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Article

Facile Synthesis of Binuclear Imidazole-Based Poly(ionic liquid) via Monomer Self-Polymerization: Unlocking High-Efficiency CO2 Conversion to Cyclic Carbonate

by
Ranran Li
1,
Yuqiao Jiang
1,
Linyan Cheng
1,
Cheng Fang
2,
Hongping Li
3,
Jing Ding
1,*,
Hui Wan
1 and
Guofeng Guan
1,*
1
State Key Laboratory of Materials-Oriented Chemical Engineering, College of Chemical Engineering, Jiangsu National Synergetic Innovation Center for Advanced Materials, Nanjing Tech University, Nanjing 210009, China
2
College of Chemical Engineering, Nanjing Forestry University, Nanjing 210037, China
3
Institute for Energy Research of Jiangsu University, Jiangsu University, Zhenjiang 212013, China
*
Authors to whom correspondence should be addressed.
Catalysts 2025, 15(5), 406; https://doi.org/10.3390/catal15050406
Submission received: 16 March 2025 / Revised: 14 April 2025 / Accepted: 20 April 2025 / Published: 22 April 2025
(This article belongs to the Special Issue Ionic Liquids and Deep Eutectic Solvents in Catalysis)
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Abstract

:
Strategic utilization of carbon dioxide as both a carbon mitigation tool and a sustainable C1 feedstock represents a pivotal pathway toward green chemistry. Although poly(ionic liquid)s (PILs) exhibit promise in CO2 conversion, conventional divinylbenzene (DVB) cross-linked architectures are limited by reduced ionic density and limited accessibility of active sites. Herein, we reported a binuclear imidazolium-functionalized PIL catalyst (P-BVIMCl), synthesized through a simple self-polymerization process, derived from rationally designed ionic liquid monomers formed by quaternization of 1,4-bis(chloromethyl)benzene with N-vinylimidazole. The dual active sites in P-BVIMCl-quaternary ammonium cation (N+) and nucleophilic chloride anion (Cl−) synergistically enhanced CO2 adsorption/activation and epoxide ring-opening. Under optimal catalyst preparation conditions (100 °C, 24 h, water/ethanol = 1:3 (v/v), 10 wt% AIBN initiator) and reaction conditions (100 °C, 2.0 MPa CO2, 10 mmol epichlorohydrin, 6.7 wt% catalyst loading, 3.0 h), P-BVIMCl catalyzed the synthesis of glycerol carbonate (GLC) with a yield of up to 93.4% and selectivity of 99.6%, maintaining activity close to 90% after five cycles. Systematic characterization and density functional theory (DFT) calculations confirmed the synergistic activation mechanism. This work established a paradigm for constructing high-ionic-density catalysts through molecular engineering, advancing the development of high-performance PILs for industrial CO2 valorization.

Graphical Abstract

1. Introduction

Over the past decades, CO2 has emerged not merely as an essential greenhouse gas but also as an abundant, low-cost, and renewable C1 feedstock in green chemistry, gaining significant industrial attention within carbon capture, utilization, and storage (CCUS). Notably, the CO2-epoxide cycloaddition reaction has gained prominence as one of the most promising technical pathways due to its inherent advantages: zero byproduct generation and 100% atom economy, aligning perfectly with green chemistry principles and the atom economy concept [1,2]. This thermodynamically favorable process has driven the extensive development of catalysts over recent decades [3,4,5]. The catalytic landscape for this transformation has expanded across two primary fields: homogeneous systems including organic bases [6,7], metal halides/complexes [8,9], and ionic liquids [10,11]; and heterogeneous platforms featuring metal oxides [12,13], porous organic polymers (POPs) [14,15], poly(ionic liquid)s (PILs) [16,17,18], and metal–organic frameworks (MOFs) [19,20].
While homogeneous catalytic systems, including ionic liquids, have achieved remarkable progress, heterogeneous catalytic systems present compelling yet challenging opportunities by integrating easy separation of the catalyst with superior catalytic activity [21,22,23,24]. Among these, PILs, whose polymeric architectures incorporate recurring ionic liquid motifs, uniquely combine the physicochemical properties of ionic liquids with heterogeneous characteristics [25,26]. PILs have garnered substantial research interest due to their inherent recyclability, exceptional stability, tailorable molecular frameworks, and versatile polymerization methodologies. However, conventional PILs exhibit critical limitations in CO2 cycloaddition: suboptimal nucleophilic site density, insufficient CO2 activation capacity, and compromised stabilization of zwitterionic intermediates. These deficiencies collectively impair CO2/epoxide dual activation efficiency, resulting in diminished catalytic performance. To address these challenges, Yang et al. synthesized a series of poly (bisimidazolium) ionic liquids (PBIL-m) and utilized them as homogeneous catalysts for CO2 cycloaddition reactions [27]. Notably, these catalysts could be readily separated in a heterogeneous form post-reaction, significantly enhancing their recyclability. Zou et al. developed poly(ionic liquid)s functionalized with triethylenetetramine-modified imidazolium units [28], along with a heterogeneous catalyst (PIMDIL) [29]. This design effectively integrated high-density ionic active sites and hydrogen bond donors, demonstrating superior catalytic performance in CO2-epoxide cycloaddition. Despite these advancements, critical challenges remain [30,31]. For instance, during polymerization, the introduction of divinylbenzene (DVB) to enhance structural rigidity inevitably reduced the ionic density of the catalysts, thereby diminishing their CO2 conversion efficiency. To overcome this limitation, future efforts should focus on designing poly(ionic liquid)s that simultaneously retain high ionic density and structural rigidity. One promising strategy involves incorporating rigid benzene ring structures directly into the monomer units, which may synergistically enhance ionic density, catalytic activity, and stability.
Herein, the rational preparation of binuclear imidazole-based poly(ionic liquid)s (P-BVIMCl) through a free radical copolymerization strategy using 1,4-bis(chloromethyl)benzene (DCX) and N-vinylimidazole (VIM) as precursors was reported. The synthesized PILs were systematically characterized via scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS) to elucidate their chemical composition, hierarchical pore structure, and active sites distribution. The corresponding CO2 catalytic cycloaddition performance was evaluated under different catalyst preparation parameters and reaction conditions. Meanwhile, the stability and substrate universality of P-BVIMCl were studied. In addition, a possible reaction mechanism was proposed.

2. Results and Discussion

2.1. Catalysts Characterization

The functional groups of P-BVIMCl and BVIMCl were characterized by Fourier-transform infrared spectroscopy (FT-IR). As shown in Figure 1 and Figure S3, for P-BVIMCl, a peak at 1150 cm−1 was attributed to C-N stretching vibrations in the imidazolium cation structure. A band at 1550 cm−1 corresponded to imidazole ring vibrations. A characteristic absorption at 1440 cm−1 was assigned to C-C stretching vibrations of aromatic rings, confirming the presence of imidazolium ionic moieties within the framework of poly(ionic liquid) [32]. Comparative analysis of BVIMCl and P-BVIMCl revealed critical polymerization evidence: The characteristic absorption peak of the C=C double bond located at 1650 cm−1, as well as the vibrational peak of the unsaturated C-H on the vinyl group located at 970 cm−1, showed a significant decrease in intensity compared to the peak at 1550 cm−1 after the polymerization reaction. This change clearly confirms that the polymerization reaction was successfully carried out [33].
The microstructural morphology and elemental distribution of the P-BVIMCl catalyst were analyzed through SEM and EDS mapping, as shown in Figure 2. As shown in Figure 3a, P-BVIMCl consisted of primary particles stacked upon one another. These structural variations were attributed to modified polymerization parameters that induced changes in the polymer architecture [34]. Furthermore, the corresponding EDS mapping images of P-BVIMCl (Figure 2b–e) revealed uniform distributions of C, N, and Cl elements, demonstrating homogeneous dispersion of imidazole units within the framework of poly(ionic liquid)s.
The chemical states of elements in P-BVIMCl were investigated using X-ray photoelectron spectroscopy (XPS), as shown in Figure 3. The XPS survey spectrum (Figure 3a) displayed characteristic peaks corresponding to C, N, and Cl elements. In the N 1s spectrum (Figure 3c), the peak at 401.44 eV was attributed to imidazolium nitrogen, while an additional peak observed at 399.18 eV likely originated from electron transfer caused by the strong interactions with surrounding charged ions [35]. The C 1s spectrum (Figure 3b) could be deconvoluted into two characteristic signals corresponding to C-C and C-N bonds, with binding energies at 284.80 eV and 286.32 eV, respectively [36]. The chlorine XPS spectrum (Figure 3d) exhibited two distinct peaks at 196.86 eV and 198.51 eV, which were assigned to the 2p3/2 and 2p1/2 orbitals of Cl− ions [37]. The presence of free chloride ions confirmed the successful occurrence of the quaternization reaction.
The pore structure and textural properties of P-BVIMCl were investigated by N2 adsorption–desorption analysis (Figure 4a,b). The isotherm of P-BVIMCl exhibits a Type II profile with a distinct hysteresis loop at high relative pressures (p/p0), indicative of a uniform mesoporous structure. The average pore diameter was determined to be 3.72 nm, and the BET surface area was calculated as 6.0164 m2·g−1 (Table 1).
Moreover, CO2 adsorption performance tests revealed that P-BVIMCl achieved a CO2 adsorption capacity of 1.853 cm3·g−1 under the specified conditions (Figure 4c). Additionally, thermal stability analysis of BVIMCl and P-BVIMCl catalysts was investigated by thermogravimetric (TG) characterization. As shown in Figure 4d and Figure S4, the weight loss observed in the TG curve of BVIMCl between 250 and 380 °C could be attributed to the thermal decomposition of its own structure of ionic liquid, while the weight loss above 380 °C resulted from the collapse of the rigid benzene ring structure in the ILs [38]. For P-BVIMCl, the weight loss below 280 °C corresponded to the removal of adsorbed and bound water from the pores of poly(ionic liquid). The weight loss in the 280–500 °C range exhibited essentially the same decomposition trend as BVIMCl, with poly(ionic liquid)s demonstrating slightly higher decomposition temperatures compared to the corresponding ionic liquid [39]. Both BVIMCl and P-BVIMCl initiated thermal decomposition above 250 °C, significantly exceeding the reaction temperature required for CO2 cycloaddition, indicating that the P-BVIMCl catalyst possessed excellent thermal stability.

2.2. Evaluation of Catalytic Performance

2.2.1. Catalyst Preparation Condition Optimization

To investigate the impact of P-BVIMCl preparation conditions on CO2 catalytic performance, we synthesized a series of poly(ionic liquid) catalysts by adjusting various synthesis parameters, including solvent type, reaction temperature, reaction time, and the amount of AIBN used. Research has found that the amount of initiator AIBN and the duration of polymerization have a negligible effect on the yield of the cycloaddition reaction (Figure 5a,b). As shown in Figure 5c, using the binuclear imidazole-based poly(ionic liquid) as the catalyst, the study revealed that both the amount of initiator AIBN and the polymerization time exhibited negligible effects on the yield of GLC. When varying polymerization temperatures, self-polymerization failed at 80 °C. Increasing the temperature enabled polymer formation, with an increase in GLC yield. When the temperature reached 100 °C, the yield had already exceeded 90%. Further temperature elevation showed no significant yield improvement, indicating equilibrium attainment at 100 °C.
For solvent effects, water/ethanol mixtures demonstrated optimal CO2 catalytic performance (Figure 5e). Systematic investigation of water/ethanol ratios revealed no product formation at a 1:1 (v/v) ratio. The yield of GLC initially increased and then decreased with increasing ethanol proportion, achieving the highest yield of GLC of 92.6% at a 1:3 (v/v) water/ethanol ratio. These results established the optimal polymerization conditions as follows: 100 °C, 24 h, water/ethanol = 1:3 (v/v), and 10 wt% AIBN initiator, obtaining 92.6% conversion of glycidol (GO) and 99.0% selectivity of GLC (Figure 5d).
Additionally, in order to compare the effects of self-polymerization and copolymerization with DVB on ion density and catalytic performance, the CO2 catalytic performance of the copolymerization of BVIMCl with divinylbenzene (DVB) at a 1:1 molar ratio and P-BVIMCl was evaluated. Remarkably, the poly(ionic liquid) copolymerized with BVIMCl and divinylbenzene (DVB) at a 1:1 molar ratio under optimal conditions showed inferior catalytic performance compared to BVIMCl self-polymerization. This reduction was attributed to the decrease in ionic density and the diminishment of active sites caused by DVB incorporation, consequently lowering CO2 cycloaddition efficiency (Figure 5f).

2.2.2. Effects of Reaction Conditions on CO2 Cycloaddition Performance

The influence of reaction conditions on CO2 cycloaddition performance in the presence of P-BVIMCl was studied. The GLC yield increased from 81.1% to 93.4% with temperature elevation from 70 °C to 100 °C. However, a further increase in temperature to 110 °C resulted in only marginal improvement, indicating reaction equilibrium was essentially achieved at 100 °C. This temperature was therefore selected as optimal (Figure 6a). Figure 6b demonstrates the pressure dependence under 0.5–2.5 MPa. The yield improved remarkably from 75.9% to 93.4% with pressure increasing from 0.5 MPa to 2.0 MPa, attributed to the enhancement of CO2 dissolution in GO and interfacial contact efficiency. Beyond 2.0 MPa, the yield dropped slightly, likely attributed to GO molecular escaping into the gas phase under excessive CO2 pressure. Thus, 2.0 MPa was identified as the optimal pressure [40,41].
Increasing the catalyst loading from 4.50 wt% to 6.70 wt%, the GLC yield was boosted from 80.9% to 93.4%, suggesting that the availability of the active site had increased. Further increasing the catalyst loading showed negligible enhancement, possibly caused by the catalyst deposition-induced contact blockage between GO and active sites [40,42] (Figure 6c). Time-dependent studies (Figure 6d) revealed rapid conversion kinetics, achieving 93.4% GLC yield within 3.0 h. Prolonged reaction times (4.0–5.0 h) maintained identical yields, confirming reaction completion at 3.0 h. The systematic optimization established 100 °C, 2.0 MPa, 6.7 wt% catalyst loading, and 3.0 h as optimal parameters, delivering the GLC yield of 93.4% and the selectivity of 99.6%.

2.2.3. Recyclability Investigation

Catalyst reusability was a critical parameter for evaluating industrial applicability. The stability of P-BVIMCl was systematically examined through hot filtration tests and cycling experiments. As shown in Figure 7a,b, the reaction system exhibited an almost negligible GLC yield increase after catalyst removal at 2.0 h through hot filtration, indicating little leaching of active components. After five consecutive reaction cycles, the catalyst demonstrated marginally decreased activity, confirming effective retention of active species throughout catalytic operations. FT-IR analysis of recycled P-BVIMCl (Figure 7c) revealed that recycled P-BVIMCl preserved spectral features compared to the fresh catalyst. SEM characterization (Figure 7d) further confirmed the maintained spherical particle morphology in both fresh and recycled catalysts. These comprehensive evaluations demonstrated the excellent stability of the P-BVIMCl catalyst and operational robustness under repeated cycling conditions.

2.2.4. Substrate Universality Investigation

To assess P-BVIMCl’s capability in converting various epoxides into corresponding cyclic carbonates, we systematically investigated its catalytic performance toward epoxides with different substituents, as summarized in Table 2. The exceptional 93.4% yield for GLC synthesis originated from hydrogen activation of terminal hydroxyl groups in GO, which facilitated reaction progression. Both epichlorohydrin and epibromohydrin demonstrated excellent conversions (>93.0% yield) with high selectivity (>95.0%), attributed to electron-withdrawing effects at the terminal position that enhanced nucleophilic attack by Cl− anions. However, epoxides bearing long-chain terminal groups exhibited reduced efficiency. Butyl glycidyl ether showed moderate conversion (84.7% yield), likely due to diffusion limitations caused by steric hindrance from its long-chain terminal group [43]. Notably, cyclohexene oxide displayed dramatically lower reactivity under identical conditions (17.9% yield after 10 h at 120 °C), primarily constrained by severe steric effects from its bulky terminal benzene ring [44]. Surprisingly, styrene oxide achieved 92.4% carbonate yield despite its aromatic structure, suggesting effective accommodation of this substrate within the catalyst’s active sites.

2.3. Mechanistic Study of CO2 Cycloaddition

2.3.1. Active Site Identification

The catalytic active sites of P-BVIMCl were determined through average local ionization energy (ALIE) analysis and dual-orbital weighted Fukui function calculations (Figure 8). Chloride ions exhibited ALIE values of 7.39 and 7.45 eV at minimum energy points, indicating preferred nucleophilic attack sites. Fukui function analysis revealed the following: Blue isosurfaces at chloride ions confirmed nucleophilic attack on the β-carbon of GO; green isosurfaces at imidazole C-H groups suggested electrophilic activation of GO’s oxygen atom for ring-opening.

2.3.2. Reaction Pathway Analysis

Previous studies suggested a three-stage CO2 cycloaddition mechanism: (1) GO ring-opening, (2) CO2 insertion, and (3) GLC ring-closing [16]. Through modeling and transition state analysis (Figure 9), we confirmed this pathway for P-BVIMCl. Energy calculations (Figure 10) revealed that the GO ring-opening step had the highest energy barrier (48.04 kcal/mol), and this rate-determining step aligned with prior mechanistic studies [45,46].
To investigate the interactions among P-BVIMCl, epoxides, and CO2 molecules, we conducted Interaction Region Indicator (IRI) analysis on the transition states of three reaction stages [47,48] (Figure 11). Blue isosurfaces corresponded to strong intermolecular attractions (e.g., hydrogen bonds, halogen bonds), red isosurfaces represented strong repulsions (e.g., ring strain), and green isosurfaces indicated van der Waals interactions. Ring-opening stage (Figure 11a,b): Blue-green isosurfaces between Cl⁻ and the β-C atom of GO demonstrated halogen bond-like interactions, indicating the formation of a new C-Cl bond. Blue isosurfaces between the imidazole C-H group and the oxygen atom (O−) of the opened GO ring confirmed strong hydrogen-bonding interactions (C-H···O), facilitating ring-opening. CO2 molecules adopt an activated bent configuration (176.11°) under the synergistic effect of Cl− and imidazole groups, promoting subsequent insertion. CO2 insertion stage (Figure 11c,d): The newly formed C-Cl bond was evidenced by characteristic peaks in the IRI scatter plot (sign(λ2) ρ < −0.05 regions). Blue isosurfaces emerged between the CO2 carbon atom and the O− ion from the opened GO ring, signaling the formation of a new C-O bond. GLC ring-closure stage (Figure 11e,f): Red and blue isosurfaces between the newly formed O− ion and the original β-C atom of GO indicated cyclic C-O bond formation. The disappearance of the C-Cl bond peak in Figure 11d confirmed Cl− departure, marking reaction completion. This analysis systematically revealed the bond formation/breaking sequence and interaction evolution during the catalytic cycle.
We proposed the CO2 catalytic cycloaddition mechanism over P-BVIMCl (Figure 12). The process involved three key steps: 1. Nucleophilic Activation: Cl− attacked the β-C of GO while activating CO2, and the imidazole C-H acted as an electrophilic site to protonate GO’s oxygen, triggering ring-opening to form an O− intermediate. 2. CO2 Insertion: The activated CO2 (bent at 176.11°) is inserted into GO under O− attraction, forming a GLC precursor. 3. Cyclization: The terminal O− attacks β-C, expelling Cl− and closing the ring to generate GLC. This mechanism highlighted the dual role of Cl− (nucleophilic) and imidazole C-H (electrophilic) in driving CO2 conversion.

3. Experimental Section

3.1. Materials

All chemicals and reagents were used as received without any further purification unless otherwise stated. 1,4-Dichloroxylene (DCX, 99%), 1-vinylimidazole (VIM, 99%), 2,2′-Azobis (2-methylpropionitrile) (AIBN, 98%), acetonitrile (99%), ethyl acetate (99%), glycidol (96%), epichlorohydrin (99%), and epibromohydrin (98%) were purchased from Aladdin Chemistry Co., Ltd. (Shanghai, China). Ethanol (99%) was obtained from Shanghai Ling Feng Chemical Reagent Co., Ltd. (Shanghai, China).

3.2. Characterization

This study comprehensively utilized a variety of advanced analytical techniques, including 1H and 13C NMR spectroscopy, infrared spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, scanning electron microscopy, N2 adsorption-desorption testing, and CO2 adsorption isotherm measurements, to conduct a thorough and in-depth characterization of the samples, thereby ensuring the accuracy and reliability of the research results. Detailed operational procedures for each characterization technique have been provided in the supporting information for the reference of readers.

3.3. Catalyst Preparation

3.3.1. Preparation of Binuclear Ionic Liquid Monomer

A mixture of 1-vinylimidazole (VIM, 40 mmol, 3.765 g) and 1,4-dichloroxylene (DCX, 20 mmol, 3.501 g) was dissolved in 40 mL of acetonitrile. The homogeneous solution was refluxed at 70 °C under vigorous stirring for 24 h. The solvent was evaporated under reduced pressure, and the resulting precipitate was washed three times with ethyl acetate (3 × 20 mL), followed by vacuum drying at 50 °C for 12 h to obtain a white solid, which was binuclear ionic liquid monomer (BVIMCl) [49]. [1H NMR (400 MHz, D2O) δ (ppm) = 7.69 (d, 2H), 7.46 (d, 2H), 7.40 (s, 4H), 7.02 (dd, 2H), 5.69 (dd, 4H), 5.37 (s, 4H), 5.32 (dd, 2H). 13C NMR (101 MHz, D2O) δ (ppm) = 134.26, 129.49, 128.10, 122.82, 119.72, 109.60, 52.60.]

3.3.2. Synthesis of Binuclear Imidazole-Based Poly(ionic liquid)

The binuclear ionic liquid monomer BVIMCl (5 mmol, 1.815 g) and azobisisobutyronitrile (AIBN, 1.1 mmol, 0.1815 g) were dissolved in a mixed solvent of ethanol/water (3:1, v/v). After stirring at room temperature for 2 h, the solution was transferred into a 50 mL Teflon-lined autoclave and heated at 100 °C for 24 h (Figure 13). The resulting solid was filtered, thoroughly washed with ethanol and deionized water, and dried under vacuum at 80 °C for 24 h to obtain binuclear imidazole-based poly(ionic liquid), which was abbreviated as P-BVIMCl. Yield: 96%.
A series of binuclear imidazole-based poly(ionic liquid)s were synthesized by systematically varying synthetic parameters, including the types and compositions of solvent, initiator (AIBN) concentration, and reaction temperature. The results of the elemental analysis of P-BVIMCl are shown in Table 3.

3.4. CO2 Cycloaddition Reaction

The catalyst and 10 mmol glycidol (GO) were loaded into a 50 mL autoclave. High-purity CO2 was introduced through 2–3 purging–pressurizing cycles to achieve the specified pressure. The reaction was initiated by heating the system to the target temperature and maintaining it for the designated duration. Upon completion, the autoclave was cooled to ambient temperature, and unreacted CO2 was carefully released. The resultant mixture was dissolved in acetonitrile with n-butanol added as an internal standard. The catalyst was separated from the filtrate via centrifugation, followed by washing with ethanol and drying at 60 °C for subsequent reuse.

4. Conclusions

This study successfully synthesized a binuclear imidazole-based poly(ionic liquid)s, P-BVIMCl, achieving efficient preparation through free radical polymerization. Under meticulously optimized catalyst preparation conditions (100 °C, 24 h, water/ethanol mixed solvent volume ratio 1:3, 10 wt% AIBN initiator) and reaction conditions (100 °C, 2.0 MPa CO2, 10 mmol GO, 6.7 wt% catalyst loading, 3.0 h), the P-BVIMCl catalyst exhibited exceptional performance in the CO2 cycloaddition reaction, achieving a remarkable GLC yield of 93.4% and selectivity of 99.6%. This study proposed a cooperative activation mechanism involving nucleophilic Cl− and electrophilic imidazole C-H groups, opening up new avenues for the design and application of poly(ionic liquids) in the efficient conversion of CO2.
However, there was still room for further improvement in this work. Although the prepared poly(ionic liquid) significantly increased the ionic density, the number of active sites remained insufficient, and the catalyst loading was relatively high. Future research could focus on enhancing the number of active sites and their utilization efficiency. In terms of catalyst characterization, it is anticipated that future efforts will overcome the challenge of calculating the polymerization degree of solid poly(ionic liquid) materials, providing strong support for a deeper understanding and optimization of catalyst performance.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/catal15050406/s1, Figure S1: Schematic view of product peak position; Figure S2: (a) Standard curve of GO; (b) Standard curve of GLC; Figure S3: FT-IR spectra of P-BVIMCl and BVIMCl; Figure S4: The DSC curves of P-BVIMCl and BVIMCl at temperature (25 to 600) °C. Table S1: Comparison of the performance of different catalysts [50,51,52,53].

Author Contributions

Investigation, methodology, validation, visualization, writing—original draft, and writing—review and editing, R.L. Data curation and investigation, Y.J. Writing—original draft and writing—review and editing, L.C. Formal analysis and software, C.F. Software, H.L. Conceptualization, data curation, funding acquisition, project administration, supervision, and writing—review and editing, J.D. Data curation, supervision, and writing—review and editing, H.W. Data curation, project administration, resources, supervision, and writing—review and editing, G.G. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China (No. 22478192, 21878159, 22078159, and 22278213) and the State Key Laboratory of Materials–Oriented Chemical Engineering (No. SKL-MCE-512 23A13), and the High-Performance Computing Center of Nanjing Tech University generously offered the computational resources.

Data Availability Statement

The authors confirm that the data supporting the findings of this study are available within the article and its Supplementary Materials.

Conflicts of Interest

The authors declare no conflicts of interest.

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Catalysts 15 00406 g001
Figure 1. FT-IR spectra of P-BVIMCl and BVIMCl.
Figure 1. FT-IR spectra of P-BVIMCl and BVIMCl.
Catalysts 15 00406 g001
Catalysts 15 00406 g002
Figure 2. SEM (a) of P-BVIMCl and EDS mapping (b–e) of P-BVIMCl.
Figure 2. SEM (a) of P-BVIMCl and EDS mapping (b–e) of P-BVIMCl.
Catalysts 15 00406 g002
Catalysts 15 00406 g003
Figure 3. XPS survey and C 1s spectrum (a,b); N 1s and Cl 2p spectrum (c,d).
Figure 3. XPS survey and C 1s spectrum (a,b); N 1s and Cl 2p spectrum (c,d).
Catalysts 15 00406 g003
Catalysts 15 00406 g004
Figure 4. (a) N2 adsorption–desorption isotherms of P-BVIMCl (red: desorption isotherms; blue: adsorption isotherms); (b) pore size distribution profiles of P-BVIMCl; (c) CO2 adsorption isotherms of P-BVIMCl; and (d) TG curves of P-BVIMCl and BVIMCl (red background: the weight loss interval).
Figure 4. (a) N2 adsorption–desorption isotherms of P-BVIMCl (red: desorption isotherms; blue: adsorption isotherms); (b) pore size distribution profiles of P-BVIMCl; (c) CO2 adsorption isotherms of P-BVIMCl; and (d) TG curves of P-BVIMCl and BVIMCl (red background: the weight loss interval).
Catalysts 15 00406 g004
Catalysts 15 00406 g005
Figure 5. Catalyst synthesis conditions: (a) the mass percentage of AIBN; (b) polymerization time; (c) polymerization temperature; (d) the ratio of solvents; (e) the type of solvents; and (f) the copolymerization reaction with DVB. Catalytic capabilities of catalysts: GO 5 mmol, temperature 100 °C, CO2 pressure 2.0 MPa, and time 3.0 h.
Figure 5. Catalyst synthesis conditions: (a) the mass percentage of AIBN; (b) polymerization time; (c) polymerization temperature; (d) the ratio of solvents; (e) the type of solvents; and (f) the copolymerization reaction with DVB. Catalytic capabilities of catalysts: GO 5 mmol, temperature 100 °C, CO2 pressure 2.0 MPa, and time 3.0 h.
Catalysts 15 00406 g005
Catalysts 15 00406 g006
Figure 6. Effects of temperature (a), CO2 initial pressure (b), catalyst dosage (c), and reaction time (d) on cycloaddition performance.
Figure 6. Effects of temperature (a), CO2 initial pressure (b), catalyst dosage (c), and reaction time (d) on cycloaddition performance.
Catalysts 15 00406 g006
Catalysts 15 00406 g007
Figure 7. Thermal filtration test (a) and cycle test (grey line: original P-BVIMCl; red line: hot filtration test.) (b) of P-BVIMCl; FT-IR spectra (c) of fresh and recycled P-BVIMCl; SEM images (d) of P-BVIMCl.
Figure 7. Thermal filtration test (a) and cycle test (grey line: original P-BVIMCl; red line: hot filtration test.) (b) of P-BVIMCl; FT-IR spectra (c) of fresh and recycled P-BVIMCl; SEM images (d) of P-BVIMCl.
Catalysts 15 00406 g007
Catalysts 15 00406 g008
Figure 8. The (a) average local ionization energy (red: maximum; blue: minimum.) and (b) dual descriptor Fukui function analysis of P-BVIMCl.
Figure 8. The (a) average local ionization energy (red: maximum; blue: minimum.) and (b) dual descriptor Fukui function analysis of P-BVIMCl.
Catalysts 15 00406 g008
Catalysts 15 00406 g009
Figure 9. The reaction process of CO2 cycloaddition catalyzed by P-BVIMCl.
Figure 9. The reaction process of CO2 cycloaddition catalyzed by P-BVIMCl.
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Catalysts 15 00406 g010
Figure 10. Energy barrier of cycloaddition reaction process relative energy of CO2 cycloaddition (a) without catalysts and (b) catalyzed by P-BVIMCl.
Figure 10. Energy barrier of cycloaddition reaction process relative energy of CO2 cycloaddition (a) without catalysts and (b) catalyzed by P-BVIMCl.
Catalysts 15 00406 g010
Catalysts 15 00406 g011
Figure 11. IRI analysis of transition states of (a,b) GO ring-opening step, (c,d) CO2 insert step, and (e,f) CPC ring-closing step.
Figure 11. IRI analysis of transition states of (a,b) GO ring-opening step, (c,d) CO2 insert step, and (e,f) CPC ring-closing step.
Catalysts 15 00406 g011
Catalysts 15 00406 g012
Figure 12. Mechanism of CO2 cycloaddition catalyzed by P-BVIMCl.
Figure 12. Mechanism of CO2 cycloaddition catalyzed by P-BVIMCl.
Catalysts 15 00406 g012
Catalysts 15 00406 g013
Figure 13. Synthetic illustration of the P-BVIMCl catalyst.
Figure 13. Synthetic illustration of the P-BVIMCl catalyst.
Catalysts 15 00406 g013
Table 1. Textural properties and CO2 adsorption capacities of P-BVIMCl.
Table 1. Textural properties and CO2 adsorption capacities of P-BVIMCl.
CatalystSBET
(m2·g−1)		VP
(cm3·g−1)		Dave
(nm)		CO2 Adsorption (cm3·g−1)
P-BVIMCl6.01640.028553.721.853
Table 2. Catalytic performances of P-BVIMCl for different epoxides a.
Table 2. Catalytic performances of P-BVIMCl for different epoxides a.
EntrySubstrateProductTemperature (°C)Time (h)Y (%)S (%)
1Catalysts 15 00406 i001Catalysts 15 00406 i002100393.499.6
2 bCatalysts 15 00406 i003Catalysts 15 00406 i0041001291.295.8
3Catalysts 15 00406 i005Catalysts 15 00406 i006120493.798.9
4Catalysts 15 00406 i007Catalysts 15 00406 i008120494.095.0
5Catalysts 15 00406 i009Catalysts 15 00406 i0101201084.798.1
6Catalysts 15 00406 i011Catalysts 15 00406 i0121001092.498.4
7Catalysts 15 00406 i013Catalysts 15 00406 i0141201017.993.0
a Reaction pressure: 2 MPa; b Ambient pressure (0.1 MPa).
Table 3. Elemental analysis of P-BVIMCl.
Table 3. Elemental analysis of P-BVIMCl.
CatalystC (wt%) aN (wt%) aH (wt%) aCl (mmol·g−1) b
P-BVIMCl54.5214.005.415.00
a The mass fraction of C, N, and H in the catalyst b Cl content (mmol·g−1) = N content (wt%) × Quaternary nitrogen ratio in total nitrogen (%)/14.
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Li, R.; Jiang, Y.; Cheng, L.; Fang, C.; Li, H.; Ding, J.; Wan, H.; Guan, G. Facile Synthesis of Binuclear Imidazole-Based Poly(ionic liquid) via Monomer Self-Polymerization: Unlocking High-Efficiency CO2 Conversion to Cyclic Carbonate. Catalysts 2025, 15, 406. https://doi.org/10.3390/catal15050406

AMA Style

Li R, Jiang Y, Cheng L, Fang C, Li H, Ding J, Wan H, Guan G. Facile Synthesis of Binuclear Imidazole-Based Poly(ionic liquid) via Monomer Self-Polymerization: Unlocking High-Efficiency CO2 Conversion to Cyclic Carbonate. Catalysts. 2025; 15(5):406. https://doi.org/10.3390/catal15050406

Chicago/Turabian Style

Li, Ranran, Yuqiao Jiang, Linyan Cheng, Cheng Fang, Hongping Li, Jing Ding, Hui Wan, and Guofeng Guan. 2025. "Facile Synthesis of Binuclear Imidazole-Based Poly(ionic liquid) via Monomer Self-Polymerization: Unlocking High-Efficiency CO2 Conversion to Cyclic Carbonate" Catalysts 15, no. 5: 406. https://doi.org/10.3390/catal15050406

APA Style

Li, R., Jiang, Y., Cheng, L., Fang, C., Li, H., Ding, J., Wan, H., & Guan, G. (2025). Facile Synthesis of Binuclear Imidazole-Based Poly(ionic liquid) via Monomer Self-Polymerization: Unlocking High-Efficiency CO2 Conversion to Cyclic Carbonate. Catalysts, 15(5), 406. https://doi.org/10.3390/catal15050406

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