4.7 Article

Cation-exchange mediated synthesis of hydrogen and sodium titanates heterojunction: Theoretical and experimental insights toward photocatalyic mechanism

Journal

APPLIED SURFACE SCIENCE
Volume 538, Issue -, Pages -

Publisher

ELSEVIER
DOI: 10.1016/j.apsusc.2020.148137

Keywords

Heterojunction; Nanotubes; Charge carrier transfer mechanism; Z-scheme

Funding

  1. CEPID/CDMF
  2. Sao Paulo Research Foundation (FAPESP) [2013/07296-2, 2018/01914-0, 2017/19143-7, 2019/08928-9, 2016/25500-4, 2019/12430-6, 2017/24405-0, 2019/12114-7]
  3. National Council for Scientific and Technological Development (CNPq) [142035/2017-3]
  4. Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES)

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Na2Ti3O7/H2Ti3O7 heterojunction nanotubes were synthesized via microwave-assisted hydrothermal method with different band gap energy engineering, showing activity for Rhodamine-B dye discoloration under visible light, with the material having the highest sodium concentration exhibiting the best performance. The theoretical results revealed a staggered gap heterojunction band offset between Na2Ti3O7 and H2Ti3O7, with a Z-scheme charge carrier transfer mechanism for dye discoloration.
Na2Ti3O7/H2Ti3O7 heterojunction nanotubes were obtained through the microwave-assisted hydrothermal method (MAH) with different band gap energy engineering. This study aimed to synthesize sodium titanate nanotubes and evaluate the influence of H+ insertion on their photocatalytic properties. Heterojunctions were identified by X-ray diffraction, Raman spectroscopy and high-resolution transmission electron microscopy, and their electronic levels and defects were investigated using diffuse reflectance and photoluminescence spectroscopies in the UV-Vis region. The cation exchange process promotes the formation of Na2Ti3O7/H2Ti3O7 heterojunction with coexistence of both phases in the nanotube. Photocatalytic results of Rhodamine-B (Rh-B) dye discoloration show that the prepared materials have activity under visible and UV light irradiation, and are dependent on the proportion of hydrogen and sodium-titanate phases present. The material with highest sodium concentration showed discoloration with a half-life time of 23 min under visible light irradiation. Theoretical results reveal the heterojunction band offset as a staggered gap, with the effective bandgap occurring between the O-2p of Na2Ti3O7 and Ti-3d of H2Ti3O7. The charge carrier transfer mechanism in the heterojunctions is well described by Z-scheme, with H2Ti3O7 and Na2Ti3O7 as the main oxidation and reduction phases for dye discoloration.

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