Next Article in Journal
Combined Effect of pH and Neutralizing Solution Molarity on the Rheological Properties of Chitosan Hydrogels for Biomedical Applications
Previous Article in Journal
Preliminary Investigation into the Use of Amino-Acid-Derived Ionic Liquids for Extracting Cellulose from Waste Biomass to Prepare Cellulose Aerogel Adsorbents
Previous Article in Special Issue
Adsorption of Bisphenol A from Water Using Chitosan-Based Gels
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Gels
Volume 11
Issue 3
10.3390/gels11030211
gels-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Simultaneous Removal of Heavy Metals and Dyes on Sodium Alginate/Polyvinyl Alcohol/κ-Carrageenan Aerogel Beads

by
Taesoon Jang
,
Soyeong Yoon
,
Jin-Hyuk Choi
,
Narae Kim
and
Jeong-Ann Park
*
Department of Environmental Engineering, Kangwon National University, Chuncheon 24341, Republic of Korea
*
Author to whom correspondence should be addressed.
Gels 2025, 11(3), 211; https://doi.org/10.3390/gels11030211
Submission received: 1 March 2025 / Revised: 10 March 2025 / Accepted: 14 March 2025 / Published: 16 March 2025
(This article belongs to the Special Issue Eco-Friendly Gels for Adsorption)
Browse Figures
Versions Notes

Abstract

Industrial textile wastewater containing both heavy metals and dyes has been massively produced. In this study, semi-interpenetrating polymer network structures of sodium alginate (SA)/polyvinyl alcohol (PVA)/κ-carrageenan (CG) aerogel beads were synthesized for their simultaneous reduction. The SA/PVA/CG aerogel beads were synthesized through a cost-effective and environmentally friendly method using naturally abundant biopolymers without toxic cross-linkers. The SA/PVA/CG aerogel beads were spheres with a size of 3.8 ± 0.1 mm, exhibiting total pore areas of 15.2 m2/g and porous structures (pore size distribution: 0.04–242.7 μm; porosity: 93.97%) with abundant hydrogen bonding, high water absorption capacity, and chemical resistance. The adsorption capacity and mechanisms of the SA/PVA/CG aerogel beads were investigated through kinetic and isotherm experiments for heavy metals (Cu(II), Pb(II)), cationic dye (methylene blue, MB), and anionic dye (acid blue 25, AB)) in both single and binary systems. The maximum adsorption capacities of the SA/PVA/CG aerogel beads based on the Langmuir model of Cu(II), Pb(II), and MB were 85.17, 265.98, and 1324.30 mg/g, respectively. Pb(II) showed higher adsorption affinity than Cu(II) based on ionic properties, such as electronegativity and hydration radius. The adsorption of Cu(II), Pb(II), and MB on the SA/PVA/CG aerogel beads was spontaneous, with heavy metals and MB exhibiting endothermic and exothermic natures, respectively.

1. Introduction

The textile industry is a significant consumer of water, leading to the generation of large volumes of wastewater containing both dye and heavy metal pollutants [1]. Dyes, which are widely used in paper, leather, fiber, and rubber manufacturing, are non-biodegradable and recalcitrant due to their complex structures [2,3], while heavy metals, such as copper (Cu) and lead (Pb), are employed to produce the color pigments for textile dyes [4]. To effectively remove these heavy metals and dyes from industrial wastewater, various physical and chemical treatments have been developed, including chemical precipitation, ion exchange, adsorption, and electrochemical treatment [5,6]. Of these methods, adsorption is the most common due to its low establishment costs, simple design, and ease of operation [7,8].
However, when heavy metals and dyes are present together in wastewater, their interactions can complicate the adsorption process [9,10,11,12]. This is because the formation of complexes introduces coordination and steric effects, while competition for adsorption sites or bridging effects can also occur. Therefore, it is necessary to compare the adsorption mechanisms in binary-pollutant systems with those in single-pollutant systems and develop more effective strategies for the effective simultaneous removal of heavy metals and dyes. In line with this, several studies have developed adsorbents for use in these binary systems based on activated carbon [13], carbon nanotubes [14], iron oxides’ nanoparticles [15], layered double hydroxides [16], and biomass-incorporating composites [17]. Although these adsorbents show demonstrated promise in removing heavy metals and dyes in binary systems, the spent adsorbent, which includes inorganic nanomaterials and/or carbon materials, becomes a form of secondary waste that requires an additional disposal process to ensure that it does not pose potential environmental risks [18].
A number of recent studies have reported the synthesis of adsorbents based on environmentally friendly biopolymers using green synthesis methods as a means to reduce the environmental risks and protect public health. For example, sodium alginate (SA) is an inexpensive and natural polysaccharide polymer extracted from algae [19] that possesses abundant carboxyl (–COOH) and hydroxyl (–OH) groups, making it suitable for cationic heavy metal adsorption [20]. ĸ-carrageenan (CG) is another useful polysaccharide polymer with a high number of hydroxyl and sulfate groups (–OSO3⁻) [21]. Although SA and CG can be cross-linked using Ca(II) [19], they have low physical and chemical resistance [22,23]. Alginate was susceptible to hydrolysis or degradation in strong acid and alkali solution, and sulfate groups on CG dissociate more readily than carboxylate groups on alginate [19,24]. Yu et al. [22] confirmed that CG/SA hydrogel beads shows a high swelling rate. On the other hand, polyvinyl alcohol (PVA) is a non-toxic and biocompatible synthetic polymer with high chemical resistance, remaining stable in pH 1–13 [25] and also offering numerous hydroxyl groups [26]. Due to these complementary advantages, the removal of heavy metals or dyes using composite adsorbents containing SA, CG, and PVA has been widely investigated. Croitoru et al. [27] synthesized an SA/PVA hydrogel with high stability in solutions with various ionic strengths and pH levels that exhibited a maximum adsorption capacity for crystal violet of 121.4 mg/g. Radoor et al. [28] also reported a PVA/CG membrane with a methylene blue (MB) adsorption capacity of 147.8 mg/g, the highest of various carrageenan-based adsorbents. However, no previous research has been conducted to remove both heavy metals and dyes simultaneously with a composite based on an SA, PVA, and CG polymer networks.
In a semi-interpenetrating polymer network (semi-IPN), a cross-linked polymer and a linear polymer are interlaced and entangled [29]. Because one of the polymers is not cross-linked, functional groups, such as hydroxyl groups, can participate in the adsorption of pollutants, while the interlaced and entangled network improves the mechanical strength. Although chemically cross-linked pure hydrogels are inflexible and can easily break when in a swollen state, PVA can effectively transfer stress through non-covalent bonding with other polymers, improving the performance of polymer networks [30,31]. Kim and Min synthesized a semi-IPN with calcium alginate and a PVA hydrogel that demonstrated two to five times greater mechanical and physiochemical stability compared to a pure alginate hydrogel [32]. Although the semi-IPN structure preserves the distinctive characteristics of polymers while alleviating their weakness, to the best of our knowledge, the development and testing of a semi-IPN structure containing environmentally friendly and cost-effective polymers (SA, CG, and PVA) for adsorption of pollutants has not yet been reported. Also, aerogel has several advantages over hydrogel, such as its high pore area, rapid adsorption rate, and light weight. In addition, although many adsorption studies have investigated heavy metals and dyes in mono-polluted systems, no previous research has investigated the potential simultaneous removal of two pollutants in wastewater. Therefore, the objectives of the present study were to (1) characterize SA-, CG-, and PVA-based semi-IPN aerogel bead types of adsorbents synthesized using an environmentally friendly method, (2) compare the adsorption capacities of these adsorbents in single-pollutant systems (Cu(II), Pb(II), and MB or acid blue 25(AB)) and verify the associated adsorption mechanisms, (3) investigate the removal capacity of the adsorbents in binary-pollutant systems, and (4) evaluate their acute toxicity with Daphnia magna (D. magna) and biodegradability in soil.

2. Results and Discussion

2.1. Comparison of the Characteristics and Adsorption Capacity of the SA-Based Aerogel Beads

FE-SEM images of the surface and cross-section of the SA, SA/PVA, SA/PVA, and SA/PVA/CG aerogel beads are presented in Figure 1. All beads were spherical in shape owing to the drop-wise synthesis procedure. The SA aerogel beads had a crumbled surface (Figure 1a,b), while the other aerogel beads exhibited a spherical shape with a relatively smooth surface (Figure 1c–h). As shown in Figure 1, the introduction of both PVA and CG to SA resulted in a densely porous structure with a uniform distribution of smaller pores. Due to the rapid cross-linking of the outer surface of the SA/PVA/CG aerogel beads, small pores formed close to the bead’s surface, with pore sizes gradually increasing towards the interior. The size of the SA/PVA/CG aerogel beads is 3.8 ± 0.1 mm, and the total pore area of 15.2 m2/g. The pore sizes of the SA/PVA/CG aerogel beads ranged from 0.04 to 242.7 μm, with an average diameter of 8.9 μm and a porosity of 73.97%.
Figure 2a displays the FTIR spectra for the SA, SA/PVA, SA/CG, and SA/PVA/CG aerogel beads. All of the beads exhibited peaks from 3000 to 3600 cm−1, corresponding to the stretch vibrations of the –OH groups. The peaks observed at 1586 cm−1 and 1411 cm−1 for the SA aerogel beads were ascribed to asymmetric and symmetric O-C=O stretching vibrations [31], while the peak at 1024 cm−1 indicated the presence of –C-O-C groups [33]. In the spectra for the SA/PVA aerogel beads, the addition of PVA produced a new peak at 1732 cm−1, corresponding to C=O stretching vibrations from the residual ester groups of PVA. It was confirmed that PVA was not cross-linked in SA/PVA aerogel beads, providing an additional –OH group. In the SA/CG and SA/PVA/CG aerogel beads, peaks of 1153 cm−1, 933 cm−1, and 818 cm−1 were assigned to ester sulfate -S=O stretching, 3, 6-anhydro-D-galactose, and ester sulfate stretching, respectively [27,34,35]. The SA/PVA/CG aerogel beads exhibited the strongest peak for the –OH groups, indicating that it could potentially have higher pollutant adsorption. These results indicated that SA/PVA/CG aerogel beads had high density due to hydrogen bonding (Figure 1).
The water absorption capacity of the SA-based aerogel beads is summarized in Figure 2b. All of the beads were buoyant in water due to the presence of large pores and their low density. Due to the high hydrophilicity of CG, the SA/CG (2539.86 ± 68.57%) and SA/PVA/CG (2492.76 ± 87.69%) aerogel beads demonstrated high water absorption capacity. The SA/PVA/CG aerogel beads showed slightly lower water absorption capacity than that of SA/CG beads due to containing less CG, which has higher hydrophilicity than PVA. However, the value is still very high, confirming high hydrophilicity. The high water absorption affinity was related to the flexibility of the porous network, which facilitated expansion and, potentially, the rapid diffusion of pollutants, thus increasing the number of contact sites [36,37]. The Cu(II), Pb(II), and MB adsorption capacities for the SA-based beads are presented in Figure 2c. SA aerogel beads exhibited the highest Cu(II) adsorption capacity at 84.8 ± 2.45 mg/g, while the SA/CG aerogel beads had the highest Pb(II) and MB adsorption capacity (189.49 ± 0.13 and 198.30 ± 0.12 mg/g, respectively). However, all of the SA-based aerogel beads had a similar adsorption capacity for Cu(II) (74.04–84.80 mg/g), Pb(II) (183.15–189.49 mg/g), and MB (178.81–198.3 mg/g), which indicated that incorporation of the polymers maintained the initial adsorption capacity of SA while also introducing the useful characteristics of the polymers.
The chemical stability of the SA, SA/PVA, SA/CG, and SA/PVA/CG aerogel beads was also evaluated in soaking experiments using both acidic (pH 2) and basic (pH 9) solutions. All of the aerogel beads were buoyant in the initial stages of the experiment; however, the SA aerogel beads in the pH 2 solution and the SA, SA/PVA, and SA/CG aerogel beads in the pH 9 solution gradually settled on the bottom of the container after 10 days of exposure. The SA aerogel beads crumbled and shrank under both acidic (Figure S1a–c) and basic (Figure S1d–f) conditions. Chen et al. [38] also reported that alginate is prone to shrinking at low pH. As shown in Figure S1g–i, the SA, SA/PVA, and SA/CG aerogel beads in the basic solution also exhibited deformation and the expansion of their pore networks, possibly due to swelling in the weak basic solution, followed by erosion and disintegration [39]. Only the SA/PVA/CG aerogel beads maintained their buoyancy in both the acidic and basic solutions, likely due to hydrogen bonding interactions between the three types of polymers. Because the SA/PVA/CG aerogel beads exhibited the strongest chemical stability under extreme pH conditions, they were used for further analysis.

2.2. Adsorption Mechanisms for the SA/PVA/CG Aerogel Beads in Single-Pollutant Removal

2.2.1. Adsorption Kinetics

The effect of the reaction time on the adsorption of single pollutants (Cu(II), Pb(II), MB, and AB) using the SA/PVA/CG aerogel beads was evaluated (Figure 3a). The adsorption capacity of Cu (II), Pb(II), and MB rapidly increased over the initial 4 h and reached an adsorption equilibrium before 24 h had passed. The adsorption kinetic parameters for each pollutant using the SA/PVA/CG aerogel beads are listed in Table S1. The adsorption kinetic data for Cu(II) and Pb(II) fit the pseudo-second-order model well, indicating that chemical adsorption was the main rate-controlling step [40]. The adsorption capacity (qe) and rate constant (k2) for Pb(II) were higher than those for Cu(II), suggesting that the adsorption of Pb(II) occurred more rapidly and may be preferred on the SA/PVA/CG aerogel beads. Generally, aerogels exhibit rapid adsorption rates due to their open porous structure filled with air and high surface area, enhancing the fast diffusion of heavy metals into the interior of the beads. The beads exhibited a greater adsorption affinity for Pb(II) than for Cu(II) because Pb(II) has greater electronegativity (2.33) and a smaller hydration radius (4.01 Å), leading to stronger electrostatic interactions with the SA/PVA/CG aerogel beads [41,42].
The adsorption of MB more closely followed the pseudo-first-order model (R2 = 0.912) than the pseudo-second-order model (R2 = 0.873). This indicates that MB adsorption was likely due to physical adsorption [43]. On the other hand, the adsorption of AB onto the SA/PVA/CG aerogel beads was insignificant after 48 h. This could be explained by the negatively charged surface of the SA/PVA/CG aerogel beads (zeta potential = −26.9 ± 0.4 mV at pH 5.7; Figure S2), which repelled the anionic dye AB. Because of this lack of adsorption, AB was excluded from further single-pollutant adsorption experiments.

2.2.2. Adsorption Isotherms

As shown in Figure 3, the adsorption isotherm data for the single pollutants (Cu(II), Pb(II), and MB) using the SA/PVA/CG aerogel beads were fitted using the Langmuir, Freundlich, and Temkin models. The parameters for the isotherm experiments are summarized in Table S2. The results indicated that the adsorption of Cu(II) and Pb(II) most closely followed the Temkin model. This means that multilayer adsorption was dominant, with a uniform binding energy distribution on the SA/PVA/CG aerogel beads up to the maximum binding energy [44]. The adsorption of MB was more accurately described by the Langmuir model (R2 = 0.982) than the Freundlich (R2 = 0.937) and Temkin models (R2 = 0.876). This suggested that the main adsorption mechanism for MB was monolayer adsorption [45]. In addition, the bT of Cu(II), Pb(II), and MB was positive, suggesting that the adsorption process was an endothermic reaction [46]. The maximum adsorption capacity (qm) of Cu(II), Pb(II), and MB on the SA/PAV/CG aerogel beads was determined to be 85.17, 265.98, and 1324.30 mg/g, respectively, using the Langmuir model. The 1/n values for the Freundlich model (Cu(II) = 0.18; Pb(II) = 0.22; and MB = 0.40) were lower than 1, indicating that the adsorption of Cu(II), Pb(II), and MB onto the SA/PVA/CG aerogel beads was favorable [47,48,49].
The maximum adsorption capacities of Cu(II), Pb(II), and MB using SA-, PVA-, and CG-based adsorbents reported in previous studies are presented in Table S3. The adsorption capacity for Cu(II) in these past studies had a range of 29.1–114.94 mg/g, with the highest capacity obtained by incorporating graphene oxide (GO) (98.0–105.93 mg/g) [50,51] or Fe3O4 (114.94 mg/g) [52]. However, the SA/PVA/CG aerogel beads synthesized in the present study had the highest adsorption capacity (85.17 mg/g) among those adsorbents composed only of polymers (29.19–70.45 mg/g) [53]. The adsorption capacity of the SA/PVA/CG aerogel beads for Pb(II) (265.98 mg/g) was comparable to previously reported adsorbents containing GO (191.94–327.9 mg/g) [51,54], while the SA/PVA/CG aerogel beads had a higher MB adsorption capacity (1324.30 mg/g) than the other reported adsorbents (94.3–628.93 mg/g) [55,56]. The high pore area, porosity, and hydrophilic nature of the SA/PVA/CG aerogel beads provide sufficient adsorption sites for both MB and heavy metals. These results confirmed that the SA/PVA/CG aerogel beads, produced using environmentally friendly materials and chemicals and a simple synthesis method, are a promising adsorbent for the removal of heavy metals and dyes.

2.2.3. Effects of pH and Temperature

The pH of a solution can affect the ionization stage of the functional groups in both the SA/PVA/CG aerogel beads and the pollutants, thus influencing the adsorption behavior of the system. The SA/PVA/CG aerogel beads exhibited an increase in adsorption capacity for Cu(II), Pb(II), and MB with an increase in the pH (Figure 4a). The adsorption capacity was the lowest at pH 2 (Cu(II): 8.52 ± 3.18 mg/g; Pb(II): 74.36 ± 1.41 mg/g; MB: 119.21 ± 15.6 mg/g) and the highest at pH 5 (Cu(II): 78.32 ± 2.79 mg/g; Pb(II): 186.35 ± 0.38 mg/g; MB: 190.42 ± 20.18 mg/g). The pH levels up until pH 5 because Cu(II) ions form a Cu(OH)2 precipitate at pH ≥ 6 (Figure 4b) [57]. The pH species distribution for Cu(II), Pb(II), and MB is presented in Figure 4b–d, showing that Cu and Pb were present in an ionic state as Cu(II) and Pb(II) at pH levels below 5, while MB was strongly positive with fully protonated amine groups at a pH lower than 3.8 (pKa) and present as MB+ at a pH of over 3.8 [58,59].
As shown in Figure S2, the zeta potential of the SA/PVA/CG aerogel beads was negative from pH 2 to 5.8 and became more negative as the pH increased, resulting in a stronger adsorption capacity for the cationic pollutants (Cu(II), Pb(II), and MB). In addition, at higher pH levels, the proportion of neutral MB (MB0) increases, leading to stronger non-electrostatic interactions, such as hydrophobic interactions [60]. On the other hand, at low pH levels, the adsorption capacity for Cu(II), Pb(II), and MB decreased because the adsorption sites on the SA/PVA/CG aerogel beads were partially protonated, weakening the electrostatic interaction between the negatively charged aerogel beads and the cationic pollutants.
A thermodynamic analysis was conducted to investigate the spontaneity and thermodynamic properties of the adsorption process. The effect of temperature was tested at 288, 298, and 308 K (Figure 5), and the thermodynamic parameters for the adsorption of the individual pollutants (Cu(II), Pb(II), or MB) on the SA/PVA/CG aerogel beads are presented in Table S4. For Cu(II) and Pb(II), the negative ΔG0 (Cu(II) = −1.96 to −2.41 KJ/mol; Pb(II) = −10.16 to −11.55 KJ/mol) and the positive ΔH0 (Cu(II) = 4.48 KJ/mol; Pb(II) = 9.79 KJ/mol) indicated that their adsorption was spontaneous and endothermic. In addition, a positive ΔH0 is suggestive of a chemical adsorption process, while higher values indicate the possibility of stronger bonding between the adsorbent and the adsorbate [61]. Therefore, a higher adsorption affinity for Pb(II) than for Cu(II) was observed, which was in correspondence with the adsorption isotherm and kinetic data. The positive values of ΔS0 for the adsorption of Cu(II) (22.36 J/mol·K) and Pb(II) (69.29 J/mol·K) indicated that the randomness increased at the solid–liquid interface during the adsorption process. Positive values of ΔH0 and ΔS0 when cationic heavy metals, including Cu(II) and Pb(II), are adsorbed onto SA/PVA-based composites have also been reported by Isawi [61] and Zhang et al. [53].
For MB adsorption, all of the thermodynamic parameters were negative, including ΔG0 (−8.38 to −9.64 KJ/mol), ΔH0 (−27.78 KJ/mol), and ΔS0 (−62.95 J/mol·K). This indicated that the adsorption of MB was spontaneous and exothermic, and randomness at the interface between the MB and the SA/PVA/CG aerogel beads decreased during the adsorption process. Similarly, Mohammed et al. [62] and Almuslem et al. [63] found that MB adsorption onto cellulose-based films and alginate hydrogels, respectively, tended to be exothermic (ΔH0 < 0) and demonstrated lower randomness (ΔS0 < 0). The decrease in the adsorption capacity for MB as the temperature increase was due to the weaker physical interaction through hydrogen bonding and van der Waals interactions [64].

2.3. Adsorption Mechanisms for the SA/PVA/CG Aerogel Beads in Binary-Pollutant Removal

Kinetic adsorption using the SA/PVA/CG aerogel beads in the binary systems (Cu–Pb, Cu–MB, Cu–AB, Pb–MB, and Pb–AB) was tested to compare with the adsorption of the pollutants individually (Figure 6). The calculated kinetic parameters are summarized in Table S5. In the binary systems, the adsorption capacity for Cu(II), Pb(II), and MB increased slightly but continuously, meaning that an equilibrium had not been reached by 48 h (Figure 6a–c). For the adsorption of Cu(II) and Pb(II) in both the single and binary systems, the pseudo-second-order model provided the best fit for the data (R2 = 0.980–0.989) than the pseudo-first-order model (R2 = 0.948–0.949). This indicated that chemical adsorption was still the dominant adsorption mechanism in the binary systems. However, for MB in the binary systems (Cu–MB and Pb–MB), the pseudo-second-order model led to a better fit (R2 = 0.893–0.901), while the pseudo-first-order model was favored for the single MB system. These findings suggested that the adsorption mechanisms have the potential to remain unchanged or vary between single- and binary-pollutant systems.
In the binary Cu–Pb system, the adsorption capacity (qe) for both Pb(II) and Cu(II) decreased, suggesting competitive interactions between the heavy metal ions. The qe for Cu(II) (36.87 mg/g) and Pb(II) (147.33 mg/g) decreased by 54.3% and 21.5% compared to their respective single-pollutant systems. However, Pb(II) maintained a higher adsorption affinity than Cu(II). This can be attributed to the higher electronegativity (2.33) and the smaller hydration radius (4.01 Å) of Pb compared to those of Cu (1.90 and 4.19 Å, respectively), resulting in stronger attraction to the negatively charged surface of the SA/PVA/CG aerogel beads and better diffusion into the surface and pores [41]. The k2 value (0.11 g/mg/h) for Cu(II) was about four times higher than that in the Cu(II) single-pollutant system (0.03 g/mg/h), while the k2 for Pb(II) did not change significantly. This indicates that most of the Cu(II) adsorption occurred quickly but was limited by the competitive effect of Pb(II).
In the binary Cu–MB and Pb–MB systems, the presence of MB did not significantly reduce the adsorption capacity for Pb(II) and Cu(II). However, the MB adsorption capacity in these binary systems was about 61–68% lower than in the single-pollutant MB system (204.53 mg/g). These results suggest that the heavy metals and MB partially competed for adsorption sites on the SA/PVA/CG aerogel beads, with heavy metals exhibiting a stronger adsorption preference for these sites. As described in Section 2.2, the adsorption of Cu(II) and Pb(II) occurred primarily through chemical adsorption mechanisms, while physical adsorption was the dominant mechanism for MB removal. Because of these different adsorption mechanisms between the heavy metals and MB, the total amount of adsorbed pollutants increased despite their competitive effects. Therefore, the SA/PVA/CG aerogel beads could remove the organic dye without inhibiting heavy metal adsorption.
During the adsorption process using the SA/PVA/CG aerogel beads, precipitates were observed in the two binary systems containing AB (Cu–AB and Pb–AB). This precipitate formed instantly after the mixing of the Pb(II) and AB solutions. Generally, Pb(II) naturally forms a precipitate with insoluble sulfates, carbonates, and chloride–hydroxides [65]. Thus, Pb(II) rapidly formed a precipitate with the sulfonate (–SO3−) of AB. As the reaction time increased, the Pb(II) removal capacity was gradually increased before reaching an equilibrium (Figure 6b), while there was an unusual decrease in the AB removal capacity in the Pb–AB system (Figure 6d). This may have been due to the partial dissociation of the Pb–AB complex when interacting with the released Ca(II) with the addition of the SA/PVA/CG aerogel beads, with the dissociated Pb(II) then adsorbed onto the beads. This was supported by the finding that the Pb’s peak intensity at 1.8 keV was lower and the Ca’s peak intensity at 0.22 keV was stronger after the addition of the SA/PVA/CG aerogel beads (Figure S3a,b).
In the Cu–AB system, no precipitation occurred during the first 2 h of the reaction. However, after this initial period, the AB was removed rapidly due to the formation of a precipitate between the AB and the Ca(II) released from the SA/PVA/CG aerogel beads due to ion exchange via Cu(II). The Ca(II) concentration was found to be 15.1 mg/L after 24 h in the single Cu(II) adsorption reaction. Based on preliminary experiments, Ca(II) and AB (50 mg/L) formed a precipitate when the Ca(II) concentration exceeded 10 mg/L. This finding, along with the observation of a high-intensity peak for Ca in the precipitate (Figure S4c), suggest that the adsorption mechanism for Cu(II) involved ion exchange with Ca(II) in the SA/PVA/CG aerogel beads, and the released Ca(II) subsequently formed a complex with AB. Over time, the release of more Ca(II) led to a greater AB removal capacity. The removal capacity for Cu(II) was also greater than in the Cu system due to both ion exchange and partial complex formation, as confirmed by SEM-EDS data (Figure S3).

2.4. Verification of the Adsorption Mechanisms Using XPS Analysis

The XPS spectra for the SA/PVA/CG aerogel beads before and after single-pollutant adsorption (Cu(II), Pb(II), MB, and AB) and binary-pollutant adsorption are presented in Figure 7a. After the adsorption experiment, the beads maintained their morphology well, as shown in Figure S4. The fact that they maintain their shape well suggests a high potential for reusability in future applications. The full spectrum for the unused SA/PVA/CG aerogel beads shows peaks at 164.48, 285.98, 347.24, and 532.17 eV corresponding to S 2p, C 1s, Ca 2p, and O 1s, respectively. The presence of Ca 2p indicated that the SA/PVA/CG aerogel beads were successfully cross-linked by Ca(II). The full-scan XPS spectra for the binary systems are presented in Figure 7b. In the Cu and Pb binary systems, Cu 2p, Pb 4p, Pb 4d, and Pb 4f peaks were also detected, as observed in the single-pollutant system, while in the MB binary systems, N 1s and S 2p peaks appeared for MB. The distinctive XPS spectrum peaks for AB were not vividly observed in the binary systems because the removal of AB was mainly attributed to precipitation with the metal ions. Therefore, these results suggest that Cu(II), Pb(II), and MB were successfully absorbed onto the SA/PVA/CG aerogel beads in the binary systems in a manner similar to the single-pollutant system.
Peaks for Cu 2p3/2 and Cu 2p1/2 at 932.75 and 952.59 eV, respectively, were present in the Cu single-pollutant system (Figure 7c). The presence of Cu 2p3/2 at 932.7 eV and 934.9 eV indicates that the copper oxidation state is Cu(II) [66], meaning that Cu(II) was successfully adsorbed onto the SA/PVA/CG aerogel beads. After Pb(II) adsorption, peaks for Pb 4p (645.5 eV), Pb 4d (414.0 and 436.4 eV), and Pb 4f (138.8 and 143.7 eV) appeared, indicating that Pb was present on the surface of the SA/PVA/CG aerogel beads. As shown in Figure 7d, the presence of peaks for Pb 4f7/2 (138.8 eV) and Pb 4f5/2 (143.7 eV) was characteristic of Pb(II) species [67], confirming that Pb(II) was coordinated by the SA/PVA/CG beads [68]. In particular, the peak for Pb 4f7/2 represented the bonding between Pb(II) and carboxylate groups [69]. The lower energy levels observed for Cu 2p3/2 and Cu 2p1/2 also confirmed the coordination reaction with the SA/PVA/CG aerogel beads. In the Cu–Pb system, the intensities of the Cu 2p and Pb 4f peaks were significantly lower than those in the respective single-pollutant systems (Figure 7e,f). This indicates that the XPS signals for Cu(II) and Pb(II) on the surface were lower in the Cu–Pb system due to a lower adsorption capacity arising from competitive effects.
In the MB single-pollutant system, N 1s peaks appeared at 399.04 and 400.14 eV (Figure S5a), corresponding to the –N(CH3)2 and –C=N- of MB, respectively [70], thus confirming the successful adsorption of MB onto the SA/PVA/CG aerogel beads. The S 2p peak observed at around 168 eV was attributed to the sulfate group of CG in the SA/PVA/CG aerogel beads (Figure S5b) [71,72]. After the adsorption of MB (Figure S5c), new peaks for S 2p3/2 and S 2p1/2 appeared at 163.7 and 165.2 eV, respectively, indicating C-S-C in the aromatic ring of MB [73]. Similarly, Zhang et al. [53] also found that S 2p3/2 and S 2p1/2 peaks appeared after the adsorption of MB. Figure S6 shows the O 1s peaks of the SA/PVA/CG aerogel beads before and after adsorption in the Cu(II), Pb(II), and MB single-pollutant systems. No obvious change in the O 1s peak was observed for MB, indicating that non-electrostatic interactions, such as van der Waals and hydrophobic interactions, were primarily involved in the removal process. These results corresponded well with Section 2.2.1 and Section 2.2.3, which indicated that the adsorption mechanism of MB was dominated by physical adsorption. The predicted adsorption mechanisms of heavy metals and dye in both single and binary systems are presented in Figure 8.

2.5. Acute Toxicity and Biodegradability Assessment of the SA/PVA/CG Aerogel Beads

To evaluate the acute toxicity of the SA/PVA/CG aerogel beads, D. magna was exposed to various doses of the SA/PVA/CG beads (0.03–0.5 g/L). No immobile D. magna individuals were observed after 24 and 48 h of exposure for any of the concentrations. Optical microscopic images of D. magna in the control and exposure groups (dose = 0.5 g/L, 48 h) are presented in Figure S7, showing no significant difference between the two. These results indicated that the SA/PVA/CG aerogel beads have no acute toxic effect on D. magna. SA and CG are natural polysaccharide-based biopolymers, and PVA is a synthetic polymer that is non-toxic, biocompatible, and biodegradable [20,26,74]. Additionally, only CaCl2 was used as an environmentally friendly cross-linker to synthesize the semi-IPN structure of the SA/PVA/CG beads by cross-linking SA and CG, thus avoiding the need for toxic cross-linking agents, such as glutaraldehyde. Therefore, because the constituent polymers are inherently non-toxic and D. magna toxicity testing of the composite revealed no toxic effect, the SA/PVA/CG beads are very likely to be safe for use in aquatic ecosystems.
To assess the biodegradability of SA/PVA/CG beads, the weight and FT-IR spectra of the buried beads were measured for 14 days. The weight reduction of SA/PVA/CG beads after 7 and 14 days was 31.65 ± 1.29% and 61.33 ± 1.13%, respectively. FT-IR spectra of the SA/PVA/CG beads before and after biodegradation are presented in Figure S8. The peaks of O-C=O of SA (1586 cm−1) and 3,6-anhydro-D-galactose of CG (933 cm−1) were distinctively reduced after 14 days. These results indicate that the SA/PVA/CG beads could be biodegraded in natural soil, providing eco-friendly disposal after application for water treatment.

3. Conclusions

The SA/PVA/CG aerogel beads were successfully synthesized with a semi-IPN structure using a simple drop-wise procedure. The synthesis utilized naturally abundant biopolymers and required no toxic chemicals. The spherical SA/PVA/CG beads exhibited a densely porous structure, a large pore area, high hydrophilicity, and chemical resistance. These characteristics provided sufficient adsorption sites for heavy metals and dyes, as investigated in both single- and binary-pollutant systems. The adsorption of Cu(II) and Pb(II) was primarily attributed to chemical adsorption via electrostatic interactions and ion exchange, while MB adsorption was dominated by physical adsorption mechanisms, such as van der Waals forces and hydrogen bonding. Due to these distinct mechanisms, the SA/PVA/CG aerogel beads demonstrated the ability to simultaneously adsorb MB without reducing adsorption affinity for Pb(II) and Cu(II). Additionally, the anionic pollutant AB, which was not adsorbed onto the negatively charged SA/PVA/CG aerogel beads in the single-pollutant system, was removed through precipitation in the binary-pollutant system. The synthesized aerogel beads proved non-toxic to D. magna and biodegradable in soil. This study expands our understanding of biopolymers as alternative adsorbents in wastewater treatment and elucidates important factors in the removal of coexisting pollutants from wastewater.

4. Materials and Methods

4.1. Materials

SA (C6H7NaO6)n), PVA ((C2H4O)n, degree of hydrolysis: 86.0–89.0%), calcium chloride dihydrate (CaCl2·2H2O), copper nitrate trihydrate (Cu(NO3)2·3H2O), hydrochloric acid (HCl, 36%), sodium hydroxide (NaOH), and nitric acid (HNO3, 60–62%) were supplied by Daejung Chemicals & Metals (Gyeonggi-do, Korea). CG (C24H36O25S2)n was purchased from Tokyo Chemical Industry (Tokyo, Japan). MB dihydrate (C18H18ClN3S·2H2O, MW = 355.89) and AB (C20H13N2NaO5S, MW = 416.38) were obtained from Showa Chemical (Tokyo, Japan) and Sigma-Aldrich (St. Louis, MO, USA), respectively. Lead nitrate (Pb(NO3)2) was obtained from Mallinckrodt Chemical Works (St. Louis, MO, USA).

4.2. Synthesis of SA-Based Aerogel Beads

Four types of SA-based aerogel beads (SA, SA/PVA, SA/CG, and SA/PVA/CG) were synthesized to compare their characteristics and adsorption capacities for Cu(II) and Pb(II). The synthesis procedure was illustrated in Figure 9. Briefly, to synthesize SA aerogel beads, 100 mL of SA (1.5 wt%) solution was prepared using distilled water by dissolving it at 85 °C. For the other formulations, 100 mL solutions of SA/PVA (1:1, 3 wt%), SA/CG (1:1, 2 wt%), and SA/PVA/CG (1:1:1, 3 wt%) were similarly prepared using distilled water. After cooling each solution to room temperature under stirring, the solutions were added drop-wise to a 0.2 M CaCl2 solution using a syringe pump (NE-300, New Era Pump Systems Inc., Farmingdale, NY, USA) at a flow rate of 0.3 mL/min. During this step, SA and CG underwent cross-linking. The optimum ratio of SA/PVA/CG (1:1:1) was determined based on its uniform shape, strong cross-linking, and excellent adsorption capacity. The resulting spherical beads were maintained in the CaCl2 solution overnight, with stirring at 200 rpm to ensure sufficient cross-linking. The beads were subsequently rinsed with distilled water to remove excess ions, frozen at −20 °C for 24 h, and freeze-dried under vacuum for 48 h. Prior to experiments, the beads were stored in a desiccator.

4.3. Comparison of the Characteristics and Adsorption Capacity of the SA-Based Beads

The morphology of the SA, SA/PVA, SA/CG, and SA/PVA/CG beads was observed using field emission scanning electron microscopy (FE-SEM, S-4800, Hitachi, Tokyo, Japan). The porosity, average pore diameter, and pore size range of the beads were assessed using a porosimeter (Autopore V 9620, Micromeritics, Norcross, GA, USA), while the surface functional groups were examined using a Fourier transform infrared spectrophotometer (FTIR, iS-50, Thermo Fisher Scientific, Waltham, WA, USA). The water absorption efficiency of the beads was also evaluated by first soaking the dried beads in distilled water for 24 h and then removing the surface water using tissue paper. The weight of the dried and swollen beads (M0 and M1, respectively) was used to calculate the water absorption efficiency (%) via Equation (1) [75]:
Water absorption efficiency (%) = (M1 − M0)/M0 × 100
To compare the adsorption capacity of the SA, SA/PVA, SA/CG, and SA/PVA/CG beads, two heavy metals (Cu(II) and Pb(II)) and a dye (MB) were used in batch experiments. Each type of bead (5 mg) was added to conical tubes containing 20 mL of a Cu(II), Pb(II), or MB solution (initial conc. = 50 mg/L). The mixtures were shaken at 25 °C and 150 rpm in a shaking incubator for 24 h. After the reaction, the samples were filtered using a syringe filter (PVDF, pore size = 0.45 μm) and a 1 mm stainless sieve to separate the beads from the pollutants (Cu(II), Pb(II), or MB). The initial and final concentrations of Cu(II) and Pb(II) were determined using an inductively coupled plasma optical emission spectrometer (ICP-OES, Avio 200, Thermo Fisher Scientific, USA). The adsorption capacity (qt) of Cu(II) and Pb(II) was calculated using Equation (2):
qt = ((Ci − Ct) × V/m
where Ci (mg/L) and Ct (mg/L) are the initial concentrations of Cu(II), Pb(II), or MB and their concentrations at time t, respectively, V (L) is the volume of the solution, and m (g) is the mass of the beads.
The chemical stability of the SA, SA/PVA, SA/CG, and SA/PVA/CG beads was also evaluated under both acidic and basic conditions. The beads were immersed in distilled water adjusted to a pH of 2 or 9 using 0.1 M HCl and 0.1 M NaOH, respectively, for 10 days. The beads were then collected, frozen at −20 °C, and freeze-dried again to examine their morphology using FE-SEM.

4.4. Adsorption Mechanisms for the SA/PVA/CG Beads in Single-Pollutant Systems

The effects of the reaction time on the adsorption of the individual pollutants (Cu(II), Pb(II), MB, or AB) onto the SA/PVA/CG beads were evaluated. The SA/PVA/CG beads (5 mg) were mixed with a 20 mL solution of each pollutant (initial conc. = 50 mg/L) and left to react at 25 °C and 150 rpm. Samples were subsequently collected after 0.5, 1, 2, 4, 8, 12, 24, and 48 h. To measure the MB and AB concentrations, the collected samples were filtered through a 1 mm stainless sieve, and the absorbance of the filtrate was measured using a UV–vis spectrophotometer (UV–vis, GENESYS 150, Thermo Fisher Scientific, Waltham, MA, USA) at 665 and 600 nm for MB and AB, respectively. The kinetic data were fitted using pseudo-first-order and pseudo-second-order models, as described in the Supplementary Information (SI).
Adsorption isotherm experiments were conducted with the SA/PVA/CG beads at various initial concentrations of the heavy metal and dye pollutants: 10–125 mg/L for Cu(II) or Pb(II) and 10–500 mg/L for MB. The SA/PVA/CG beads (5 mg) were mixed with 20 mL of each pollutant and left to react at 25 °C and 150 rpm for 48 h. The isotherm data were fitted to the Langmuir, Freundlich, and Temkin models (see the Supplementary Materials for more details).
The effects of the temperature and pH on the adsorption of the individual pollutants (Cu(II), Pb(II), or MB) using SA/PVA/CG beads were also investigated. The SA/PVA/CG beads (5 mg) were added to a 20 mL solution of each pollutant (initial conc. = 50 mg/L) and left for 24 h under temperatures of 288, 298, or 308 K. The Gibb’s free energy (ΔG0, kJ/mol), enthalpy (ΔH0, kJ/mol), and entropy (ΔS0, J/mol∙K) were calculated using the equations listed in the Supplementary Materials). The pH of the initial solution was also adjusted to a range of 2–5 using HCl (0.1 M) and NaOH (0.1 M) solutions. This pH range was selected because the hydroxide precipitation of Cu(II) and Pb(II) occurs above pH 6. The heavy metal species were predicted according to changes in the pH using Visual MINTEQ 4.0. The zeta potential of the SA/PVA/CG beads was measured using a zeta potential analyzer (ZSP, Malvern Instruments, Malvern, UK). XPS analysis was also employed using an X-ray photoelectron spectrometer (K-Alpha+, Thermo Fisher Scientific, USA) before and after the adsorption of the individual pollutants (Cu(II), Pb(II), MB, and AB) onto the SA/PVA/CG beads to determine the adsorption mechanisms. The amount of Ca(II) released after the adsorption of Cu(II) and Pb(II) was measured using ion chromatography (Dionex ICS-5000, Thermo Fisher Scientific, USA).

4.5. Adsorption Performance of the SA/PVA/CG Beads Under Binary-Pollutant Conditions

The effect of the reaction time was tested for five binary solutions (Cu–Pb, Cu–MB, Cu–AB, Pb–MB, and Pb–AB) that were prepared by mixing each pollutant at a concentration of 50 mg/L. The SA/PVA/CG beads (5 mg) were added to 20 mL of each binary solution and left to react at 150 rpm and 25 °C for 0.5, 1, 2, 4, 8, 12, 24, and 48 h. To analyze both the heavy metals and the dyes in the same sample, the collected samples were filtered using a PVDF syringe filter (pore size = 0.45 μm), and MB or AB were measured using a UV-vis spectrophotometer. The dye was then completely removed using nitric acid digestion before measuring the Cu(II) and Pb(II) levels using ICP-OES. The results were fitted to pseudo-first-order and pseudo-second-order models to compare them with the data from the single-pollutant systems. The precipitates that formed during the experiments were also analyzed using an SEM–energy dispersive X-ray spectrometer (SEM-EDS, S-4800, Hitachi, Tokyo, Japan).

4.6. Acute Toxicity and Biodegradation of the SA/PVA/CG Beads

Acute toxicity testing of the SA/PVA/CG beads was conducted using D. magna (Daphtoxkit F™ magna, MicroBioTests, Gent, Belgium). The experiment process followed OECD guideline 202 [76]. Various doses of the SA/PVA/CG beads (0.03125, 0.0625, 0.125, 0.25, and 0.5 g/L) in 10 mL of standard freshwater were loaded into a multi-well plate with five neonates (age < 24 h) (four replicates for each treatment). The tested neonates were maintained at 20 °C in the dark, and the number of immobilized individuals was recorded after 24 and 48 h of exposure to different doses of the SA/PVA/CG beads. Digital images of D. magna were acquired using an optical microscope (Leica DM500, Leica Microsystems, Wetzlar, Germany) at a magnification of ×100.
To investigate the biodegradability of the SA/PVA/CG beads, the beads were enclosed in nylon fabric bags and buried at a depth of 5 cm in soil. The temperature and humidity were maintained at 25 °C and 70%, respectively, in a SMART Plant Growth Chamber (GC-450, Daihan Scientific Co., Ltd., Wonju, Korea) to ensure consistent conditions. To maintain the moisture levels of the soil, 40 mL of distilled water was added every 7 days for 2 weeks. The weight of the beads and their FT-IR spectra were recorded after 0, 7, and 14 days to monitor the degradation progress of the beads.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/gels11030211/s1, Figure S1: FE-SEM images of settled beads after chemical stability experiment: (a–c) SA beads in pH 2 and (d–f) pH 9 solution, (g–i) SA/PVA, and (j–l) SA/CG in pH 9 solution; Figure S2: Zeta potential of SA/PVA/CG bead; Figure S3: SEM-EDS spectra of the precipitates formed in the binary system after 24 h reaction: (a) Pb-AB solution; (b) Pb-AB solution with SA/PVA/CG beads; and (c) Cu-AB with SA/PVA/CG beads; Figure S4: FE-SEM images of the SA/PVA/CG aerogel bead after adsorption experiment. Figure S5: XPS spectra of (a) N 1s region after MB adsorption; (b) S 2p of the SA/PVA/CG beads; and (c) S 2p region after MB adsorption; Figure S6: High-resolution of XPS spectra O 1s region before and after adsorption. (a) raw SA/PVA/CG beads; and after single (b) Cu(II), (c) Pb(II), (d) MB adsorption, and (e) Cu-Pb system; Figure S7: Optical microscope images of D. magna after 48 h: (a) control and (b) 5 g/L dose of SA/PVA/CG beads; Figure S8: FTIR spectra of SA/PVA/CG beads before and after biodegradation for 14 days; Table S1: Adsorption kinetic model parameters of SA/PVA/CG beads with single pollutant (Cu(II), Pb(II), and MB); Table S2: Adsorption isotherm model parameters of the SA/PVA/CG beads for the adsorption of Cu(II), Pb(II), and MB; Table S3: Comparison of the adsorption capacities of Cu(II), Pb(II), and MB on SA, PVA, and CG based adsorbents; Table S4: Thermodynamic parameters of the SA/PVA/CG beads (dose = 0.25 g/L) for the adsorption of Cu(II), Pb(II), or MB (initial conc. = 50 mg/L); Table S5: Single and binary pollutant adsorption kinetic model parameters for the adsorption of Cu(II), Pb(II), MB, and AB using the SA/PVA/CG beads; Table S6: SEM-EDS analysis of precipitates on binary system.

Author Contributions

Conceptualization, T.J. and J.-A.P.; methodology, T.J. and J.-A.P.; formal analysis, T.J.; investigation, T.J., S.Y., J.-H.C. and N.K.; resources, J.-A.P.; data curation, T.J.; visualization, T.J.; writing—original draft preparation, T.J. and J.A Park.; supervision, J.-A.P.; project administration, J.-A.P.; funding acquisition, J.-A.P.; writing—review and editing, J.-A.P. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Ministry of Education (MOE) (2021R1I1A3046581).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Adel, M.; Ahmed, M.A.; Elabiad, M.A.; Mohamed, A.A. Removal of heavy metals and dyes from wastewater using graphene oxide-based nanomaterials: A critical review. Environ. Nanotechnol. Monit. Manag. 2022, 18, 100719. [Google Scholar] [CrossRef]
  2. Sinha, A.; Osborne, W.J. Biodegradation of reactive green dye (RGD) by indigenous fungal strain VITAF-1. Int. Biodeterior. Biodegrad. 2016, 114, 176–183. [Google Scholar] [CrossRef]
  3. Islam, M.A.; Ali, I.; Karim, S.M.A.; Hossain Firoz, M.S.; Chowdhury, A.-N.; Morton, D.W.; Angove, M.J. Removal of dye from polluted water using novel nano manganese oxide-based materials. J. Water Process Eng. 2019, 32, 100911. [Google Scholar] [CrossRef]
  4. Hammood, Z.A.; Chyad, T.F.; Al-Saedi, R. Adsorption Performance of Dyes Over Zeolite for Textile Wastewater Treatment. Ecol. Chem. Eng. S 2021, 28, 329–337. [Google Scholar] [CrossRef]
  5. Velusamy, S.; Roy, A.; Sundaram, S.; Kumar Mallick, T. A Review on Heavy Metal Ions and Containing Dyes Removal Through Graphene Oxide-Based Adsorption Strategies for Textile Wastewater Treatment. Chem. Rec. 2021, 21, 1570–1610. [Google Scholar] [CrossRef]
  6. Chen, X.; Hossain, M.F.; Duan, C.; Lu, J.; Tsang, Y.F.; Islam, M.S.; Zhou, Y. Isotherm models for adsorption of heavy metals from water—A review. Chemosphere 2022, 307, 135545. [Google Scholar] [CrossRef] [PubMed]
  7. Shaheen, T.I.; Radwan, E.K.; El-Wakeel, S.T. Unary and binary adsorption of anionic dye and toxic metal from wastewater using 3-aminopropyltriethoxysilane functionalized porous cellulose acetate microspheres. Microporous Mesoporous Mater. 2022, 338, 111996. [Google Scholar] [CrossRef]
  8. Aslam, A.A.; Hassan, S.U.; Saeed, M.H.; Kokab, O.; Ali, Z.; Nazir, M.S.; Siddiqi, W.; Aslam, A.A. Cellulose-based adsorbent materials for water remediation: Harnessing their potential in heavy metals and dyes removal. J. Clean. Prod. 2023, 421, 138555. [Google Scholar] [CrossRef]
  9. Hernandez-Montoya, V.; Perez-Cruz, M.A.; Mendoza-Castillo, D.I.; Moreno-Virgen, M.R.; Bonilla-Petriciolet, A. Competitive adsorption of dyes and heavy metals on zeolitic structures. J. Environ. Manag. 2013, 116, 213–221. [Google Scholar] [CrossRef]
  10. Zhao, F.; Repo, E.; Yin, D.; Meng, Y.; Jafari, S.; Sillanpaa, M. EDTA-Cross-Linked beta-Cyclodextrin: An Environmentally Friendly Bifunctional Adsorbent for Simultaneous Adsorption of Metals and Cationic Dyes. Environ. Sci. Technol. 2015, 49, 10570–10580. [Google Scholar] [CrossRef]
  11. Liu, Y.; Ke, Y.; Shang, Q.; Yang, X.; Wang, D.; Liao, G. Fabrication of multifunctional biomass-based aerogel with 3D hierarchical porous structure from waste reed for the synergetic adsorption of dyes and heavy metal ions. Chem. Eng. J. 2023, 451, 138934. [Google Scholar] [CrossRef]
  12. Zeng, X.; Zhu, J.; Zhang, G.; Wu, Z.; Lu, J.; Ji, H. Molecular-level understanding on complexation-adsorption-degradation during the simultaneous removal of aqueous binary pollutants by magnetic composite aerogels. Chem. Eng. J. 2023, 468, 143536. [Google Scholar] [CrossRef]
  13. Tovar-Gomez, R.; Rivera-Ramirez, D.A.; Hernandez-Montoya, V.; Bonilla-Petriciolet, A.; Duran-Valle, C.J.; Montes-Moran, M.A. Synergic adsorption in the simultaneous removal of acid blue 25 and heavy metals from water using a Ca(PO3)2-modified carbon. J. Hazard. Mater. 2012, 199–200, 290–300. [Google Scholar] [CrossRef] [PubMed]
  14. Chen, B.; Yue, W.; Zhao, H.; Long, F.; Cao, Y.; Pan, X. Simultaneous capture of methyl orange and chromium(vi) from complex wastewater using polyethylenimine cation decorated magnetic carbon nanotubes as a recyclable adsorbent. RSC Adv. 2019, 9, 4722–4734. [Google Scholar] [CrossRef]
  15. Zeng, X.; Zhang, G.; Wen, J.; Li, X.; Zhu, J.; Wu, Z. Simultaneous removal of aqueous same ionic type heavy metals and dyes by a magnetic chitosan/polyethyleneimine embedded hydrophobic sodium alginate composite: Performance, interaction and mechanism. Chemosphere 2023, 318, 137869. [Google Scholar] [CrossRef] [PubMed]
  16. Soltani, R.; Marjani, A.; Shirazian, S. A hierarchical LDH/MOF nanocomposite: Single, simultaneous and consecutive adsorption of a reactive dye and Cr(vi). Dalton Trans. 2020, 49, 5323–5335. [Google Scholar] [CrossRef]
  17. Saravanan, A.; Karishma, S.; Kumar, P.S.; Varjani, S.; Yaashikaa, P.R.; Jeevanantham, S.; Ramamurthy, R.; Reshma, B. Simultaneous removal of Cu(II) and reactive green 6 dye from wastewater using immobilized mixed fungal biomass and its recovery. Chemosphere 2021, 271, 129519. [Google Scholar] [CrossRef]
  18. Chen, L.; Li, Y.; Hu, S.; Sun, J.; Du, Q.; Yang, X.; Ji, Q.; Wang, Z.; Wang, D.; Xia, Y. Removal of methylene blue from water by cellulose/graphene oxide fibres. J. Exp. Nanosci. 2016, 11, 1156–1170. [Google Scholar] [CrossRef]
  19. Li, L.; Zhao, J.; Sun, Y.; Yu, F.; Ma, J. Ionically cross-linked sodium alginate/ĸ-carrageenan double-network gel beads with low-swelling, enhanced mechanical properties, and excellent adsorption performance. Chem. Eng. J. 2019, 372, 1091–1103. [Google Scholar] [CrossRef]
  20. Yi, X.; Sun, F.; Han, Z.; Han, F.; He, J.; Ou, M.; Gu, J.; Xu, X. Graphene oxide encapsulated polyvinyl alcohol/sodium alginate hydrogel microspheres for Cu (II) and U (VI) removal. Ecotoxicol. Environ. Saf. 2018, 158, 309–318. [Google Scholar] [CrossRef]
  21. Voron’ko, N.G.; Derkach, S.R.; Vovk, M.A.; Tolstoy, P.M. Complexation of kappa-carrageenan with gelatin in the aqueous phase analysed by (1)H NMR kinetics and relaxation. Carbohydr. Polym. 2017, 169, 117–126. [Google Scholar] [CrossRef] [PubMed]
  22. Yu, F.; Cui, T.; Yang, C.; Dai, X.; Ma, J. kappa-Carrageenan/Sodium alginate double-network hydrogel with enhanced mechanical properties, anti-swelling, and adsorption capacity. Chemosphere 2019, 237, 124417. [Google Scholar] [CrossRef] [PubMed]
  23. Gao, X.; Guo, C.; Hao, J.; Zhao, Z.; Long, H.; Li, M. Adsorption of heavy metal ions by sodium alginate based adsorbent-a review and new perspectives. Int. J. Biol. Macromol. 2020, 164, 4423–4434. [Google Scholar] [CrossRef]
  24. Tonnesen, H.H.; Karlsen, J. Alginate in drug delivery systems. Drug Dev. Ind. Pharm. 2002, 28, 621–630. [Google Scholar] [CrossRef]
  25. Mohd Zain, N.A.; Mohd Suardi, S.; Idris, A. Hydrolysis of liquid pineapple waste by invertase immobilized in PVA–alginate matrix. Biochem. Eng. J. 2010, 50, 83–89. [Google Scholar] [CrossRef]
  26. Mahdavinia, G.R.; Massoudi, A.; Baghban, A.; Shokri, E. Study of adsorption of cationic dye on magnetic kappa-carrageenan/PVA nanocomposite hydrogels. J. Environ. Chem. Eng. 2014, 2, 1578–1587. [Google Scholar] [CrossRef]
  27. Croitoru, C.; Pop, M.A.; Bedo, T.; Cosnita, M.; Roata, I.C.; Hulka, I. Physically Crosslinked Poly (Vinyl Alcohol)/Kappa-Carrageenan Hydrogels: Structure and Applications. Polymers 2020, 12, 560. [Google Scholar] [CrossRef]
  28. Radoor, S.; Kandel, D.R.; Park, K.; Jayakumar, A.; Karayil, J.; Lee, J. Low-cost and eco-friendly PVA/carrageenan membrane to efficiently remove cationic dyes from water: Isotherms, kinetics, thermodynamics, and regeneration study. Chemosphere 2024, 350, 140990. [Google Scholar] [CrossRef]
  29. Farooq, U.; Teuwen, J.; Dransfeld, C. Toughening of Epoxy Systems with Interpenetrating Polymer Network (IPN): A Review. Polymers 2020, 12, 1908. [Google Scholar] [CrossRef]
  30. Liu, X.J.; Ren, X.Y.; Guan, S.; Li, H.Q.; Song, Z.K.; Gao, G.H. Highly stretchable and tough double network hydrogels via molecular stent. Eur. Polym. J. 2015, 73, 149–161. [Google Scholar] [CrossRef]
  31. Wang, W.; Liu, X.; Wang, X.; Zong, L.; Kang, Y.; Wang, A. Fast and Highly Efficient Adsorption Removal of Toxic Pb(II) by a Reusable Porous Semi-IPN Hydrogel Based on Alginate and Poly(Vinyl Alcohol). Front. Chem. 2021, 9, 662482. [Google Scholar] [CrossRef]
  32. Kim, Y.J.; Min, J. Property modulation of the alginate-based hydrogel via semi-interpenetrating polymer network (semi-IPN) with poly(vinyl alcohol). Int. J. Biol. Macromol. 2021, 193, 1068–1077. [Google Scholar] [CrossRef] [PubMed]
  33. Ayouch, I.; Barrak, I.; Kassab, Z.; El Achaby, M.; Barhoun, A.; Draoui, K. Impact of the drying process on the efficiency of alginate beads for cadmium removal from water: Kinetic, isotherm and thermodynamic study. Environ. Technol. Innov. 2020, 20. [Google Scholar] [CrossRef]
  34. Lim, H.-P.; Ooi, C.-W.; Tey, B.-T.; Chan, E.-S. Controlled delivery of oral insulin aspart using pH-responsive alginate/κ-carrageenan composite hydrogel beads. React. Funct. Polym. 2017, 120, 20–29. [Google Scholar] [CrossRef]
  35. Rather, R.A.; Bhat, M.A.; Shalla, A.H. Multicomponent interpenetrating metal based Alginate-Carrageenan biopolymer hydrogel beads substantiated by graphene oxide for efficient removal of methylene blue from waste water. Chem. Eng. Res. Des. 2022, 182, 604–615. [Google Scholar] [CrossRef]
  36. Crini, G. Recent developments in polysaccharide-based materials used as adsorbents in wastewater treatment. Prog. Polym. Sci. 2005, 30, 38–70. [Google Scholar] [CrossRef]
  37. Panão, C.O.; Campos, E.L.S.; Lima, H.H.C.; Rinaldi, A.W.; Lima-Tenório, M.K.; Tenório-Neto, E.T.; Guilherme, M.R.; Asefa, T.; Rubira, A.F. Ultra-absorbent hybrid hydrogel based on alginate and SiO2 microspheres: A high-water-content system for removal of methylene blue. J. Mol. Liq. 2019, 276, 204–213. [Google Scholar] [CrossRef]
  38. Chen, S.C.; Wu, Y.C.; Mi, F.L.; Lin, Y.H.; Yu, L.C.; Sung, H.W. A novel pH-sensitive hydrogel composed of N,O-carboxymethyl chitosan and alginate cross-linked by genipin for protein drug delivery. J. Control. Release 2004, 96, 285–300. [Google Scholar] [CrossRef] [PubMed]
  39. Shilpa, A.; Agrawal, S.S.; Ray, A.R. Controlled Delivery of Drugs from Alginate Matrix. J. Macromol. Sci. Part C Polym. Rev. 2003, 43, 187–221. [Google Scholar] [CrossRef]
  40. Cai, W.; Tan, L.; Yu, J.; Jaroniec, M.; Liu, X.; Cheng, B.; Verpoort, F. Synthesis of amino-functionalized mesoporous alumina with enhanced affinity towards Cr(VI) and CO2. Chem. Eng. J. 2014, 239, 207–215. [Google Scholar] [CrossRef]
  41. Wang, H.; Wang, Z.; Yue, R.; Gao, F.; Ren, R.; Wei, J.; Wang, X.; Kong, Z. Functional group-rich hyperbranched magnetic material for simultaneous efficient removal of heavy metal ions from aqueous solution. J. Hazard. Mater. 2020, 384, 121288. [Google Scholar] [CrossRef] [PubMed]
  42. Kothavale, V.P.; Sharma, A.; Dhavale, R.P.; Chavan, V.D.; Shingte, S.R.; Selyshchev, O.; Dongale, T.D.; Park, H.H.; Zahn, D.R.T.; Salvan, G.; et al. Carboxyl and thiol-functionalized magnetic nanoadsorbents for efficient and simultaneous removal of Pb(II), Cd(II), and Ni(II) heavy metal ions from aqueous solutions: Studies of adsorption, kinetics, and isotherms. J. Phys. Chem. Solids 2023, 172, 111089. [Google Scholar] [CrossRef]
  43. Granados-Correa, F.; Corral-Capulin, N.G.; Olguín, M.T.; Acosta-León, C.E. Comparison of the Cd(II) adsorption processes between boehmite (γ-AlOOH) and goethite (α-FeOOH). Chem. Eng. J. 2011, 171, 1027–1034. [Google Scholar] [CrossRef]
  44. Kim, Y.; Kim, C.; Choi, I.; Rengaraj, S.; Yi, J. Arsenic removal using mesoporous alumina prepared via a templating method. Environ. Sci. Technol. 2004, 38, 924–931. [Google Scholar] [CrossRef]
  45. Zhou, N.; Chen, H.; Xi, J.; Yao, D.; Zhou, Z.; Tian, Y.; Lu, X. Biochars with excellent Pb(II) adsorption property produced from fresh and dehydrated banana peels via hydrothermal carbonization. Bioresour. Technol. 2017, 232, 204–210. [Google Scholar] [CrossRef] [PubMed]
  46. Ray, S.S.; Gusain, R.; Kumar, N. Adsorption equilibrium isotherms, kinetics and thermodynamics. In Carbon Nanomaterial-Based Adsorbents for Water Purification, 1st ed.; Kumar, N., Gusain, R., Sinha, R.S., Eds.; Elsevier: Amsterdam, The Netherlands, 2020; pp. 101–118. [Google Scholar]
  47. Oladoja, N.; Ololade, I.; Idiaghe, J.; Egbon, E. Equilibrium isotherm analysis of the sorption of congo red by palm kernel coat. Open Chem. 2009, 7, 760–768. [Google Scholar] [CrossRef]
  48. Nharingo, T.; Shoniwa, V.; Hunga, O.; Shumba, M. Exploring the biosorption of methylene blue dye onto acid treated sugarcane bagasse. Int. J. Curr. Res. 2013, 5, e2175. [Google Scholar]
  49. Deng, L.; Zeng, H.; Shi, Z.; Zhang, W.; Luo, J. Sodium dodecyl sulfate intercalated and acrylamide anchored layered double hydroxides: A multifunctional adsorbent for highly efficient removal of Congo red. J. Colloid Interface Sci. 2018, 521, 172–182. [Google Scholar] [CrossRef]
  50. Jiao, C.; Xiong, J.; Tao, J.; Xu, S.; Zhang, D.; Lin, H.; Chen, Y. Sodium alginate/graphene oxide aerogel with enhanced strength-toughness and its heavy metal adsorption study. Int. J. Biol. Macromol. 2016, 83, 133–141. [Google Scholar] [CrossRef]
  51. Jiang, H.; Yang, Y.; Lin, Z.; Zhao, B.; Wang, J.; Xie, J.; Zhang, A. Preparation of a novel bio-adsorbent of sodium alginate grafted polyacrylamide/graphene oxide hydrogel for the adsorption of heavy metal ion. Sci. Total Environ. 2020, 744, 140653. [Google Scholar] [CrossRef]
  52. Rahmani, Z.; Ghaemy, M.; Olad, A. Removal of heavy metals from polluted water using magnetic adsorbent based on κ-carrageenan and N-doped carbon dots. Hydrometallurgy 2022, 213, 105915. [Google Scholar] [CrossRef]
  53. Zhang, W.; Deng, Q.; He, Q.; Song, J.; Zhang, S.; Wang, H.; Zhou, J.; Zhang, H. A facile synthesis of core-shell/bead-like poly (vinyl alcohol)/alginate@PAM with good adsorption capacity, high adaptability and stability towards Cu(II) removal. Chem. Eng. J. 2018, 351, 462–472. [Google Scholar] [CrossRef]
  54. Bai, C.; Wang, L.; Zhu, Z. Adsorption of Cr(III) and Pb(II) by graphene oxide/alginate hydrogel membrane: Characterization, adsorption kinetics, isotherm and thermodynamics studies. Int. J. Biol. Macromol. 2020, 147, 898–910. [Google Scholar] [CrossRef]
  55. Godiya, C.B.; Xiao, Y.; Lu, X. Amine functionalized sodium alginate hydrogel for efficient and rapid removal of methyl blue in water. Int. J. Biol. Macromol. 2020, 144, 671–681. [Google Scholar] [CrossRef] [PubMed]
  56. Yang, M.; Liu, X.; Qi, Y.; Sun, W.; Men, Y. Preparation of kappa-carrageenan/graphene oxide gel beads and their efficient adsorption for methylene blue. J. Colloid Interface Sci. 2017, 506, 669–677. [Google Scholar] [CrossRef] [PubMed]
  57. Wang, X.; Qin, Y. Equilibrium sorption isotherms for of Cu2+ on rice bran. Process Biochem. 2005, 40, 677–680. [Google Scholar] [CrossRef]
  58. Senobari, S.; Nezamzadeh-Ejhieh, A. A comprehensive study on the photocatalytic activity of coupled copper oxide-cadmium sulfide nanoparticles. Spectrochim. Acta A Mol. Biomol. Spectrosc. 2018, 196, 334–343. [Google Scholar] [CrossRef]
  59. Mirsalari, S.A.; Nezamzadeh-Ejhieh, A. Focus on the photocatalytic pathway of the CdS-AgBr nano-catalyst by using the scavenging agents. Sep. Purif. Technol. 2020, 250, 117235. [Google Scholar] [CrossRef]
  60. El Jery, A.; Aldrdery, M.; Shirode, U.R.; Gavilán, J.C.O.; Elkhaleefa, A.; Sillanpää, M.; Sammen, S.S.; Tizkam, H.H. An Efficient Investigation and Machine Learning-Based Prediction of Decolorization of Wastewater by Using Zeolite Catalyst in Electro-Fenton Reaction. Catalysts 2023, 13, 1085. [Google Scholar] [CrossRef]
  61. Isawi, H. Using Zeolite/Polyvinyl alcohol/sodium alginate nanocomposite beads for removal of some heavy metals from wastewater. Arab. J. Chem. 2020, 13, 5691–5716. [Google Scholar] [CrossRef]
  62. Mohammed, N.; Grishkewich, N.; Berry, R.M.; Tam, K.C. Cellulose nanocrystal–alginate hydrogel beads as novel adsorbents for organic dyes in aqueous solutions. Cellulose 2015, 22, 3725–3738. [Google Scholar] [CrossRef]
  63. Almuslem, A.S.; Alnaim, N.; Ibrahim, S.S.; Ibrahim, M.A. Green Synthesis and Characteristics of Cellulose Nanocrystal/Poly Acrylic Acid Nanocomposite Thin Film for Organic Dye Adsorption during Water Treatment. Polymers 2023, 15, 2154. [Google Scholar] [CrossRef] [PubMed]
  64. Chatterjee, S.; Chatterjee, S.; Chatterjee, B.P.; Guha, A.K. Adsorptive removal of congo red, a carcinogenic textile dye by chitosan hydrobeads: Binding mechanism, equilibrium and kinetics. Colloids Surfaces A Physicochem. Eng. Asp. 2007, 299, 146–152. [Google Scholar] [CrossRef]
  65. Ram, R.; Morrisroe, L.; Etschmann, B.; Vaughan, J.; Brugger, J. Lead (Pb) sorption and co-precipitation on natural sulfide, sulfate and oxide minerals under environmental conditions. Miner. Eng. 2021, 163, 106801. [Google Scholar] [CrossRef]
  66. Cano, E.; Torres, C.L.; Bastidas, J.M. An XPS study of copper corrosion originated by formic acid vapour at 40% and 80% relative humidity. Mater. Corros. 2001, 52, 667–676. [Google Scholar] [CrossRef]
  67. d’Halluin, M.; Rull-Barrull, J.; Bretel, G.; Labrugère, C.; Le Grognec, E.; Felpin, F.-X. Chemically Modified Cellulose Filter Paper for Heavy Metal Remediation in Water. ACS Sustain. Chem. Eng. 2017, 5, 1965–1973. [Google Scholar] [CrossRef]
  68. Jiang, X.; An, Q.-D.; Xiao, Z.-Y.; Zhai, S.-R.; Shi, Z. Versatile core/shell-like alginate@polyethylenimine composites for efficient removal of multiple heavy metal ions (Pb2+, Cu2+, CrO42−): Batch and fixed-bed studies. Mater. Res. Bull. 2019, 118. [Google Scholar] [CrossRef]
  69. Sheng, P.X.; Ting, Y.P.; Chen, J.P.; Hong, L. Sorption of lead, copper, cadmium, zinc, and nickel by marine algal biomass: Characterization of biosorptive capacity and investigation of mechanisms. J. Colloid Interface Sci. 2004, 275, 131–141. [Google Scholar] [CrossRef]
  70. Chen, P.; Cao, Z.-f.; Wen, X.; Wang, J.; Yang, F.; Qiu, P.; Yue, Y.-j.; Liu, G.-y.; Wang, S.; Zhong, H. A novel mesoporous silicate material (MS) preparation from dolomite and enhancing methylene blue removal by electronic induction. J. Taiwan Inst. Chem. Eng. 2017, 80, 128–136. [Google Scholar] [CrossRef]
  71. Lima, P.H.; Pereira, S.V.; Rabello, R.B.; Rodriguez-Castellon, E.; Beppu, M.M.; Chevallier, P.; Mantovani, D.; Vieira, R.S. Blood protein adsorption on sulfonated chitosan and kappa-carrageenan films. Colloids Surf. B Biointerfaces 2013, 111, 719–725. [Google Scholar] [CrossRef]
  72. Berton, S.B.R.; de Jesus, G.A.M.; Sabino, R.M.; Monteiro, J.P.; Venter, S.A.S.; Bruschi, M.L.; Popat, K.C.; Matsushita, M.; Martins, A.F.; Bonafe, E.G. Properties of a commercial kappa-carrageenan food ingredient and its durable superabsorbent hydrogels. Carbohydr. Res. 2020, 487, 107883. [Google Scholar] [CrossRef] [PubMed]
  73. Fantauzzi, M.; Elsener, B.; Atzei, D.; Rigoldi, A.; Rossi, A. Exploiting XPS for the identification of sulfides and polysulfides. RSC Adv. 2015, 5, 75953–75963. [Google Scholar] [CrossRef]
  74. Kumar, A.; Sood, A.; Han, S.S. Poly (vinyl alcohol)-alginate as potential matrix for various applications: A focused review. Carbohydr. Polym. 2022, 277, 118881. [Google Scholar] [CrossRef]
  75. Sun, C.; Wang, Z.; Zheng, H.; Chen, L.; Li, F. Biodegradable and re-usable sponge materials made from chitin for efficient removal of microplastics. J. Hazard. Mater. 2021, 420, 126599. [Google Scholar] [CrossRef] [PubMed]
  76. OECD. Test. In OECD Guidelines for the Testing of Chemicals, Section 2; OECD Publishing: Paris, France, 2004. [Google Scholar] [CrossRef]
Gels 11 00211 g001
Figure 1. FE-SEM images of surface (a,b) SA, (c,d) SA/PVA, (e,f) SA/CG, and (g,h) SA/PVA/CG beads and cross-section images of (i,j) SA, (k,l) SA/PVA, (m,n) SA/CG, and (o,p) SA/PVA/CG beads.
Figure 1. FE-SEM images of surface (a,b) SA, (c,d) SA/PVA, (e,f) SA/CG, and (g,h) SA/PVA/CG beads and cross-section images of (i,j) SA, (k,l) SA/PVA, (m,n) SA/CG, and (o,p) SA/PVA/CG beads.
Gels 11 00211 g001
Gels 11 00211 g002
Figure 2. Characteristics of the SA/PVA, SA/CG, and SA/PVA/CG aerogel beads: (a) FT-IR spectra, (b) water absorption efficiency, (c) and adsorption capacity for Cu(II), Pb(II), and MB.
Figure 2. Characteristics of the SA/PVA, SA/CG, and SA/PVA/CG aerogel beads: (a) FT-IR spectra, (b) water absorption efficiency, (c) and adsorption capacity for Cu(II), Pb(II), and MB.
Gels 11 00211 g002
Gels 11 00211 g003
Figure 3. Adsorption of single pollutants (Cu(II), Pb(II), MB, or AB) onto the SA/PVA/CG aerogel beads: (a) kinetic and isotherm data for (b) Cu(II) (C0 = 10–125 mg/L), (c) Pb(II) (C0 = 10–125 mg/L), and (d) MB (C0 = 10–500 mg/L).
Figure 3. Adsorption of single pollutants (Cu(II), Pb(II), MB, or AB) onto the SA/PVA/CG aerogel beads: (a) kinetic and isotherm data for (b) Cu(II) (C0 = 10–125 mg/L), (c) Pb(II) (C0 = 10–125 mg/L), and (d) MB (C0 = 10–500 mg/L).
Gels 11 00211 g003
Gels 11 00211 g004
Figure 4. Effect of pH on (a) Cu(II), Pb(II), and MB adsorption using the SA/PVA/CG aerogel beads and distribution of (b) Cu(II), (c) Pb(II), and (d) MB.
Figure 4. Effect of pH on (a) Cu(II), Pb(II), and MB adsorption using the SA/PVA/CG aerogel beads and distribution of (b) Cu(II), (c) Pb(II), and (d) MB.
Gels 11 00211 g004
Gels 11 00211 g005
Figure 5. Effect of temperature on (a) Cu(II), (b) Pb(II), and (c) MB adsorption using the SA/PVA/CG aerogel beads.
Figure 5. Effect of temperature on (a) Cu(II), (b) Pb(II), and (c) MB adsorption using the SA/PVA/CG aerogel beads.
Gels 11 00211 g005
Gels 11 00211 g006
Figure 6. Adsorption kinetic data for single and binary systems using the SA/PVA/CG beads: (a) Cu(Ⅱ), (b) Pb(Ⅱ), (c) MB, and (d) AB.
Figure 6. Adsorption kinetic data for single and binary systems using the SA/PVA/CG beads: (a) Cu(Ⅱ), (b) Pb(Ⅱ), (c) MB, and (d) AB.
Gels 11 00211 g006
Gels 11 00211 g007
Figure 7. XPS spectra for the SA/PVA/CG aerogel beads (a) before and after the adsorption of single pollutants (Cu(II), Pb(II), MB, or AB), (b) after the adsorption of two pollutants, (c) the Cu 2p region after Cu(II) adsorption, (d) the Pb 4f region after Pb(II) adsorption, (e) high-resolution version of the Cu 2p region, and (f) high-resolution version of the Pb 4f region in the Cu–Pb system.
Figure 7. XPS spectra for the SA/PVA/CG aerogel beads (a) before and after the adsorption of single pollutants (Cu(II), Pb(II), MB, or AB), (b) after the adsorption of two pollutants, (c) the Cu 2p region after Cu(II) adsorption, (d) the Pb 4f region after Pb(II) adsorption, (e) high-resolution version of the Cu 2p region, and (f) high-resolution version of the Pb 4f region in the Cu–Pb system.
Gels 11 00211 g007
Gels 11 00211 g008
Figure 8. Predicted adsorption mechanism of single and binary system using the SA/PVA/CG aerogel beads.
Figure 8. Predicted adsorption mechanism of single and binary system using the SA/PVA/CG aerogel beads.
Gels 11 00211 g008
Gels 11 00211 g009
Figure 9. Synthesis procedure of the SA-based aerogel beads.
Figure 9. Synthesis procedure of the SA-based aerogel beads.
Gels 11 00211 g009
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Jang, T.; Yoon, S.; Choi, J.-H.; Kim, N.; Park, J.-A. Simultaneous Removal of Heavy Metals and Dyes on Sodium Alginate/Polyvinyl Alcohol/κ-Carrageenan Aerogel Beads. Gels 2025, 11, 211. https://doi.org/10.3390/gels11030211

AMA Style

Jang T, Yoon S, Choi J-H, Kim N, Park J-A. Simultaneous Removal of Heavy Metals and Dyes on Sodium Alginate/Polyvinyl Alcohol/κ-Carrageenan Aerogel Beads. Gels. 2025; 11(3):211. https://doi.org/10.3390/gels11030211

Chicago/Turabian Style

Jang, Taesoon, Soyeong Yoon, Jin-Hyuk Choi, Narae Kim, and Jeong-Ann Park. 2025. "Simultaneous Removal of Heavy Metals and Dyes on Sodium Alginate/Polyvinyl Alcohol/κ-Carrageenan Aerogel Beads" Gels 11, no. 3: 211. https://doi.org/10.3390/gels11030211

APA Style

Jang, T., Yoon, S., Choi, J.-H., Kim, N., & Park, J.-A. (2025). Simultaneous Removal of Heavy Metals and Dyes on Sodium Alginate/Polyvinyl Alcohol/κ-Carrageenan Aerogel Beads. Gels, 11(3), 211. https://doi.org/10.3390/gels11030211

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop