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. 2022 Oct 13;7(42):38015–38024. doi: 10.1021/acsomega.2c05253

Competitive Adsorption of Cr(III) and Cu(II) on Electron Beam-Irradiated Sheep Wool from Binary Solutions Can be Controlled by the Absorbed Dose

Jana Braniša 1, Karin Koóšová 1, Karolína Lendelová 1, Mária Porubská 1,*
PMCID: PMC9608415  PMID: 36312384

Abstract

graphic file with name ao2c05253_0013.jpg

Sheep wool irradiated by an electron beam was tested for adsorption of Cr(III) and Cu(II) from binary solutions within the same concentration of each cation from 15 to 35 mmol·dm–3. The wool sorptivity examination was aimed at searching the effect of the dose absorbed by wool on simultaneous sorption of these cations due to surface and bulk changes. The partners affected each other under these conditions. In the whole concentration range, the sorptivity of nonirradiated wool (0 kGy) for Cu(II) fluctuated within the range of 14.5–20.7 mg·g–1, while sorptivity for Cr(III) ranged from 14.8 to 7.5 mg·g–1. However, sorptivity for Cu(II) was always superior to Cr(III). At a 24 kGy dose, the wool sorptivity for both cations decreased approximately by half and tended to converge, whereby at 20 mmol·dm–3, a slight predominance for Cr(III) was already observed. However, the sorptivity of 100 kGy dosed wool acquired a clear predominance for Cr(III) over Cu(II) in the entire concentration range, showing some leveling around 14.5 mg·g–1. Sorptivity for Cu(II) was suppressed and increased nonlinearly with concentrations from 1.7 to 10.2 mg·g–1. It was concluded that optimally dosed wool could provide a special adsorbent suitable to control preferential sorption of some cations from binary solutions.

1. Introduction

Better use of biomaterials is an imperative challenge at this time. Sheep wool is a renewable material and, it is worth exploring its larger use. Sheep crossbred for mild climate mountain and foothill areas, or special milk–meat types, generally have coarser fiber and their textile use is very limited. In addition, synthetic fibers are a serious competitor for wool. The necessity to shear sheep regularly without selling such wool reduces the profitability of breeding. Wool thus becomes waste, and the costs of its disposal increase the risk of illegal landfill formation. However, due to the chemical composition of wool keratin, wool has considerable potential for other uses as well. Among others, these are good adsorption properties that can be used to remove harmful substances from the environment or conversely recover valuable components from industrial waste. Studies dealing with sheep wool as an adsorbent are not numerous.1−3 Moreover, none of them describes simultaneous adsorption of several components and their mutual effect on the adsorption capacity of wool, although real conditions almost always comprise various substances in solution. On the other hand, adsorption from binary solutions using other virgin or chemically modified biomass, biochar, inorganic or organic materials, and composites can be found in scientific sources.

Regarding biomaterial or composite adsorbents, most of the published papers deal with heavy metal adsorption characteristics. de Carvalho et al.4 and Chong and Volesky5 reported the use of Ascophyllum nodosum seaweed biomass as an adsorbent to test Cu(II), Cd(II), and Zn(II) ions in their binary or ternary mixtures. Reynel-Avila et al.6 reported the sorption of Cd(II), Pb(II), and Ni(II) ions in binary mixtures using raw and tartaric acid-treated flamboyant and bush mango biomasses. The removal of Pb(II) and Hg(II) using nanocrystalline cellulose–bentonite nanocomposite as an adsorbent is presented by Putro et al.7 The study8 presents the feasibility and characteristics of microalgae waste treatment using a mixture of Spirulina platensis and polyacrylamide as an adsorbent system for removing Pb(II) and Cd(II) from simulated wastewater in single and binary solution systems. Sellaoui et al.9 reported single and ternary isotherms of the adsorption of Pb(II), Hg(II), and Zn(II) ions on an adsorbent obtained from the pyrolysis of flamboyant biomass. The adsorption of three metal ions on pine bark10 was studied focused on single, and three binary systems Cu(II)–Cd(II), Cu(II)–Ni(II), and Cd(II)–Ni(II). Bediako et al.11 tested a banana peel and its derivatives after sequential extraction of biochemical components for the selective recovery of gold from multimetal systems. Simultaneous adsorption of Cd(II) and Pb(II) on vermiculite functionalized with octylamine was investigated by Ahmed et al.12 Application of sawdust modified with thioglycolic acid in batch sorption experiments conducted to determine the effect of the presence of Co(II) ions on the uptake of Pb(II) ions showing antagonism.13 Also, Zheng et al.14 examined the chitosan–EDTA-modified magnetic biochar to remove Cd(II), Cu(II), and Ni(II) from single and binary systems. Chitosan and chitosan beads cross-linked with sodium tripolyphosphate were tested for the adsorption of Ni(II) and Cd(II) ions from single and binary metal solutions, too.15 A composite synthesized by Bacillus sp. K1 loaded onto Fe3O4 biochar provided new biosorption sites such as amine and hydroxyl groups in the composite surface. This adsorbent was used by Wang et al.16 to remove Cd(II) and As(III) from aqueous solution. Meng et al.17 investigated the effects of competitive adsorption with Ni(II) and Cu(II) on the adsorption of Cd(II) using original rice straw biochar, KMnO4-modified biochar, and biochar coated with acidic soil. Platanus orientalis(18) and Ulmus leaves19 as well as their ashes were tested for Cr(VI) adsorption in the presence of Ca(II), Mg(II), Na(I), and K(I) under optimized conditions. The effect of leaves and their ashes showed good Cr(VI) removal and an increase in chemical oxygen demand in wastewater. Adsorptive removal of organic substances, pharmaceutics, or metabolites from wastewater can be found, too. Thakur et al.20 investigated the potential of using rice husk ash for the removal of pharmaceutical compounds, such as ofloxacin hydrochloride, a fluoroquinolone antibiotic, and paracetamol from wastewater. The examination of methylene blue and Cu(II) adsorption on magnetic graphene oxide/alginate beads in single and binary systems is described.21

The abovementioned researchers have tried to improve the adsorption potential of (bio)sorbents using physical–chemical or chemical modification of the surfaces. Mutual competitive effects in binary systems, positive or negative, were observed in comparison with corresponding single systems. In most cases, the complexity of the reasoning and interpretation of the competitive adsorption results is observed.

Some time ago, Porubská et al. started to investigate wool modification by accelerated electron beam irradiation.22 Such a process is waste-free and dry technology without any chemicals or wastewater. Sheep wool modified in such a manner has acquired new properties as a result of physical–chemical changes in the surface and/or bulk. Inter alia, improved sorptivity toward certain substances was observed.23−27 As mentioned, adsorption data on irradiated wool for metal ions from binary systems as well as about the impact of energy dose absorbed by the wool on such adsorption are completely absent so far. That is why we cannot compare our results with other authors because they are not yet available. Therefore, the present study aims to obtain at least basic data. For a start, Cr(III) and Cu(II) were selected as model cations whose sorption would respond to changes in the wool surface/bulk.

2. Results and Discussion

2.1. VIS Spectral Calibration Measurements

Stock solutions of both Cr(III) and Cu(II) salts were prepared by dissolving an appropriate amount of the mentioned salts in deionized water to prepare binary testing baths following the specifications listed in Tables 1 and 2. The mentioned concentrations of 15–35 mmol·dm–3 allow analysis by UV–vis spectroscopy.

Table 1. Composition of Both Experimental and Calibration Cr(III) Solutions Supplemented with Cu(II).

  concentration of components in binary solutions (mmol·dm–3)
component supplement Cu(II) sample Cu–Cr15 sample Cu–Cr20 sample Cu–Cr25 sample Cu–Cr30 sample Cu–Cr35
Cu(II) 25 25 25 25 25 25
Cr(III)   15 20 25 30 35
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Table 2. Composition of Both Experimental and Calibration Cu(II) Solutions Supplemented with Cr(III).

  concentration of components in binary solutions (mmol·dm–3)
component supplement Cr(III) sample Cr–Cu15 sample Cr–Cu20 sample Cr–Cu25 sample Cr–Cu30 sample Cr–Cu35
Cr(III) 25 25 25 25 25 25
Cu(II)   15 20 25 30 35
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2.2. Adjusting pH

Since Cr(III) is rather sensitive to pH, the calibration samples for VIS spectral measurements were adjusted to pH corresponding to the bath final pH for each dosed wool. NaOH (c = 0.4 mmol·dm–3) was added to the exact volumes of the calibration solutions with a micropipette until the required pH value was reached. The added volume of NaOH was taken into account when recalculating the final exact concentration of the calibration solutions. The value of pH was measured using an Orion2 Star pH meter (Thermo Scientific) equipped with a Sen Tix 42 plastic electrode with a temperature sensor with an accuracy of ±0.02 pH unit. The measurement was carried out after 24 h consisting of 6 h shaking and 18 h static mode. The pH value slightly varied depending on the mutual ratio of both salts. Therefore, the pH was set as an acceptable compromise, since real residual ionic concentrations in the final baths could not be known yet (Table S3).

The VIS spectra of both Cr(III) and Cu(II) calibration solutions whose compositions are given in Tables 1 and 2 are shown in Figures 1 and 2.

Figure 1.

Figure 1

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Spectra of single Cu(II) solution (c = 25 mmol·dm–3 in deionized water, pH = 4.22, dashed line) and binary calibration solutions of Cr(III) each supplemented with 25 mmol·dm–3 Cu(II) (pH set following a 0 kGy wool bath, see Table S3).

Figure 2.

Figure 2

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Spectra of single Cr(III) solution (c = 25 mmol·dm–3 in deionized, pH = 3.45, dashed line) and binary calibration solutions of Cu(II) each supplemented with 25 mmol·dm–3 Cr(III) (pH set following a 0 kGy wool bath, see Table S3).

From Figure 1, it is obvious that the presence of Cr(III) within the applied concentrations does not affect Cu(II) absorbance at all. However, an opposite situation is in the case of Cr(III) (Figure 2).

In the binary solutions, the presence of Cu(II) reduces Cr(III) transmittance and increases absorbance.

Analogous calibration spectra were taken from the solutions having pH set to 24 and 100 kGy dosed wool. The data of the corresponding linear calibration equations (y = ax + b) confirmed that each absorbed dose generates its own medium in wool. The slopes corresponding to the a term are practically the same for 0 and 100 kGy and differ from the 24 kGy sample. The b term corresponding to the y-intercept is dissimilar in each case, and the interval is 0.0163 (Table S4).

Different conditions induced by variant doses are also reflected in the calibration equations for Cu(II) (Table S5). Dispersion in the a term values of both cations is acceptable and can be attributed to an experimental error. Slightly larger differences are in the b term within an interval of 0.0186. By comparing the b terms for both cation groups, it can be seen that the same absorbed dose affects the background differently, too, which is reflected in the pH variations (Table S3) and, as expectably, in corresponding chemical changes linked with variant interactions of wool with the relevant cations.

By observing Figures 1 and 2, it is worth noting that even if a lower absorbance value is observed in the single Cr(III) solution than that in the presence of Cu(II) (Figure 2), Cr(III) does not indicate any new Cr(III) species, since λmax does not differ from the single Cr(III) solution. Single Cr(III) absorbance for λ415 is lower by 0.0362 than that of Cr(III) in the binary solution.

2.3. VIS Spectral Measurements of Cr(III) Residual Baths and Cr(III) Sorptivity Estimation

Residual concentrations of Cr(III) and Cu(II) in the bath after 24 h contact of the wool with the binary solutions (x) were calculated using the corresponding equations in Tables S4 and S5. By analyzing the resulting sorptivity courses (Tables S6 and S7), it is worth noting that both Cr(III) and Cu(II) cations form complex salts very readily. The Cr(III) complexes have always a coordination number of 6 and the octahedral form,28 while Cu(II) complexes exhibit various polyhedrons with regular or distorted structures.29−31 The ligands coming from different keratin chains cause a cross-link and can be a certain hindrance to the diffusion of the cations into the fiber bulk. At the applied concentrations of both cations, it is characteristic that the sorption dependences are nearly always polynomial.

With regard to the Cr(III) spectrum (Figure 2), the sorptivity from the binary solution was calculated using absorbance corrected by subtracting the absorbance shift of 0.0362 at λ415 for the one-component Cr(III) solution. The corresponding sorptivity results are displayed in Figures 3–5.

Figure 3.

Figure 3

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Sorptivity of nonirradiated wool (0 kGy) for Cr(III) from the binary solution of Cr(III) + Cu(II).

Figure 5.

Figure 5

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Sorptivity of 100 kGy dosed wool for Cr(III) from the binary solution of Cr(III) + Cu(II).

In finding an explanation for the increase in Cr(III) absorption in the presence of Cu(II) (Figure 2), we considered two facts related to the limitation of the Lambert–Beer law validity.

The total concentration of electrolytes in solution affects important properties such as the dissociation constant or solubility of other salts. Increased salt concentration in solution increases ionic strength I(32)

2.3. 1

where 1/2 takes into account the contribution of both anions and cations, ci is the molar concentration of the ioni, zi is the charge of the given ion, and the sum includes all ions present in the solution.

It follows that higher charged ions will contribute more weight to the ionic strength. Thus, the contribution of Cr(III) is higher than Cu(II). In fact, comparable published works almost exclusively applied lower concentrations of adsorbates than those used in this study, and, possibly, the effect of ionic strength may have been neglected. The ionic strength of the solution is a measure of the global ionic interaction. It is responsible for creating some agglomerates or clusters of various sizes. When they reach a certain size, Rayleigh scattering begins to apply.33 The condition of this scattering is that the size of the scattering object is at most one-tenth of the light wavelength. The Cr(III) agglomerates could satisfy Rayleigh scattering conditions by absorbing light with a shorter λCr of 415 nm. Part of the scattered VIS radiation reduces the passing light flow, i.e., increases the absorbance in the binary solution. The Cu(II) absorption of λCu = 809 nm is already out of Rayleigh scattering conditions. Therefore, Cu absorbance is not affected by Cr(III) presence in the binary solution.

As can be seen from the dependences in Figures 3–5, the wool sorptivity for Cr(III) varies significantly with the absorbed energy dose. In addition, adsorption from both single and binary solutions can be significantly affected by the character of a partner solute.

The nonirradiated wool shows a first rapid and then lighter decreasing trend or even leveling (Figure 3) in the binary solution. It should be emphasized that the ion-exchange binding sites in the nonirradiated wool represent mostly H+ in carboxylic acids and cysteic acid originally present in a small amount and maybe in some −OH groups. The Cr(III) and Cu(II) being Lewis acids readily form complex salts with wool keratin. Here, available potential co-ordinative ligands are amino-, imino-, −OH, or sulfhydryl groups. Since the fiber bulk is not impaired yet, only surface functional groups can participate in the adsorption process. Cu(II) is able to form multiple types of complexes, while Cr(III) always has six ligands.28 Therefore, Cu(II) complexes preferentially occupy the fiber surface and make access difficult for Cr(III), which takes ligands selectively. That is why the sorption of Cr(III) on the surface is less than that of Cu(II).

An opposite course is observed for wool with a 24 kGy absorbed dose (Figure 4). Such absorbed dose is already sufficient to start the S–S bond breaking and disrupt the keratin structural integrity. Namely, in the region of 20–80 kGy dose, the −S–S– bonds are attacked, generating several S-oxidized species as cystine monoxide −S–SO–, cystine dioxide −S–SO2–, and S-sulfonate R–S–SO3– (Bunte salt).22 In these cases, the oxidation state of the sulfur changes. The reaction schemata can be designed as follows

2.3. 2
2.3. 3
2.3. 4

As resulted from FTIR spectra,22 in this region, the presence of the individual species pulses is observed, and the decrease of one is related to the increase of the other. This fluctuation can be attributed to the increasing difficulty of oxygen access to the inner layers of the only partially disrupted fiber. Therefore, the individual species do not appear in the spectrum together as common cumulative bands but follow the gradual access of oxygen to the inner layers of the fiber corresponding to the degree of the structure opening. Finally, all species are transformed into cysteic acid R–SO3H. Thus, the original −S–S– nonpolar groups become semipolar to polar species. Such a situation affects the initial overall negative charge on the wool surface34 and, in some cases, causes “anomalies” in cation adsorption.25,35 Here, in adsorption interactions, the active points are all of the mentioned forms available on the surface and inside the partially impaired fiber bulk with an undefined representation. In the case of the binary solution (Figure 4), the sorptivity of 24 kGy dosed wool increases, but the ultimate value of about 9 mg·g–1 reaches a value almost comparable to the minimum level of the nonirradiated wool.

Figure 4.

Figure 4

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Sorptivity of 24 kGy dosed wool for Cr(III) from the binary solution of Cr(III) + Cu(II).

A dissimilar dependence is obtained also for 100 kGy dosed wool, which varies mildly only (Figure 5). In practice, it can already be considered independent of concentration, which indicates the full occupancy of active sites suitable for interaction with Cr(III). Here, the sorptivity for Cr(III) achieves the highest values in comparison with 0 and 24 kGy dosed samples. Regarding the previous finding of the dose effect on sheep wool, such similar results could be expected. The 100 kGy dose no longer generates S-sulfonate but cysteic acid R–SO3H immediately.22 Thus, cysteic acid is added to carboxylic acids, making the disrupted fiber volume more accessible to a sorbate. The result is almost double the sorptivity of the 100 kGy wool sample. This indicates that more fiber bulk is impaired by the electric beam breaking the S–S bridges. Then, subsequent oxidation of S-radicals takes place, and the inlet for Cr(III) inside the fiber is facilitated. This inlet is possibly supported by a higher charge density of the Cr(III) cation than that of Cu(II). In addition, it can be assumed that Cr(III) forms salts more readily with cysteic acid, the content of which increases with the absorbed dose, unlike carboxyl groups whose content does not change.

2.4. VIS Spectral Measurements of Cu(II) Residual Baths and Cu(II) Sorptivity Estimation

As shown in Figure 1, the Cu(II) spectrum is independent of Cr(III) concentration and the calculation of the sorptivity is simpler.

The nonirradiated wool shows the highest sorptivity toward Cu(II) (Figure 6).

Figure 6.

Figure 6

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Sorptivity of nonirradiated wool (0 kGy) for Cu(II) from the binary solution of Cu(II) + Cr(III).

We assume that regarding the larger variability of the complex structures, Cu(II) finds enough ligands already on the wool surface. So, the generated Cu(II) complex salts can occupy a considerable part of the fiber surface. On the contrary, Cr(III) needs six selective ligands on the surface to create a regular structure. Thus, its position is harder and adsorption minor. In comparison with native wool, the sorptivity of wool with an absorbed dose of 24 kGy is smaller by more than half (Figure 7). Competition between both cations manifests itself here.

Figure 7.

Figure 7

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Sorptivity of 24 kGy dosed wool for Cu(II) from the binary solution of Cu(II) + Cr(III).

It can be seen that the fiber structure partially disrupted by S-sulfonate formation makes it more advantageous for Cr(III) adsorption than Cu(II) adsorption. The higher the absorbed dose, the smaller the wool sorptivity toward Cu(II) within the range of concentrations applied. This is valid also for 100 kGy dosed wool (Figure 8).

Figure 8.

Figure 8

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Sorptivity of 100 kGy dosed wool for Cu(II) from the binary solution of Cu(II) + Cr(III).

So, it is clear that besides the type of partner in a binary solution, absorbed dose is a determining factor; it affects the corresponding fiber structure, the availability of appropriate active points to interact with an adsorbate, and the space conditions for adsorbate accession. In the case of cations with a predisposition to create complex salts, the space availability of ligands is also significant.

In general, the ionic radius and charge density of the cation may play a role in this process, too. However, the ionic radius varies with the coordination number. While the Cr(III) coordination number is steady, the Cu(II) coordination number varies, as shown in Table 3.

Table 3. Ionic Radii of Cr(III) and Cu(II)36.

ion proton number charge coordination number ionic radius (1.10–12 m)
Cr 24 3 VI 61.5
Cu 29 2 IV 57
V 65
VI 73
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In the case of Cu(II) coordination on sheep’s wool, we do not know the coordination number and we can assume that there may not be only one because keratin provides different ligands. As above mentioned, Cu(II) itself generates various complex structures. Thus, we do not know the relevant ionic radii either, and we cannot determine the charge density with certainty, which is important in the affinity of the cation to the sheep wool. The higher charge of the Cr(III) cation indicates that its charge density should be higher than that of the Cu(II) cation. This may favor the sorption of Cr(III) on irradiated wool.

2.5. Cumulative Comparison of the Effect of the Dose Absorbed by Wool on Simultaneous Sorption of the Cations

The concurrent sorption of Cr (III) and Cu (II) from the binary solution on wool is summarized in Figures 9–11.

Figure 9.

Figure 9

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Concurrent sorptivity of wool nonirradiated (0 kGy) for Cr(III) and Cu(II) in the binary solution.

Figure 11.

Figure 11

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Concurrent sorptivity of 100 kGy dosed wool for Cr(III) and Cu(II) in the binary solution.

Figure 10.

Figure 10

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Concurrent sorptivity of 24 kGy dosed wool for Cr(III) and Cu(II) in the binary solution.

Figures 9–11 show that each dose of energy absorbed by the wool has an essential effect on its sorptivity due to different physical and chemical changes in keratin as described.22 As expected, the cation sorption from single solutions25,26 does not coincide with sorption from the binary solutions despite a comparable concentration in the bath. Furthermore, variation of the absorbed dose also changes the sorption preferences, which may even change upside down. If so, an optimally selected absorbed dose for wool can be used for recycling purposes or elimination of some unwanted present components. Such findings open up the opportunity for wider use of radiation-modified sheep wool.

3. Conclusions

Sheep wool irradiated by an electron beam with different absorbed energy doses was examined for sorption of Cr(III) and Cu(II) from binary solutions with the concentration of each component in the range of 15–35 mmol·dm–3. Regarding both cations being disposed to form complex salts with keratin, the sorption dependences are mostly polynomial. Based on conducted sorption experiments, the following conclusions can be drawn:

  • When Cr(III) and Cu(II) are adsorbed from the binary solutions, the partners affect each other competing for bonding spots and differently according to the absorbed dose.

  • The wool sorptivity for both cations is a function of the concentration and dose absorbed by the wool from the electron beam.

  • The sorptivity of nonirradiated wool (0 kGy) is higher for Cu(II) than that for Cr(III) in the whole concentration range.

  • The sorptivity of 24 kGy dosed wool converges for both cations, and at concentrations above 20 mmol·dm–3, the Cr (III) sorptivity acquires a slight predominance.

  • The sorptivity of 100 kGy dosed wool acquires a clear predominance for Cr(III) over Cu(II), showing a leveling effect in the applied concentration range.

The results obtained indicate that by choosing an optimal absorbed dose, it could be possible to control preferential sorption of the selected cation from the binary solution. Thus, wool has potential to be used for targeted separation of selected components; however, further investigation is needed.

4. Experimental Section

4.1. Materials

Sheep wool came from spring sheep-shearing (2018) of a Merino–Suffolk crossbreed bred in the region of Central Slovakia. The fiber thickness was in the range of 27–33 μm. The wool was scoured in tap water using an ultrasonic bath (K5LE, Kraintek, Slovakia) for 3 × 10 min at 40 °C, dried freely, irradiated in a UELR–5–1S linear electron accelerator (FGUP NIIEFA, Petersburg, Russia) with an installed energy of 5 MeV, and operated by Progress Final AK company. The samples with absorbed doses of 0–24–100 kGy were stored under common conditions and room temperature and used for sorption batch experiments.

Chemicals chromium potassium sulfate dodecahydrate (KCr(SO4)2·12H2O) and copper sulfate pentahydrate (CuSO4·5H2O) were used as Cr(III) and Cu(II) adsorbates, respectively. Natrium hydroxide NaOH was used to adjust pH when necessary. All chemicals were supplied by Labo-SK Ltd. (Bratislava, Slovakia) in analytical grade.

4.2. Spectral Measurements

A UV–vis spectrophotometer (Specord 50 Plus, Analytikjena, Germany) with a 1 cm cell was used to determine both Cr(III) (λ = 415 nm) and Cu(II) (λ = 808 nm) contents in the final bath.

The calibration VIS spectra of Cr(III) and Cu(II) were taken against deionized water. The comparative sample for the residual component in the final bath was always the aqueous extract from the wool with a dose corresponding to the measured sample obtained after 24 h contact of the sample with deionized water under the same conditions.

4.3. Adsorption Experiments

The batch sorption experiments were conducted with the particular wool samples and solutions (Tables 1and 2). After being cut to 3–5 mm, 0.2 g of wool fibers were placed in a glass cup with a cap and the testing solution of 20 cm3 in volume was added. The content of the glass cup was shaken for the first 6 h at room temperature on a laboratory horizontal shaker (Witeg SHR–2D, Labortechnik GmbH, Wertheim, Germany) and then kept in static mode for the next 18 h. Then, the remaining solution was filtered through a KA5 filter paper and used for determination of residual Cr(III) or Cu(II). Every sorption procedure was carried out in triplicate, and the standard deviation was calculated.

The parameter qe as a measure of wool sorptivity at equilibrium was calculated for each component using eq 1

4.3. 5

where qe is the sorptivity defined as the equilibrium amount of the sorbate in mmol per 1 g of the sorbent for individual wool samples when a particular testing solution is applied in a specified concentration, x1 is the amount of solute added to the initial solution (mmol), x2 is the residual equilibrium amount of the solute in solution after its contact with the wool sample (mmol), and m is the mass of the wool sample taken for analysis (g).

Acknowledgments

The authors would like to acknowledge Slovak Research and Development Agency (APVV) for funding J.B. (grant number APVV-19-0087). The authors wish to thank the company Progresa Final SK, Bratislava, for irradiating the wool samples in the electron beam accelerator.

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.2c05253.

  • Data of calibration spectra; data of pH values in calibration samples; calibration equations; numeric values of sorptivity including standard deviations (PDF)

The authors declare no competing financial interest.

Supplementary Material

ao2c05253_si_001.pdf (109.2KB, pdf)

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