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Structure-designed squaramide-based IL shows excellent activity as single-component and recyclable catalyst platform for chemical fixation of CO 2 to cyclic carbonates under mild conditions. • Multiple hydrogen bond donors-based squaramide ionic liquids (SAILs) were developed and characterized. • The SAIL showed excellent activity and reusability for transformation of CO 2 into cyclic carbonates. • The protocol solved the problems of cocatalyst leaching and complex separation/purification. • The protocol performed in the absence of toxic transition metal ions and organic solvents. • An insight into the catalytic mechanism deriving from the synergistic interaction of cation-anion was proposed. Novel squaramide-based ionic liquids (SAILs) were first presented through properly molecular structure design. They were successfully applied to the cycloaddition of CO 2 and epoxide to form cyclic carbonate as single-component catalyst. The catalytic behaviors of SAILs with different structures were thoroughly studied for the cycloaddition reaction. The squaramide groups were easy to form strong hydrogen bonds with oxygen atoms of epoxide, leading to an intensive activation of the epoxide. Under the optimum reaction conditions, good to excellent product yields with satisfactory selectivities were obtained. The structure-designed catalyst was easily recovered and showed excellent reusability with no significant loss of catalytic activity after six cycles. An insight into the synergistic catalytic mechanism deriving from the multiple hydrogen bond donors and bromine anions was proposed. The new strategy helps to solve the problems of cocatalyst/nucleophile leaching and complex separation/purification existed in binary organocatalysts. The multiple hydrogen bond catalysis shows a green and promising alternative to Lewis acid catalysis in the relevant CO 2 conversion applications. [ABSTRACT FROM AUTHOR]

Novel eco-friendly, facilely synthesized N -hydroxysuccinimide based DESs show excellent activity for conversion of CO 2 into cyclic carbonates at ambient temperature in the absence of cocatalyst, metal and solvent. • The eco-friendly, easily available N -hydroxysuccinimide based DESs were first presented and characterized. • The ChI/NHS showed excellent synergetic effects and unparalleled activity on coupling of CO 2 and epoxides. • The ChI/NHS-catalyzed cycloaddition reaction was proformed under mild conditions. • The protocol avoids the pollution caused by toxic transition metal ions and organic solvents. • The ChI/NHS is easily recyclable and shows excellent stability and reusability. Novel N -hydroxysuccinimide (NHS) based deep eutectic solvents (DESs) were facilely synthesized and structurally characterized by FT-IR, NMR and TGA techniques. The NHS-based DESs were demonstrated as a promising platform for efficient conversion of CO 2 into cyclic carbonate. The optimized DES, i.e. iodide choline (ChI)/NHS with molar ratio of 1:2 exhibited excellent catalytic performance at 30 °C and 1.0 MPa CO 2 pressure in the absence of cocatalyst, metal and solvent. The catalytic behaviour, catalyst recyclability and versatility were studied in details. The hydrogen-bond interaction between the ChI/NHS and substrate were also investigated. Based on the results, an insight into the synergetic catalytic mechanism involving hydrogen bond activation and ring-opening of epoxide was proposed. Compared with the reported DESs media, the NHS-based DESs present the higher-efficiency and greater advance in the synthesis of cyclic carbonate under ambient conditions. [ABSTRACT FROM AUTHOR]

The combination of pyrrolidine-2,5-dione-derived ionic liquids with silver acetate (AgOAc) were developed as binary catalysts for conversion of simulated flue gas CO 2 and propargylic alcohols to α-alkylidene cyclic carbonates. By tuning different catalyst components, the [HTMG][Pyrro]/AgOAc system was confirmed to be the most efficient and exhibited an excellent synergistic action in facilitating the carboxylic cyclization under room temperature and solvent-free conditions. The influence of reaction parameters on carboxylic cyclization of CO 2 with 2-methylbut-3-yn-2-ol were optimized. Under the determined conditions, the [HTMG][Pyrro]/AgOAc system was stable enough to show durable high activity in eight recycles, and also versatile in carboxylic cyclization of flue gas CO 2 with other propargylic alcohols. Moreover, a thorough comparison of [HTMG][Pyrro]/AgOAc with the reported catalysts was provided and evaluated, the results suggested that the developed catalytic system has significant advantages in practical application. Finally, the mechanistic details for the conversion of CO 2 into α-alkylidene cyclic carbonates catalyzed by [HTMG][Pyrro]/AgOAc was also elucidated on the basis of reactants activation. [Display omitted] • [HTMG][Pyrro]/AgOAc system is developed for direct CO 2 conversion from flue gases. • The system realizes ambient and clean synthesis of α-alkylidene cyclic carbonates. • [HTMG][Pyrro]/AgOAc system shows higher activity than most reported catalysts. • The catalytic system is easily separated and exhibits durable high-activity. • Detailed activation behaviors and synergistic catalytic mechanism are revealed. [ABSTRACT FROM AUTHOR]

Experimental and theoretical insights into robust PIL-Br@ZIF-8 hetero-frameworks for the selective conversion of CO 2 into cyclic carbonates under mild conditions. [Display omitted] • A novel strategy is developed for fabricating core–shell PILs@ZIF-8 composites. • PIL-Br@ZIF-8 enables simultaneous adsorption and activation of CO 2 and epoxide. • Low-concentration/low-pressure CO 2 conversion into cyclic carbonates was achieved. • PIL-Br@ZIF-8 is recyclable and exhibits good thermal and structural stability. • Valuable insight into the cycloaddition mechanism is theoretically elucidated. The present study, for the first time, reports the fabrication of core–shell poly(ionic liquids)@ZIF-8 nanocomposites through a facile in-situ polymerization strategy. These composites exhibited exceptional structural characteristics including high specific surface areas and the integration of high-density Lewis acid/base and nucleophilic active sites. The structure–activity relationship, reusability, and versatility of the poly(ionic liquids)@ZIF-8 composites were investigated for the cycloaddition reaction between CO 2 and epoxide. By optimizing the composites structures and their catalytic performance, PIL-Br@ZIF-8(2:1) was identified as an exciting catalyst that exhibits high activity and selectivity in the synthesis of various cyclic carbonates under mild or even atmospheric pressure or simulated flue gas conditions. Moreover, the catalyst demonstrated excellent structural stability while maintaining its catalytic activity throughout multiple usage cycles. By combining DFT calculations, we investigated the transition states and intermediate geometries of the cycloaddition reaction in different coordination microenvironments, thereby proposing a synergistic catalytic mechanism involving multiple active sites. [ABSTRACT FROM AUTHOR]

Novel ZIF-8(Zn/Co)@g-C 3 N 4 nanocomposites are developed and exhibit superior dual functions for atmospheric CO 2 capture and conversion. [Display omitted] • The study demonstrates a simple method for preparation of advanced nanocomposites. • Robust ZIF-8(Zn/Co)@g-C 3 N 4 nanocomposites with multiple active sites are developed. • The material exhibits superior performance for atmospheric CO 2 capture and conversion. • The optimal ZCN-60 is recyclable and exhibits excellent reusability and versatility. The development of novel catalytic materials that integrate multifunctional sites has significant implications for expanding the utilization of CO 2 resources. However, simultaneously achieving high activity and stability remains a formidable challenge. In this study, a series of ZIF-8(Zn/Co)@g-C 3 N 4 nanocomposites were prepared by employing a thermo-physical compounding strategy that involved the combination of nitrogen-rich graphitic carbon nitride (g-C 3 N 4) nanosheets with ZIF-8(ZnCo). The influences of different compositions of g-C 3 N 4 and ZIF-8(Zn/Co) on the catalyst structure were systematically investigated. Subsequently, the catalytic activities of these nanocomposites towards the cycloaddition reaction between CO 2 and epoxide were examined under different conditions. The presence of abundant Lewis base sites in g-C 3 N 4 facilitates CO 2 activation, while multiple Lewis acid sites in ZIF-8(Zn/Co) enable efficient epoxide activation. By working synergistically with a co-catalyst, tetrabutylammonium bromide (TBAB), CO 2 and epoxides can be efficiently reacted to synthesize the corresponding cyclic carbonates under mild or even atmospheric pressure conditions. The catalytic reaction conditions were optimized, and both the catalyst's recycling performance and the scope of epoxides with various substituents were investigated. The integration of g-C 3 N 4 and ZIF-8(Zn/Co) endows the catalytic material with exceptional structural stability and remarkable catalytic activity, thereby providing a new platform for highly efficient CO 2 conversion. [ABSTRACT FROM AUTHOR]

Novel phenylpyridine-based HCPs are facilely prepared and exhibit superior dual functions for atmospheric CO 2 capture and conversion. [Display omitted] • Phenylpyridine-based HCPs with excellent characteristics are facilely prepared. • The HCPs exhibit superior performance for atmospheric CO 2 capture and conversion. • The optimal TPA-HCP-Py catalyst shows good reusability and versatility. • Valuable insight into the cycloaddition mechanism is theoretically elucidated. Several phenylpyridine- and phenyl-based hypercrosslinked polymers (HCPs) were prepared via a one-step Friedel-Crafts polymerization and used as catalysts for the cycloaddition reaction between atmospheric CO 2 and epoxides to produce cyclic carbonates. The structural characteristics and catalytic activity of different HCP catalysts were compared, while the recycling performance and universality to various substituted epoxides were investigated. The as-prepared catalysts exhibited regular pore structure and high specific surface area (1133 m2/g). Under the synergistic effect of tetrabutylammonium iodide (TBAI), the optimized TPA-HCP-Py efficiently converted atmospheric CO 2 into cyclic carbonates with good to excellent product yields. Furthermore, the TPA-HCP-Py catalyst was easy to recover, and no significant changes were observed after reusing for five times, which demonstrated its excellent recycling performance. The interactions between different active sites and reactants in the TPA-HCP-Py/TBAI catalytic system were investigated by DFT calculation, revealing the catalytic reaction mechanism and providing valuable guidance for developing new multifunctional catalysts. [ABSTRACT FROM AUTHOR]

Heterogeneous Co@PTPOFs with multiple Lewis acid/basic sites are developed and show excellent activity for cycloaddition of CO 2 and epoxides. [Display omitted] • Novel M@PPOFs with multiple Lewis acid/basic active sites are prepared facilely. • The M@PPOFs exhibit high specific surface area and good structural stability. • The 1.0Co@PPOFs-mediated CO 2 coupling reaction can conduct under mild conditions. • The optimum catalyst shows excellent reusability and broad substrate scope. • An insight into the M@PPOFs-catalyzed cycloaddition mechanism is proposed. A series of metal-decorated porous organic frameworks (M@PTPOFs) with cross-linked pyridyl and triazinyl were fabricated through a two-step method. The structures of the PTPOFs and M@PTPOFs were systematically characterized. As heterogeneous catalysts with Lewis acid/basic sites, the M@PTPOFs were applied to catalyze the model cycloaddition of CO 2 and epoxides. The optimal catalytic system and reaction parameters were investigated in detail. It was found that 1.0Co@PTPOF-400-15 cooperating with tetrabutylammonium iodide (TBAI) achieved the best catalytic performance, with a 96% product yield and 99% selectivity under mild conditions of 60 °C and 2.0 MPa CO 2 for 5.0 h. Moreover, 1.0Co@PTPOF-400-15 could be easily recycled by centrifugation and reused multiple times with nearly unchanged catalytic activity. Finally, the product yield and reaction parameters were compared with those of reported heterogeneous catalysts, and the possible synergistic catalytic mechanism of 1.0Co@PTPOF-400–15/TBAI was proposed. The multiple Lewis acid/basic active sites, robust structure and excellent catalytic performance are useful for the development of other high-efficiency heterogeneous catalysts. [ABSTRACT FROM AUTHOR]

Robust ZPOFs with multiple active sites are facilely constructed and show remarkable CO 2 adsorption and conversion performance under mild/green conditions. [Display omitted] • Novel ZPOFs with multiple active sites are prepared via ionothermal polymerization. • The ZPOFs show exciting dual-functions for CO 2 adsorption and conversion. • The ZPOF-mediated CO 2 coupling reaction can proceed under mild/green conditions. • The present ZPOF is easily separated and shows good stability and reusability. • The optimum catalyst exhibits excellent broad substrate scope. Porous organic frameworks fabricated by well-defined monomeric compounds with different active sites have been regarded as the promising nano-materials for improving the efficiency of CO 2 capture and utilization. In this study, novel zwitterionic porous organic frameworks (ZPOFs) alternately connected by benzimidazole, triazine and imidazolium modules were prepared facilely via ZnCl 2 -catalyzed bi-component polymerization. The influences of different monomer concentration and polymerization temperature on structural properties of the ZPOFs were discussed in detail. It indicates that the ZPOFs present attractive structure characteristics of high specific surface area and hierarchical pore structure, and have abundant hydrogen bond donors, Lewis bases and nucleophilic groups, respectively. The ZPOFs as-obtained were applied to CO 2 adsorption and conversion into cyclic carbonate by coupling with epoxide. The experiment results showed that the ZPOFs could afford the highest CO 2 adsorption capacity of 2505 μmol/g at 273 K and 1.0 bar CO 2 pressure. The effects of ZPOFs structures and reactions conditions on the catalytic performance were investigated. Under the optimized conditions of 70 °C, 2.0 MPa CO 2 for 2.0 h, and cooperating with tetrabutylammonium iodide (TBAI) cocatalyst, the ZPOF-450–30 could efficiently and selectively catalyze the CO 2 /epoxides cycloaddition reaction to yield corresponding cyclic carbonates. Moreover, the ZPOF-450–30 catalyst could be simply separated with durable high stability and activity. Finally, we compared the catalytic behaviors with reported similar heterogeneous catalysts and proposed a feasible ZPOFs-catalyzed mechanism. [ABSTRACT FROM AUTHOR]