 96 94 92 90 Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
Fig. 10. Reusability of AC-Fe3O4 nanocomposite for removing promazine from wastewater. Conditions: initial concentration of promazine ¼ 40 mg L 1; and dosage of AC-Fe3O4 ¼ 10 mg.
Acknowledgments
to both the Langmuir and Freundlich isotherm models. The obtained isotherm data showed a better fit with the Langmuir model (Fig. 9b) and produced a higher R2 value, as listed in Table 2. These findings imply that the adsorption process follows a monolayer molecular adsorption, with a maximum adsorption capacity of 101.01 mg g 1 (no published data for promazine). A summary of the contaminants adsorbed by the AC-Fe3O4 nano composite in comparison with our findings is reported in Table 3. The prepared nanocomposite showed remarkable and rapid removal of promazine from water in approximately 6 min, with an efficiency of 99.97%.
The authors acknowledge the funding support of the Kuwait Foun dation for the Advancement of Sciences (KFAS) (grant no. PN17-24SC01). Special thanks are extended to the Research Sector Projects Unit (RSPU) Facilities (nos. GS 01/01, GS 01/05, GS 03/01, and GS 02/01), KUNRF general facility no. GE 01/07 for the Zeta potential measure ment, and the Department of Chemistry at Kuwait University for the Raman spectroscopy measurements. Finally, special thanks to Dr. Kamlesh Kumari for performing magnetic susceptibility measurement. References [1] J.W. Peterson, B. Gu, M.D. Seymour, Surface interactions and degradation of a fluoroquinolone antibiotic in the dark in aqueous TiO2 suspensions, Sci. Total Environ. 532 (2015) 398–403. [2] V. Homem, L. Santos, Degradation and removal methods of antibiotics from aqueous matrices – a review, J. Environ. Manag. 92 (10) (2011) 2304–2347. [3] N.N. Nassar, Rapid removal and recovery of Pb(II) from wastewater by magnetic nanoadsorbents, J. Hazard Mater. 184 (1) (2010) 538–546. [4] R.-S. Juang, Y.-C. Yei, C.-S. Liao, K.-S. Lin, H.-C. Lu, S.-F. Wang, A.-C. Sun, Synthesis of magnetic Fe3O4/activated carbon nanocomposites with high surface area as recoverable adsorbents, J Taiwan Inst. Chem. Eng. 90 (2018) 51–60. [5] B. Hameed, F. Daud, Adsorption studies of basic dye on activated carbon derived from agricultural waste: hevea brasiliensis seed coat, Chem. Eng. J. 139 (1) (2008) 48–55.
3.3. Reusability of magnetic AC-Fe3O4 nanocomposite To demonstrate the feasibility of practical applications, the reus ability of the magnetic nanocomposite was evaluated by studying the removal process for 5 cycles, as shown in Fig. 10. The nanocomposite exhibited removal efficiencies of 99.97, 99.76, 99.61, 99.42, and 99.19% for cycles 1, 2, 3, 4, and 5, respectively. An insignificant decrease in the adsorption performance was observed between cycles, indicating that the magnetic nanocomposite could effectively adsorb promazine from wastewater, and then be easily regenerated and reused 8
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9
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Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys
Efficient and recoverable magnetic AC-Fe3O4 nanocomposite for rapid removal of promazine from wastewater Bessy D’Cruz, Metwally Madkour **, Mohamed O. Amin, Entesar Al-Hetlani * Department of Chemistry, Faculty of Science, Kuwait University, P.O. Box 5969, Safat, 13060, Kuwait
H I G H L I G H T S
G R A P H I C A L A B S T R A C T
� AC-Fe3O4 nanocomposite was used as efficient and reusable magnetic nanoadsorbent. � Antipsychotic drug, promazine pharma ceutical waste was used as the adsorbate. � The adsorption equilibrium was ach ieved after 6 min with complete removal of 99.9%.
A R T I C L E I N F O
A B S T R A C T
Keywords: Adsorption AC-Fe3O4 nanocomposite Promazine Kinetics Isotherms
Because of its high adsorption efficiency, facile magnetic separation process, and rapid adsorption kinetics, a magnetic activated carbon-Fe3O4 (AC-Fe3O4) nanocomposite was fabricated and applied as a nanoadsorbent for the effective exclusion of a pharmaceutical substance from wastewater. This nanocomposite was characterized using several analytical techniques, including X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, Raman spectroscopy, N2 sorptometry, transmission electron microscopy (TEM), magnetic property analysis, and isoelectric point (pHIEP) analysis. The efficacy of the mag netic nanocomposite adsorption was studied using a type of phenothiazine antipsychotic drug (promazine) as the adsorbate. Adsorption parameters such as the nanoadsorbent dosage, initial drug concentration, pH of the so lution, and adsorption kinetics were investigated. The results demonstrated that the adsorption equilibrium was rapidly attained after 6 min with almost complete elimination (99.97%) of the promazine. A batch system was used to determine the adsorption kinetics and isotherm of promazine onto the AC-Fe3O4 nanocomposite, and the obtained results corresponded to pseudo-second-order-kinetic and Langmuir isotherm model, respectively. The nanocomposite exhibited an adsorption capacity of 101.01 mg g 1, with a negligible loss in efficiency after five adsorption cycles. Therefore, this nanocomposite could be used as an efficient platform to remove contaminants from wastewater.
1. Introduction Pharmaceuticals are extensively used in medicine, industry,
agriculture, and people’s daily lives. The disposal of these compounds directly or indirectly in water can make them ubiquitous pollutants and a challenging environmental issue [1]. Therefore, several removal
* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (M. Madkour), [email protected] (E. Al-Hetlani). https://doi.org/10.1016/j.matchemphys.2019.122109 Received 15 May 2019; Received in revised form 2 August 2019; Accepted 30 August 2019 Available online 5 September 2019 0254-0584/© 2019 Elsevier B.V. All rights reserved.
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Materials Chemistry and Physics 240 (2020) 122109
a 1800
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b 2+
Fe 2+ Fe (724.6 eV) (725.5 eV)
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800
2+
Fe 2+ (710.7 eV) Fe (711.9 eV)
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Fe (713.7 eV)
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Intensity (a.u.)
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(A) Fe3O4 NPs
C-C (284.6 eV)
500
311
735
60
2-Theta (in degree)
70
80
Fig. 1. a–c XPS spectra of AC-Fe3O4 nanocomposite: (a) Fe 2p, (b) O 1s, and (c) C 1s. (d) XRD spectra of (A) Fe3O4 NPs, (B) bare AC, and (C) AC-Fe3O4 nanocomposite.
approaches have been investigated, such as adsorption, coagulation, photolysis, biological, and advanced oxidation approaches [2]. Because of its high effectiveness, speed, and lack of undesired derivatives, adsorption has been effectively exploited in the elimination of envi ronmental effluents from water sources. Owing to their large surface areas and efficiencies in both very low (~1 ppm) and very high pollutant concentration ranges (~1000 ppm), nanoadsorbents have shown rela tively large adsorption capacities [3]. Activated carbon (AC) is commonly used as a sorbent to eliminate different contaminants from aquatic environments because of its distinctive structure and high adsorption capacity [4]. AC has a large surface area and is commercially available at a low cost, which renders it ideal for adsorption applications. Furthermore, the surface of AC con tains different functional groups that aid in the adsorption process through different interaction mechanisms [5]. However, one of the major drawbacks of using AC is its isolation and removal from water after the adsorption is completed. Therefore, laborious methods such as filtration [6] and centrifugation [7] are commonly adopted. The use of magnetic nanoadsorbents for wastewater treatment has gained much attention due to their facile preparation and phase sepa ration, in addition to their potential for treating a large quantity of wastewater in a short period of time [8]. Previously, magnetic nano adsorbents such as a γ-Fe2O3@Fe3O4 composite [9] and C-dots/Fe3O4 [10] were employed as sorbents for heavy metals from contaminated water. Furthermore, the application of these nanoadsorbents was
extended to the removal of pharmaceuticals, including the use of an Fe3O4/methacrylic acid nanocomposite for the removal of carbamaze pine and diatrizoate [11], Fe3O4/pectin and Fe3O4/silica/pectin nano composites for the removal of the ciprofloxacin and moxifloxacin antibiotics [12], and an Fe3O4@GO nanocomposite for the removal of tetracyclines [13]. Therefore, in this study, an AC-Fe3O4 nanoadsorbent was success fully fabricated as a magnetic nanocomposite and utilized for the exclusion of the drug promazine from wastewater. The prepared nano composite was characterized via X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier-transform infrared (FTIR) Raman spectroscopy, transmission electron microscopy (TEM), mag netic susceptibility, and isoelectric point analysis. Several parameters that influence the adsorption efficiency were investigated, including the nanoadsorbent dosage, initial drug concentration, pH of the solution, reusability, adsorption kinetics, and isotherm. 2. Experimental 2.1. Materials and methods Ferric chloride 97% (FeCl3), ferrous chloride 98% (FeCl2), ammo nium hydroxide (NH4OH, 28–30%), activated charcoal (AC), sodium hydroxide, hydrochloric acid, and promazine hydrochloride were ob tained from Sigma Aldrich. All of these chemicals were used as received. 2
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Materials Chemistry and Physics 240 (2020) 122109
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concentration (1, 10, 20, 40, 80, 100, or 120 mg L 1). The solution mixture was stirred and then subjected to an external magnet to isolate the magnetic nanocomposite. The supernatant solution was filtered through membrane filters, and the filtrate was subjected to UV–vis analysis (Agilent Cary 5000 Scan UV–vis–near-infrared spectrometer) at 252 nm to evaluate the concentration of promazine remaining in the supernatant at different time periods. In the pH experiment, 0.1 mol L 1 of HCl or NaOH was used to adjust the solution pH of the promazine from 7.0 to 9.5. To assess the effect of the contact time on the promazine adsorption, experiments to determine the batch adsorption kinetics were performed with an adsorbent dosage of 10 mg and 10 mL of promazine (40 mg L 1) at pH 8.5 at different time intervals. The amount of promazine adsorbed (mg g 1) at any time (t) and the adsorption efficiency (% Removal) of the sorbent could be determined using equations (1) and (2), respectively.
B
100 50
Fig. 3. N2 adsorption isotherms of bare AC, Fe3O4 NPs, and AC-Fe3O4 nanocomposite.
681 278 346
500 1000 1500 2000 2500 3000 3500 4000 -1
Raman shift (cm )
Fig. 2. (a) FTIR and (b) Raman spectra of (A) bare AC and (B) AC-Fe3O4 nanocomposite.
qt ¼
The water used throughout the experiments was DI water from a water deionizer (Elix Milli Q).
%Removal ¼
Ct Þ
ðC0 m
(1)
V Ct Þ
ðC0 C0
� 100
(2)
where Co and Ct are the promazine concentrations at the initial time and time t (mg L 1), respectively; V is the promazine solution volume (L), and m is the mass of the magnetic adsorbent (g). On the other hand, the amount of promazine adsorbed at equilibrium (qe) is calculated using equation (1) while replacing Ct with Ce, which is the promazine equi librium concentration (mg L 1). Batch isotherms were obtained using 10 mg of the magnetic nano composite at a pH of 8.5, while investigating an initial promazine con centration range of 40–120 mg L 1. After mixing for 6 min, the magnetic nanocomposite was magnetically collected, and the resulting solution was subjected to UV–vis analysis.
2.2. Preparation of AC-Fe3O4 nanocomposite The magnetic AC-Fe3O4 nanocomposite was synthesized by sus pending 0.2 g of AC in 100 mL of DI water and sonicating for 15 min. Subsequently, 1.41 g of FeCl3 and 0.55 g of FeCl2 were added under vigorous stirring. Thereafter, an aqueous solution of NH4OH (28%) was added dropwise to adjust the pH of the mixture to ~11. The solution was stirred for 60 min. Then, the precipitate was collected using an external magnet and washed repeatedly with DI water and ethanol. Finally, the obtained nanocomposite was dried at 80 � C overnight. 2.3. Promazine removal from wastewater
2.4. Regeneration of AC-Fe3O4 nanocomposite
The removal of promazine by the AC-Fe3O4 nanocomposite was investigated and optimized in a series of experiments. The parameters investigated included the initial adsorbent dosage, initial promazine concentration, and solution pH. Generally, batch adsorption studies were conducted by mixing 10 mg of the AC-Fe3O4 nanocomposite and 10 mL of an aqueous solution of promazine with a known initial
The promazine-loaded AC-Fe3O4 nanocomposite was magnetically separated from the solution for reuse, and the supernatant was subjected to UV–vis analysis. Thereafter, the removal of the adsorbed promazine from the nanocomposite was achieved by ultrasonication with DI water for 30 min. The nanocomposite was then thoroughly washed with DI 3
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Materials Chemistry and Physics 240 (2020) 122109
Fig. 4. TEM of AC-Fe3O4 nanocomposite. The scale bar is 200 nm.
water and ethanol, followed by drying at 80 � C. Then, the reusability was tested by mixing the dried nanoadsorbent with a fresh promazine solution using the procedure described in section 2.3. Using this regeneration procedure, the magnetic nanocomposite was recycled five times and reused in adsorption experiments.
were ascribed to Fe 2p3/2 and Fe 2p1/2 of Fe3O4, and were further deconvoluted into six peaks at 711.9, 713.65, 719.2, 725.5, 727.1, and 733.2 eV. The peaks at 711.9 and 725.5 eV are ascribed to Fe2þ, and the peaks at 713.7 and 727.1 eV are related to the Fe3þ in the Fe3O4 phase. Furthermore, the satellite peaks present at 719.2 and 733.2 eV proved the existence of Fe3þ in the Fe2O3 phase, revealing that the surface of the magnetic nanocomposite was faintly oxidized in the air environment [14]. The O 1s spectrum was de-convoluted into two peaks located at 530.4 and 531.7 eV, which can be allocated to the oxygen bonds of Fe–O and H–O, respectively, as presented in Fig. 1b [15]. The C 1s XPS spectra for the AC-Fe3O4 nanocomposite (Fig. 1c) were further de-convoluted into three peaks positioned at 284.6, 285.6, and 288.5 eV, which were – O, respectively assigned to C–C, oxygen containing group C–O, and C– [14]. The XRD patterns of the Fe3O4, AC, and AC-Fe3O4 nanocomposite are shown in Fig. 1d. Several significant diffraction peaks at 2θ ¼ 30.20, 35.6, 43.4, 57.1, and 62.9 were indexed to the 220, 311, 400, 511, and 440 reflections, respectively, which confirmed the formation of pure cubic spinel Fe3O4 [16]. The same series of characteristics peaks were also obtained with the AC-Fe3O4 nanocomposite. However, the in tensities of these peaks were significantly reduced as a result of the coating of amorphous AC on the surface of the Fe3O4 NPs. FTIR spectral analysis was performed to confirm the formation of the AC-Fe3O4 nanocomposite, as shown in Fig. 2a. The peaks at 1577 and –C 1120 cm 1 and the broad peak at 3434 cm 1 correspond to C– stretching vibrations of the benzene ring skeleton, C–O stretching vi brations, and O–H stretching vibration, respectively [17]. On the other hand, in the FTIR spectrum of the AC-Fe3O4 nanocomposite, the observed peaks at 3434, 1629, and 1427 cm 1 correspond to the O–H – C stretching, and C–C bending vibrations, respectively, stretching, C– confirming the presence of AC in the magnetic nanocomposite [18]. In addition, the FTIR spectrum showed two strong, overlapped peaks at 587 and 632 cm 1 attributed to Fe–O bond stretching vibrations of Fe3O4, which confirmed the presence of iron oxide [19]. Further investigation was performed using Raman spectroscopy, as illustrated in Fig. 2b. Bands were clearly observed at 681, 346, and 278 cm 1, which corresponded to the Fe–O–Fe bond in Fe3O4. Additionally, in both spectra, the Raman peaks for the D and G bands of carbonaceous ma terials appeared at 1340 and 1600 cm 1, which confirmed the successful
2.5. Characterization of AC-Fe3O4 nanocomposite Surface elemental analysis of the magnetic nanocomposite was per formed through XPS using an ESCALAB250 xi spectrometer equipped with an Al Kα radiation source. The powder XRD patterns were obtained via a Bruker D8 advanced diffractometer with a Cu-Kα radiation source (λ ¼ 0.1542 nm). The functional groups of the nanocomposite were studied using FTIR spectroscopy with a Jasco FTIR-6300. The Raman spectra were obtained using a Renishaw inVia confocal Raman spec trometer. The 514 nm line of an argon ion laser was used for the exci tation wavelength, with an exposure time of 10 s and a 24001/mm grating linked to a CCD camera detector. The Brunauer–Emmett–Teller (BET) surface area of the nanocomposite was determined using nitrogen sorption isotherms at 195 � C (on a model Gemini VII, ASAP 2020 automatic Micromeritics sorptometer, USA). Before the analysis, the sample was degassed for 12 h at 110 � C. The morphology of the magnetic nanocomposite was analyzed using transmission electron microscopy (TEM) (model: JEOL JEM 1230 (JEOL Ltd., Japan) operating at 120 KV. The magnetic properties were determined using magnetic susceptibility balance (Sherwood Scientific, Cambridge England). A Zetasizer Nano ZS (Malvern Instruments Ltd, Malvern, UK) was employed to determine the isoelectric point (pHIEP). 3. Results and discussion 3.1. Characterization of AC-Fe3O4 nanocomposite XPS analyses were conducted to determine the composition and chemical states of the nanomagnetic AC-Fe3O4 composite. Fig. 1a–c shows the XPS spectra of the magnetic nanocomposite, which confirm the presence of iron, oxygen, and carbon. Fig. 1a displays the Fe 2p XPS spectrum showing binding energies (BEs) at 710.7 and 724.6 eV which 4
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Materials Chemistry and Physics 240 (2020) 122109
Fig. 5. Effects of AC-Fe3O4 nanocomposite dosage on (a) adsorption capacity and (b) adsorption efficiency for removal of promazine. Conditions: promazine concentration ¼ 100 mg L 1 and total volume ¼ 10 mL.
Fig. 6. Effects of initial promazine concentration on (a) adsorption capacity and (b) adsorption efficiency of AC-Fe3O4 nanocomposite. Conditions: adsor bent dosage ¼ 10 mg and total volume ¼ 10 mL.
formation of the AC-Fe3O4 nanocomposite [20]. N2 sorption measurements were conducted to evaluate the surface properties of the Fe3O4 NPs, bare AC, and AC-Fe3O4 nanocomposite, as shown in Fig. 3. The N2 isotherm obtained for all the materials can be classed as type IV, which confirmed their mesoporous nature [21]. On the other hand, the hysteresis of AC and AC-Fe3O4 can be classified as H3, while that of Fe3O4 NPs can be classified between H1 and H3 [22]. Moreover, N2 sorpometry measurements revealed that the surface area of the Fe3O4 NPs was enhanced 7.5 fold from 105.44 to 788.66 m2 g 1 with the introduction of AC. Additionally, the pore diameter (Dp) of the magnetic nanocomposite dramatically decreased from 13.5 to 3.48 nm compared to that of the Fe3O4 NPs. Consequently, the enlarged surface area of the magnetic nanocomposite could enhance and improve its adsorption performance. The morphological properties the Fe3O4-AC nanocomposite were determined using TEM (Fig. 4). TEM images of the Fe3O4-AC nano composite showed that it is almost spherical in shape and is approxi mately 20 nm in size. Mass susceptibility measurements for the prisitne Fe3O4 NPs and the Fe3O4-AC magnetic nanocomposite were 4.348 � 10 4 cm3 g 1 and 2.575 � 10 4 cm3 g 1, respectively. The low
value of the magnetic nanocomposite could be attributed to the presence of AC in the nanocomposite. 3.2. Adsorption experiments 3.2.1. Effect of AC-Fe3O4 dosage Initially, to quantify the adsorption of promazine onto glass bottles, the adsorption experiment was conducted without adsorbent, and it was noticed that no adsorption occurred during the experiment. The ability to remove large quantities of harmful materials present in water with a minimum amount of adsorbent has economic benefits. Therefore, to determine the impact of various amounts of AC-Fe3O4 on the removal of promazine, adsorbent dosages from 6 to 14 mg were used. The amount of promazine adsorbed at equilibrium (qe) at each concentration was evaluated using a modification of equation (1) and is shown in Fig. 5a. Patently, the amount of promazine adsorbed at equi librium decreased as the adsorbent dosage increased, which can be attributed to the overlapping of adsorption sites on the nanocomposite at a high adsorbent dosage. This resulted in a reduction of the sites available for adsorption [23]. However, the promazine adsorption 5
B. D’Cruz et al.
Zeta potential(mV)
a
30 20 10 0 -10 -20 -30 20 15 10 5 0 -5
Materials Chemistry and Physics 240 (2020) 122109
(A) Promazine pH (IEP)= 6.5
(B) AC-Fe3O4
pH (IEP)= 9.35
2
3
4
5
6
pH
7
8
9
10
b Adsorption efficiency (%)
100.0 99.5 99.0 98.5 98.0 97.5 97.0 96.5 96.0 7.0
7.5
8.0
pH
8.5
9.0
9.5 Fig. 8. (a) Effect of adsorption time on amount of promazine adsorbed. (b) Pseudo-second-order plot of adsorption of promazine onto AC-Fe3O4 nano composite. Conditions: initial concentration of promazine ¼ 40 mg L 1, dosage of AC-Fe3O4 ¼ 10 mg, and pH ¼ 8.5.
Fig. 7. (a) Isoelectric points of (A) promazine and (B) AC-Fe3O4 in pH range of 1–10, with isoelectric points highlighted using green dotted lines, and (b) effect of pH on removal of promazine by magnetic AC-Fe3O4 nanocomposite. Con ditions: adsorbent dosage ¼ 10 mg, initial concentration of promazine: 40 mg L 1, and total volume ¼ 10 mL.
Table 1 Fitting parameters of pseudo-first-order (mass transfer) and pseudo-secondorder (chemical reaction) adsorption kinetic models for promazine uptake by AC-Fe3O4 nanocomposite.
efficiency increased with an increase in the adsorbent dosage in the range of 6–10 mg and then plateaued at higher concentrations (Fig. 5b). This could be ascribed to the large surface area and availability of more active sites for adsorption [24]. Above 10 mg of the AC-Fe3O4 nano composite, the adsorption equilibrium of the drug was reached, and therefore, 10 mg was used as the adsorbent dosage in further experiments.
Pseudo-first-order model
Pseudo-second-order model
k1 (min 1)
qe (mg g 1)
R2
k2 (g mg
0.402
16.80
0.9137
0.119
1
min
1
)
qe (mg g 1)
R2
40.65
0.9997
percentage was high at a lower initial drug concentration and decreased at higher concentrations [25]. Hence, 40 mg L 1 was used as the opti mum promazine concentration in further experiments.
3.2.2. Effect of initial promazine concentration Various initial concentrations of promazine ranging from 1 to 100 mg L 1 were examined to elucidate the effect of the concentration on the adsorption capacity of the AC-Fe3O4 nanocomposite, as repre sented in Fig. 6a and b. Notably, the amount of promazine adsorbed increased with the initial drug concentration. However, the percentage of promazine removed increased and then plateaued, which revealed that the promazine removal was dependent on its initial concentration. At a lower initial drug concentration, a greater number of active adsorption sites on the nanocomposite were accessible. However, at a higher drug concentration, the number of active adsorption sites could not accommodate the number of drug molecules. Thus, the drug removal
3.2.3. Effect of pH The pH of the drug solution influenced the surface charge, ionization degree, and dissociation of the functional groups present on the surface of the nanocomposite [26]. The isoelectric points (pHIEP) of the pro mazine and synthesized nanocomposite were determined using Zeta potential (ζ) measurements (pH ¼ 1 to 10) and are shown in Fig. 7a. The pHIEP values of the promazine and AC-Fe3O4 nanocomposite were ~ 6.5 and 9.35, respectively. When the pH of the solution was below 9.3, the 6
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Materials Chemistry and Physics 240 (2020) 122109
the potential with the variation of the pH. At a pH value of 7.1, the potential was þ2 mV, while it increased to þ5.5 mV at pH 8.5, sug gesting that the surface of the nanoadsorbent had a more positive charge. Hence, the removal percentage showed a slight increase with an increase in pH from 7.1 to 8.5 and almost reached 100%. 3.2.4. Kinetics of adsorption The effect of the adsorption time on the amount of promazine adsorbed (qt) by the magnetic nanocomposite is shown in Fig. 8a. Initially, the adsorption capacity and promazine removal percentage increased, it then equilibrated after 6 min with 99.3% removal. The magnetic nanocomposite acted as a fast adsorbent compared to other adsorbents, where equilibrium is reached after hours rather than mi nutes [28]. The adsorption kinetics revealed valuable data regarding the adsorption process and mechanism. Thus, two models were employed to fit the adsorption kinetic parameters using equations (3) and (4) [29], as listed in Table 1. lnðqe
qt Þ ¼ lnqe
t 1 1 ¼ tþ qt qe k2 q2e
k1 t
(3) (4)
where k1 (min 1) and k2 (g mg 1 min 1) are the equilibrium rate con stants of pseudo-firstt-order and pseudo-second-order models, respec tively; while qe and qt (mg g 1) are the adsorbed amounts of promazine at equilibrium and at any time t (min), respectively. The kinetic parameters and correlation coefficients (R2) for these models were calculated from the straight line plots of ln (qe - qt) and t/qt versus t and are given in Table 1. The adsorption kinetics data followed the pseudo-second-order model (Fig. 8b), with an R2 value of 0.999 [30]. These findings sug gested that the amount of promazine adsorbed at equilibrium was highly affected by the promazine adsorption rate. 3.2.5. Adsorption isotherms Langmuir and Freundlich models were employed to elucidate the nature of the interaction between the drug molecules and nano composite surface active sites, as well as to determine the adsorption capacity at equilibrium [34]. The Langmuir isotherm is a theoretical model that describes the formation of a monolayer of the adsorbate on a homogeneous surface without any interaction between the adsorbent and adsorbate. The Langmuir linear equation is expressed as follows [32, 35]:
Fig. 9. (a) Plot of qe versus Ce for adsorption of promazine onto AC-Fe3O4 nanocomposite. (b) Langmuir plot of promazine adsorption by AC-Fe3O4 nanocomposite. Adsorbent dosage: 10 mg and pH ¼ 8.5.
Table 2 Isotherm parameters for removal of promazine by AC-Fe3O4 nanocomposite. Langmuir isotherm model KL (mL g 0.103
1
)
Qm (mg g
101.01
Ce Ce 1 ¼ þ qe Qm Qm KL
Freundlich isotherm model 1
)
R2 0.999
KF (mL g
52.49
1
)
n
R2
4.21
0.9675
(5)
On the other hand, the Freundlich isotherm is more applicable to the adsorption over a heterogeneous surface, where strong interaction oc curs between the adsorbent and the adsorbate molecules. The linear form of the Freundlich equation is as follows [33,36]:
nanoadsorbent was positively charged, and the promazine was nega tively charged. Thus, it is theorized that the binding of the promazine onto the nanoadsorbent was governed by electrostatic interactions over the investigated pH values. A study was performed to investigate the effect of the solution pH on the promazine removal, and the results are shown in Fig. 7b. The batch experiment for the pH study was conducted in a pH range of 7–9.5 to avoid insufficient resolutions (pH < 7) and/or precipitation of the pro mazine (pH > 9) [27]. Fig. 7b shows the amount of promazine removal (percentage) in a range of pH values, and the findings confirmed that the adsorption efficiency dramatically increased and reached a maximum value of 99.7% in the range of 8.5–8.9. However, the adsorption effi ciency drastically decreased beyond a pH of 8.9. The increase in the promazine removal amount with pH can be attributed to the change in
lnqe ¼ lnKF þ
lnCe n
(6)
where Ce and qe represent the equilibrium concentration of promazine in solution (mg L 1) and the equilibrium promazine concentration adsor bed on the materials (mg g 1), respectively. In addition, Qm is the maximum adsorption capacity of promazine, KL (mL g 1) is the Lang muir constant concerning the affinity of the adsorption sites, and KF (mL g 1) and n are constants correlated to the adsorption capacity and adsorption intensity, respectively. Plots of Ce/qe versus Ce and lnqe versus lnCe were employed to determine the Langmuir and Freundlich constants, respectively. The equilibrium adsorption of promazine onto the AC-Fe3O4 nanocomposite is presented in Fig. 9a, and the equilibrium adsorption data were fitted 7
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Materials Chemistry and Physics 240 (2020) 122109
Table 3 Removal of different contaminants using AC-iron oxide magnetic nanocomposite. Compound
Concentration
Equilibrium adsorption (min)
Percentage of removal (%)
Equilibrium isotherm model
Kinetic model
Maximum adsorption capacity (mg g 1)
Ref
Promazine
1–100 ppm
6
99.97
Langmuir
101.01
100
–
Langmuir
270–324
This work [4]
120
85.20
393.7
[37]
300
76.4
Langmuir and Temkin Freundlich
90.91
[38]
90
44.22–95.26
142.85
[39]
– 180
– 99.2–99.8
Freundlich and Langmuir Langmuir Langmuir
321 2.41
[40] [41]
2880 (48 h)
97
Sips and Langmuir
Pseudo-secondorder Pseudo-secondorder pseudo-secondorder Pseudo-secondorder Pseudo-secondorder – Pseudo-secondorder pseudo-1st and -second-order
327.85
[42]
MO
a
600 mg L
Isonicotinic acid Aniline
1
1.23–6.6 g L
1
50–300 ppm 1
Amoxicillin
50–300 mg L
MBb MO MB
– 0.2–2.0 mmol L
Trinitrophenol
23–228 ppm
a b
1
MO ¼ Methyl orange. MB ¼ Methylene blue.
with high efficiency. 4. Conclusion
Adsorption Efficiency (%)
100
A magnetic AC-Fe3O4 nanocomposite was successfully synthesized for the efficient adsorptive removal of the widely used antipsychotic drug promazine from an aqueous solution and was effectively charac terized by several analytical techniques. Batch adsorption studies were conducted and indicated that the adsorption efficiency of the nano composite is dependent on various conditions. The obtained kinetic data followed the pseudo-second-order model, while the Langmuir model showed a good fit with the obtained equilibrium data, with a maximum monolayer adsorption capacity of 101.01 mg g 1. Additionally, the repeated use of the magnetic nanocomposite over five consecutive cy cles showed an adsorption efficiency decrease of less than 1%. There fore, the synthesized magnetic nanocomposite has remarkable potential as an effective adsorbent for the removal of contaminants such as drugs in wastewater. More interestingly, the resulting AC-Fe3O4 nano composite exhibited a strong response to the external magnetic field, thus adding the advantage of a facile and efficient method for separating the nanocomposite from an aqueous solution.
98 96 94 92 90 Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
Fig. 10. Reusability of AC-Fe3O4 nanocomposite for removing promazine from wastewater. Conditions: initial concentration of promazine ¼ 40 mg L 1; and dosage of AC-Fe3O4 ¼ 10 mg.
Acknowledgments
to both the Langmuir and Freundlich isotherm models. The obtained isotherm data showed a better fit with the Langmuir model (Fig. 9b) and produced a higher R2 value, as listed in Table 2. These findings imply that the adsorption process follows a monolayer molecular adsorption, with a maximum adsorption capacity of 101.01 mg g 1 (no published data for promazine). A summary of the contaminants adsorbed by the AC-Fe3O4 nano composite in comparison with our findings is reported in Table 3. The prepared nanocomposite showed remarkable and rapid removal of promazine from water in approximately 6 min, with an efficiency of 99.97%.
The authors acknowledge the funding support of the Kuwait Foun dation for the Advancement of Sciences (KFAS) (grant no. PN17-24SC01). Special thanks are extended to the Research Sector Projects Unit (RSPU) Facilities (nos. GS 01/01, GS 01/05, GS 03/01, and GS 02/01), KUNRF general facility no. GE 01/07 for the Zeta potential measure ment, and the Department of Chemistry at Kuwait University for the Raman spectroscopy measurements. Finally, special thanks to Dr. Kamlesh Kumari for performing magnetic susceptibility measurement. References [1] J.W. Peterson, B. Gu, M.D. Seymour, Surface interactions and degradation of a fluoroquinolone antibiotic in the dark in aqueous TiO2 suspensions, Sci. Total Environ. 532 (2015) 398–403. [2] V. Homem, L. Santos, Degradation and removal methods of antibiotics from aqueous matrices – a review, J. Environ. Manag. 92 (10) (2011) 2304–2347. [3] N.N. Nassar, Rapid removal and recovery of Pb(II) from wastewater by magnetic nanoadsorbents, J. Hazard Mater. 184 (1) (2010) 538–546. [4] R.-S. Juang, Y.-C. Yei, C.-S. Liao, K.-S. Lin, H.-C. Lu, S.-F. Wang, A.-C. Sun, Synthesis of magnetic Fe3O4/activated carbon nanocomposites with high surface area as recoverable adsorbents, J Taiwan Inst. Chem. Eng. 90 (2018) 51–60. [5] B. Hameed, F. Daud, Adsorption studies of basic dye on activated carbon derived from agricultural waste: hevea brasiliensis seed coat, Chem. Eng. J. 139 (1) (2008) 48–55.
3.3. Reusability of magnetic AC-Fe3O4 nanocomposite To demonstrate the feasibility of practical applications, the reus ability of the magnetic nanocomposite was evaluated by studying the removal process for 5 cycles, as shown in Fig. 10. The nanocomposite exhibited removal efficiencies of 99.97, 99.76, 99.61, 99.42, and 99.19% for cycles 1, 2, 3, 4, and 5, respectively. An insignificant decrease in the adsorption performance was observed between cycles, indicating that the magnetic nanocomposite could effectively adsorb promazine from wastewater, and then be easily regenerated and reused 8
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