Effective photocatalytic degradation of malachite green dye by Fe(III)-Cross-linked Alginate-Carboxymethyl cellulose composites

https://doi.org/10.1016/j.jphotochem.2022.113867Get rights and content

Highlights

  • Fe(III) ion cross-linked alginate-CMC composite beads (Fe@(Alg-CMC) were prepared.

  • Biopolymer composite provided reactive radicals under UV light in an aqueous solution.

  • Fe@(Alg-CMC beads worked as photocatalysts for the degradation of malachite green.

  • Effective degradation of the dye was carried out without adding H2O2 to the medium.

Abstract

Fe(III) ion cross-linked alginate-carboxymethyl cellulose composite beads (Fe@(Alg-CMC)) were prepared and used as a novel photocatalyst for the degradation of malachite green (MG) dye. Fe (III) ions bound to the carboxyl groups of the biopolymer composite provided reactive radicals under UV light, and degradation of the dye in an aqueous solution occurred at a high percentage and in a short time. Unlike Fenton’s reaction, effective degradation of the dye was carried out without adding H2O2 to the medium. Optimum conditions of dye degradation were investigated. Under UV-A light, 98.8%±0.7% dye degradation was achieved at pH 4 of 10 ppm MG solution with 0.1 g of Fe@(Alg-CMC) beads in 30 min. Experimental results fitted Langmuir-Hinshelwood kinetic modeling, which explains the kinetics of the heterogeneous catalytic processes. A rate constant (k) of 0.115 ± 0.001 min−1 and correlation coefficient (R2) of 0.9628 was obtained. Hereby, we offer Fe@(Alg-CMC) beads as a promising, environmentally friendly, easy to prepare, and low-cost catalyst for the degradation of dyes and organic substances under UV light.

Introduction

Pollution of water with toxic industrial wastes is the most critical environmental problem. Many techniques and materials are being developed to clean the waters [1], [2], [3]. Many thousands of synthetic dyes are the leading water-polluting materials. Since most of these dyes are not biodegradable, they remain in the water for a long time. Besides their toxic properties, even minimal concentrations threaten aquatic life by preventing sunlight. Malachite green (MG) (N-methylated diaminotriphenylmethane) is one of the industrial dyes which shows a toxic effect on mammalian cells. MG is used as a dye for cotton, paper, jute, silk, wool, leather products, and acrylic industries and is also used as an antiseptic and fungicidal product [4]. Tewari et al. reviewed adsorption techniques to remove MG from waters [5]. Although the most widely used methods for dye removal are adsorption methods as efficient and inexpensive methods, a secondary pollutant problem arises since the pollutants are converted from one phase to another in these applications. Therefore, there are intensive studies on the removal of pollutants by photodegradation [6], [7], [8], [9], [10], [11], [12].

Advanced oxidation technologies (AOTs) are wastewater treatment methods that have been used effectively in the decomposition of toxic compounds in recent years [13], [14]. The basis of AOTs is to break down toxic pollutants through reactive free radicals. The hydroxyl radical (·OH) is the most important one [15]. Fenton and photo Fenton reactions, which are based on the generation of hydroxyl radicals from H2O2 with iron (II) salts, are the most used AOTs technologies for wastewater purifications [16], [17]. The disadvantage of homogeneous Fenton reactions is the requirement to remove the formed iron sludge and the necessity of working around pH = 2 with strict pH control [18]. The sludge problem is eliminated in the heterogeneous Fenton catalysis prepared by immobilizing the iron ions or iron oxide nanoparticles to the solid phase such as clay, zeolite, activated carbon, alumina, or natural polymers [19], [20], [21], [22], [23], [24]. Moreover, the working pH range can be extended with heterogeneous Fenton catalysis. However, the use of H2O2 in both homogeneous and heterogeneous Fenton processes increases the cost of this process.

Furthermore, low-molecular-weight Fe(III)-hydroxyl complexes in an aqueous solution have photochemical properties. When irradiated with UV light, these species can produce hydroxyl radicals and Fe(II) ions. In the hydrolysis of Fe(III) salts in an aqueous solution, different iron-hydroxyl species are formed, and between pH 2.5–5, the dominant species is Fe(OH)2+. The yield of ·OH radicals formed by photolysis of Fe(OH)2+ is much higher than other hydroxy species [25]. After UV irradiation the formed Fe(II) ions are reoxidized by dissolved oxygen to Fe(III). While the redox circle of Fe(III)/Fe(II) is completed, hydroxyl radical is produced from several circle reactions. Wu and Deng reviewed the possible mechanism of photolysis of Fe(III)-hydroxy complexes and the feasibility of the photochemical methods using Fe(III) salts in wastewater treatments [25]. In addition, Fe(III)-polycarboxylate complexes have been shown to be more efficient than Fe(III)-hydroxy complexes in accelerating the photodegradation of the dyes [26], [27], [28]. Recently, Nawar et al. showed efficient Fe(III) - aqua complex-mediated photodegradation of methylene blue dye in homogenous solution [29]. Li et al. reported high photocatalytic efficiency of Fe-alginate gel against MG dye with the incorporation of citric acid [30]. Effective dye removal was achieved with the contribution of citric acid to radical formation under UV light.

Alginate is one of the most widely used polysaccharides. Alginate hydrogels cross-linked with metal ions are frequently used as adsorbents and drug encapsulation [31], [32]. However, since alginate gels have low durability in an aqueous solution, it is preferred to use it in composite form with other biopolymers. Alginate and CMC can form compatible composites [33], [34], [35].

The present study aims to propose a simple and efficient photocatalytic degradation of MG dye in an aqueous solution under UV light with alginate-CMC composites cross-linked with Fe(III) ions without the addition of H2O2. As far as we know, the Fe@Alg-CMC composite material is being tested for the first time in dye photocatalytic degradation. In this study, the optimal conditions for maximum photodegradation of MG in an aqueous solution are reported.

Section snippets

Materials

Sodium alginate (Medium viscosity, Product number: A2033), sodium carboxymethyl cellulose (Low viscosity, Product number: C5678), and malachite green oxalate salt (Product number: M9015), and ferric chloride hexahydrate (FeCl3·6H2O) were obtained from Sigma-Aldrich (St. Louis, MO). Calcium chloride dihydrate (CaCl2·2H2O) was obtained from J.T. Baker (Deventer, The Netherlands). All chemical reagents were analytical grade and were used without further purification. Distilled water from Elga

Size, SEM Morphology, FTIR and XRD analysis

From digital photographs given in Fig. 1, it is seen that Fe@(Alg-CMC) beads are in their wet (Fig. 1a) and dry state (Fig. 1b). After completely drying, the beads have lost their light orange color and turned to orange-brown color. The dimensions of the beads were measured in width and length as 2.41 ± 0.20 mm and 3.45 ± 0.31 mm in their wet state and as 1.21 ± 0.05 mm and 1.60 ± 0.04 mm in their dry state, respectively.

Fig. 2 introduces SEM images of Fe@(Alg-CMC) beads. In Fig. 2a and Fig. 2

Discussion

With the prepared Fe@(Alg-CMC) composite gels, a very high percentage of dye degradation was achieved in a very short time. Although the degradation mechanism of Fenton-type applications is not completely clear, it is predicted that the •OH radicals formed due to UV irradiation of the hydroxyl complexes of Fe(III) ions are the active species. In the pH range of 2.5 to 5, [Fe(OH)(H2O)5]2+ is the predominant monomeric Fe(III) hydroxyl complex [29]. Maintaining the pH in this range, reduction of

Conclusion

Alginate-carboxymethyl cellulose composite material was prepared by a simple, fast, and inexpensive method. The composite material cross-linked with Fe(III) ions removed the malachite green dye from water under UV light with an excellent degradation percentage and time. The radicals formed by the iron ions of the composite material with UV light served as photocatalysis. The photocatalysis task of the composite material prepared in this study without using hydrogen peroxide could well be used

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. The research was done at Istanbul Technical University, Capillary Electrophoresis, and Biopolymer Applications Research Laboratory. The research facilities of the laboratory are covered by the Research Foundation of Istanbul Technical University.

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