One-pot synthesis of trifunctional chitosan-EDTA-β-cyclodextrin polymer for simultaneous removal of metals and organic micropollutants

The global contamination of water resources with inorganic and organic micropollutants, such as metals and pharmaceuticals, poses a critical threat to the environment and human health. Herein, we report on a bio-derived chitosan-EDTA-β-cyclodextrin (CS-ED-CD) trifunctional adsorbent fabricated via a facile and green one-pot synthesis method using EDTA as a cross-linker, for the adsorption of toxic metals and organic micropollutants from wastewater. In this system, chitosan chain is considered as the backbone, and the immobilized cyclodextrin cavities capture the organic compounds via host-guest inclusion complexation, while EDTA-groups complex metals. The thoroughly characterized CS-ED-CD was employed for batch adsorption experiments. The adsorbent displayed a monolayer adsorption capacity of 0.803, 1.258 mmol g−1 for Pb(II) and Cd(II) respectively, while a heterogeneous sorption capacity of 0.177, 0.142, 0.203, 0.149 mmol g−1 for bisphenol-S, ciprofloxacin, procaine, and imipramine, respectively. The adsorption mechanism was verified by FT-IR and elemental mapping. Importantly, the adsorbent perform is effective in the simultaneous removal of metals and organic pollutants at environmentally relevant concentrations. All these findings demonstrate the promise of CS-ED-CD for practical applications in the treatment of micropollutants. This work adds a new insight to design and preparation of efficient trifunctional adsorbents from sustainable materials for water purification.

could be attributed to the new stretching peak of -NH 2 at about 3200 cm −1 that overlapped with the -OH group 33 . Moreover, the new peak at 1552 cm −1 could be assigned to the bending vibration of -N-H-group 34 , confirming the successful amination of β-CD. Finally, the spectrum of CS-ED-CD exhibited -OH stretching band at around 3260 cm −1 , aliphatic C-H stretching near 2914 cm −1 , C-C/C-O stretching at 1137 cm −1 , C-O-C stretching at 1016 cm −1 , and R-1,4-bond skeleton vibration of β-CD at 931 cm −1 , which are consistent with the characteristic peaks of β-CD 2,35 . From the CS-ED-CD spectrum, C-H bonds in -CH 2 (v = 2914 cm −1 ) and -CH 3 (v = 2875 cm −1 ), asymmetric vibrations of C-O in the oxygen bridge at 1149 cm −1 , skeletal stretching of C-O-C at 1092 and 1040 cm −1 are features of the saccharine structure of chitosan 36 . More significantly, two new vibration peaks at 1616 and 1722 cm −1 in the CS-ED-CD spectrum could be ascribed to the carbonyl groups of amides formed and carboxylic groups introduced, respectively 37, 38 . Therefore, all these confirmed that CS-ED-CD comprised of a copolymer with tri-functional structures of chitosan, EDTA, and β-CD moieties.
The results for the elemental analysis are summarized in Table S2. The evident difference of nitrogen content between β-CD and amino-β-CD, further confirmed the successful introduction of amine group on β-CD. The molar amount of -NH 2 group on amino-β-CD was calculated to be 2.843 mmol g −1 , in the basis of its nitrogen content (3.98 wt.%). The portions of the tri-functional components in CS-ED-CD polymer were estimated based on the difference of N, C, and H contents between CS-ED-CD polymer and its monomers (chitosan, EDTA, and amino-β-CD). As shown in Table S2, CS-ED-CD has the following composition: 20.75% of chitosan, 59.73% of EDTA, and 19.52% of amino-β-CD. The molar amounts of total EDTA and total amino-β-CD groups in CS-ED-CD polymer were further determined to be 2.046 mmol g −1 and 0.162 mmol g −1 , respectively. However, a part of carboxyl functionalities on EDTA were covalently bonded to chitosan or amino-β-CD via amide bonds, thus they may not participate in the adsorption of metal or organic molecules. Moreover, the cross-linking process will also have an impact on the activity of CD cavities. Hence the activities of EDTA and CD cavities on the adsorbent were further quantified by conductometric-potentiometric titration and photometric titration methods 39 respectively. Conductometric-potentiometric titration has been widely used to determine the amounts of weak acids on polysaccharides 40,41 . As a typical procedure, 8 mg of CS-ED-CD was dispersed in 30 mL of deionized water, followed by adjusting the pH of the solution to ~3 using 0.1 M HCl. Under gentle stirring, the solution was titrated with 0.05 mM NaOH with the simultaneous measurement of conductivity and pH, and the titration curve is shown in Fig. 2b. The three regions from left to right are related to the neutralization of strong acid, neutralization of weak acid, and the addition of excessive base. Based on the titrated amount of NaOH in the second region, the carboxyl amount on CS-ED-CD was determined to be approximately 5.44 mmol g −1 . By assuming four carboxyl groups on one active EDTA molecule, the molar amount of active EDTA moieties on the adsorbent was estimated to be 1.36 mmol g −1 , which is lower than the total EDTA content determined from elemental analyses (2.046 mmol g −1 ). This could be attributed to the fact that some of EDTA groups participate as cross-linkers between the polysaccharides 28 . The amounts of active β-CD cavities were quantified by photometric titration using alkaline phenolphthalein as indicator 28,39 : the phenolphthalein molecule could insert into the active β-CD cavities, reducing the color and UV absorbency. The absorbency of phenolphthalein displayed a negative correlation with the weight of β-CD. As shown in Fig. 2c, the weight of active β-CD in 20 mg CS-ED-CD was estimated to be 3.34 mg, based on the absorbency at 548 nm (0.896 a.u.) and the calibration curve. Thus, the amount of active β-CD cavities on CS-ED-CD was calculated to be 0.147 mmol g −1 , which is in agreement with the total β-CD content (0.162 mmol g −1 ) obtained from elemental analyses. This indicates that the cross-linking did not significantly affect the activity of CD cavities. The amounts of active functional groups obtained were correlated with the adsorption capacities of metals and organic pollutants, and this will be discussed in isotherms section.
SEM images were acquired to elucidate the microstructure and morphologies of the freeze-dried CS-ED-CD composite polymer (Fig. 3). A thin polymer layer with pores was observed on the surface (Fig. 3a,b), which is related to the collapse of surface pores during the freeze-drying process. The cross-sectional morphologies (Fig. 3c,d) possessed a continuous and porous structure, with pore sizes ranging from 20 to 200 μm. The pores were produced from the ice crystal formation, similar to other natural macromolecular hydrogel structures 42,43 . The freeze-dried hydrogel was very light such that it could be supported on the stamens of a lilium flower (Fig. 3e). The multipoint BET surface area, average pore diameter and DFT cumulative pore volume of CS-ED-CD were examined by BET measurements and the results are presented in Fig. 3f. The CS-ED-CD material has a similar specific surface area and pore volume to the β-CD polymer modified electrospun polyester (PET/CDP) nanofibers reported previously 44 . The porosity measurements are inconsistent with the porous structure observed in SEM, due to the fact that BET measurements determine the pores with diameters less than 250 nm, while the pore sizes in SEM are at µm level. Like most other biopolymer, the specific surface area and porosity of CS-ED-CD were not significantly higher, but this does not affect the removal efficiency toward pollutants, since the removal mechanisms are mainly related to the functional groups on the biopolymers 44 .
The ζ-potential of the polymer was measured at different pHs and the results are shown in Fig. 4a. The isoelectric point of CS-ED-CD was approximately 3.8, which is lower than those of pristine chitosan (7.5) 45 and EPI-cross-linked β-CD (4.42) 28,46 . This could be a result of the introduction of carboxylate groups of EDTA on the surface of CS-ED-CD polymer. The stability of CS-ED-CD polymer was evaluated by thermal analyses (Fig. 4b). Similar to our previous reported EDTA-CD, three thermal transitions at 60-120, 150-270, and 270-1000 °C were observed in the TGA curve of CS-ED-CD, which corresponded to water loss, EDTA decomposition, and the decomposition of polysaccharides (chitosan and CD), respectively 24,28 . The temperatures of water loss and polysaccharide decomposition of CS-ED-CD were slightly higher than those of EDTA-CD, due to the fact that chitosan owns better water-retaining and heat resistance properties than β-CD. Moreover, these three pyrolysis processes were more clearly presented in the DTG curve described by the three peaks at 80.5, 224.5, and 293.5 °C.

Effect of pH.
It is well known that the adsorption of pollutants from water are dependent on the solution pH, which controls the surface charge of the adsorbents as well as the ionization degree of the pollutants 24 . Alkaline solutions were not tested for metal to avoid the formation of metal hydroxides (Visual MINTEQ ver. 3.0). Figure 5 and Fig. S1 show the effect of pH on the removal of metals and organic pollutants by CS-ED-CD and other controlled adsorbents. Resembling that of CS-EDTA 45 , the ζ-potential of CS-ED-CD decreased with increasing pH and it possessed a relatively low isoelectric point of 3.8 (Fig. 4a). Thus at pH < 3.8, the surface of CS-ED-CD was positively charged, repelling the metal ions and cationic organic molecules. With increasing pH, the decrease in the surface potential reduced the electrostatic repulsion and enhanced the electrostatic attraction, resulting in the rise of the removal efficiency. At pH above 3.8, the surface of CS-ED-CD became negatively charged and favored the adsorption. It is important to note that CS-ED-CD showed excellent adsorption efficiency of heavy metals, in stark contrast to EPI-CD, confirming that EDTA functional groups not only act as cross-linkers but also as adsorption sites for metal ions. The adsorption efficiency of heavy metals by CS-ED-CD was slightly lower than that of CS-EDTA, and this may be attributed to the higher EDTA amount on CS-EDTA compared to CS-ED-CD 38 . However, CS-ED-CD displayed much better adsorption performance than CS-EDTA for organic pollutants. This could be ascribed to the successful grafting of CD moieties on the polymer chains. Moreover, CS-ED-CD has substantially higher adsorption efficiency for organic pollutants than EPI-CD at pH range of 3-8 due to two reasons: (1) the electrostatic interactions between EDTA-groups and cationic BPS promoted the adsorption, and (2) probably more importantly, the EDTA-functionalization has endowed the nonpolar CD cavities more polar property and that favors inclusion interaction with cationic organic molecules 47 . Notably, the as-prepared CS-ED-CD also showed better removal efficiency than EDTA-CD for both metals and organic pollutants, attributed to the introduction of chitosan, which has been widely used in the adsorption of metals, dyes, and pharmaceutical pollutants 20,24 . The effect of pH on the adsorption of CIP by CS-ED-CD was different from other organic pollutants due to its zwitterionic behavior (Fig. S1b). The CIP removal efficiency increased with pH and reached a plateau at pH 4 to 6, and then decreased with increasing pH. This is because pH affects not only the surface charge of the adsorbent but also the speciation of CIP, which has two pK a values (pK a1 6.1; pK a2 8.7), possessing positive charges at pH < 6.1 and negative charges at pH > 8.7 48 . Thus when the solution pH exceeded 6.1, the CIP was zwitterionic or anionic, thereby reducing the interaction with negatively charged CS-ED-CD adsorbent 49 .
Adsorption kinetics. The effect of contact time on the uptake of each pollutant by CS-ED-CD is presented in Fig. 6 and the UV-vis spectra of four organic pollutants at varying contact time are shown in Fig. S2. In general, the adsorption rates were found to be rapid, attaining 35-75% of adsorption equilibrium uptake within the first 5 min, approaching an equilibrium after 60 min for metals and 180 min for organic pollutants, respectively. Thus, an excessive contact time of 360 min was chosen for the subsequent adsorption experiments. Moreover, for the purpose of investigating the kinetic mechanism of the adsorption process, pseudo-second-order model was applied as follows 50 .  where q t and q e (mg g −1 ) are the sorption capacities at time t and at equilibrium, respectively, whereas k (g mg −1 min −1 ) is the rate constant. As shown in Fig. S2, the pseudo-second-order model gave the perfect fit to the kinetic experimental data of CS-ED-CD toward both metals and organic pollutants. Accordingly, the kinetic parameters and correlation coefficient R 2 values were determined by linear regressions and presented in Table 1. Both the R 2 values greater than 0.996 and the excellent agreement between the calculated q e (q e,cal ) and experimental q e (q e,exp ), clearly indicated that the pseudo-second-order model can describe the sorption kinetics of the process. Interestingly, the metals displayed faster kinetics (higher k values, Table 1) than the organic compounds, probably suggesting that there are much more abundant adsorption sites for metal ions than those for organic pollutants on CS-ED-CD 9 . Pb(II) had a faster kinetic compared to Cd(II), which may be due to the smaller hydration number of Pb(II) 25 . The kinetic constants of organic pollutants followed the order of BPS > procaine > CIP > Imipramine, almost consistent with the order of their molecule sizes (Fig. S2, Table 1).

Adsorption isotherms.
To learn more about sorption characteristics of metals and organic pollutants on CS-ED-CD, two typical isotherms, i.e., Langmuir and Sips (Langmuir-Freundlich) models, were used to fit the experimental equilibrium data. The classical Langmuir isotherm, which is based on the assumption of a monolayer adsorption on a homogeneous adsorbent surface with finite and equal affinity sorption sites toward adsorbate 50 , is expressed as follows.
The Sips model, which is a combination of the Langmuir and Freundlich models and takes heterogeneity into consideration 28 , is expressed as follows. where q e (mmol g −1 ) and C e (mmol L −1 ) are the adsorption capacity and equilibrium concentration of the adsorbate respectively, while q m (mmol g −1 ), K L /K S (L mmol −1 ), and n s are the maximum sorption capacity, the energy constant, and the heterogeneity factor attained from nonlinear fitting of experimental data, respectively. The Langmuir and Sips fits are shown in Fig. 7a,b, and the regression parameters for the isotherm models for all pollutants are summarized in Table 2.
It is observed that metals (Pb and Cd) uptake onto CS-ED-CD could be better described by Langmuir model, displaying a higher correlation coefficient R 2 values and better curve fitting to experimental data (Fig. 7a) compared to the Sips model. Besides, the calculated q m values determined from the Langmuir model were closer to the   Table 2), suggesting a homogeneous distribution of active adsorption sites (EDTA-groups) for metals on CS-ED-CD 51 . In the case of organic pollutants uptake, conversely, the Sips model gave a much better fit to the experimental data than the Langmuir model (Fig. 7b). Moreover, both the higher R 2 values and the between agreement between the experimental and calculated q m values obtained by Sips model, indicated heterogeneous active sites (CD cavities and EDTA-groups) for organic pollutants on the adsorbent 28 . In addition, the resulting heterogeneity exponent n S values of organic pollutants were not equal to unity confirming the heterogeneous adsorption 38 . The higher adsorption affinity K L /K S values of organic pollutants compared to metals revealed that CS-ED-CD appeared to display higher affinity toward organic pollutants 16 .
Remarkably, the maximum sorption capacities (Table 2) corresponded to the capture of 0.590 Pb(II) ion and 0.925 Cd(II) ion per active EDTA group in the adsorbent, while for organic compounds corresponded to the capture of 1.200 BPS, 0.966 CIP, 1.381 procaine, and 1.014 imipramine molecule per active CD cavity, indicating the accessibility of the functional groups in CS-ED-CD 51 . The capture of organic compound molecules per CD group ≥ 1 presumably suggested that chitosan and EDTA groups were also involved in the uptake of organic compounds 2,52 . This behaviour could also be seen in Fig. 5b that about 15% BPS could be removed by CS-EDTA. The results were consistent with the heterogeneous adsorption of organic compound predicted by Sips model.

Adsorption mechanisms. The elemental distribution for CS-ED-CD after simultaneous adsorption of
Cd(II) and BPS is presented in Fig. 8. The colored elemental signal spots depict that the sulfur and cadmium were distributed over the whole surface of CS-ED-CD, indicating the successful load of Cd(II) and BPS (sulphur is from BPS) and the well-distributed adsorption sites on CS-ED-CD. Moreover, the elemental mapping clearly shows the higher amount of Cd than that of S on the adsorbent, which is in good agreement with the maximum adsorption capacity results obtained from the isotherms. Importantly, it is noticed that the distribution of sulphur (BPS) coincided with the signal spots of carbon and nitrogen, indicating the affinity between BPS and amino-β-CD (β-CD-(NHCH 2 CH 2 NH 2 ) 1.72 ) groups. The correspondence between Cd(II) and oxygen revealed the roles of -COOH in the metal coordination. To gain more insights into the adsorption mechanism, the FT-IR spectra of CS-ED-CD before and after the adsorption of Cd(II) and/or BPS, were compared in Fig. S3. In the case of BPS and BPS-Cd(II) adsorption systems, it is clearly evident that the -OH bond at 3260 cm −1 appeared as a wide, broad peak in the range from 3407 to 3241 cm −1 , which could be ascribed to the introduction of phenolic hydroxyl group of BPS. Similar behavior has also been reported for BPA adsorption 53 . Moreover, the characteristic peaks of BPS, such as aromatic ring stretch at 1583 cm −1 and two peaks at 1134 and 1099 cm −1 corresponding to sulfonyl groups, were observed in the spectra of the BPS and BPS-Cd(II) adsorptive adducts, indicating that BPS formed host-guest complex with the CD 54 . Similar FT-IR results for the CD/organic molecules were previously reported 28,55 . After Cd(II) adsorption, the peak at 1616 cm −1 was bathochromically shifted to 1579 cm −1 as well as the peak at 1722 cm −1 , which was apparently weakened, reflecting the interaction between Cd(II) ion and   EDTA carboxylate groups. Similar behavior was observed in our previous study for Cd (II) and Pb(II) adsorption onto ethylene glycol-bis(2-aminoethylether)-N,N,N′,N′-tetraacetic acid (EGTA) modified chitosan 25 . Besides, both these varieties were also found for only BPS adsorption, revealing that EDTA groups were also involved in the cationic organic molecule adsorption, consistent with the adsorption isotherm study. On the basis of isotherms, SEM elemental mapping, and FT-IR studies, a possible adsorption mechanism for the removal of inorganic and organic pollutants is proposed in Fig. 9. The superior sorption onto CS-ED-CD could be ascribed to the following aspects. (1) The EDTA moieties act not only as cross-linkers but also as  sorption sites for metal ions complexation. EDTA forms intra-or inter-molecular cross-links with chitosan chains to produce hydrogel. EDTA also interacts with chitosan and amino-CD to immobilize CD cavities on chitosan backbones. The EDTA chelating property endows the polymer with preferential metal sorption ability 9 . (2) The immobilized CD cavities sequester the target organic compound molecules through host-guest inclusion interaction. As shown in Fig. S4, the molecular sizes of the most studied organic pollutants are suitable for β-CD cavity with inner diameter of 0.78 nm 17 . Noticeably, the full size of imipramine (0.94 × 0.97 × 0.58 nm) is somewhat larger than the inner diameter of β-CD cavity. Thus, it is possible that the aromatic rings of imipramine molecules (Fig. S4d) were embedded into CD cavities and the rest branched parts remained outside. This could also explain why imipramine displayed relatively lower sorption capacity than other compounds. (3) The negative-charged COO − groups (from EDTA) within polymer matrix capture the cationic organic pollutant molecules via electrostatic interaction.
Regeneration. The reusability is a significant feature of an advanced adsorbent for feasible and practical application. In this study, Cd(II)-loaded CS-ED-CD was regenerated using 1 M HNO 3 according to the previous regeneration approaches for metal loaded EDTA-modified adsorbents 28,38 . In the case of organic compound-loaded CS-ED-CD, on account of its main sorption mechanism of host-guest inclusion interaction, organic solvents such as ethanol was chosen for organic pollutant desorption 56 . Moreover, EDTA-groups partly participated in the cationic organic compound adsorption, thus 5% HCl in ethanol solution (v/v) was further applied for the regeneration of BPS-loaded CS-ED-CD 28 . Figure 10 shows the regeneration of the adsorbent over five cycles. Evidently, Cd(II)-loaded CS-ED-CD could be successfully regenerated using 1 M HNO 3 , and the regeneration efficiency was 99.67% and 99.25% in the first two cycles and 92.62% and 90.48% in the fourth and fifth cycles, respectively. This also indicated its resistance to extreme pH. It is observed that the BPS loaded adsorbent could not be effectively regenerated by absolute ethanol (≤70%), however, it could be successfully accomplished using 5% HCl in ethanol solution. It was found that the regeneration efficiency was 96.88% and 96.21% in the first two cycles and decreased slightly to 88.36% and 86.24% at the fourth and fifth cycles, respectively. The results revealed the stability and recyclability of CS-ED-CD in practical applications.
Evaluating the performance of CS-ED-CD in mixture of pollutants at environmentally (μg L −1 ) relevant concentrations. The simultaneous removal of inorganic and organic pollutants was also investigated at environmentally relevant (μg L −1 ) concentrations and in a mixture solution of Cd(II) at 100 μg L −1 and CIP at 50 μg L −1 , the concentration which many inorganic and organic micropollutants mostly present in wastewater 57 and drinking water resources 1 . As shown in Fig. 11, CS-ED-CD performed equal uptake of Cd(II) but with a much larger uptake of CIP than CS-EDTA, whereas both the pollutants showed overwhelming uptake by CS-ED-CD over EPI-CD. These demonstrate that CS-ED-CD could effectively and simultaneously remove inorganic and polar organic pollutants at environmentally relevant concentrations, suggesting that CS-ED-CD serves as a promising adsorbent for practical removal of a wide range of micropollutants from aqueous solutions.

Conclusions
A novel and environmentally friendly trifunctional adsorbent, CS-ED-CD, was fabricated via a facile one-pot synthesis by using EDTA-groups as cross-linkers. The adsorbent exhibited high absorptivity toward Pb(II), Cd(II), BPS, CIP, procaine, and imipramine with maximum adsorption capacities of 0.803, 1.258, 0.177, 0.142, 0.203, 0.149 mmol g −1 , respectively. This study, based on the adsorption behavior and characterization results, provides evidence that each component of CS-ED-CD has a crucial role in its functioning: chitosan is the backbone of this novel polymer; importantly, the EDTA-groups play the role not only as cross-linkers but also as complexation sites for metal ions; on the other hand, the adsorption mechanism of organic pollutants onto CS-ED-CD is primarily the host-guest inclusion of CD cavities. Additionally, the adsorbent performed an efficient and simultaneous removal of inorganic and organic pollutants at environmental concentrations. In summary, this work adds a new insight to design and preparation of a trifunctional cyclodextrin-based polymer adsorbent, which can remove targeted inorganic and organic micropollutants from aqueous solution simultaneously. It is believed that this green cross-linking technology can be extended to prepare a wide variety of trifunctional materials for various applications.

Materials and Methods
Materials. All reagents were purchased from Sigma-Aldrich (Finland/Canada) and were used without further purification. β-cyclodextrin (β-CD) was 97+% pure, and chitosan flakes 85+% deacetylated had a molecular weight ranging from 190 000 to 375 000 g mol −1 and a viscosity of 200-2000 MPa. All other chemicals were analytical grade. All aqueous solutions of pollutants were prepared using 18 MΩ deionized water. The chemical properties of model organic compounds are presented in Table S3. Adjustment of pH was conducted using 0.1 M NaOH/HNO 3 for metals while 0.1 M NaOH/HCl for organic compounds, respectively.

Synthesis of amino-β-cyclodextrin (amino-β-CD).
Prior to cross-linking, β-CD was functionalized with amino group via two steps of tosylation and amination, by reference to the previous literatures 23,58 . Briefly

Synthesis of Chitosan-EDTA-β-cyclodextrin (CS-ED-CD).
The as-prepared amino-β-CD (0.5 g) and 1.0 g chitosan were dissolved in 20 mL of 10% (v/v) acetic acid solution and then diluted four times with methanol. Subsequently, as a cross-linking agent, 6.0 g of EDTA dianhydride synthesized according to Repo et al. 59 was suspended in 5 mL methanol, which was added dropwise to the solution. The mixture was stirred at 500 rpm for about 24 h at room temperature. The resulted yellowish gel was filtered and mixed with ethanol under continuous stirring for an additional 5 h. The residual EDTA was removed by washing the gel with an excess of 0.1 M NaOH. Then the product was repeatedly rinsed with deionized water, 0.1 M HCl, and deionized water. Finally, the swollen hydrogel was rapidly frozen in liquid nitrogen and dried in a freeze-dryer (FreeZone, Labconco) under a high vacuum at −42 °C for 72 h and stored in a desiccator until use.

Synthesis of Chitosan-EDTA (CS-EDTA), EDTA-cross-linked β-cyclodextrin (EDTA-CD), and
Epichlorohydrin β-cyclodextrin (EPI-CD). As a blank control, an insoluble EDTA-cross-linked chitosan (CS-EDTA) and an EDTA-cross-linked β-cyclodextrin (EDTA-CD) were synthesized according to our previous reports 28,38 . Meanwhile, for comparison purpose, an epichlorohydrin cross-linked β-CD (EPI-CD), which is the most widely studied β-CD polymer that has been commercialized for water treatment 60 , was also synthesized according to the typical procedures 16 .  pore volume of the synthesized CS-ED-CD were examined at 77.35 K using Brunauer-Emmett-Teller (BET) surface area analyzer (Tristar ® II Plus) with nitrogen adsorption isotherms measured in the range of relative pressures from 0.0 to 1.0. Elemental Mapping was performed during the SEM examination (acceleration voltage 20.0 kV) by Thermo Scientific Ultra Dry SDD Energy-dispersive X-ray spectroscopy (EDS). The ζ-potential of the adsorbent was measured using a Zetasizer Nano ZEN3500 (Malver, U.K.). Thermogravimetric analysis (TGA) and derivative thermogravimetric (DTG) tests were conducted using a NETZSCH TG 209F1 (Germany) at a heating rate of 10 °C min −1 under a nitrogen atmosphere from 25 °C to 1000 °C. Adsorption Experiments. All adsorption experiments were conducted by mixing 10 mg of adsorbents with 10 mL of pollutant solutions. The effect of pH was investigated at an initial concentration of 50 mg L −1 in the pH range of 1-6 for metals and pH of 2-10 for organic pollutants, respectively. Adsorption kinetics were performed at time intervals ranging between 5 and 300 min at metal concentrations of 50 mg L −1 and organic pollutant concentrations of 25 mg L −1 , respectively. After each experiment, the adsorbents were separated from solutions using a 0.45 μm polypropylene syringe filter. The concentrations of initial organic pollutants as well as in the filtrates were determined by UV-vis spectrometry (PerkinElmer Lambda 45, U.S.A.) at their maximum absorbance (Table S3). After dilution with 5% HNO 3 , the metal concentrations before and after adsorption were analyzed by an inductively coupled plasma optical atomic emission spectrometry (ICP-OES) Model Icap 6300 instrument (Thermo Electron Corporation, U.S.A.).
The removal efficiency of pollutant (in %) by the adsorbent was calculated using the following equation: where R% is the removal efficiency, whereas C 0 and C t are the initial and residual concentrations (mmol L −1 ) of pollutants, respectively.
The adsorption capacities (mmol g −1 ) of adsorbents were calculated from the following equation: where C 0 and C t are the initial and residual concentrations (mmol L −1 ) of pollutants, respectively, whereas M (g) and V (L) are the weight of the adsorbents and the volume of the solutions, respectively.

Regeneration experiments.
To investigate the reusability of CS-ED-CD, the desorption of Cd(II) and BPS was performed as models for inorganic pollutants and organic pollutants, respectively. Firstly, 50 mg of dry CS-ED-CD adsorbent was mixed with 50 mL of 100 mg L −1 Cd(II) or 50 mL of 50 mg L −1 BPS solution for 360 min to reach saturation. Then the adsorbents were separated and regenerated by soaking them in 10 mL of 1 M HNO 3 for Cd(II), and in either 10 ml of absolute ethanol or 5% HCl in ethanol (v/v) for BPS. After 10 min soaking, the adsorbents were filtered and washed with deionized water and reconditioned for sorption in subsequent cycles.
Evaluating the performance of CS-ED-CD in mixture of pollutants at environmentally (μg L −1 ) relevant concentrations. 100 mg of the adsorbent (CS-EDTA, EPI-CD, or CS-ED-CD) was mixed with 100 mL of the diluted mixture (100 μg L −1 Cd(II) and 50 μg L −1 CIP). After a 360 min contact at room temperature, the adsorbent was separated using a 0.45 μm polypropylene syringe filter and the residual Cd(II) concentrations were analyzed by ICP-OES, as well as the CIP concentrations in filtrates were analyzed by ultra-high performance liquid chromatography (UHPLC) coupled with a Xevo TQ mass spectrometer (MS) (Waters, UK). Deuterated ciprofloxacin ( 2 H 8 ) was used as an internal standard. Samples were injected and loaded onto an Acquity UPLC BEH (Waters) C18 Column (2.1 mm × 50 mm, particle size 1.7 µm). Elution was performed with mobile phase A, containing of 0.1 vol.% formic acid in water, and mobile phase B of methanol. Flow rate was 0.5 mL min −1 . The MS was operated in multiple reaction monitoring (MRM) mode of channel ES+. The quantifier MRMs were 332.2 > 231.1 for ciprofloxacin and 340.2 > 235 for deuterated ciprofloxacin. Retention times were 3.48 for ciprofloxacin and 3.47 min for deuterated ciprofloxacin, respectively. The limit of detection for ciprofloxacin was determined as the lowest calibration concentration which has the relative standard deviation below 10%. The limit of detection for Cd(II) was calculated as three times the standard deviation of ten runs of the blank solutions according to literature 29 .