Black titania with increased defective sites for phenol photodegradation under visible light
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Black titania with increased defective sites for phenol photodegradation under visible light Keyla M. Fuentes1 · Doménico Venuti2 · Paulino Betancourt3 Received: 1 June 2020 / Accepted: 2 August 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract Herein, the effect of an acid pre-treatment over T iO2 reduction was studied to obtain black titania with increased defectives sites. A commercial TiO2 (anatase > 99%; Merck) was pre-treated with aqueous solutions of boric, nitric, phosphoric and sulfuric acids at 353 K. Afterwards, the solids were annealed for 2 h at 773 K under 50 mL min−1 H2 flow. The above materials were analyzed by XRD, FTIR, XPS and UV–Vis to relate the chemical changes induced by the acid pre-treatment with crystalline and optical characteristics and; hence, to the photoactivity. The O/Ti surface ratio nor the energy band gap value of the TiO2 was altered by the pre-treatment using sulfuric acid; therefore, the photocatalytic activity was not modified using this acid. Despite the fact that pre-treatment with boric and phosphoric acid decreased the energy band gap to 2.1 and 2.9; respectively (which is favorable for the absorption of visible light), the incorporation of borate and phosphate species in the surface was detrimental for the photocatalytic process. The O/Ti ratio dropped from 2.0 to 1.5 after the reduction of the sample pretreated with nitric acid. Since more oxygen vacancies are introduced by using nitric acid, the visible-light absorption was increased and the phenol photodegradation was boosted. The modulation of the defective sites allows to engineering the T iO2 band-gap for solar-driven applications. Keywords Black TiO2 · Visible-driven photocatalysis · Band gap engineering
Introduction Semiconductor photocatalysis is a widely studied advanced oxidation process to remove persistent organic pollutants, such as phenol, from wastewaters [1–4]. For this process, the most common photocatalyst is the titanium dioxide (e.g., as anatase Electronic supplementary material The online version of this article (https://doi.org/10.1007/s1114 4-020-01832-6) contains supplementary material, which is available to authorized users. * Keyla M. Fuentes [email protected]; [email protected] Extended author information available on the last page of the article
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phase) due to its affordable cost, low toxicity and high stability. However, it is activated by irradiation with UV light because of its wide band gap energy (~ 3.2 eV) [5]. In the search of lowering the costs, visible-light driven photocatalysis has become a suitable approach to exploit sunlight as photons source [6, 7]. The visiblelight photoexcitation of TiO2 is feasible through band-gap engineering by including foreign atoms (dopants) to reduce its threshold energy [8–11]. Nevertheless, it has been suggested recently that the induced oxygen-deficient sites are the responsible for the activation under visible light since they introdu
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