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Abstract

In this study, a new category of sulfone-modified chitosan derivatives as surface-selective adsorbents for the extraction of toxic Hg(II) metal has been synthesized in good yield. Sulfone-modified chitosan/5–20 based on variable loading of the corresponding phenacyl bromide (5, 10, 15, and 20% with respect to the original weight of the pure chitosan) was synthesized. The β-ketosulfone derivative, namely 1–(4-bromophenyl)-2-(phenylsulfonyl)ethanone, was first prepared by treatment of the corresponding phenacyl bromide with a sufficient amount of sodium benzene sulfinate; its chemical structure was confirmed by spectral analyses, including Fourier transform infrared spectroscopy, ¹H-NMR, ¹³C-NMR, and mass spectrometry. Then, sulfone-modified chitosan/5–20 derivatives were synthesized by the interaction of chitosan with a freshly prepared p-bromo-β-ketosulfone derivative in a mildly acidic aqueous solution using the solution-blending technique. Sulfone-modified chitosan/5–20 derivatives were identified and characterized using common characterization techniques, including Fourier transform infrared spectroscopy, ﬁeld-emission scanning electron microscope, powder X-ray diffraction, and thermal behaviour. A strong interaction was displayed between chitosan and its corresponding β-ketosulfones in powder X-ray diffraction, which was confirmed by significant 2θ shifts. Sulfone-modified chitosan/5–20 derivatives were detected as catalysts, which efficiently increased the thermal decomposition of pure chitosan. More particularly, the efficiency of sulfone-modified chitosan/5–20 derivatives for Hg(II), Pb(II), Ni(II), Al(III), Sr(II), Cr(III), Fe(III), Zn(II), and Mn(II) detection and adsorption was also investigated using inductively coupled plasma optical emission spectrometry. The sulfone-modified chitosan/5 derivative exhibited the highest adsorption efficiency. The most effective quantitative adsorption onto the sulfone-modified chitosan/5 surface was detected at pH = 2. In addition to that, the adsorption isotherm showed that the adsorption capacity of sulfone-modified chitosan/5 for Hg(II) was 122.47 mg g⁻¹ and that its adsorption isotherm was in agreement with the Langmuir adsorption isotherm.

Keywords

Chitosan β-ketosulfone sulfone-modified chitosan Hg(II)adsorption capacity batch method inductively coupled plasma-optical emission spectrometer

Introduction

Heavy metals have attracted particular interest within the framework of environmental studies. Industrial production, life cycle assessment, food pollution, and extraction of the highest amounts of heavy metals from surface and ground water are the most interesting topics for many researchers. Toxic elements in soil and transfer into crops are of great concern owing to the probability of toxic element introduction into the food chain and the influence of essential elements. Anthropogenic activities are considered as one of the most common sources of heavy metals in the environment, as are domestic activities (Ene et al., 2009). This toxic heavy metal contamination may affect the entire universe and all of humankind. The bioavailability of toxic metals causes the presence of metal ion speciation in the soil. Mercury (Hg) is one of the most hazardous metals that can be found worldwide and its toxic nature has been explored. The elimination of mercury ions from water and wastewater is essential. Therefore, the appropriate methods to control and determine mercury ions are important. However, direct evaluations of metal ions using different systematic methods (such as chemical precipitation, coagulation, ion exchange, flocculation, adsorption, etc.) are not sufficient due to high concentrations and the interfering matrix components (Babel and Kurniawan, 2003; Bailey et al., 1999). Thus, an effective separation procedure is required before metal ion determination for sensitive, accurate, and interference-free determination of metal ions. There are many treatment techniques for the separation of metal ions, including precipitation (Souza et al., 2011), liquid–liquid extraction (Akinobu et al., 1997), ion exchange (Hershey and Keliher, 1989), cloud point extraction (Manzoori et al., 2007), and solid-phase extraction (Ahmed, 2008; Montero Alvarez et al., 2007). Among the various treatments, the adsorption technique is the most frequently used method. Solvent extraction has been used as an efficient method owing to effective extraction, selective separation, and economical costs (Biparva and Hadjmohammadi, 2011; Dave et al., 2010; Diniz and Volesky, 2005; Hang et al., 2002; Jain et al., 2001; Jankowski et al., 2005; Jelinek et al., 2007; Kim et al., 2006; Lemos et al., 2008; Liang et al., 2005; Marwani et al., 2012a, 2012b; Mashhadizadeh et al., 2008; Pasinli et al., 2005; Rauf et al., 1993; Zhang et al., 2007). The use of adsorbents containing natural polymers has generated great interest, especially regarding polysaccharides such as chitin and its derivate, chitosan (Crini, 2005; Kurita, 2006; Varma et al., 2004). It is well known that the most abundant natural biopolymer is cellulose; the second is chitin, which can be found in the shells of crustaceans, skeletons of molluscs, and in the cell walls of some fungi (Gooday, 1990; Zhang et al., 2000). Chitin exists in nature as crystalline microﬁbrils. Depending on its source, three different crystalline polymorphic forms of chitin have been explored (Jang et al., 2004). Chitosan is a copolymer that is composed of (1→4) linkages of 2-amino-2-deoxy-d-glucopyranose units. Chitosan is found naturally in some fungal cell walls (Jayakumar et al., 2005; Synowiecki and Al-Khateeb, 2003). Chitosan has been widely used in several biological and medical applications (Brine et al., 1992; Colwell et al., 1985; Dutta et al., 2002; Kawamura et al., 1993; Muzzarelli, 1973). Scientists have been working on different methods to modify chitosan through physical or chemical methods to enhance its adsorption capacity (Guibal, 2004; Jeon and Höll, 2003; Matsumura et al., 1998). Cross-linking with glutaraldehyde or epi-chlorohydrin is an example of chitosan chemical modification. Another chemical modification of chitosan derivatives can be obtained through functional group grafting onto the backbone of chitosan. Functional groups can affect different factors such as increasing the density of sorption sites, changing the pH range for metal sorption, and modifying the sorption sites in order to increase sorption selectivity for the metal (Donia et al., 2008; Elwakeel and Guibal, 2015; Kurita, 2006). The chemical methods of modiﬁcation provide a wide range of derivatives with new properties, which can be applied in pharmaceutical and biomedical settings (Mourya and Inamdar, 2008). On the other hand, the important factor that explains why we should study the adsorption behaviour of chitosan in aqueous acid solutions is based on the presence of acetic acid as an acidic media. Acetic acid is predominantly used as a stimulator in the waste removal process, in which the pH of the dye solution is normally adjusted to 3–4. However, chitosan formed gels below pH 5.5 and could not be determined. The acid streaming could severely limit the use of chitosan as an adsorbent in removing dyes, metal ions, and other waste materials due to the dissolution tendency of chitosan in the acid effluent. Therefore, it is preferable to study the prepared sulfone-modified chitosan (SMC)/5–20 derivatives as surface adsorbents, which will be discussed in this work. Thus, β-ketosulfone derivatives (SMC) will be prepared from the reaction of chitosan with phenacyl bromide and sodium benzene sulfinate. Furthermore, the analytical potential of newly synthesized SMC towards a selective extraction of various metal ions, especially Hg(II), will be explored. Additionally, factors such as pH and the concentrations of metals that affect the selectivity and adsorption of SMC will be evaluated.

Experiment

Chemicals and reagents

Chitosan (degree of deacetylation > 75% and molecular weight of 800–2000) was purchased from Sigma Aldrich (Germany). 4-bromo-4-bromoacetophenone was also purchased from Sigma Aldrich. Sodium benzene sulfinate was purchased from PDH. All other chemicals and reagents were purchased from Duksan Chemical Co., Ltd (Ansan, Korea). Sulfone derivatives were prepared according to the reported literature procedures (Curti et al., 2007).

Preparation of the new solid-phase extractor

Preparation of β-ketosulfone

A mixture of sodium benzene sulfinate (2 mmol) and an ethanolic solution of 4-bromo-4-bromoacetophenone (2 mmol) was refluxed for 6 h. After cooling, the reaction mixture was treated with water, and the solid product was washed with water and recrystallized from the appropriate solvent. Yield (90%); m.p. 143°C. The elemental and spectral characteristic data of 1-(4-bromophenyl)-2-(phenylsulfonyl)ethanone are shown in Table 1.

Table 1.

The elemental and spectral characteristic data of 1-(4-bromophenyl)-2-(phenylsulfonyl)ethanone.

Property	Characteristic data
IR (KBr) υmax/cm⁻¹	1691 (C=O), 1181, 1391 (SO₂)
¹H NMR (CDCl₃)	δ 4.68 (s, 2H, CH₂), 7.54 (t, 1H), 7.61 (d, 1H), 7.67 (t, 1H), 7.80 (d, 1H), 7.86 (d, 1H)
¹³C NMR (CDCl₃)	δ 63.60, 128.33, 130.07, 130.81, 132.28, 134.42, 134.46, 138.54, 187.10
Mass spectrum MS (m/z)	339 (M⁺)
Elemental analysis for C₁₄H₁₁BrO₃S (339.20)	Anal. Calcd: C, 49.57; H, 3.27; S, 9.45% Found: C, 49.54; H, 3.25; S, 9.48%

Preparation of SMC/5–20 derivatives

SMC/5–20 derivatives were prepared as follows: 1 g powdered chitosan was first dissolved in a mixture of water:acetic acid (9:1). Different weight percentages of p-bromo-β-ketosulfone (5, 10, 15, and 20%) were then added to the previous solution with constant stirring until the complete disappearance of the starting material (monitored by thin layer chromatography). The reaction was found to be completed within 1 h of each phase. Then, the solvent was evaporated, and the residual phase was dried and analysed. Depending on the sulfone content, the samples were coded as SMC/5, SMC/10, SMC/15, and SMC/20 derivatives, which represent 5, 10, 15, and 20%, respectively.

Adsorption method procedure

All stock standard solutions of Hg(II), Pb(II), Ni(II), Al(III), Sr(II), Cr(III), Fe(III), Zn(II), and Mn(II) were prepared in 18.2 million ohm cm (MΩ cm) distilled deionized water and stored in the dark at 4°C. This value (18.2 MΩ cm) represents the resistivity of deionized water. For the selectivity study, standard solutions of 2 mg l⁻¹ of Hg(II) (or other metal ions) were prepared and individually mixed with 20 mg SMC phases. In addition, standard solutions of 2 mg l⁻¹ Hg(II) ion were prepared and adjusted to pH values ranging from 1.0 to 11.0 with appropriate buffer solutions. All standard solutions were individually mixed with 20 mg SMC/5 derivative in order to study the effect of pH on the selectivity of SMC/5 derivative adsorption towards Hg(II). All mixtures were mechanically shaken for 1 h at 150 r min⁻¹ at room temperature. For the study of the adsorption capacity of Hg(II) under batch conditions, standard solutions of 1, 5, 10, 15, 20, 25, 30, 50, 75, 100, 120, 150 mg l⁻¹ Hg(II) were prepared as above, adjusted to the optimum pH value of 2.0, and individually mixed with 20 mg SMC/5 derivative.

Instrumentation

All melting points were measured on a Gallenkamp melting point apparatus. The infrared spectra were recorded on Pye Unicam SP 3-300 and Shimadzu FT-IR 8101 PC infrared spectrophotometers using the KBr disk technique over the wavenumber range 4000–400 cm⁻¹. The NMR spectra were measured on a Varian Mercury VXR-400 NMR spectrometer (¹H-NMR (400 MHz) and ¹³C-NMR (75.46 MHz)) and Bruker-500 NMR spectrometer (¹H-NMR (500 MHz) and ¹³C-NMR (125.77 MHz)) in deuterated chloroform (CDCl₃). Chemical shifts were related to that of the solvent. Mass spectra were recorded on a Shimadzu GCMS-QP1000 EX mass spectrometer at 70 eV. A pH meter (InoLabpH 7200, IL, USA) was employed for the pH measurements with absolute accuracy limits of pH measurements being deﬁned by NIST buffers. XRD patterns were performed for the nanoparticles and composites in the 2θ range from 10 to 80° using a Bruker diffractometer (Bruker D8 advance target). The patterns were run with copper Kα1 and a monochromator (l = 1.5405 Å) at 40 kV and 40 mA. The thermal gravimetric analysis (TGA) and its differential thermogravimetry (DTG) curves were recorded with a TA instrument apparatus model TGA-Q500 using a heating rate of 10°C min⁻¹ under a nitrogen atmosphere. The average masses of the samples were 5 mg. The morphological properties of the new composites were analysed by a ﬁeld-emission scanning electron microscope (FE-SEM) on a JEOL model JSM-7600F microscope. A Perkin Elmer inductively coupled plasma-optical emission spectrometer (ICP-OES), model Optima 4100 DV (USA), was used for the evaluation of metal ions. The ICP-OES instrument was optimized daily before evaluation. The ICP-OES spectrometer was used at the following parameters: FR power, 1300 kW; frequency, 27.12 MHz; demountable quartz torch, Ar/Ar/Ar; plasma gas (Ar) ﬂow, 15.0 l min⁻¹; auxiliary gas (Ar) ﬂow, 0.2 l min⁻¹; nebulizer gas (Ar) ﬂow, 0.8 l min⁻¹; nebulizer pressure, 2.4 bar; glass spray chamber according to Scott (Ryton), sample pump ﬂowrate, 1.5 ml min⁻¹; integration time, 3 s; replicates, 3; wavelength range of monochromator, 165–460 nm. The concentrations of selected metal ions were evaluated at wavelengths of 194.17 nm for Hg(II), 220.35 nm for Pb(II), 257.61 nm for Mn(II), 231.60 nm for Ni(II), 394.40 nm for Al(III), 232.23 nm for Sr(II), 239.56 nm for Fe(III), 267.72 nm for Cr(III), and 213.86 nm for Zn(II).

Results and discussion

Preparation of SMC/5–20 derivatives and their physical properties

The synthesis of β-ketosulfones is carried out in numerous ways. The most accessible and largely used synthetic route to synthesize β-ketosulfone derivatives is the alkylation of metallic aryl sulfinates with α-halo ketones. Therefore, 4-bromophenacyl bromide 1 reacts with the sodium salt of sulfinic acid 2 under reflux conditions to afford the corresponding β-ketosulfone derivative in good yield, as illustrated in Figure 1. The structure of the synthesized β-ketosulfone derivative 3 was confirmed by elemental as well as spectroscopic data as given in the “Experiment” section.

Figure 1.

The synthetic route of β-ketosulfone derivative 3.

The synthesis of SMC derivatives was carried out through the condensation of the freshly synthesized β-ketosulfone derivative 3 with chitosan in similar conditions. SMC/5–20 derivatives are mainly based on the variable loading of β-ketosulfone derivatives over the chitosan main chain. Hence, SMC/5–20 derivatives are prepared by stirring a mixture of chitosan and different weight percentage (5–20%) of p-bromo-β-ketosulfone in a mildly acidic aqueous solution at room temperature, as shown in Figure 2.

Figure 2.

Synthesis of SMC/5–20 derivatives.

A rotary evaporator was used to remove the solvent from the products. The final residues were exposed to oven drying. The prepared SMC/5–20 derivatives were characterized by multiple characterization techniques including FE-SEM, Fourier transform infrared spectroscopy (FT-IR), powder X-ray diffraction (PXRD), and thermal behaviour.

The FE-SEM images of pure chitosan host molecule, SMC/5 and SMC/15 derivatives as selected examples, are illustrated in Figure 3(a) to (f). The addition of p-bromo-β-ketosulfone will interact with the polar group present in the chitosan polymer host materials, modifying its morphology. The chitosan has a sheet-like morphology, as indicated in Figure 3(a) and (b). FE-SEM images for SMC/5 and SMC/15 derivatives show a significant change in the pure chitosan morphology. The organic substituent is accommodated on the surface of the chitosan molecule through strong chemical interactions, as shown in Figure 3(c) to (f). The interactions between the chitosan matrix and β-ketosulfone derivatives are effectively elucidated through hydrogen bonding and the formation of an imine linkage, which makes p-bromo-β-ketosulfone stable through many hydrophilic sites at the surface. Figure 3(c) and (d) of the SMC/5 derivative shows a porous molecular structure; however, increasing the content of organic molecules generates a nearly complete sheet morphology, on which small particles of an organic molecule are present on the polymer host molecule. This might be due to the reaction of the organic molecule with the polymer; the remaining organic molecule is accommodated on the surface of a polymer in the form of particles.

Figure 3.

FE-SEM of pure chitosan (a,b), SMC/5 derivative (c,d), and SMC/15 derivative (e,f).

FT-IR spectra of the pure chitosan and SMC/5–20 derivatives are indicated in the inclusion of Figure 4. The FT-IR spectrum of pure chitosan exhibits a peak at 3305 cm⁻¹ for the asymmetric stretching vibration of the OH group, while an OH bend appears at 1550 cm⁻¹. The amide group appears at 1657 cm⁻¹ and the C–O stretching at 1085 cm⁻¹. The 4-bromophenacyl bromide indicated a peak at 2953 cm⁻¹. The 4-bromophenacyl bromide indicated a C–H asymmetric stretch at 2953 cm⁻¹ and a keto group at 1691 cm⁻¹. The downshift of the carbonyl is due to the presence of conjugation of the carbonyl group to the aromatic moieties, which lengthens the bond, weakens the bond strength, and thus decreases the absorption energy. The FT-IR spectrum of p-bromo-β-ketosulfone is indicated in Figure 4(b). The absorbance at 2953 cm⁻¹ exhibited the presence of a C–H asymmetric stretching vibration. Similarly, the peak at 1100–1400 cm⁻¹ is due to the presence of S = O cm⁻¹ (sulfone group), and the S–O cm⁻¹ vibrations appeared from 700 to 1000, as can clearly be observed in Figure 4(b). In the region of 1000–1100 cm⁻¹, a C–O stretching vibration is observed as seen in the inset of Figure 4(b). The FT-IR spectra of sulfone-based modified chitosan in the form of SMC/5–20 derivatives are given in Figure 4(c) to (g). The entire peak showed an N–H stretch at approximately 3400 cm⁻¹. Additionally, a C–O stretch at 1085 cm⁻¹ has appeared in all of the modified chitosan from Figure 4(c) to (f). Similarly, amide group N–C = O and N–H deformation peaks have appeared at 1650 and 1555 cm⁻¹, respectively (Figure 4). These results indicated that the incorporation of p-bromo-β-ketosulfone does not change the chitosan nucleus.

Figure 4.

FT-IR spectra of 4-bromophenacyl bromide (a), p-bromo β-ketosulfone (b), SMC/5 derivative (c), SMC/10 derivative (d), SMC/15 derivative (e), SMC/20 derivative (f), and pure chitosan (g).

Generally, X-ray spectroscopy is considered as one of the most widely used techniques utilized in characterizing new materials of all forms. Furthermore, it is also a powerful supplementary tool to other characterization techniques used for structural identification and characterization (UV–Vis, FT-IR, ¹H, ¹³C-NMR, and Raman spectroscopy) (Guo, 2009). The PXRD data for pure chitosan and all SMC/5–20 derivatives are illustrated in Figure 5(a) to (e) over the range of 2θ = 10–80°. Figure 5 shows a broad and strong peak at 2θ = 20°, which confirms the presence of polymeric material and the absence of metallic constituents. Furthermore, the organic molecules did not appear in the powdered XRD spectrum due to their amorphous nature, as depicted in the inset of Figure 5(a) to (e). A PXRD diffractogram of chitosan shows a typical broad and amorphous peak in the range of 2θ = 15–25°, with a peak maximum at approximately 2θ = 20°, which indicates the amorphous pattern of chitosan as a reason for the highly disordered crystal structure; additionally, a minor hump at 2θ = 38–42° with a peak maximum at approximately 2θ = 40° (Islam et al., 2011; Kumar et al., 2009; Ogawa et al., 2004), together with minor reflections at lower 2θ values approximately 2θ = 11°, is also considered as typical diffraction peaks of chitosan resulting from amorphous character (Bangyekan et al., 2006; Muzzarelli et al., 2004). The SMC/5–20 phases also show similar strong, broad peaks together with minor reflections, which significantly shift to higher 2θ values at 2θ = 20.5–34° and 2θ = 14.3°. These reflection peaks also indicate the lower degree of crystallinity. Such a broad peak also indicates the highly disordered structure of the crystalline morphology of these SMC/5–20 derivatives. The observed 2θ shift can be considered as evidence for SMC/5–20 derivatives formation as an alternative compound to pure chitosan. The PXRD diffractograms of p-bromo-β-ketosulfone derivatives also display strong interactions found between chitosan and its corresponding-β-ketosulfones, which have been confirmed by 2θ shift. More particularly, the PXRD results for SMC/5–20 derivatives show a noticeable decrease in the crystallinity with increasing degree of cross-linking. This behaviour is attributed to the presence of a lower number of free NH₂ groups within the molecular structure, which decrease the intermolecular hydrogen bonding, reduce the packing of the macromolecular polymeric chains, and consequently decrease the crystallinity (De Vasconcelos et al., 2007).

Figure 5.

PXRD diffractograms of SMC/5 derivative (a), SMC/10 derivative (b), SMC/15 derivative (c), SMC/20 derivative (d), and pure chitosan (e).

The thermal stabilities of the pure chitosan and its modified SMC/5–20 derivatives are scrutinized by their TGA and corresponding DTG, as illustrated in Figure 6(a) and (b). The TGA thermograms are provided in Figure 6(a), while the DTG curves are exhibited in Figure 6(b). The essential thermal effect of chitosan and its cross-linked derivatives, as important modified polysaccharides, is mainly based on the molecular weight and the acetylation degree of the macromolecules. TGA curves of pure chitosan and its modified SMC/5–20 derivatives showed two important degradation steps over the thermal screening in the temperature range of 35–800°C. The degradation does not start before 200°C due to the moderate thermal stability of pure chitosan and its derivatives. Chitosan, with a polysaccharide backbone, carries hydrophilic groups (hydroxyl and/or amino groups); therefore, the aforementioned degradation transition step is attributed to the release of entrapped solvents, humidity, or attached moisture, which are readily released and vaporized by heating chitosan. This process is nearly complete at approximately 100°C. SMC/5–20 derivatives show identical behaviour with heating over similar conditions, with a slight increase in reactive solvent as a reason for the thermal treatment which is attributed to the higher stability of the chitosan matrix (Ray et al., 2010). The second degradation step refers to the main decomposition step of both pure chitosan and its SMC/5–20 modified derivatives. Similar decomposition behaviour was observed over this step in all tested samples, although with a significantly lower temperature shift. Such degradation occurs over a temperature range of 250–350 and 200–300°C for pure chitosan and its modified derivatives, respectively. TGA curves also show that SMC/5–20 modified derivatives act as catalysts, which enhance and facilitate the decomposition of pure chitosan due to its degradation over lower temperatures than those of pure chitosan. The addition of organic components to the cellulose acetate polymer chains in the form of β-ketosulfone-modified chitosan derivatives readily decreases the Van der Waals force interaction between chitosan chains; this leads to increased chain packing (Park et al., 2006), which is also confirmed from the FE-SEM images.

Figure 6.

TGA (a) and DTG (b) curves of pure chitosan and its SMC/5–20 derivatives. SMC: sulfone-modified chitosan.

The DTG curves of Figure 4(b) show the polymer decomposition temperature maximum (PDT_max) for pure chitosan and its modified SMC/5–20 derivatives, referring to the maximum temperature at which the decomposition occurs (Hussein et al., 2013, 2012). The PDT_max value of pure chitosan is observed at 280.4°C; similarly, PDT_max values for SMC/5–20 derivatives are nearly identical but shifted to lower temperatures over the range of 183.8–188.7°C. DTG curves also indicate that the thermal stability of pure chitosan decreases with increasing the degree of modification from SMC/5 (PDT_max value = 188.7°C) to SMC/20 (PDT_max value = 183.8°C), an observation in agreement with the previously mentioned TG study. PDT_max values for the SMC/10 derivative and SMC/15 derivative are 185.2 and 184.04°C, respectively.

Surface selectivity study

Chitosan has been extensively used, either alone or in combination with other materials, to remove diverse environmental pollutants and can be classified as one of the most remarkable eco-friendly materials (Farzana and Meenakshi, 2013; Viswanathan and Meenakshi, 2009) because of its superior adsorption properties. However, neat chitosan does not perform well as an adsorbent because of its high solubility in acidic solution and its weak chemical resistance (Du et al., 2014). Chitosan forms gels below pH 5.5 and cannot be evaluated. Acid streaming could severely limit the use of chitosan as an adsorbent to remove dyes, metal ions, and any other waste materials because of chitosan’s dissolution susceptibility in acid effluent. Therefore, SMC/5–20 derivatives are used as surface-selective adsorbents to extract toxic Hg(II) metal from aqueous solution. All prepared SMC/5–20 derivatives yielded significant adsorption efficiency when compared with pure chitosan. More particularly, the SMC/5 derivative exhibits the highest adsorption efficiency among all SMC/5–20 derivatives; thus, it is chosen as a surface selectivity study example in this work, as listed in Table 2. The distribution coefficient selectivity of the SMC/5 derivative towards different metal ions was obtained. The distribution coefficient (K_d) is calculated using the following equation

K_{d} = \frac{(C_{o} - C_{e})}{C_{e}} \times \frac{V}{m}

(1)where C_o and C_e are the initial and ﬁnal concentrations before and after ﬁltration with the adsorbent, respectively; V refers to the volume (ml); and m is the weight of the adsorbent (g). The distribution coefficient values for all metal ions investigated in this study are presented in Table 2.

Table 2.

Selectivity study of different SMC/5–20 derivatives (20 mg) adsorption towards different metal ions (N = 3).

Phase	Metal ion	q_e (mg g⁻¹)	K_d (ml g⁻¹)
SMC/5 derivative	Hg(II)	2.50	2.38 × 10⁶
	Pb(II)	2.40	2.89 × 10⁴
	Ni(II)	1.97	4.65 × 10³
	Al(III)	1.86	3.62 × 10³
	Sr(II)	1.55	2.02 × 10³
	Cr(III)	1.40	1.59 × 10³
	Fe(III)	0.88	6.73 × 10²
	Zn(II)	0.29	1.66 × 10²
	Mn(II)	0.28	1.60 × 10²
SMC/10 derivative	Hg(II)	2.49	3.24 × 10⁵
SMC/15 derivative	Hg(II)	2.43	4.64 × 10⁴
SMC/20 derivative	Hg(II)	2.39	2.73 × 10⁴

SMC: sulfone-modified chitosan.

As shown in Table 2, SMC/5 shows the greatest distribution coefficient value (2.38 × 10⁶ ml g⁻¹) towards Hg(II) among all metal ions. These results indicate that the selectivity of such a synthesized derivative towards Hg(II) is most preferable compared to other metal ions investigated in this study, as illustrated in Figure 7.

Figure 7.

Schematic illustrations of surface selectivity of newly synthesized SMC/5–20 derivatives towards Hg(II).

Effect of pH

The occurrence of H⁺ ions in the solution plays a vital role in the extraction of metal ions from aqueous media by adsorption and affects the degree of ionization and species of adsorbate (Zhang et al., 2008). Therefore, the effect of pH on the adsorption of Hg(II) by the newly synthesized SMC/5 derivative is investigated. A concentration of 2 mg l⁻¹ Hg(II) is taken into account, and the effect of pH on the reaction is studied by changing the solution pH range from 1.0 to 11.0 with corresponding buffer solutions. All standard solutions are individually mixed with 20 mg SMC/5. Figure 8 shows the effect of solution pH on the extraction %; pH has a direct effect on the extraction process. The experiments were conducted using 20 mg SMC/5 at 25°C and under a range of pH values from 1.0 to 11.0. The results in Figure 8 show an increase followed by a subsequent decrease on the extraction % of Hg(II) with increasing pH values.

Figure 8.

The effect of pH on the adsorption of 2 mg l⁻¹ Hg(II) on 20 mg SMC/5 at 25°C.

At pH 2.0, the highest % extraction of Hg(II) is reached (99.95), which indicated that the SMC/5 derivative is most selective towards Hg(II) at this pH value. The cause of the highest percentage of Hg(II) extraction and selectivity with SMC/5 at this pH value is explained by the electrostatic interaction between protonated sites, presented on carbonyl groups and amino groups of SMC/5 at pH 2.0, as well as negatively charged species (HgCl₄^–, the primary form of Hg(II) in HCl solution). Thus, Hg(II) is selectively removed from the matrix. According to the results, the optimum pH value of 2.0 is selected for the study of other parameters controlling the maximum uptake on the SMC/5 derivative under static conditions.

Determination of adsorption capacity

The investigation of the uptake capacity of Hg(II) is determined by different amounts of Hg(II) individually mixed with 20 mg SMC/5 derivative at pH 2.0 under a batch procedure. From the adsorption isotherm study, the adsorption capacity of SMC/5 for Hg(II) is found to be 122.47 mg g⁻¹, as shown in Figure 9, which is significantly higher than the previously reported adsorption capacity for Hg(II) with other chitosan-based compounds (Bayramoğlu et al., 2003; Genç et al., 2002, 2003; Kyzas and Deliyanni, 2013; Tabakci and Yilmaz, 2008; Yang et al., 1999) as adsorbents, as presented in Table 3.

Figure 9.

Adsorption proﬁle of Hg(II) on 20 mg SMC 0.5 in relation to the concentration at pH 2.0 and 25°C.

Table 3.

Some selected adsorption capacity reports for Hg(II) with different adsorbents.

Adsorbent	q_m (mg g⁻¹)	pHTemp. (°C)	References
Chitosan immobilized reactive yellow 2 dye	39.60	pH = 5.520°C	Bayramoğlu et al. (2003)
Procion Green H-4G immobilized pHEMA/chitosan	48.10	pH = 5.520°C	Genç et al. (2003)
Procion brown MX 5BR immobilized pHEMA/chitosan)	68.20	pH = 520°C	Genç et al. (2002)
Chitosan-linked calix[4]arene (C[4]BCP)	74.22	pH = 1.525°C	Tabakci and Yilmaz (2008)
Azacrown ether chitosan derivatives (CCAE-I, CCAE-II)	84.30	pH = 5.520°C	Yang et al. (1999)
Chitosan-glutaraldehyde (CS-GLA)	145	pH = 525°C	Kyzas and Deliyanni (2013)
Chitosan-glutaraldehyde/Fe₃O₄ (CSm-GLA/Fe₃O₄)	152	pH = 525°C	Kyzas and Deliyanni (2013)
Sulfone-modified chitosan (SMC)/5	122.47	pH = 225°C	Our study

It can also be noticed from Figure 9 that there is a minimal decrease in the uptake capacity of the SMC/5 derivative for Hg(II) after saturation. Such an observation is displayed due to the saturation of the binding sites of SMC/5 with HgCl₄⁻ species, particularly at the highest concentration of Hg(II): 150 mg l⁻¹. Thus, an insignificant impact of concentration might be noted in the maximum uptake capacity of SMC derivatives for Hg(II) after this saturation process. The stability of the SMC/5 derivative has been verified over three cycles, yielding nearly the same adsorption capacity due to its excellent stability for reuse with complete efficiency.

Adsorption isotherm models

The study of adsorption isotherm models plays an important role in predicting the analysis of results. Isotherms can be described by both the Langmuir and Freundlich adsorption models (Ho and McKay, 1999; Mckay, 1984). Experimental data are fitted well by the Langmuir equation, as illustrated in Figure 10.

Figure 10.

Langmuir adsorption isotherm model of Hg(II) adsorption on 20 mg SMC/5 at pH 2.0 and 25°C. Adsorption experiments were obtained at different concentrations (1–150 mg l⁻¹) of Hg(II) under batch conditions.

The uniformity of non-interacting surface area sites is measured by the Langmuir isotherm model. The Langmuir classical adsorption isotherm is expressed as follows (Langmuir, 1917)

C_{e} / q_{e} = (C_{e} / Q_{o}) + 1 / Q_{o} b

(2)where C_e is the concentration of metal ion in solution at equilibrium (mg ml⁻¹) and q_e represents the amount of metal ion per gram of the adsorbent at equilibrium (mg g⁻¹). The symbols Q_o and b refer to the Langmuir constants for SMC/5 and are related to the maximum Hg(II) adsorption capacity (mg g⁻¹) and affinity parameter (l mg⁻¹), respectively. Langmuir constants Q_o and b can be calculated from a linear plot of C_e/q_e against C_e with a slope and intercept equal to 1/Q_o and 1/Q_ob, respectively. Moreover, the essential characteristics of the Langmuir adsorption isotherm model can be obtained in terms of a dimensionless constant separation factor or equilibrium parameter, R_L, which is deﬁned as follows

R_{L} = 1 / (1 + b C_{o})

(3)where b is the Langmuir constant, which describes the adsorption nature and different isotherm shapes, and C_o denotes the initial concentration of Hg(II). The value of R_L indicates the adsorption isotherm nature, and values between 0 < R_L < represent a favourable adsorption (Mckay et al., 1982). A linear plot is obtained from the Langmuir isotherm equation based on the least-squares ﬁt, conﬁrming the validity of the Langmuir adsorption isotherm model for the adsorption process as given in Figure 10. By examining the above results, a homogeneous SMC/5 surface is a monolayer during the adsorption process. Langmuir constants were calculated for Q_o and b as 119.23 mg g⁻¹ and 0.73 l mg⁻¹, respectively. The correlation coefficient (R²) obtained from the Langmuir model is found to be 0.991 for adsorption of Hg(II) on SMC/5, indicating that the data could be ﬁtted with the Langmuir model. The R_L value of Hg(II) adsorption on SMC/5 is 0.011, which increases the chance of a highly favourable adsorption process based on the Langmuir model. In addition, the Hg(II) adsorption capacity (119.23 mg g⁻¹) calculated from the Langmuir equation was in good agreement with that (122.47 mg g⁻¹) experimentally obtained from the adsorption isotherm study.

Conclusion

A new class of SMC derivatives has been synthesized in satisfactory yield by the interaction of chitosan with freshly prepared p-bromo-β-ketosulfone derivative in mildly acidic aqueous solution using a solution blending technique. SMC derivatives have been explored as surface-selective adsorbents for removal of toxic Hg(II) metal. SMC derivatives with the general formula SMC/5–20 are mainly dependent on variable loading of 2-bromo-4-bromoacetophenone (5, 10, 15, and 20%) with respect to the chitosan weight. A β-ketosulfone derivative has been freshly prepared and its chemical structure was confirmed by spectral analyses. The produced SMC/5–20 derivatives are identified and characterized using common characterization techniques. FE-SEM shows a significant change in the surface morphology as opposed to that of pure chitosan. FT-IR exhibits clear evidence for the formation of SMC/5–20 derivatives. PXRD shows obvious evidence for the strong interaction occurring between chitosan and its corresponding β-ketosulfones. SMC/5–20 derivatives also decrease the thermal stability of pure chitosan and act as catalysts for more rapid thermal degradation. Furthermore, inductively coupled plasma optical emission spectrometry has been utilized as an effective tool for the study of the surface selectivity of SMC/5–20 derivatives towards different metal ions. These ions include Hg(II), Pb(II), Ni(II), Al(III), Sr(II), Cr(III), Fe(III), Zn(II), and Mn(II). The SMC/5 derivative exhibits the highest adsorption efficiency, with the maximum quantity adsorbed at pH= 2. The adsorption capacity of SMC/5 for Hg(II) is 122.47 mg g⁻¹, and its adsorption isotherm is in agreement with the Langmuir adsorption isotherm.

Footnotes

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

References

Ahmed

(2008) Alumina physically loaded by thiosemicarbazide for selective preconcentration of mercury(II) ion from natural water samples. Journal of Hazardous Materials 156: 521–529.

Akinobu

Yamauchi

Sekine

(1997) Solvent extraction of copper(I) and (II) as thiocyanate complexes with tetrabutylammonium ions into chloroform and with trioctylphosphine oxide into hexane. Analytical Sciences 13: 903–911.

Babel

Kurniawan

(2003) Low-cost adsorbents for heavy metals uptake from contaminated water: A review. Journal of Hazardous Materials 97: 219–243.

Bailey

Olin

Bricka

et al . (1999) A review of potentially low-cost sorbents for heavy metals. Water Research 33: 2469–2479.

Bangyekan

Aht-Ong

Srikulkit

(2006) Preparation and properties evaluation of chitosan-coated cassava starch films. Carbohydrate Polymers 63: 61–71.

Bayramoğlu

Yalçın

Genç

et al . (2003) Dye-ligand immobilized IPNs membrane for removal heavy metal ions. In: Macromolecular symposia, pp.219–224. Wiley Online Library.

Biparva

Hadjmohammadi

(2011) Selective separation/preconcentration of silver ion in water by multiwalled carbon nanotubes microcolumn as a sorbent. Clean – Soil, Air, Water 39: 1081–1086.

Brine

Sandford

Zikakis

(1992) Advances in Chitin and Chitosan. London: Elsevier Applied Science.

Colwell

Pariser

Sinskey

(1985) Biotechnology of marine polysaccharides. In: MIT Sea Grant College Program Lecture and Seminar, 1984. Massachusetts Institute of Technology), Washington: Hemisphere Pub. Corp.; Auckland: Distribution outside the U.S., McGraw-Hill International Book Co.

10.

Crini

(2005) Recent developments in polysaccharide-based materials used as adsorbents in wastewater treatment. Progress in Polymer Science 30: 38–70.

11.

Curti

Laget

Carle

et al . (2007) Rapid synthesis of sulfone derivatives as potential anti-infectious agents. European Journal of Medicinal Chemistry 42: 880–884.

12.

Dave

Kaur

Menon

(2010) Selective solid-phase extraction of rare earth elements by the chemically modified Amberlite XAD-4 resin with azacrown ether. Reactive and Functional Polymers 70: 692–698.

13.

De Vasconcelos

Bezerril

Dantas

et al . (2007) Adsorption of bovine serum albumin on template-polymerized chitosan/poly (methacrylic acid) complexes. Langmuir 23: 7687–7694.

14.

Diniz

Volesky

(2005) Biosorption of La, Eu and Yb using sargassum biomass. Water Research 39: 239–247.

15.

Donia

Atia

Elwakeel

(2008) Selective separation of mercury(II) using magnetic chitosan resin modified with Schiff’s base derived from thiourea and glutaraldehyde. Journal of Hazardous Materials 151: 372–379.

16.

Pei

et al . (2014) Preparation, characterization and application of magnetic Fe₃O₄-CS for the adsorption of orange I from aqueous solutions. PLoS One 9: e108647.

17.

Dutta

Ravikumar

Dutta

(2002) Chitin and chitosan for versatile applications. Journal of Macromolecular Science, Part C: Polymer Reviews 42: 307–354.

18.

Elwakeel

Guibal

(2015) Selective removal of Hg(II) from aqueous solution by functionalized magnetic-macromolecular hybrid material. Chemical Engineering Journal 281: 345–359.

19.

Ene

Popescu

Stihi

(2009) Applications of proton-induced X-ray emission technique in materials and environmental science. Ovidius University Annals of Chemistry 20: 35–39.

20.

Farzana

Meenakshi

(2013) Removal of acid blue 158 from aqueous media by adsorption onto cross-linked chitosan beads. Journal of Chitin and Chitosan Science 1: 50–58.

21.

Genç

Arpa

Bayramoğlu

et al . (2002) Selective recovery of mercury by Procion Brown MX 5BR immobilized poly (hydroxyethylmethacrylate/chitosan) composite membranes. Hydrometallurgy 67: 53–62.

22.

Genç

Soysal

Bayramoğlu

et al . (2003) Procion green H-4G immobilized poly (hydroxyethylmethacrylate/chitosan) composite membranes for heavy metal removal. Journal of Hazardous Materials 97: 111–125.

23.

Gooday

(1990) The ecology of chitin degradation. In K. C. Marshall (ed.), Advances in Microbial Ecology. Springer, pp.387–430. New York: Plenum Press.

24.

Guibal

(2004) Interactions of metal ions with chitosan-based sorbents: A review. Separation and Purification Technology 38: 43–74.

25.

Guo

(2009) More power to X-rays: New developments in X-ray spectroscopy. Laser & Photonics Review 3: 591–622.

26.

Hang

Qin

Jiang

et al . (2002) Direct analysis of trace rare earth elements through nanometer-size titanium dioxide separation/concentration and fluorination assisted ETV-ICP-AES with slurry sampling. Chemical Journal of Chinese Universities 24: 1980–1983.

27.

Hershey

Keliher

(1989) Some atomic absorption hydride generation inter-element interference reduction studies utilizing ion exchange resins. Spectrochimica Acta Part B: Atomic Spectroscopy 44: 329–337.

28.

Y-S

McKay

(1999) Pseudo-second order model for sorption processes. Process Biochemistry 34: 451–465.

29.

Hussein

Abdel Rahman

Aly

(2013) New polymer syntheses part 56: Novel Friedel-Crafts polyketones containing naphthalene moiety: Synthesis, characterization and antimicrobial activity. Journal of Macromolecular Science, Part A 50: 99–109.

30.

Hussein

Abdel-Rahman

Geies

(2012) New heteroaromatic polyazomethines containing naphthyridine moieties: Synthesis, characterization, and biological screening. Journal of Applied Polymer Science 126: 2–12.

31.

Islam

Masum

Rahman

et al . (2011) Preparation of chitosan from shrimp shell and investigation of its properties. International Journal of Basic & Applied Sciences 11: 116–130.

32.

Jain

Handa

Sait

et al . (2001) Pre-concentration, separation and trace determination of lanthanum(III), cerium(III), thorium(IV) and uranium(VI) on polymer supported o-vanillinsemicarbazone. Analytica Chimica Acta 429: 237–246.

33.

Jang

Kong

Jeong

et al . (2004) Physicochemical characterization of α-chitin, β-chitin, and γ-chitin separated from natural resources. Journal of Polymer Science Part A: Polymer Chemistry 42: 3423–3432.

34.

Jankowski

Yao

Kasiura

et al . (2005) Multielement determination of heavy metals in water samples by continuous powder introduction microwave-induced plasma atomic emission spectrometry after preconcentration on activated carbon. Spectrochimica Acta Part B: Atomic Spectroscopy 60: 369–375.

35.

Jayakumar

Prabaharan

Reis

et al . (2005) Graft copolymerized chitosan – Present status and applications. Carbohydrate Polymers 62: 142–158.

36.

Jelinek

Wei

Arai

et al . (2007) Selective Eu(III) electro-reduction and subsequent separation of Eu(II) from rare earths(III) via HDEHP impregnated resin. Solvent Extraction and Ion Exchange 25: 503–513.

37.

Jeon

Höll

(2003) Chemical modification of chitosan and equilibrium study for mercury ion removal. Water Research 37: 4770–4780.

38.

Kawamura

Mitsuhashi

Tanibe

et al . (1993) Adsorption of metal ions on polyaminated highly porous chitosan chelating resin. Industrial & Engineering Chemistry Research 32: 386–386.

39.

Kim

J-S

Han

Wee

J-H

et al . (2006) Effect of polyvinyl alcohol on rare earths (Gd and Tb) separation by extraction resin. Talanta 68: 963–968.

40.

Kumar

Dutta

(2009) Preparation and characterization of N-heterocyclic chitosan derivative based gels for biomedical applications. International Journal of Biological Macromolecules 45: 330–337.

41.

Kurita

(2006) Chitin and chitosan: Functional biopolymers from marine crustaceans. Marine Biotechnology 8: 203.

42.

Kyzas

Deliyanni

(2013) Mercury(II) removal with modified magnetic chitosan adsorbents. Molecules 18: 6193–6214.

43.

Langmuir

(1917) The constitution and fundamental properties of solids and liquids. Journal of the Franklin Institute 183: 102–105.

44.

Lemos

Teixeira

LSG

Bezerra

MdA

et al . (2008) New materials for solid‐phase extraction of trace elements. Applied Spectroscopy Reviews 43: 303–334.

45.

Liang

Liu

Guo

(2005) Determination of trace rare earth elements by inductively coupled plasma atomic emission spectrometry after preconcentration with multiwalled carbon nanotubes. Spectrochimica Acta Part B: Atomic Spectroscopy 60: 125–129.

46.

McKay

(1984) The adsorption of basic dye onto silica from aqueous solution-solid diffusion model. Chemical Engineering Science 39: 129–138.

47.

McKay

Blair

Gardner

(1982) Adsorption of dyes on chitin. I. Equilibrium studies. Journal of Applied Polymer Science 27: 3043–3057.

48.

Manzoori

Abdolmohammad-Zadeh

Amjadi

(2007) Simplified cloud point extraction for the preconcentration of ultra-trace amounts of gold prior to determination by electrothermal atomic absorption spectrometry. Microchimica Acta 159: 71–78.

49.

Marwani

Albishri

Jalal

et al . (2012a) Activated carbon immobilized dithizone phase for selective adsorption and determination of gold(III). Desalination and Water Treatment 45: 128–135.

50.

Marwani

Albishri

Soliman

et al . (2012b) Selective adsorption and determination of hexavalent chromium in water samples by chemically modified activated carbon with tris (hydroxymethyl) aminomethane. Journal of Dispersion Science and Technology 33: 549–555.

51.

Mashhadizadeh

Pesteh

Talakesh

et al . (2008) Solid phase extraction of copper(II) by sorption on octadecyl silica membrane disk modified with a new Schiff base and determination with atomic absorption spectrometry. Spectrochimica Acta Part B: Atomic Spectroscopy 63: 885–888.

52.

Matsumura

Shiomori

Kawano

(1998) Selective adsorption of mercury(II) on chitosan derivatives from hydrochloric acid. Analytical Sciences 14: 687–690.

53.

Montero Alvarez

Estévez Alvarez

Padilla Alvarez

(2007) Heavy metal analysis of rainwaters: A comparison of TXRF and ASV analytical capabilities. Journal of Radioanalytical and Nuclear Chemistry 273: 427–433.

54.

Mourya

Inamdar

(2008) Chitosan-modifications and applications: Opportunities galore. Reactive and Functional Polymers 68: 1013–1051.

55.

Muzzarelli

Francescangeli

Tosi

et al . (2004) Susceptibility of dibutyryl chitin and regenerated chitin fibres to deacylation and depolymerization by lipases. Carbohydrate Polymers 56: 137–146.

56.

Muzzarelli

(1973) Natural Chelating Polymers; Alginic Acid, Chitin and Chitosan. Oxford, New York: Pergamon Press.

57.

Ogawa

Yui

Okuyama

(2004) Three D structures of chitosan. International Journal of Biological Macromolecules 34: 1–8.

58.

Park

Côté

et al . (2006) Exceptional chemical and thermal stability of zeolitic imidazolate frameworks. Proceedings of the National Academy of Sciences 103: 10186–10191.

59.

Pasinli

Eroğlu

Shahwan

(2005) Preconcentration and atomic spectrometric determination of rare earth elements (REEs) in natural water samples by inductively coupled plasma atomic emission spectrometry. Analytica Chimica Acta 547: 42–49.

60.

Rauf

Hussain

Hasany

(1993) Adsorption of europium on manganese dioxide from binary mixtures of aqueous sulfuric acid and methanol. Separation Science and Technology 28: 2237–2245.

61.

Ray

Pal

Anis

et al . (2010) Development and characterization of chitosan-based polymeric hydrogel membranes. Designed Monomers and Polymers 13: 193–206.

62.

Souza

Lemos

Oliveira

(2011) A method for Ca, Fe, Ga, Na, Si and Zn determination in alumina by inductively coupled plasma optical emission spectrometry after aluminum precipitation. Spectrochimica Acta Part B: Atomic Spectroscopy 66: 383–388.

63.

Synowiecki

Al-Khateeb

(2003) Production, properties, and some new applications of chitin and its derivatives. Critical Reviews in Food Science and Nutrition 43: 145–171.

64.

Tabakci

Yilmaz

(2008) Synthesis of a chitosan-linked calix [4] arene chelating polymer and its sorption ability toward heavy metals and dichromate anions. Bioresource Technology 99: 6642–6645.

65.

Varma

Deshpande

Kennedy

(2004) Metal complexation by chitosan and its derivatives: A review. Carbohydrate Polymers 55: 77–93.

66.

Viswanathan

Meenakshi

(2009) Enhanced and selective fluoride sorption on Ce(III) encapsulated chitosan polymeric matrix. Journal of Applied Polymer Science 112: 1114–1121.

67.

Yang

Wang

Tang

(1999) Preparation and adsorption properties of metal ions of crosslinked chitosan azacrown ethers. Journal of Applied Polymer Science 74: 3053–3058.

68.

Zhang

Wei

Kumagai

(2007) Separation of minor actinides and rare earths from a simulated high activity liquid waste by two macroporous silica-based polymeric composites. Separation Science and Technology 42: 2235–2253.

69.

Zhang

Chang

Zhai

et al . (2008) Selective solid phase extraction of trace Sc(III) from environmental samples using silica gel modified with 4-(2-morinyldiazenyl)-N-(3-(trimethylsilyl) propyl) benzamide. Analytica Chimica Acta 629: 84–91.

70.

Zhang

Haga

Sekiguchi

et al . (2000) Structure of insect chitin isolated from beetle larva cuticle and silkworm (Bombyx mori) pupa exuvia. International Journal of Biological Macromolecules 27: 99–105.

Sulfone-modified chitosan as selective adsorbent for the extraction of toxic Hg(II) metal ions

Abstract

Keywords

Introduction

Experiment

Chemicals and reagents

Preparation of the new solid-phase extractor

Preparation of β-ketosulfone

Preparation of SMC/5–20 derivatives

Adsorption method procedure

Instrumentation

Results and discussion

Preparation of SMC/5–20 derivatives and their physical properties

Surface selectivity study

Effect of pH

Determination of adsorption capacity

Adsorption isotherm models

Conclusion

Footnotes

Declaration of Conflicting Interests

Funding

References