Post-Synthesis Heat Treatment Induces Polymorphic Homogenization and Band-Tail Narrowing in Sol–Gel TiO2 Nanostructures
- 1Grupo de Óptica e Informática, Universidad Popular del Cesar, Valledupar 200001, Colombia
Abstract
Post-synthesis heat treatment provides a route for tuning the structural and optical response of TiO2 without necessarily altering its particle architecture. In this study, TiO2 nanostructures prepared by the sol–gel method were evaluated before and after a stepwise heat treatment from 250 to 400 °C using XRD/Rietveld, Raman spectroscopy, FE-SEM/EDS, statistical morphometry, and UV–Vis diffuse reflectance spectroscopy, with XPS performed on TiO2-400. TiO2-250 consisted of 96.76 ± 1.22 wt.% anatase and 3.24 ± 0.47 wt.% brookite, whereas anatase was the only crystalline phase detected in TiO2-400 within the XRD detection limit. Concurrently, the coherent crystalline domain size increased from 44.3 ± 2.6 to 53.6 ± 1.9 nm, without a statistically significant increase in the equivalent circular diameter of the particles. The apparent optical band gap increased from 3.14 ± 0.03 to 3.25 ± 0.03 eV, while the Urbach energy decreased by approximately 48%, from 189.4 ± 1.1 to 98.0 ± 0.4 meV. These results show that moderate heat treatment is accompanied by polymorphic homogenization and predominantly intraparticle crystalline/electronic reorganization, together with narrowing of the band-tail distribution without appreciable external particle growth. Overall, the study establishes a multiscale correlation between phase evolution, coherent-domain growth, morphological stability, and optical-edge narrowing in sol–gel TiO2 nanostructures.
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BibTeX
@article{jimenezonate2026postsynthesis,
title = {{Post-Synthesis Heat Treatment Induces Polymorphic Homogenization and Band-Tail Narrowing in Sol–Gel TiO2 Nanostructures}},
author = {Angiee C. Jiménez-Oñate and Ana B. González-Rojas and Edgar D. Peduzine-Orozco and Juan P. Molina-Jiménez and Duber A. Avila and Sindi D. Horta-Piñeres},
journal = {Nanomaterials},
year = {2026},
month = oct,
doi = {10.3390/nano16211369},
url = {https://www.mdpi.com/2079-4991/16/21/1369},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Post-Synthesis Heat Treatment Induces Polymorphic Homogenization and Band-Tail Narrowing in Sol–Gel TiO2 Nanostructures
AU - Angiee C. Jiménez-Oñate
AU - Ana B. González-Rojas
AU - Edgar D. Peduzine-Orozco
AU - Juan P. Molina-Jiménez
AU - Duber A. Avila
AU - Sindi D. Horta-Piñeres
PY - 2026
DA - 2026/10/27
JO - Nanomaterials
DO - 10.3390/nano16211369
UR - https://www.mdpi.com/2079-4991/16/21/1369
AB - Post-synthesis heat treatment provides a route for tuning the structural and optical response of TiO2 without necessarily altering its particle architecture. In this study, TiO2 nanostructures prepared by the sol–gel method were evaluated before and after a stepwise heat treatment from 250 to 400 °C using XRD/Rietveld, Raman spectroscopy, FE-SEM/EDS, statistical morphometry, and UV–Vis diffuse reflectance spectroscopy, with XPS performed on TiO2-400. TiO2-250 consisted of 96.76 ± 1.22 wt.% anatase and 3.24 ± 0.47 wt.% brookite, whereas anatase was the only crystalline phase detected in TiO2-400 within the XRD detection limit. Concurrently, the coherent crystalline domain size increased from 44.3 ± 2.6 to 53.6 ± 1.9 nm, without a statistically significant increase in the equivalent circular diameter of the particles. The apparent optical band gap increased from 3.14 ± 0.03 to 3.25 ± 0.03 eV, while the Urbach energy decreased by approximately 48%, from 189.4 ± 1.1 to 98.0 ± 0.4 meV. These results show that moderate heat treatment is accompanied by polymorphic homogenization and predominantly intraparticle crystalline/electronic reorganization, together with narrowing of the band-tail distribution without appreciable external particle growth. Overall, the study establishes a multiscale correlation between phase evolution, coherent-domain growth, morphological stability, and optical-edge narrowing in sol–gel TiO2 nanostructures.
SN - 2079-4991
ER -