{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,26]],"date-time":"2026-09-26T10:10:52Z","timestamp":1790417452107,"version":"4.1.0"},"reference-count":58,"publisher":"MDPI AG","issue":"3","license":[{"start":{"date-parts":[[2023,1,18]],"date-time":"2023-01-18T00:00:00Z","timestamp":1674000000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Department of Chemical Sciences of Padova University","award":["P-DiSC#11NExuS_BIRD2019-UNIPD"],"award-info":[{"award-number":["P-DiSC#11NExuS_BIRD2019-UNIPD"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Nanomaterials"],"abstract":"<jats:p>Halloysite nanotubes can be used for the preparation of solid catalysts. Owing to their natural availability at low-cost as well as to their large and easy-to-functionalize surface, they can be conveniently activated with mineral acids or derivatized with acidic groups. Nevertheless, the use of HNTs as catalysts in complex transformations is still limited. Herein, we report two strategies to utilize HNT-based materials as solid acidic catalysts for the Biginelli reaction. To this aim, two methods for increasing the number of acidic sites on the HNTs were explored: (i) the treatment with piranha solution (Pir-HNTs) and (ii) the functionalization with phenylboronic acid (in particular with benzene-1,4-diboronic acid: the sample is denoted as HNT-BOA). Interestingly, both strategies enhance the performance of the multicomponent reaction. Pir-HNTs and HNT-BOA show an increased reactivity (72% and 89% yield, respectively) in comparison with pristine HNTs (52%). Additionally, Pir-HNTs can be reused up to five times without significant performance loss. Moreover, the method also displays good reaction scope, as demonstrated by the preparation of 12 different 3,4-dihydropyrimidinones in up to 71% yield. Therefore, the described strategies are promising for enhancing the acidity of the HNTs as catalysts for the organic reaction.<\/jats:p>","DOI":"10.3390\/nano13030394","type":"journal-article","created":{"date-parts":[[2023,1,19]],"date-time":"2023-01-19T03:45:16Z","timestamp":1674099916000},"page":"394","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":18,"title":["Halloysite Nanotubes as Bimodal Lewis\/Br\u00f8nsted Acid Heterogeneous Catalysts for the Synthesis of Heterocyclic Compounds"],"prefix":"10.3390","volume":"13","author":[{"given":"Jiaying","family":"Yu","sequence":"first","affiliation":[{"name":"Department of Chemical Sciences, University of Padova, Via F. Marzolo 1, 35131 Padova, Italy"},{"name":"College of Chemistry and Environmental Engineering, Shenzhen University, 3688 Nanhai Ave, Shenzhen 518060, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2358-9183","authenticated-orcid":false,"given":"Javier","family":"Mateos","sequence":"additional","affiliation":[{"name":"Department of Chemical Sciences, University of Padova, Via F. Marzolo 1, 35131 Padova, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1194-6147","authenticated-orcid":false,"given":"Mauro","family":"Carraro","sequence":"additional","affiliation":[{"name":"Department of Chemical Sciences, University of Padova, Via F. Marzolo 1, 35131 Padova, Italy"},{"name":"ITM-CNR, UoS of Padova, Via F. Marzolo 1, 35131 Padova, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2023,1,18]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"5366","DOI":"10.1021\/cr068042e","article-title":"Acid catalysts in industrial hydrocarbon chemistry","volume":"107","author":"Busca","year":"2007","journal-title":"Chem. Rev."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"63","DOI":"10.1016\/S1359-0286(97)80107-6","article-title":"Solid acid catalysts","volume":"2","author":"Corma","year":"1997","journal-title":"Curr. Opin. Solid State Mater. 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