Preparation and characterization of “green” hybrid clay-dye nanopigments

Journal of Physics and Chemistry of Solids 78 (2015) 95–100

Contents lists available at ScienceDirect

Journal of Physics and Chemistry of Solids journal homepage: www.elsevier.com/locate/jpcs

Preparation and characterization of “green” hybrid clay-dye nanopigments Mehmet Kaya a, Yavuz Onganer b,n, Ahmet Tabak a a b

Recep Tayyip Erdoğan University, Faculty of Art and Science, 53100 Rize, Turkey Department of Chemistry, Atatürk University, Faculty of Sciences, 25240 Erzurum, Turkey

art ic l e i nf o

a b s t r a c t

Article history: Received 21 July 2014 Received in revised form 13 October 2014 Accepted 21 October 2014 Available online 26 November 2014

We obtained a low cost and abundant nanopigment material composed of Rhodamine B (Rh-B) organic dye compound and Unye bentonite (UB) clay from Turkey. The characterization of the nanopigment was investigated using scanning electron microscopy (SEM), particle size distribution, powder X-ray diffraction (PXRD), Fourier transformed infra-red spectroscopy (FT-IR) and thermal analysis techniques. According to the result of texture analyses, we showed that the particle size distribution (d: 0.5-mean distribution) of Rh-B/UB nanopigment material was around 100 nm diameter. It was also demonstrated that the samples had a particle size around nm diameter in SEM images. As seen in the PXRD and thermal analysis, there is a difference in basal spacing by 1.46° (2θ) and a higher mass loss by 7.80% in the temperature range 200–500 °C compared to the raw bentonite. & 2014 Elsevier Ltd. All rights reserved.

Keywords: Thermogravimetric analysis (TGA) Nanostructures Electron microscopy Surface properties

1. Introduction Some synthetic dyes affect the environment and humans because of their highly toxic potential,even though they are utilized adjusting wavelength of electromagnetic radiation in dye lasers, colorizing several plastics and polymers and improving the surface properties of some materials [1–3]. This situation has led toso significant interests in natural colorants and enlightening projects for an environmentally friendly improvement called as “green”. So, recent studies have seen a number of attempts in development of nanopigments, because they are used in coating, plastics and printing inks and they offer many advantages such as photosensitivity and color strength [4,5]. Withregardtotheseadvances, numerous substances such as clay [5] andpolymer [6] have been used to synthesize “green” nanopigments. Bentonite, which is a low cost, eco-friendly and efficientadsorbent material,is preferredto other materials because of its high-specific surface area and microporous structure [7–10]. Bentonite clay, which is mainly composed of montmorillonite clay mineral, has been lately employed in many separation applications with or without modification. An organo-clay/dye nanopigment is obtained by the treatment of a clay with an organic colorant [11]. As a result of the penetration of cationic dye species into the interlayer, nanopigments can be formed [12]. For instance, pigment particles must yield a colloidal dispersionwhen printing ink applications. This means n

Corresponding author. Fax: þ 90 442231 4109. E-mail address: [email protected] (Y. Onganer).

http://dx.doi.org/10.1016/j.jpcs.2014.10.016 0022-3697/& 2014 Elsevier Ltd. All rights reserved.

particles suspended in a medium have diameters within the nanometer scale. So, researchers haveespecially focused on the usage of bentonites intercalated by organic dyes, e.g., methylene blue, proflavine, acridine orange, thionine, crystal violet, methylene green, rhodamine B, and rhodamine 6G [13–15]. In this study, the aim is the synthesis and characterization of Rh-B/UB eco-friendly hybrid nanopigment by using Fourier transform infrared spectroscopy (FT-IR), molecular absorption spectroscopy, thermal analysis, powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and particle size analysis techniques. Although numerous studies on the interactions mentioned above have been available in the literature, there seemed not many comparable studies on nanopigment synthesis, which obtained Rh-B cationic dye and Unye bentonite clay. Besides, Unye bentonite (UB), which is an important clay mineral source in Turkey, is preferred owing to its being a low cost material and having thermal stability and higher adsorbing ability. Also, strong interactions between Rh-B and UB raised thermal durability of the nanopigment incomparison with natural dye. We consider that this work will offer an insight intovarious studies such as printing ink application and dye-sensitized solar cells.

2. Experimental 2.1. Materials Rh-B dye, which is purchased from Merck, was used without further purification and its chemical formula was presented in

96

M. Kaya et al. / Journal of Physics and Chemistry of Solids 78 (2015) 95–100

CuKα radiation (λ ¼1.54050 Å; 40 kV and 40 mA). Bragg's law, defined as nλ ¼2d sin θ, was used to compute the crystallographic spacing (d) for the examined bentonite samples. The TG and DTA curves were scanned using a PRIS Diamond TG/DTG apparatus in a dynamic nitrogen atmosphere (heating rate: 10 °C min  1, platinum crucibles, mass ∼10 mg and temperature range: 20–1000 °C). The DSC curves were collected on a PYRIS Diamond DSC apparatus in a static air atmosphere (heating rate: 10 °C/min, platinum crucibles, mass ∼10 mg and temperature range: 20–750 °C). Surface and particle size analyses of materials were obtained using devices Zeis EVO LS 10 and Malvern Mastersizer 2000, respectively.

Fig. 1. The molecular structure of Rhodamine B (Rh-B).

Fig. 1. The cation exchange capacity (CEC) of the bentonite from Ordu/Unye, Turkey, was determined as 74 meq/100 g clay by the methylene blue adsorption technique [16,17]. 2.2. Preparation of bentonite samples 10 g of raw bentonite sample from Ordu/Unye region of Turkey was washed with deionized water several times to remove the soluble impurities prior to the application of the adsorption procedure, centrifuged, filtered and then dried at 105 °C for 12 h. The obtained bentonite product was sieved to 38–106 μm and kept for spectroscopic characterization measurements and sorption studies. 2.3. Preparation of dye/clay nanopigments Rh-B/UB nanopigments were prepared by adding 0.5 g bentonite to 10.0 mL of aqueous solution containing concentrated (0.5 g/L) Rh-B. Preliminary adsorption experiments have indicated that the mixture of the bentonite and Rh-B dye in the ratio of 3.0% CEC was sufficient to attain the optimum interaction. The resulted suspension was placed into a plastic tube and then stirred vigorously for 60 min (the sorption equilibrium time) at 25 °C in a thermostatic shaker. Afterwards, the suspension was centrifuged at 6000 rpm, decanted, filtered and then dried at 60 °C for 24 h. Finally the particle size of the obtained dye/clay (Rh-B-bentonite) nanopigment was measured by a mastersizer 2000 particle size analyzer. Particle size of the nanopigment was around 100 nm. 2.4. Preparation of colloidal suspensions Unye bentonite (0.5 g) was suspended in 10.0 ml of deionized water for the preparation of the suspension. A solution of 0.5 g of cationic Rh-B dye in 10 ml of deionized water was preparedseparately. When the clay formed a translucent colloidal suspension after a period of time, the dye solution was added and stirred for an hour using a magnetic stirrer. The samples were centrifuged at 6000 rpm to separate the fine particles from the coarse ones. The fine particles were redispersed in water to form the nanopigments suspension.

3. Results and discussion 3.1. Characterization of Rh-B/UB nanopigments FTIR spectra of the raw and PyY-bentonite samples were recorded in the region 4000–450 cm  1 on a Spectrum-100 FTIR spectrometer at a resolution of 4 cm  1. XRD patterns were taken on a Rigaku DMAX-3C automated diffractometer using Ni filtered

3.1.1. FT-IR analysis Fig. 2 shows the IR spectra of raw bentonite and Rh-B/UB nanopigment samples. Rh-B/UB samples (Fig. 2a) display that there are different peaks, which are large and small corresponding to the functional groups of the Rh-B in the range 1250–1650 cm  1compared to the raw bentonite [18]. The IR peaks appeared in the ranges of 1647–1467 cm  1 can be based to the aromatic ring vibrations resulting from the C ¼C skeleton stretching.In addition to these bands, two characteristic peaks are observed for stretching and bending modes involving CH3 and CH2 alkyl groups at 2978–2928 cm  1 and 1467–1340 cm  1, respectively [19]. All functional groups are ascribed tothe replacement of interlayer exchangeable cations by organic dye cations. Owing to the distinction of the binding ability of water species coordinating the organic cations, the decrease in intensities of OH stretching and bending peaks at 1641 and 3422 cm  1, respectively, may be also considered as another indication confirming this result (Fig. 2b). During the formation of composite, shifting of wavenumber from 3422 to 3436 cm  1 denotes strongly the coordination of water molecules [20,21]. Also seen in the same spectrum is the shift to the lower frequency (1340 cm  1) of the C–N aromatic stretch in comparison with Rh-B molecule (1349 cm  1). It is an evidence of binding through the N atoms of the organic molecule as well as the electrostatic interactions between cationic dye species and negatively charged clay layers (Fig. 2b and c). Moreover, the changes in the position of the ring vibrations exhibited the contribution from the π interactions occurring between the O-plane of bentonite silicate layers and Rh-B with aromatic rings lying parallel to the alumina silicate layers and tilting at a definite angle with respect to the clay surface [18]. 3.1.2. PXRD analysis The PXRD patterns of UB and the Rh-B/UB nanopigments are given in Fig. 3a and b, respectively. Depending on the CEC and water content of the material, the specific diffraction peak d(001) of montmorillonite clay minerals in bentonite is generally found in the range 14.0–15.0 Å [22,23]. In order to avoid the interference caused by adsorbed water, the samples used for this study were all dried at 105 °C night long. The maximum scattering for the sample of UB corresponding to the main montmorillonite (M) component (80%) analyzed was found with the refection angle 2θ of 5.84° which equals to an interlayer space of 15.12 Å (1.51 nm). Also, d values of 17.61° (d003), 19.68° (d20–110) and 34.70° (d130–200) were in agreement with the basal distances of 5.03, 4.50 and 2.58 Å, respectively. The Powder X-Ray diffraction patterns for the samples of montmorillonite with adsorbed Rh-B dye are shown in Fig. 3b. The comparison of the measurements of UB clay and Rh-B/UB nanopigments shows a shifting of the reflection band from a value of 2θ ¼5.84° to a shorter value of 2θ ¼4.38° for Rh-B/UB. This much shifting (1.46°) represents the expansion of the interlayer space by the mechanism of adsorption of dye molecules [24]. An interlayer opening caused by this insertion process was estimated to be 11.15 Å by substracting the thickness of SiO2–Al2O3–SiO2 sheets

M. Kaya et al. / Journal of Physics and Chemistry of Solids 78 (2015) 95–100

97

Fig. 2. The FTIR spectra of (a) Unye bentonite (UB) and (b) Rh-B/UB nanopigment(c) Rh-B.

(9.0 Å) [25] from the d(001) value of Rh-B/UB nanopigments. Taking into account the possibility of different arrangements, it was from the geometrical consideration of the d001 value concluded that the Rh-B cations might be oriented as a monolayer form in the interlamellar spacing with aromatic rings parallel to the clay layers. 3.1.3. Thermal analysis The TG and DTA analyses for UB clay and Rh-B adsorbed in UB clay are shown in Fig. 4a and b, respectively. In the case of UB clay, it is demonstratedthat the interlayer water with a total mass loss of 11.1% occurs up to 200 °C. The endothermic DTA peaks can be seen around at this temperature. This initial loss corresponds to the elimination of interlayer water. So, in this dehydration stage, the endothermic peak maximum of 100 °C on the DTA curve represents the removal of adsorbed water in the region 20–120 °C. At the nextstep, the DTA endotherm at 187 °C is ascribed to the evolution of the water species coordinated to the interlayer cations. The next losstakes place at 500–750 °C and it is accompanied by a mass loss of 2.5% and is related to the dehydroxylation of the clay. The data were taken until 750 °C, from this point on there is a major degradation of the inorganic structure of the clay [26,27]. Comparison with UB, for the Rh-B/UB sample, at the low temperature range, the mass losses are at around 4.9% and it is related to the loss of interlayer adsorbed water due to the

hydrophilic characteristic of the dye (Fig. 4b and Table 1) [28]. This difference in the total mass loss and the water types of lower decomposition energy of composite comparing to that of rawbentonite in the same temperature range support the change of water molecule numbers in the environment of the cationic dye species penetrated into the interlayer space of clay. The next stage occurs at the temperature range of 200–500 °C, where usually all the organic matter degrades. Besides, resulting from the efficient displacement of the exchangeable cations by the organic dye cations dye into the clay inter layers, it is seen that there is higher mass loss in the range 200–500 °C and the total mass loss of UB and Rh-B/UB which are at 7.8% and 22.40%, respectively (Table 1). The mass loss at this temperature range is at 7.80%, which corresponds to the dye adsorbed on the clay surface. In the third stage (500–750 °C), the mass loss is at 9.70% and is associated with the dye in the interlayer space interacting with theoxygen plane of the clay layers. In addition, thermal analysis results of the Rh-B/UB composite exhibits the increase in the thermal stability up to 750 °C while Rh-B is stable in the temperature up to 200–220 °C [29]. Also, an extra thermal stability of Rh-B/UB generates from the presence of π interactions between oxygen planes of the clay sheets and aromatic rings of the dye molecule as well as shielding effect of the alumina-silicate layers [23]. 3.1.4. SEM analysis Morphology and particle sizes of nanopigments were studied using scanning electron microscopy (SEM). Nanoparticle layered

98

M. Kaya et al. / Journal of Physics and Chemistry of Solids 78 (2015) 95–100

Fig. 4. Thermal analysis curves of (a) Unye bentonite (UB) (b) Rh-B/UB nanopigment.

Table 1 Thermal analysis results of Unye bentonite (UB) and Rh-B/UB nanopigment.

Fig. 3. The XRD spectra of (a) Unye bentonite (UB) (b) Rh-B/UB nanopigment.

with the ultrasonic treatment was used for the main purposes since this method is widely used for efficient clay/water suspension preparation [30]. Scanning electron micrograph of the synthesized Rh-B/UB nanopigment is depicted in Fig. 5c and d. Both nanopigments and raw samples were irregular in shape and mostly present in aggregates owing to the electrostatic attraction forces. The surface of the particles was rough due to structure of the clay providing a good possibility for dyes to be trapped and adsorbed. In comparison to UB, which is about 25–100 mm with large and small sizein Fig. 5a and b, it is seen that the size of Rh-B/ UB particles are minor and around nanoscale length. Because of the large Rh-B molecule, it can extend interparticles as a result of intercalation [31,32] and is attributed smaller particles obtained than those of raw bentonite (UB) (Fig. 6). Therefore, this causes self-assembly smaller particles with nanoscale. This situation is shown in Fig. 7 representatively. One of the principal requirements of the pigment particles for the applications i.e. printing ink and coating is the particle size. The particle size for these applications should be below 300 nm. According to the microscopic analysis, the particles are in partially nm scale and partially ensure to fulfill

Sample

DTAmax (ºC) Temperature range (ºC)

Mass loss (%)

Total mass loss (%)

UB

100 187 – 650

20–100 100–200 200–500 500–750

4.90 6.20 1.40 2.50

15.00

Rh-B/UB 75 165 324 –

20–100 100–200 200–500 500–750

3.20 1.70 7.80 9.70

22.40

the principal condition [5]. 3.1.5. Particle size analysis Particle size analysis is a measurement of the size distribution of individual particles in a composite sample. The major features of particle size analysis are the destruction or dispersion of the sample aggregates into discrete units by chemical, mechanical, or ultrasonic means and the separation of particles according to size limits by such means as sieving and sedimentation, as well as other methods. Particle size analysis data was presented and used in several ways, the most common being a cumulative particle size distribution curve. For this purpose, Malvern Mastersizer 2000 particle size analyzer was used to determine the percentage of particles less than a given particle size which is plotted against the logarithm of the effective particle diameter [33]. When differentiated graphically, the particle-size distribution curves produce frequency distribution curves for various particle sizes. Frequency curves usually exhibit a peak or peaks representing the most

M. Kaya et al. / Journal of Physics and Chemistry of Solids 78 (2015) 95–100

99

Fig. 5. SEM analysis of (a) Unye bentonite (UB) (b) Rh-B/UB nanopigment, magnifications of x500 (a–b.) and x2500 (c–d).

Fig. 6. SEM analysis of Rh-B/UB nano composite, magnifications of x55,000 (a) and x30,000 (b).

Fig. 7. Intercalation of Rh-B to UB.

prevalent particle sizes d(0.5). The results of Rh-B/UB nanopigment and raw bentonite are shown Fig. 8a and b. As a result of nanopigment formation, the particle size distribution turns from 25 mm into ∼100 nm. 3.2. Enhancement of light fastness The Rh-B/UB samples were exposed to visible light irradiation and the spectral changes were traced. Along with the irradiation, the absorption in the visible region decreased and no other changes in band maxima of the spectra were observed, indicating the simple decomposition of Rh-B under irradiation. These changes in the absorption spectra depending on contact time of Rh-B/

UB in suspension media during irradiation are illustrated in Fig. 9. The photostability of Rh-B/UB could be judged not to be very low, because shift of absorption band spectra was not observed after 15 days of irradiation. Rh-B/UB showed nearly 50% of absorption intensity was maintained. Therefore, it exhibited very high durability against visible light irradiation. This result suggested that the Rh-B dye showed no changed photostability of Rh-B.

4. Conclusions In recent years, there have been important developments in design, synthesis and characterization of clay and dye based

100

M. Kaya et al. / Journal of Physics and Chemistry of Solids 78 (2015) 95–100

Fig. 8. Particle size analysis of (a) Unye bentonite (UB) (b) Rh-B/UB nanopigment.

Fig. 9. Normalized absorption spectra depending on contact time of Rh-B/UB in suspension media.

nanopigments. Moreover, there are vast interests about a whole field of study on the direct use of organic dyes (based mainly in plants and microorganisms) in design and synthesis of nanopigments for principal applications. For this purpose, we have aimed the synthesis of clay/dye based nanopigment would offer an insight into the novel investigations and nanocomposite materials. As regarded the results of PXRD, FT-IR, thermal analyses, SEM and particle size analyses, this study showed that the Rh-B and cationic organic dye are highly interacted with clay minerals having negative charged surface. Characterization studies proved that UB is an effective, environmentally friendly, cheap, regional source and natural material for being formed of “green” nanopigments.

References [1] E.I. Unuabonah, K.O. Adebowale, F.A. Dawodu, Equilibrium, kinetic and sorber design studies on the adsorption of Aniline blue dye by sodium tetraboratemodified Kaolinite clay adsorbent, J. Hazard. Mater. 157 (2–3) (2008) 397–409. [2] K.R. Ramakrishna, T. Viraraghavan, Dye removal using low cost adsorbents, Water Sci. Technol. 36 (2–3) (1997) 189–196.

[3] V.K. Garg, et al., Dye removal from aqueous solution by adsorption on treated sawdust, Bioresour. Technol. 89 (2) (2003) 121–124. [4] G. Rytwo, The use of clay-polymer nanocomposites in wastewater pretreatment, Sci. World J. (2012) 1–7. [5] E. Baez, et al., Stability study of nanopigment dispersions, Adv. Powder Technol. 20 (3) (2009) 267–272. [6] Y.Q. Li, et al., Highly solar radiation reflective Cr2O3–3TiO(2) orange nanopigment prepared by a polymer-pyrolysis method, Acs. Sustain. Chem. Eng. 2 (2) (2014) 318–321. [7] C.A.P. Almeida, et al., Removal of methylene blue from colored effluents by adsorption on montmorillonite clay, J. Colloid Interface Sci. 332 (1) (2009) 46–53. [8] G. Ozdemir, S. Yapar, Adsorption and desorption behavior of copper ions on Na-montmorillonite: effect of rhamnolipids and pH, J. Hazard. Mater. 166 (2–3) (2009) 1307–1313. [9] P. Liu, L. Zhang, Adsorption of dyes from aqueous solutions or suspensions with clay nano-adsorbents, Sep. Purif. Techno. 58 (1) (2007) 32–39. [10] S.H. Lin, R.S. Juang, Y.H. Wang, Adsorption of acid dye from water onto pristine and acid-activated clays in fixed beds, J. Hazard. Mater. 113 (1–3) (2004) 195–200. [11] A. Tabak, et al., Pyronin Y (basic xanthene dye) bentonite composite: a spectroscopic study, J. Mol. Struct. 1059 (0) (2014) 271–279. [12] S. Yariv, H. Cross, Organo-Clay Complexes and Interactions, viii, Marcel Dekker, New York (2002) 688. [13] G. Mckay, M. Elgeundi, M.M. Nassar, Equilibrium studies during the removal of dyestuffs from aqueous-solutions using bagasse pith, Water Res. 21 (12) (1987) 1513–1520. [14] S.J. Allen, G. Mckay, K.Y.H. Khader, Multi-Component sorption isotherms of basic-dyes onto peat, Environ. Pollut. 52 (1) (1988) 39–53. [15] H. Boukhatem, et al., Synthesis, characterization and photocatalytic activity of CdS–montmorillonite nanocomposites, Appl. Clay Sci. 72 (0) (2013) 44–48. [16] R.K. Taylor, Cation-exchange in clays and mudrocks by methylene-blue, J. Chem. Technol. Biotechnol. Chem. Technol. 35 (4) (1985) 195–207. [17] K. Meral, et al., The molecular aggregation of pyronin Y in natural bentonite clay suspension, J. Luminesc. 131 (10) (2011) 2121–2127. [18] A. Tabak, et al., Adsorption of Reactive Red 120 from aqueous solutions by cetylpyridinium-bentonite, J. Chem. Technol. Biotechnol. 85 (9) (2010) 1199–1207. [19] S.K. Das, et al., Adsorption of rhodamine B on Rhizopus oryzae: role of functional groups and cell wall components, Colloids Surfaces B-Biointerfac. 65 (1) (2008) 30–34. [20] D. Sternik, et al., Influence of Basic Red 1 dye adsorption on thermal stability of Na-clinoptilolite and Na-bentonite, J. Thermal Anal. Calorim. 103 (2) (2011) 607–615. [21] N.D. Hutson, M.J. Hoekstra, R.T. Yang, Control of microporosity of Al2O3-pillared clays: effect of pH, calcination temperature and clay cation exchange capacity, Microporous Mesoporous Mater. 28 (3) (1999) 447–459. [22] M. Pospisil, et al., Intercalation of octadecylamine into montmorillonite: Molecular simulations and XRD analysis, J. Colloid Interface Sci. 245 (1) (2002) 126–132. [23] A. Tabak, et al., Structural analysis of naproxen-intercalated bentonite (Unye), Chem. Eng. J. 174 (1) (2011) 281–288. [24] S. Raha, et al., Photo-stability of rhodamine-B/montmorillonite nanopigments in polypropylene matrix, Appl. Clay Sci. 42 (3–4) (2009) 661–666. [25] E. Ruiz-Hitzky, et al., Inorganic-organic nanocomposite materials based on macrocyclic compounds, Rev. Inorg. Chem. 21 (1–2) (2001) 125–159. [26] K. Chrissafis, D. Bikiaris, Can nanoparticles really enhance thermal stability of polymers? Part I: an overview on thermal decomposition of addition polymers, Thermochim. Acta 523 (1–2) (2011) 1–24. [27] P. Capriel, P. Harter, D. Stephenson, Influence of management on the organicmatter of a mineral soil, Soil Sci. 153 (2) (1992) 122–128. [28] A. Tabak, et al., Pyronin Y (basic xanthene dye)-bentonite composite: a spectroscopic study, J. Mol. Struct. 1059 (2014) 271–279. [29] A.A.M. Farag, I.S. Yahia, Rectification and barrier height inhomogeneous in Rhodamine B based organic Schottky diode, Synth. Metals 161 (1–2) (2011) 32–39. [30] J. Vartiainen, et al., Biohybrid barrier films from fluidized pectin and nanoclay, Carbohydr. Polym. 82 (3) (2010) 989–996. [31] L. Wang, A. Wang, Adsorption behaviors of Congo red on the N,O-carboxymethyl-chitosan/montmorillonite nanocomposite, Chem. Eng. J. 143 (1–3) (2008) 43–50. [32] Z. Klika, et al., The rhodamine B intercalation of montmorillonite, J. Colloid Interface Sci. 275 (1) (2004) 243–250. [33] S.J. Xu, T. Wang , Comparative study of grain size characteristics in loess-red clay deposit both in Miaodao Islands and the Western Chinese Loess Plateau, Advanced Technology in Teaching, in: Proceedings of the 2009 3rd International Conference on Teaching and Computational Science (Wtcs 2009). 2 (117), 2012, 841–847.