PHYSICO-CHEMICAL ANALYSIS OF COMPOSITE MATERIALS (ALGINATE-BENTONITE-ACTIVATED
CARBON)
Nassima Djebri
1, 2, Nadia Boukhalfa
2, Mokhtar Boutahala
2, Nacer Eddine Chelleli
1[email protected] Abstract— New low cost materials consisting of alginate,
bentonite and activated carbon were prepared according to the ionic gelation method. Physical characteristics of composites were characterised by X-ray diffraction, Fourier transform infrared spectroscopy, surface mesurment by Brunauer, Emmett and Teller method (BET), and morphological characterization by SEM. Alginate beads containing activated carbon and bentonite have been successfully applied for water treatment.
Keywords— encapsulation, composite beads, characterization.
I. INTRODUCTION
Composite materials are based on the concept that a combination of different materials can attain properties that the constituent materials cannot attain individually by themselves [1]. This concept has been applied to create a variety of composite materials having a wide range of desirable properties superior to conventional materials. The development and use of composite materials has been increasing ever since. After the development of carbon, boron and aramid fibers, composites were widely used in the structural parts of aircrafts especially during World War II.
After World War II, composites were introduced in automobiles and have gained popularity in many other fields due to their superior mechanical properties
Activated carbon is an extensively used material because of its high specific surface area and surface reactivity [2].
Activated carbon is prepared from naturally occurring carbonaceous materials such as coal, petroleum, coconut husks, peat and many more. Activation involves mild oxidation of the solid in such a way that small voids are formed by removal of a portion of the solid. These voids are called pores. The carbonaceous substances have to go through two stages. The first stage is carbonization (devolatilization), followed by a second stage of activation. A simultaneous devolatilization and activation can be obtained chemically by impregnation with dehydrating agents such as phosphoric acid and zinc chloride. The adsorptive properties of activated carbon vary with the source materials and the activation process [3].
Clay minerals have also been recognized as very good material because of their amazing textural properties,
abundance, and inexpensiveness [4, 5]. The structural characteristics of montmorillonite, a smectic clay, are the octahedral aluminate sheet sandwiched between tetrahedral silicate layers, and the layer charge can easily be generated by replacement of cations in the layer with cations of different charges; e.g., replacement of Al3+in the aluminate sheet with M2+ or Fe2+ produces negatively charged aluminate layers, and cations (Na+ or K+) are newly incorporated into the interlayer spaces to maintain charge neutrality. Hence, in the case where the interlayer is incorporated with Na+, the hydrophilic property must be enhanced, which in turn leads to easy penetration and high degree of water swelling. Modified clays are also used in other applications such as adsorbents of organic pollutants in soil, water and air; rheological control agents; paints; cosmetics; refractory varnish; thixotropic fluids, etc.
Alginates are natural polysaccharides that are produced by brown algae. Based on the exact nature of the seaweed species, they represent 10–45 wt.% of dry matter [6]. Their high bioavailability and easy extraction process explain their low cost. Alginates are widely used in many different applications because of their versatile properties that can be monitored according to different stimuli (concentration, temperature, pH, etc.). In aqueous solution, alginates are usually employed as thickening agents to increase the viscosity of the medium [7]. In the presence of cations (usually divalent or trivalent), they can produce a hydrogel according to a complexation mechanism. The transformation is known under the designation ‘‘ionotropic gelation.’’ Given its biocompatibility, Ca2+ is the most applied and studied gelling agent [8]. Calcium alginate is widely used in immobilizing activated carbon [9], carbon nanotubes [10], titania nanoparticles [11].
Alginate is composed of guluronic acid and mannuronic acid an considered to be biocompatible, non-toxic; non- immunogenic and biodegradable. In addition to its biocompatibility, source abundance, and low prices, it has been widely used in the food industry as thickener, emulsifying agent and tissue engineering material. Alginate- based biomaterials for orthopedic applications have been extensively discussed by Lee et al. [12].
The individual features of activated carbon, bentonite, and alginate toward adsorption are not always very promising and
1Laboratoire Matériaux et systèmes Electroniques (LMSE), Faculté des Sciences et de la Technologie,
Université de Bordj Bou Arreridj, El Annasser, 34000 BBA, Algérie
2Laboratoire de Génie des Procédés Chimiques (LGPC), Faculté de Technologie,
Université Ferhat Abbas Sétif-1, 19000 Sétif, Algérie
identical; thus, the idea of combining them to make an effective composite material for dye removal was conceptualized. Moreover, the inherited problems linked with the individual adsorbents might be minimized by combining them. In this study, the prepared activated carbon named ‘AC’
was used as activated carbon, which was produced by steam activation of apricot stone under carefully controlled conditions. Therefore, the objectives of this study were as follows: first, to prepare a variety of composite beads from the combination of bentonite–alginate beads (A-OAB), activated carbon–alginate beads (A-AC), and activated carbon–
bentonite–alginate beads (A-OAC) via a simple fabrication method; second, to characterize all prepared samples by SEM, BET, FTIR and pHPZC.
II. MATERIALS AND METHODS A. Chemicals
The bentonite clay was supplied by the Enterprise Nationale des Substances Utiles, et des Produits Non Ferreux, Hammam Boughrara, Algeria, it was grinded to a particle size that ranges from 20 µm to 45 µm. Sodium alginate and calcium chloride were purchased from R&M Chemicals, R&M Marketing Essex, UK, and the apricot stone obtained from fruit preserving plant located in the region of Setif (Algeria) were used as the raw material for the production of activated carbons. Methylene blue (chemical formula:
C16H18N3SCl, molecular weight: 319.85 g/mol, solubility in water: 40 g/L) were supplied by Merck Chemical Company.
All other chemicals were used without any further purification. Deionized water was used for the preparation of all the required solutions.
B. Preparation of the OAB, AC and theirs composites A- OAB, A-AC and A-OAC:
Preparation of Organo-Acid-Activated Bentonite (OAB):
The purified Bentonite was subjected to acid treatment with sulfuric acid. Acid leaching was carried out by placing the sample in contact with H2SO41 M (1:1 w/w) with stirring and reflux heating (90 °C) for 5 h. The resulting solid was immediately centrifuged, washed with distilled water until it was free from sulfate ions, dried at 80 °C and named: AB.
In order to increase its hydrophobicity by co-adsorption with a surfactant, a suspension of AB was treated with cetyltrimethylammonium bromide (CTAB) by adding the amount of the cationic surfactant equivalent to 100 % of the value of CEC. The surfactant was dissolved in 1 L of distilled water at 80 °C and stirred for 3 h. 10 g of sample (AB) were added to the surfactant solution. The dispersion was stirred for 3 h at 80 °C. The resulting solid, named OAB, was separated, washed several times with distilled water until the supernatant solution was free of bromide ions and dried at 80 °C for 48 h.
Preparation of activated carbon AC:
The activated carbon was synthesized from this waste apricot stone from Algeria. This was dried under laboratory conditions and then dried again at 100 ◦C.
In the first step of activation, the starting material was mixed with H3PO4at the H3PO4/starting material weight ratio of 1:1 and the mixture was kneaded with adding distillated water.
The mixture was then dried at 110 ◦C to prepare the impregnated sample.
In the second step, the impregnated sample was placed on a quartz dish, which was then inserted in a quartz tube (i.d. = 60 mm). The impregnated sample was heated up to activation temperature (500 ◦C) under N2flow (100 Ml.min−1) at the rate of 10 ◦C min−1and hold at the activation temperature for 1 h.
After activation, the sample was cooled down under N2 flow and 0.5N HCl was added on to activated sample. Activated sample was washed sequentially several times with hot distillated water to remove residual chemical until it did not give chloride reaction with AgNO3. The washed sample was dried at 110 ◦C to prepare activated carbon and then sieved to
−200 mesh fraction (average particle size 0.075 mm)
Preparation of composites materials A-OAB, A-AC and A-OAC:
A 2% (w/v) sodium alginate solution was prepared by mixing 2 g of sodium alginate in 100 mL deionized water with stirring for 2 h, and then 2 g of OAB and 2 g of AC were added.
The mixture was stirred overnight. When the mixture became homogeneous, it was dropped through a burette into 4% (w/v) calcium chloride to form beads with vigorous stirring. The excess unbounded calcium chloride from the bead surface was removed by washing many times with deionized water. The washed beads were then dried for 48 h at room temperature, stored in a clean bottle and named A-OAC.
The same method was employed for the preparation of A- OAB and A-AC composites.
C. Characterization of adsorbents
The scanning electron microscope (SEM) micrographs of the adsorbents were obtained using Zeiss (SEM model (JSM- 6830LV, JEOL)).
Brunauer–Emmett–Teller (BET) surface area was determined by N2 adsorption–desorption method using (NOVA 1000, Quantachrome) surface area analyzer at 77 K.
The sample was degassed at 200 °C for 2 h before BET analysis.
Fourier transform infrared spectroscopy (FTIR) analysis of the adsorbent before and after adsorption was carried out in KBr pellets in the range of 4000–400 cm-1 with 4 cm-1 resolution using Perkin-Elmer spectrum FT-IR model 65 spectrometer.
The point of zero charge (pHpzc) was determined according to the method described by Auta and Hameed [2]. In brief, the initial, pH (pHi) of aqueous solutions (200 mL) were adjusted to a pH range of 2–12 using 0.1 M HCl or NaOH. Then, 0.2 g of adsorbent was added to each sample. The dispersions were stirred for 48 h at 30°C, and the final pH of the solutions (pHf) was determined. The point of zero charge was obtained from a plot of (pHf- pHi) versus pHi.
III. RESULTS AND DISCUSSION A. Scanning Electron Microscope (SEM)
SEM photographs shown in Fig 1 were taken at 4000 × (Figure 1(a) and 50 × (Figure 1(b, c) magnifications to observe the surface morphologies of OAB, Alginate and A-OAB. The surface of OAB (Fig 1(a)) show aggregated morphology with a large number of crumpled structures small flakes and the plates become relatively flat layers. More voids are seen due to an increase of basal space in organoclays [13], while the surface of alginate beads (Fig 1(b)) had a relatively uniform morphology. From Fig 1(c) the introduction of OAB in the structure of biopolymer revealed that the beads have spherical shape, their surface is relatively smooth and has undulations [14], and shows that the A-OAB beads exhibit a bright and clear morphology with a heterogeneous surface.
(a) (b)
(c)
Figure 1:SEM images of the (a) OAB, (b) alginate and (c) A-OAB samples
SEM photographs shown in Fig. 2 were taken at 1200×
magnification to observe the surface morphologies of AC, alginate and A-AC. The surface of alginate had a uniform morphology while the surface of AC with irregular porosity which explains the effect of phoqphoric acid as activating agent at 750◦C. The surface of A-AC with porosity less than in pure activated carbon sample (AC).
(a) (b)
Figure 2: SEM images of the (a) AC, (b) alginate and (c) A-(c) AC samples
SEM images were taken at 3000 (Fig. 3 (a, b, c)) magnifications to observe the surface morphologies of A- OAB, A-AC, and A-OAC, as shown in Fig. 2. A heterogeneous and rough surface caused by numerous bulges on the beads of all composites was observed. More bulges with folds were observed in A-OAC (Fig. 3 (c)) than in A-AC (Fig. 2 (b)) and A-OAB (Fig. 2 (a)). Similar images were also observed in previous studies on alginate-activated carbon composite [2].
(a) (b)
(c)
Figure 3: SEM images of the (a) A-OAB, (b) A-AC and (c) A-OAC samples
Textural properties
The nitrogen adsorption–desorption isotherms at 77 K for raw bentonite, activated bentonite and OAB is shown in Fig.
4, from which it can be seen that these isotherms are of type II of the Brunauer, Deming, Deming and Teller (BDDT) classification [15]. The textural properties are summarized in Table 1. The acid-activation has markedly affected the nitrogen adsorption characteristics of the bentonite. After the activation, the nitrogen uptake relatively increased. After exchange with surfactant solutions, the nitrogen adsorption capacity of the organo-bentonite decreases and it was decreased more when loading with alginate. In this case, the organic matter may block the access of nitrogen molecules to the adsorption sites and the pore network [16].
Figure 4: N2adsorption–desorption isotherms for RB,AB, OAB and A-OAB.
The results included in Table 1 shows also that, specific surface area and pore volume of AB decreased from 337 m2/g and 0.335 cm3/g to 180 m2/g and 0.285 cm3/g for OAB and 9.9 m2/g and 0.025 cm3/g for A-OAB, indicating that surfactant with large molecular size occupied part of the interlayer space resulting in inaccessibility of the internal surface to nitrogen molecules and the blocking of the pores in the organobentonite. The micropore volume compared with a mesopore volume (seeTable 1) of the samples indicates that bentonite has high mesoporosity.
Table 1:Textural characteristics of the chemical modified clays and their composite
Samples SBET(m2/g) Sext(m2/g) VpT(cm3/g) Vμp(cm3/g)
RB 84 32 0.105 0.026
AB 337 42 0.335 0.254
OAB 180 55 0.286 0.180
A-OAB 9.9 / 0.025 /
Upon inspection of Table 2 (i) surface area for alginate/activated carbon beads sample (A-AC) is very low compared with that of sodium phosphoric activated sample and surface area of calcium alginate/activated carbon composite beads (A-AC) recorded about 770 m2/g (represent about 45% of the total surface area of sodium phosphoric activated sample) which could be related to the decrease in porosity of activated carbon sample by the effect of alginate polymer deposition which is confirmed by the sharp decrease in total pore volume of AC from 1.105 mL/g to 0.49 mL/g for A-AC.
Table 2: Textural properties for raw apricot stone (AS) phosphoric activated carbon based apricot stone (AC), and calcium alginate/activated carbon composite beads (A-AC).
Samples SBET(m2/g) Sext(m2/g) VpT(cm3/g) Vμp(cm3/g)
AS 120 57 1.105 0.026
AC 1680 889 0.79 0.15
A-AC 770.49 219 0.49 /
The BET surface area and cumulative pore volume for A- OAC obtained were 530.37m2/g and 0.38 cm3/g, respectively.
A clear hysteresis loop, which is associated with type IV isotherm according to IUPAC classification, is observed from the isotherm. The isotherm also suggests the typical characteristics of mesoporous materials [17]. Based on Table 3, the average pore size is approximately 5.97 nm, and most of the pores fall within the range of mesoporous structure according to the IUPAC pore size classification [18].
Table 3: Textural characteristics of OAB, AC and their composite A-OAC.
Samples SBET(m2/g) Sext(m2/g) VpT(cm3/g) Vμp(cm3/g)
OAB 180 55 0.286 0.180
AC 1680 889 0.79 0.15
A-OAC 530.37 / 0.38 /
B. Fourier transform infrared spectroscopy (FTIR) analysis FTIR spectra of OAB, alginate and A-OAB are shown in Fig.5.Broad peaks between 3100 and 3700 cm−1were due to stretching vibration of O-H bond in hydroxyl groups. FTIR spectrum of alginate shows absorption bands at 3390, 1618 and 1412 cm−1 that are assigned to vibrations of O-H, and COO- asymmetric stretching, symmetric stretching, respectively. The band at 2924cm-1 is attributed to the C-H stretching vibration, the band at 1125 cm−1is due to the –C–O stretching of ether groups and the band at 1065 cm−1 is assigned to the –C–O stretching of alcoholic groups [ 19]. In the case of OAB and A-OAB, the bands at 2925-2923, 2853- 2850, 1475-1430 and 792-790 cm-1 are assigned to the antisymmetric stretching, symmetric stretching, the scissoring and rocking vibration of methylene group (CH2) of hexadecyl chain, respectively. These observed FTIR peaks also confirm the intercalation of the surfactant cations into the interlayer galleries of the bentonite [20]. FromFig 5, little change was observed after modification of alginate with OAB (1638, 1430 cm-1 COO- asymmetric and symmetric stretching, 3435 cm-1 OH groups). This can be attributed to an interaction between the carbonyl group of alginate and the modification agents in the OAB [21]. The bands at 518 and 462 cm-1 from Al–O stretching and Si–O bending in A-OAB spectra disappeared after adsorption of MB (A-OAB (MB) spectra) and reduced peaks at 1043 cm−1 from Si–O stretching, this could suggest that the binding of the MB molecule is on Al as an octahedral cation [22]. On the other hand, A-OAB (MB) showed shifting peaks position and the reduced peaks heights reveals the strong optimization of methylene blue dye on the surface of the adsorbents especially for A-OAB.
Figure 5:FTIR spectra of Alginate, OAB, A-OAB and A- OAB loaded MB
Fig. 6 shows the FTIR spectra of the three prepared materials AC, ALG, and A-AC. The FTIR spectrum of A-AC beads in Fig. 6 indicates the presence of predominant peaks at 3 431 cm−1(O—H and N—H), 1 605 cm−1(C=O), and 1 032 cm−1 (O—H). The band in spectra with wavenumber range 3431 cm−1correspond to vibration of O H (stretching), peak at 2922 cm−1which could be related to aliphatic C H vibrations.
The band at 2855 cm−1are attributed to O-CH3or two bands for aldehyde group. The band around 3423 cm−1can be assigned to OH vibrations suggesting the presence of phenol groups. Peaks located around 1630 and 1032 cm−1could be related to C-C stretching for unsaturated aliphatic structures and C-O-C ether groups, respectively.
The FTIR spectrum of the A-AC composite loaded MB is shown in Fig. 6, compared with that of the unloaded A-AC beads, the characteristic absorption band around 1094 cm−1is not observed, the peaks at 1 605 cm−1and 3431 cm−1 shift to 1602 cm−1 and 3423 cm−1, respectively, and the stretching vibration of C—O at 1032 cm−1 is weakened. These observations are involved in binding the MB to A-AC composite.
Figure 6:FTIR spectra of Alginate, A-AC and A-AC loaded MB
The FTIR spectraof A-OAC is depicted inFig .7. The wide band at approximately 3424 cm-1 is responsible for the O–H vibrations, which suggest the existence of a phenolic group.
The strong asymmetric and weak symmetric stretching vibration bands of C–O–O observed at 1627 and 1388 cm-1are caused by the alginate molecule. The peaks at 1130 and 1045
cm-1 are ascribed to C–O stretching and O–C–O ring (shoulder). The adsorption band near 775 cm-1 can be attributed to the stretching of the Al–O bond in A-OAC, and the adsorption band around 470 cm-1 is due to the Si–O stretching that originated from bentonite clay [23].
Figure 7:FTIR spectra of Alginate, OAB, AC and A-OAC.
The PZC can be affected by the pH, The PZC is also considered as an indicator for the oxidation of composite surfaces, since it points out the increase in surface acidity/basicity after treatment. PZC was 6.5, 4.8 and 3.5 for A-OAB, A-ACB and A-AC, respectively
IV. CONCLUSION
The present work shows three different composite materials alginate/organobentonite(A-OAB),alginate/activated carbon (A-AC) and calcium alginate/activated carbon/organobentonite (A-OAC) prepared according to the ionic gelation method. Physical characteristics of composites were characterised by X-ray diffraction, Fourier transform infrared spectroscopy, surface mesurment by Brunauer, Emmett and Teller method (BET), and morphological characterization by SEM. Textural characterization of all prepared samples indicate that, the porosity, SBET and total pore volume of A-AC>A-OAC>A- OAB. A heterogeneous and rough surface caused by numerous bulges on the beads of all composites was observed. More bulges with folds were observed in A-OAC than in A-AC and A-OAB. In the A-OAC, posed more functional groups than A-AC and A-OAB according the results of FTIR spectra.
Alginate beads containing activated carbon and bentonite have been successfully applied for water treatment.
References
[1] A. B. Strong, (2nd ed.) (2008). Society of Manufacturing Engineers (SME).
[2] A.F. Hassan, A.M. Abdel-Mohsen, M.M.G. Fouda, Carbohyd.
Polym. 102 (2014) 192-198.
[3] B. A. Akash, Int. J. of Energy Research, vol. 20,913--922 (1996) [4] E. Errais, J. Duplay, F. Darragi, I. M'Rabet, A. Aubert, F. Huber, G.
Morvan, Desalination 275 (2011) 74-81.
[5] E. Errais, J. Duplay, M. Elhabiri, M. Khodja, R. Ocampo, R.
Baltenweck-Guyot, F. Darragi, Colloid. Surface. A.403 (2012) 69- 78.
[6] S. Sellimi, I. Younes, H.B. Ayed, H. Maalej, V. Montero, M.
Rinaudo, M. Dahia, T. Mechichi, M. Hajji, M. Nasri, Int. J. Biol.
Macromol.
[7] D. Bosscher, M. Van Caillie-Bertrand, H. Deelstra, Nutrition 17 (2001) 614-618.
[8] P. Agulhon, M. Robitzer, J.-P. Habas, F. Quignard, Carbohyd.Polym.
112 (2014) 525-531.
[9] T.Y. Kim, H.J. Jin, S.S. Park, S.J. Kim, S.Y. Cho, J. Ind. Eng.
Chem.14 (2008) 714-719.
[10] Y. Li, F. Liu, B. Xia, Q. Du, P. Zhang, D. Wang, Z. Wang, Y. Xia, J.
Hazard. Mater. 177 (2010) 876-880.
[11] N.M. Mahmoodi, B. Hayati, M. Arami, H. Bahrami, Desalination 275 (2011) 93-101.
[12] J. Venkatesan , I. Bhatnagar, P. Manivasagan, K. Kang, S. K. Kim, International Journal of Biological Macromolecules Volume 72, January 2015, Pages 269–281
[13] ] L. Zhang, B. Zhang, T. Wu, D. Sun, L. Yujiang, Colloids and Surfaces A: Physicochem. Eng. Aspects. 484 (2015) 118–129 [14] M. Lezehari, J. Basly, M. Baudu, O. Bouras, Colloids Surf., A:
Physicochem. Eng. Aspects., 366 (2010) 88-94.
[15] C. H. Giles, T. H. Mac Ewan, S. N. Nakhwa, D. Smith, J. Chem. Soc.
111 (1960) 3973.
[16] H. Z-Boudiaf , M. Boutahala, S. Sahnoun, C. Tiar, F. Gomri, Applied Clay Science. 90 (2014) 81-87.
[17] K. Sing, Pure. Appl. Chem. 54 (1982) 2201-2218.
[18] R.L. Burwell Jr, Heterogeneous Catalysis, Adv. Catal. 26 (1977) 351- [19] 392.] Manal F. AbouTaleb, Dalia E. Hegazy, Sahar A. Ismail, Carbohydr.
Polym. 87, (2012) 2263-2269
[20] B. Caglar, C. Topcu, F. Coldur, G. Sarp, S. Caglar, A. Tabak, E.
Sahin, J. Macromol. Struc. 1105 (2016) 70-79.
[21] A. A. Oladipo, M. Gazi, J. Water Process Eng. 2 (2014) 43–52.
[22] B. Singh, D.K. Sharma, R. Kumar, A. Gupta, Appl. Clay. Sci. 45 (2009) 76-82.
