Thermally Sensitive Molecularly Imprinted Polymers on Mesoporous

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

pubs.acs.org/jced

Thermally Sensitive Molecularly Imprinted Polymers on Mesoporous Silica Nanospheres: Preparation, Characterization, and Properties as Novel Adsorbents for Dichlorophen Jifeng Guo,*,†,‡ Hui Chen,†,‡ and Xiao Wei*,†,‡ †

Key Laboratory of Subsurface Hydrology and Ecological Effects in Arid Region, Ministry of Education and ‡School of Environmental Science and Engineering, Chang’an University, Xi’an 710054, China

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S Supporting Information *

ABSTRACT: Novel thermally responsive mesoporous silica nanosphere molecularly imprinted polymers (T-MMIPs) were prepared via a two-step precipitation polymerization process for selective adsorption and removal of dichlorophen (DCP) in aquatic environments. The innovative part was that TMMIPs were first used for the identification and separation of DCP. The obtained materials were characterized by SEM, TEM, FT-IR, and XRD. Static adsorption, kinetic, temperature sensitivity, and selective recognition experiments were implemented to test adsorption performance of T-MMIPs and T-MNIPs (thermally responsive mesoporous silica nanosphere molecularly nonimprinted polymers). Langmuir and pseudo-second-order kinetic models were found more consistent with experimental data, and T-MMIPs had a higher selective adsorption capacity and better temperature response. T-MMIPs have the best adsorption performance, and their adsorption equilibrium capacity can reach 108.35 mg/g at 298 K. In addition, regeneration and real-sample experiments demonstrated that T-MMIPs have good repeatability and practicality. Therefore, this study provides a potential application for the adsorption of dichlorophen in wastewater environments.

1. INTRODUCTION Pharmaceuticals and personal care products (PPCPs) contain a large and diverse range of organic compounds such as preservatives, sunscreens, and fungicides,1 which are increasingly left in the environment due to their extensive applications and mediocre removal of conventional treatments.2 Among the PPCPs, dichlorophen (DCP) can effectively control or kill microorganisms such as bacteria, fungi, and algae in the aquatic ecosystem and become an important part of PPCPs. It is often added to medical drugs, soaps, and personal care products.3 Although the half-life of most drugs is inferior to persistent organic pollutants (POPs), their concentration accumulates due to long-term emissions. Therefore, drug contaminants are also considered as “pseudo-persistent” organic pollutants.4 It was reported that DCP was detected at amounts of 10−450 ng/L in wastewater effluents.5 The hydrophobic property of DCP (log Kow = 4.3)6 allows it to accumulate easily in aquatic organisms; consequently, it produces highly toxic effects to aquatic organisms and humans.7 Hence, just like using Ladoped UiO-66 (La-UiO-66) to remove phosphate from wastewater,8 we must find a simple, efficient, fast, and sensitive method for detecting and separating the DCP in water. Molecularly imprinted polymers (MIPs) are synthetic materials that can form special three-dimensional cavities with a designated recognition attribute for some contaminant molecules.9 In fact, the molecular imprinting technique plays a © XXXX American Chemical Society

vital role in efficient separation of target substances from multiple and lowly abundant components in the environment.10 Aside from having high sensitivity and excellent separation properties, MIPs also provide extreme thermal stability and mechanical strength. Due to their numerous advantages, they are widely applied to chromatographic analysis,11 chiral compound resolution,12 analog sensors,13 enzyme catalysis,14 and targeted drug delivery.15 In most cases, MIPs exhibit typical recognition sites for template molecules due to the fact that the functional monomer and the target molecule are first allowed to bind via covalent or noncovalent bonds. Then, the formed material is fixed in the presence of a cross-linking agent, and the template is removed in the last step.16 Polymers are prepared by using a conventional bulk polymerization method, which generally produces disordered shapes and deeper binding sites, resulting in undesirable polymer adsorption properties.17 Surface molecular imprinting, an approach for forming identified sites onto the material surface, has been applied to prepare many imprinted polymers due to the easy elution of the template molecules.18 Despite great progresses having been achieved, some issues, such as the low adsorption capacity and Received: May 4, 2019 Accepted: August 2, 2019

A

DOI: 10.1021/acs.jced.9b00393 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

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recognition sites, still exist, which significantly impedes their practical applications in water treatment.19 Mesoporous silica nanospheres (MSNs) possess large and ordered pore sizes, remarkable hydrothermal stability, and high specific surface areas,20 making them a topic to be more and more concerned about. Given these advantages, MSNs are used as a carrier in combination with surface molecular imprinting. Wang’s group prepared mesoporous silica imprinted polymers based on surface molecular imprinting technology and successfully selected trace dicyandiamide in milk.21 Highly selective surface molecularly imprinted polymers (FDU-12@MIPs) were prepared using structural analogues of aflatoxins as the template molecule and mesoporous silica FDU-12 as the carrier, and the FDU-12@MIPs could be used as an efficient adsorbent of solid-phase extraction for enrichment of aflatoxins in real samples, which not only were beneficial to improve mass transmission and reduce residue of templates but also could form more imprint sites to enhance recognition ability.22 Achieving stimuli response recognition behavior is one of the goals of molecular recognition. The combination of the template and intelligent functional monomers has attracted great attention from many scholars, which has brought in unprecedented stimuli-responsive MIPs,23 such as thermoresponsive MIPs,24 pH-responsive MIPs,25 and photoresponsive MIPs.26 Recently, due to its temperature-sensitive nature, poly(N-isopropylacrylamide) (NIPAM) has been receiving increasing attention. As founded in research,27 NIPAM has a lower critical solution temperature (LCST) of approximately 33 °C. When the solution temperature is higher than the LCST, the hydrogen bond between the thermosensitive molecule and water is destroyed,28 which limits the diffusion in water, and the hydrophobic state predominates. Conversely, NIPAM swells in water at a lower critical solution temperature.29 Due to these characteristics, NIPAM can be used to design intelligent smart sorbent materials that exhibit maximum adsorption at near room temperature, which is cost effective and environmentally friendly.30 So far, ordered mesoporous silica nanospheres have been used as a carrier for adsorbent materials in numerous studies. However, there are no publications about the preparation of temperature-sensitive molecularly imprinted adsorbents to remove dichlorophen by combining a temperature-sensitive monomer and mesoporous silica nanospheres. Hence, in this paper, we first designed a novel thermosensitive molecularly imprinted polymer with mesoporous silica nanospheres as the support skeleton and NIPAM as the temperature-responsive functional monomer to select DCP. The route of fabrication of T-MMIPs and the swelling/contraction transition of NIPAM are shown in Figure 1. NIPAM and acrylamide (AM) as dual monomers are beneficial for forming hollow pores and have time-saving recognition of target molecules. Morphology and chemical properties of T-MMIPs were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR), and X-ray diffraction (XRD). Meanwhile, binding property, selectivity, temperature-regulated behavior, regeneration, and real-sample experiments were also systematically studied.

Figure 1. Schematic illustration of the preparation of thermally responsive mesoporous silica nanosphere molecularly imprinted polymers (T-MMIPs) and the reversible thermosensitive swelling/ shrinking transition of T-MMIPs.

analytical grade and can be applied directly in no other special instructions. Deionized water was obtained in the laboratory. 2.2. Characterizations. UV−vis experiments were carried out on a UV−vis spectrophotometer (UV-2550, Shimadzu, Japan); the Fourier transform infrared (FT-IR) spectra were recorded with the Spectrum Two FTIR spectrophotometer (PerkinElmer, U.S.A.) using KBr pellets; scanning electron microscopy (SEM) images of materials were obtained using a S-4800 SEM (Hitachi, Japan); the morphological evaluation was performed using a transmission electron microscope (TEM, JEM-2100HR) produced by the Japanese electronics company. The identification of the crystalline phase was performed using a Rigaku D/max-γ B X-ray diffractometer (D8 Advance, Bruker-AXS, Germany) with monochromatized Cu Kα radiation over the 2θ range of 10−90° at a scanning rate of 5°/min. 2.3. Synthesis of Mesoporous Silica Nanospheres (MSNs). The method of preparing mesoporous silica nanospheres (MSNs) using CTAB as a surfactant is as follows: 0.50 g of CTAB was dissolved into a conical flask containing 240 mL of H2O. NaOH (2.0 M, aqueous solution, 1.75 mL) was added to the abovementioned flask, and then the prepared liquid was placed in a water bath at a temperature of 80 °C and vigorously stirred using a mechanical stirrer. Then, 2.5 mL of TEOS was added to the mixture. Subsequently, the solution in the Erlenmeyer flask changed from clear to cloudy after stirring for a few minutes. The reaction system was continued at 80 °C for 2 h. The solution was filtered, and the product was collected, washed three times with water and methanol, and was dried under vacuum at 60 °C for 12 h. In order to completely remove the surfactant CTAB, the dried solid product was placed in a muffle furnace and calcined at 550 °C for 6 h at a heating rate of 5.0 °C / min. 2.4. Synthesis of Thermally Responsive Mesoporous Silica Molecularly Imprinted Polymers (T-MMIPs). The surface of the nanoparticles was modified and functionalized with vinyl. In brief, 0.5 g of the above mesoporous silica nanospheres was added to a 100 mL flask containing 50 mL of absolute ethanol and ultrasonically dispersed for 30 min. MPS (KH570) (2.0 mL) was added dropwise to the mixed solution under continuous shaking in a water bath shaker, and then the

2. EXPERIMENTAL SECTION 2.1. Materials. Table S1 lists the information of chemicals, which includes molecular formulas, CAS numbers, and mass fractions used in this study. The reagents and drugs are of B



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Figure 2. SEM and TEM images of the (a, c) MSNs and (b, d) T-MMIPs.

mixture was reacted at 50 °C for 12 h. The products were centrifuged and washed three times with distilled water and absolute ethanol and then dried under vacuum at 60 °C for 12 h. The modified products were obtained and called MSNs@ KH570. After the modification, T-MMIPs were prepared by a twostep polymerization process. The template molecule (DCP), temperature-sensitive functional monomer (NIPAM), and functional monomer (AM) (n1/n2/n3 = 1:3:1) were dissolved in 60 mL of acetonitrile. EGDMA (1.6 mmol), AIBN (10 mg), MSNs@KH570 (100 mg) were also added to the mixture. The mixture was ultrasonically dispersed for 30 min. After nitrogen was purged for 30 min in order to remove oxygen, the solution was placed in the flask in a thermostatic water bath shaker. Preparation of T-MMIPs by two polymerization methods: the reaction system was first polymerized at 50 °C for 6 h and then polymerized at 60 °C for 24 h. The products were dried at 60 °C for 12 h after centrifugation and washing. The template molecule in the polymer layer was extracted using Soxhlet extraction for 22 h with a mixture of methanol and acetic acid (v/v = 9:1) three times. The final products were obtained and called T-MMIPs. The thermally responsive mesoporous silica nanosphere molecularly nonimprinted polymers (T-MNIPs) were synthesized under the same manner and condition except that no DCP was added in the polymerization process. 2.5. Evaluating the Binding Property. For the equilibrium experiments, T-MMIPs/T-MNIPs (2.0 mg) were suspended in a series of DCP ethanol aqueous solution (9.0 mL) with initial concentrations ranging from 20 to 80 mg/L. The series of mixtures were allowed to rest for 12 h at 298 K,

and then the equilibrium concentrations of DCP were detected. The adsorption capacity Qe (mg/g) at equilibrium was calculated according to the following equation Qe =

(C0 − Ce)V m

(1)

where C0 and Ce (mg/L) are the initial and equilibrium concentrations of DCP, respectively, V (mL) is the volume of the solution, and m (g) is the mass of polymers. Similarly, for the kinetic experiments, T-MMIPs/T-MNIPs (2.0 mg) were added into 50 mg/L DCP ethanol aqueous solution. The mixtures were placed at 298 K, and the concentrations of DCP in the supernatant at a certain interval (5, 10, 15, 30, 60, 90, and 120 min) were analyzed. Then, the adsorption capacity Qt (mg/g) at different contact times t was calculated as Qt =

V (C0 − Ct ) m

(2)

where C0 and Ct (mg/L) represent the initial and t time concentrations of DCP, V (mL) is the volume of the solution, and m (g) is the mass of polymers. The imprinting factor was defined as α = QMIP/QNIP. 2,4-Dichlorophenol (2,4-DCP), 2,6-dichlorophenol (2,6DCP), and sulfonamide (SN) were selected as the references to study the selectivity property of the T-MMIPs. Two milligrams of T-MMIPs/ T-MNIPs was added into 9.0 mL of 2,4-DCP, 2,6-DCP, and SN solutions with the initial concentration of 50 mg/L. These mixtures were allowed to rest for 12 h at 298 K. C



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Figure 3. (a) Fourier transform infrared (FT-IR) spectra and (b) XRD images of materials.

2.6. Temperature Sensitivity. In order to investigate the temperature-responsive effect of the polymers, T-MMIPs/TMNIPs (2.0 mg) were added into 50 mg/L DCP ethanol aqueous solution (9.0 mL) and were allowed to rest for 12 h at different temperatures (298, 308, and 318 K). 2.7. Regeneration Performance of T-MMIPs. To test the reusability and stability of the polymers, 2.0 mg of TMMIPs/T-MNIPs was added into the 50 mg/L DCP solution, and the mixtures were incubated at 298 K for 30 min. The concentration of DCP remaining in the solution was measured when the amount of adsorption reached equilibrium. TMMIPs and T-MNIPs were then eluted in methanol/acetic acid (v/v, 9:1) until no target was detected. The process was repeated several times to record the amount of adsorbed DCP before each cleaning cycle. 2.8. Real-Sample Experiments. In order to further investigate the adsorption performance and practical application value of the T-MMIPs, the real water sample was collected from the Fenghe River Basin in Xi’an, which was pretreated and spiked with DCP at three concentration levels (5, 10, and 20 mg/L). T-MMIPs and T-MNIPs were added to the spiked water sample for enrichment detection and separation of DCP at 298 K.

Figure 4. Selectivity of T-MMIPs and T-MNIPs toward DCP, 2,4DCP, 2,6-DCP , and SN.

Table 1. Removal of Dichlorophen by Different Methods methodology laccase-catalyzed photodegradation photocatalytic molecular imprinting polymerization molecular imprinting polymerization molecular imprinting polymerization

3. RESULTS AND DISCUSSION 3.1. Characterization of Nanoadsorbents. Figure 2 demonstrated the size and shape of MSNs and T-MMIPs by the SEM and TEM technique. The SEM images of MSNs and T-MMIPs are shown in Figure 2a,c, respectively. MSNs showed spherical nanoparticles with a size of ∼100 nm and a uniform shape (Figure 2a). T-MMIPs were extremely similar to MSNs except that the surface became smooth and the size slightly increased after the imprinted polymerization reaction (Figure 2c). In TEM images of Figure 2b,d, the mesoporous structures were clearly exhibited in both MSNs and T-MMIPs, indicating the mesoporous structure stability of MSNs after the loading. The FT-IR spectra can determine the presence or change of functional groups or chemical bonds in a sample by using different functional groups, chemical bond vibration, or rotation. Figure 3a displayed the FT-IR spectra of MSNs, MSNs@KH570, and T-MMIPs. The peaks of MSNs at 796.8 and 1081 cm−1 were attributed to asymmetric stretching of Si− O and Si−O−Si from the spectrum of Figure 3a. The wide and strong peak at 3442.1 cm−1 indicates the presence of hydroxyl functional groups on the surface of mesoporous silica. As

Qm (removal rate)

reference

318

90 60 210 90

nontoxic 87.2% 90.0% 56.0 mg/g

7 33 34 31

318

40

63.3 mg/g

35

298

30

108.35 mg/g

this study

T (K)

equilibrium time (min)

298

Table 2. Analytical Performance of Polymers T-MMIPs performance parameters

T (K)

Qe (mg/g)

t

α

temperature effect

298 308 318 298

108.35 83.86 44.04 114.94

12 h

92.66 60.08 40.17 94.876

12 h

1.17 1.40 1.09 1.21

298

60.82

30 min

43.54

60 min

1.39

maximum adsorption by Langmuir fitting adsorption equilibrium time

D

T-MNIPs Qe (mg/g)

t



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Qt =

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

(4)

After a formal change, eqs 5 and 6 were linear equations. (5)

t 1 t = + 2 Qt Q k 2Q e e

(6)

where Qt (mg/g) and Qe (mg/g) are the adsorption amount at any time t (min) and at equilibrium, respectively, and k1 (g· min/mg) and k2 (g·min/mg) are the rate constants of pseudofirst-order and pseudo-second-order, respectively. The model parameter fitting results are shown in Table S2. As shown, the pseudo-second-order could more accurately describe the effect of time in the adsorption process, indicating that chemical bonding played a major role on the adsorption of T-MMIPs and T-MNIPs. 3.3. Static Adsorption Experiment. The solution’s initial concentration, which may produce some effects on the surface change of the adsorbent and speciation of the contaminants, plays a large role in the chemisorption process. Therefore, the adsorption isothermal experiments were carried out in order to explore the adsorption amount of T-MMIPs and T-MNIPs. As shown in Figure S2a, in a certain concentration range, the adsorption capacity of DCP increased with the increase of concentration. The greater the concentration of DCP in the solution, the more prominent the difference in concentration between the polymer surface and the solution, which made the adsorption power of T-MMIPs to DCP stronger. T-MNIPs displayed a trend similar to that of T-MMIPs but lower adsorption amounts. The maximum adsorption amounts of TMMIPs and T-MNIPs were 108.35 and 92.66 mg/g, respectively, and the α was 1.17. Meanwhile, the adsorption processes of T-MMIPs and T-MNIPs were fitted by Langmuir and Freundlich adsorption models. The linear form of the Langmuir and Freundlich models emerged as eqs 7 and 8

Figure 5. Reusability of T-MMIPs.

shown in the curve of MSNs@KH570, a new peak could be observed at 1631.7 cm−1, corresponding to the CC absorption peak, which means that the surface of the silicon sphere was successfully modified by KH570. We could see the significant peak at 1726 cm−1 that was due to CO stretching of EGDMA from the curve of T-MMIPs. Meanwhile, several vibration peaks at 1461.7 and 1390 cm−1 (deformation of the methyl groups of −C(CH3)2) could be presumed to be the characteristic peaks of NIPAM. The peak at 2973 cm−1 was the C−H stretching vibration due to the presence of the −CH2 and −CH3 functional groups. All these results suggested that T-MMIPs were successfully synthesized. The XRD patterns of MSNs and T-MMIPs are shown in Figure 3b. In the 2θ range of 10−90°, a broad characteristic peak at 21.8° appears on the curve of MSNs, which corresponds to amorphous silica. Also can be seen is a peak at approximately 20° from the curve of T-MMIPs, and we can speculate that it formed a relatively thin polymer layer owing to the intensity of the peak that did not change drastically. 3.2. Adsorption Kinetics Experiment. The experimental results of adsorption kinetics of T-MMIPs and T-MNIPs are shown in Figure S1. The kinetic adsorption of T-MMIPs and T-MNIPs increased rapidly in the first 15 min, reaching 92.03% and 87.47% of the adsorption equilibrium, respectively. The adsorption rate of T-MNIPs gradually became slower within 30−60 min and reached equilibrium after 60 min, while T-MMIPs reached equilibrium after 30 min. In addition, the adsorption capacity of T-MMIPs was higher than that of TMNIPs, and thereby the imprinted factor (α) was 1.39, indicating that it stemmed from the presence of imprinted holes in the T-MMIPs. Compared with other imprinted layers prepared by a similar method, this research reached a faster equilibrium time and a larger equilibrium adsorption amount, and the temperature required for the maximum adsorption amount was close to room temperature.31 In order to further explore the mechanism of adsorption kinetics, experimental data was analyzed by applying pseudo-first-order and pseudosecond-order kinetic models. The nonlinear equations are as follows: Q t = Q e − Q e e −k1t

ln(Q e − Q t ) = ln Q e − k1t

Ce C 1 = + e Qe KLQ m Qm

(7)

i1y ln Q e = ln KF + jjj zzzln Ce kn{

(8)

where Qe (mg/g) and Qm (mg/g) are the equilibrium and maximum adsorption amounts, respectively, Ce (mg/L) is the concentration at equilibrium, KL (L/mg) is the Langmuir adsorption equilibrium constant, and KF (mg/g) and n are the Freundlich adsorption equilibrium constants. Compared with the Freundlich model, the adsorption isotherm of T-MMIIPs was more consistent with the Langmuir model (Table S3), which implied that the adsorption process was carried out on a single layer and uniform surface, and all the binding site energies were uniform. In contrast, T-MNIPs were more in

(3)

Table 3. Recoveries and RSD of DCP in River Water Using T-MMIPs and T-MNIPs T-MMIPs

T-MNIPs

sample

added (mg/L)

measured value (mg/L)

recovery (%)

RSD (%)

measured value (mg/L)

recovery (%)

RSD (%)

river water

5 10 20

4.70 9.79 19.29

94.02 97.93 96.49

1.38 1.24 2.65

4.55 9.42 18.72

91.15 94.25 93.62

2.16 2.62 1.96

E



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randomly distributed in the imprinted polymer space, and there were no imprinting sites to make them have good adsorption properties for various molecules. Hence, they did not exhibit special selective adsorption on the molecules in the system. In Table 1, removal of dichlorophen using different methods is listed, and the significant performance of polymers is shown in Table 2. In the above two tables, we can conclude that the influence of temperature on the adsorption amount is large, and the adsorption performance is better at room temperature. In addition, the presence of the mesoporous silica carrier produces not only a large adsorption amount but also a short adsorption equilibrium time. Therefore, the high efficiency of DCP removal by temperature-sensitive mesoporous silica nanosphere molecularly imprinted polymers can be well demonstrated. 3.6. Regeneration Performance of T-MMIPs. Regeneration ability is one of the key factors for the application performance of adsorbents. The regeneration performance of T-MMIPs adsorbing DCP was investigated. The experimental results are shown in Figure 5. It could be observed that the adsorption efficiency decreased slightly after six desorption− regeneration cycles. The results indicated that T-MMIPs have good regeneration performance and can be used in practical applications. 3.7. Real-Sample Experiments. Some experiments were implemented to investigate the practical use of T-MMIPs. As listed in Table 3, high recoveries of 94.02%−97.93% with the relative standard deviations (RSD) of 1.24%−2.65% were obtained for the real water sample. Compared with T-MMIPs, the recoveries of the water sample by using T-MNIPs were 91.15%−94.25%, and the RSD were 1.96%−2.62%. The results indicated that the T-MMIPs were potentially suitable for effective separation, extraction, and determination of trace DCP in real samples.

line with the Freundlich adsorption model, indicating that adsorption occurred in a heterogeneous manner. 3.4. Temperature Sensitivity. To study the temperatureresponsive attribute of the T-MMIPs and T-MNIPs, the adsorption of DCP on T-MMIPs and T-MNIPs were investigated at three different temperatures (298, 308, and 318 K). Figure S3 shows the change in the amount of adsorption of T-MMIPs and T-MNIPs as a function of temperature at seven different concentrations. As observed, the increasing temperature was not beneficial to adsorption. Under the same conditions, the adsorption amounts of T-MMIPs and T-MNIPs at 298 K were greater than those at the other two temperatures, and the lowest adsorption amounts of T-MMIPs and T-MNIPs were at 318 K. The phenomenon that the adsorption amount of T-MMIPs for DCP changed with temperature was related to the presence of temperaturesensitive functional monomers. One reason was that the solution temperature was above the LCST; the hydrogen bond between the imprinting site and the template molecule was destroyed to some extent, and the hydrophobic interaction of the polymer was enhanced. The molecular chains aggregated with each other to make the polymer into a collapsed structure, and the imprinting sites were too tight, so the adsorption amount was reduced. And another reason was that the hydrophilic groups of the imprinted material formed a hydrogen bond with water, and the polymer molecular chains was fully extended by hydration, which led to the identification sites in T-MMIPs becoming larger and polymer materials swelling at lower temperatures, making the template molecules easily adsorbed by the materials.32 3.5. Selectivity Adsorption Experiments of T-MMIPs. Figure 4 explains the selective adsorption of T-MMIPs and TMNIPs for the template, other dichlorophenol analogs (2,4DCP, 2,6-DCP), and structural dissimilarity (sulfonamide). We can see that the amount of T-MMIPs for DCP was higher than that of the other three substances, indicating that the imprinted sites matched with the DCP template in size, structure, and chemical groups. Table S4 shows some results obtained by using eqs 9, 10, and 11 Kd =

4. CONCLUSIONS To conclude, new thermoresponsive mesoporous silica nanosphere molecularly imprinted polymers were prepared by twostep precipitation polymerization. The morphology and structure characterization results clearly demonstrated that thin and uniform polymeric layers were formed. In addition, TMMIPs showed higher adsorption amounts and faster binding kinetics than those of T-MNIPs. The Langmuir isotherm and the pseudo-second-order kinetic model fitted our experimental data. More importantly, both T-MMIPs and T-MNIPs presented excellent thermosensitivity, which could reach the maximum adsorption amounts at below LCST. The novel imprinting system is efficient, cost-effective, and lowconsuming. Moreover, the regeneration experiments indicated that T-MMIPs had excellent stability. Upon the results of our study, this kind of material is promising and has plenty potential applications for pollution monitoring and separation.

Qe Ce

(9)

k=

Kd(DCP) Kd(X)

(10)

K ′=

KT − MMIPs KT − MNIPs

(11)

where Kd (L3/g) is the distribution coefficient, Qe (mg/g) and Ce (mg/L) are the equilibrium adsorption amount and concentration, respectively. k is the selectivity coefficient, k′ is the relative selectivity coefficient, and X represents 2,4-DCP, 2,6-DCP, and SN, respectively. From Table S4, we can know that T-MMIPs exhibited outstanding selectivity to DCP, and the sequential capacity was DCP > 2,4-DCP > 2,6-DCP > SN, which suggested that adsorption properties of the imprinting cavity for those with structural similarities were stronger than for those with no structural similarities. It might be due to the fact that structural analogs could better bind to the imprinting sites to some extent. However, the adsorption amount of TMNIPs for several different molecules was lower than that of T-MMIPs. Maybe because the reactive functional groups were

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.9b00393. Dynamic adsorption curves and kinetic fitting of TMMIPs and T-MNIPs, static binding isotherms and isotherms linear fitting of T-MMIPs and T-MNIPs, temperature sensibility of T-MMIPs and T-MNIPs, list and information of chemicals, parameters of kinetic F



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models for DCP adsorption onto T-MMIPs and TMNIPs, parameters of isotherm constants for DCP adsorption onto T-MMIPs and T-MNIPs, adsorption selectivity of T-MMIPs and T-MNIPs (PDF)

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. Phone: +86 029 82339956. Fax: +86 029 82339281 (J.G.). *E-mail: [email protected] (X.W.). ORCID

Xiao Wei: 0000-0002-4092-3059 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This study was financially supported by the Fund Project of Shaanxi Key Laboratory of Land Consolidation (no. 2019JC03), Shaanxi Nature Science Basic Research Program (no. 2019JM-429), Chang’an University Graduate Research and Practice Innovation Project (no. 300103002027), Fundamental Research Funds for the Central Universities of Chang’an University (nos. 310829172002, 310829163406, and 310829161002), Natural Science Foundation of China (no. 21607015), and Science and Technology Support Foundation of Shaanxi Province (nos. 2018JQ2025 and 2016JQ2008).

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Thermally Sensitive Molecularly Imprinted Polymers on Mesoporous

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