{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,3]],"date-time":"2026-08-03T21:45:04Z","timestamp":1785793504786,"version":"3.56.0"},"reference-count":32,"publisher":"MDPI AG","issue":"5","license":[{"start":{"date-parts":[[2026,2,27]],"date-time":"2026-02-27T00:00:00Z","timestamp":1772150400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Research projects of the Shanxi Provincial Bureau of Cultural Relics","award":["2025KT04"],"award-info":[{"award-number":["2025KT04"]}]},{"name":"Shaanxi Province Special Guide Program for Technological Innovation","award":["2024QY-SZX-04"],"award-info":[{"award-number":["2024QY-SZX-04"]}]},{"name":"Central Government Guides Local Science and Technology Development Fund Project","award":["2024ZY-JCYJ-04\u201306"],"award-info":[{"award-number":["2024ZY-JCYJ-04\u201306"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Materials"],"abstract":"<jats:p>Earthen immovable cultural relics, such as murals and painted clay sculptures, are prone to deterioration (e.g., efflorescence, flaking, and cracking) under long-term preservation conditions. While conventional restoration materials primarily offer reinforcement, they fail to regulate the migration of soluble salts within the relics, which is the main cause of such damage. Herein, aimed at protecting the painted sculptures and murals of the Yungang Grottoes, nano calcium-aluminum layered double hydroxides (Ca-Al LDHs) were prepared, and their effectiveness in regulating salt crystallization within the earthen ground layer, as well as their reinforcement performance were investigated. Simulated salt crystallization tests revealed that coating the ground layer with Ca-Al LDHs delayed salt-induced damage time by 150%. This can be attributed to the ability of Ca-Al LDHs to adsorb sulfate ions from soluble salts, thereby inhibiting the crystallization of magnesium sulfate on the surface of the ground layer. After curing Ca-Al LDHs-coated samples at 35 \u00b0C and 55% relative humidity (RH) for 7 days, their surface Leeb hardness increased by 3.1%, and the weight loss rate (measured via tape peeling test) decreased by 38.3%. These results indicate that the surface bonding strength was enhanced following Ca-Al LDHs coating, with the underlying mechanism being the transformation of part of the LDHs into calcium carbonate under the influence of water and carbon dioxide. This study demonstrates that Ca-Al LDHs not only suppress magnesium sulfate crystallization but also provide effective surface consolidation, showing promising potential for application in conserving painted sculptures and murals at the Yungang Grottoes.<\/jats:p>","DOI":"10.3390\/ma19050912","type":"journal-article","created":{"date-parts":[[2026,3,5]],"date-time":"2026-03-05T14:19:21Z","timestamp":1772720361000},"page":"912","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":1,"title":["Nano Calcium-Aluminum Layered Double Hydroxides for the Conservation of Earthen Immovable Cultural Heritage"],"prefix":"10.3390","volume":"19","author":[{"given":"Jie","family":"Zhou","sequence":"first","affiliation":[{"name":"School of Material Science and Engineering, Shaanxi University of Science and Technology, Xi\u2019an 710021, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Pingchuan","family":"Gao","sequence":"additional","affiliation":[{"name":"Centre of the Protection and Monitoring for Cultural Heritage, Yungang Academy, Datong 037007, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Weiwei","family":"Cao","sequence":"additional","affiliation":[{"name":"School of Material Science and Engineering, Shaanxi University of Science and Technology, Xi\u2019an 710021, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ting","family":"Zhao","sequence":"additional","affiliation":[{"name":"School of Material Science and Engineering, Shaanxi University of Science and Technology, Xi\u2019an 710021, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yuan","family":"Fang","sequence":"additional","affiliation":[{"name":"School of Material Science and Engineering, Shaanxi University of Science and Technology, Xi\u2019an 710021, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yi","family":"Qin","sequence":"additional","affiliation":[{"name":"School of Material Science and Engineering, Shaanxi University of Science and Technology, Xi\u2019an 710021, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Wenzong","family":"Yang","sequence":"additional","affiliation":[{"name":"School of Material Science and Engineering, Shaanxi University of Science and Technology, Xi\u2019an 710021, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6246-9857","authenticated-orcid":false,"given":"Zhuo","family":"Wang","sequence":"additional","affiliation":[{"name":"School of Material Science and Engineering, Shaanxi University of Science and Technology, Xi\u2019an 710021, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jianfeng","family":"Zhu","sequence":"additional","affiliation":[{"name":"School of Material Science and Engineering, Shaanxi University of Science and Technology, Xi\u2019an 710021, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yi","family":"Liu","sequence":"additional","affiliation":[{"name":"School of Material Science and Engineering, Shaanxi University of Science and Technology, Xi\u2019an 710021, China"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,2,27]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"494","DOI":"10.1016\/j.culher.2011.03.008","article-title":"Deterioration of Yungang Grottoes: Diagnosis and research","volume":"12","author":"Liu","year":"2011","journal-title":"J. Cult. Herit."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"103781","DOI":"10.1016\/j.vibspec.2025.103781","article-title":"Multi-technique analysis of the mural materials and techniques in the 5th cave of the five temple grottoes in Subei, China","volume":"137","author":"Li","year":"2025","journal-title":"Vib. Spectrosc."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"105","DOI":"10.1016\/j.culher.2018.01.002","article-title":"A scientific investigation of five polymeric materials used in the conservation of murals in Dunhuang Mogao Grottoes","volume":"31","author":"Su","year":"2018","journal-title":"J. Cult. Herit."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"163476","DOI":"10.1016\/j.scitotenv.2023.163476","article-title":"Capillary rise induced salt deterioration on ancient wall paintings at the Mogao Grottoes","volume":"881","author":"Hu","year":"2023","journal-title":"Sci. Total Environ."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"522","DOI":"10.1016\/j.culher.2024.04.011","article-title":"Quantitative analysis on the impact factors of salt weathering for sandstone grottoes along Silk Road, China","volume":"67","author":"Shen","year":"2024","journal-title":"J. Cult. Herit."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"107989","DOI":"10.1016\/j.enggeo.2025.107989","article-title":"The mechanisms of salt weathering responsible for sandstone deterioration in the Yungang Grottoes, China","volume":"350","author":"Yang","year":"2025","journal-title":"Eng. Geol."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"109194","DOI":"10.1016\/j.cclet.2023.109194","article-title":"Application of epoxy resin in cultural relics protection","volume":"35","author":"Chen","year":"2024","journal-title":"Chin. Chem. Lett."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"1127","DOI":"10.1016\/j.porgcoat.2013.03.018","article-title":"The preservation damage of hydrophobic polymer coating materials in conservation of stone relics","volume":"76","author":"Zhang","year":"2013","journal-title":"Prog. Org. Coat."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"e52953","DOI":"10.1002\/app.52953","article-title":"Nano-silica\/fluorinated polyacrylate composites as surface protective coatings for simulated stone cultural relic protection","volume":"139","author":"Xu","year":"2022","journal-title":"J. Appl. Polym. Sci."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"445","DOI":"10.1016\/j.conbuildmat.2016.06.008","article-title":"Effect of inorganic silicate consolidation on the mechanical and durability performance of sandstone used in historical sites","volume":"121","author":"Chen","year":"2016","journal-title":"Constr. Build. Mater."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"2618","DOI":"10.1039\/c2nj40708f","article-title":"New calcium alkoxides for consolidation of carbonate rocks. Influence of precursors\u2019 characteristics on morphology, crystalline phase and consolidation effects","volume":"36","author":"Ossola","year":"2012","journal-title":"New J. Chem."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"133750","DOI":"10.1016\/j.colsurfa.2024.133750","article-title":"Translucent superhydrophobic coating for murals protection","volume":"689","author":"Zhou","year":"2024","journal-title":"Colloids Surf. A-Physicochem. Eng. Asp."},{"key":"ref_13","doi-asserted-by":"crossref","unstructured":"Liu, Y., Li, Q., Zhou, R., and Yusufu, R. (2024). Research Progress of Superhydrophobic Coatings in the Protection of Earthen Sites. Coatings, 14.","DOI":"10.3390\/coatings14060710"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"137548","DOI":"10.1016\/j.colsurfa.2025.137548","article-title":"Homogeneous integration of CaCO3 oligomers with zwitterionic siloxane polymers for protecting sandstone against salt damage","volume":"725","author":"Chen","year":"2025","journal-title":"Colloids Surf. A-Physicochem. Eng. Asp."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"139097","DOI":"10.1016\/j.conbuildmat.2024.139097","article-title":"The salt removal from ancient sandstone using CaCO3 oligomer- and POSS siloxane-enhanced zwitterionic polymer","volume":"453","author":"Li","year":"2024","journal-title":"Constr. Build. Mater."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"100","DOI":"10.1002\/bkcs.12649","article-title":"Recent advances in the synthesis of layered double hydroxides nanosheets","volume":"44","author":"Xie","year":"2023","journal-title":"Bull. Korean Chem. Soc."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"232","DOI":"10.1016\/j.jmst.2021.05.078","article-title":"Layered double hydroxide (LDH) for multi-functionalized corrosion protection of metals: A review","volume":"102","author":"Cao","year":"2022","journal-title":"J. Mater. Sci. Technol."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"122974","DOI":"10.1016\/j.ces.2025.122974","article-title":"Adsorption performance and mechanism analysis of hydrotalcite derived CaFe-bimetal materials for highly efficient Cd2+ removal process from kinetic and isotherm aspects","volume":"321","author":"Li","year":"2026","journal-title":"Chem. Eng. Sci."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"175509","DOI":"10.1016\/j.scitotenv.2024.175509","article-title":"Development and validation of an adsorption process for phosphate removal and recovery from municipal wastewater based on hydrotalcite-related materials","volume":"951","author":"Maggetti","year":"2024","journal-title":"Sci. Total Environ."},{"key":"ref_20","doi-asserted-by":"crossref","unstructured":"Ion, R.M., Rizescu, C.E., Vasile, D.A., Vasilievici, G., Atkinson, I., Rusu, A., Predoana, L., and Miculescu, F. (2022). Layered Double Hydroxides (LDHs) as New Consolidants for Cultural Heritage Masonry. Crystals, 12.","DOI":"10.3390\/cryst12040490"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"D1670","DOI":"10.1093\/nar\/gkae973","article-title":"Generic Diagramming Platform (GDP): A comprehensive database of high-quality biomedical graphics","volume":"53","author":"Jiang","year":"2025","journal-title":"Nucleic Acids Res."},{"key":"ref_22","first-page":"7","article-title":"Material and technical study of the mural paintings at Ta\u2019erliang Village, Inner Mongolia","volume":"30","author":"Shen","year":"2019","journal-title":"Sci. Conserv. Archaeol."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"2855","DOI":"10.1002\/esp.5862","article-title":"Driving mechanisms and hydro-chemical variation for assessing salt-induced weathering of sandstone in grotto relics","volume":"49","author":"Wang","year":"2024","journal-title":"Earth Surf. Process. Landf."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"7","DOI":"10.1016\/j.culher.2025.10.014","article-title":"Consolidating tomb mural plaster layer with nanolime","volume":"77","author":"Wu","year":"2026","journal-title":"J. Cult. Herit."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"881","DOI":"10.1016\/j.cej.2009.08.003","article-title":"Facile preparation of pure CaAl-layered double hydroxides and their application as a hardening accelerator in concrete","volume":"155","author":"Xu","year":"2009","journal-title":"Chem. Eng. J."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"435","DOI":"10.1016\/S0022-0248(02)01429-X","article-title":"Salt damage in porous materials: How high supersaturations are generated","volume":"242","author":"Flatt","year":"2002","journal-title":"J. Cryst. Growth"},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"336","DOI":"10.1021\/cg060688c","article-title":"Hydration of MgSO4\u00b7H2O and generation of stress in porous materials","volume":"8","author":"Steiger","year":"2008","journal-title":"Cryst. Growth Des."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"265503","DOI":"10.1103\/PhysRevLett.109.265503","article-title":"Damage mechanisms of porous materials due to in-pore salt crystallization","volume":"109","author":"Schiro","year":"2012","journal-title":"Phys. Rev. Lett."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"106030","DOI":"10.1016\/j.still.2024.106030","article-title":"Characteristics and mechanisms of soil structure damage under salt weathering","volume":"238","author":"Duan","year":"2024","journal-title":"Soil Tillage Res."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"216","DOI":"10.1016\/j.culher.2024.06.002","article-title":"In-situ growth of Ba(OH)2 nanoparticles on bacterial cellulose: A composite material for reinforcement of ancient murals-A preliminary study","volume":"68","author":"Jia","year":"2024","journal-title":"J. Cult. Herit."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"39169","DOI":"10.1021\/acsomega.2c05067","article-title":"First-Principles Study on Interlayer Spacing and Structure Stability of NiAl-Layered Double Hydroxides","volume":"7","author":"Wang","year":"2022","journal-title":"ACS Omega"},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"141399","DOI":"10.1016\/j.chemosphere.2024.141399","article-title":"Sorption of cadmium by layered double hydroxides: Performance, structure-related mechanisms, and sequestration stability assessment","volume":"352","author":"Zhang","year":"2024","journal-title":"Chemosphere"}],"container-title":["Materials"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1996-1944\/19\/5\/912\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,3,5]],"date-time":"2026-03-05T14:28:09Z","timestamp":1772720889000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1996-1944\/19\/5\/912"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,2,27]]},"references-count":32,"journal-issue":{"issue":"5","published-online":{"date-parts":[[2026,3]]}},"alternative-id":["ma19050912"],"URL":"https:\/\/doi.org\/10.3390\/ma19050912","relation":{},"ISSN":["1996-1944"],"issn-type":[{"value":"1996-1944","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,2,27]]}}}