{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,23]],"date-time":"2026-10-23T21:09:42Z","timestamp":1792789782283,"version":"4.5.0"},"reference-count":47,"publisher":"MDPI AG","issue":"19","license":[{"start":{"date-parts":[[2026,9,28]],"date-time":"2026-09-28T00:00:00Z","timestamp":1790553600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Ministero dell'universit\u00e0 e della ricerca","award":["NEST code PE0000021"],"award-info":[{"award-number":["NEST code PE0000021"]}],"id":[{"id":"https:\/\/ror.org\/0341vw408","id-type":"ROR","asserted-by":"crossref"}]},{"award":["NEST code PE0000021"],"award-info":[{"award-number":["NEST code PE0000021"]}],"id":[{"id":"https:\/\/ror.org\/0341vw408","id-type":"ROR","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Molecules"],"abstract":"<jats:p>Tungsten oxide (WO3) is an attractive phase-sensitive chromogenic material whose photoinduced optical response produces reversible coloration of interest light responsive optical devices. Here, WO3 nanoparticles (NPs) are synthesized via a simple surfactant-free sol\u2013gel precipitation route by systematically varying acid content and reaction temperature then characterized to establish a correlation among synthesis conditions, crystalline phase morphology and photochromic response. Morphological, structural and optical characterizations show that by gradually heating the precursors at 90 \u00b0C and varying the acid content, predominantly sheet-like orthorhombic and hydrated-orthorhombic WO3 NPs are yielded, characterized by an intense yellow color, optical band-gap values of approximately 2.4 eV, and negligible photochromism. In contrast, in a highly acidic environment. the temperature tuning promotes the formation of rod-like WO3 NPs with whitish color and higher band gap. The crystalline structures change from hexagonal to hexagonal hydrogen bronze phase, decreasing the reaction temperature. Under UV irradiation, these samples exhibit markedly higher photochromic efficiency than the orthorhombic phase, up to 18-fold higher, due to more accessible proton intercalation pathways offered by the hexagonal tunnel structure. The incorporation into poly(vinylpyrrolidone) allows the production of nanocomposite films that preserve and enhance the photochromic response. Overall, the reaction temperature is identified as the key synthetic parameter controlling WO3 crystalline phase that consequently affects photochromic behaviors, while polymer integration provides a practical route toward processable, flexible, and device-compatible photochromic coatings.<\/jats:p>","DOI":"10.3390\/molecules31193460","type":"journal-article","created":{"date-parts":[[2026,9,28]],"date-time":"2026-09-28T15:57:57Z","timestamp":1790611077000},"page":"3460","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Phase Engineering of WO3 Nanoparticles Towards Efficient Photochromic Nanocomposites"],"prefix":"10.3390","volume":"31","author":[{"ORCID":"https:\/\/orcid.org\/0009-0004-6795-2767","authenticated-orcid":false,"given":"Nicola","family":"Caggiano","sequence":"first","affiliation":[{"name":"Dipartimento di Chimica, Universit\u00e0 degli Studi di Bari, Via Orabona 4, 70126 Bari, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9246-2496","authenticated-orcid":false,"given":"Carlo Nazareno","family":"Dibenedetto","sequence":"additional","affiliation":[{"name":"CNR-Istituto per i Processi Chimico Fisici (CNR-IPCF), Via Orabona 4, 70126 Bari, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6293-9388","authenticated-orcid":false,"given":"Elisabetta","family":"Fanizza","sequence":"additional","affiliation":[{"name":"Dipartimento di Chimica, Universit\u00e0 degli Studi di Bari, Via Orabona 4, 70126 Bari, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Pierluigi","family":"Lasala","sequence":"additional","affiliation":[{"name":"Dipartimento di Chimica, Universit\u00e0 degli Studi di Bari, Via Orabona 4, 70126 Bari, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4907-2473","authenticated-orcid":false,"given":"Annamaria","family":"Panniello","sequence":"additional","affiliation":[{"name":"CNR-Istituto per i Processi Chimico Fisici (CNR-IPCF), Via Orabona 4, 70126 Bari, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7741-1436","authenticated-orcid":false,"given":"Teresa","family":"Sibillano","sequence":"additional","affiliation":[{"name":"CNR-Istituto di Cristallografia (CNR-IC), Via Amendola, 122\/O, 70126 Bari, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0983-2885","authenticated-orcid":false,"given":"Cinzia","family":"Giannini","sequence":"additional","affiliation":[{"name":"CNR-Istituto di Cristallografia (CNR-IC), Via Amendola, 122\/O, 70126 Bari, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Maria Lucia","family":"Curri","sequence":"additional","affiliation":[{"name":"CNR-Istituto per i Processi Chimico Fisici (CNR-IPCF), Via Orabona 4, 70126 Bari, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5366-691X","authenticated-orcid":false,"given":"Marinella","family":"Striccoli","sequence":"additional","affiliation":[{"name":"Dipartimento di Chimica, Universit\u00e0 degli Studi di Bari, Via Orabona 4, 70126 Bari, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,9,28]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"127","DOI":"10.1039\/B612174H","article-title":"Electrochromics for smart windows: Thin films of tungsten oxide and nickel oxide, and devices based on these","volume":"17","author":"Niklasson","year":"2007","journal-title":"J. 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