Hydrogen Bonding of Acylamino-Modified ... - ACS Publications

Article Cite This: J. Chem. Eng. Data XXXX, XXX, XXX−XXX

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Hydrogen Bonding of Acylamino-Modified Macroporous CrossLinked Polystyrene Resins with Phenol Fa Zhou, Jianhan Huang,* and Ruilin Man* College of Chemistry and Chemical Engineering, Central South University, Changsha, 410083, China S Supporting Information *

ABSTRACT: Hydrogen bonding plays an important role in the adsorption of organic compounds on polymeric adsorbents. Herein, three acylamino-modified macroporous crosslinked polystyrene resins, namely, PMVBA, PVBA, and PVBU, are synthesized and their adsorption of phenol is investigated in detail from hexane. The results indicate that about 3.70 mmol/g acylamino groups are uploaded on the resins, the adsorption of these resins to phenol is efficient, and the equilibrium capacity has an order of PVBU > PMVBA > PVBA. The isosteric enthalpy of adsorption is calculated, and it possesses a similar order of PVBU (−63.38 ± 9.2 kJ/ mol) > PVBA (−55.81 ± 7.8 kJ/mol) > PMVBA (−39.87 ± 5.5 kJ/mol) at the zero fractional loading. Analysis of the adsorption mechanism suggests that hydrogen bonding is the main driving force for the adsorption, double hydrogen bonding is involved for phenol adsorption on PVBA and PVBU, and an approximate hexahydric ring is formed during this process.

1. INTRODUCTION Hydrogen bonding is an attractive interaction of an acidic hydrogen atom with an electronegative atom such as nitrogen, oxygen, or fluorine.1 It is well recognized that there are many processes in chemistry, biochemistry, and supermolecular chemistry in which hydrogen bonding plays an important role.2−4 In particular, hydrogen bonding is a main mechanism for the adsorption of organic compounds on polymeric adsorbents from aqueous or nonaqueous solution.5−11 The low energy of hydrogen bonding (8−50 kJ/mol) ensures the adsorption reversibility, whereas its directionality and the short range confer the adsorption selectivity. As a result, introduction of hydrogen bonding acceptors (HBAs) or hydrogen bonding donors (HBDs) as the functional groups on the polymeric adsorbents will develop a series of new-style hydrogen bonding polymeric adsorbents.12,13 As concerns the hydrogen bonding polymeric adsorbents, it is of great importance to introduce HBAs or HBDs as the functional groups on the surface, and these functional groups can form hydrogen bonds with the adsorbates containing HBDs or HBAs. Generally, the polymeric adsorbents based on hydrogen bonding can be divided into three series, adsorbents with HBAs, adsorbents with HBDs, and adsorbents with both HBAs and HBDs. Amberlite XAD-7 resin,14 a macroporous copolymer of methyl methacrylate and trimethylolpropane triacrylate, is a typical adsorbent with HBAs. The two lone electron pairs in the nonbonding sp2 orbital of each carbonyl oxygen atom can form hydrogen bonds with the adsorbates containing HBD like acidic O−H groups. In addition, HBDcontaining adsorbents include sulfonated polystyrene, copolymers of p-hydroxylstyrene, and polystyrene-azo-pyrogallol. For example, copolymers of p-hydroxylstyrene and divinylbenzene contain phenolic O−H groups, which can form hydrogen bonds with the carbonyl groups. In particular, the adsorbents © XXXX American Chemical Society

with HBAs and HBDs are those adsorbents with acylamino groups15−17 in which the carboxyl groups can act as HBAs,16 whereas the hydrogen atoms of the amido groups can act as HBDs,15 and double hydrogen bonding can be formed between the adsorbents and the adsorbates. Some specific papers focus on the hydrogen bonding adsorption mechanism between the polymeric adsorbents and organic compounds in aqueous and nonaqueous solution.18−21 In aqueous solution, hydrophobic interaction is the main mechanism for the adsorption, and hydrogen bonding is greatly restrained due to the existence of water.22,23 Hydrogen bonding will be straightforward and effective in nonpolar solution, and thus, such a specific interaction will be better exploited in adsorption and separation.15,16,24 In addition, some organic compounds, especially some of the active components of alkaloid and flavones in the Chinese Traditional and Herbal Drugs, are insoluble in water and extraction of these compounds from aqueous solution based on adsorption will be challenging, while adsorption in nonaqueous solution will be feasible. Furthermore, these compounds possess HBDs or HBAs, and forming hydrogen bonding is possible if applying polymeric adsorbents functionalized with HBAs or HBDs to adsorb these compounds in nonaqueous solution. Acylamino groups are considered HBAs as well as HBDs.15,16 The carboxyl portion (CO) of the acylamino groups can act as a HBA, whereas the hydrogen atom on the amido portion (NH) can act as a HBD. If acylamino groups are uploaded on the surface of the polymeric adsorbents, double hydrogen bonding should be possible. However, this kind of double hydrogen bonding is not clearly clarified in detail. For this Received: November 19, 2017 Accepted: April 30, 2018

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DOI: 10.1021/acs.jced.7b01016 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

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resultant solid particles, namely, poly(N-methyl-p-vinylbenzylacetamide) (PMVBA), were filtrated, washed with deionized water, and extracted with ethanol for 8 h. For PVBA,15 11 g of HMTA and 13 g of KI was dissolved with 200 mL of DMF, and the mixed solution was applied to swell 20 g of CMPS. The reaction solution was then heated to 373 K and kept at this temperature for 10 h. The solid particles were filtered and successively washed with 6 mol/L HCl (w/v), deionized water, 10% NaOH (w/v), and deionized water until neutral pH. Thereafter, the intermediate product (aminomodified resin) was acetylated, and hence, the acetamidemodified resin PVBA was prepared. For PVBU,16 15 g of CMPS was swollen with 60 mL of toluene overnight. Twenty g of urea, 4 g of NaOH, and 2 g of KF were dissolved with distilled water and added in the reaction mixture. After that, 5 mL of TBAH was added, and the reaction was carried out at 350 K for 20 h. Thus, the acylamino-modified resin PVBU was prepared. 2.3. Equilibrium Isotherms. Equilibrium isotherms of phenol adsorption on the resins were measured at 288, 293, 298, 303, and 308 K from hexane. Accurately weighed resin (about 0.1 g) was introduced in a 100 mL flask directly. A 50 mL phenol solution with known concentration, C0 (mg/L), was then added to the flasks. The flasks were completely sealed and shaken in a thermostatic oscillator at a presettled temperature until the adsorption reached equilibrium. The equilibrium concentration of phenol, Ce (mg/L), was determined, and the equilibrium capacity, qe (mg/g), was calculated as

purpose, in this study, three acylamino-modified macroporous cross-linked polystyrene resins, namely, poly(N-methyl-p-vinylbenzylacetamide) (PMVBA), poly(N-p-vinylbenzylacetamide) (PVBA), and poly(N-p-vinylbenzylurea) (PVBU), were prepared. In particular, the amido portion on the surface of PMVBA does not contain a hydrogen atom,16 whereas those of PVBA and PVBU contain a hydrogen atom,15 and the adsorption mechanism may be possibly different than using them for adsorption of the adsorbates like phenol from nonaqueous solution. Hence, their adsorption to phenol from hexane was investigated and the adsorption mechanism was expounded in detail.

2. EXPERIMENTAL SECTION 2.1. Materials. Macroporous cross-linked chloromethylated polystyrene (CMPS) was purchased from Langfang Chemical Co. Ltd. (Hebei province, China), and its textural parameters were summarized in Table 1. Phenol used as the adsorbate was Table 1. Textural Parameters of the Polymeric Adsorbents 2

BET surface area (m /g) pore volume (cm3/g) residual chlorine content (mmol/g) average pore diameter (nm) water regain (mL/g)

CMPS

PMVBA

PVBA

PVBU

6.3 0.033 4.87 25.2 0.38

22.5 0.042 0.71 22.5 0.42

26.4 0.044 0.84 25.7 0.45

86.3 0.050 1.01 20.5 0.62

distilled before use. The other agents such as 1,2-dichloroethane (DCE), methylamine aqueous solution (purity: 30%), hexamethylenetetramine (HMTA), toluene, dimethylformamide (DMF), acetic anhydride, potassium iodide (KI), HCl aqueous solution (purity: 38%), sodium hydroxide (NaOH), tetrabutylammonium hydroxide (TBAH), potassium fluoride (KF), urea, and o-nitrophenol were used without further purification. 2.2. Synthesis of PMVBA, PVBA, and PVBU. According to the methods in the literature,15,16 the three resins PMVBA, PVBA, and PVBU were prepared from CMPS and Scheme 1

qe = (C0 − Ce)V /W

(1)

where V is the volume of phenol solution (L) and W is the weight of the resins (g). 2.4. Analysis. Fourier transform infrared (FT-IR) spectra of the resins were recorded by KBr disks on a Nicolet 510P FTIR instrument (USA) ranging from 500 to 4000 cm−1. The pore structure of the resins was determined by N2 adsorption− desorption isotherms at 77.3 K via a Micromeritics ASAP 2020 surface area and porosity analyzer. Before the N2 adsorption, a degassing procedure under N2 flushing was pretreated for the resins, the degassing temperature was 363 K, and the duration time was 4 h. The surface area was calculated using the Brunauer−Emmett−Teller (BET) model in the range P/P0 = 0.05−0.30, the pore volume was calculated from the isotherm at P/P0 = 0.99, and the pore size distribution was calculated by applying the Barrett−Joyner−Halenda (BJH) method to the N2 desorption data. The chlorine content of the resins was measured according to the Volhard method.25 The weak basic exchange capacity of the resins was determined according to the method in ref 26. The concentration of phenol in hexane was analyzed by UV analysis performed on a UV 2450 spectrophotometer at a wavelength of 270.9 nm. 2.5. Small Molecular Simulations. Density functional theory (DFT) calculations were applied to predict the optimized molecular geometries by the Gaussian 03 program package.27 To simplify the calculation, N,N-dimethylacetamide, N-methylacetamide, and N-methylurea (N-methyl-N′-methylurea) were employed as the molecular analogues for PMVBA, PVBA, and PVBU, respectively. The labeling of the carbon, nitrogen, and oxygen atoms of the analogues was shown in Figure S1. The computational results gave information on the molecular geometries, total energies, and vibrational frequencies of the molecules, and the optimized structure was achieved if there was no imaginary frequency. The bond length, bond

Scheme 1. Synthetic Procedure of the Three Resins PMVBA, PVBA, and PVBU

shows the detailed synthetic procedure. For PMVBA,16 20 g of CMPS was first swollen with 100 mL of DCE at room temperature overnight. DCE was filtered, and 60 mL of methylamine aqueous solution was then added. The reaction mixture was kept at 323 K for 12 h so that methylamino groups substituted the chlorine of CMPS and uploaded on the resins. The intermediate product (methylamino-modified resin) was filtrated and acetylated by acetic anhydride for 10 h. The B



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angle, dihedral angle, and bond energy were determined from the optimized structures.

3. RESULTS AND DISCUSSION 3.1. Characters of the Resins. The method for the preparation of PMVBA, PVBA, and PVBU in this study is similar to ref 15 and ref 16. However, the raw materials are quite different. The macroporous cross-linked styrene-codivinylbenzene with a cross-linking degree of 33.3% (the ratio of styrene to divinylbenzene was 2:1, w/w) was used for preparation of the resin in the literature,15,16 and the present used raw material is CMPS with a cross-linking degree of 6%. In addition, the pore-foaming agents in these methods are different. These obvious differences will induce quite a difference in chemical structure as well as the pore structure for these resins. The chlorine content of CMPS is measured to be 4.87 mmol/g, higher than the reported one in ref 16 (3.88 mmol/g). After the reaction of CMPS with methylamine, HMTA, and urea, the residual chlorine content is measured to be 0.71, 0.84, and 1.01 mmol/g for methylamino-modified resin, amino-modified resin, and PVBU, respectively, and the CCl stretching of CMPS at 1265 cm−1 is sharply weakened (Figure 1). In addition, the weak basic exchange capacities of the amino-modified resins are determined to be 4.02 and 3.93 mmol/g, respectively, and the NH stretching related to the NH2/NH groups appears in the FT-IR spectra.19 These results indicate that the amino groups substitute the chlorine of CMPS successfully, and they are uploaded on resins. After the further acylation reaction, the weak basic exchange capacities are much decreased (0.32, 0.28, and 0.02 mmol/g for PMVBA, PVBA, and PVBU, respectively); other bands present at 1680, 1662, and 1691 cm−1, respectively, and they can be assigned to the CO stretching of carbonyl groups.15,16 These results suggest that the acylamino groups are chemically modified on PMVBA, PVBA, and PVBU, and the uploading amounts are 3.70, 3.65, and 3.74 mmol/g, respectively. According to the N2 adsorption−desorption isotherms, the textural parameters of the resins were obtained, and the results are summarized in Table 1. It is seen that the chemical modification does not change the macroporous structure, and the pore size distribution of the resins confirms this conclusion (Figure S2). The BET surface area and pore volume have an increase with various degrees after the modification, which may be from the fact that the functional groups occupy the pores of CMPS. In particular, the BET surface area and pore volume of PVBU are much higher than the other two resins; the possible reason may be from the fact that urea is used as the crosslinking agent and it reacts with 2 mol of CMPS and hence cross-links between two CMPS fragments listed in Scheme 1, and it is observed that considerable micropores and mesopores appear for PVBU (Figure S2). In addition, the textural parameters such as the BET surface area and pore volume of the three resins are much less than the results in ref 15 and ref 16. Since hexane is being used as the media for the following adsorption, the surface adsorption from hexane due to the BET surface area and pore volume may be excluded, and adsorption due to the functional groups (HBA or HBD) may be more specific, resulting in the straightforward and effective exploration of the adsorption mechanism. The water regains of PMVBA, PVBA, and PVBU are measured to be 0.52, 0.45, and 0.62 mL/g, respectively, revealing that these resins are more hydrophilic after the chemical modification.

Figure 1. FT-IR spectra of (a) PMVBA, (b) PVBA, and (c) PVBU.

3.2. Equilibrium Isotherms. Figure 2 displays the equilibrium isotherms of phenol adsorption on PMVBA, PVBA, and PVBU from hexane at 288 K. It is evident that the equilibrium capacity increases with increasing equilibrium concentration, and the adsorption is not saturated in the

Figure 2. Equilibrium isotherms of phenol adsorption on PMVBA, PVBA, and PVBU from hexane. C



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present system. As compared with the equilibrium capacity on the three resins, it follows an order of PVBU (89.6 mg/g) > PVBA (63.8 mg/g) > PMVBA (52.5 mg/g) at an equilibrium concentration of 50 mg/L. These data are a little less than the reported resins in the literature (PVBU of 92.6 mg/g and PMVBA of 54.3 mg/g).16 However, this difference is not significant ( 0.99; this suggests that the adsorption occurs via a multilayer process with the resins possessing a heterogeneous surface. 3.3. Isosteric Enthalpy of Adsorption. To clarify the interaction strength between phenol and the resins, the isosteric enthalpy of adsorption was calculated. According to the Clausius−Clapeyron equation,23,24 d ln Ce ΔH = dT RT 2

Figure 3. Isosteric enthalpy for phenol adsorption on PMVBA, PVBA, and PVBU as a function of the fractional loading.

bonding may be the main reason. The ΔH of PMVBA is very close to ref 15 (−39.87 kJ/mol) and ref 16 (−38.70 kJ/mol), while that of PVBA (−55.81 kJ/mol) differs about 2 times from ref 15 (−91.4 kJ/mol) and ref 17 (−29.58 kJ/mol). At the same time, the ΔH of PVBU (−63.38 kJ/mol) is a little less than the ref 15 value (−74.55 kJ/mol), and the discrepancies of the ΔH for the tested samples in this study from the literature may be from the different preparation methods for the resins. To confirm the hydrogen bonding mechanism, Figure 4a compares the equilibrium isotherm of o-nitrophenol on PVBA

(2)

here ΔH is the isosteric enthalpy of adsorption (kJ/mol) and R is the ideal gas constant. When ΔH is independent of the temperature or changes little with temperature, ΔH will be a constant and eq 2 will be integrated as ln Ce = −ΔH /(RT ) + C′

(3)

where C′ is the integral constant. In the present study, the equilibrium isotherms at 288, 293, 298, 303, and 308 K were first converted to the isosteres, a plot of ln Ce versus 1/T at a given fractional loading (θ, θ = qe′/qm, where qe′ is the given equilibrium capacity and qm is the maximum capacity). The ΔH was then calculated from the slopes of the isosteres. As can be observed in Figure 3, the ΔH is negative, indicating an exothermic process.26 It decreases as θ increases, which may be ascribed to the heterogeneous surface of the resins.15,30,31 The electrostatic interaction including ionic bond, covalent bond, and coordinate bond, hydrophobic interaction, van der Waals force, and hydrogen bonding are the main driving forces for adsorption of organic compounds on polymeric adsorbents.32,33 It is impossible to form an ionic bond, covalent bond, and coordinate bond between the resins and phenol in hexane; hydrophobic interaction is also not existent in this nonaqueous system. The ΔH of PMVBA ranges from −29.50 to −16.67 kJ/ mol, and the predicted ΔH at the zero fractional loading is −38.74 ± 5.5 kJ/mol. This energy is much greater than the van der Waals force, and it falls in the range of hydrogen bonding.34 Thus, it is deduced that hydrogen bonding is principally responsible for the adsorption. The ΔH of PVBA is a little greater than that of PMVBA, and the ΔH at θ = 0 can be predicted to be −55.81 ± 7.8 kJ/mol. In particular, the ΔH of PVBU is much greater than that of PMVBA, and the ΔH at θ = 0 is inferred to be −63.38 ± 9.2 kJ/mol; the multiple hydrogen

Figure 4. Equilibrium adsorption isotherms of (a) phenol and onitrophenol on PVBA and CMPS from hexane at 288 K and (b) phenol on PVBA from hexane and from aqueous solution at 288 K.

from hexane with that of phenol and Figure 4b shows the equilibrium isotherm of phenol on PVBA from aqueous solution. It is observed that the equilibrium capacity of onitrophenol on PVBA is much smaller than phenol, and phenol D



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phenol interacting with N-methylacetamide, it is interesting to see that adduct a is more stable than adduct b, which suggests that there should be another specific interaction between phenol and structure a. Figure 5a exhibits the adduct of phenol

adsorption on PVBA from aqueous solution is also much weakened. Hydrogen bonding and polar interaction play a crucial role in the adsorption of the adsorbates on the adsorbents from nonpolar solution. For the adsorbates with significant hydrogen bonding acidicity (α) or hydrogen bonding basicity (β), hydrogen bonding is proven as the main mechanism, and α/ β of the adsorbates determines the adsorption affinity.35,36 In the system we considered, o-nitrophenol has intramolecular hydrogen bonding between the nitro group and hydroxyl group, and its α value is 0.05, much less than phenol (α = 0.60).37,38 The intramolecular hydrogen bonding reduces the possibility of forming intermolecular hydrogen bonding between PVBA and o-nitrophenol. On the other hand, the van der Waals force is the main driving force for the adsorption of phenol on CMPS.32 Therefore, the smaller capacity of onitrophenol on PVBA and the much weakened adsorption of phenol on CMPS confirm the hydrogen bonding adsorption mechanism. In aqueous solution, water molecules are hydrogen bonding donors as well as hydrogen bonding acceptors. Water can form hydrogen bonds with the resin PVBA as well as the adsorbate phenol, which reduces the probability of forming hydrogen bonds between PABA and phenol, and the adsorption is quite weakened. 3.4. Small Molecular Simulation. PVBA has a greater ΔH than PMVBA, meaning that the interaction strength between PVBA and phenol is stronger. The surfaces of PMVBA and PVBA are both uploaded with acylamino groups, and the only difference of these two resins is that the acylamino groups of PMVBA are CH3CON(CH3)−, whereas those of PVBA are CH3CONH−. Meanwhile, the similar acylamino groups, namely, −NHCONH2 or −NHCONH−, are uploaded on PVBU, inducing the much greater ΔH. We applied a small molecular simulation to demonstrate the phenomenon. Phenol is a planar molecule with a hydroxyl group in the plane of the benzene ring. For N,N-dimethylacetamide, all carbon, oxygen, and nitrogen atoms are in the same plane. After interaction of phenol with N,N-dimethylacetamide, few changes are detected for the benzene ring of phenol and methyl groups of N,N-dimethylacetamide, while considerable changes occur for the hydroxyl group of phenol as well as the acylamino group of N,N-dimethylacetamide. The bond lengths O7−H of phenol and C1−O3 of N,N-dimethylacetamide are lengthened by 0.017 and 0.010 Å, respectively (Table S2 and Table S3), whereas C1−O7 and C1−N4 are shortened by 0.010 and 0.014 Å, respectively. In addition, the angles of ∠C1O7H of phenol and ∠O3C1N4 and ∠C1N4C5 of N,N-dimethylacetamide increased by 1.7, 0.8, and 1.6°, respectively. The above results imply that some special interaction must exist between phenol and a N,N-dimethylacetamide. The hydrogen of the hydroxyl group of phenol has an α value of 0.60,36 while the oxygen of the acylamino group of N,N-dimethylacetamide has a β value of 0.44.16 Hence, a hydrogen bond is formed. Actually, the bond length (O···H−O) is 1.722 Å, the bond angle (∠OHO) is 170.8°, and the bond energy is predicted to be −55.23 kJ/mol (Figure S4). This calculation tells the truth that phenol is adsorbed on PMVBA from hexane through hydrogen bonding and hydrogen bonding contributes to the ΔH primarily. As for interaction of PVBA with phenol, N-methylacetamide is applied as the molecular analogue for PVBA. NMethylacetamide has two optimized structures (Figure S5). Structure b is more stable than structure a because the Nmethyl group is far away from the C1-methyl group. After

Figure 5. Optimized molecular structure of adducts between phenol and N-methylacetamide.

with structure b; a single hydrogen bond is formed between phenol and N-methylacetamide, having a bond length (O···H− O) of 1.726 Å, a bond angle (∠OHO) of 169.6°, and a bond energy of −58.85 kJ/mol, similar to the adduct of phenol with N,N-dimethylacetamide. On the other hand, Figure 5b displays the adduct of phenol with structure a. The bond lengths O7−H of phenol and C1−O3 of N-methylacetamide are lengthened by 0.027 and 0.018 Å, respectively, while C1−O7 of phenol and C1−N4 of N-methylacetamide are shortened by 0.006 and 0.016 Å, respectively (Table S2 and Table S3), which reveals that a hydrogen bond is also formed between the hydrogen of the hydroxyl group of phenol and the oxygen of the acylamino group of N-methylacetamide. The bond length (O···H−O) is 1.708 Å, the bond angle (∠OHO) is 155.4°, and the bond energy is −68.28 kJ/mol. The bond length (O···H−O) of phenol with N-methylacetamide (1.708 Å) is shorter than that of phenol with N,N-dimethylacetamide (1.722 Å), while the bond angle (∠OHO) (155.4°) is much smaller (170.8°) and the bond energy (−68.28 kJ/mol) is much greater (−55.23 kJ/ mol). The current results imply that there should be another specific interaction between phenol and N-dimethylacetamide in addition to hydrogen bonding between the hydrogen of the hydroxyl group of phenol and the oxygen of the acylamino group of N-methylacetamide. The bond length N4−H of N-methylacetamide is seen to be lengthened by 0.006 Å. The bond length C1−O7 of phenol is shortened by 0.006 Å, while the shortened extent is decreased (0.010 Å for phenol with N,N-dimethylacetamide). In addition, H (N4) of N-methylacetamide has hydrogen bonding acidity (α = 0.40), while oxygen of the hydroxyl group of phenol has hydrogen bonding basicity (α = 0.30).36,37 Thus, it can be deduced that a weak hydrogen bond is formed between H (N4) of N-methylacetamide and oxygen of the hydroxyl group of phenol, having a bond length (N−H···O) of 2.076 Å and a bond angle (∠NHO) of 139.7°. In conclusion, a double hydrogen bond is formed between phenol and N-methylE



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Figure 6. Optimized molecular structure of adducts between phenol and N-methylurea.

structures. After interacting with phenol (Figure S8), the interaction energy between phenol and structure b is the least (−63.02 kJ/mol), while the other two are almost equal (−72.57 and −75.96 kJ/mol for structures a and c, respectively). For the adduct of phenol with structure b, a single hydrogen bond is formed, while, for the adducts of phenol with structures a and c, a double hydrogen bond is formed; the first strong hydrogen bond is formed between the oxygen of the acylamino group and the hydrogen of the hydroxyl group of phenol with its hydrogen bonding bond length (O···H−O) of 1.682 Å and bond angle (∠OHO) of 157.2°, respectively, and the second weak hydrogen bond is related to the hydrogen of the amino group and the oxygen of the hydroxyl group of phenol with its hydrogen bond length (O···H−N) of 2.088 Å and bond angle (∠OHN) of 139.8°, respectively. Moreover, the hydroxyl group of phenol is almost in the same plane of the involved carbon, nitrogen, and oxygen of N,N′-dimethylurea, and an approximate hexahydric ring is certainly formed between phenol and N-methyl-N′-methylurea.

acetamide; one is related to the strong hydrogen bonding between the hydrogen of the hydroxyl group of phenol and the oxygen of the acylamino group of N-methylacetamide, and the other corresponds to the weak hydrogen bonding between H (N4) of the acylamino of N-methylacetamide and the oxygen of the hydroxyl group of phenol. It is this double hydrogen bonding that induces a much greater ΔH. In particular, the hydroxyl group of phenol is almost in the plane of O3, C5, N4, and H (N4) of N-methylacetamide, and the dihedral angle is detected to be 7°. An approximate hexahydric ring is possibly formed between phenol and N-methylacetamide. Due to the approximate hexahydric ring, the bond angle (∠OHO) is lessened to 155.4°, while the bond energy increases to −68.28 kJ/mol. The reaction of CMPS with urea can be an equivalent molar reaction, and N-methylurea can be the molecular analogue of PVBU (Figure S6). Moreover, this reaction can also be 2 mol of CMPS reacting with 1 mol of urea, and N-methyl-N′methylurea will be the analogue (Figure S7). N-Methylurea has two optimized structures. Structure b is more stable than structure a because the N-methyl group is far away from N′−H. Parts a and b of Figure 6 show the optimized adducts of phenol with structure a, and Figure 6c shows the optimized adduct of phenol with structure b. After phenol interacting with Nmethylurea, it is noticed that the stabilities of the three adducts are similar. Double hydrogen bonding is formed between phenol and N-methylurea for the three adducts. The bond length (O···H−O) of the strong hydrogen bonding is 1.687, 1.687, and 1.695 Å, respectively, and the bond angle (∠OHO) is detected to be 156.6, 156.8, and 156.7°, respectively. Additionally, the bond length (N−H···O) of the weak hydrogen bonding is 2.089, 2.097, and 2.101 Å, respectively, and the bond angle (∠OHO) is 139.3, 136.4, and 136.5°, respectively. The bond energy is predicted to be −70.54, −70.32, and −70.83 kJ/mol, respectively. The hydroxyl group of phenol is almost in the plane of N-methylurea, and the dihedral angle is 5, 4, and 4°, respectively. Thus, an approximate hexahydric ring is formed between phenol and N-methylurea. On the other hand, N-methyl-N′-methylurea has three optimized structures (Figure S7). Structure b is the most stable, and structure c is the least among the three optimized

4. CONCLUSIONS In summary, CMPS was used as the raw material in this study for the synthesis of three acylamino-modified macroporous resins, namely, PMVBA, PVBA, and PVBU. Although the synthetic method for the three resins is similar to the literature, the obvious difference of the raw materials induces quite a difference in their pore structural parameters, which affords them with some distinction in the adsorption.15−17 PMVBA, PVBA, and PVBU can adsorb phenol effectively from hexane, and the equilibrium capacity is not significantly different from the literature, implying that the surface adsorption due to the BET surface area and pore volume may be negligible, and the functional groups play important and predominant roles in the adsorption. The equilibrium capacity follows an order of PVBU (89.6 mg/g) > PVBA (63.8 mg/g) > PMVBA (52.5 mg/g) at an equilibrium concentration of 50 mg/L. The ΔH follows an order of PVBU (−63.38 ± 9.2 kJ/mol) > PVBA (−55.81 ± 7.8 kJ/mol) > PMVBA (−39.87 ± 5.5 kJ/mol) at the zero fractional loading, and PVBU possesses the greatest ΔH. Notably, the ΔH for the tested samples in this study has different discrepancies from the literature due to the different F



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preparation methods for the resins.15−17 Hydrogen bonding is shown to be the main driving force for phenol adsorption on the resins, and it involves the hydrogen of the hydroxyl group of phenol and the oxygen of the acylamino group of the resins. For PVBA and PVBU, a double hydrogen bond is formed; one is the strong hydrogen bond between the hydrogen of the hydroxyl group of phenol and the oxygen of the acylamino group of PVBA (PVBU), and the other is the weak hydrogen bond between the oxygen of the hydroxyl group of phenol and H (N4) of PVBA (PVBU), and an approximate hexahydric ring is formed.

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macroporous crosslinked poly(N-vinyl-2-pyrrolidinone). React. Funct. Polym. 2008, 68, 768−774. (8) Zhang, T.; Huang, J. H. N-vinylimidazole modified hyper-crosslinked resins and their adsorption toward Rhodamine B: Effect of the cross-linking degree. J. Taiwan Inst. Chem. Eng. 2017, 80, 293−300. (9) Shao, L. S.; Li, Y.; Huang, J. H.; Liu, Y. N. Synthesis of triazinebased porous organic polymers derived N-enriched porous carbons for CO2 capture. Ind. Eng. Chem. Res. 2018, 57, 2856−2865. (10) Shao, L. S.; Wang, S. Q.; Liu, M. Q.; Huang, J. H.; Liu, Y. N. Triazine-based hyper-cross-linked polymers derived porous carbons for CO2 capture. Chem. Eng. J. 2018, 339, 509−518. (11) Liu, M. Q.; Shao, L. S.; Huang, J. H.; Liu, Y. N. O-containing hyper-cross-linked polymers and porous carbons for CO2 capture. Microporous Mesoporous Mater. 2018, 264, 104−111. (12) Shao, L. S.; Huang, J. H. N-vinylimidazole-modified hyper-crosslinked resins with controllable porosity and polarity and their efficient adsorption towards p-nitrophenol from aqueous solution. J. Colloid Interface Sci. 2017, 507, 42−50. (13) Ren, P.; Zhao, X. L.; Zhang, J.; Shi, R. F.; Yuan, Z.; Wang, C. H. Synthesis of high selectivity polymeric adsorbent and its application on the separation of ginkgo flavonol glycosides and terpene lactones. React. Funct. Polym. 2008, 68, 899−909. (14) Pan, B. J.; Pan, B. C.; Zhang, W. M.; Lv, L.; Zhang, Q. X.; Zheng, S. R. Development of polymeric and polymer-based hybrid adsorbents for pollutants removal from waters. Chem. Eng. J. 2009, 151, 19−29. (15) Li, H. T.; Xu, M. C.; Shi, Z. Q.; He, B. L. Isotherm analysis of phenol adsorption on polymeric adsorbents from nonaqueous solution. J. Colloid Interface Sci. 2004, 271, 47−54. (16) Huang, J. H.; Zhou, Y.; Huang, K. L.; Liu, S. Q.; Luo, Q.; Xu, M. C. Adsorption behavior, thermodynamics, and mechanism of phenol on polymeric adsorbents with amide group in cyclohexane. J. Colloid Interface Sci. 2007, 316, 10−18. (17) Xu, M. C.; Zhou, Y.; Huang, J. H. Adsorption behaviors of three polymeric adsorbents with amide groups for phenol in aqueous solution. J. Colloid Interface Sci. 2008, 327, 9−14. (18) Chang, Z. S.; Dai, J. D.; Xie, A. T.; He, J. S.; Zhang, R. L.; Tian, S. J.; Yan, Y. S.; Li, C. X.; Xu, W.; Shao, R. From lignin to threedimensional interconnected hierarchically porous carbon with high surface area for fast and superhigh-efficiency adsorption of sulfamethazine. Ind. Eng. Chem. Res. 2017, 56, 9367−9375. (19) Shao, L. S.; Li, Y.; Zhang, T.; Liu, M. Q.; Huang, J. H. Controllable synthesis of polar modified hyper-cross-linked resins and their adsorption toward 2-naphthol and 4-hydroxybenzoic acid from aqueous solution. Ind. Eng. Chem. Res. 2017, 56, 2984−2992. (20) Zhang, T.; Zhou, F.; Huang, J. H.; Man, R. L. Ethylene glycol dimethacrylate modified hyper-cross-linked resins: Porogen effect on pore structure and adsorption performance. Chem. Eng. J. 2018, 339, 278−287. (21) Wang, X. M.; Zhang, T.; Huo, J. Q.; Huang, J. H.; Liu, Y. N. Tunable porosity, and polarity of polar post-cross-linked resins and selective adsorption. J. Colloid Interface Sci. 2017, 487, 231−238. (22) Kuang, W.; Liu, Y. N.; Huang, J. H. Phenol-modified hypercross-linked resins with almost all micro/mesopores and their adsorption to aniline. J. Colloid Interface Sci. 2017, 487, 31−37. (23) Jianguo, C.; Li, A. M.; Shi, H. Y.; Fei, Z. H.; Long, C.; Zhang, Q. X. Adsorption characteristics of aniline and 4-methylaniline onto bifunctional polymeric adsorbent modified by sulfonic groups. J. Hazard. Mater. 2005, 124, 173−180. (24) Wang, X. M.; Li, H. B.; Huang, J. H. Adsorption of pchlorophenol on three amino-modified hyper-cross-linked resins. J. Colloid Interface Sci. 2017, 505, 585−592. (25) Wu, C. P.; Zhou, C. H.; Li, F. X. Experiments of Polymeric Chemistry; Anhui Science and Technology Press: Hefei, China, 1987. (26) He, B. L.; Huang, W. Q. Ion Exchange and Adsorption Resin; Shanghai Science and Technology Education Press: Shanghai, China, 1995. (27) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.;

ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.7b01016. Additional tables (Tables S1−S3) and figures (Figures S1−S8) as described in the text, including the correlated parameters for the equilibrium adsorption, the structural parameters for phenol interaction with the resins, the pore size distribution, the equilibrium isotherms of phenol adsorption on the resins, and the optimized molecular structure of the small molecules (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*Phone/Fax: 86-731-88879616. E-mail: jianhanhuang@csu. edu.cn. *Phone/Fax: 86-731-88879616. E-mail: [email protected]. ORCID

Jianhan Huang: 0000-0002-3838-0622 Funding

The authors are grateful to the financial support from the National Natural Science Foundation of China (No. 51673216). Notes

The authors declare no competing financial interest.

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REFERENCES

(1) Shao, W. Y.; Liu, J. X.; Yang, K. G.; Liang, Y.; Weng, Y. J.; Li, S. W.; Liang, Z.; Zhang, L. H.; Zhang, Y. K. Hydrogen-bond interaction assisted branched copolymer HILIC material for separation and Nglycopeptides enrichment. Talanta 2016, 158, 361−367. (2) Smith, G. D.; Bedrov, D. A molecular dynamics simulation study of the influence of hydrogen-bonding and polar interactions on hydration and conformations of a poly(ethylene oxide) oligomer in dilute aqueous solution. Macromolecules 2002, 35, 5712−5719. (3) Koehler, J. A.; Wallace, K. K.; Smith, P. J.; Payne, G. F. Selective adsorption of sterically hindered phenols through a single-point binding mechanism. Ind. Eng. Chem. Res. 1999, 38, 3076−3082. (4) Mardis, K. L.; Brune, B. J.; Vishwanath, P.; Giorgis, B.; Payne, G. F.; Gilson, M. K. Intramolecular versus intermolecular hydrogen bonding in the adsorption of aromatic alcohols onto an acrylic ester sorbent. J. Phys. Chem. B 2000, 104, 4735−4744. (5) Liu, C.; Liao, Y. M.; Huang, X. J. Fabrication of polymeric ionic liquid-modified magnetic adsorbent for extraction of apolar and polar pollutants in complicated samples. Talanta 2017, 172, 23−30. (6) Shao, L. S.; Liu, M. Q.; Huang, J. H.; Liu, Y. N. CO2 capture by nitrogen-doped porous carbons derived from nitrogen-containing hyper-cross-linked polymers. J. Colloid Interface Sci. 2018, 513, 304− 313. (7) Zhao, R. Y.; Yan, Y.; Li, M. X.; Yan, H. S. Selective adsorption of tea polyphenols from aqueous solution of the mixture with caffeine on G



Article

Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, revision B.05; Gaussian, Inc.: Pittsburgh, PA, 2003. (28) Langmuir, I. The constitution and fundamental properties of solids and liquids. II. Liquids. J. Am. Chem. Soc. 1917, 39, 1848−1906. (29) Freundlich, H. Over the adsorption in solution. J. Phys. Chem. 1906, 57, 1100−1107. (30) Balathanigaimani, M. S.; Shim, W. G.; Park, K. H.; Lee, J. W.; Moon, H. Effects of structural and surface energetic heterogeneity properties of novel corn grain-based activated carbons on dye adsorption. Microporous Mesoporous Mater. 2009, 118, 232−238. (31) Cao, J. X.; Zhou, C. Y.; Wang, Y.; Sun, Y. Y.; Pan, D. D. The effect of oxidation on the structure of G-actin and its binding ability with aroma compounds in carp grass skeletal muscle. Food Chem. 2018, 240, 346−353. (32) Xiao, G. Q.; Wen, R. M.; Liu, A. J.; He, G. W.; Wu, D. Adsorption performance of salicylic acid on a novel resin with distinctive double pore structure. J. Hazard. Mater. 2017, 329, 77−83. (33) Zhang, T.; Huang, J. H. Tunable synthesis of the polar modified hyper-cross-linked resins and application to the adsorption. J. Colloid Interface Sci. 2017, 505, 383−391. (34) Wang, Q. W.; Yang, Y. C.; Gao, H. B. Problems on Hydrogen Bonding in Organic Chemistry; Tianjin University Press: Tianjin, China, 1993. (35) Shan, S. J.; Zhao, Y.; Tang, H.; Cui, F. Y. Linear solvation energy relationship to predict the adsorption of aromatic contaminants on graphene oxide. Chemosphere 2017, 185, 826−832. (36) Marcus, Y. The properties of organic liquids that are relevant to their use as solvating solvents. Chem. Soc. Rev. 1993, 22, 409−421. (37) Brune, B. J.; Koehler, J. A.; Smith, P. J.; Payne, G. F. Correlation between adsorption and small molecule hydrogen bonding. Langmuir 1999, 15, 3987−3992. (38) Abraham, M. H. Scales of solute hydrogen-bonding: Their construction and application to physicochemical and biochemical processes. Chem. Soc. Rev. 1993, 22, 73−92.

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