Highly selective separation of toluene and methylcyclohexane based on nonporous adaptive crystals of hybrid[3]arene

Abstract

The efficient separation of toluene and methylcyclohexane is one of the biggest challenges in the field of chemical separation. Due to their closely matched boiling points, traditional distillation separation methods consume a lot of energy. Therefore, it is imperative to develop novel separation techniques to obtain toluene and methylcyclohexane with high purities. Herein, we develop an economical strategy for adsorptive separation based on nonporous adaptive crystals of hybrid[3]arene H (Hα). Hα selectively separate toluene from the mixture of toluene and methylcyclohexane (v : v = 1 : 1) with a purity of 100% via the vapor–solid adsorption and a purity of 98.98% via the liquid–solid adsorption. The selectivity arises from the stability of the new crystal structure after the capture of the preferred guest, toluene, by Hα. The reversible transition between guest-free and guest-loaded structures endows Hα with excellent recyclability.

---

Introduction

The separation of toluene (Tol) and methylcyclohexane (MCH) is crucial in the domains of chemistry and petrochemistry.¹ Tol is an organic compound that is used as a raw material for various chemicals, including pesticides, dyes and synthetic resins.^2,3 MCH is obtained by hydrogenation of Tol, which is widely used as an effective solvent in the manufacture of pharmaceutical intermediates, nylons, and varnishes.^4,5 However, due to incomplete hydrogenation, Tol will be mixed with MCH, resulting in a mixture of Tol and MCH. In order to obtain high purity of MCH, Tol needs to be separated from the mixture of Tol and MCH.⁶ Extractive and azeotropic distillations are the primary industrial techniques used to separate the mixture containing Tol and MCH.⁷ However, because of the close boiling points of Tol (383.75 K) and MCH (374.15 K), these methods require considerable energy, complicated processes, and high operating costs.^8–10 Developing economically viable methods for separating the mixture of Tol and MCH can reduce global energy consumption. Therefore, the development of novel and energy-efficient separation technologies is essential for the effective separation of Tol and MCH.

Adsorptive separation methods using porous materials offer an economical alternative to traditional separation techniques.^11–17 Zeolites, porous organic cages, metal–organic frameworks (MOFs), and covalent organic frameworks (COFs) have enabled the cost-effective and energy-efficient separation of a wide range of aromatic and aliphatic compounds.^18–28 Hitherto, the adsorptive separation of Tol and MCH has been mainly achieved using porous materials such as MOFs and COFs.^29,30 However, there are still some drawbacks associated with the utilization of porous materials in practical applications. For example, MOFs exhibit comparatively poor chemical stability, resulting in low reusability.^31–34 While the stability of COFs is limited by the formation of reversible covalent bonds required for crystallization.³⁵ Therefore, there is an urgent need to develop adsorption materials with simple synthesis process and easy recovery for the separation of Tol and MCH.

In recent years, nonporous adaptive crystals (NACs) have performed well in separating hydrocarbons.^36–43 Unlike traditional porous materials, NACs are initially nonporous.^44–50 However, as the guest molecules are induced, NACs form intrinsic or extrinsic pores to load guest molecules, accompanied by crystal structure transformation.^51–65 Due to their distinctive characteristics, NACs are employed as new supramolecular adsorptive separation materials.^66–69 Hybrid[n]arenes represent an innovative category of supramolecular hosts with the potential to be designed as NACs materials.^70,71 The unique structural properties and versatility of these NACs materials make them suitable for applications in the field of adsorptive separation.⁷²

Hybrid[3]arene H, a novel and important hybrid[n]arenes family member, has been synthesized and designed into NACs material for the first time by our group.⁷³ In the previous report, we successfully achieved the separation of benzene and cyclohexane using NACs of H (Hα) as the adsorptive separation materials.⁷⁴ Additionally, Hα have shown potential for adsorptive separation of other important hydrocarbons.^75,76 Herein, we discovered that Hα were capable of effectively separating Tol and MCH (Fig. 1). Specifically, Hα efficiently separated Tol from the mixture of Tol and MCH (v : v = 1 : 1) with a purity of 100% via vapor–solid adsorption and a purity of 98.98% via liquid–solid adsorption. Additionally, the adsorbed Tol could be effectively removed by heating, thus recovering Hα without loss of adsorption properties.

Fig. 1 Chemical structures of: (a) NACs of hybrid[3]arene H (Hα); (b) toluene (Tol) and methylcyclohexane (MCH).

Results and discussion

Hybrid[3]arene H was synthesized and activated using previous methods.⁷³ To characterize NACs of H (Hα), ¹H NMR and thermogravimetric analysis (TGA) were employed (Fig. S1 and S2, ESI†), confirming the removal of the solvent. Hα were shown to be crystalline analyzed by powder X-ray diffraction (PXRD) (Fig. S3, ESI†).

Single-component time-dependent vapor–solid adsorption experiments were carried out to explore the ability of Hα to capture Tol or MCH vapor. The results revealed a gradual increase in the adsorption of Tol vapor by Hα over time, reaching the saturation point within about 12 h (Fig. 2a). According to the ¹H NMR, the amount of Tol vapor adsorbed by Hα was determined to be 0.8 Tol/Hα, whereas the amount of MCH vapor adsorbed by Hα was negligible (Fig. S4 and S5, ESI†). TGA further demonstrated that Hα had the capability to adsorb Tol vapor, with a weight loss of 12.22% below 150 °C, corresponding to 0.9 Tol/Hα (Fig. S6, ESI†). However, no weight loss of Hα was observed until 300 °C after adsorption of MCH vapor (Fig. S7, ESI†). Based on these results, it could be inferred that Hα adsorbed Tol vapor but not MCH vapor. Besides, the PXRD pattern of Hα apparently changed after the capture of Tol vapor (Fig. 2b, III), indicating that Hα adsorbed Tol vapor to form a novel guest-loaded crystal structure. In contrast, the PXRD pattern of Hα remained unchanged following the adsorption of MCH vapor (Fig. 2b, II). The results validated the adsorption ability of Hα to Tol vapor.

Fig. 2 (a) Time-dependent vapor–solid adsorption of Hα for single-component Tol or MCH vapor. (b) PXRD patterns of: (I) origin Hα; (II) Hα after adsorption of MCH vapor; (III) Hα after adsorption of Tol vapor.

Single crystal X-ray diffraction (SCXRD) analysis revealed the host–guest interaction between H and Tol. Single crystal of Tol-loaded H (Tol@H) was obtained through slow volatilization of the Tol in which H was dissolved at room temperature. From the crystal structure of Tol@H, H molecules were arranged in infinite channels. The Tol molecule was located between two H molecules, rather than within the cavity of H, forming a host–guest complex with H in a ratio of 1 : 1 (Fig. 3a–c). It is noteworthy that the primary driving force for the formation of the host–guest complex after Tol adsorption was C–H⋯π and C–H⋯O interactions between H molecule and Tol molecule (Fig. 3d and Fig. S8, ESI†). Moreover, the PXRD pattern of Hα after the adsorption of Tol was identical to that simulated from the crystal structure of Tol@H (Fig. S9, ESI†), indicating that the crystal structure of Hα changed to Tol@H. In addition, visual studies of weak intermolecular interactions based on density-functional theory calculations revealed that the host–guest complex of Tol@H was stabilized by C–H⋯π and C–H⋯O interactions (Fig. S10, ESI†). The calculation result was consistent with the host–guest interaction between H and Tol obtained through SCXRD analysis.

Fig. 3 Single crystal structure of Tol@H at different views: (a) along the a-axis; (b) along the b-axis; (c) along the c-axis. (d) Illustration of C–H⋯π and C–H⋯O interactions between H and Tol, H–π-plane distances: a = 2.921 Å, b = 2.784 Å; H–O distances: c = 2.660 Å; d = 2.882 Å; e = 2.914 Å; C–H⋯O angles: θ₁ = 108.40°; θ₂ = 93.79°; θ₃ =149.74°. See ESI† for the structural detail and CCDC number.

Hirshfeld surface analysis further demonstrated the host–guest interaction in Tol@H.⁷⁷ The two-dimensional fingerprint plots showed the relative contributions of various interactions in the crystal structure of Tol@H. The results revealed that the C–H⋯π interaction contributed the most (over 37%), which ensured the stability of Tol@H (Fig. 4a and b). In addition, the contribution of the C–H⋯O interaction was 5.6% (Fig. 4c). These results suggested that the interaction between Tol and H was mainly stabilized by C–H⋯π and C–H⋯O interactions (Fig. 4d).

Fig. 4 (a)–(c) Two-dimensional fingerprint plots of Tol@H and the relative contributions of various interactions in the crystal structure of Tol@H. (d) Percentage contributions of various interactions in Tol@H based on Hirshfeld surface area analysis.

Given the adsorption capacity of Hα, we wondered whether Hα could effectively separate the mixture of Tol and MCH. Time-dependent vapor–solid adsorption experiments were conducted on the vapor mixture of Tol and MCH (v : v = 1 : 1) by Hα. Over a period of time, the amount of Tol vapor adsorbed by Hα steadily increased, reaching the saturation point after about 20 h. However, the MCH vapor adsorbed by Hα could be negligible (Fig. 5a). These results agreed with the single-component adsorption experiments in which Hα captured Tol vapor but not MCH vapor. At the saturation point, the amount of Tol adsorbed by Hα was about 0.8 Tol/Hα, as determined by ¹H NMR (Fig. S11, ESI†). TGA results indicated a weight loss of 10.62% below 150 °C, and it was determined that one Hα molecule adsorbed 0.8 Tol molecule (Fig. S12, ESI†). Similarly, after exposing Hα to the vapor mixture of Tol and MCH, the resulting PXRD pattern of Hα matched that of Hα adsorbed for Tol vapor (Fig. 5b). Meanwhile, the PXRD pattern was simulated using the single crystal data of Tol@H and subsequently compared with the pattern of Hα following the adsorption of the vapor mixture of Tol and MCH. The finding showed that the two patterns were consistent (Fig. S13, ESI†), suggesting a structure transition from Hα to Tol@H. In addition, head space gas chromatography (HS-GC) verified that Tol vapor was adsorbed by Hα with 100% purity (Fig. 5c and Fig. S14, ESI†), confirming the outstanding selectivity of Hα to Tol vapor. The results suggested that Hα were capable of selectively capturing Tol from the vapor mixture of Tol and MCH (Fig. 5e).

Fig. 5 (a) Time-dependent vapor–solid adsorption of Hα for the vapor mixture of Tol and MCH (v : v = 1 : 1). (b) PXRD patterns of: (I) origin Hα; (II) Hα after adsorption of MCH vapor; (III) Hα after adsorption of Tol vapor; (IV) Hα after adsorption of the vapor mixture of Tol and MCH. (c) Relative uptakes of Tol and MCH vapors adsorbed by Hα after 24 h by head space gas chromatography. (d) Relative uptakes of Tol and MCH vapors adsorbed by Hα after 5 cycles. (e) Schematic diagrams representing the selective adsorption of Tol from a vapor mixture of Tol and MCH (v : v = 1 : 1) using Hα and the subsequent release of Tol upon heating.

The recyclability of adsorbents is crucial to evaluate their suitability in practical industrial processes.⁷⁸ After heating Tol@H for 2 h, the adsorbed Tol was removed and new crystal was formed. The newly formed crystal was Hα, as confirmed by the PXRD analysis (Fig. S15, ESI†). Moreover, ¹H NMR and HS-GC tests confirmed that the newly formed Hα could still selectively capture Tol from the mixture of Tol and MCH without losing performance after recycling for 5 times (Fig. 5d and Fig. S16 and S17, ESI†).

Furthermore, due to the remarkable selective adsorption capacity of Hα for Tol in vapor–solid adsorption studies, we were intrigued by the possibility of Hα effectively separating Tol from the liquid mixture of Tol and MCH. After 60 min of single-component liquid–solid adsorption, the amount of Tol liquid adsorbed by Hα was saturated with 0.9 Tol/Hα (Fig. 6a and Fig. S18, ESI†). However, the amount of MCH liquid adsorbed by Hα was neglected, as proven by ¹H NMR (Fig. S19, ESI†), implying that Hα could adsorb Tol liquid but not MCH liquid. Besides, the PXRD pattern of Hα showed no significant change after adsorption of MCH liquid, but there was an evident change after adsorption of Tol liquid (Fig. 6b and Fig. S20, ESI†). This suggested that the adsorption of Tol liquid by Hα resulted in the formation of a new crystal structure.

Fig. 6 (a) Time-dependent liquid–solid adsorption of Hα for single-component Tol or MCH liquid. (b) PXRD patterns of: (I) origin Hα; (II) Hα after adsorption of MCH liquid; (III) Hα after adsorption of Tol liquid; (IV) Hα after adsorption of the liquid mixture of Tol and MCH. (c) Time-dependent liquid–solid adsorption of Hα for the liquid mixture of Tol and MCH (v : v = 1 : 1). (d) Relative uptakes of Tol and MCH liquids adsorbed by Hα after 140 min by head space gas chromatography. (e) Schematic diagrams representing the selective adsorption of Tol from a liquid mixture of Tol and MCH (v : v = 1 : 1) using Hα and the subsequent release of Tol upon heating.

Subsequently, time-dependent liquid–solid adsorption experiments were conducted on the liquid mixture of Tol and MCH (v : v = 1 : 1). The Tol liquid was absorbed by Hα, resulting in a 0.9 Tol/Hα amount at saturation after 140 min. Meanwhile, the MCH liquid adsorbed by Hα was negligible, as evidenced by ¹H NMR (Fig. 6c and Fig. S21, ESI†). After exposure to the liquid mixture of Tol and MCH, the PXRD pattern of Hα was consistent with the simulated pattern based on single crystal data of Tol@H (Fig. S22, ESI†), indicating a crystal structure transition from Hα to Tol@H. The HS-GC experiment showed that Hα had good selectivity for Tol liquid, achieving the adsorption purity of 98.98% (Fig. 6d and Fig. S23, ESI†). These experimental results indicated that Hα preferred Tol liquid, demonstrating the high selectivity in liquid–solid adsorption (Fig. 6e).

Conclusions

In summary, for the first time, we have developed a novel approach for separating Tol from both vapor and liquid mixtures of Tol and MCH utilizing nonporous adaptive crystals of hybrid[3]arene H (Hα). Hα can separate Tol from the vapor and liquid mixtures of Tol and MCH (v : v = 1 : 1) with purities of 100% and 98.98%, respectively, showing that Hα are excellent materials for adsorption and separation. The selectivity can be attributed to the stable crystal structure formed when the preferential guest molecule, Tol, is adsorbed. In addition, the reversible transformation between the guest-containing structure and the non-guest-containing structure endows Hα with high recyclability. Owing to the straightforward synthesis process, outstanding separation efficiency and excellent recovery property, Hα hold great promise for appliances in chemical industries. In future studies, efforts will be made to develop more applications of Hα for adsorptive separations involving isotopes, configuration isomers, and other complex substances.

Data availability

The data that support the findings of this study are available in the ESI† of this article. Experimental details, NMR spectra, crystallography and other materials. X-ray crystallographic data for Tol@H.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (22101043), the Fundamental Research Funds for the Central Universities (N2205013, N232410019, N2405013), Natural Science Foundation of Liaoning Province (2023-MSBA-068), the Opening Fund of State Key Laboratory of Heavy Oil Processing (SKLHOP202203006) and Northeastern University. Special thanks are due to the instrumental or data analysis from Analytical and Testing, Northeastern University.

References

1. D. S. Sholl and R. P. Lively, Seven Chemical Separations to Change the World, Nature, 2016, 532, 435–437.
2. M. Huda, K. Minamisawa, T. Tsukamoto, M. Tanabe and K. Yamamoto, Aerobic Toluene Oxidation Catalyzed by Subnano Metal Particles, Angew. Chem., Int. Ed., 2019, 58, 1002–1006.
3. C.-C. Chen, M. Dai, L. Zhang, J. Zhao, W. Zeng, M. Shi, J.-W. Huang, W. Liu, R.-T. Guo and A. Li, Molecular Basis for a Toluene Monooxygenase to Govern Substrate Selectivity, ACS Catal., 2022, 12, 2831–2839.
4. A. A. Taimoor, I. Pitault and F. C. Meunier, Correlation between Deactivation and Pt-Carbonyl Formation during Toluene Hydrogenation Using a H₂/CO₂ Mixture, J. Catal., 2011, 278, 153–161.
5. L. Chen, P. Verma, K. Hou, Z. Qi, S. Zhang, Y.-S. Liu, J. Guo, V. Stavila, M. D. Allendorf, L. Zheng, M. Salmeron, D. Prendergast, G. A. Somorjai and J. Su, Reversible Dehydrogenation and Rehydrogenation of Cyclohexane and Methylcyclohexane by Single-Site Platinum Catalyst, Nat. Commun., 2022, 13, 1092.
6. P. Wang, T. Minegishi, G. Ma, K. Takanabe, Y. Satou, S. Maekawa, Y. Kobori, J. Kubota and K. Domen, Photoelectrochemical Conversion of Toluene to Methylcyclohexane as an Organic Hydride by Cu₂ZnSnS₄-Based Photoelectrode Assemblies, J. Am. Chem. Soc., 2012, 134, 2469–2472.
7. R. Kumar, R. K. Velamati and S. Kumar, Combustion of Methyl Cyclohexane at Elevated Temperatures to Investigate Burning Velocity for Surrogate Fuel Development, J. Hazard. Mater., 2021, 406, 124627.
8. P. G. Tiverios and V. Van Brunt, Extractive Distillation Solvent Characterization and Shortcut Design Procedure for Methylcyclohexane-Toluene Mixtures, Ind. Eng. Chem. Res., 2000, 39, 1614–1623.
9. F. S. Oliveira, A. B. Pereiro, L. P. Rebelo and I. M. Marrucho, Deep Eutectic Solvents as Extraction Media for Azeotropic Mixtures, Green Chem., 2013, 15, 1326–1330.
10. E. Quijada-Maldonado, G. W. Meindersma and A. B. de Haan, Pilot Plant Study on the Extractive Distillation of Toluene–Methylcyclohexane Mixtures Using NMP and the Ionic Liquid [Hmim][TCB] as Solvents, Sep. Purif. Technol., 2016, 166, 196–204.
11. B. Smit and T. L. M. Maesen, Molecular Simulations of Zeolites: Adsorption, Diffusion, and Shape Selectivity, Chem. Rev., 2008, 108, 4125–4184.
12. T. A. Makal, J.-R. Li, W. Lu and H.-C. Zhou, Methane Storage in Advanced Porous Materials, Chem. Soc. Rev., 2012, 41, 7761–7779.
13. W. J. Roth, B. Gil, W. Makowski, B. Marszalek and P. Eliášová, Layer Like Porous Materials with Hierarchical Structure, Chem. Soc. Rev., 2016, 45, 3400–3438.
14. X. Meng, H.-N. Wang, S.-Y. Song and H.-J. Zhang, Proton-Conducting Crystalline Porous Materials, Chem. Soc. Rev., 2017, 46, 464–480.
15. Z. Li and Y.-W. Yang, Macrocycle-Based Porous Organic Polymers for Separation, Sensing, and Catalysis, Adv. Mater., 2022, 34, 2107401.
16. Z. Chen, K. O. Kirlikovali, K. B. Idrees, M. C. Wasson and O. K. Farha, Porous Materials for Hydrogen Storage, Chem, 2022, 8, 693–716.
17. J. Li and B. Chen, Flexible Hydrogen-Bonded Organic Frameworks (HOFs): Opportunities and Challenges, Chem. Sci., 2024, 15, 9874–9892.
18. J.-R. Li, R. J. Kuppler and H.-C. Zhou, Selective Gas Adsorption and Separation in Metal–Organic Frameworks, Chem. Soc. Rev., 2009, 38, 1477–1504.
19. Y. Xu, Y. Li, Y. Han, X. Son and J. Yu, A Gallogermanate Zeolite with Eleven-Membered-Ring Channels, Angew. Chem., Int. Ed., 2013, 52, 5501–5503.
20. H. Furukawa, K. E. Cordova, M. O’Keeffe and O. M. Yaghi, The Chemistry and Applications of Metal–Organic Frameworks, Science, 2013, 341, 1230444.
21. P. J. Bereciartua, Á. Cantín, A. Corma, J. L. Jordá, M. Palomino, F. Rey, S. Valencia, E. W. Corcoran, P. Kortunov, P. I. Ravikovitch, A. Burton, C. Yoon, Y. Wang, C. Paur, J. Guzman, A. R. Bishop and G. L. Casty, Control of Zeolite Framework Flexibility and Pore Topology for Separation of Ethane and Ethylene, Science, 2017, 358, 1068–1071.
22. K. Dey, M. Pal, K. C. Rout, S. Kunjattu, A. Das, R. Mukherjee, U. K. Kharul and R. Banerjee, Selective Molecular Separation by Interfacially Crystallized Covalent Organic Framework Thin Films, J. Am. Chem. Soc., 2017, 139, 13083–13091.
23. Z. Wang, S. Zhang, Y. Chen, Z. Zhang and S. Ma, Covalent Organic Frameworks for Separation Applications, Chem. Soc. Rev., 2020, 49, 708–735.
24. X. Chi, M. Li, J. Di, P. Bai, L. Song, X. Wang, F. Li, S. Liang, J. Xu and J. Yu, A Highly Stable and Flexible Zeolite Electrolyte Solid-State Li-Air Battery, Nature, 2021, 592, 551–557.
25. K. Su, W. Wang, S. Du, C. Ji and D. Yuan, Efficient Ethylene Purification by a Robust Ethane-Trapping Porous Organic Cage, Nat. Commun., 2021, 12, 3703.
26. Y. Li and J. Yu, Emerging Applications of Zeolites in Catalysis, Separation and Host–Guest Assembly, Nat. Rev. Mater., 2021, 6, 1156–1174.
27. P.-F. Cui, X.-R. Liu, Y.-J. Lin, Z.-H. Li and G.-X. Jin, Highly Selective Separation of Benzene and Cyclohexane in a Spatially Confined Carborane Metallacage, J. Am. Chem. Soc., 2022, 144, 6558–6565.
28. J.-R. Wang, K. Song, T.-X. Luan, K. Cheng, Q. Wang, Y. Wang, W. W. Yu, P.-Z. Li and Y. Zhao, Robust Links in Photoactive Covalent Organic Frameworks Enable Effective Photocatalytic Reactions under Harsh Conditions, Nat. Commun., 2024, 15, 1267.
29. Y. Xiong, Q. Feng, L. Lu, X. Qiu, S. Knoedler, A. C. Panayi, D. Jiang, Y. Rinkevich, Z. Lin, B. Mi, G. Liu and Y. Zhao, Metal–Organic Frameworks and Their Composites for Chronic Wound Healing: from Bench to Bedside, Adv. Mater., 2024, 36, 2302587.
30. C. Liu, J. Hou, M. Yan, J. Zhang, H. G. Alemayehu, W. Zheng, P. Liu, Z. Tang and L. Li, Regulating the Layered Stacking of a Covalent Triazine Framework Membrane for Aromatic/Aliphatic Separation, Angew. Chem., Int. Ed., 2024, 63, e202320137.
31. D. Wu, K. Yang, Z. Zhang, Y. Feng, L. Rao, X. Chen and G. Yu, Metal-Free Bioorthogonal Click Chemistry in Cancer Theranostics, Chem. Soc. Rev., 2022, 51, 1336–1376.
32. J. R. Long and O. M. Yaghi, The Pervasive Chemistry of Metal–Organic Frameworks, Chem. Soc. Rev., 2009, 38, 1213–1214.
33. L. K. Macreadie, R. Babarao, C. J. Setter, S. J. Lee, O. T. Qazvini, A. J. Seeber, J. Tsanaktsidis, S. G. Telfer, S. R. Batten and M. R. Hill, Enhancing Multicomponent Metal–Organic Frameworks for Low Pressure Liquid Organic Hydrogen Carrier Separations, Angew. Chem., Int. Ed., 2020, 59, 6090–6098.
34. Z. He, X. Huang, C. Wang, X. Li, Y. Liu, Z. Zhou, S. Wang, F. Zhang, Z. Wang, O. Jacobson, J.-J. Zhu, G. Yu, Y. Dai and X. Chen, A Catalase-Like Metal–Organic Framework Nanohybrid for O₂-Evolving Synergistic Chemoradiotherapy, Angew. Chem., Int. Ed., 2019, 58, 8752–8756.
35. M. Liu, L. Guo, S. Jin and B. Tan, Covalent Triazine Frameworks: Synthesis and Applications, J. Mater. Chem. A, 2019, 7, 5153–5172.
36. P. K. Thallapally, L. Dobrzańska, T. R. Gingrich, T. B. Wirsig, L. J. Barbour and J. L. Atwood, Acetylene Absorption and Binding in a Nonporous Crystal Lattice, Angew. Chem., Int. Ed., 2006, 45, 6506–6509.
37. M. Yan, Y. Wang and J. Zhou, Separation of Toluene and Alcohol Azeotropes by Nonporous Adaptive Crystals of Pillar[n]arenes with Analytical Purity of 100%, Cell Rep. Phys. Sci., 2023, 4, 101637.
38. X.-Y. Hu, T. Xiao, C. Lin, F. Huang and L. Wang, Dynamic Supramolecular Complexes Constructed by Orthogonal Self-Assembly, Acc. Chem. Res., 2014, 47, 2041–2051.
39. W. Yang, K. Samanta, X. Wan, T. U. Thikekar, Y. Chao, S. Li, K. Du, J. Xu, Y. Gao, H. Zuilhof and A. C.-H. Sue, Tiara[5]arenes: Synthesis, Solid-State Conformational Studies, Host–Guest Properties, and Application as Nonporous Adaptive Crystals, Angew. Chem., Int. Ed., 2020, 59, 3994–3999.
40. H. Yao, Y. Wang, M. Quan, M. U. Farooq, L.-P. Yang and W. Jiang, Adsorptive Separation of Benzene, Cyclohexene, and Cyclohexane by Amorphous Nonporous Amide Naphthotube Solids, Angew. Chem., Int. Ed., 2020, 59, 19945–19950.
41. J.-R. Wu and Y.-W. Yang, Synthetic Macrocycle-Based Nonporous Adaptive Crystals for Molecular Separation, Angew. Chem., Int. Ed., 2021, 60, 1690–1701.
42. M. Yan, Y. Wang, J. Chen and J. Zhou, Potential of Nonporous Adaptive Crystals for Hydrocarbon Separation, Chem. Soc. Rev., 2023, 52, 6075–6119.
43. K. Jie, Y. Zhou, E. Li and F. Huang, Nonporous Adaptive Crystals of Pillararenes, Acc. Chem. Res., 2018, 51, 2064–2072.
44. Y. Ding, L. O. Alimi, B. Moosa, C. Maaliki, J. Jacquemin, F. Huang and N. M. Khashab, Selective Adsorptive Separation of Cyclohexane over Benzene Using Thienothiophene Cages, Chem. Sci., 2021, 12, 5315–5318.
45. S. N. Talapaneni, D. Kim, G. Barin, O. Buyukcakir, S. H. Je and A. Coskun, Pillar[5]arene Based Conjugated Microporous Polymers for Propane/Methane Separation through Host–Guest Complexation, Chem. Mater., 2016, 28, 4460–4466.
46. J.-R. Wu and Y.-W. Yang, Geminiarene: Molecular Scale Dual Selectivity for Chlorobenzene and Chlorocyclohexane Fractionation, J. Am. Chem. Soc., 2019, 141, 12280–12287.
47. M. Wang, J. Zhou, E. Li, Y. Zhou, Q. Li and F. Huang, Separation of Monochlorotoluene Isomers by Nonporous Adaptive Crystals of Perethylated Pillar[5]arene and Pillar[6]arene, J. Am. Chem. Soc., 2019, 141, 17102–17106.
48. M. Yan, S. Wu, Y. Wang, M. Liang, M. Wang, W. Hu, G. Yu, Z. Mao, F. Huang and J. Zhou, Recent Progress of Supramolecular Chemotherapy Based on Host–Guest Interactions, Adv. Mater., 2024, 36, 2304249.
49. X. Zhao, Y. Liu, Z. Y. Zhang, Y. Wang, X. Jia and C. Li, One-Pot and Shape-Controlled Synthesis of Organic Cages, Angew. Chem., Int. Ed., 2021, 60, 17904–17909.
50. M. Wang, S. Fang, S. Yang, Q. Li, N. M. Khashab, J. Zhou and F. Huang, Separation of Ethyltoluene Isomers by Nonporous Adaptive Crystals of Perethylated and Perbromoethylated Pillararenes, Mater. Today Chem., 2022, 24, 100919.
51. B. Lu, X. Yan, J. Wang, D. Jing, J. Bei, Y. Cai and Y. Yao, Rim-Differentiated Pillar[5]arene Based Nonporous Adaptive Crystals, Chem. Commun., 2022, 58, 2480–2483.
52. S. Wang, S. Mukherjee, E. Patyk-Kaźmierczak, S. Darwish, A. Yang, Q. Bajpai and M. J. Zaworotko, Highly Selective, High-Capacity Separation of o-xylene from C₈ Aromatics by a Switching Adsorbent Layered Material, Angew. Chem., Int. Ed., 2019, 58, 6630–6634.
53. N. Sun, S.-Q. Wang, R. Zou, W.-G. Cui, A. Zhang, T. Zhang, Q. Li, Z.-Z. Zhuang, Y.-H. Zhang, J. Xu, M. J. Zaworotko and X.-H. Bu, Benchmark Selectivity p-xylene Separation by a Non-Porous Molecular Solid Through Liquid or Vapor Extraction, Chem. Sci., 2019, 10, 8850–8854.
54. M. Wang, Q. Li, E. Li, J. Liu, J. Zhou and F. Huang, Vapochromic Behaviors of a Solid-State Supramolecular Polymer Based on Exo-Wall Complexation of Perethylated Pillar[5]arene with 1,2,4,5-Tetracyanobenzene, Angew. Chem., Int. Ed., 2021, 60, 8115–8120.
55. D. Luo, J. Tian, J. L. Sessler and X. Chi, Nonporous Adaptive Calix[4]pyrrole Crystals for Polar Compound Separations, J. Am. Chem. Soc., 2021, 143, 18849–18853.
56. J. Chen, S. Wu, Y. Wang and J. Zhou, Near-Perfect Separation of Alicyclic Ketones and Alicyclic Alcohols by Nonporous Adaptive Crystals of Perethylated Pillar[5]arene and Pillar[6]arene, Chin. Chem. Lett., 2024 DOI:10.1016/j.cclet.2024.110102.
57. H.-Y. Zhou, D.-W. Zhang, M. Li and C.-F. Chen, A Calix[3]acridan-Based Host–Guest Cocrystal Exhibiting Efficient Thermally Activated Delayed Fluorescence, Angew. Chem., Int. Ed., 2022, 61, e202117872.
58. H.-Y. Zhou and C.-F. Chen, Adsorptive Separation of Picoline Isomers by Adaptive Calix[3]acridan Crystals, Chem. Commun., 2022, 58, 4356–4359.
59. Y. Zhao, H. Xiao, C.-H. Tung, L.-Z. Wu and H. Cong, Adsorptive Separation of Cyclohexanol and Cyclohexanone by Nonporous Adaptive Crystals of RhombicArene, Chem. Sci., 2021, 12, 15528–15532.
60. Z.-Y. Zhang and C. Li, Biphen[n]arenes: Modular Synthesis, Customizable Cavity Sizes, and Diverse Skeletons, Acc. Chem. Res., 2022, 55, 916–929.
61. G. Zhang, X. Zhu, L. O. Alimi, X. Liu and A. Chen, Adsorptive Molecular Sieving of Aromatic over Cyclic Aliphatic via Intrinsic/Extrinsic Approach, J. Mater. Chem. A, 2024, 12, 6875–6879.
62. W. Yang, W. Zhang, J. Chen and J. Zhou, Mono-Functionalized Pillar[n]arenes: Syntheses, Host–Guest Properties and Applications, Chin. Chem. Lett., 2024, 35, 108740.
63. Z. Liu, S. K. M. Nalluri and J. F. Stoddart, Surveying Macrocyclic Chemistry: from Flexible Crown Ethers to Rigid Cyclophanes, Chem. Soc. Rev., 2017, 46, 2459–2478.
64. Y. Wang, K. Xu, B. Li, L. Cui, J. Li, X. Jia, H. Zhao, J. Fang and C. Li, Efficient Separation of cis- and trans-1,2-Dichloroethene Isomers by Adaptive Biphen[3]arene Crystals, Angew. Chem., Int. Ed., 2019, 58, 10281–10284.
65. J. Zhou, L. Rao, G. Yu, T. R. Cook, X. Chen and F. Huang, Supramolecular Cancer Nanotheranostics, Chem. Soc. Rev., 2021, 50, 2839–2891.
66. M. Yan and J. Zhou, Methylene-Bridged Naphthotubes: New Macrocyclic Arenes with Great Potential for Supramolecular Chemistry, Org. Chem. Front., 2023, 10, 2340–2345.
67. L. Yue, K. Yang, X.-Y. Lou, Y.-W. Yang and R. Wang, Versatile Roles of Macrocycles in Organic-Inorganic Hybrid Materials for Biomedical Applications, Matter, 2020, 3, 1557–1588.
68. W. Zhu, E. Li, J. Zhou, Y. Zhou, X. Sheng and F. Huang, Highly Selective Removal of Heterocyclic Impurities from Toluene by Nonporous Adaptive Crystals of Perethylated Pillar[6]arene, Mater. Chem. Front., 2020, 4, 2325–2329.
69. E. Li, W. Zhu, S. Fang, K. Jie and F. Huang, Reimplementing Guest Shape Sorting of Nonporous Adaptive Crystals via Substituent-Size-Dependent Solid-Vapor Postsynthetic Modification, Angew. Chem., Int. Ed., 2022, 61, e202211780.
70. Z. Zhang, J. M. Lim, M. Ishida, V. V. Roznyatovskiy, V. M. Lynch, H.-Y. Gong, X. Yang, D. Kim and J. L. Sessler, Cyclo[m]pyridine[n]pyrroles: Hybrid Macrocycles That Display Expanded π-Conjugation upon Protonation, J. Am. Chem. Soc., 2012, 134, 4076–4079.
71. J. Chen, W. Zhang, W. Yang, F. Xi, H. He, M. Liang, Q. Dong, J. Hou, M. Wang, G. Yu and J. Zhou, Separation of Benzene and Toluene Associated with Vapochromic Behaviors by Hybrid[4]arene-Based Co-crystals, Nat. Commun., 2024, 15, 1260.
72. I.-T. Ho, Z. Zhang, M. Ishida, V. M. Lynch, W.-Y. Cha, Y. M. Sung, D. Kim and J. L. Sessler, A Hybrid Macrocycle with a Pyridine Subunit Displays Aromatic Character upon Uranyl Cation Complexation, J. Am. Chem. Soc., 2014, 136, 4281–4286.
73. J. Zhou, J. Yang, B. Hua, L. Shao, Z. Zhang and G. Yu, The Synthesis, Structure, and Molecular Recognition Properties of a [2]Calix[1]biphenyl-Type Hybrid[3]arene, Chem. Commun., 2016, 52, 1622–1624.
74. J. Zhou, G. Yu, Q. Li, M. Wang and F. Huang, Separation of Benzene and Cyclohexane by Nonporous Adaptive Crystals of a Hybrid[3]arene, J. Am. Chem. Soc., 2020, 142, 2228–2232.
75. Y. Wang, S. Wu, S. Wei, Z. Wang and J. Zhou, Selectivity Separation of Ortho-Chlorotoluene Using Nonporous Adaptive Crystals of Hybrid[3]arene, Chem. Mater., 2024, 36, 1631–1638.
76. Y. Wang, Z. Wang, S. Wei, S. Wu, M. Wang, G. Yu, P. Chen, X. Liu and J. Zhou, Efficient Separation of Xylene Isomers by Nonporous Adaptive Crystals of Hybrid[3]arene in both Vapor and Liquid Phases, Mater. Chem. Front., 2024, 8, 2273–2281.
77. P. R. Spackman, M. J. Turner, J. J. McKinnon, S. K. Wolff, D. J. Grimwood, D. Jayatilakab and M. A. Spackmanb, CrystalExplorer: a Program for Hirshfeld Surface Analysis, Visualization and Quantitative Analysis of Molecular Crystals, J. Appl. Cryst., 2021, 54, 1006–1011.
78. A. V. Baskar, N. Bolan, S. A. Hoang, P. Sooriyakumar, M. Kumar, L. Singh, T. Jasemizad, L. P. Padhye, G. Singh, A. Vinu, B. Sarkar, M. B. Kirkham, J. Rinklebe, S. Wang and H. Wang, Recovery, Regeneration and Sustainable Management of Spent Adsorbents from Wastewater Treatment Streams: A Review, Sci. Total Environ., 2022, 822, 153555.

---

Footnote

† Electronic supplementary information (ESI) available. CCDC 2304364. For ESI and crystallographic data in CIF or other electronic format see DOI: https://doi.org/10.1039/d4qm00590b

---