Adsorptive removal of triarylmethane dye (Basic Red 9) from aqueous solution by sepiolite as effective and low-cost adsorbent

https://doi.org/10.1016/j.micromeso.2015.02.040Get rights and content

Highlights

  • The adsorption of BR9 onto brown sepiolite was investigated comprehensively.

  • Pseudo second-order and Freundlich models fitted well with the experimental data.

  • Electrostatic interactions are negligible in the adsorption process.

  • A very short contact time is sufficient for the equilibrium time.

  • Sepiolite is a suitable adsorbent for the removal of triarylmethane dyes from waters.

Abstract

In this study, the adsorption of Basic Red 9 (BR9) from aqueous solution onto sepiolite was investigated. Batch experiments were carried out to determine the effects of various parameters including contact time, initial dye concentration, temperature and pH on the adsorptive removal of BR9 by sepiolite. Both kinetic and isotherm data were obtained. The kinetic and isotherm data fitted very well with the pseudo second-order kinetic model and Freundlich isotherm model, respectively. The calculated thermodynamic parameters indicated that the adsorption process was spontaneous, favorable, and exothermic. The pH of dye solution and electrostatic interaction do not play an important role on the adsorption process. The increase in the adsorption amount of BR9 led to a decrease in the zeta potential of sepiolite. The interaction between sepiolite and BR9 was investigated by Fourier transform infrared (FTIR) spectroscopy. Desorption of BR9 from spent adsorbent was studied in water, ethyl alcohol and benzyl alcohol. The highest desorption amount was obtained by benzyl alcohol. This study revealed that sepiolite could be used as effective and low-cost adsorbent in the treatment of wastewater contaminated with triarylmethane dyes.

Introduction

Dyes have been widely used in textile, leather, paper, plastics, printing, electroplating, food and cosmetic industries [1]. It has been estimated that approximately 2% of produced dyes are directly discharged into waters [2]. The dyes in wastewaters can absorb the sunlight entering the water, so the photosynthesis of aquatic plants is hindered. In addition, many dyes have a mutagenic or carcinogenic influence on human beings [1]. Especially cationic dyes can easily interact with negatively charged cells on membrane surfaces within body and enter into cells. This situation causes some health problems [3].

Several physical, chemical and biological methods such as sedimentation, coagulation, flotation, membrane filtration, adsorption, oxidation and aerobic or anaerobic treatment have been developed to remove the dyes from wastewaters. Some of these methods are expensive. In addition, they are effective if the small volumes of wastewater are used. Chemical methods need the use of excess chemicals. In chemical methods, some toxic byproducts may occur. Furthermore, many dyes are generally resistant to biodegradation [4]. To remove the dyes from wastewaters, adsorption is considered as an appropriate technique compared with other techniques due to its simple design, easy operation and effectiveness [5]. Moreover, adsorption technique does not lead to the formation of harmful byproducts. The most commonly used adsorbent for the adsorption process in industrial wastewater treatment systems is activated carbon due to its large specific surface area [4]. Owing to the high cost of activated carbon, the use of this adsorbent is limited [6]. Therefore, researches have been continued for inexpensive alternative adsorbents having reasonable adsorption efficiencies [7].

Sepiolite, which has a Si12O30Mg8(OH)4(OH2)4.8H2O unit cell formula, is a natural clay mineral. The structural formula of sepiolite is illustrated in Fig. 1. Sepiolite can be used as the alternative low-cost adsorbent because of its unique physicochemical properties [8], [9]. It has a fibrous structure formed by an alteration of blocks and channels that grow up in the fiber direction [10], [11]. Each block is composed of two tetrahedral silica sheets and a central octahedral sheet containing Mg. Due to the discontinuity of the external silica sheets, a number of silanol groups exist on the sepiolite surface [12]. The channels of sepiolite are filled by zeolitic water which forms hydrogen bonds with oxygen atoms on the tetrahedral sheet or with other water molecules. The terminal Mg2+ ions located at the edges of the octahedral sheet complete their octahedral coordination with other water molecules [13]. Isomorphic substitutions of Si4+ in the tetrahedral sheet of the mineral lattice with Al3+ form negatively charged sites on the sepiolite surface. These sites are occupied by exchangeable cations which compensate the electrical charge [12].

When the chemical structures of dyes are considered, they can be classified as azo, vat, anthraquinone, indigo, triarylmethane, polymethine, nitro, carbonium and phthalocyanine dyes [14], [15]. In literature, there are many studies about dye adsorption onto sepiolite. The adsorption of azo dyes including Acid Blue 193 [16], [17], Brilliant Yellow [18], Basic Red 46 [19], Direct Blue 85 [19] and Remazol Red B [20], anthraquinone dye including Acid Blue 25 [21] and reactive dyes including Reactive Blue 21 [22] and Reactive Blue 221 [23] onto sepiolite has been studied. In sepiolite-dye adsorption studies, the most widely investigated dyes are azo type dyes. Although triarylmethane dyes form an important commercial dye class, the adsorption behavior of these dyes by sepiolite has not been examined sufficiently.

Triamino derivatives of triphenylmethane have the largest dye group within the triarylmethane dye class and the first member of this group is Basic Red 9 (BR9). The other triamino derivatives of triphenylmethane dyes are produced by the connection of various functional compounds to the amino groups on the triphenylmethane [24]. BR9 is commonly used to color the products in textile, leather, paper and ink industries. From these industries, the discharge of BR9 into natural streams can cause serious problems. BR9 is toxic and carcinogenic. It has poor biodegradation [25]. Therefore, wastewaters containing dangerous BR9 require treatment before being released into the environment [26]. In this study, we have investigated the adsorptive properties of sepiolite for the removal of BR9 as a model triarylmethane dye.

The aim of this study is to evaluate the adsorption efficiency of sepiolite as an adsorbent for the removal of toxic Basic Red 9 (BR9) dye from aqueous solution, to investigate the effect of contact time, initial dye concentration, pH and temperature on the adsorption process, to calculate the kinetic, isotherm and thermodynamic parameters and to understand the interactions between sepiolite and dye molecule by zeta potential measurement and FTIR spectroscopy.

Section snippets

Materials

Sepiolite used as an adsorbent was kindly supplied from Zafer Mining Co. (Balıkesir, Turkey). Basic Red 9 (BR9) used as a model triarylmethane dye was purchased from Sigma-Aldrich (Germany). The chemical structure of BR9 is illustrated in Fig. 2. All other chemicals used in the experiments were of analytical grade. In addition, deionized water was used in the experiments.

Purification of sepiolite

A purification procedure was applied to the clay mineral in order to prevent the desorption of some impurities during the

Characterization of sepiolite

Fig. 3 shows the XRD pattern of purified sepiolite. The 2θ values observed at 7.18, 19.70, 20.58, 23.74, 26.65, 27.98, 34.74, 36.81 and 39.86° were compared with the 2θ values reported for sepiolite by Brindley [30]. The results indicate that the clay mineral used in this study is mainly sepiolite. The chemical composition of sepiolite obtained from XRF analysis is given in Table 1. As seen from this table, sepiolite is of mainly Si4+, Mg2+, Al3+ and Fe3+.

SEM images of sepiolite recorded at

Conclusions

Adsorption of BR9 onto sepiolite was investigated as a function of contact time, initial dye concentration, pH and temperature. The adsorption amount of BR9 onto sepiolite showed an increase with decreasing temperature and increasing initial dye concentration. The pH of dye solution had little effect on the adsorption process. This result indicated that electrostatic interaction was not effective force in the adsorption of BR9 onto sepiolite. The kinetic data were treated according to pseudo

Acknowledgments

Central Laboratory of Middle East Technical University and TUBITAK are acknowledged for determining the some characterization properties of sepiolite samples.

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