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N‑Vinylimidazole-Modified Post-Cross-Linked Resin with Pendent Vinyl Groups and Their Adsorption of Phenol from Aqueous Solution Fa Zhou, Jianhan Huang,* and Ruilin Man College of Chemistry and Chemical Engineering, Hunan Provincial Key Laboratory of Efficient and Clean Utilization of Manganese Resources, Central South University, Changsha 410083, China

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S Supporting Information *

ABSTRACT: Herein N-vinylimidazole (VIM) was employed as the polar monomer in the polymerization, and a series of VIM-modified post-cross-linked resins with vinyl groups were prepared by altering the initial cross-linking degree and mass percentage of toluene in the porogens. The results indicate that the initial cross-linking degree and the porogens have great influence on the porosity and adsorption performance. The resins with a higher initial cross-linking degree and a higher mass percentage of toluene in the porogens possess higher Brunauer−Emmett−Teller surface area and pore volume. Moreover, the Friedel−Crafts alkylation reaction induces the greater increased micropore area and micropore volume. HPDV-90%−50% with the initial cross-linking degree of 90% and using 50% (w/w) toluene and 50% (w/w) benzyl alcohol (TA) in the porogens has the largest equilibrium capacity to phenol. The equilibrium data are well characterized by the Freundlich model, and the isosteric heat of adsorption decreases dramatically with increasing the fractional loading. The adsorption can reach equilibrium within 80 min, and the intraparticle diffusion is the ratelimiting step. HPDV-90%−50% exhibits a dynamic capacity of 40.3 mg/mL wet resin at an initial concentration of 520 mg/L and a flow rate of 1.6 mL/min, and it can be completely regenerated with an excellent regeneration property. introducing amino/amide groups on the surface,11 and a large improvement of adsorption appears for the amino-/amidemodified post-cross-linked resins. The physicochemical characters of the porogens used in the polymerization play an important role in the porosity. Zhou et al.12 found that the increased BET surface area was higher using a lower mass percentage of n-heptane in the porogens, and the porogen amounts influenced the porosity of the synthesized resins. Aleksieva et al.13 reported that the residual amount of the vinyl groups of the precursors using 1,2dichloroethane as the porogen was a little higher than those using gasoline as the porogen. Hao et al.14 found that the postcross-linked resins using toluene as the porogen held a much higher BET surface area than those using n-heptane as the porogen. Our group15 reported that the porogens had great influences on the adsorption performance of the post-crosslinked resins, and the resin using 50% (w/w) toluene and 50% (w/w) 3-methyl-1-butanol had the largest equilibrium capacity to phenol. Imidazole is an N-substituted polar heterocyclic compound with strong affinity to acidic aromatic compounds like phenol and heavy metals like Hg(II).5,16,17 The equilibrium capacity is relatively enhanced via copolymerization of imidazole-based monomers such as N-vinylimidazole (VIM) on the skeleton of

1. INTRODUCTION In 1988, Ando et al.1 fabricated a kind of post-cross-linked resin with vinyl groups, and these resins are proven efficient for purification of cephalosporin C and adsorptive removal of the bitter component in fruit juice.2 They have also been used as the column packing materials in high-performance liquid chromatography (HPLC) and solid-phase extraction materials for organic contaminants and organic vapors.3−5 These resins are generally synthesized from macroporous styrene-divinylbenzene (St-DVB) copolymers by further self-cross-linking,1,5 and no external cross-linking agents are added in the reaction. The reason is that for the highly cross-linked St-DVB copolymers a considerable number of vinyl groups remain in the dense cores due to the much lowered reactivity of the second vinyl groups after initiating the first vinyl groups of divinylbenzene (DVB).5−7 By treating the swollen St-DVB copolymer with the Friedel−Crafts alkylation catalysts, these remaining vinyl groups can react with the neighboring phenyl rings, and this post-cross-linking will lead to an increased Brunauer−Emmett−Teller (BET) surface area and preferable porosity.7,8 Nevertheless, the above starting St-DVB copolymers for synthesizing the post-cross-linked resins are nonpolar. Thus, some polar monomers such as methacrylate (MA) and vinylpyrrolidone (VP) are introduced in the polymerization,9,10 and the as-prepared polar-modified post-cross-linked resins reveal an obviously enhanced adsorption to the polar compounds. More recently, our group further improved the surface polarity of the post-cross-linked resins by further © XXXX American Chemical Society

Received: June 8, 2018 Accepted: July 25, 2018

A

DOI: 10.1021/acs.jced.8b00473 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

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Scheme 1. Synthetic Procedure of VIM-Modified Post-Cross-Linked Resins

2.2. Preparation of the Starting Copolymers. Scheme 1 shows the detailed synthetic procedure for the starting copolymers. The organic phase composed of DVB, VIM, toluene, TA, and AIBN (0.2 g) was added to 200 mL of 1 wt % PVA aqueous solution. DVB was the cross-linking agent, and VIM was the polar monomer. The total mass of the two monomers was 20 g, and the mass ratio between DVB and VIM was 80:20, 85:15, 90:10, and 95:5 wt %. Thus, the initial cross-linking degree of the as-prepared starting copolymers was 80, 85, 90, and 95 wt %, respectively. Toluene and TA were the porogens. The total mass of the porogens was 40 g, and the mass ratio between toluene and TA was defined as 0:40, 10:30, 20:20, 30:10, and 40:0. Thus, the mass percentage of toluene in the porogens was 0, 25, 50, 75, and 100 wt %, respectively. The reaction mixture was polymerized at 358 K for 12 h, and hence the starting copolymers labeled as PDV-X-Y (X denotes the initial cross-linking degree, while Y represents the mass percentage of toluene in the porogens) were obtained. They were washed with hot water and extracted with petroleum ether for 12 h and dried under vacuum at 333 K for 12 h. 2.3. Friedel−Crafts Alkylation Reaction of the Starting Copolymers. The Friedel−Crafts alkylation reaction was performed for the starting copolymers using DCE as the solvent and anhydrous ferric (III) chloride as the catalyst.18,19 An amount of 10 g of the copolymers was swollen with 100 mL of DCE overnight, and 2 g of anhydrous ferric (III) chloride was added. The Friedel−Crafts alkylation reaction was kept at 358 K for 12 h, and hence VIM-modified post-cross-linked resins with vinyl groups named HPDV-X-Y were synthesized. The synthesized post-cross-linked resins were washed with acetone containing 1 wt % HCl and extracted with ethanol for 8 h in a Soxhlet apparatus and dried under vacuum at 333 K for 12 h. 2.4. Equilibrium Adsorption. About 0.05 g of the resins was accurately weighed and mixed with 50 mL of standard phenol solution. The initial concentration of standard phenol solution, C0 (mg/L), was preset to be 200.4, 400.8, 601.2, 801.6, and 1002 mg/L, respectively. The standard phenol solution was directly used without pH adjustment. The series of mixed solutions were shaken at a desired temperature (298, 308, or 318 K) until adsorption equilibrium was reached. The equilibrium concentration of phenol, Ce (mg/L), was determined, and the equilibrium capacity of phenol on the resins, Qe (mg/g), was calculated as

the starting copolymers. For example, we adopted VIM and pvinylbenzyl chloride (VBC) as the monomers and prepared the linear VIM−VBC copolymers.18 The chlorine of the VBC moiety of the copolymers was then consumed in the Friedel− Crafts alkylation reaction, and hence VIM-modified hypercross-linked resin was fabricated. It is found that the linear VIM−VBC copolymers are excellent precursors for the polarmodified hyper-cross-linked resins. In addition, we added DVB as the cross-linking agent in the VIM−VBC copolymers,6 and hence VIM was uploaded on the surface of the hyper-crosslinked resins. The feeding amount of VIM can change the polarity and porosity of the obtained resins, which endowed them with selective adsorption. However, the porosity and the adsorption performance of the hyper-cross-linked resins using VBC as the monomer are much different from that of the postcross-linked resins using DVB as the cross-linking agent.6,15 Using VBC as the monomer in the polymerization, after performing the Friedel−Crafts reaction, the high amount of benzyl chloride from VBC will make the produced hyper-crosslinked resins with high cross-linking degree, high BET surface area, and predominant micropores, which endow them with excellent adsorption to aromatic compounds like phenol. On the contrary, using DVB as the monomer, the residual vinyl groups are relatively lower, and the produced resins are postcross-linked resins with high BET surface area with dominant narrow mesopores. Therefore, the adsorption of the post-crosslinked resins is relatively inferior to the hyper-cross-linked resins. For this purpose, in the present study, VIM was adopted as the polar monomer; DVB was applied as the cross-linking agent; toluene and benzyl alcohol (TA) were applied as the porogens; and a series of starting copolymers were prepared by altering the initial cross-linking degree and using different mass percentage of toluene in the porogens. The Friedel−Crafts alkylation reaction was then carried out for the starting copolymers, and VIM-modified post-cross-linked resins with different porosity were synthesized accordingly. The adsorption performance of as-prepared resins was comparatively evaluated using phenol as the adsorbate.

2. MATERIALS AND METHODS 2.1. Materials. DVB (purity: 80%) was washed by 5 wt % of NaOH and followed by deionized water and then dried by anhydrous MgSO4 before use. The initiator 2,2-azobis(isobutyronitrile) (AIBN) was recrystallized with methanol. Poly(vinyl alcohol) (PVA), VIM, toluene, TA, 1,2-dichloroethane (DCE), anhydrous ferric (III) chloride, and phenol were analytical agents and used as received.

Q e = (C0 − Ce)V /W B

(1) DOI: 10.1021/acs.jced.8b00473 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

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where V is the volume of the solution (L), and W is the mass of the resin (g). 2.5. Kinetic Adsorption. About 0.5 g of the resins was mixed with 500 mL of phenol solution, and the initial concentration of phenol, C0 (mg/L), was 601.2 mg/L. The mixed solutions were shaken at 298, 308, or 318 K until adsorption equilibrium was reached. In this process, 0.5 mL of phenol solution was withdrawn at a desired time. The concentration of phenol, Ct (mg/L), was determined, and the capacity of phenol on the resins, Qt (mg/g), was calculated as Q t = (C 0 − C t )V / W

(2)

2.6. Dynamic Adsorption and Desorption. A glass column with a diameter of 10 mm was packed with 10 mL of wet resins, and it was assembled as the resin column for the dynamic adsorption. The phenol aqueous solution at an initial concentration of 520 mg/L passed through the resin column at a flow rate of 1.6 mL/min until the adsorption was completed. In this process, the concentration of phenol in the effluent from the column exit, C (mg/L), was continuously recorded until it nearly reached the initial concentration. Then the resin column was subjected to 10 mL of deionized water, and the desorption solvent was used for desorbing phenol from the resin column. The flow rate of the desorption solvent was set to be 0.6 mL/min, and the concentration of phenol in the effluent was determined until it was close to zero. 2.7. Analysis. Fourier transform infrared spectra (FT-IR) of the resins were recorded on a Nicolet 510P Fourier transform infrared instrument in 500−4000 cm−1. The porosity of the resins was measured by N2 adsorption− desorption isotherms at 77.3 K by Micromeritics ASAP 2020 surface area and porosity analyzer. Specific surface area (SBET) was derived from the Brunauer−Emmett−Teller (BET) method using the adsorption data range at P/P0 = 0.05− 0.30. Pore volume (Vtotal) was calculated from the N2 adsorption isotherm at P/P0 = 0.99. The micropore area (Smicro) and micropore volume (Vmicro) were calculated from the V−t plot method, and pore size distribution (PSD) was calculated by applying the Barrett−Joyner−Halenda (BJH) model to the N2 desorption data. The concentration of phenol in aqueous solution was determined by a UV-2450 spectrophotometer at the wavelength of 269.5 nm.

Figure 1. FT-IR spectra of (a) the starting copolymers PDV-95%− 100%, PDV-90%−100%, and PDV-80%−100%; (b) the starting copolymers PDV-90%−100% and PDV-90%−50%; and (c) the starting copolymers PDV-90%−100% and VIM-modified post-crosslinked resins HPDV-90%−100%.

3. RESULTS AND DISCUSSION 3.1. Characterization of VIM-Modified Post-CrossLinked Resins. The FT-IR spectra in Figure 1(a) reveal a successful copolymerization of DVB with VIM. The strong absorption concerned with the CN stretching appears at 1480 cm−1,6,19 and the vinyl groups have a frequency at 1631 cm−1.15,20 Notably, the intensity of vinyl groups for PDV95%−100% is relatively greater than PDV-80%−100%, and PDV-90%−100% has greater intensity of vinyl groups than PDV-90%−50% (Figure 1(b)), which implies that PDV-95%− 100% and PDV-90%−100% have higher amounts of vinyl groups than PDV-80%−100% and PDV-90%−50%. Due to the higher cross-linking degree, PDV-95%−100% has a higher residual amount of vinyl groups than PDV-80%−100%. Bartholin et al.21 showed that the second vinyl groups of DVB will not react with macroradicals because of decreasing mobility of the growing chains’ end. Zeng et al.10 and Zhou et al.12 got similar results that the residual amounts of vinyl

groups increase as the initial cross-linking degree increased. PDV-90%−100% has a higher residual amount of vinyl groups than PDV-90%−50%, which implies that the porogens have an obvious effect, and using a higher mass percentage of toluene induces a higher amount of vinyl groups. Jerabek et al.13 reported similar results to the starting copolymers using the thermodynamically good solvent, as the porogens own a higher residual amount of vinyl groups. After the Friedel−Crafts alkylation reaction, the intensity of vinyl groups is greatly weakened (Figure 1(c)), implying they are consumed during the post-cross-linking, and the post-cross-linked resins are prepared successfully.15,22 According to the N2 adsorption−desorption isotherms, the textual parameters of the resins were achieved, and the results are summarized in Table 1. When using toluene as the porogen while altering the initial cross-linking degree from 80% to 95%, the SBET and Vtotal of the starting copolymers increase as the initial cross-linking degree increased. Additionally, when the C

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from 80% to 95%, HPDV-95%−100% has the highest increased Smicro and Vmicro (57 m2/g and 0.06 cm3/g, respectively). When altering the mass percentage of toluene in the porogens from 100% to 0%, HPDV-90%−100% has the highest increased Smicro and Vmicro (52 m2/g and 1.0 cm3/g, respectively). It is worth mentioning that more micropores are generated for the starting copolymers using a higher mass percentage of toluene in the porogens. As compared with the starting copolymers (Figure S5(a) and (b) as well as Figure S6(a) and (b)), VIM-modified postcross-linked resins have much greater pore volume (Figure 2(a) and (b)), especially in the micropore region. Thus, the

Table 1. Textual Parameters of the Starting Copolymers and VIM-Modified Post-Cross-Linked Resins

PDV-80%-100% PDV-85%-100% PDV-90%-100% PDV-95%-100% HPDV-80%-100% HPDV-85%-100% HPDV-90%-100% HPDV-95%-100% PDV-90%-0% PDV-90%-25% PDV-90%-50% PDV-90%-75% HPDV-90%-0% HPDV-90%-25% HPDV-90%-50% HPDV-90%-75%

SBET/ (m2/g)

Smicro/ (m2/g)

Vtotal/ (m2/g)

Vmicro/ (m2/g)

617 633 647 660 712 835 920 946 320 582 618 639 420 741 854 904

139 141 155 199 182 188 207 256 3 20 43 100 5 25 68 145

0.76 0.85 0.96 0.98 1.21 1.6 1.96 2.1 0.35 0.55 0.78 0.85 0.43 0.77 1.43 1.82

0.1 0.11 0.12 0.15 0.12 0.14 0.16 0.21 0.01 0.03 0.06 0.08 0.02 0.04 0.08 0.12

initial cross-linking degree is fixed to 90%, while the mass percentage of toluene is ranged from 100% to 0%, the SBET and Vtotal decrease as the mass percentage of toluene decreases. Similar results are reported in the literature.23,24 After the Friedel−Crafts alkylation reaction, the SBET and Vtotal are obviously increased. Due to sufficient swelling of the starting copolymers in the solvent (DCE), the vinyl groups will have a electrophilic substitution reaction with the adjacent phenyl rings with the help of Friedel−Crafts catalysts,12,14,25 as depicted in Scheme 1. The Friedel−Crafts alkylation reaction will consume the vinyl groups of the starting copolymers, and the rigid methylene groups will connect the polymer chains, making the SBET and Vtotal enhanced. Moreover, the increased SBET and Vtotal before and after the Friedel−Crafts alkylation reaction increase with increasing the initial cross-linking degree (Figure S1(a) and (b)). That is, HPDV-95%−100% has the highest increment of SBET and Vtotal (286 m2/g and 1.12 cm3/g, respectively), whereas HPDV-80%−100% has the lowest increment (95 m2/g and 0.45 cm3/g, respectively). The reason may be due to the fact that PDV-95%−100% has higher amounts of vinyl groups.12 Notably, when the initial crosslinking degree is 90%, while the mass percentage of toluene is altered from 100% to 0%, the increased SBET and Vtotal before and after the post-cross-linking decrease as the mass percentage of toluene decreases (Figure S2(a) and (b)). The increment of SBET and Vtotal for HPDV-90%−0% is the lowest (100 m2/g and 0.08 cm3/g, respectively), while HPDV-90%− 100% has the highest increment (265 m2/g and 0.97 cm3/g, respectively). The reason can be ascribed to the swelling ability of the starting copolymers in the solvent used for the postcross-linking.20 The Smicro and Vmicro of the starting copolymers are very low. After the post-cross-linking, a considerable increase of the Smicro and Vmicro is presented for the resins. These results imply that a quite large number of methylene bridges are generated,25,26 producing many new micropores. In particular, the Smicro and Vmicro increase with elevating the initial crosslinking degree and mass percentage of toluene (Figure S3(a) and (b) as well as Figure S4(a) and (b)), and the increased Smicro and Vmicro before and after the post-cross-linking have the same tendency. When altering the initial cross-linking degree

Figure 2. Pore size distribution of (a) the starting copolymers PDV95%−100% and VIM-modified post-cross-linked resins HPDV-95%− 100% and (b) the starting copolymers PDV-90%−50% and VIMmodified post-cross-linked resins HPDV-90%−50%.

new pores formed during the post-cross-linking are mainly micropores. In fact, the average pore size of the starting copolymers decreases from 7.83 nm (PDV-95%−100%) to 7.27 nm (HPDV-95%−100%), which could be attributed to the increased cross-linking density.27 Additionally, Figure 2(a) and (b) reveals that some new pores are produced in the macropore region. It is predicted that some of the newly formed methylene bridges may be glued together in the highly solvated state, while the overall dimension of the whole system for the obtained post-cross-linked resins will keep almost constant; hence the glued-together regions will create some wide channels (macropores). 3.2. Equilibrium Adsorption. To understand the structure−adsorption relationship of the resins, phenol was employed as the adsorbate, and the equilibrium adsorption of the resins was measured at 298 K. The Qe was plotted at an equilibrium concentration of 400 mg/L for the resins, and the results are depicted in Figure 3(a) and (b). It is observed that D

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Figure 3. Effect of (a) the initial cross-linking degree and (b) mass percentage of toluene in the porogens on the equilibrium capacity of phenol on the starting copolymers and VIM-modified post-cross-linked resins. (c) The equilibrium isotherms of phenol on HPDV-90%−50% with the temperature at 298, 308, and 318 K and (d) isosteric heat of adsorption of phenol on HPDV-90%−50% as a function of the fractional loading (θ).

linking first increases and then decreases, and HPDV-90%− 50% possesses the largest incremental Qe (41.3 mg/g). To investigate the equilibrium adsorption of phenol on the resins, the equilibrium isotherms of phenol on HPDV-90%− 50% were measured at three different temperatures (298, 308, and 318 K), and the results are depicted in Figure 3(c). It is evident that the Qe increases with elevating Ce, and the adsorption is not in equilibrium in the present Ce. Meanwhile, the Qe decreases as the temperature increases, demonstrating that the adsorption is an exothermic process.30 Langmuir and Freundlich models were employed in this study to describe the equilibrium data,31,32 and the corresponding parameters such as qm, KL, KF, and n as well as the correlation coefficients R2 are summarized in Table S1. The Freundlich model appears to be more suitable than the Langmuir model due to R2 > 0.99. The n values are greater than 1, implying that the adsorption is a favorable process.32 Notably, a higher temperature induces less n values (1.75 (298 K) > 1.51 (308 K) > 1.30 (318 K)). The KF values decrease as the temperature increases (4.56 (mg/ g)(L/mg)1/n (298 K) > 2.12 (mg/g)(L/mg)1/n (308 K) > 1.05 (mg/g)(L/mg)1/n (318 K)), indicating that the adsorption at a lower temperature is more effective. Meanwhile, comparing the Qe of phenol on HPDV-90%−50% (Qmax = 251.7 mg/g) to some other adsorbents in the literature (Table S2),6,33−37 it is found that HPDV-90%−50% is superior to many other adsorbents reported in the literature. To clarify the interaction strength of the resins with phenol, isosteric heat of adsorption (ΔH) was determined from the isotherms at 298, 308, and 318 K using the Clausius− Clapeyron equation,8,26,28 and the ΔH is plotted as a function of the fractional loading (θ, θ = Qe′/Qm, where Qe′ is the given

the Qe increases as the initial cross-linking degree increased for both the starting copolymers and post-cross-linked resins, and HPDV-95%−100% has the largest Qe (98.1 mg/g). This tendency is the same as the SBET and Vtotal. Particularly interestingly, the increased Qe before and after the post-crosslinking first increases and then slightly decreases, and HPDV90%−100% possesses the largest increased Qe (32.8 mg/g). This tendency is different from the increased SBET, Vtotal, Smicro, and Vmicro. To expound the possible reason the increased percentage of Qe was considered as a function of the initial cross-linking degree (Figure S7(a)), it is seen that HPDV80%−100%, HPDV-85%−100%, and HPDV-95%−100% have an increased percentage of 18, 34, and 44%, respectively, which is similar to the increased percentage of SBET (15, 31, and 43%, respectively). Thus, the increased Qe on the three resins may result from the increased SBET. However, the increased percentage of Qe is 52% for HPDV-90%−100%, much higher than the increased percentage of SBET (42%). It is surprising to observe that the increased percentage of Smicro has the same tendency as the increased percentage of Qe (Figure S7(b)), which suggests that micropore filling gives a contribution for phenol adsorption in the present study.28,29 As the initial crosslinking degree is fixed to 90%, the mass percentage of toluene in the porogens is altered. It is found that the Qe first increases and then slightly decreases; HPDV-90%−50% has the largest Qe (99.2 mg/g); and the Qe is a little larger than HPDV-95%− 100% (98.1 mg/g). HPDV-90%−75% and HPDV-90%−100% have a much higher SBET than HPDV-90%−50% but possess lower Qe, suggesting that some other factors may take effect. In addition, the increased Qe before and after the post-crossE

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equilibrium capacity and Qm is the maximum capacity). Figure 3(d) indicates that the ΔH is negative.30 Moreover, as the fractional loading increased, ΔH decreased rapidly first and then slowly and finally reached the physical adsorption category ( 0.99. In addition, the k2 values ascend as the temperature increases (7.224 × 10−4 g/(mg·min) (298 K) < 1.859 × 10−3 g/(mg·min) (308 K) < 4.579 × 10−3 g/ (mg·min) (318 K)). Notably, the internal mass transfer in the

Figure 5. Dynamic adsorption and desorption curves of phenol on HPDV-90%−50% from aqueous solution. (a) The survey and (b) the effluent below Chinese wastewater discharge standard.

Chinese wastewater discharge standard, the allowable emission concentration of phenol should be below 0.5 mg/L. Figure 5(a) indicates that the concentration of phenol from the effluent reaches this point (C = 0.495 mg/L) after 395 mL of phenol solution at an initial concentration of 520 mg/L passing through the resin column (Figure 5(b)). Thus, the dynamic capacity can be calculated to be 24.4 mg/mL of wet resin, which implies that HPDV-90%−50% can make the phenol solution at a medium concentration attain the discharge standard. In addition, the effluent to arrive at the saturation point (C/C0 = 0.95) is measured to be 1155 mL, and the dynamic capacity is 43.2 mg/mL of wet resin. As the total mass of the dry resins is considered (3.02 g), the dynamic capacity is F

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The Freundlich model was more suitable for fitting the equilibrium data, and the KF values decrease as the temperature increases (4.56 (mg/g)(L/mg)1/n (298 K) > 2.12(mg/g)(L/mg)1/n (308 K) > 1.05 (mg/g)(L/mg)1/n (318 K)). The ΔH sharply decreased with increasing the fractional loading. The adsorption is fast, and about 20 min is enough for the adsorption to reach equilibrium at 318 K. The k2 values are ascended as the temperature increases (7.224 × 10−4 g/(mg· min) (298 K) < 1.859 × 10−3 g/(mg·min) (308 K) < 4.579 × 10−3 g/(mg·min) (318 K)). The intraparticle diffusion is the rate-limiting step for the kinetic adsorption, and the kd is predicted to be 17.11, 20.52, and 27.13 mg/(g·min1/2) at 298, 308, and 308 K, respectively. At an initial concentration of 520 mg/L and a flow rate of 1.6 mL/min, HPDV-90%−50% could make the phenol solution attain the discharge standard, and it could be completely regenerated and repeatedly used.

predicted to be 143.0 mg/g, close to the fitting results from the Langmuir (158.8 mg/g) and Freundlich (163.2 mg/g) models. After the dynamic adsorption, different desorption solvents were employed for deosorbing phenol from the resin column, and the desorption solvent containing 0.01 mol/L of NaOH (w/v) and 75% ethanol (v/v) is the most efficient with a recovery ratio of 99.7% (Figure 6(a)). This desorption solvent

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.8b00473. Additional tables (Table S1 to S3) and figures (Figure S1 to S7) as described in the text (PDF)

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AUTHOR INFORMATION

Corresponding Author

*Tel./Fax: 86-731-88879616. E-mail: [email protected]. cn (J. Huang). ORCID

Jianhan Huang: 0000-0002-3838-0622 Funding

The National Natural Science Foundation of China (No. 51673216) and the Hunan Provincial Science and Technology Plan Project, China (No. 2016TP1007), are gratefully acknowledged for the financial support.

Figure 6. (a) Desorption ratio of phenol from the resins with different desorption solvents. (b) Repeated use and regeneration property of HPDV-90%−50%.

Notes

The authors declare no competing financial interest.

was used for the dynamic desorption, and 39.2 mg/mL of desorption capacity is collected. That is, nearly 100% regeneration efficiency is achieved for the dynamic desorption. The resins were repeatedly used for five adsorption− desorption cycles, and the adsorption ratio decreases to 95.7% (Figure 6(b)), exhibiting a good reusability and remarkable regeneration.

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4. CONCLUSIONS A series of VIM-modified post-cross-linked resins with vinyl groups were prepared by altering the initial cross-linking degree and the mass percentage of toluene in the porogens. The initial cross-linking degree and porogens used in the polymerization played an important role in the porosity and adsorption performance of the post-cross-linked resins. With increasing the initial cross-linking degree and mass percentage of toluene in the porogens, the SBET, Smicro, Vtotal, and Vmicro of the post-cross-linked resins increased, and the increased SBET, Smicro, Vtotal, and Vmicro before and after the post-cross-linking had the same tendency. On the other hand, the Qe of the postcross-linked resins increased as the initial cross-linking degree increased, while it increased first and then slightly decreased as the mass percentage of toluene in the porogens increased. HPDV-90%−50% holds the largest Q (Qmax = 251.7 mg/g), and it is superior to many other adsorbents in the literature. G

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DOI: 10.1021/acs.jced.8b00473 J. Chem. Eng. Data XXXX, XXX, XXX−XXX