Dual-Functional Mesoporous Films Templated by Cellulose

Article pubs.acs.org/jced

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

Dual-Functional Mesoporous Films Templated by Cellulose Nanocrystals for the Selective Adsorption of Lithium and Rubidium Xudong Zheng,† Yuanyuan Wang,‡ Fengxian Qiu,‡ Zhongyu Li,*,† and Yongsheng Yan*,‡ †

School of Environmental & Safety Engineering, Changzhou University, Changzhou 213016, PR China School of Chemistry & Chemical Engineering, Jiangsu University, Zhenjiang 212013, PR China

‡

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ABSTRACT: Lithium resources are an emerging issue due to lithium ion batteries. Rubidium is also widely used in the field of energy and medicine, so it makes sense for the dual adsorption of lithium and rubidium at the same time. Cellulose nanocrystalline (CNC) is used as a biotemplate to synthesis mesoporous films, and hydrogen manganese oxide (HMO) is immobilized on a mesoporous film. Then Rb(I) ionic imprinted layer is grafted onto the surface of a mesoporous film to obtain a dual-functional mesoporous film. Dual-functional mesoporous films possess high selective adsorptions of Li(I) and Rb(I) and show excellent adsorption kinetic properties of Li(I) and Rb(I). The adsorption capacities of Li(I) and Rb(I) are 6.30 and 6.21 mg g−1 under optimum conditions, respectively. HMO ion sieves and ionic imprinting make films demonstrating a high selectivity in the adsorption of Li(I) and Rb(I), enhancing their potential for industrial applications.

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INTRODUCTION Lithium (Li) has received considerable attention as a core component of lithium batteries.1−3 With the development of high-tech and expansive applications of lithium, the surging demand of lithium implies a future challenge on its supply. There are virtually inexhaustible lithium resources in seawater and the Salt Lake as it holds a total of approximately 230 billion tons.4,5 However, the Li(I) concentration in seawater is low (0.17 mg L−1). Thus, the recovery of Li(I) from Salt Lake brine is more feasible.6 Salt Lake brine contains a large number of common metal ions, such as Na(I), K(I), Mg(II), and Ca(II) ions and high value metals such as Rb(I) and Li(I) ions. In particular, Rb(I) has significant applications in thermal ion conversion power, so extracting Rb(I) from brine is also very significant. The adsorption of Li(I) or Rb(I) from brine is complex and difficult. The main obstacle is that brine has a lots of interfering ions (such as Na(I) and Mg(II)) which have a strong impact on the adsorption of Li(I) and Rb(I). Traditional methods mainly include precipitation or liquid−liquid extraction.7−9 Precipitation is suitable for low magnesium lithium ratio brine, whereas sodium hydroxide needs to be added to remove Mg(II) ions after concentration, which increases industrial costs. Liquid−liquid extraction can separate and purify the © XXXX American Chemical Society

required element by multistep extraction. However, plenty of organic solvents used in the process lead to great amounts of organic wastes and radioactive wastes. Moreover, liquid−liquid extraction cannot separate two different ions (Li(I) and Rb(I)) simultaneously and selectively. To improve the separation efficiency, solid−liquid extraction is proposed. Adsorbents can selectively adsorb different ions by multimodification. However, Salt Lake brine is a complex system, so the adsorption selectivity of Li(I) and Rb(I) needs to be resolved. Cellulose nanocrystallines (CNCs) have attracted intense interest as biotemplates because of their surface area and physicochemical properties. CNCs are cheap and environmentally friendly templates for porous materials compared to other templates. We used CNCs as a template for preparing mesoporous films for the adsorption of Li(I) and Rb(I). Ionic imprinted materials are considered to be highly efficient and selective materials with specific recognition sites for the adsorption of template ions.10,11 Ionically imprinted materials can be employed as adsorbents for the specific adsorption of template ions, making them widely useful in Received: August 17, 2018 Accepted: February 1, 2019

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DOI: 10.1021/acs.jced.8b00731 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

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Scheme 1. Schematic Diagram of Free-Standing Dual-Functional Mesoporous Silica Films

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solid−liquid extraction.12−14 The incorporation of two different ionic imprinted materials into one adsorbent will advance their application in the selective adsorption of different ions. Hydrogen manganese oxide (HMO), an imprinted material, is considered to be an efficient adsorbent for the recovery of Li(I) from Salt Lake brine. HMO is derived from lithium manganese oxide (LMO) after the extraction of lithium from the manganese oxide framework, which gives it high selectivity for the adsorption of Li(I).15,16 For the adsorption of Rb(I), high selective functional monomer (such as N-[(3-trimethoxysilyl) propyl] ethylendiamine triacetic acid trisodium salt (TMS-EDTA) can enhance the adsorption capacity. HMO is a powdered material that is difficult to recycle from solution systems, so we immobilized HMO on film materials to improve its industrial application prospect. The HMO powder is tightly fixed on the surface of mesoporous silica material, which has a large porosity and a large surface area to improve the diffusion rate and simple subsequent processing. Our freestanding mesoporous film templated by cellulose nanocrystals exhibits excellent mechanical strength, ordered mesoporous structure, and high specific surface.17 These properties are advantageous for HMO supporting materials because adsorbents of Li(I) require superior stability for the Li(I) desorption process (acid treatment). Moreover, the surface hydroxyl of mesoporous films provides conditions for followup Rb(I) surface ionic imprinting. Then, TMS-EDTA is used as a functional monomer. Rb(I) is used as an imprinted template. A dual-function mesoporous film was proposed to increase the adsorption capacity and adsorption selectivity of Rb(I). In this work, HMO is immobilized on mesoporous films, and then a Rb(I) ionic imprinted layer is grafted onto the surface of mesoporous films, which makes these free-standing dual-functional mesoporous films highly selective to the adsorption of Li(I) and Rb(I). Films are characterized by scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption−desorption. The adsorption capacities, isotherms, and kinetics of Li(I) and Rb(I) were evaluated. Moreover, the adsorption selectivity of two different ions is a key parameter in evaluating the value of materials. We use HCl as an eluant for the desorption of Li(I) and Rb(I) simultaneously. In addition, five cycled experiments were carried out to determine the long-term stability of films.

EXPERIMENTAL SECTION All reagents and solvents were analytical standards purchased from Sinopharm Chemical Reagent Co., Ltd. and used without further purification. Preparation of Free-Standing Mesoporous Films. For the preparation of free-standing mesoporous films, CNCs were prepared in a reported method first.18 Briefly, 50 wt % sulfuric acid was used to hydrolyze degreasing cotton for 120 min at 45 °C. The CNCs gained after reaction were put into dialysis membrane tubes and dialyzed until the pH equals 2.4. The CNCs were dispersed by ultrasound for 10 min before use. Tetraethyl orthosilicate (TEOS, 400 μL) was added to 10 mL of a CNC suspension, and the mixture was stirred at 60 °C for 2 h. The solution was allowed to dry on a polystyrene Petri dish. After evaporation at room temperature, free-standing films of the CNCs/silica composite materials were obtained. Subsequently, the film was held at 100 °C for 2 h and then calcined at 540 °C for 6 h. After slowly cooling to room temperature, free-standing films were obtained. Immobilization of HMO on Free-Standing Mesoporous Films. Various concentrations of lithium acetate and manganese acetate solutions (Li/Mn = 1 mol/mol) were prepared. Pretreated free-standing mesoporous films were put into the Li/Mn acetate solution and mixed for 1 h. The Li/Mn acetate solution saturated with films was separated by sieving and dried at 60 °C for 3 h. Subsequently, they were calcinated at 500 °C for 8 h to achieve LMO. Then, 0.3 M HCl was used to convert LMO to HMO. Preparation of Free-Standing Dual-Imprinted Mesoporous Film (DIMFs). For surface imprinting, 20 mg of RbCl, 350 μL of glacial acetic acid, and 734 μL of TMS-EDTA were added to 100 mL of methanol and water (85:15 v/v) and stirred for 2 h, and then 2 g of HMO modified films was added. The solution was refluxed under nitrogen for 24 h. Then, Rb(I) was removed by using Soxhlet extraction with a 2 M HCl solution. After that, the final free-standing dual-functional mesoporous films were obtained. Nonimprinted mesoporous silica (NIMFs) was synthesized in parallel but without the addition of template RbCl. The synthesis approach to DIMFs is showed in Scheme 1. Instrumentation. The surface morphologies of DIMFs and NIMFs were obtained by scanning electron microscopy (SEM, JEOL, JSM-7001F). The inner morphologies of films were obtained by transmission electron microscopy (TEM, JEOL, JEM-2100) at an accelerating voltage of 200 kV with a LaB6 filament. Nitrogen adsorption−desorption isotherms of the B



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Figure 1. SEM images of DIMFs-5 (a, b), DIMFs-10 (c, d), DIMFs-25 (e, f), and DIMFs-50 (g, h) samples at different magnifications and transversal surfaces of DIMFs-5 (i), DIMFs-10 (j), DIMFs-25 (k), and DIMFs-50 (l).

films were determined using nitrogen adsorption isotherms with a Micromeritics TriStar II 3020 analyzer (Micromeritics Instrument Corporation, USA). All materials were outgassed for 12 h at 100 °C prior to N2 adsorption analysis, which was carried out at −196 °C. The specific surface area (SBET) was calculated using the Brunauer−Emmett−Teller equation in the range of P/P0 = 0.05−0.20. The total pore volume (Vtotal) was estimated from the adsorbed amount of nitrogen at a relative pressure of P/P0 = 0.98. Pore size distributions were obtained from the adsorption isotherm branch by Barrett−Joyner− Hallenda (BJH) calculations. FTIR spectra (4000−400 cm−1) of film materials were recorded with a Nicolet NEXUS-470 FT-IR apparatus (USA) using KBr discs. Inductively coupled plasma−optical emission spectrometry (ICP−OES) was employed to measure the concentration of metal ions in solution. Batch Adsorption Experiments. The adsorption capacities (Qt(mg g−1)) were calculated with eq 1 Qt =

Isotherm Studies. DIMFs and NIMFs (10 mg) were immersed in Li(I) and Rb(I) solutions with a range of concentrations (10 mL, pH 7.0). After equilibrium, the concentrations of Li(I) and Rb(I) were determined by ICP− OES. Selectivity Test. Selectivity experiment of DIMFs and NIMFs were evaluated with a mixed system. Mixed solutions of Li(I), Rb(I), Cs(I), K(I), Na(I), Ca(II), and Mg(II) were prepared from standards solutions (pH 7.0, 50 mg L−1 for each cation). DIMFs and NIMFs (10 mg) were added to 10 mL of solution. The final concentration of each ion was determined by ICP−OES. Cycling Test. Upon reaching equilibrium, DIMFs and NIMFs were obtained from the solution. Materials were regenerated with eluant (HCl/ethanol = 1:9 (v/v)). Then the same procedure was used for five adsorption cycles.

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RESULTS AND DISCUSSION In the immobilization of HMO on mesoporous films, we synthesized four different materials by changing the molar ratio of Mn to Si. We noted DIMFs as DIMFs-5, DIMFs-10, DIMFs-25, and DIMFs-50 for Mn/Si = 1/5, 1/10, 1/25, and 1/50. The morphology of DIMFs and NIMFs was confirmed by SEM and TEM. Figure 1 shows SEM images of DIMFs-5, DIMFs-10, DIMFs-25, and DIMFs-50 samples at different magnifications. SEM images clearly show the HMO crystal on the films for DIMFs-5 (Figure 1a,b). Other SEM images show smooth surfaces and the construction of CNCs at high magnification. The transversal surface of all four different films showed the replication of chiral nematic order in Figure 1i,j,k,l, which indicates that free-standing imprinted mesoporous films were successfully synthesized. SEM images of NIMFs also exhibited the same construction in Figure S1, which indicates that NIMFs also maintained their mesoporous construction. TEM images of DIMFs-5, DIMFs-10, DIMFs-25, and DIMFs50 show distinct pores in ordered arrays in all images, adding

V (Co − Ct(e)) M

(1)

where C0(mg L−1) and Ct(e)(mg L−1) are the initial and residual concentrations at time t (or equilibrium), respectively. M and V are the weight of the adsorbent (10 mg) and the volume of the solution (10 mL), respectively. Effect of pH. DIMFs and NIMFs (10 mg) were immersed in 10 mL of a solution of Li(I) and Rb(I) (50 mg L−1 for each ion) with the initial pH ranging from 3.0 to 7.0. Finally, the concentrations of Li(I) and Rb(I) were determined by ICP− OES. Kinetic Studies. DIMFs and NIMFs (10 mg) were immersed in 10 mL of a solution of Li(I) and Rb(I) (50 mg L−1 for each ion, pH 7.0). The concentrations of Li(I) and Rb(I) at different times were determined by ICP−OES. C



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Figure 2. TEM images of DIMFs-5 (a), DIMFs-10 (b), DIMFs-25 (c), and DIMFs-50 (d)

to confidence for the ordered pores of the film materials (Figure 2a−d), which is in agreement with the SEM images. In Figure 2a,b, we can see that HMO and ordered pore construction become obscured because large doses of HMO crystallize on the surface of films and basically completely block the pore. SEM mapping analysis was also carried out to verify the distribution of active sites for Rb(I) ions in Figure S2. From the mapping analysis, the distribution of Rb(I) ions on the materials is very uniform. Table S1 summarizes the quantitative results of DIMF-10 by SEM mapping images. All of the SEM and TEM images of the materials prove that imprinted mesoporous films had been successfully prepared by the immobilization of HMO and imprinting. Physicochemical parameters of pore structure for different materials were obtained with a nitrogen adsorption− desorption test. Nitrogen adsorption−desorption isotherms of DIMFs-5, DIMFs-10, DIMFs-25, and DIMFs-50 are shown in Figure 3. DIMFs-5, DIMFs-10, DIMFs-25, and DIMFs-50 show type IV isotherms with a distinctive H1 hysteresis loop. Isotherm curves remarkably decrease from DIMFs-50 to

DIMFs-5. Corresponding physicochemical parameters are compiled in Table 1. From the table, DIMFs-50 shows the Table 1. Physicochemical Parameters Obtained by N2 Adsorption−Desorption Measurements for DIMFs-5, DIMFs-10, DIMFs-25, and DIMFs-50 materials

SBET (m2 g−1)

pore size (nm)

Vproe (cm3 g−1)

DIMFs-5 DIMFs-10 DIMFs-25 DIMFs-50

11.16 27.34 33.72 70.21

2.1214 2.1945 2.2390 2.4402

0.0125 0.0290 0.0354 0.0859

highest BET surface area of 70.21 m2 g−1, with pore size of 2.4402 nm and Vpore = 0.0859 cm3 g−1. All of the parameters (BET surface area, pore size, and Vpore) distinctly decease from DIMFs-50 to DIMFs-5. And DIMFs-5 has the lowest BET surface area of 11.16 m2 g−1, with a pore size of 2.1214 nm and Vpore = 0.0125 cm3 g−1. The decrease in pore parameters is due to the HMO immobilization process blocking pores of films. The HMO content of DIMFs-5 is the highest. HMO blocked mesoporous channels to a certain extent, so DIMFs-5 has the smallest pore parameters. The grafting efficiency of TMS-EDTA onto the surface of the DIMFs and NIMFs was confirmed by FTIR analysis. FTIR spectra of TMS-EDTA (a), DIMFs-5 (b), NIMFs-5 (c), DIMFs-50 (d), and NIMFs-50 (e) are shown in Figure 4. For DIMFs-5, NIMFs-5, DIMFs-50, and NIMFs-50, the adsorption peaks are similar. The strong, wide band around 1091 cm−1 corresponds to the antisymmetric stretching vibration absorption peak of Si−O−Si from TMS-EDTA. The peak at 3408 cm1, attributed to the N−H stretching vibration absorption peak, is assigned to the amino group in TMSEDTA. The presence of the band at 1650 cm−1 is consistent with the CO adsorption band of carboxyl, permitting the confirmation of successful modifications by TMS-EDTA. The peaks at 1091 and 805 cm−1 resulting from the ring vibrations

Figure 3. N2 adsorption−desorption isotherms for DIMFs-5, DIMFs10, DIMFs-25, and DIMFs-50. D



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10 are similar because of both DIMFs-10 and NIMFs-10 immobilization of HMO. For Rb(I), because of surface imprinted sites, which led to easier access of Rb(I) to the binding sites in the imprinting cavities, the Rb(I) adsorption capacity of DIMFs-10 is much larger than that of NIMFs-10. The pseudo-first-order kinetic model (PFOKM) and pseudosecond-order kinetic model (PSOKM) were employed for fitting experimental uptake kinetics of DIMFs-10 and NIMFs10. Nonlinear forms of PFOKM and PSOKM are reported in eqs 2 and 3, respectively, Q t = Q e − Q ee−k1t Figure 4. FTIR spectra for TMS-EDTA (a), DIMFs-5 (b), NIMFs-5 (c), DIMFs-50 (d), and NIMFs-50 (e).

Qt =

(2)

k 2Q e 2t 1 + k 2Q et

(3)

where Qt (mg g−1) and Qe (mg g−1) are adsorption capacities at time t and at equilibrium, respectively. k1 (L min−1) and k2 (g mg−1 min−1) are rate constants of PFOKM and PSOKM, respectively. The initial adsorption rate h (mg g−1 min−1) and half equilibrium time t1/2 (min) of PSOKM were also analyzed according to eqs 4 and 5:

of glucoside bonds are assigned to the characteristic absorption bands of the cellulose structures. In addition, the characteristic peaks from panels b to e show a slight blue shift that is probably due to the interaction of the metal with the active sites. However, the resolution of the infrared spectrometer limits further detection. . Effect of Solution pH. Because of the immobilization of HMO and the imprinting structure, DIMFs can adsorb Li(I) and Rb(I) selectively. Therefore, adsorption experiments were tested in a mixed system of Li(I) and Rb(I) solution. First, the effect of pH on the DIMFs was investigated. Figure 5 shows Li(I) and Rb(I) adsorption capacities with four different ratios of DIMFs. From Figure 5, all of the DIMFs show distinct increases in the Li(I) and Rb(I) adsorption capacities with increasing pH (from 3.0 to 7.0). This indicates that the acidic system influences imprinted sites as a result of the lower extent of dissociation of functional groups of DIMFs and the ion exchange system. Therefore, the best adsorption condition of pH is 7.0. The Li(I) and Rb(I) adsorption capacities of DIMFs-5 are greater than those of DIMFs-10, DIMFs-25, and DIMFs-50. Taking into account the use efficiency and adsorption performance of HMO, DIMFs-10 was applied at pH 7.0 for subsequent adsorption experiments. Adsorption Kinetics. Adsorption kinetic experiments for Li(I) and Rb(I) of DIMFs-10 and NIMFs-10 were carried out in mixed stock solutions. Figure 6 shows the adsorption kinetic curves of DIMFs-10 and NIMFs-10, representing about 90% of the total adsorption in the first 100 min. For the adsorption of Li(I), the adsorption kinetic curves of DIMFs-10 and NIMFs-

h = k 2Q e 2 t1/2 =

1 k 2Q e

(4)

(5)

Table 2 reports the adsorption parameters of PFORE and PSORE models. The PFOKM correlation coefficient (R2) of DIMFs-10 is 0.978 for Li(I) and 0.986 for Rb(I) which are both lower than 0.993 (the PSOKM R2 of DIMFs-10). This indicates that the PSOKM model fits the experimental data much better, and the chemical process is likely to be the ratelimiting step of the adsorption mechanism. Values of h and t1/2 of DIMFs-10 for Li(I) were close to those of NIMFs-10, while for Rb(I), the values of DIMFs were apparently better than the values of NIMFs-10. These indicate that ionic imprinting leads to advanced adsorption kinetic properties of DIMFs-10 for the adsorption of Rb(I). Adsorption Isotherms. Equilibrium curves of DIMFs-10 and NIMFs-10 are shown in Figure 7. Equilibrium curves for Li(I) of DIMFs-10 and NIMFs-10 show similar increases in the adsorption capacity, and the adsorption capacity for Li(I) of DIMFs-10 is slightly higher than that for NIMFs-10. The adsorption of Li(I) is due to the immobilization of HMO on

Figure 5. Effect of pH on the adsorption capacities of Li(I) and Rb(I) for DIMFs-5, DIMFs-10, DIMFs-25, and DIMFs-50 (adsorbent dose: 10 mg, 10 mL of solution, and a 50 mg L−1 concentration of both Li(I) and Rb(I)). E



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Figure 6. Kinetics data and modeling for the adsorption of Li(I) and Rb(I) for DIMFs-10 and NIMFs-10 (10 mg of DIMFs-10 and NIMFs-10, 10 mL of solution with a 50 mg L−1 concentration of both Li(I) and Rb(I), pH 7.0).

Table 2. Kinetic Constants for the Pseudo-First-Order and Pseudo-Second-Order Models pseudo-first-order kinetics model materials

ions

Qe,exp (mg g−1)

DIMFs-10

Li(I) Rb(I) Li(I) Rb(I)

4.10 2.96 4.17 1.61

NIMFs-10

pseudo-second-order kinetics model

Qe,c (mg g−1)

k1 (min−1)

R2

Qe,c (mg g−1)

3.90 2.84 4.01 1.56

0.0617 0.0435 0.0546 0.0215

0.978 0.986 0.983 0.994

4.32 3.19 4.45 1.84

k2 × 10−2(g mg−1 min−1) h (mg g−1 min−1) t1/2(min) 1.972 1.801 1.681 1.310

0.368 0.183 0.333 0.044

R2

11.75 17.41 13.36 41.56

0.993 0.993 0.992 0.99645

Figure 7. Equilibrium data and modeling for the adsorption of Li(I) and Rb(I) for DIMFs-10 and NIMFs-10 (10 mg of DIMFs-10 and NIMFs-10, 10 mL of solution with a concentration of Li(I) and Rb(I) from 10 mg L−1 to 150 mg L−1, pH 7.0).

Table 3. Adsorption Equilibrium Constants for Langmuir and Freundlich Isotherm Equations Langmuir isotherm equation

Freundlich isotherm equation

materials

ions

R2

KL(L mg−1)

Qm(mg g−1)

RL

R2

KF(mg g−1)

1/n

DIMFs-10

Li(I) Rb(I) Li(I) Rb(I)

0.995 0.992 0.998 0.997

0.0209 0.0273 0.0177 0.0098

8.68 7.91 6.62 5.50

0.2418 0.1963 0.2736 0.4050

0.951 0.965 0.978 0.988

0.6350 0.8024 0.4063 0.1570

0.4796 0.4263 0.5048 0.61450

NIMFs-10

both DIMFs-10 and NIMFs-10, but for Rb(I), we can observe that the adsorption capacity of DIMFs-10 is obviously higher than that of NIMFs-10. Imprinting sites on DIMFs-10 provide a better adsorption environment. The adsorption capacities of DIMFs-10 and NIMFs-10 are summarized in Table 3. All equilibrium curves represent an asymptotic plateau phenomenon which is a characteristic of monolayer saturation. Langmuir and Freundlich isotherm models19,20 were utilized to fit the equilibrium data. The equations of the Langmuir and Freundlich isotherm models are expressed as follows

Qe =

KLQ mCe 1 + KLCe

Q e = KFCe1/ n

(6) (7)

where Ce (mg L−1) is the equilibrium concentration of Li(I) or Rb(I) and Qe (mg g−1) is the adsorption capacity at equilibrium. Qm (mg g−1) is the maximum adsorption capacity of adsorbents. KL (L g−1) is the Langmuir affinity constant, KF (mg g−1) represents the Freundlich isotherm constant, and 1/n indicates favorable adsorption conditions. F



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both DIMFs-10 and NIMFs-10. The greater Kd is due to the ion exchange of HMO on the DIMFs-10 and NIMFs-10. Kd of Rb(I) for DIMFs-10 is higher than that for NIMFs-10, demonstrating that TMS-EDTA has distinct selectivity for the coordination of Rb(I). Moreover, the ionic imprinting plays a crucial role in DIMFs-10 selectivity compared to NIMFs-10 selectivity. It provides an oriented specific size of imprinting sites for Rb(I) that is not appropriate for other ions. There are no imprinting sites on the surface of NIMFs-10, so the Kd of Rb(I) is relatively low. Table 4 lists the adsorption effects of other adsorbents (including our previous research) and DIMFs upon the adsorption of Li(I) or Rb(I). HMO ion sieving and ionic imprinting allow DIMFs to achieve adsorption equilibrium within a short time and maintain excellent adsorption efficiency. Moreover, the use of green template CNCS will further reduce environmental pollution. It is conceivable that DIMFs can be employed as a potential adsorbent for Li(I) or Rb(I). Reusability Tests. Reusability is a significant indicator of adsorbents. DIMFs-10 can be quickly separated from the solution without additional operations, so the cyclic operation of DIMFs-10 is very convenient. Reusability experiments were carried out in a mixture system (Li(I) and Rb(I), pH 7.0), and the results are shown in Figure 9 and Table S2. From Figure 9,

Fitting parameters of the Langmuir and Freundlich models were also compiled in Table 3. They demonstrates that the Langmuir model fits the experimental data of DIMFs-10 and NIMFs-10 better than does the Freundlich model. The “favorability” of the adsorption can be evaluated using the separation factor, RL (dimensionless), which was calculated with eq 8 1 RL = 1 + CmKL (8) where Cm is the maximum initial concentration of the metal ion in the relevant experiment. The value of RL can provide a favorable estimate of the adsorption of the given ion. RL of DIMFs-10 is 0.2418 for Li(I) and 0.1963 for Rb(I), which are far smaller than 0.2736 for Li(I) and 0.4050 for Rb(I) of NIMFs-10. This confirms that DIMFs-10 is more favorable for the adsorption of Li(I) and Rb(I). Selectivity. Salt Lake brine contains a large number of common metal ions, such as Li(I), Na(I), K(I), Mg(II), Ca(II), Rb(I), and Cs(I). Therefore, it is necessary to adsorb Li(I) and Rb(I) selectivity from brine. For different areas of Salt Lake brine, its ionic composition and concentration are very different, so in this selectivity test, we studied the selective adsorption ability by using the same concentration for each ion (50 mg L−1). The selectivity of DIMFs-10 and NIMFs-10 relative to Li(I) and Rb(I) was evaluated by the distribution coefficients (Kd, mL g−1) based on eq 9 Kd =

Co − Cf V × Cf m

(9)

where Co and Cf stand for the initial and final concentrations of ions, respectively. V and m represent the volume of solution and the mass of sorbent material, respectively. The results of the selectivity experiment are presented in Figure 8. Obviously, Kd of Li(I) is the highest in all ions for

Figure 9. Regeneration of DIMFs-10 over five cycles.

after five recycles, the adsorption capacities of DIMFs-10 for Li(I) and Rb(I) are about 81% and 82% of the first cycle, respectively. The results indicate that DIMFs-10 displays excellent reusability as an efficient adsorbent for the simultaneous recovery of Li(I) and Rb(I).

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CONCLUSIONS In this work, HMO was immobilized on mesoporous films, and then a Rb(I) ionic imprinted layer was was grafted onto the surface of mesoporous films. Free-standing dual-functional mesoporous films (DIMFs) were successfully prepared and applied to selectively separate Li(I) and Rb(I). Saturated

Figure 8. Kd values of DIMFs-10 and NIMFs-10 for a mixture of Li(I), Na(I), K(I), Mg(II), Ca(II), Rb(I), and Cs(I) ions (10 mg of DIMFs-10 and NIMFs-10, 10 mL of solution with a 50 mg L−1 concentration of each cation, pH 7.0).

Table 4. Comparison of Li(I) and Rb(I) Adsorption Performance for Different Adsorbents sorbent

metal

equilibration time

pH

adsorption capacity (mg g−1)

selectivity

ref

Li/Rb IHPS calix[4]arene-functionalized dual imprinted mesoporous film Fe3O4@SiO2@IIP DIMFs

Li(I), Rb(I) Li(I), Rb(I) Li(I) Li(I), Rb(I)

120 min 240 min 10 min 100 min

7.0 6.0 6.0 7.0

0.166 (Li(I)), 0.141 (Rb(I)) 16.07 (Li(I)), 10.59 (Rb(I)) 4.1 (Li(I)) 6.30 (Li(I)), 6.21 (Rb(I))

high high high high

21 22 23 this work

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Nanofiber as a Flow-through Membrane Adsorber for Continuous Li+ Recovery from Seawater. J. Membr. Sci. 2016, 510, 141−154. (9) Virolainen, S.; Fallah Fini, M.; Miettinen, V.; Laitinen, A.; Haapalainen, M.; Sainio, T. Removal of Calcium and Magnesium from Lithium Brine Concentrate via Continuous Counter-current Solvent Extraction. Hydrometallurgy 2016, 162, 9−15. (10) Ye, L.; Mosbach, K. Molecular Imprinting: Synthetic Materials as Substitutes for Biological Antibodies and Receptors†. Chem. Mater. 2008, 20, 859−868. (11) Chen, L.; Xu, S.; Li, J. Recent Advances in Molecular Imprinting Technology: Current Status, Challenges and Highlighted Applications. Chem. Soc. Rev. 2011, 40, 2922−2942. (12) Qin, L.; He, X. W.; Zhang, W.; Li, W. Y.; Zhang, Y. K. Macroporous Thermosensitive Imprinted Hydrogel for Recognition of Protein by Metal Coordinate Interaction. Anal. Chem. 2009, 81, 7206−7216. (13) Lee, S.-H.; Hoshino, Y.; Randall, A.; Zeng, Z.; Baldi, P.; Doong, R.-a.; Shea, K. J. Engineered Synthetic Polymer Nanoparticles as IgG Affinity Ligands. J. Am. Chem. Soc. 2012, 134, 15765−15772. (14) Bognár, J.; Szucs, J.; Dorkó, Z.; Horváth, V.; Gyurcsányi, R. E. Nanosphere Lithography as a Versatile Method to Generate Surface Imprinted Polymer Films for Selective Protein Recognition. Adv. Funct. Mater. 2013, 23, 4703−4709. (15) Zhang, Q.-H.; Li, S.-P.; Sun, S.-Y.; Yin, X.-S.; Yu, J.-G. LiMn2O4 Spinel Direct Synthesis and Lithium Ion Selective Adsorption. Chem. Eng. Sci. 2010, 65, 169−173. (16) Wang, L.; Meng, C. G.; Ma, W. Study on Li+ Uptake by Lithium Ion-sieve via the pH Technique. Colloids Surf., A 2009, 334, 34−39. (17) Shopsowitz, K. E.; Hamad, W. Y.; MacLachlan, M. J. Flexible and Iridescent Chiral Nematic Mesoporous Organosilica Films. J. Am. Chem. Soc. 2012, 134, 867−870. (18) Zheng, X. D.; Pan, J. M.; Zhang, F. S.; Liu, E. L.; Shi, W. D.; Yan, Y. S. Fabrication of Free-standing Bio-template Mesoporous Hybrid Film for High and Selective Phosphate Removal. Chem. Eng. J. 2016, 284, 879−887. (19) Mazzotti, M. Equilibrium Theory based Design of Simulated Moving Bed Processes for a Generalized Langmuir Isotherm. J. Chromatogr. A 2006, 1126, 311−322. (20) Allen, S. J.; McKay, G.; Porter, J. F. Adsorption Isotherm Models for Basic Dye Adsorption by Peat in Single and Binary Component Systems. J. Colloid Interface Sci. 2004, 280, 322−333. (21) Xu, X.; Li, Y.; Yang, D.; Zheng, X.; Wang, Y.; Pan, J.; Zhang, T.; Xu, J.; Qiu, F.; Yan, Y. A Facile Strategy toward Ion-imprinted Hierarchical Mesoporous Material via Dual-template Method for Simultaneous Selective Extraction of Lithium and Rubidium. J. Cleaner Prod. 2018, 171, 264−274. (22) Wang, Y.; Xu, J.; Yang, D.; Zhang, T.; Qiu, F.; Pan, J. Calix[4]arenes Functionalized Dual-Imprinted Mesoporous Film for the Simultaneous Selective Recovery of Lithium and Rubidium. Appl. Organomet. Chem. 2018, 32, No. e4511. (23) Luo, X.; Guo, B.; Luo, J.; Deng, F.; Zhang, S.; Luo, S.; Crittenden, J. Recovery of Lithium from Wastewater Using Development of Li Ion-Imprinted Polymers. ACS Sustainable Chem. Eng. 2015, 3, 460−467.

adsorption capacities of optimum condition toward Li(I) and Rb(I) were 6.30 mg g−1 and 6.21 mg g−1 with excellent adsorption kinetics. In addition, ion sieving and ionic imprinting caused DIMFs to possess high selectivity during the adsorption of Li(I) and Rb(I). At the same time, DIMFs displayed excellent reusability as efficient adsorbents for the simultaneous recovery of Li(I) and Rb(I), which enhances their potential for industrial applications.

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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.8b00731. Surface and transversal SEM images of NIMFs-10; SEM mapping images and quantitative results of DIMF-10; and adsorption capacity and adsorption percentage in cycle tests (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Xudong Zheng: 0000-0003-2688-4855 Yongsheng Yan: 0000-0003-4065-0369 Funding

This work was financially supported by the National Natural Science Foundation of China (nos. 21876015, 21808018, and U1507115), the Natural Science Foundation of Jiangsu Province (no. BK20140534), and the Natural Science Foundation of the Jiangsu Higher Education Institutions of China (no. 18KJB610002). Notes

The authors declare no competing financial interest.

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REFERENCES

(1) Kaassis, A. Y. A.; Xu, S.-M.; Evans, D. G.; Williams, G. R.; Wei, M.; Duan, X. Combined In Situ and In Silico Studies of Guest Intercalation into the Layered Double Hydroxide [LiAl2(OH)6]X· yH2O. J. Phys. Chem. C 2015, 119, 18729−18740. (2) Meggiolaro, D.; Gigli, G.; Paolone, A.; Reale, P.; Doublet, M. L.; Brutti, S. Origin of the Voltage Hysteresis of MgH2 Electrodes in Lithium Batteries. J. Phys. Chem. C 2015, 119, 17044−17052. (3) Liu, Y.; He, X.; Hanlon, D.; Harvey, A.; Khan, U.; Li, Y.; Coleman, J. N. Electrical, Mechanical, and Capacity Percolation Leads to High-Performance MoS2/Nanotube Composite Lithium Ion Battery Electrodes. ACS Nano 2016, 10, 5980−5990. (4) Meshram, P.; Pandey, B. D.; Mankhand, T. R. Extraction of Lithium from Primary and Secondary Sources by Pre-treatment, Leaching and Separation: A Comprehensive Review. Hydrometallurgy 2014, 150, 192−208. (5) Chitrakar, R.; Kanoh, H.; Miyai, Y.; Ooi, K. Recovery of Lithium from Seawater Using Manganese Oxide Adsorbent (H1.6Mn1.6O4) Derived from Li1.6Mn1.6O4. Ind. Eng. Chem. Res. 2001, 40, 2054− 2058. (6) Ö zmal, F.; Erdogan, Y. Li+ Adsorption/Desorption Properties of Lithium Ion-sieves in Aqueous Solution and Recovery of Lithium from Borogypsum. J. Environ. Chem. Eng. 2015, 3, 2670−2683. (7) Kang, J.; Sohn, J.; Chang, H.; Senanayake, G.; Shin, S. M. Preparation of Cobalt Oxide from Concentrated Cathode Material of Spent Lithium Ion Batteries by Hydrometallurgical Method. Adv. Powder Technol. 2010, 21, 175−179. (8) Park, M. J.; Nisola, G. M.; Vivas, E. L.; Limjuco, L. A.; Lawagon, C. P.; Seo, J. G.; Kim, H.; Shon, H. K.; Chung, W.-J. Mixed Matrix H


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