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ISSN 2522-1841 (Online) ISSN 0005-2531 (Print)
UDC 667.622.547.869
SYNTHESIS, CHARACTERIZATION AND APPLICATION OF Bi2Fe4O9-GO NANOCOMPOSITE FOR THE REMOVAL OF METHYLENE BLUE DYE FROM
AQUEOUS EFFLUENT
1 2 Taznur Ahmed , Susmita Sen Gupta
department of chemistry, Science College, Kokrajhar, PIN 783370, Assam, India 2Department of chemistry, B N College, Dhubri, PIN 78332 7, Assam, India
ahmed.tazu@gmail.com
Received 20.08.2022 Accepted 06.04.2023
The nano-composite Bi2Fe4O9-GO is prepared in solvothermal approach as adsorbent for the purposes of removal of Methylene Blue (MB) dye from aqueous effluents. The material Bi2Fe4O9-GO is characterized by XRD, FESEM, EDX, BET surface area measurement, XPS and Zeta potential measurement at various pH. The adsorption process attribute good agreement for the pseudo 2nd order adsorption kinetics at various temperature. Isotherm analysis in dye uptake at various concentration shows closeness towards Langmuir isotherm with monolayer capacity value (qe = 55.46 mgg-1). The nature of adsorption is endothermic and pH sensitive. The Gibb's free energy calculation and reusability study suggest phy-sisorption interaction between adsorbent-adsorbate, indicating perfect adsorbent for adsorption process.
Keywords: Bi2Fe4O9rGO nano composite, methylene blue, kinetics, isotherm, thermodynamics.
doi.org/10.32737/0005-2531-2023-2-78-96
Introduction
Rapid modernization and urbanization of the society are being affected significantly, specially the water resources because of the huge toxic organic and inorganic effluents being released into them. Out of all the releasing effluents of dye coming from different kinds of factories like paper factory, textile, paints, carpets, plastics, cosmetics, printing as well as the food processing factories with no proper treatment results in more and more pollution in the water bodies. Dyes are the types of material having complex aromatic structure with extreme stability towards light, oxidation or temperature makes them highly difficult to act as biodegradable substance and hence has the highest impact on the quality of the water. The muta-genic as well as its carcinogenic nature, along with properties like sunlight inhabitation of the dyes it helps in maximizing the chances of bioaccumulation in living organism imparting sever diseases and disorders that makes dye the most hazardous pollutant. One of the important members of common dye family is MB (Methylene Blue) chemically known as the Tetra-Methylthionine-Chloride) a basic thiazine element used in microbiology and histology staining procedures. The toxic effects of MB had also been reported in Neonate [1] and can cause
acute renal failure, Parathyroid Adenoma [2] hyperbilirubinemia, Alzheimer's Disease [3], hemolytic anemia, and etc. Hence, diminishing the adverse effects of such dues on the ecosystem is becoming necessary leading to removal of excess dyes from the water before discharging them into the nature.
Graphene is a new class with a honeycomb structure with a single atomic thickness, with two-dimensional carbons nanomaterials. Due to its outstanding mechanical, huge surface area, electrical, mobilized charge bearing capacity and good thermal stability, it draws tremendous attention to probable applications in multi-disciplinary studies. Graphene oxide (GO) is highly oxygenated hydrophilic materials that is easily exfoliated in water to yield stable well dispersed single layered sheets [4]. The high dispersion stability of GO in water enable it prominent to form single layered on many substrates and make it a functional nanomaterials [5]. As a as precursor for economical mass production of grapheme-based products, the trends of GO attracted much more attention. Present researchers establish, because of huge surface area and it contains diverse surface oxygen group, that GO can be a promising material for absorbing water pollutant. For adsorption purposes some functional GO materials were developed, although
the adsorption capacity still low. The adsorption of dyes onto GO from effluent was investigated in many studies [6]. There are some restrictions for the use of GO like efficiency of solid liquid separation mechanism is low and the water adsorption is high. If GO is kept in filtered water, it can lead to a high risk for human, animal and aquatic organisms [7]. Thus, it remains a face up to the improvement of grapheme-based materials like adsorption capability is high, chemical strength is strong and the treatment mechanism followed for separation of solid-liquid for wastewater is the simple.
Wide ranges of nanoparticles have recently documented to be deposited by chemical or physical deposition on the GO layer or on their inter-plane[8]. In situ reduction of the metallic salts on grapheme-oxide sheets, the metal gra-phene composites are commonly obtained. Ferrite of the type MFe2O4 (M= Zn, Co, Mn, Ni etc.) were successfully incorporated in GO sheets and have been reported its good utility to adsorption study purpose [9]. In recent years, only graphene and bismuth ferrite composites
[10] have been reported for their synthesis and applications found in treatment of wastewater
[11]. Overall, three structures of bismuth ferrites consist of sillenite (Bi25FeO40), mullite (Bi2Fe4O9) and perovskite (BiFeO3). Bismuth ferrites have significantly properties of magnetic
[12], electronic [13] and dielectric [14]. However, few researchers reported the preparation and application of Bismuth ferrite in limited field. Zhao et al. successfully prepared Bi2Fe4O9 using. Ethylenediaminetetraacetic
acid (EDTA) as chelating agent and Ethylene glycol as esterification agent [15], Hu et al. have the composites synthesis of Bi2Fe4O9 with reduced graphene oxide via co-precipitation methods and show its adsorptive property on Bi-phenyl A [16], Lin et al. reported the preparation of the composites of porous Bi2Fe4O9 with reduced graphene oxide multilayer sheets [17].Thus combining the advantage of GO with magnetic Bismuth ferrite particle a promising adsorbent is achieved for desirable adsorption.
In this analysis, the preparation of mul-lite bismuth ferrite-GO composites using an easy hydrothermal low-temperature process is successfully achieved. For the mullite bis-
muth ferrite-GO composite, a structural characterization has been performed. By analyzing the adsorption process, we studied the performance of Bismuth ferrite-GO composites for MB extraction.
Materials and methods
Materials
Graphite powder, H2SO4, H3PO4, ethylene glycol(EG), Fe(NO3)3.9H2O, NaOH, C2H5OH, Bi(NO3)3.5H2O, has been procured from"Mark Chemical Laboratory Reagent Co. Ltd. (Worli Mumbai)"and utilized without purifying it. The Methylene Blue (MB) (Molecular formula: C16H18Cl N3S, CI Classification Number: 52015) (Figure 1) has been procured from "Mark chemical laboratory reagent Co. Ltd. (Worli, Mum-bai)". The chemical was analytical grade and utilized as received without purifying it.
ci
Fig. 1. Structure of Methylene blue(MB) dye.
Synthesis of adsorbent
Graphene Oxide Preparation
GO (Graphene oxide), made with modified Hummer process[18], using Graphite flakes of 1.5 g and KMnO4 of 9.0g has been carefully integrated into a concentration mixture of conc. H3PO4 and conc. H2SO4 of ratio 1:9 by volume, through continuous mixing to twelve hours at 323K. This well stimulated mixture has been cooled down and with dynamically mixing, slowly poured into ice-chilled beaker containing thirty percent of H2O2, then the mixture was washed over and over again with thirty percent ethanol and HCl and at 353K then dried.
Preparation of Bismuth ferrite (Bi2Fe4O9)
Bismuth ferrite (Bi2Fe4O9) were synthesized by following the procedure in which 6 mmol of Fe(NO3)3.9H2O and 3 mmol of Bi(NO3)3.5H2O has been simultaneously dissolved in HNO3 (10 mL, 1 M) after 5-minutes of ultrasonic dissolution. To balance the pH=8, the 37 mL of 1M NaOH have been added in the
solution under continuous stirring until a brown suspension were obtained. The precursor (brown suspension) dispersed again into NaOH (40 mL, 12 M) were poured into Teflon beaker and heat up at 365 K with continuous steady mixingin oil bath for up to six hours to obtain the final product(Bi2Fe4O9). The obtained material was thoroughly washed with water and then with ethanol [16].
In situ preparation of Bi2Fe4OgrGO composite
Up to 3 hours, the synthesized GO (0.9 g) were exfoliating through ultra-sonication in 80 mL of EG. In parallel 1.5 g of NaOH, 0.725 g of Bi(NO3)2.5H2O and 1.72 g of Fe(NO3V9H2O has been dissolved into solution of GO-EG at atmospheric temperature. After thorough mixing approximately up to 30 min, the solution has been drained into Teflon-lined stainless-steel autoclave of 200 mL as well as held at 473 K up to 6 hours approximately to cooled down naturally at atmospheric temperature. This made the black precipitate centrifuged and washed by EtOH many times. At temperature 333 K, the extracted materials were eventually dried in the vacuum oven.
Batch Adsorption experiment
The adsorptions of dye in solvent solution on the synthesized Bi2Fe4O9-graphene oxide composite (Bi2Fe4O9-GO) were achieved in a batch experiment. The standard method for applying the predefined volume of adsorbent to the preferred dye solution of initial concentration in 50 mL and shaken at a prefixed time by the thermo-static shaking water bath (SUPERIOR SCIENTIFIC INDUSTRY, ISO 9001:2008). The solution is isolated from the blend by centrifuga-tion at predefined time intervals. Concentrations of adsorbed dye in the supernatant solution is calculated by Visible spectrometer (Elico SL 177).The volume of dye adsorbed by adsorbent mass (q) per unit and adsorption extent(percent) is measured with mass balanced equation,
q = (1)
100 (2)
Adsorption Extent(%) =
where, "q" is (mgg-1) the adsorbed quantity of adsorbate is adsorbent/gram. The original and
(Co - Ce)
C
equilibrium concentration of dye are "C0"(mgL-1) and "Ce" (mgL-1). The volume of the solution measured in Litre (L) while experiment is performed, is represented by "V" and "m" is the adsorbent mass in gram (g). Adsorption has been examined under several test conditions, including initial concentrations of dye, solvent temperature, adsorbent load, pH, and interaction time. Table 1 lists the various experimental variables. The reusability analysis for the adsorbent 's adsorption potential after the loaded adsorbent has been desorbed.
Characterization of adsorbent The powdered XRD (X-ray diffraction) pattern, which focuses on a monochromatized CuKa wavelength radiation at 0.15418 nm with a phase sizes of 0.02°(29), was investigated with Bruker AXS (Germany) X-ray powder diffrac-tometer Model D8. Brunauer-Emmet-Teller (BET) N2 gas processes using automated-gassorption analyzer ("Quantachrome® ASiQ win™ Instrument, N0VA-1000 version 3.70") have defined particular surfaces, pore diameters as well as pore quantity of Bi2Fe4O9-GO composites. The FESEM image and EDX were obtained using Carl Zeiss (Germany) SUPRA 55VP, Gemini Column with air lock system model. Laser Raman microscope Labram HR Evolution, Horiba was used to obtain the Raman spectrum. The measurement of X-ray pho-toelectron spectroscopy (XPS) was performed in the Multilab2000 X ray photoelectron spectrometer. In order to know the existence of the charge on the surface the zeta potential was calculated (Zeta sizer, Malvern). The DSC (Differential scanning calorimetry) and TGA (Ther-mogravimetric analysis) were studied out in DSC1 Star System Mettler Toledo model to study the thermal stability.
Result and discussion
Adsorbent characterization X- Ray diffraction pattern analysis The XRD pattern of Bi2Fe4O9 and Bi2Fe4O9-GO reveals that the diffraction peak for GO is missing (Figure 2).
The XRD peak for GO should be in between 10 to 15 (2 theta) value and inter layering water trapped among the GO nanosheet's
stack[19] can be attributed. The intercalation of nanoparticle in the synthesis of Bi2Fe4O9-GO composite can also easily damage these loosely stacks of water[20].Therefore, in the XRD pattern of the Bi2Fe4O9-GO composite there is no measurable characteristic GO diffraction peak. The as synthesized XRD pattern of Bi2Fe4O9-GO composite exhibits the characteristic peak at 2theta value of 13.20, 30.40, 30.80, 31.50, 32.90, 33.20, 47.10 and 57.10, these can be attributed to the different faces of (001), (121), (211), (002), (220), (112), (141) and (332)
(JCPDS PDF 04-009-6352)[16]. At the same time the XRD pattern of Bi2Fe4O9 exhibits the characteristics peak at the 2theta value of 27.30, 27.50, 28.10, 32.40, 42.80 and 58.10 for the faces (121), (211), (002), (220), (112), (141) and (332) with the excellent accord of ICCD file 741098 [21].
Field Emission scanning Electron Microgram (FESEM) and EDX analysis
The morphological insight into the Bi2Fe4O9-GO composite is derived from FESEM images (Figure 3).
Fig. 2. XRD pattern of (a) Bi2Fe4O9 and (b) Bi2Fe4O<rGO composite.
Fig.3. FESEM images of Bi2Fe4O9-GO composite.
Spectrum 4
0
=e
Na 1 Bi Fe Bi /L Bi Bi ®
) 5 10 15 rull Scale 1559 cts Cursor: 0.000 20 keV
Fig. 4. EDX analysis of Bi2Fe4O9-GO composite.
The FESEM images clearly indicating the Bi2Fe4O9 particles have good dispersity throughout and flower like Bi2Fe4O9 micro-sphere are all around the GO sheet. It prevents the GO sheet from agglomeration and make easy to peel off by ultrasonication. It is also clear from the figure that the GO sheets are separated largely by the introduction of Bi2Fe4O9 particles.
The EDX (Figure 4) study confirms the existence of the element carbon, iron, oxygen as well as bismuth in the as prepared Bi2Fe4O9-GO composite.
Surface area determination (N2-gas BET isotherm analysis)
The adsorbent surface area was determined in BET ("Brunauer-Emmett-Teller") study. The
BET study for the Bi2Fe4O9-GO composite micro-structural parameter was defined by the use of N2 gas sorption isotherm of Bi2Fe4O9-GO composites (Figure 5). The isothermal has a broader hysteresis loop, suggesting type H1 as per IUPAC classification at a high relative pressure [22], the isothermal function showed the high adsorption efficiency in a Bi2Fe4O9-GO composite with narrow pores in the slit.
Figure 5 (inset) illustrated the pore size distribution which indicates that the size of pore was very narrow. A well-designed BET specific Surface area (Bi2Fe4O9-GO) had 73.967 m2g-1, compared to a specific GO surface area as recorded of 31.4 m2g-1 [23], average pore diameter is 3.472 nm and total pore quantity is 0.168 cc/g determined from the nitrogen isotherm.
Fig. 5. N2 adsorption-desorption isotherm and pore size distribution of Bi2Fe4O9-GO composite.
Fig. 6. Raman spectra of Bi2Fe4O9-GO composite.
Raman spectra analysis
Raman spectra of Bi2Fe4O9-GO composite (Figure 6) display two prominent peaks at 1344.22 and 1593.93 cm-1correspondingly D and G band. This is renowned that for the sp2 carbon domain, the G band usually allocated to E2g mode and the D band connected with the defects in structure and disorders, the symmetry as well as selection law could be violated[24]. To determine the disorder, the intensity proportion between D band and G band (ID/IG) can be used[25] and it is found to be 0.998 shows an enhanced value indicating localized sp3 defects within the sp3 carbon network. In addition to the D and G band the Raman spectra also exhibits complex Raman bands typically for the mullite structure of Bi2Fe4O9. The Bi2Fe4O9 crystal belongs to the orthorhombic space group Pbam and group theoretical calculation shows forty two Raman band 12Ag +12B1g + 9B2g + 9B3g [26].
X-Ray Photoelectron spectroscopy
Further XPS has been studied to determine the chemical state of Bi2Fe4O9-GO composites. The collected data were analyzed using the accidental carbon at its binding site. It was reported earlier by researcher that grapheme oxide(GO) consists of two main peak, hydro-phobic n- conjugated sp2 domain and hydro-philic oxygen containing functional group with sp3 domain [27]. The full screen XPS spectrums (Figure 7) exhibits the presence of Bi, C, O and Fe elements at the binding energy of 159.49eV, 284.66, 530.25 and 710.79 eV for Bi2Fe4O9-GO composites. The ratio of Carbon and Oxygen content implies that more number of oxygen containing group were successfully introduced. Multi-peak resolution XPS computational methods of C 1s band deconvoluted into four peaks at 284.83, 285.65, 286.78 and 288.88 eV, corresponding to the C=C/C-C, C-O, C=O and COOH groups [28].
Fig. 7. XPS anlysis of Bi2Fe4O9-GO composite.
Thermal property analysis
The TGA and DSC curve of Bi2Fe4O9-GO composites are presented in Figure 8 and the TGA curve indicates that the loss of weight of ~5% was attributed to water vapor losses up to 346.8K. In DSC curve, an endothermic peak at 300.6 K also indicates the dehydration of the OH group present in the composite. In the temperature range 346.8 K to 868.37 K 14% of weight loss observed, that may be because of carbon oxidation[29]. Around 81% of the weights found after oxidation compared to the
weight of Bi2Fe4O9-GO composites. In DSC curve an exothermic peak is observed at nearly 376.97K, it can be attributed to the complete crystallization of the composite [30].
Zeta potential analysis
The calculation of zeta potential indicates in the pH-range (~ 5.0 to 9.0) of Bi2Fe4O9-GO composites for zero-point charge used in this study was not at all available, suggesting the adsorbent's negative surface charge. The Zeta potentials value for the pH variation shown in Figure 9.
Fig. 8. Thermal property of Bi2Fe4O9-GO composite (a) TGA curve and (b) DSC curve.
Fig. 9. Zeta potential variation with solution P .
Adsorption Study
Time Influence on MB
The effect of contact time on Methylene Blue dye adsorption onto Bi2Fe4O9-GO were achieved at various temperatures (30, 40, 50 and 600C) (Figure 10). It has been seen that the adsorption of MB per unit mass of the Bi2Fe4O9-GO composite elevated from 27.44 -36.03 mgg-1 (10 min) to 41.16 - 49.38 mgg-1(240 min) steadily within 240 minutes, the adsorption process achieved equilibrium. At the beginning of the adsorption, the maximum adsorption was generated and then slowed down by achieving balance within 240 minutes. The wide active sites in the adsorbent may be due to the high adsorption potential during the initial periods encouraging the dye molecule to proficiently bind the adsorbent. As the adsorption process continued with time, the active sites
which available are less in number and attained equilibrium mechanism [31].
pH Influence on MB
The pH value is considered as essential parameter for adsorption process. The experimental results indicate (Figure 11) that the adsorption of MB preferred at higher pH[32].The pH value of solution will impact a surface charge of the adsorbent which might be in proton competition with the dye molecule due the partial negative charge at the surface of the adsorbent. With the increased pH value, the electrostatic attraction among the cationic MB and the surface of Bi2Fe4O9-GO composite increases, the dye molecule was therefore found to attract more easily(indicated by "zeta potential measurement") from the adsorbent negative surface.
Fig. 10. Effect of time on the adsorption of MB onto Bi2Fe4O9-GO composite. Table 1. Experimental Conditions for Adsorption Study
Sl No. Parameter for adsorption process Experimental set-up
1 time adsorbent 0.2 gL-1, dye concentration 10 mgL-1, pH 7.19, temperature 303-333 K, time 240 min
2 dye concentration adsorbent 0.2 gL-1, pH 7.19, time 240 min, temperature 303 K, dye concentration 10-30 mgL-1
3 adsorbent load dye concentration 10 mgL-1, pH 7.19, temperature 303K, time 240 min, adsorbent 0.08 - 0.36 gL-1
4 pH adsorbent 0.2 gL-1, dye concentration 10 mgL-1, temperature 303 K, time 240 min, pH 2.0- 12.0
Fig. 11. Effect of P on the adsorption of MB onto Bi2Fe4O9-GO composite.
Influence of initial MB concentration
Adsorption of MB per adsorption unit weight grew from 41.16 mgg-1 to 53.005 mgg-1 at 303 K by rising concentration of dye levels from 10 to 30 mgL-1(Figure 12). When the dye concentration is increased, the greater driving power is given to resolve the dye mass transfer resistance among the solid and the water phase, this will result in a further dye molecule collision and adsorbent solid phase. When the dye concentration is at peak, the adsorbent unit mass is to expose more dye forms and the incremental filling of the required binding sites increases the amount of dyes taken up. This raises the qe while the net adsorption drops [33].
Influence of adsorbent load
Figure 13 describes the effect of the adsorbent dose variance on MB adsorption. When amount of adsorbent increased from 0.08 gL-1
to 0.36 gL-1, adsorption capability (qe) was reduced. On the other hand, there has been a steady increase in adsorption with the rising adsorbent charge. The increase in adsorption percentage could be caused when negative surface charge is increased and potential of electrostatic near solid surface is decreased, that favors adsorbent interaction with adsorbate.
However, as the utility of adsorption sites was decreased effectively and correspondingly by a high volume of adsorbent, there was a comparatively reduced number of these sites per unit mass leading to higher adsorbent doses of adsorption. Moreover, a limited quantity of adsorbent yields high qe value could easily lead to the adsorption sites. As adsorbent load increased, particles overcrowding (by solid concentration) reduced the adsorbent usage of the adsorbent increase in unit weight adsorption [34].
c„ (mg/L)
Fig. 12. Effect of MB concentration in the adsorption onto Bi2Fe409-G0 composite.
005 0.10 0 15 020 0.25 0 30 0.35 040 Adsorbent dose (g/L)
Fig. 13. Effect of adsorbent dose on the adsorption of MB onto Bi2Fe409-G0 composite.
Influence of temperature on MB
Figure 10 shows the variation of equilibrium concentration (ce) as well as equilibrium capacity (qe) of MB at distinct temperature (303, 313, 323 and 333 K). It was noticed that the temperature significantly impacts the adsorption of MB. The adsorption potential of MB increased from 303 to 333 K, indicating the adsorbent-dye interaction in endothermic form. The porosity and pore volume of adsorbent may be effected by higher temperature that enables the adsorbate molecule to quick diffusion into the outer layer of boundary and into the pores of the Bi2Fe4O9-GO composites [35, 36]. The increase in adsorption capacity of MB on adsorbent requires an activation energy and increase in temperature provide higher driving force to overcome and bind to surface this energy barrier [37].
Kinetics model study of the adsorption process
Adsorption is a diverse phenomenon which involves transportation of soluble particles, and can be a slow-moving mechanism from a liquid state to the surface solid phase of the adsorbent. This concept contributes to the kinetics of dye adsorption, using the experimental data for different kinetic models. The kinetics of MB adsorption on Bi2Fe4O9-GO are analyzed, the Lagergren pseudo first and second order, Elovich, intra-particle diffusion and the kinetics models of Boyd film diffusion was examined at room temperature.
Pseudo first and pseudo second order kinetics
Pseudo first [38] and second order kinetics
[39] were widely used in adsorption phenomenon. The integral linear form of the pseudo first and second order model at distinctive temperature can be used as equation 3 and equation 4, MB dye adsorption on the Bi2Fe4O9-GO composite.
log(qe - qt) = log4e - Ki_t/2.303
t
qt
-2 + —
K2qe qe
(3)
(4)
where, qe and qt were MB absorbed(mgg-1) at equilibrium and at any time t(min) while adsorption mechanism for the pseudo first-order and pseudo second-order version, k1(min-1) and k2(g mg-1 min-1) were the rate of constant. The curve log linearity of kinetic model, pseudo first order (Figure 14.a) is represented as (qe-qt) vs t and pseudo second order is represented as (Fi-gure14.b) t/qt vs t. The slope and interception of the linear fitting plots explain the constant rate (k1, k2) and adsorption capacity(qe).
It was experienced that, the calculated capacity of adsorption value (qe,cal.) obtained for pseudo first order kinetics models differ with the experimental valu (qe, exp). The data obtained with a deviation at different temperature are tabulated in Table 2. The deviation of experimental value from pseudo kinetics model of the second order is comparatively less, suggesting the closeness of experimental value to theoretical value. The minute deviations observed in pseudo second order model may occur because of certain experimental error. But the adsorption mechanism was far similar to kinetics model of second order.
A 6 8 10 12 -4 16
t^Cmir05)
Fig. 14. (a) Pseudo first order kinetic plots for MB adsorption, (b) Pseudo second order kinetic plots for MB adsorption, (c) Elovich kinetic plots for MB adsorption. (d) Intra-particle diffusion kinetic plots for MB adsorption. (e) Boyed's film diffusion kinetic plots for MB adsorption.
Table 2. Kinetic parameters for the MB adsorption
Co (mgL-1) Pseudo first-order kinetics
10 Temperature (K) K1 (min-1) qe, cal. (mg g-1) qe, exp. (mg g-1) Deviation (%) R2
303 1.88 x 10-2 24.85 41.16 39.62 0.995
313 1.9 x 10-2 28.06 44.76 37.31 0.990
323 1.63 x 10-2 21.99 47.35 53.56 0.997
333 1.74 x 10-2 22.65 49.38 54.13 0.990
Pseudo second-order kinetics
Temperature (K) K2 (g mg-1 min-1) qe, cal. (mg g-1) qe, exp. (mg g-1) Deviation (%) R2
303 1.01 x 10-3 44.46 41.16 -8.01 0.999
313 1.03 x 10-3 48.54 44.76 -8.44 0.999
323 1.21 x 10-3 50.42 47.35 -6.48 0.999
333 1.32 x 10-3 52.30 49.38 -5.91 0.999
Elovich kinetics
Temperature (K) a (adsorption co-efficient) (mg g-1) P (desorption co-efficient) (min g mg-1) R2
303 129.0119334 0.15203691 0.967
313 121.8666429 0.13863549 0.980
323 1316.546977 0.15458101 0.985
333 2537.143526 0.15326516 0.979
Intraparticle diffusion kinetics
Temperature (K) K, K2 K3 C1 C2 C3 (R1)2 (R2)2 (R3)2
303 2.30 0.931 0.421 15.04 27.98 34.62 0.979 0.971 0.999
313 2.22 1.21 0.407 18.23 27.83 38.45 0.979 0.926 -
323 2.05 0.968 0.546 22.98 33.28 38.88 0.998 0.989 -
333 2.51 1.12 0.356 22.31 35.42 43.08 0.999 - 0.966
Elovich kinetics model
The Elovich kinetics model [40] can be applied to adsorption phenomenon considering that (i) The adsorbent surface are energetically heterogeneous and (ii) At the low surface coverage, no adsorbed dyes may significantly affect adsorption kinetics or their desorption interaction. The Elovich equation is -
qt = (1)ln(aP) + (1/P)lnt (5)
The a parameter is regarded as initial rate at t = 0 (dqt/dt = a) and P is the Elovich con-stant.The linearity of the qt vs lnt curve (Fig-ure14.c) showed good proximity for precisely calculate the Elovich kinetic model equation. The calculated values for the correlation coefficient from the plots at various temperatures, the constant a (co-efficient of adsorption) and P (coefficient of desorption) is tabulated in Table 2. Intra-particle diffusion model The dye molecules diffused into adsorbing pores, cannot be denied for porous adsorbent. This model is therefore also intended to evaluate the optimal kinetics models for the adsorption mechanism. Weber and Morris[41] have simplified the intra-particle diffusion model and written as:
qt = kit05 + C (6)
The intra-particle diffusion rate is ki (mgg-1min05).The data obtained for rate constant (ki) with stage i and constant C is computed with the linear plots of the qt vs t05, interpreted as the effect of boundary layer. The intercept (C) indicates the limit layer's thickness. The higher intercept value increases the sorption's contribution to the rate regulation. The interception value at zero means, in compliance with this model, that intra-particle diffusion regulates the complete adsorption process rate. The non-linearity of the curve qt vs t05 indicated that diffusion of the intra-particle cannot contribute significant role for the entire adsorption of the dye process.
The transfer of the solution can involve either the stage of mass transfer (film diffusion) or intra-particle diffusion or both during the solid/liquid sorption process. The diffusion mechanism passes through the multi-step process in dye extraction the aqueous solution through adsorption [41]. The qt vs t05 plots (Figure 14 d) is
found to be multi linear consisting three linear segments, multiple steps during the adsorption process have been suggested. The base segments with a high slope due to MB transport by film diffusion from the solution to the outer Bi2Fe4O9-GO surface. The next segment describes the gradual adsorption phases that corresponds in the adsorbent pore (intra-particle diffusion) to the diffusion of the MB molecule from the exterior surface. The third segment defined the small slope at final balance stage, where the diffusion of the intra-particle begins to minimize. The non-zero value of the intercept (C) for every linear segment indicating that the diffusion of intra-particle is not the only rate control phase in all stages in diffusion process [42]. Earlier adsorption stages are regulated by the diffusion of the film. The sorption process is regulated by intra-particle diffusion once the solution particle is charged.
Boyd's Film diffusion model
Usage of the Boyd model [43] to get insight into the actual rate-control phase in the process of adsorption were further analyzed.
F = 1- (6/n2)exp(-Bt)
(7)
The mathematical function of F is Bt, where F is the partial attainment of equilibrium at different time (t)
(8)
p = 2l
Qe
where qt and qe is the dye adsorption capacity at time "t" as well as at equilibrium.
Equation 7 can be rewritten as: Bt = -0.4977 - ln(1 - F) (9)
Therefore, from equation (9), the Bt value can be determined for every F value. The linearity of these graphs is a reliable indicator that the adsorption rate is regulated by an external mass transmission (film dissemination) or intra-particle dissemination. The plots of calculated Bt Vs time for the MB adsorption at the initial stages shows linear relation and did not passes through the origin(Figure 14.e) indicating the diffusion dominated the rate of adsorption in the early stages and then the adsorption controlled the diffusion intra-particle diffusion process. Adsorption Isotherm Adsorption helps chemical species to accumulate between adsorbents in the solid phase and interfaces. The empirical isothermal models
give experimental findings details. The various isothermal models to explain a phase of adsorption are Dubinin-Radushkevich, Langmuir-Freundlich, Temkin, and BET Isotherm model. Langmuir and Freundlich Isotherm For Langmuir[44] and Freundlich[45] Isotherm, adsorption isotherm is testedthe dye's Bi2Fe4O9-GO composites adsorption at room temperature. Langmuir and Freundlich model's [46] linear form is represented via the equations 10 and 11.
1 (10) (11)
Ce _ Ce Qe Qm
bqm
log(qe) = logkf + log(Ce)/n
where, ce (mgL-1) is the the MB solution equilibrium concentration, qe (mgg-1) is equilibrium capacity of adsorption, qm (mgg-1) is the maximum adsorption potential for theoretical saturation of Langmuir is the full monolayer coverage and b is constant Langmuir to the connecting sites affinity and adsorbent energy. In Freundlich equation the kf (mg1-1/n L1/n g-1) is Freundlich constant related to capacity of adsorption (the binding energy constant reflecting the affinity of adsorbent to dye molecule) and 1/n is a factor of heterogeneity suggesting adsorption process feasibility.
The linear relation has been obtained
among ce/qe vs ce plots (Figure15 a) for Langmuir isotherm model. The values for isotherm and coefficient of correlation are stated in Table 3. Another important parameter RL [47], a dimensionless separation constant is given by the equation as-
RL = (12)
L 1+bCo v '
where co is initial highest MB concentration (mg/L).The separation constant shows that the isotherm is unfavorable to the RL>1value, the value Rl<1 is favorable, the value RL = 1 is linear and the value RL = 0 is irreversible [48, 49]. The investigation suggests that the calculated value between 0.007-0.02, proves the favorable adsorption process.
The linear fitting curve of log qe vs log ce of dye adsorption (Figure15 b) for the Freundlich isotherm is investigated and the correlation co- efficient (R2) is found to be much less than Langmuir isotherm curve. The experimental value better suits the Langmuir isother-mic model than the Freundlich isothermic model. Calculated capacity is 55.46 mgg-1 for MB for Langmuir adsorption monolayers. The Langmuir monolayer capacity with the similar kind of adsorbents reported earlier are compared in Table 4.
Fig. 15. MB adsorption onto Bi2Fe4O9-GO composite. (a) Langmuir isotherm model (b) Freundlich isotherm model (c) Temkin isotherm model (d) D-R isotherm model (e) BET isotherm model.
Table 3. Correlation coefficient for the adsorption isotherm of MB adsorption at 303K
Langmuir Isotherm
qm (mg g"1) b R2 Rl
55.46 9.1 x 10"1 0.999 0.0351
Freundlich Isotherm
kf(mg1-1/n L1/n g"1) n R2
37.27 8.41 0.995
Tempkin Isotherm
At (g"1) B (Jmol"1) R2
668.34 5.58 0.994
D - R Isotherm
qs( mgg"1) E ( kJmol"1 ) R2
50.59 1.38 0.733
BET Isotherm
qm (mg g"1) Kb R2
16.61 "4.9 0.940
Table 4. Comparison of Langmuir monolayer capacity for MB from literature
Adsorbent Langmuir monolayer capacity qm (mgg"1) Reference
GNS/Fe3Ü4 43.82 [50]
rGO/ZnFe2Ü4 9.73 [51]
Barium(II)"dopped rGO/ZnFe2O4 9.99 [52]
Bi2Fe4Ü9"GO 55.46 This work
Temkin Isotherm study
Temkin believes that the adsorption heat of all molecules decreased linearly with coverage because of adsorbent - adsorbate interactions. Consistent binding energy to the highest binding energy can be characterized this adsorption mechanism [53]. As defined in the linear form, Temkin Isotherm [54] can implant by equation (13) in the mechanism of adsorption. qt = 2.303RT/bT (log AT + logqCe) (13)
where the Temkin constant was RT/bT = B (Jmol-1), it was the sorption, AT(g-1) represents the binding equilibrium constant that matched the highest binding power, the gas constant was R (JK-1mol-1) and the solvent temperature was in Kelvin ( K).
For Temkin Isotherm, the correlation coefficient values showed the received information from the linear fitting qe vs log ce curve (Figure 15 c) in table-3, R2 = 0.994, the monolayer MB adsorption to Bi2Fe4O9-GO appreciated.
Dubinin - Radushkevich Isotherm model In the adsorption mechanism of porous adsorbing with a large variety of pore sizes and shapes, the Dubunin-Rudushkevich (D-R) Iso-
therm [55] plays a major role. Equation (14) and Equation (15) demonstrate the linear structure and energy desorption of the D-R isother-mic equation [56].
logqe = logqs - Kdr s2/2.303 (14) E = (2Kdr)-05 (15)
where qs (mgg-1) is the Dubinin-Raduschkevich capacity of theoretical saturation, Kdr (mol2/J2)' is D-R constant of isotherm which relates to free energy, s was the Polanyi potential, expressed as s = RTln(1+ 1/ce) and E (kJmol-1) is the adsorbate's molecule energy that allows the molecule to be extracted from the sorption site to endlessness.
For Dubin-Raduschkevich Isotherm, the parameter value for (Table-3) was qs= 50.59 mgg-1 and E = 1.38 kJmol-1 from the linear fitting lnqevs s2 curve (Figure 15 d). The physical adsorption of MB on the adsorbent was suggested.
BET adsorption Isotherm model
The model for BET Adsorption was based on the statement in which adsorbate can randomly adsorbed in the dye distribution on the adsorbent surface[57], resulting in multilayer for-
mation. It is also assumed that the first mono-layer and the following layer were adsorbed with the adsorption energy and condensation energy. The BET linear form equation [58] is-
ce _ ce(Kb —
(co - ce)qe Kbqmco
+
1
Kbqm
(16)
The adsorbate equilibrium concentration in solution (ppm) is represented as ce. The adsorbate saturation concentration (mg/L) is given as co, qe is an adsorbent in adsorbent quantity (mg/g), The adsorptive quantity of the whole monolayer (mg/g) is qm,the constant BET is kb.
The study of the plots of
Vs ce/co
(co-ce)Qe
(Figure 15 e) indicate that the MB adsorption onto Bi2Fe4O9-GO may be in multilayer formation (Table 3).
Thermodynamic study To analyze the temperature impact on the adsorption of MB in the composite Bi2Fe4O9-GO, the thermodynamics parameters involving the change in enthalpy (AH), entropy (AS), and the equation is used to measure Gibb's free energy (AG) for dye adsorption [59] of the adsorbent.
= AS/R - AH/RT (17)
AG = AH - TAS (18)
where, Kd (qe/ce)is determined by experimentation in the distribution coefficient, T is the Kelvin (K) temperature, R represents ideal gas constant (8.314 JK-1mol-1).
The Arrhenius equation is implemented with the following equation to determine the activation energy of adsorption.
logfc2 = log A - £a/2.303RT (19)
Ea (kJmol-1) is the Arrhenius adsorption activation energy where k2 (g mg-1min-1) is the pseudo second order constant obtained from the kinetics model and Arrhenius factor is A.
The AS value and AH value for the intercept and plot slope of the linear fitting of the plot lnKdVs 1/T plots (Figure 16) and AG value from the equation-18 is calculated.
Table 5 lists all thermodynamic values. The AH positive value indicates the endother-mic adsorbing-adsorbent interaction. The AS positive value suggested the random increase at solid interface solution, which may be attributed to certain structural variations of adsorbate and adsorbent in adsorption mechanism. The negative free energy of the Gibb's(AG) for adsorption decreased from -7.4 to -15.8 KJmol-1 with temperature rises of 303K to 333K and also showed the spontaneity of MB adsorption mechanism at higher temperatures to be more favorable [60]. The free energy value of Gibb between 0 to -20 KJmol-1indicates that the adsorption mechanism is physisorption, whereas for chemisorptions -80 to -400 KJmol-1 [49]. Thus, the MB adsorption to Bi2Fe4O9-GO may be considered to involve physisorption, based on the AG value. A linear fit curve of logk2 Vs 1/T is used to evaluate the Arrhenius Parameter, provided that the slope of -Ea/2.303R is present and the logA is intercepted (Figure 17). The result is 8.894 kJ mol-1 for activation energy. Where the mechanism of adsorption can be regulated physically [61].
Fig. 16. Thermodynamics analysis of MB adsorption onto Bi2Fe4O9-GO composite.
c
o
Table 5. Thermodynamic data for dye adsorption_
Dye AH (KJmol-1) AS (JK-1mol-1) Ea ( kJ mol-1) AG (kJK-1mol-1)
303 K 313 K 323 K 333 K
MB +77.5 +280.18 8.89 -7.4 -10.2 -12.9 -15.8
—i—■—i—'—i—*—i—■—i—>—i—>—i—» 0 00300 0.00305 0.00310 0.00315 0 00320 0 00325 0 00330
1/T(K')
Fig. 17. Arrhenius plots of MB adsorption onto Bi2Fe409-G0 composite.
Renewability evaluation study
The study of reusability is a crucial factor in adsorbent economics and applicability. The recyclability of Bi2Fe4O9-GO-is investigated performing five times adsorption/desorption cycle. After agitating approximately 12 hours with a magnet stirrer at room temperature, the adsorbed MB dye is desorbed from the etha-nol/acetic acid solution then the adsorbents are reused for successive adsorption process. The adsorbent shows diminishing effect, its adsorption ability in each consecutive cycle reduced from 94.9 to 82.4% after the 5th cycle of the original adsorption capacity. Without desorption, adsorbents decreased their adsorption potential after the first cycle to nearly 50 percent, which decreased further after the fifth cycle to 15.3 percent of their original value. The efficiency of adsorption of Bi2Fe4O9-GO is recovered via the desorption in ethanol/acetic acid solution. The results show that Bi2Fe4O9-GO Composites could, just because of attractive regeneration efficiency, be cost effectively and potentially adsorbent to remove MBs.
Conclusion
The Bi2Fe4O9-GO composite has been
tested for adsorption of Methylene Blue dye. The study results were summed up as follows:
• The Bi2Fe4O9-GO adsorbent had been prepared successfully and the characterization analysis indicated that the composite was within nano range.
• The method of extracting the dye ideally followed the Langmuir isotherm with adsorption monolayer capacities of 55.46 mgg-1.
• The second order kinetic models was followed by the adsorption mechanism.
• Endothermic in nature were the dye adsorptions.
• Random and decreased Gibb's free energy interactions with Bi2Fe4O9-GO dye.
• PH-sensitive dye adsorptions.
Acknowledgement
The authors are thankful to CSIR-Central Electrochemical Research Institute, Karaikudi, Tamilnadu,India, USIC, Gauhati University, India and IIAST, Assam, India for measuring XRD, BET surface area, FESEM images, EDX, Raman Spectroscopy, XPS analysis, Thermo-gravimetric analysis and Zeta potential respectively. We are grateful to chemistry department, B N College, Dhubri for encouraging us for the experimental work.
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NBi2Fe4O9-GO NANOKOMPOZÍTÍNÍN SÍNTEZÍ, XARAKTERÍSTÍKASI VO 0RKAB SULARINDAN METÍLEN ABISI BOYASININ CIXARILMASI Ü£ÜN TOTBÍQÍ
Taznur Ahmed, Susmita Sen Gupta
NBi2Fe4O9-GO nanokompoziti metilen abisi boyasinin girkab sularindan gixanlmasi adsorbenti kimi solvotermik üsulla hazirlanmi§dir. Materialin xassalari XRD, FESEM, EDX, ВЕТ, XPS üsullari ila, ZETA potensilin müxtalif pH-larda ólgülmasi ila 0yranilmi§dir. Adsorbsiya prosesi müxtalif temperaturlarda psevdo ikinci tartib adsorbsiyanin kinetikasina müvafiq galir. Boyanin müxtalif qatiliqlarda udulma izoterminin analizi onun Lenqmür izontrmina yaxin oldugunu gostarir (monolayin hacmi qe = 55.46 mgg-1). Adsorbsiya tabiatca endotermikdir va pH-a hassasdir. Sarbast Hibbs ener-jisinin hesablanmasi va takrar istifada olunma mümkünlüyünün tadqiqi adsorbent va adsorbat arasinda fiziki adsorbsiya qar§iliqli tasirinin oldugu ehtimalini dogurur ki, bu da adsorbsiya ügün ideal adsorbenti sübut edir.
Afar sozlar: NBi2Fe4Og-GO nano kompoziti, metilen abisi, kinetika, izoterm, termodinamika.
СИНТЕЗ, ХАРАКТЕРИСТИКА И ПРИМЕНЕНИЕ НАНОКОМПОЗИТА Bi2Fe4O9-GO ДЛЯ УДАЛЕНИЯ КРАСИТЕЛЯ МЕТИЛЕНОВОГО СИНЕГО ИЗ ВОДНЫХ СТОКОВ
Тазнур Ахмед, Сусмита Сен Гупта
Нанокомпозит Bi2Fe4O9-GO приготовлен сольвотермическим способом в качестве адсорбента для удаления красителя метиленового синего (МС) из водных стоков. Материал Bi2Fe4O9-GO характеризуется измерением площади поверхности методами XRD, FESEM, EDX, ВЕТ, включая метод XPS и измерением дзета-потенциала при различных pH. Процесс адсорбции хорошо соответствует кинетике адсорбции псевдо 2-го порядка при различных температурах. Анализ изотермы поглощения красителя при различных концентрациях показывает близость к изотерме Ленгмюра со значением емкости монослоя ^э = 55,46 мгг-1). По своей природе адсорбция является эндотермической и чувствительной к pH. Расчет свободной энергии Гиббса и исследование возможности повторного использования предполагают физическое адсорбционное взаимодействие между адсорбентом и адсорбатом, что указывает на идеальный адсорбент для процесса адсорбции.
Ключевые слова: нанокомпозит Bi2Fe4Og-GO, метиленовый синий, кинетика, изотерма, термодинамика.
