Study on Amino-functionalized Porous Carbon Materials for MB and Cr(VI) Adsorption

From the perspective of environmental protection, high removal rate, reusable and degradable, amino-functionalized porous hydrogel material P-(EA-β-CD/KHA/AC) was synthesized by introducing ethylamino cyclodextrin, humic acid, and activated carbon, using polyacrylic acid as the carrier. MB and Cr (VI) are common wastewater pollutants, thus, Such contaminants must be removed from the water. The gel materials before and after adsorption were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The removal of MB and Cr(VI) showed high adsorption capacity. At 298 K and pH 8, the adsorption capacities of P-(EA-β-CD/KHA/AC) hydrogel for MB and Cr(VI) were as high as 262.31 and 170.12 mg/g, respectively, and the removal rates were 98.96% and 70.27%, respectively. The adsorption behavior follows the pseudo-second-order kinetic equation, conforming to the Langmuir model; and through intermolecular forces, π–π conjugation, chelation, and other interactions, entropy-increasing, endothermic, and spontaneous process is formed. The regeneration and degradability experiments of P-(EA-β-CD/KHA/AC) hydrogel were conducted and its recycling performance was verified.


Introduction
Water resources are essential for survival and social development. However, organic chemicals, dyes, and heavy metals are freely discharged without treatment into water bodies, causing pollution. These contaminants also accumulate in the food chain and negatively affect organisms [1][2][3]. Among them, methylene blue (MB) is a common cationic dye [4,5]. Long-term exposure can cause symptoms, such as difficulty in breathing, burning eyes, and nausea, and in severe cases, cancer. Hexavalent chromium (Cr(VI)) is a potentially toxic and carcinogenic substance derived from human activities and leather, electroplating, and other industries [6,7]. Therefore, MB and Cr(VI) must be eliminated from the environment, soil, and aqueous solutions. Karthik Rathinam [8] prepared chitosan -lysozyme biocomposite (CLC) by glutaraldehyde crosslinking Chitosan lysozyme, Used for removal of MO and Cr (VI) in water, the adsorption quantity of 435 and 216 mg/g. Md. Masudur Rhaman [9] synthesized a new magnetic biological adsorbent (MB-JSP), using jute stick powder as raw material by in-situ co-precipitation method and used it to remove Cr (VI) from water. The adsorption quantity of 30.42 mg/g, it is consistent with Langmuir and quasi-second-order dynamics model. In addition, the removal process is very efficient and quickly separates from the aqueous solution. A. Santhana Krishna Kumar [10] prepared hexagonal boron nitride nanosheets (h-BNNSs) as a lightweight adsorbent, it can effectively remove Cr(VI), As(V), MB and AO, the maximum adsorption capacity can reach 833, 426, 415, 286 mg/g, respectively. The adsorption of Cr(VI), As(V), MB and AO followed Freundlich isothermal model and quasi-second-order kinetic model. It was found that Cr(VI), As(V), MB and AO have multi-layer chemisorption and excellent heterobinding behavior.

3
Presently, there are various water treatment methods, such as ion exchange, molecular sieve, coagulation, precipitation, and flocculation, reverse osmosis, ozone oxidation, membrane filtration, and adsorption. Among them, the adsorption method stands out due to its advantages of green environmental protection and recyclability [11][12][13][14]. Hydrogels are excellent sort of polymeric adsorbents. Compared with traditional adsorbents, polymeric adsorbents are cost effective and have simple synthesis and high removal efficiency [15][16][17][18]. Elham Jafarigol [19] used xanthan gum as a raw material to synthesize highstrength and double-network hydrogels by solution polymerization to remove heavy metal ions. Janaı´na Oliveira Gonçalves [20] used glutaraldehyde to cross-link chitosan and doped activated carbon to prepare a hydrogel material for heavy metal ion adsorption. However, these hydrogels use toxic cross-linking agents, and the gel itself is difficult to degrade. Therefore, there it is urgent to develop environmentally friendly hydrogel adsorption materials with better adsorption performance Cyclodextrin (CD) is a cyclic oligosaccharide with physical properties of external affinity and internal sparseness, which can be widely used in studying organic matter removal. There are abundant hydroxyl on the surface of cyclodextrins, which can cause reactions, such as etherification and sulfonation. [21][22][23]. Bailey Phillips [24] crosslinked β-CD via a methanesulfonic acid-mediated condensation reaction for efficient removal of dye molecules. Ícaro F.T [25] used citric acid to cross-link hydroxypropyl methylcellulose and β-CD, synthesizing a hydrogel material to remove bisphenol A, which can effectively remove pollutants under weak alkaline conditions. Activated carbon (AC) is a traditional adsorption material with a large adsorption capacity and a large specific surface area. It is an efficient dye adsorbent, but it is difficult to remove after use. Besides, secondary pollution occurs after its use, thereby fading out of people's attention [26]. In recent years, studies have found that the chemical and physical properties of AC can be changed by various methods, which can achieve the purpose of adsorption without causing secondary pollution [27][28][29][30].
Herein, green and natural cyclodextrin was used a as raw material, and EA-β-CD was obtained by introducing an ethylamine group to the sixth position carbon of the cyclodextrin molecule through etherification modification. The adsorption performance of the material is improved by modification, and simultaneously, the pore size and porosity of the material are increased. Besides, AC was introduced into the porous material. Herein, a simple and easy-to-recycle porous hydrogel material is synthesized by polymerizing acrylic acid (AA), EA-β-CD, and KHA in a solution for dye and heavy metal wastewater treatment.

Synthesis of P-(EA-β-CD/KHA/AC)
β-CD was first soaked in an aqueous solution of 2-chloroethylamine (20%) (on the weight of β-CD) and dissolved in deionized water. After thorough mixing, it was placed in a 50 °C oven and dried until the water completely evaporated. The reaction was transferred to a three-necked flask, 50 mL of 3 mol/L NaOH solution was added, and it was placed in a 70 °C water bath to condense and reflux for 4 h. After the reaction was stopped, it was precipitated in a methanol solution and dried to obtain EA-β-CD.
Furthermore, 10 mL of 1 wt% KHA and 20 mL of 15 wt% EA-β-CD were weighed and put into a 250-mL distillation flask and stirred for 0.5 h until completely mixed. Further, 10 mL of 1 wt% AC was dispersed in the above system, transferred to 50 °C water bath, and stirred well for 0.5 h. 10-mL AA with a neutralization degree of 60 wt%, MBA (10 mL, 0.8 wt%), and KPS (10 mL, 1.2 wt%) dissolved in 20 mL deionized water were added dropwise to the reaction system. The mixture was fully stirred to achieve homogeneity, and the temperature was raised to 70 °C to react until the system became fully viscous. Finally, heating was stopped, and the material was taken out and freeze-dried for 48 h to obtain the P-(EA-β-CD/KHA/AC) hydrogel material.

Characterization
The crystal structure of the samples was determined by Fourier transform infrared spectroscopy (FTIR, on Vertex 70; Bruker Co.; Germany). FTIR spectra were recorded in the spectral range of 4000-500 cm −1 . The morphology of the adsorbent was investigated using scanning electron microscopy (SEM, on S4800; Rigaku Co.; Japan) with an accelerating voltage of 20 kV. The Thermal Gravimetric Analyzer (TG, TGA-55); TA Instruments of the United States, Hitachi Company of Japan: the heating rate is 10 °C/ min, 25-600 °C. X-ray diffraction (XRD, on D8 Advance; Bruker AXS Co.; Germany) patterns were obtained through a powder diffractometer, with Cu Kα radiation at 30 KV and 20 mA. The scanning range was 5°-60° with a scanning rate of 2°/ min under normal air at a heating rate of 10 ℃/min. X-ray photoelectron spectroscopy (XPS, Thermo Fisher Scientific Co.; USA) measurements were performed in an Escalab 250Xi spectrometer to obtain information concerning the elemental variation and bonding on hydrogel before and after adsorption. The C1s peak (284.80 eV) was used to calibrate the binding energy values.

Water Absorption Performance
The water absorption rate (SR) of the P-(EA-β-CD/KHA/ AC) hydrogel material was measured under conditions of 0-300 min and pH 2-10. An accurate mass of hydrogel (W d ) was immersed in a solution of a certain pH, taken out of the solution at a predetermined time during swelling, and the surface water of the gel was absorbed by filter paper and weighed (W S ), SR was calculated as follows: In Eq. (1), Ws and Wd represent mass (g) of MB and Cr(VI) before and after water absorption, respectively.

Adsorption Performance of Methylene blue (MB) and Hexavalent Chromium (Cr(VI))
P-(EA-β-CD/KHA/AC) hydrogel of 40 mg was added to a three-necked flask along with 200 mg/L MB and Cr(VI), and the pH of the solution was adjusted to 8 and 3 with NH 3 ·H 2 O and HCl, respectively. The mixture was isothermally shaken for 310 min in a constant temperature shaking box at 298 K, 308 K, and 318 K. After taking out the centrifuge and standing for 30 min, the absorbance values of MB and Cr(VI) supernatant were measured using a visible spectrophotometer at 662 and 540 nm. The equilibrium adsorption amounts of MB and Cr(VI) after adsorption were calculated using Eq. (2), and the removal rates were determined using Eq. (3).
Here, C 0 and C e represent the initial and equilibrium concentrations of MB and Cr(VI), respectively, V (L) is the volume of MB and the Cr(VI) solution, and m (g) and Q t (mg/g) are the mass and adsorption capacity of the added hydrogel, respectively.

Cyclic Adsorption Performance
Based on the adsorption experiment in Section "Adsorption performance of methylene blue (MB) and hexavalent chromium (Cr(VI))",cyclic adsorption was conducted. The P-(EA-β-CD/KHA/AC) hydrogels after adsorbing MB and Cr(VI) were desorbed in 0.3 M HCl and C 2 H 5 OH solutions, respectively. After shaking in a constant temperature water bath for 310 min, the absorbance value of the solution was determined. Further, the P-(EA-β-CD/KHA/AC) hydrogel was washed to neutrality with deionized water, and the treated adsorbent was quantitatively weighed for five cycles. Afterward, the equilibrium adsorption capacity and removal rate were measured.

Effect of EA-β-CD, KHA and AC on Adsorption of P -(EA-β-CD /KHA/AC) Hydrogel
Figure 1a-c shows the effects of different dosage of EA-β-CD, KHA and AC on the adsorption of P-(EA-β-CD/ KHA/AC) hydrogel. With the increase of the amount of EA-β-CD, there can be adsorption between multiple sites and multiple cavities, when increasing to saturation, the adsorption capacity showed a decreasing trend as the dosage continued to increase. Therefore, the optimal dosage of EA-β-CD is 15%. Similarly, the optimal dosage of KHA and AC is 2% and 4%, respectively. Figure 2A, B show the structure and characterization test analysis of the hydrogel materials.. To study the changes in functional groups during the preparation of P-(EA-β-CD/ KHA/AC), the synthetic materials and products were characterized by infrared spectroscopy. Evidently, the -OH characteristic absorption peak of β-CD appears at 3400 cm −1 . Furthermore, a characteristic absorption peak appears at 3490 cm −1 , with a wider peak shape. Additionally, -NH-appears at 1490 cm −1 ; the peak shape becomes wider and is accompanied by a redshift phenomenon. This trend is probably because the -OH on β-CD is replaced by -NH 2 . Since the characteristic peak of C-N appears at 1350 cm −1 , it is enough to prove that the S N 1 nucleophilic substitution reaction of β-CD has occurred. P-(EA-β-CD/KHA/AC) hydrogel exhibits characteristic absorption peaks around 1740 and 1200 cm −1 . In the spectrogram of P-(EA-β-CD/KHA/AC) hydrogel material, the characteristic absorption of -NH 2 was found at 3300cm -1 , and O-H at 3680 cm -1 . This indicates that oxygen-containing functional groups, such as amide bonds and ester groups, appear in the adsorbent. It was further confirmed that esterification and acylation occurred during the synthesis, Consistent with the literature values [31,32]. As shown in Fig. 2C, raw materials β-CD、EA-β-CD, KHA and P-(EA-β-CD/KHA/AC) XRD spectrum, It is found from the XRD spectrum that β-CD and EA-β-CD has a similar skeleton structure. In the XRD spectrum of KHA, The diffraction peak of KHA is 25.78° at 2θ, and also appears on P-(EA-β-CD/KHA/AC) spectrum. It was confirmed that KHA was successfully introduced into the hydrogel structure and enough to explain P-(EA-β-CD/KHA/ AC) hydrogel material was successfully prepared. Figure 2D shows the SEM images of Figures a and b at 400 and 200 µm magnification, respectively. The surface of the adsorbent material is rough, and there are porous structures with different pore sizes. Therefore, the dye molecules and heavy metal ions can be attached, creating favorable conditions for subsequent adsorption. Figure c is an SEM image at 50 µm magnification; the surface of the material is irregular and wrinkled and presents multiple sites available for MB and Cr(VI) adsorption. Figure d shows that the cross-sectional morphological structure of the material presents a cross-linked network structure. Through the network structure, the material can further absorb water and swell in the solution environment and more adsorption sites are exposed, facilitating adsorption. Figure 2E shows the BET test spectrum of the P-(EA-β-CD/KHA/AC) hydrogel material, from BET test, the material does exist pore structure, and the specific surface area is 30.078 m 2 /g. According to SEM images, SEM images showed that the material could provide active sites for MB and Cr (VI) and adsorb them. Figure 2F shows the thermogravimetric analysis of the P-(EA-β-CD/KHA/AC) hydrogel. According to the thermogravimetric analysis of the hydrogel material, its thermal decomposition comprises mainly three steps. The initial and end decomposition temperatures are 60 °C and 480 °C, respectively, the maximum decomposition temperature rate is 400°C. The first stage of weight loss occurs at 100-200 °C, and this stage is the process in which the P-(EA-β-CD/KHA/AC) hydrogel loses bound water. At 200-300 °C, the hydroxyl groups of KHA and EA-β-CD molecules in P-(EA-β-CD/KHA/AC) dissociate from the intermolecular hydrogen bonds. The third stage of weightlessness is ~ 400°C. It has a maximum decomposition rate and mainly decomposes the molecular structure of EA-β-CD and KHA in P-(EA-β-CD/KHA/AC). The figure shows that  Figure 3 shows the swelling properties of P-(EA-β-CD/ KHA/AC) hydrogels under different pH conditions. As the alkalinity increases, the swelling of the hydrogel material increases because its structure contains abundant hydrophilic groups, such as -OH and -COOH. At pH 8, the maximum swelling capacity is observed and it is as high as 96 times. Thereafter, as the pH increases, these hydrophilic groups form hydrogen bonds and hinder the movement of water molecules, which decreases the swelling capacity. Simultaneously, these hydrophilic groups expose more adsorption sites, which are available for combination with dye molecules and metal ions. Thus, increasing its adsorption performance. Figure 4 shows the effect of different adsorption times and pH conditions on the adsorption capacities of MB and Cr(VI). When the adsorption time was 0-20 min, the adsorption capacity of the hydrogel material to remove MB and Cr(VI) increases, with a high adsorption rate and large number of vacant sites for MB and Cr(VI) binding.

Effect of Different Adsorption and pH Conditions on the Adsorption Capacity of P-(EA-β-CD/KHA/AC) Hydrogel to Remove MB and Cr(VI)
Subsequently, the active sites on the hydrogel surface are occupied by MB and Cr(VI), resulting in slow increase in the adsorption capacity, and the adsorption rate decreases until saturation occurs. The adsorption amount stabilizes and no longer increases. Figures 4c, d show the effects of different pH conditions on the adsorption capacity. When adsorbing MB, acidic conditions are not conducive to the swelling of hydrogels, adsorption sites are difficult to expose, and the adsorption capacity is low. As the pH increases the adsorption sites are exposed and the adsorption and alkalinity increase. As the alkalinity increases, the gel structure is damaged and the adsorption capacity decreases accordingly. When adsorbing chromium at pH 1-3, Cr(VI) is reduced to Cr(III) as the pH changes. With the coordination of the hydroxyl and carboxyl groups on the material surface, adsorption increases. When the pH is 3-7, the oxygen-containing functional groups on the surface of the gel material are protonated, and Cr 2 O 7 2− is absorbed by electrostatic interaction. The adsorption capacity reduces when pH > 8 due to the deprotonation of oxygen-containing functional groups on the surface of the gel. When repelled with Cr(VI), the adsorption capacity decreases.

Effect of Different Ions on Adsorption of MB and Cr (VI) by P-(EA-β-CD/KHA/AC) Hydrogel
In the wastewater environment, there will be a variety of ions coexist, and different ions, and different ions have different effects on the adsorption process. As shown in Fig. 5, the influence of Na + , K + , NO 3 -, SO 4 2on the adsorption process were studied (NaCl, KNO 3 , NaNO 3 , Na 2 SO 4 with concentration of 0.1mol/L), As can be seen from the figure, containing a small amount of Na + and K + will promote the adsorption, The reason is that Na + and K + will reduce the molecular structure of MB in the solvent, and small pores on the surface of gel material can be absorbed MB. NO3and SO 4 2have strong inhibitory effect on Cr (VI), these ions will adsorb functional groups on the surface and compete with adsorption sites of materials to inhibit the adsorption process.

Adsorption Kinetics of P-(EA-β-CD/KHA/AC) Hydrogels
Adsorption kinetics is very important for exploring adsorption mechanism. The adsorption process was fitted by referring to the kinetic equations (5), (6) and the equation of intra-particle diffusion model (7). For details, please refer to reference [33,34] Tables 1 and 2 show the data obtained by fittingcalculation. As seen from Figure 6, the correlation coefficients (R 2 )of the quasi-secondorder exceed those of the quasi-first-order correlation (R 2 ) and both exceed 0.99. It can be concluded that the adsorption process ofP-(EA-β-CD/KHA/AC) hydrogel is more in line with the quasi-second-order kineticmodel. Also, it shows that the adsorption process is mainly chemicaladsorption. The equilibrium adsorption capacity (Qe, cal) fitted under the quasi-second-orderkinetic model is more in line with the equilibrium adsorption capacity (Qe, cal)of the experimental value. From the fitting analysis of the intraparticlediffusion model, C is nonzero. Therefore, the intraparticle diffusion processis not a rate-controlling step in the adsorption process, and the wholeadsorption process is a combination of physical and chemical adsorption. Figure 7 shows the fitting diagram of the hydrogel adsorption isotherm and adsorption thermodynamics. Langmuir Eq. (8) and Freundlich Eq. (10) fittings were performed on the adsorption isotherms in Fig. 7. Combined with the theoretical calculation, the adsorption isotherm-related parameters   Table 3. Among them, the correlation coefficient (R 2 ) of Langmuir exceeds that of Freundlich. This analysis shows that the adsorption isotherm is more in line with the Langmuir model. However, Langmuir's theoretical value is closer to the experimental value. Therefore, P-(EAβ-CD/KHA/AC) hydrogels are mainly monolayer adsorption models for both MB and Cr(VI). Under the condition of a specific adsorption temperature, the theoretical analysis is conducted by thermodynamic correlation equations (Equations (11, 12, 13 and 14)), respectively, and Table 4 is calculated. Table 4 shows that the adsorption of MB and Cr(VI) on P-(EA-β-CD/KHA/AC) hydrogel is a spontaneous and endothermic process. During the adsorption process, the Chaos increases and the whole adsorption is a process of increasing entropy [35,36]. Langmuir adsorption isotherm model:

P-(EA-β-CD/KHA/AC) Hydrogel Adsorption Isotherm and Adsorption Thermodynamics
Freundlich adsorption isotherm adsorption model:   Figure 8 shows the FTIR and XRD spectra before and after adsorption. Figure 8a shows P-(EA-β-CD/KHA/AC)-MB has a strong C-N absorption peak at 1300 cm −1 , and the -NH 2 peak near 3300 cm −1 disappeared the molecular force and hydrogen bond between P-(EA-β-CD/KHA/AC) hydrogel and MB. At 900-1600 cm −1 , most of the absorption peaks of P-(EA-β-CD/KHA/AC)-MB weakened or even disappeared. This trend is due to the π-π conjugation between the MB and the adsorbent material. In the infrared spectrum of P-(EA-β-CD/KHA/AC)-Cr(VI), the characteristic absorption peak weakens around 1720 cm −1 ; this is attributed to the chelation of the carboxyl group with Cr (III) and chromate. Figure 6b shows the changes in the spectra of P-(EAβ-CD/KHA/AC) hydrogels before and after the adsorption of MB and Cr(VI). Because -OH and -NH 2 produce hydrogen bond association, intermolecular force, and electrostatic effect, some absorption peaks at 10°-20° disappear. The overall performance of the adsorbed MB is that the peak shape widens and weakens. Besides, there are multiple absorption peaks at 22.4°, 30.2°, and 49.3°. It was confirmed that the hydrogels successfully adsorbed MB. The overall performance of the adsorbed Cr(VI) shows that the peak shape becomes sharper. Additionally, new absorption peaks appear around 22.8° and 40.4°. It was further demonstrated that P-(EA-β-CD/KHA/AC) hydrogels adsorbed MB and Cr(VI).

SEM-EDS Analysis of P-(EA-β-CD/KHA/AC) Hydrogel After Adsorption
As shown in Fig. 9, SEM-EDS analysis of P-(EA-β-CD/ KHA/AC) hydrogel adsorption material before and after adsorption of MB and Cr (VI), Fig. 9a shows the SEM spectrum of the hydrogel material, Fig. 9b-f are the distribution of O, C, N, S and Cr elements after adsorption by hydrogel materials, It can be known from EDS distribution, description MB and Cr are P-(EA-β-CD/KHA/AC) hydrogel material was successfully adsorbed. Figure 10 shows the XPS spectra before and after adsorption. The characteristic peaks of S2p and Cr2p appear in the  After adsorption, a coordination bond is formed between -COOH and Cr(III); -OH and the dye molecules form intermolecular forces, -OH and Cr(III) form hydration, and -OH and the π-π conjugation of benzene rings in dye molecules. Furthermore, the electron cloud density on O decreases, and the binding energy increases. N in Fig. 10d is shown as two categories: 399.29 represents -NH and -NH 2 , and 400.89 represents -NH 3 + . After adsorption, owing to the interaction of lone pair electrons in N with Cr(III) and chromate, the electron cloud density decreases, and the binding energy increases. Figure 10e, f show the characteristic absorption spectra of S2p and Cr2p, respectively. The S2p peaks at 165.81 and 166.51 eV are assigned to S2p3/2 and S2p1/2, respectively. Also, the Cr2p peaks at 575.83, 584.52, 576.6, and 584.4 eV are assigned to Cr(VI)2p1/2, Cr(III)2p1/2, Cr(III)2p3/2, and Cr(VI)2p3/2, respectively. Consistent with the literature values [37].

Adsorption Mechanism of P-(EA-β-CD/KHA/AC) Hydrogels
Combined with the analysis of the FTIR, XRD, and XPS data before and after adsorption, it can be seen that the hydrogel material adsorbs MB, mainly through electrostatic action and π-π conjugation. When adsorbing Cr(VI) at pH < 3, Cr(VI) is reduced to Cr(III), and coordination with hydroxyl and carboxyl groups on the surface of the material occurs at pH 3-7. The oxygen-containing functional groups on the surface of the gel material are protonated, and the adsorption of chromate ions occurs by electrostatic action. When the pH > 8 during the deprotonation of oxygen-containing functional groups on the surface of the gel repel with Cr(VI), not conducive to adsorption [30][31][32]. The adsorption process and mechanism are shown in Fig. 12.

P-(EA-β-CD/KHA/AC) Hydrogel Recycling
The recyclability of the adsorbent material is important for evaluating the practical value of the material. Figure 11 shows the cyclic adsorption test results of multiple adsorption-desorption cycles. The adsorption of MB and Cr(VI) by the hydrogel material is at a higher removal rate when adsorbing dyes and heavy metal ions. The first removal rates of MB and Cr(VI) are 98.96% and 70.27%, respectively. After five cycles of adsorption-desorption experiments, there is still a high removal rate, the removal rates of MB and Cr(VI) after five cycles are 80.57% and 43.62%, respectively (Fig. 12).

Conclusions
Herein, EA-β-CD was obtained by etherification of β-CD, and humic acid and AC were introduced simultaneously by free radical polymerization to synthesize an amino-modified hydrogel P-(EA-β-CD/KHA/AC) that was biodegradable and environmentally friendly. P-(EA-β-CD/KHA/AC) presents an irregular multifold state, forms a cross-linked network structure, and exposes the hydrophilic groups, which facilitate adsorption.
The adsorption process of MB and Cr(VI) by P-(EA-β-CD/ KHA/AC) was simulated by the pseudo-second-order kinetics and the Langmuir model. At 298 K and pH = 8, the adsorption capacities were as high as 262.3 and 170.12 mg/g, respectively. FTIR, XRD, and XPS investigations before and after adsorption indicated that the adsorption of MB by P-(EA-β-CD/ KHA/AC) had intermolecular forces and π-π conjugation. The adsorption of Cr(VI) is mainly accomplished by converting