Azo-dye degradation by Mn–Al powders

Journal of Environmental Management 258 (2020) 110012

Contents lists available at ScienceDirect

Journal of Environmental Management journal homepage: http://www.elsevier.com/locate/jenvman

Research article

Azo-dye degradation by Mn–Al powders Mitra AboliGhasemabadi a, Wael Ben Mbarek b, Andrea Cerrillo-Gil c, Helena Roca-Bisbe c, �nquez d, Eloi Pineda a, c, e, *, Lluïsa Escoda f, Joan J. Sun ~ ol f Oriol Casabella c, Paqui Bla a

Departament de Física, Centre de Recerca en Ci�encia i Enginyeria Multiescala de Barcelona, Universitat Polit�ecnica de Catalunya - BarcelonaTech, 08019, Barcelona, Spain b Laboratoire de Chimie Inorganique, Facult�e des Sciences, Universit�e de Sfax, Ur-11-Es-73, Tunisia c Escola Superior d’Agricultura de Barcelona, Universitat Polit�ecnica de Catalunya - BarcelonaTech, 08860, Castelldefels, Spain d Departament d’Enginyeria Química Biol� ogica i Ambiental, Escola d’Enginyeria, Universitat Aut� onoma de Barcelona, 08193, Bellaterra, Barcelona, Spain e Institut de T�ecniques Energ�etiques (INTE), Universitat Polit�ecnica de Catalunya - BarcelonaTech, 08028, Barcelona, Spain f Departament de Física, Universitat de Girona, 17071, Girona, Spain

A R T I C L E I N F O

A B S T R A C T

Keywords: Wastewater treatment Textile effluents Biocompatible metals Zero-valent particles Mechanical alloying

Manganese–Aluminum powders were recently reported to show high efficiency and fast reaction rates as decolorization materials for azo-dye aqueous solutions. This work presents a detailed study of different aspects of this material. Firstly, the influence of the crystalline phase and the microstructure was studied by comparing the efficiency of powders obtained by different production protocols. Secondly, the decolorization efficiency was investigated on various types of dyes, including real textile wastewater samples. The analysis of the treated water and the particles showed that the main reaction mechanism was the breaking of the azo-dye molecules, although important adsorption on the metallic surface was observed for some colorants. Finally, the reusability of the particles and the reduction of toxicity achieved during the treatments were assessed. The simple production and application methods, the high efficiency and the use of environmentally friendly metallic elements are the main advantages of Manganese–Aluminum powders compared to other high-efficient decolorizing metallic materials.

1. Introduction The use of dyes in various processes of textile and other industries results in extensive amounts of water containing important loads of these substances. The treatment of these wastewaters consists of multi­ ple steps, one of them is the decolorizing process. This step is needed in order to fulfill legal requirements as well as to enhance the effectivity of posterior biological and chemical treatments. Among other methodol­ ogies and materials (Weng et al., 2013) (Weng, 2017) (Liu et al., 2018b), a widely studied decolorizing technology is the use of metallic zero-valent metals (ZVM), which are able to activate the degradation of many types of dye molecules and other pollutants when put in contact with the dyed water (Qin et al., 2015) (Deng et al., 2018). This can be an important process in sequential biological-chemical methods, as the end products of the degradation reaction are usually less resistant than the original molecule and may be subjected to posterior treatments like aerobic biodegradation (Patel and Suresh, 2006). The most studied material for this application is zero-valent iron (ZVI), which shows good

efficiency in the degradation of many different compounds in aqueous solutions (Zhang, 2003) (Weng et al., 2014) (Weng and Huang, 2015), among them azo-dyes (Nam and Tratnyek, 2000) (Raman and Kanmani, 2016) (Weng and Tao, 2018) (Liu et al., 2018a). These type of colorant compounds are the main family of dyes used in the textile industry and are frequently used as benchmark compounds to test the efficiency of decolorizing materials. The effectivity of the decolorizing reaction by means of metallic particles depends on two fundamental aspects. Firstly, the chemical interaction between the metallic material, the dye molecules and the aqueous media, which is usually highly sensitive to temperature and pH conditions. Secondly, the specific physical parameters of the process such as the total surface of the decolorizing material in contact with the dyed water, the agitation or filtration protocols and the geometrical and dynamical parameters of the reactor. The research in new decolorizing metallic materials is focused on improving the effectiveness of the chemical mechanism under different water conditions as well as on designing new production methods to obtain the maximum active

* Corresponding author. Department of Physics, Universitat Polit�ecnica de Catalunya EEBE, Av. Eduard Maristany 16 - Edifici C, 08019, Barcelona, Catalonia, Spain. E-mail address: [email protected] (E. Pineda). https://doi.org/10.1016/j.jenvman.2019.110012 Received 9 September 2019; Received in revised form 23 November 2019; Accepted 17 December 2019 Available online 7 January 2020 0301-4797/© 2019 Elsevier Ltd. All rights reserved.

M. AboliGhasemabadi et al.

Journal of Environmental Management 258 (2020) 110012

surface per gram of material (Deng et al., 2018). One approach to improve the efficiency of the decolorizing reaction is to produce new intermetallic phases with metastable structures. The aim is to increase the reactivity of the materials by combining different metallic elements and by introducing defects in the metallic atomicscale structure. Metastable phases like amorphous metals (metallic glasses) have been proven to show high reactivity (Zhang et al., 2010) (Wang et al., 2012) (Zhang et al., 2019) and improved decolorizing ef­ ficiency in comparison with more stable phases with the same chemical composition (Zhang et al., 2012a). Another approach is to increase the specific surface area, either by the production of nano-particles (Zhang, 2003) (Fan et al., 2009) (Bhakya et al., 2015) (Raman and Kanmani, 2016) or by the generation of nano-scale rough or porous metal surfaces (Luo et al., 2014). A simple method to produce metallic particles for decolorizing applications is the use of mechanical alloying in metallur­ gical ball mills (Suryanarayana, 2001). This classic metallurgical method introduces enough mechanical energy to produce new inter­ metallic or solid solution phases promoting the inter-diffusion of the initial raw components. Furthermore, the ball milled particles usually show highly metastable nanocrystalline or amorphous atomic-scale structures as well as small particles with rough surfaces. Recent works reported the high efficiency of Manganese–Aluminum (Mn–Al) particles in the degradation of azo-dyes like Reactive Black 5 (RB5) (Ben Mbarek et al., 2017) and Orange II (AboliGhasemabadi et al., 2018). Both Mn and Al have the advantage of being biocompatible materials used in many environmental and biomedical applications (Hermawan et al., 2008). In this work, new results assessing different aspects of the Mn–Al particles will be presented, such as the effect of composition and structure in the degradation efficiency, the toxicity, the efficiency on different types of dye molecules and the reutilization capability. The aim is to provide enough information to environmental engineers and scientists to consider their possible application in water treatment processes.

with different pH were performed adding the required amounts of hy­ drochloric acid (1 M) or sodium hydroxide (1 M) in order to reach the desired initial pH values. The temperature was maintained constant at the desired value by adjusting the power of the heating plate of the magnetic stirrer. After reaching stable temperature and pH conditions, a certain amount of Mn–Al powder was added to the solution. The dosage of particles used in each test was chosen in order to optimize the study of the reaction kinetics, avoiding reactions too fast to be monitored with enough accuracy. The samples of dyed aqueous solution with Mn–Al powder were kept in continuous agitation (400–500 r.p.m.). During the decolorizing tests, samples of the dyed solution were taken at specific time intervals. The amount of solution extracted each time was 5 mL. The metallic particles were separated during the extraction by using a filter with a light pass of 1.2 μm (Titan 3TM Thermo Fisher Scientific). After the extraction, the absorbance of the samples was measured for wavelengths between 200 and 800 nm in a UV-2600 Shimadzu UV–vis spectrophotometer. The dyes used in this study were Orange II (C16H11N2O4NaS), Reactive Black 5 (C26H21N5Na4O19S6), Orange G (C16H10N2O7Na2S2), Acid Black 58 (C19H17N3O5S) and Brilliant Green (C27H34N2O4S), all obtained from Sigma Aldrich in powder form. The first four dyes have a molecular structure containing an azo bond, as referred above this bond is expected to be broken due to the interaction with the ZVM particles. On the contrary, Brilliant Green is not an azo dye and was chosen to test the effectiveness of the Mn–Al powder in other types of compounds. Real wastewater from a textile industry was also used in order to realize a preliminary test in solutions similar to real conditions. The chemical composition of the real wastewater samples is mostly unknown, due to the multiple processes performed in the textile industry, although it is expected to contain significant concentrations of dying compounds. Two different wastewaters coming from different batches were used, one was dark and reddish while the other lighter and brownish. The solutions came from the process of coloring textile fibers with Dianix Plus Red (DYSTAR); The dark solution is expected to contain a significant con­ centration of DYSTAR. This dye is used in the coloring of polyesters and is formulated to maintain the color of the fiber and therefore be stable against oxidation, reduction and changes in pH. A part from the DYSTAR colorant other pollutants coming from the industrial process are ex­ pected to be present in the wastewater samples. An analysis of the original wastewater was not made, the only aim of the tests was to check if the addition of Mn–Al powder triggered any kind of decolorization in real wastewater containing a mixture of colorants and other pollutants. One of the experimental concerns was to assess the filter effect, as some materials can produce a decolorization effect by adsorption of the dye molecules. Absorbance analyses of the initial solution, without adding Mn–Al particles, were performed before and after filtering and only in the case of the solutions with Acid Black 58 the filtering showed a perceptible effect on the absorbance spectrum, as will be discussed below. The separation of the particles by filtering instead of centrifu­ gation, which is used in many other studies of ZVM-mediated decolor­ ization reactions, has the advantage of being an almost ‘instantaneous’ process. This reduces artefact effects during the determination of the fast kinetics that can be caused due to the time elapsed between extraction, separation and color analysis. After some decolorization experiments the particles were recovered with the aim of analyzing the state of the particles after the reaction as well as to use these particles in new decolorizing experiments in order to check their reusability. The particle recuperation process was as follows. After the decolorization experiments the particles were sedimented during 24 h, afterwards the free-particle liquid was retired and the remaining wet powder was heated in order to evaporate the water content. The dried particles were either analyzed or reused in decolor­ izing experiments. In order to check if the state of the particles changed depending on the sedimentation time, recuperation of particles after waiting 48 h was also performed. The use of the latter in decolorizing experiments showed the same efficiency as the ones recovered after 24

2. Materials and methods Metallic particles of Mn–Al were prepared by mechanical alloying in a mechanical mill SPEX 8000 under protective argon atmosphere. The pure, raw elements were introduced into a container together with hard material balls in order to produce powder by mechanical milling. Different milling times of 20, 30 and 60 h were used, applying intervals of 10 min of milling and 5 min of resting in order to avoid overheating and the formation of particle aggregates. An alternative route, with a previous rapid quenching of the Mn–Al alloy, was also used. In this case the Mn and Al raw materials were firstly melted in an induction furnace and rapidly quenched by the melt spinning technique (Chen et al., 1980), obtaining thin ribbons of Mn–Al alloy. These ribbons were sub­ sequently milled as described before to obtain a Mn–Al powder. Scanning electron microscopy (SEM) and compositional analysis using X-ray dispersive energy spectroscopy (EDS) were performed in a FIB-SEM Zeiss Neon40 and a Phenom XL Desktop SEM. Analysis of the images and the computation of particle size distributions was performed using the ImageJ software (version 1.51j8, National Institutes of Health, Bethesda, MD, USA). X-ray diffraction (XRD) was carried out in a Siemens D500 using CuKα radiation and the phase identification was achieved by means of X’pert High Score Plus software (PANalytical, version 2.0.1, Almelo, The Netherlands). Specific surface area mea­ surements were performed by means of the Brunauer-Emmett-Teller (BET) model in a Micrometrics ASAP 2020 apparatus using nitrogen as adsorbate and helium as non-adsorbing gas for the dead volume calibration. The decolorization experiments consisted of the following steps. A quantity of colorant powder, measured with a precision scale (Semimicro Discovery 8), was dissolved in a volume of 1 L of distilled water. Once these mother solutions were prepared, a beaker with 100 mL of solution was used to perform each decolorizing test. The experiments 2

M. AboliGhasemabadi et al.

Journal of Environmental Management 258 (2020) 110012

h, suggesting that the sedimentation time did not affect the surface state of the recuperated particles significantly. For some batches of recovered particles additional washing protocols were assayed (Pouretedal and Saedi, 2014). The dried particles were washed using ethanol, acetone and an HCl aqueous solution with pH ¼ 3. The ethanol washing consisted in adding 0.2 mL of ethanol per mg of powder and drying the particles by evaporation after 4 h of being in contact with the washing liquid. In the case of acetone and the HCl so­ lution, the washing consisted in adding 0.4 mL of the washing liquid per mg of powder and evaporation after 2 h. High-resolution liquid chromatography (HPLC) and Mass spec­ trometry (MS) were used to analyze the presence of Orange II and the reaction products generated during the decolorization (Bromley-Chal­ lenor et al., 2000) (El Nemr et al., 2018). The HPLC-MS analyses were performed at 30 � C in a Beckman Gold equipment injecting 50 μL as blank, 20 μL of Orange II solution and 50 μL of decolorized water samples, using a Zorbax Eclipse Plus C18 column, Narrow Bore (2.1 � 150 mm) 5-μm. Ammonium acetate and methanol 90:10 (v/v) solution was applied as a mobile phase and the pressure was fixed at 400 bars, the flow rate and the stop time were 0.5 mL min 1 and 30 min respectively. Flame Atomic Absorption Spectrometry (A-2000, Hitachi) was realized in order to analyze the presence of metal ions in the decolorized solutions. The toxicity of the samples was assessed by a Microtox System (Microbis Corporation) based on the bioluminescent Photobacterium phosphoreum microorganism. The reagents were: Lyophilized Photo­ bacterium phosphoreum, stored at 20 � C and re-suspended at the time of the trial (Microtox Acutue Reagent Ref. AZF686010A); Reconstitutive solution (Microtox Diluent Ref. AZF686004); MOOS osmotic solution (NaCl 22 wt%); and Dilute solution (NaCl 2 wt%). The toxicity was measured by determining the EC50 value, which is the concentration of sample that provokes the death of 50% of the microorganism population and the corresponding decrease of luminosity. Measurements were done with trial times of 5 min at 15 � C and pH 7. The toxicity units are given in TU(%) ¼ 100/EC50 (Ghoveisi et al., 2018).

Fig. 1. Evolution of Orange II dye concentration after application of 50 mg/ 100 mL of Mn70Al30 powder produced by ball milling during 60 h. All tests were performed at room temperature. Results for different initial pH values are shown. (Inset) Evolution of the absorbance spectrum of the solution and view of the initial and treated solutions. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

the reaction times reported for fast degradation materials are usually of the order of few minutes. Some protocols like centrifugation may in­ crease the contact time between particles and dyed solution after the sample extraction significantly. In most studies it is assumed that the reaction follows pseudo-first order reaction kinetics CðtÞ ¼ C∞ þ ½C0

C∞ �expð ktÞ;

1

with C0 and C∞ the initial and final colorant concentrations respectively, and k the reaction rate constant, usually given in units of min 1 in the literature. One useful parameter to compare the intrinsic efficiency of different decolorizing materials is the logarithm of the reaction rate constant, k, normalized by the specific surface area and the dosage of decolorizing material and multiplied by the initial concentration of the dye in the solution (Wang et al., 2015)

3. Results and discussion 3.1. Efficiency of Mn–Al particles for azo-dye degradation The effectiveness of Mn–Al particles was already reported in previ­ ous works (Ben Mbarek et al., 2017) (AboliGhasemabadi et al., 2018). The effect of temperature was studied determining an Arrhenius behavior of the reaction rate constants with relatively low activation energies (AboliGhasemabadi et al., 2018), similar to the ones found for metallic glass particles as discussed in (Zhang et al., 2019). Fig. 1 shows the evolution of the absorbance spectra (inset) and the corresponding values of dye concentration as a function of time after the application of Mn70Al30 powder on Orange II dye solutions with different initial pH values. In the case of room temperature and no pH modification, the dyed solution becomes completely transparent after 20 min since the application of 50 mg/100 mL of Mn–Al particles produced by ball milling. As observed in the majority of studies related to decolorizing materials, the decrease of the pH favors the reaction rate. The comparison of the decolorizing efficiency between Mn–Al powder and other types of decolorizing materials reported in literature is affected by the different experimental conditions and the different types of dyes used in each study. As will be shown below, the reaction rate and final efficiency may differ completely depending on the specific dye used in the experiment, even in the case of dyes all belonging to the azo-group. Moreover, some experimental parameters, like the ratio be­ tween the initial dye concentration and the dosage of particles, the agitation and filtration protocols, or the time elapsed from extraction to particle separation and color analyses, are expected to be very different depending on the study. The separation protocol of the particles previ­ ous to the color analysis of the dyed water is particularly important as

logðkS C0 Þ; kS ¼ k = ma;

2

where m is the dosage of decolorizing material (mass per volume of solution) and a is its specific surface (surface area per unit of mass). The use of the logarithm gives a number that is adequate for comparing the efficiency of the different materials taking into account the possible variations in measuring reaction rates due to different experimental protocols. Of course, the use of logðkS C0 Þ as a measure of material effi­ ciency only has real meaning if the experiments reach a complete decolorization (C∞ � 0). (Wang et al., 2015) reported the values of logðkS C0 Þ for different types of ZVM particles computing kSC0 in units of μmol m 2 min 1. This values are within a range of 0.5 to 3.0 and include different materials such as zero-valent iron (ZVI) microparticles and nanoparticles, Mg and MgZn alloys and Fe and Co-based amorphous alloys. The reaction of Mn70Al30 particles shown in Fig. 1 gives logðkS C0 Þ ¼ 1.48, this is a good number compared to many materials used in this kind of applications although lower than the ones reported for Fe–Si–B (Zhang et al., 2012a) (Zhang et al., 2011) and Co–Si–B (Qin et al., 2015) metallic glass particles, which are the only materials giving values above 2. In these cases, the highly metastable amorphous structure is suggested to be responsible of the high reactivity shown by these materials (Zhang et al., 2019). However, as will be discussed below, the Mn–Al particles described in this work have the advantage of being synthesized by 3

M. AboliGhasemabadi et al.

Journal of Environmental Management 258 (2020) 110012

simple ball milling method in comparison with the more complex routes needed for metallic glass formation or the synthesis of nano-particles (Fan et al., 2009) (Raman and Kanmani, 2016). Another advantages are the easy application, as compared to other decolorization processes (Cai et al., 2017), and the good response shown in alkaline conditions. Although the reaction is slightly hindered in the pH 10 solution, the effect is small if compared to most decolorizing materials in which the acidic conditions favor the redox process (Zhang et al., 2012b) (Zhang et al., 2019). The relatively low sensitivity to pH conditions was also found in decolorizing experiments of RB5 solutions (Ben Mbarek et al., 2017), and it could be attributed to the presence of Al in the material as observed in other Al-containing materials (Wang et al., 2017). Although the origin of the good decolorization performance of this material in alkaline solutions is not clear, some possible origins are proposed below in the discussion of the reaction mechanism. 3.2. Effect of composition, phase and microstructure The high intrinsic efficiency of the decolorizing reaction prompted by the Mn–Al particles, once normalized by the specific surface area and dosage of particles, can be attributed to different variables: a) the inherent chemical properties of Mn and Al; b) the internal microstruc­ ture of the metallic particles; or c) the chemical properties of the com­ bination of Mn and Al in the intermetallic phases generated during the mechanical alloying process. The first question arising is therefore, which ones of these factors are responsible of the high decolorizing efficiency? The decolorizing ability of Mn–Al particles of same composition but different metallic phases was compared in (AboliGhasemabadi et al., 2018). On one hand, rapidly quenched alloys were produced by the melt spinner technique, obtaining a solid solution of β-Mn(Al) (Cubic P4132). This Mn phase accepts up to 25 wt% of dissolved Al in its crystalline lattice. On the other hand, Mn–Al particles were produced by direct ball milling of pure Mn and Al raw materials. These latter particles were composed of a mixture of α-Mn(Al) (Cubic I-43 m) and Al (fcc). Fig. 2 shows the XRD patterns obtained for the different production protocols: melt spinning and subsequent ball milling for 15 h (labeled as MS þ BM15h) and direct ball milling for 20, 30 and 60 h (labeled as BM20h, BM30h and BM60h, respectively). The position of the peaks clearly shows the different metallic phases present in the particles, while their broadness indicates that the inner structure of the particles is composed of crystalline grains of nanometer size. A Scherrer calculation of the crystallite size gives the results re­ ported in Table 1. In the case of the particles produced by direct ball milling, the increase in milling time does not change the phase but re­ duces the grain size and therefore increases the lattice distortion. It should be noted that, as shown in (AboliGhasemabadi et al., 2018), the powders produced by direct ball milling were not composed of separated particles of α-Mn(Al) and Al (fcc) but of particles composed by nano­ crystals of both phases. In other words, the majority of the particles produced by direct ball milling contained both Mn and Al-rich regions. As previously reported (AboliGhasemabadi et al., 2018), the high reactivity of Mn–Al particles increases as the particle size is reduced. In addition to the intrinsic decolorization properties of the material, the ball milling process generates a large specific surface area of the pow­ ders due to highly irregular surfaces as shown in Fig. 3. This large spe­ cific surface is a principal parameter making Mn–Al powders highly reactive and it is increased as the ball milling process is extended in time producing smaller particles. For instance, using 100 mg/100 mL of Mn70Al30 BM30h and Mn70Al30 BM60h, the reaction rate constants of the degradation of 40 mg L 1 solutions of Orange II were found to change from k ¼ 0.091 min 1 to k ¼ 0.182 min 1 respectively. However, once normalized by the specific area given by the average particle size they become kS ¼ 0.161 and kS ¼ 0.166 L m 2 min 1. Therefore, the change in reaction rates of the powder samples produced by different milling times can be attributed only to the different amount of contact

Fig. 2. X-ray diffraction of Mn70Al30 powders produced by different protocols. From top to down: Melt spinning and subsequent ball milling for 15 h (labeled as MS þ BM15h), ball milling for 60 h (BM60h), ball milling for 30 h (BM30h) and ball milling for 20 h (BM20h). Table 1 Average size of the crystalline grains (obtained from XRD results) and average size of the particles (obtained from SEM images) of Mn70Al30 powders produced by different methods. Decolorizing material

Crystallite size (nm)

Particle size (μm)

Mn70Al30 MS þ BM15h Rapid quenching þ ball milling for 15 h Mn70Al30 BM20h Ball milling of Mn and Al for 20 h

13 � 5 (β-Mn(Al) crystals)

4�2

26 � 3 (α-Mn(Al) crystals) 43 � 8 (fcc Al crystals) 33 � 9 (α-Mn(Al) crystals) 36 � 6 (fcc Al crystals) 23 � 2 (α-Mn(Al) crystals) 33 � 3 (fcc Al crystals)

120 � 60

Mn70Al30 BM30h Ball milling of Mn and Al for 30 h Mn70Al30 BM60h Ball milling of Mn and Al for 60 h

100 � 30 50 � 10

surface between the particles and the medium. Even though the inner microstructure of the ball milled particles is slightly changed by the milling time, as seen by the increase of the width of the XRD peaks in Fig. 2, the intrinsic decolorization ability of the material is not signifi­ cantly altered. Table 2 shows the reaction rate constants of the decolorizing process of an RB5 aqueous solution using particles of pure Mn, β-Mn(Al) and α-Mn(Al) þ fcc Al. In the table, the reaction rate constants, k, are normalized by the total surface of the powder dosage used in the decolorizing experiments. These normalized reaction rates are ks ¼ k/ am, where a is the specific surface area determined by BET analysis (m2 of area per gram of material) and m the applied dosage (grams of metallic powder per litter of dyed solution). The best performance was observed for the Mn70Al30 BM30h powder, although the use of Mn70Al30 MS þ BM15h powder also showed a fast decolorizing reaction. These 4

M. AboliGhasemabadi et al.

Journal of Environmental Management 258 (2020) 110012

Fig. 3. SEM images of the Mn70Al30 powder obtained by ball milling during 30 h. Table 2 Reaction times of the decolorizing reaction of 40 mg L powder per 100 mL of dyed solution.

1

RB5 azo dye solution by β-Mn(Al), α-Mn(Al)þAl and α-Mn particles. The dosages were 250 mg of metallic

Decolorizing material

Phase

Specific surface area (m2 g

Mn70Al30 MS þ BM15h Rapid quenching and posterior ball milling for 15 h Mn70Al30 BM30h Ball milling of Mn and Al for 30 h Ball milling of pure Mn for 30 h

β-Mn(Al)

0.55

0.197

α-Mn(Al) þ fcc Al

0.565

0.393

α-Mn

0.903

0.047

results suggest that the two different crystalline structures of the Mn–Al powders do not lead to large differences in reaction rates or decolorizing efficiency. Fig. 4 (A) shows the results obtained for decolorizing experiments of 40 mg L 1 solutions of Orange II. In this case the decolorizing efficiency is assessed for particles with four different compositions: Pure Mn, Mn70Al30, Mn50Al50 and pure Al. In all cases the particles were produced by ball milling during 30 h. The results were obtained using the same dosage for all types of particles (50 mg of particles per 100 mL of so­ lution). In this figure, the time of the reaction t is multiplied by the specific surface area of the particles a in order to account for the different amount of exposed surface. The specific surface area of the batches of particles used in this experiment was determined by BET analysis given values of 0.565, 0.179, 0.928 and 1.11 m2 g 1 for Mn70Al30, Mn50Al50, Mn and Al respectively. Although all the powders were produced with the same ball milling protocol, they showed different surface topology and different particle size distributions depending on the composition, this producing different specific surface areas. Plotting the dye degradation evolution as function of ta permits to visualize just the intrinsic effect of the composition and inner structure of the material. Fig. 4 (B and C) show the results obtained for Mn70Al30 and Mn50Al50 powders, corresponding to batches obtained by ball milling for 60 h, when added to dyed solutions with modified initial pH. It is observed that in all pH conditions the maximum efficiency is obtained by the Mn70Al30 powders. It is interesting to note that the high efficiency of this particles is much higher than the one observed for pure Mn and pure Al powders. This was also observed for the decolorizing experiments of RB5 using pure Mn particles (see Table 2). Taking into account the results detailed above, the origin of the high decolorization efficiency of the Mn–Al powders is therefore not related

1

)

Reaction rate constant kS (L m

2

min

1

)

to the individual chemical reactivity of Mn and Al and it is not signifi­ cantly altered by the crystalline structure of the Mn–Al compound used. The high efficiency is therefore related to the high specific surface area, generated by the ball milling process, and to the chemical interaction of

Fig. 4. A: Evolution of dye concentration in an Orange II solution without pH modification after adding 50 mg/100 mL of Mn70Al30, Mn50Al50, pure Mn and pure Al particles all of them produced by ball milling during 30 h. B and C: Evolution of dye concentration in solutions with initial pH values of 4 (B) and 10 (C) after adding 50 mg/100 mL of Mn70Al30 and Mn50Al50 ball milled during 60 h. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.) 5

M. AboliGhasemabadi et al.

Journal of Environmental Management 258 (2020) 110012

both species and the dyed solution once Mn and Al are both present in the same particles, independently if they are in form of a solid solution or if the particles are composed of a mixture of Mn-rich and Al-rich nanocrystals. Although a detailed scanning over different composi­ tions should be done, the optimum Mn: Al ratio is probably around Mn70Al30. 3.3. Analysis of the decolorized water The results of the HPLC and MS analysis for the case of the Orange II solutions are detailed in the supplementary materials. As shown in Figs S-1, S-2 and S-3, and according to (Cao et al., 1999), the degradation of the Orange II dye molecules occurs by splitting the molecule in two amines. Chromatography of decolorized water solutions treated with particles of different Mn–Al composition or with different initial pH values showed similar results, indicating that in all the tested conditions the main mechanism of the decolorization reaction was the rupture of the azo bond of the dye molecule. Therefore, it is deduced that the dye degradation reaction triggered by Mn–Al particles is similar to the one observed for ZV-Fe particles, which has been studied in various articles (Cao et al., 1999) (Khani et al., 2012). As outlined in Fig S-3, the analysis shows that the reaction is realized in two stages, with the appearance of a transition product before the final degradation products identified as aromatic amines by their molecular weight. The content of metal ions (Mn and Al) dissolved in the decolorized water was analyzed by flame atomic absorption spectrometry. The re­ sults obtained are detailed in supplementary materials (Fig S-4). Two main results can be highlighted. Firstly, in all the cases that were analyzed there was much more dissolution of Mn than Al ions in the water. The ratio of concentrations of Mn and Al ions dissolved in the water were found to be more than 250 : 1 while being 1 : 1 in the initial Mn50Al50 particles. Secondly, the decrease of initial pH has an important effect on the dissolution of the two species. The reduction of pH multi­ plies the concentration of dissolved Mn ions by 2 while it increases the Al ions concentration by a factor of 8. From these results it is clear that the corrosion of the Mn–Al particles is based on the dissolution of Mn. From the chemical analysis of the decolorized solutions is not possible to discern which element, manga­ nese or aluminium, is the most reactive one. At a first glance, the higher efficiency of the particles containing more Mn content could indicate that this element is the one contributing more to the reaction. However, its role could be partly indirect; The Mn dissolution generates new surface of the particles which is free of oxides, this exposes ‘fresh’ zerovalent Al to the medium which can act as reducing element. This may explain why the combination of the two elements in Mn–Al particles produces higher efficiency compared to the use of pure Mn and Al powders as discussed above. Although Mn is an abundant metal in natural conditions, the easy dissolution of Mn can be a problem if the concentration of ions becomes too high after the treatment. In case of application of Mn–Al particles in a real wastewater decolorization pro­ cess, it would be necessary to verify that the Mn concentration does not exceed the limit considered as harmful.

Fig. 5. A: Evolution of dye concentration in an Orange II solution after adding 50 mg/100 mL of Mn70Al30 produced by ball milling during 30 h. The asproduced particles (Cycle 0) are compared with recuperated particles after 1, 2 and 3 decolorization experiments (Cycles 1, 2, 3). B: Total decolorization after 60 min observed for decolorization experiments of Orange II solutions for recuperated particles using different washing methods. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

decolorization experiments of Orange II solutions. Fig. 5 (A) shows the kinetics observed for the initial particles (Cycle 0) and for posterior recuperation and decolorization experiments (Cycles 1–3). As observed in Fig. 5, the efficiency of the reaction decreases significantly after each decolorization-recuperation cycle. The recuper­ ated particles after a single decolorization experiment still maintain some degree of efficiency, although the rate of the reaction is severely reduced. For following recuperations, the efficiency is highly reduced and after four cycles the particles almost do not show decolorization activity. The use of washing methods with ethanol, acetone and HCl solutions were reported in literature to improve the efficiency of the recuperated particles in the case of some decolorizing materials (Pour­ etedal and Saedi, 2014). Fig. 5 (right) shows the percentage of decol­ orization obtained after 60 min of application of Mn70Al30-BM30h recuperated and washed by the different methods. All the washing methods experienced in this work decreased the efficiency if compared to the simple recuperation method without washing. SEM images of the recuperated particles and their semi-quantitative surface compositions obtained by EDS are shown in Figs S-5 and S-6 of the supplementary materials. It is observed that the recuperated particles show a surface thickly covered by corrosion products or adsorbed compounds. The application of washing methods after the recuperation even increase the thickness of this layer, particularly in the case of washing with HCl so­ lution. This is consequent with the diminutions in the percentage of decolorization observed in Fig. 5 (right). It is worth noting that the surface concentration of the particles (see Fig S-6) shows small amounts of S and Na which come from the Orange II molecules. This indicates that although the analysis of the treated water, discussed above, clearly detected the products of the dye molecule degradation in the decolorized water, at least some amount of either the original dye molecules or the products of their degradation are adsorbed by the metallic surface, thus contributing to the formation of the layer of precipitates observed in the SEM images of the used particles. The reduction of the decolorization ability of the recuperated parti­ cles is, in fact, a common effect in most decolorizing materials with just some exceptions (Qin et al., 2015). If the treatment consists of a direct application of the powder without recuperation, as it is meant in many cases for ZVM-decolorizing powders, the reusability is not very impor­ tant; In this case it is more important to determine the minimum dosage

3.4. Reusability of the metallic particles The efficiency of decolorizing materials decreases after being used (Qin et al., 2015) (Marcelo et al., 2018) (Pouretedal and Saedi, 2014), this being one of the main issues to take into account in case of designing a real wastewater treatment. The free surface of the zero-valent metal particles is progressively covered by reaction and corrosion products, thus reducing both the velocity of the decolorization reaction and the final efficiency. In this work, the reusability of the Mn–Al particles was characterized by recuperating them after being used in dye degradation experiments. As detailed in the Materials and methods section, the particles were recovered by sedimentation, decantation and evapora­ tion. The batches of recuperated particles were then reused in 6

M. AboliGhasemabadi et al.

Journal of Environmental Management 258 (2020) 110012

of particles necessary to degrade a given volume of dyed solution which can be related to the value of logðkS C0 Þ discussed above. However, if the application is in form of filters, or any other method in which the decolorizing material can be recuperated, the reusability is then an important issue. In this work, a first assessment of the decrease of effi­ ciency is reported together with the demonstration that simple washing methods do not improve the reusability of Mn–Al particles. Finding a recuperation method or a washing solution able to clean the particle surface would be of great importance for the use of this materials as part of decolorizing filters in a wastewater treatment process. 3.5. Discussion of the degradation reaction A possible mechanism of the degradation reaction of the dyes RB5 and Orange II by Mn–Al powders was already proposed in (AboliGha­ semabadi et al., 2018). As discussed above, the water analyses suggest that the main mechanism of the decolorization reaction is the rupture of the dye molecule triggered by the oxidation of the metals. The difference in solubility of Mn and Al (Fig S-4) suggests that the dissolution of Mn makes that non-oxidized Al atoms of the inner parts of the particles become progressively exposed to the aqueous solution, participating in this way to the reaction. In acidic aqueous solutions (pH < 3) Al oxidizes while in less acidic conditions (pH > 5) it forms Al(OH)3. In the case of Mn, it forms soluble salts in acidic conditions but its solubility is reduced as pH increases. The proposed mechanism in acidic conditions is Al→Al3þ þ 3e Mn→Mn2þ þ 2e 2H2 O→H3 Oþ þ OH 2H3 Oþ þ 2e →H2 þ 2H2 O Al3þ þ 3OH →AlðOHÞ3 R N ¼ N R’ þ H2 →R NH NH R’ R NH NH R’ þ H2 →R NH2 þ R’ NH2 At higher pH Mn forms insoluble hydroxides while the Al hydroxides become soluble, in this case the proposed mechanism is Fig. 6. Evolution of the absorbance during decolorization experiments with Mn70Al30-BM30h powder. From top to bottom: A) Brilliant green with initial concentration of 150 mg L 1 adding 100 mg/100 mL of powder dosage; B) Orange G with initial concentration of 40 mg L 1 adding 100 mg/100 mL of powder dosage; C) Acid Black 58 with initial concentration of 150 mg L 1 adding 100 mg/100 mL of powder dosage; D) Textile industry ‘Dark reddish’ wastewater adding 250 mg/100 mL of powder dosage; E) ‘Light Brownish’ wastewater adding 250 mg/100 mL of powder dosage. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

Al→Al3þ þ 3e 2H2 O þ 2e →H2 þ 2OH Al3þ þ 3OH →AlðOHÞ3 þ OH →½AlðOHÞ4 � Mn→Mn2þ þ 2e Mn2þ þ 2OH →MnðOHÞ2 R N ¼ N R’ þ H2 →R NH NH R’ R NH NH R’ þ H2 →R NH2 þ R’ NH2 Al-based alloys have been reported to show good decolorizing ability in alkaline conditions (Wang et al., 2017), contrary to most decolorizing ZVM powders which drastically decrease their efficiency if pH is increased. Good efficiency in alkaline dyed solutions is indeed observed for the Mn–Al particles as discussed above, supporting the idea that Al has a significant role in the process. The stable oxide passivating layer of Al is responsible of the low activity showed by pure Al particles (see Fig. 4), the presence of Mn and its dissolution during the reaction is therefore responsible of reinforcing the role of Al leading to metallic powders with good efficiency in both acidic and alkaline conditions. It is worth to stress here that other pathways for the decolorization reaction cannot be discarded. Combination of oxidation and adsorption mecha­ nism is also possible as 0.5 at% of S coming from the dye molecules was detected on the surface of the particles by EDS. The determination of the exact mechanism, or combination of mechanisms, would require more experimental work in the future.

decolorizing materials and they were selected for this reason. Fig. 6 show the results obtained for Brilliant green, Orange G, Acid Black 58 and two samples of real textile wastewater obtained from an industry in the Girona province of Catalonia. Only preliminary tests were performed for these types of colored solutions, with the only purpose to determine if the decolorization ability of Mn–Al particles was a general effect or restricted to specific azo-dyes. Some comments about this results can be highlighted. Firstly, the Mn–Al particles show good decolorization ability for Brilliant green and the samples of industrial wastewater. Brilliant green is not an azo-dye and the wastewater samples may contain a variety of contaminant compounds. Therefore, it seems that the decolorization ability of Mn–Al is not restricted to just azo-compounds. On the other hand, the Mn–Al powder showed some decolorization ability in Orange G solutions but with a much lower efficiency than for the other azo-dyes. Even applying a double dosage of the one used for the RB5 and Orange II experiments, the decolorization was not complete and saturated after 30 min. The case of Acid Black 58 was different. For these solutions it was observed that the decolorization did not proceed by the breakage of the molecule but by adsorption. From our observations, the molecules of this colorant

3.6. Effect on different dye molecules The results presented in (Ben Mbarek et al., 2017) and (AboliGha­ semabadi et al., 2018) were focused on decolorization of two azo-dyes, namely RB5 and Orange II. These two dyes, especially Orange II, have been used in many research works studying the efficiency of 7

M. AboliGhasemabadi et al.

Journal of Environmental Management 258 (2020) 110012

remained intact but they easily attached to metallic surfaces. The water was observed to decolorize only after the particles were allowed to precipitate after the experiment ended. Summarizing, Mn–Al particles were observed to show good decolorization efficiency in a variety of colored waters but with a significant variation of efficiencies and reac­ tion rates depending on the dying compound.

Table 3 Results of toxicity analysis (TU ¼ toxicity units). Comparison between the initial dyed solutions (150 mg of dry dye per L of solution) and the final decolorized solutions after the application of Mn70Al30 particles obtained by ball milling during 30 h.

3.7. Toxicity of the treated water Table 3 shows the results of the toxicity test for different types of colorants, as specified in the Materials and methods section. The toxicity is given in units of TU ¼ 100/EC50, where EC50 is the effective con­ centration of sample that causes the death of 50% of the microorganisms under certain conditions of time and temperature. The higher the EC50 concentration, the lower the value of TU and the less toxic the sample. A colour correction protocol, which takes into account the change in colour between the initial and treated solutions, was applied. In general terms, TU values higher than 25 (in tests based on Photobacterium phosphoreum) are considered as toxic. As shown in the table, all samples reduced their toxicity after the treatments with Mn–Al powders. The degree of decrease in toxicity reached after the treatments can be considered a good result as compared to, for example, the results ob­ tained using biological methods (Casas et al., 2007). These results of toxicity indicate that there is not a harmful effect of the treatment with Mn–Al particles, therefore the reaction does not generate toxic by-products.

Dye

Initial toxicity

Final toxicity

Orange II Orange G Brilliant Green

100 5.6 81

20 4 33.3

wastewater treatment. Author contribution section Mitra AboliGhasemabadi: Formal analysis, Investigation, Method­ ology, Writing - original draft Wael Ben Mbarek: Investigation; Meth­ odology Andrea Cerrillo-Gil: Formal analysis, Investigation, Writing original draft Helena Roca-Bisbe: Formal analysis, Investigation, Meth­ odology Oriol Casabella: Formal analysis, Investigation, Methodology Paqui Bl� anquez: Methodology, Writing - review & editing Eloi Pineda: Supervision, Writing - original draft, Writing - review & editing Lluïsa ~ ol: Escoda: Conceptualization, Investigation, Methodology Joan J. Sun Supervision, Writing - review & editing. Acknowledgements E.P. acknowledges financial support from MINECO, Spain (grant FIS2017-82625-P) and Generalitat de Catalunya, Spain (grant 2017SGR0042).

4. Conclusions The production of Mn–Al powders was obtained by ball milling as well as by rapid solidification and posterior ball milling. In the first case the particles of the powder were composed of Mn-rich and Al-rich nanocrystals while in the latter by nanocrystals of a Mn(Al) solid solu­ tion. The Mn–Al powders showed a similar high efficiency and fast re­ action rates in decolorization experiments of azo-dye solutions for both microstructures. In Reactive Black 5 and Orange II solutions the Mn–Al powders showed better intrinsic performance than zero-valent iron particles, and better than most of decolorization materials in literature except of Fe and Co-based metallic glass powders. The size of the powder particles was observed to decrease with the milling time, thus providing a way of producing powders with tunable specific surface area. The analysis of the water and the particles showed that the main decolorization mechanism of azo-dye solutions was the breaking of the azo-bond, similar to the mechanism observed for zero valent iron. The efficiency was assessed in different types of colorant compounds and in real wastewaters showing that Mn–Al particles may be used for decol­ orizing a wide range of dyes. Compared to other decolorizing materials Mn–Al powders showed good efficiency both in alkaline and acid con­ ditions. However, the recuperation and washing methods tried in this work did not improve the reusability of the Mn–Al powders. A washing solution able to reactivate the particle surface may be an important issue to investigate in the future. Finally, in spite of the significant release of metallic ions, the toxicity of the treated waters was observed to decrease after the treatments. Mn–Al powders can be produced by simple ball-milling of the raw materials. This is an important advantage in comparison to the more complex production routes used for some other high-efficiency decol­ orizing materials, in which rapid solidification or nano-particle chemical synthesis are used. Both Manganese and Aluminum are some of the most abundant metals in earth and they are present naturally in soils. Although a very high concentration of Manganese may be toxic, it is also an essential element for all living species. Both Manganese and Aluminum can be considered biocompatible and environmentally friendly metals. This work provides a detailed study of the main ad­ vantages and drawbacks of Mn–Al powders as zero-valent decolorizing materials and, hopefully, it will inspire the design of new methods of

Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.jenvman.2019.110012. References AboliGhasemabadi, M., Mbarek, W. Ben, Casabella, O., Roca-Bisbe, H., Pineda, E., Escoda, L., Su~ nol, J.J., 2018. Application of mechanically alloyed MnAl particles to de-colorization of azo dyes. J. Alloy. Comp. 741, 240–245. https://doi.org/10.1016/ J.JALLCOM.2018.01.131. Ben Mbarek, W., Azabou, M., Pineda, E., Fiol, N., Escoda, L., Su~ nol, J.J., Khitouni, M., 2017. Rapid degradation of azo-dye using Mn–Al powders produced by ball-milling. RSC Adv. 7, 12620–12628. https://doi.org/10.1039/C6RA28578C. Bhakya, S., Muthukrishnan, S., Sukumaran, M., Muthukumar, M., Senthil Kumar, T., Rao, M., 2015. Catalytic degradation of organic dyes using synthesized silver nanoparticles: a green approach. J. Biorem. Biodegrad. 1000312. https://doi.org/ 10.4172/2155-6199.1000312, 06. Bromley-Challenor, K.C., Knapp, J., Zhang, Z., Gray, N.C., Hetheridge, M., Evans, M., 2000. Decolorization of an azo dye by unacclimated activated sludge under anaerobic conditions. Water Res. 34, 4410–4418. https://doi.org/10.1016/S00431354(00)00212-8. Cai, M.-Q., Zhu, Y.-Z., Wei, Z.-S., Hu, J.-Q., Pan, S.-D., Xiao, R.-Y., Dong, C.-Y., Jin, M.-C., 2017. Rapid decolorization of dye Orange G by microwave enhanced Fenton-like reaction with delafossite-type CuFeO2. Sci. Total Environ. 580, 966–973. https:// doi.org/10.1016/J.SCITOTENV.2016.12.047. Cao, J., Wei, L., Huang, Q., Wang, L., Han, S., 1999. Reducing degradation of azo dye by zero-valent iron in aqueous solution. Chemosphere 38, 565–571. https://doi.org/ 10.1016/S0045-6535(98)00201-X. Casas, N., Bl� anquez, P., Gabarrell, X., Vicent, T., Caminal, G., Sarr� a, M., 2007. Degradation of orange G by laccase: fungal versus enzymatic process. Environ. Technol. 28, 1103–1110. https://doi.org/10.1080/09593332808618874. Chen, H.S., Leamy, H.J., Miller, C.E., 1980. Preparation of glassy metals. Annu. Rev. Mater. Sci. 10, 363–391. https://doi.org/10.1146/annurev.ms.10.080180.002051. Deng, F.-X., Yang, J.-X., Zhu, Y.-S., Ma, F., Qiu, S., 2018. A rapid azo dye decolorization of methyl orange by the foam zero-valent nickel. Environ. Prog. Sustain. Energy 37, 686–694. https://doi.org/10.1002/ep.12738. El Nemr, A., Hassaan, M.A., Madkour, F.F., 2018. HPLC-MS/MS mechanistic study of direct yellow 12 dye degradation using ultraviolet assisted ozone process. J. Water Environ. Nanotechnol. 3, 1–11. https://doi.org/10.22090/JWENT.2018.01.001. Fan, J., Guo, Y., Wang, J., Fan, M., 2009. Rapid decolorization of azo dye methyl orange in aqueous solution by nanoscale zerovalent iron particles. J. Hazard Mater. 166, 904–910. https://doi.org/10.1016/j.jhazmat.2008.11.091.

8

M. AboliGhasemabadi et al.

Journal of Environmental Management 258 (2020) 110012 Wang, A.M., Zhang, H.F., Li, H., Zhu, Z.W., Zhang, H.W., Fu, H.M., Qin, X.D., Liu, G., 2015. Ultrafast degradation of azo dyes catalyzed by cobalt-based metallic glass. Sci. Rep. 5, 1–8. https://doi.org/10.1038/srep18226. Wang, J.-Q., Liu, Y.-H., Chen, M.-W., Xie, G.-Q., Louzguine-Luzgin, D.V., Inoue, A., Perepezko, J.H., 2012. Rapid degradation of azo dye by Fe-based metallic glass powder. Adv. Funct. Mater. 22, 2567–2570. https://doi.org/10.1002/ adfm.201103015. Wang, P., Wang, J.-Q., Li, H., Yang, H., Huo, J., Wang, J., Chang, C., Wang, X., Li, R.-W., Wang, G., 2017. Fast decolorization of azo dyes in both alkaline and acidic solutions by Al-based metallic glasses. J. Alloy. Comp. 701, 759–767. https://doi.org/ 10.1016/j.jallcom.2017.01.168. Weng, C.-H., 2017. Tourmaline activated persulfate for degradation of Sirius Türkis GL 01. Acta Geochim 36, 400–404. https://doi.org/10.1007/s11631-017-0176-0. Weng, C.-H., Huang, V., 2015. Application of Fe0 aggregate in ultrasound enhanced advanced Fenton process for decolorization of methylene blue. J. Ind. Eng. Chem. 28, 153–160. https://doi.org/10.1016/J.JIEC.2015.02.010. Weng, C.-H., Lin, Y.-T., Chen, Y.-J., Sharma, Y.C., 2013. Spent green tea leaves for decolourisation of raw textile industry wastewater. Color. Technol. 129, 298–304. https://doi.org/10.1111/cote.12029. Weng, C.-H., Lin, Y.-T., Liu, N., Yang, H.-Y., 2014. Enhancement of the advanced Fenton process by ultrasound for decolorisation of real textile wastewater. Color. Technol. 130, 133–139. https://doi.org/10.1111/cote.12069. Weng, C.-H., Tao, H., 2018. Highly efficient persulfate oxidation process activated with Fe0 aggregate for decolorization of reactive azo dye Remazol Golden Yellow. Arab. J. Chem. 11, 1292–1300. https://doi.org/10.1016/J.ARABJC.2015.05.012. Zhang, C., Zhang, H., Lv, M., Hu, Z., 2010. Decolorization of azo dye solution by Fe–Mo–Si–B amorphous alloy. J. Non-Cryst. Solids 356, 1703–1706. https://doi.org/ 10.1016/j.jnoncrysol.2010.06.019. Zhang, C., Zhu, Z., Zhang, H., Hu, Z., 2012. On the decolorization property of Fe–Mo–Si–B alloys with different structures. J. Non-Cryst. Solids 358, 61–64. https://doi.org/10.1016/j.jnoncrysol.2011.08.023. Zhang, C., Zhu, Z., Zhang, H., Hu, Z., 2012. Rapid decolorization of Acid Orange II aqueous solution by amorphous zero-valent iron. J. Environ. Sci. 24, 1021–1026. https://doi.org/10.1016/S1001-0742(11)60894-2. Zhang, C.Q., Zhu, Z.W., Zhang, H.F., Hu, Z.Q., 2011. Rapid reductive degradation of azo dyes by a unique structure of amorphous alloys. Chin. Sci. Bull. 56, 3988–3992. https://doi.org/10.1007/s11434-011-4781-8. Zhang, L.-C., Jia, Z., Lyu, F., Liang, S.-X., Lu, J., 2019. A review of catalytic performance of metallic glasses in wastewater treatment: recent progress and prospects. Prog. Mater. Sci. 105, 100576. https://doi.org/10.1016/J.PMATSCI.2019.100576. Zhang, W., 2003. Nanoscale iron particles for environmental remediation: an overview. J. Nanoparticle Res. 5, 323–332. https://doi.org/10.1023/A:1025520116015.

Ghoveisi, H., Feng, N., Boularbah, A., Bitton, G., Bonzongo, J.-C.J., 2018. Effect of aging and wet-dry cycles on the elimination of the bioavailable fractions of Cu and Zn in contaminated soils by zero valent iron and magnetic separation technique. J. Environ. Eng. 144, 04018068 https://doi.org/10.1061/(ASCE)EE.19437870.0001398. Hermawan, H., Alamdari, H., Mantovani, D., Dub� e, D., 2008. Iron–manganese: new class of metallic degradable biomaterials prepared by powder metallurgy. Powder Metall. 51, 38–45. https://doi.org/10.1179/174329008X284868. Khani, A., Sohrabi, M.R., Khosravi, M., Davallo, M., 2012. Decolorization of an azo dye from aqueous solution by nano zero-valent iron immobilized on perlite in semi batch packed bed reactor. Fresenius Environ. Bull. 21, 2153–2159. https://doi.org/ 10.2478/v10026-012-0105-2. Liu, N., Ding, F., Weng, C.-H., Hwang, C.-C., Lin, Y.-T., 2018. Effective degradation of primary color direct azo dyes using Fe0 aggregates-activated persulfate process. J. Environ. Manag. 206, 565–576. https://doi.org/10.1016/J. JENVMAN.2017.11.006. Liu, N., Wang, H., Weng, C.-H., Hwang, C.-C., 2018. Adsorption characteristics of Direct Red 23 azo dye onto powdered tourmaline. Arab. J. Chem. 11, 1281–1291. https:// doi.org/10.1016/J.ARABJC.2016.04.010. Luo, X., Li, R., Zong, J., Zhang, Y., Li, H., Zhang, T., 2014. Enhanced degradation of azo dye by nanoporous-copper-decorated Mg–Cu–Y metallic glass powder through dealloying pretreatment. Appl. Surf. Sci. 305, 314–320. https://doi.org/10.1016/j. apsusc.2014.03.069. Marcelo, C.R., Puiatti, G.A., Nascimento, M.A., Oliveira, A.F., Lopes, R.P., 2018. Degradation of the reactive blue 4 dye in aqueous solution using zero-valent copper nanoparticles. J. Nanomater. 1–9. https://doi.org/10.1155/2018/4642038, 2018. Nam, S., Tratnyek, P.G., 2000. Reduction of azo dyes with zero-valent iron. Water Res. 34, 1837–1845. https://doi.org/10.1016/S0043-1354(99)00331-0. Patel, R., Suresh, S., 2006. Decolourization of azo dyes using magnesium–palladium system. J. Hazard Mater. 137, 1729–1741. https://doi.org/10.1016/J. JHAZMAT.2006.05.019. Pouretedal, H.R., Saedi, E., 2014. Dechlorination of 2,4-dichlorophenol by zero-valent iron nanoparticles impregnated MCM-48. Int. J. Ind. Chem. 5, 77–83. https://doi. org/10.1007/s40090-014-0021-9. Qin, X.D., Zhu, Z.W., Liu, G., Fu, H.M., Zhang, H.W., Wang, A.M., Li, H., Zhang, H.F., 2015. Ultrafast degradation of azo dyes catalyzed by cobalt-based metallic glass. Sci. Rep. 5, 18226. Raman, C.D., Kanmani, S., 2016. Textile dye degradation using nano zero valent iron: a review. J. Environ. Manag. 177, 341–355. https://doi.org/10.1016/J. JENVMAN.2016.04.034. Suryanarayana, C., 2001. Mechanical alloying and milling. Prog. Mater. Sci. 46, 1–184. https://doi.org/10.1016/S0079-6425(99)00010-9.

9