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. 2019 Jan 29;9(2):163.
doi: 10.3390/nano9020163.

Evaluation of Solar-Driven Photocatalytic Activity of Thermal Treated TiO₂ under Various Atmospheres

Reza Katal  1 , Saeideh Kholghi Eshkalak  2 , Saeid Masudy-Panah  3 , Mohammadreza Kosari  4 , Mohsen Saeedikhani  5 , Mehrdad Zarinejad  6 , Seeram Ramakrishna  7
Affiliations

Evaluation of Solar-Driven Photocatalytic Activity of Thermal Treated TiO₂ under Various Atmospheres

Reza Katal et al. Nanomaterials (Basel). .

Abstract

In this report, the photocatalytic activity of P25 has been explored and the influence of thermal treatment under various atmospheres (air, vacuum and hydrogen) were discussed. The samples' characteristics were disclosed by means of various instruments including X-ray diffraction (XRD), Electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS) and UV⁻vis. This study also accentuates various states of the oxygen vacancy density formed inside the samples as well as the colour turning observed in treated P25 under various atmospheres. Produced coloured TiO₂ samples were then exploited for their photocatalytic capability concerning photodegradation of methylene blue (MB) using air mass (AM) 1.5 G solar light irradiation. Our findings revealed that exceptional photocatalytic activity of P25 is related to the thermal treatment. Neither oxygen vacancy formation nor photocatalytic activity enhancement was observed in the air-treated sample. H₂-treated samples have shown better photoactivity which even could be further improved by optimizing treatment conditions to achieve the advantages of the positive role of oxygen vacancy (O-vacancy at higher concentration than optimum acts as electron trapping sites). The chemical structure and stability of the samples were also studied. There was no sign of deteriorating of O₂-vacancies inside the samples after 6 months. High stability of thermal treated samples in terms of both long and short-term time intervals is another significant feature of the produced photocatalyst.

Keywords: degradation; hydrogen; oxygen vacancy; thermal treatment; vacuum.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
X-ray diffraction (XRD) pattern of P25, A-400, V-400 and H-400.
Figure 2
Figure 2
(a) UV-vis spectra, (b) colour turning image and energy band gap of samples.
Figure 3
Figure 3
XPS spectra of Ti 2p peaks (a) and O 1s peaks (b) for P25, H-400 and V-400.
Figure 4
Figure 4
EPR spectra recorded at room temperature for P25, H-400 and V-400.
Figure 5
Figure 5
EPR spectra for P25, H-400, V-400 after and before illumination under 1.5 G solar light for 30 min.
Figure 6
Figure 6
Time profiles of photocatalytic degradation of MB for (a) without photocatalyst; (b) H-400; (c) V-400; (d) P25 without irradiation; (e) P25; (f) V-400; and (g) H-400 under 1.5 G solar light illumination.
Figure 7
Figure 7
PL spectra of P25, V-400 and H-400 (excitation wavelength was 325 nm).
Figure 8
Figure 8
Degradation (%) of MB in without quencher and in presence of scavengers.
Figure 9
Figure 9
The photo-excited electrons-transfer under the simulated sun light irradiation for V-400 and H-400.
Figure 10
Figure 10
MB degradation efficiency (%) by H-400 and V-400 under AM 1.5 G solar light irradiation at different cycles.
Figure 11
Figure 11
MB degradation efficiency by V-400 and H-400 with different storage time under AM 1.5 G solar light irradiation.
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