Self-Driven Humidity Regulation via Hygroscopic Salt Cycling

Abstract

Indoor air quality plays a crucial role in human health and daily life. Humidity control materials (HCMs) have been developed to intelligently regulate indoor humidity in an energy-efficient manner. However, there is an urgent need to explore new HCMs that offer more energy-efficient humidity control solutions. In this study, a new humidity control method based on the release and recapture of hygroscopic salts has been developed based on a series of inorganic-organic hybrid metal halides (IOMHs), namely [TEMA]₂SbCl₅ (1, TEMA = triethylmethyl ammonium), [AMIM]₃SbCl₆ (2, AMIM = 1-allyl-3-methylimidazolium), and [TAAC]₄SbCl₆·Cl (3, TAAC = allyltrimethyl ammonium). The adsorption of water could trigger the release of ACl from these A_mSbCl_n (A = cation) IOMHs, generating the mixture of A₃Sb₂Cl₉ and ACl. The hygroscopicity of released ACl results in the high-water adsorption capacity, which could reach up to 1.18 g g⁻¹ by changing the release amount of ACl. During the desorption process, the ACl would be recaptured by A₃Sb₂Cl₉, resulting in the A_mSbCl_n regeneration. Releasing energy can facilitate the unique self-driven water desorption behavior superior to that of traditional HCMs. Practical evaluation tests in a real environment demonstrate that 2 could spontaneously and rapidly maintain indoor humidity levels between 40% and 70%.

Keywords

controlled release and recapture / humidity control materials / inorganic organic hybrid metal halides / self-driven desorption / structural design

References

[1] S. Lax, C. Cardona, D. Zhao, et al., “Microbial and Metabolic Succession on Common Building Materials Under High Humidity Conditions,” Nature Communications 10 (2019): 1767.

[2] A. V. Arundel, E. M. Sterling, J. H. Biggin, and T. D. Sterling, “Indirect Health Effects of Relative Humidity in Indoor Environments,” Environmental Health Perspectives 65 (1986): 351-361.

[3] X. Liu, Z. Chen, G. Yang, and Y. Gao, “Bioinspired Ant-Nest-Like Hierarchical Porous Material Using CaCl₂ as Additive for Smart Indoor Humidity Control,” Industrial & Engineering Chemistry Research 58 (2019): 7139-7145.

[4] D. H. Vu, K. S. Wang, B. H. Bac, and B. X. Nam, “Humidity Control Materials Prepared From Diatomite and Volcanic Ash,” Construction & Building Materials 38 (2013): 1066-1072.

[5] L. Zhou, Z. Jing, Y. Zhang, K. Wu, and E. H. Ishida, “Stability, Hardening and Porosity Evolution during Hydrothermal Solidification of Sepiolite Clay,” Applied Clay Science 69 (2012): 30-36.

[6] M. G. Qin, P. M. Hou, Z. M. Wu, and J. T. Wang, “Precise Humidity Control Materials for Autonomous Regulation of Indoor Moisture,” Building and Environment 169 (2020): 106581.

[7] W. T. Lin, Y. W. Lin, M. J. Hung, W. H. Lee, B. Y. Kuo, and K. L. Lin, “Recycling of Cathode Ray Tubes and Stone Sludge for the Synthesis of Al-MCM-41 Grafted Amine Functional Group and Environmental Humidity Control Material Applications,” Materials Science and Engineering B 297 (2023): 116798.

[8] Y. Ibrahim, F. Mahmood, A. Sinopoli, A. Moursi, K. A. Mahmoud, and T. Al-Ansari, “Advancements of Metal-Organic Frameworks for Atmospheric Water Harvesting and Climate Control,” Journal of Water Process Engineering 67 (2024): 106249.

[9] W. Gong, X. F. Chen, M. Wahiduzzaman, et al., “Chiral Reticular Chemistry: A Tailored Approach Crafting Highly Porous and Hydrolytically Robust Metal-Organic Frameworks for Intelligent Humidity Control,” Journal of the American Chemical Society 146 (2024): 2141-2150.

[10] M. H. Qin, O. S. Rasmussen, J. Chen, and L. Wadsö, “Novel MOF-Based Autonomous Humidity Control Materials for Energy-Efficient Indoor Moisture Regulation,” Building and Environment 261 (2024): 111757.

[11] R. G. AbdulHalim, P. M. Bhatt, Y. Belmabkhout, et al., “A Fine-Tuned Metal-Organic Framework for Autonomous Indoor Moisture Control,” Journal of the American Chemical Society 139 (2017): 10715-10722.

[12] J. X. Fu, Y. Liu, L. H. Chen, et al., “Positional Isomers of Covalent Organic Frameworks for Indoor Humidity Regulation,” Small 19 (2023): 2303897.

[13] Q. Nan, C. Yin, R. Tian, et al., “Superhygroscopic Aerogels With Hierarchical String-bag Structure for Effective Humidity Control,” ACS Nano 19 (2025): 16696-16705.

[14] X. L. Gu, M. S. Qiu, H. X. Xue, X. J. Pei, H. Xiao, and L. H. Zhou, “Different Macroporous Characteristic LiCl/CaCl₂ Binary Salt Double Network Hygroscopic Aerogels for Atmospheric Water Harvesting,” Journal of Environmental Chemical Engineering 13 (2025): 117904.

[15] K. K. Tu, Z. D. Zhang, C. H. Dreimol, et al., “Autonomous Humidity Regulation by MOF/Wood Composites,” Materials Horizon 11 (2024): 5786-5797.

[16] J. Oppenheim, Z. T. Yang, B. Dinakar, and M. Dinca, “High-capacity Water Sorbent Cycles Without Hysteresis Under Dry Conditions,” Nature Communications 16 (2025): 4297.

[17] M. J. Hung, Y. W. Lin, W. T. Lin, W. H. Lee, B. Y. Kuo, and K. L. Lin, “Functionalization of Mesoporous Al-MCM-41 for Indoor Humidity Control as Building Humidity Conditioning Material,” Journal of Molecular Structure 1299 (2024): 137024.

[18] Y. Y. Yang, Z. H. Shen, W. D. Wu, H. Zhang, Y. Ren, and Q. G. Yang, “Preparation of a Novel Diatomite-Based PCM Gypsum Board for Temperature-Humidity Control of Buildings,” Building and Environment 226 (2022): 109732.

[19] Z. Mao, H. Zhang, Y. Li, X. Wang, Q. Wei, and J. Xie, “Preparation and Characterization of Composite Scallop Shell Powder-Based and Diatomite-Based Hygroscopic Coating Materials With Metal-organic Framework for Indoor Humidity Regulation,” Journal of Building Engineering 43 (2021): 103122.

[20] Z. Yang, W. Zhang, X. Lin, Q. Xiong, and Q. Jiang, “Optimization of Minor-LiCl-Modified Gypsum as an Effective Indoor Moisture Buffering Material for Sensitive and Long-Term Humidity Control,” Building and Environment 229 (2023): 109962.

[21] A. Karmakar, P. G. M. Mileo, I. Bok, et al., “Thermo-Responsive MOF/Polymer Composites for Temperature-Mediated Water Capture and Release,” Angewandte Chemie International Edition 59 (2020): 11003-11009.

[22] B. Zhou, J. Shi, and Z. Q. Chen, “Experimental Study on Moisture Migration Process of Zeolite-Based Composite Humidity Control Material,” Applied Thermal Engineering 128 (2018): 604-613.

[23] J. C. Jin, N. N. Shen, Z. P. Wang, Y. C. Peng, and X. Y. Huang, “Photoluminescent Ionic Metal Halides Based on s² Typed Ions and Aprotic Ionic Liquid Cations,” Coordination Chemistry Reviews 448 (2021): 214185.

[24] M. Li and Z. Xia, “Recent Progress of Zero-dimensional Luminescent Metal Halides,” Chemical Society Reviews 50 (2021): 2626-2662.

[25] Z. Zhang, Y. Lin, J. Jin, et al., “Crystalline-Phase-Recognition-Induced Domino Phase Transition and Luminescence Switching for Advanced Information Encryption,” Angewandte Chemie International Edition 60 (2021): 23373-23379.

[26] Y. C. Peng, J. C. Jin, S. H. Zhou, et al., “Regulating Photoluminescence through Single-Crystal-to-Single-Crystal Transformation of Solvent-Containing Zero-Dimensional Hybrid Metal Halide Isomers,” Chemical Engineering Journal 488 (2024): 151026.

[27] J. Q. Zhao, D. Y. Wang, T. Y. Yan, et al., “Synchronously Improved Multiple Afterglow and Phosphorescence Efficiencies in 0D Hybrid Zinc Halides with Ultrahigh Anti-Water Stabilities,” Angewandte Chemie International Edition 63 (2024): e202412350.

[28] Z. Wang and X. Huang, “Luminescent Organic-Inorganic Hybrid Metal Halides: An Emerging Class of Stimuli-Responsive Materials,” Chemical European Journal 28 (2022): e202200609.

[29] C. Sun, C. Q. Jing, D. Y. Li, et al., “In Situ Halide Vacancy Tuning of Low-Dimensional Lead Perovskites to Realize Multiple Adjustable Luminescence Performance,” Advanced Science 12 (2025): 2412459.

[30] Q. Wang, W. Jiang, T. C. Liu, et al., “Organic Indium Halides With near-unity Photoluminescence Quantum Yields for Highly Efficient Luminescent Inks and White Light Emitting Diodes,” ACS Applied Materials and Interfaces 17 (2025): 24048-24057.

[31] H. W. Lin, A. Ablez, X. P. Guo, et al., “Simultaneously Achieving Efficient Narrow-Band Emission and Large Emission Dissymmetry Factor in an Achiral Hybrid Indium Chloride,” Advanced Science 13 (2026): e22728.

[32] F. Wang, X. J. Li, T. Q. Chen, et al., “A Strategy of Chiral Cation Coordination to Achieve a Large Luminescence Dissymmetry Factor in 1D Hybrid Manganese Halides,” Chemical Science 16 (2025): 11012-11020.

[33] Z. P. Wang and X. Y. Huang, “Stepwise Structural Transformation in Hybrid Antimony Chloride for Time-resolved and Multi-stage Informational Encryption and Anti-counterfeiting,” Inorganic Chemistry Frontiers 12 (2025): 3997-4006.

[34] J. Wu, J. Qi, Y. Guo, S. Yan, W. Liu, and S. Guo, “Reversible Tri-state Structural Transitions of Hybrid Copper(i ) Bromides Toward Tunable Multiple Emissions,” Inorganic Chemistry Frontiers 11 (2024): 156-163.

[35] J. Chen, Y. Guo, B. Chen, et al., “Kinetics-Tunable Hydrochromic Luminescence Switching in Rb₃ TbF₆:Eu³⁺ Perovskite,” Advanced Optical Materials 12 (2024): 2400147.

[36] R. Jiang, G. Peng, Q. Li, H. Wang, Z. Ci, and Q. Wang, “Manganese (II) Halides for X-Ray Imaging and Moisture Detection,” Advanced Materials Technologies 9 (2024): 2301894.

[37] H. L. Liu, H. Y. Ru, M. E. Sun, Z. Y. Wang, and S. Q. Zang, “Organic−Inorganic Manganese Bromide Hybrids With Water-Triggered Luminescence for Rewritable Paper,” Advanced Optical Materials 10 (2021): 2101700.

[38] W. Ma, Q. Qian, S. M. H. Qaid, et al., “Water-Molecule-Induced Reversible Fluorescence in a One-Dimensional Mn-Based Hybrid Halide for Anticounterfeiting and Digital Encryption-Decryption,” Nano Letters 23 (2023): 8932-8939.

[39] C. Sun, H. Zhang, Z. Deng, et al., “Metal-Ion-Doped Manganese Halide Hybrids With Tunable Emission for Advanced Anti-Counterfeiting,” Nanomaterials 13 (2023): 1890.

[40] Z. P. Wang, Z. Z. Zhang, L. Q. Tao, et al., “Hybrid Chloroantimonates(III): Thermally Induced Triple-Mode Reversible Luminescent Switching and Laser-Printable Rewritable Luminescent Paper,” Angewandte Chemie International Edition 58 (2019): 9974-9978.

[41] S. K. Sharma, C. Phadnis, T. K. Das, et al., “Reversible Dimensionality Tuning of Hybrid Perovskites with Humidity: Visualization and Application to Stable Solar Cells,” Chemical Materials 31 (2019): 3111-3117.

[42] Y. Y. Ju, J. Peng, Y. Chen, et al., “Water-Sensitive Mixed-Phase PEA₆SnI₈ Perovskite Derivative Single Crystal for Humidity Detection,” Crystal Growth & Design 22 (2022): 4689-4695.

[43] L. Ren, J. Cao, S. Liu, et al., “Potential Water Collection From Air by Chloride Perovskites,” Advanced Materials 36 (2024): 2404758.

[44] H. Furukawa, F. Gándara, Y. B. Zhang, et al., “Water Adsorption in Porous Metal-Organic Frameworks and Related Materials,” Journal of the American Chemical Society 136 (2014): 4369-4381.

[45] A. Entezari, O. C. Esan, X. H. Yan, R. Z. Wang, and L. An, “Sorption-Based Atmospheric Water Harvesting: Materials, Components, Systems, and Applications,” Advanced Materials 35 (2023): 2210957.

[46] H. Shan, P. Poredos, Z. H. Chen, et al., “Hygroscopic Salt-embedded Composite Materials for Sorption-based Atmospheric Water Harvesting,” Nature Reviews Materials 9 (2024): 699-721.

[47] M. Ejeian and R. Z. Wang, “Adsorption-Based Atmospheric Water Harvesting,” Joule 5 (2021): 1678-1703.

[48] Z. P. Wang, D. L. Xie, F. Zhang, J. B. Yu, X. P. Chen, and C. P. Wong, “Controlling Information Duration on Rewritable Luminescent Paper Based on Hybrid Antimony (III) Chloride/Small-molecule Absorbates,” Science Advances 6 (2020): eabc2181.

[49] Z. P. Wang, D. D. Huang, Y. Liu, et al., “Vacancy Effect on the Luminescent and Water Responsive Properties of Vacancy-Ordered Double Perovskite Derivatives,” Angewandte Chemie International Edition 63 (2024): e202412346.

[50] J. Q. Zhao, H. S. Shi, L. R. Zeng, et al., “Highly Emissive Zero-Dimensional Antimony Halide for Anti-Counterfeiting and Confidential Information Encryption-Decryption,” Chemical Engineering Journal 431 (2022): 134336.

[51] C. X. Lei, W. X. Guan, Y. X. Zhao, and G. H. Yu, “Chemistries and Materials for Atmospheric Water Harvesting,” Chemical Society Reviews 53 (2024): 7328-7362.

[52] J. Cai, X. Zheng, Q. Pan, D. Li, and W. Wang, “Advances in Hygroscopic Metal-Organic Frameworks for Air, Water & Energy Applications,” Applied Energy 377 (2025): 124362.

[53] L. Shi, K. O. Kirlikovali, Z. J. Chen, and O. K. Farha, “Metal-Organic Frameworks for Water Vapor Adsorption,” Chem 10 (2024): 484-503.

[54] S. Sakaida, K. Otsubo, O. Sakata, et al., “Crystalline Coordination Framework Endowed With Dynamic Gate-opening Behaviour by Being Downsized to a Thin Film,” Nature Chemistry 8 (2016): 377-383.

[55] A. V. Neimark, F. X. Coudert, A. Boutin, and A. H. Fuchs, “Stress-Based Model for the Breathing of Metal−Organic Frameworks,” Journal of Physical Chemistry Letters 1 (2010): 445-449.

[56] S. Aleid, M. Wu, R. Li, et al., “Salting-in Effect of Zwitterionic Polymer Hydrogel Facilitates Atmospheric Water Harvesting,” ACS Materials Letters 4 (2022): 511-520.

[57] H. An, Y. Chen, Y. Wang, et al., “High-performance Solar-driven Water Harvesting From Air With a Cheap and Scalable Hygroscopic Salt Modified Metal-organic Framework,” Chemical Engineering Journal 461 (2023): 141955.

[58] F. Deng, C. Wang, C. Xiang, and R. Wang, “Bioinspired Topological Design of Super Hygroscopic Complex for Cost-effective Atmospheric Water Harvesting,” Nano Energy 90 (2021): 106642.

[59] Y. Guo, W. Guan, C. Lei, H. Lu, W. Shi, and G. Yu, “Scalable Super Hygroscopic Polymer Films for Sustainable Moisture Harvesting in Arid Environments,” Nature Communications 13 (2022): 2761.

[60] S. Laha and T. K. Maji, “Binary/Ternary MOF Nanocomposites for Multi-Environment Indoor Atmospheric Water Harvesting,” Advanced Functional Materials 32 (2022): 2203093.

[61] C. Lei, Y. Guo, W. Guan, H. Lu, W. Shi, and G. Yu, “Polyzwitterionic Hydrogels for Efficient Atmospheric Water Harvesting,” Angewandte Chemie International Edition 61 (2022): e202200271.

[62] R. Li, Y. Shi, M. Alsaedi, M. Wu, L. Shi, and P. Wang, “Hybrid Hydrogel With High Water Vapor Harvesting Capacity for Deployable Solar-Driven Atmospheric Water Generator,” Environmental Science & Technology 52 (2018): 11367-11377.

[63] R. Li, Y. Shi, M. Wu, S. Hong, and P. Wang, “Improving Atmospheric Water Production Yield: Enabling Multiple Water Harvesting Cycles With Nano Sorbent,” Nano Energy 67 (2020): 104255.

[64] Y. Sun, A. Spieß, C. Jansen, et al., “Tunable LiCl@UiO-66 Composites for Water Sorption-Based Heat Transformation Applications,” Journal of Materials Chemistry A 8 (2020): 13364-13375.

[65] J. Xu, T. Li, J. Chao, et al., “Efficient Solar-Driven Water Harvesting From Arid Air With Metal-Organic Frameworks Modified by Hygroscopic Salt,” Angewandte Chemie International Edition 59 (2020): 5202-5210.

[66] J. Xu, T. Li, T. Yan, et al., “Ultrahigh Solar-driven Atmospheric Water Production Enabled by Scalable Rapid-cycling Water Harvester With Vertically Aligned Nanocomposite Sorbent,” Energy & Environmental Science 14 (2021): 5979-5994.

[67] C. Kuok, W. Dianbudiyanto, and S. Liu, “A Simple Method to Valorize Silica Sludges Into Sustainable Coatings for Indoor Humidity Buffering,” Sustain Environmental Research 32 (2022): 8.

[68] Y. Lin, W. Lee, K. Lin, T. Cheng, and B. Kuo, “Utilization of Waste From the Silicon Carbide Grinding Sludge and Stone Sludge as Source of Silicon Aluminum for the Synthesis of the Amine Functional Mesoporous Humidity Control Material,” Journal of Material Cycles and Waste Management 24 (2022): 1009-1019.

[69] Y. W. Lin, W. H. Lee, B. Y. Kuo, and K. L. Lin, “Effect of the Indoor Humidity Control Characteristics for Amine Grafted Functionalized Mesoporous Silica Nanomaterials,” Journal of Chinese Institute of Engineers 46 (2023): 11-20.

[70] Y. Liu, H. Jia, G. Zhang, Z. Sun, Y. Pan, and S. Zheng, “Synthesis and Humidity Control Performances of Natural Opoka Based Porous Calcium Silicate Hydrate,” Advanced Powder Technology 30 (2019): 2733-2741.

[71] H. Lu, C. Kuok, and S. Liu, “High-performance Humidity Control Coatings Prepared From Inorganic Wastes,” Construction & Building Materials 263 (2020): 120169.

[72] P. C. Qiu, L. Guo, Y. J. Qi, M. Z. Cheng, and Z. Z. Jing, “Hydrothermal Solidification of Sepiolite Into a Cemented Sepiolite Aggregate for Humidity Regulation and Formaldehyde Removal,” Clay Minerals 55 (2020): 320-328.

[73] X. Zhou, H. Jin, A. Gu, et al., “Eco-friendly Hierarchical Porous Palygorskite/Wood fiber Aerogels With Smart Indoor Humidity Control,” Journal of Cleaner Production 335 (2022): 130367.

[74] C. F. Macrae, I. Sovago, S. J. Cottrell, et al., “Mercury 4.0: From Visualization to Analysis, Design and Prediction,” Journal of Applied Crystallography 53 (2020): 226-235.

[75] G. M. Sheldrick, “Crystal Structure Refinement With SHELXL,” Acta Crystallographica Section C, Structural Chemistry 71 (2015): 3-8.

RIGHTS & PERMISSIONS

2026 The Author(s). Aggregate published by SCUT, AIEI, and John Wiley & Sons Australia, Ltd.