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Although this reduction route has been known since the early reports of TNT, the quantitative relationship between the polarization parameters and the resulting electronic response remains to be established. Hence, a full factorial design (FFD) coupled to response surface methodology (RSM) was employed to assess simultaneously the cathodic potential, the polarization (self-doping) time, and the calcination temperature, using the cathodic current density (jc) associated with the Ti4+\/Ti3+ reduction as the response. The optimum condition, obtained by FFD\/RSM, was \u22121.5 V, applied for 480 min, to layers calcined at 450 \u00b0C, which delivered a jc of \u22120.325 mA cm\u20132. Under these conditions, SD-TNT were also investigated using electrochemical impedance spectroscopy (EIS), which revealed a decrease of the charge-transfer resistance from 831.9 to 92.35 \u03a9, together with a lower capacitance, constant phase element exponent, and a shorter time constant, consistent with a higher density of Ti3+ centers and oxygen vacancies distributed along the tube axis. Raman deconvolution of the anatase Eg mode confirmed the increase of the oxygen-vacancy contribution after cathodic polarization, whereas the calcination temperature controlled the anatase\/rutile ratio and, therefore, the apparent band gap. The multivariate approach, thus, provides quantitative criteria to select the cathodic polarization parameters of TNT.<\/jats:p>","DOI":"10.1021\/acsomega.6c08217","type":"journal-article","created":{"date-parts":[[2026,9,28]],"date-time":"2026-09-28T07:02:02Z","timestamp":1790578922000},"page":"62060-62071","source":"Crossref","is-referenced-by-count":1,"title":["Multivariate Optimization\nof Self-doped TiO2 Nanotube Synthesis for Enhanced Optical\nand Electronic Performance"],"prefix":"10.1021","volume":"11","author":[{"given":"Joa\u0303o Vitor","family":"Martins","sequence":"first","affiliation":[{"name":"State University of Londrina (UEL) , , Celso Garcia Cid Highway, PR 445, km 380 , ,","place":["Londrina, Brazil, 86055-900"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Gabrielle","family":"Sarto","sequence":"additional","affiliation":[{"name":"State University of Londrina (UEL) , , Celso Garcia Cid Highway, PR 445, km 380 , ,","place":["Londrina, Brazil, 86055-900"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Thiago Nogueira Marques","family":"Cervantes","sequence":"additional","affiliation":[{"name":"State University of Londrina (UEL) , , Celso Garcia Cid Highway, PR 445, km 380 , ,","place":["Londrina, Brazil, 86055-900"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Paulo Roge\u0301rio","family":"Catarini da Silva","sequence":"additional","affiliation":[{"name":"State University of Londrina (UEL) , , Celso Garcia Cid Highway, PR 445, km 380 , ,","place":["Londrina, Brazil, 86055-900"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6395-4309","authenticated-orcid":true,"given":"Lucio Cesar","family":"de Almeida","sequence":"additional","affiliation":[{"name":"State University of Londrina (UEL) , , Celso Garcia Cid Highway, PR 445, km 380 , ,","place":["Londrina, Brazil, 86055-900"]},{"name":"National Institute of Alternative Technologies for Detection, Toxicological Assessment and Removal of Emerging and Radioactive Contaminants\u2500(INCT-Datrem) , Rua Professor Francisco Degni, 55 , , ,","place":["Araraquara, Sa\u0303o Paulo, Brazil, 14800-060"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"316","published-online":{"date-parts":[[2026,9,28]]},"reference":[{"key":"2026101315075826400_cit1","doi-asserted-by":"publisher","first-page":"3447","DOI":"10.2147\/IJN.S249441","article-title":"Biomedical applications of TiO2 nanostructures:\nRecent advances","volume":"15","author":"Jafari","year":"2020","journal-title":"Int. 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