Copper–Chitosan-Modified Magnetic Textile as a Peroxidase-Mimetic Catalyst for Dye Removal

Abstract

Copper chitosan attached to a magnetic synthetic nonwoven textile was manufactured using a simple, rapid, and green procedure employing chitosan dissolved in diluted acetic acid and treatment with copper sulfate solution. The prepared copper–chitosan-modified textile exhibited peroxidase-mimetic activity which was subsequently used for the degradation (decolorization) of important organic dyes, namely methylene blue, Congo red, and Bismarck brown Y, in the presence of hydrogen peroxide. After 5 h of treatment at 22 °C, 87.5%, 79.5%, and 87.7% dye removal were observed for methylene blue, Congo red, and Bismarck brown Y, respectively. The textile bound catalyst can be easily recovered from the reaction mixture after the process is completed.

1. Introduction

Textiles and nanotextiles represent low-cost materials that are usually composed of natural or synthetic fibers. Both woven and nonwoven textiles and nanotextiles can be employed for interesting (bio)technology applications. Textile materials exhibit several important properties such as flexibility, mechanical strength, and high surface area [1]. Textile and textile-like materials can be efficiently used as carriers for the immobilization of affinity ligands [2,3], ionic liquids [4], polysaccharides [5], enzymes [6,7], cells [8], (nano)particles [9,10], or essential oil microcapsules [11].

There are numerous examples of textile applications outside the typical textile and apparel industry. Various types of textile and nanotextile materials were modified by iron oxide (nano)particles or microfibers to obtain textile-based composites with interesting properties, including electromagnetic shielding [12], removal of important organic pollutants from water sources [13], utilization of intrinsic peroxidase-like activity of bound iron oxide particles for the degradation and decolorization of selected organic dyes [14], or the application of magneto-responsive textiles for non-invasive heating [15]. Textile (nano)materials with immobilized enzymes can be employed for biotechnology processes in reactors of arbitrary geometry, enabling a quick separation from the reaction liquor, and the generation of a residue-free product [6]. Textile-bound yeast cells can be employed as whole-cell biocatalysts for the hydrolysis of saccharose [16]. Catalase-like manganese dioxide microparticles adsorbed on nonwoven fabric fibers were used as a recoverable catalyst for hydrogen peroxide decomposition [17]. Various metal-based nanoparticles including silver, copper, titanium dioxide, and zinc oxide enable the preparation of textiles that exhibit antibacterial properties [18]. In addition, magnetically responsive textile composites for magnetic textile solid-phase extraction have been prepared by the insertion of a piece of magnetic iron wire (e.g., a staple using an office stapler) into the textile material to simplify their rapid recovery from the analyzed solution [5].

Chitosan is the N-deacetylated derivative of chitin; this basic polysaccharide exhibits nontoxic, biodegradable, biocompatible, antimicrobial, antifungal, and anti-inflammatory properties, as well as wound healing, film formation, excellent capacity for heavy metal adsorption, etc. [19,20,21,22]. Recently, chitosan was employed for the modification of textiles [23]. In addition, the application of chitosan-modified nonwoven textiles led to the development of the new preconcentration technique “Magnetic textile solid phase extraction” which was employed for the extraction and subsequent analysis of acid dyes [5,24,25]. The photos of the textile squares with the adsorbed dye taken with a mobile phone were employed for image analysis in order to quantify the dye concentration in the analyzed solution [5].

Chitosan can adsorb transition metals via several mechanisms, including chemical interactions (chelation or complexation), ion exchange, electrostatic attractions, and nonpolar interactions, such as van der Waals forces; chitosan amine groups usually play an important role in metal ions binding [26]. Chitosan’s ability to chelate various metal ions [27,28,29,30] including Hg(II) [31], Cd(II) [32], Cr(III), Cr(VI) [33], and Cu(II) [28,34,35,36,37] can be employed for their removal and recycling from contaminated water sources. The increase in the adsorption capacity can be supported by chitosan modification, e.g., by grafting new functional groups [38].

Copper ions have been described as efficient nanozymes exhibiting peroxidase-like (P-L) activity applied to the highly sensitive detection of glypican-3 [39]. In addition, Cu²⁺ ions enhanced the P-L activity of keratin-capped gold nanoclusters used for the photometric determination of glucose [40]. Copper nanoclusters exhibiting P-L activity were prepared by the interaction of copper sulfate and bovine serum albumin as the stabilizer and reducer [41]. Also, a casein–CuS hybrid was prepared which exhibited P-L activity [42]. In an alternative procedure, copper nanozyme was prepared by the reaction of copper sulfate and tryptophan and the formed precipitate exhibited P-L activity and caused the decolorization of methyl orange in the presence of hydrogen peroxide [43]. Also, the one-pot solvothermal method was employed for the synthesis of a copper-based single-atom catalyst from polyoxyethylene bis(amine), citric acid, and chlorophyllin–copper complex; the prepared material exhibited P-L activity [44].

Both free and immobilized (bio)catalysts and nanozymes can be efficiently used in various applications. Catalyst immobilization simplifies the manipulation during and after the reaction [14,45]. An extremely simple, rapid, and green procedure for the preparation of textiles with attached Cu-chitosan as a novel enzyme-mimetic catalyst mimicking peroxidase is presented in this communication. In addition, this catalyst can be prepared in the magnetic form to enable its simple, rapid, and selective separation from the reaction mixture. The described procedure is substantially simpler than previously reported techniques for the preparation of chitosan-copper-gallic acid-based nanocomposite [46] or Cu-doped carbon dot/chitosan film composite [47], which exhibited peroxidase-like activity. The prepared textile-bound copper chitosan was studied using scanning electron microscopy and energy-dispersive X-ray analysis. Subsequently, this material was used for the removal (degradation) of important model organic dyes in the presence of hydrogen peroxide.

2. Materials and Methods

2.1. Materials

Chitosan (medium molecular weight, 75–85% deacetylated, catalog No. 448877), N,N-diethyl-p-phylenediamine sulfate (DPD), methylene blue (Basic Blue 9, Color Index Number 52015), Bismarck brown Y (Basic Brown 1, Color Index Number 21000) and Congo red (Direct Red 28, Color Index Number 22120) were from Sigma-Aldrich, Czech Republic. White 100% acrylic nonwoven textile (Bastelfiltz, 10 × 30 cm, 150 g/m²) was from Max Bringmann KG-folia, Wendelstein, Germany. Hydrogen peroxide (30%), copper(II) sulfate pentahydrate, and other chemicals were from Lach-Ner, Neratovice, Czech Republic. NdFeB magnetic testing rod (diameter 30 mm, magnetic induction approximately 5200 G, measured on the surface of the magnetic core) and small NdFeB permanent magnets (20 × 10 mm) were from Magsy, Frystak, Czech Republic. An office stapler and common magnetically responsive staples made from galvanized steel wire were obtained locally.

2.2. Preparation of Magnetic Textile Modified with Copper Chitosan

Magnetic textile modified with chitosan was prepared similarly as described previously [5,25]. The textile squares (2 × 2 cm), prepared by cutting the nonwoven fabric sheet, were immersed in 1% (w/v) chitosan solution in 5% (v/v) acetic acid, mixed overnight, and then dried individually at 22 °C. The chitosan-modified textile was treated with 1% (w/v) NaOH solution for two hours and then washed with water. Chitosan attached to the textile squares was converted into copper chitosan by mixing with an excess of 5% CuSO₄.5H₂O for 5 h and then repeatedly washed with water. After drying at 22 °C, an iron-based staple was inserted at the top of the modified textile square using an office stapler.

2.3. Decolorization of Model Dyes

Four beakers (150 mL) filled with 50 mL of a single studied dye (50 mg/L) were used for an experiment: one mL of water (two beakers) or one mL of 30% H₂O₂ (two beakers) was added. Cu–chitosan-modified pieces of textile (2 × 2 cm) were placed into one beaker with water and one beaker with hydrogen peroxide. All beakers were mixed using a standard orbital shaker (150 rpm) at 22 °C. Absorbances of all samples were measured at the appropriate wavelength in 20–30 min intervals and the percentage of dye removal was calculated.

2.4. Peroxidase-Like Activity

The peroxidase-like activity of the native, chitosan-modified, and copper–chitosan-modified non-woven textile was assayed at room temperature in test tubes containing one-quarter of the textile square (1 cm × 1 cm), acetate buffer (pH 6, 3.4 mL), and 12.53 mM DPD solution (400 μL). The reaction was initiated by the addition of 2% H₂O₂ (200 μL). The change in the absorbance of the supernatants was spectrophotometrically detected at 551 nm, against the corresponding control containing the reagents but not the textile material [48].

2.5. Further Characterization

The structures of the native, chitosan-modified, and copper–chitosan-modified non-woven textile fibers were studied by scanning electron microscopy (SEM), using a Hitachi SU6600 scanning electron microscope (Hitachi, Tokyo, Japan) with an accelerating voltage of 1.5 kV. Energy-dispersive X-ray spectra (EDS) were acquired by SEM using a Thermo Noran System 7 (Thermo Scientific, Waltham, MA, USA) with a Si(Li) detector, with an accelerating voltage of 10 kV and the acquisition time was 300 s.

3. Results

The surface of both natural and synthetic textile fibers is an ideal platform for subsequent modifications in order to prepare a wide variety of textile derivatives. Various techniques can be used for textile modification, including both traditional solution treatment and advanced technologies such as plasma treatment, physical vapor deposition, nanoparticle application, and biology approaches [10,14].

Chitosan has been used for textile modification, due to its biocompatibility, antimicrobial, antiviral, and anti-odor activities. Its easy solubility in acidic solutions and the presence of reactive amino side groups offer the possibilities of subsequent chemical modification and the formation of valuable textile derivatives [23,49]. Textile-bound copper chitosan was prepared by a simple and rapid technique using chitosan dissolved in diluted acetic acid as a precursor; ca. 38.2 mg of dried chitosan was attached to 2 × 2 cm piece (4 cm²) of nonwoven textile. Treatment with the solution of copper sulfate resulted in the formation of blue-colored textile-attached copper chitosan (Figure 1). It is well known that chitosan forms chelate compounds with copper ions accompanied by a release of hydrogen ions [50]. Due to the chitosan solubility in acidic solutions, both chitosan and copper–chitosan-modified nonwoven textiles were stable in water solutions having neutral or slightly alkaline pH.

Scanning electron microscopy (SEM) was used to confirm the modification of synthetic textile fibers (diameters between 10 and 20 µm) with chitosan and copper chitosan (Figure 2). The chitosan modification of the textile led to the surface modification of individual fibers (Figure 2B) and to the chitosan film formation among the fibers (Figure 2C). Modification of bound chitosan by copper ions did not cause a substantial change in its morphology (Figure 2D). EDS analysis confirmed the presence of C, O, and a small amount of N in the chitosan-modified textile; after copper sulfate modification a large peak related to copper at 0.93 keV was observed (Figure 3). In addition, FTIR spectra of native (unmodified) nonwoven textiles and chitosan-modified textiles have been published recently [24].

Insertion of a staple (i.e., a piece of magnetic steel wire) enabled the preparation of a magnetically responsive textile square which can be easily captured using strong permanent magnets (Figure 4). Such materials can be easily, rapidly, and selectively removed from the treated solutions at the end of the catalytic or adsorption processes, using highly efficient NdFeB permanent magnets or a magnetic testing rod, as presented in Figure 4. Magnetic separation can be useful when working with large volumes of treated liquids.

It was confirmed that the nonwoven textile-bound copper chitosan exhibits peroxidase-like activity when measured with the DPD peroxidase substrate. The oxidized reaction product exhibited a strong absorption peak at 551 nm in the presence of hydrogen peroxide (Figure 5). The same P-L activity was observed in powdered chitosan treated with copper sulfate, where the blue material formed oxidized DPD in the presence of hydrogen peroxide. Thus, copper chitosan behaves as a typical enzyme-like catalyst mimicking peroxidases. P-L activity of copper chitosan attached to a nonwoven textile was assayed, in which the average value was 1.46 nkatal per 1 cm² of copper–chitosan-modified textile. Thus, copper chitosan exhibits similar peroxidase-like activity as other copper-containing materials including copper nanoclusters [41], protein-mediated sponge-like copper sulfide [42], or copper tryptophan derivative [43].

Organic dyes represent important environmental contaminants; they are used in textile, paper, leather, rubber, plastics, printing, and cosmetics industries which subsequently leads to their presence in different water resources. Among a variety of dyes, azo dyes have found many applications due to their versatility and chemical stability. However, their durability and non-biodegradability cause pollution problems in water systems. Some of the azo dyes are very toxic, carcinogenic, and mutagenic [51], and the carcinogenicity of many azo dyes is caused due to their cleaved product including benzidine [52]. Also, triphenylmethane dyes including crystal violet and malachite green can be toxic to mammalian cells and exhibit mutagenic properties [53].

Several procedures for organic dye removal have been described in the literature, including chemical approaches such as oxidation, photochemical and ultraviolet irradiation, Fenton reaction dye removal, electrochemical destruction, ozonation, flocculation/coagulation, and biological degradation. Also, physical approaches for dye elimination including adsorption on a variety of adsorbents and biosorbents, ion exchange, and membrane filtration have been studied intensively [54,55,56].

In addition to the above-mentioned procedures, enzyme-based degradation of organic dyes from contaminated water has been performed [57]. Peroxidases (EC 1.11.1.x) catalyze reactions in the presence of hydrogen peroxide [58]; different types of native and immobilized peroxidases can be used in the course of remediation (decolorization) of organic dyes present in contaminated waters [59,60,61,62]. Decolorization of bromophenol blue and methyl orange [63], Remazol blue [59], Remazol Turquoise Blue G, and Lanaset Blue 2R [62] by peroxidases in the presence of hydrogen peroxide are typical examples.

Similarly to many other enzymes, peroxidases are sensitive biomacromolecules, and their technological applications can be limited by low thermostability and inactivation by the high concentration of the hydrogen peroxide substrate. Due to these facts, peroxidase substitution by more stable enzyme-like materials is desirable. Nanozymes and enzyme-like catalysts have a great potential for dye decolorization and other catalytic processes because they are usually less expensive and more stable. A large quantity of nanozymes and other enzyme-mimetic materials with P-L activity have already been prepared [64]. Immobilization of enzyme-mimetic materials on insoluble, magnetically responsive carriers enables their simple and rapid removal from the system after finishing the catalytic process. Textiles and magnetically responsive textiles represent low-cost, easily available materials enabling easy immobilization of different types of nanozymes [14].

Textile-bound copper chitosan was tested for the degradation of two important diazo dyes (Congo red and Bismarck brown Y) and one heteropolyaromatic dye (methylene blue) in the presence of hydrogen peroxide. All three dyes can have negative effects on human health and can contaminate water resources. Congo red and its metabolites, such as benzidine, are known to be carcinogenic, potentially leading to cancer. This dye can also exhibit mutagenic, teratogenic, and cytotoxic effects [65,66]. Bismarck brown Y can induce cellular stress and high concentrations have been linked to developmental defects, particularly in embryonic and early larval stages of aquatic organisms [67]. Methylene blue can cause serious health issues, including methemoglobinemia, and can cause headaches, vomiting, and dizziness. Methylene blue is considered toxic and potentially carcinogenic [68].

Copper chitosan bound to a nonwoven textile (without the steel staple) adsorbed partially Bismarck brown Y in the absence of hydrogen peroxide, where after five hours ca. 27% of the dye was adsorbed (see Figure 6). On the other hand, less than 7% of Congo red and methylene blue was adsorbed under the same conditions. Furthermore, the nanozyme-based decolorization played a dominant role, in which the addition of hydrogen peroxide to the dye solutions led to rapid decolorization of all three dyes. After 5 h treatment at 22 °C, 87.7%, 79.5%, and 87.5% dye removal were observed for Bismarck brown Y, Congo red, and methylene blue, respectively. An example of Congo red decolorization is shown in Figure 7. The use of a magnetic textile carrier with bound copper chitosan can facilitate a very simple and rapid separation of the bound nanozyme from a large volume of the treated solution.

Due to the extremely low cost of all the precursors and the simplicity of the immobilized enzyme mimetic catalyst preparation, there is a possibility to use newly prepared textile-based catalysts for the reactions without the need for already used catalyst regeneration. This is a great advantage of the described textile-based catalyst in comparison with alternative previously described procedures employing more difficult catalyst preparation.

4. Discussion and Conclusions

Rapid industrialization and urbanization lead to the appearance of a broad range of organic pollutants, such as polychlorinated biphenyls, phenolic compounds, pesticides, dyes, and antibiotics in the environment. Suitable procedures for the efficient removal of organic pollutants are necessary. Enzyme-based processes have been successfully employed for their removal. However, natural enzymes have specific limitations such as relatively poor stability and high cost. Nanozymes, being nanomaterials exhibiting enzyme mimetic properties, have several advantages such as low cost, high stability, and high activity, in comparison with natural enzymes. Hence, the applications of nanozymes in environmental technology are of high importance [69].

In general, both woven and nonwoven textiles and nanotextiles can be used as a successful carriers for the immobilization of a wide variety of (bio)catalysts and nanozymes. The presented results clearly indicate that textile-bound copper chitosan exhibiting peroxidase-like activity can be efficiently used as an enzyme-like catalyst for the degradation of important organic dyes in water solutions. This magnetically responsive textile with a bound peroxidase-like catalyst can be prepared in a very simple, rapid, and green way from low-cost precursors, and can be efficiently employed in biotechnology and environmental technology. The developed material exhibiting peroxidase-like activity will be used for further research focused on the degradation of other important organic pollutants.