Remarkable charge separation and photocatalytic efficiency enhancement through TiO2(B)/anatase hetrophase junctions of TiO2 nanobelts

doi:10.1016/j.ijhydene.2019.08.174

International Journal of Hydrogen Energy

Volume 44, Issue 50, 18 October 2019, Pages 27311-27318

https://doi.org/10.1016/j.ijhydene.2019.08.174 Get rights and content

Highlights

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TiO₂ nanobelts with TiO₂(B)/anatase hetrophase junctions are prepared.
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The surface coarsened nanobelt structure enhances the light absorption through reflection/refraction of light.
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The TiO₂(B)/anatase hetrophase junctions can efficiently promote the separation of photoinduced carriers.
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TiO₂ nanobelts-450 °C are highly active for producing hydrogen at 0.786 mmol h⁻¹g⁻¹ with Pt as co-catalysts.
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TiO₂ nanobelts-450 °C still show a high hydrogen evolution rate of 0.601 mmol h⁻¹g⁻¹ in the absence of co-catalysts.

Abstract

Light harvesting and charge separation are both significant to the photocatalysis, but it is challenging to synchronously realize both in a single-component material. The surface coarsened TiO₂ nanobelts with TiO₂(B)/anatase hetrophase junctions and large BET surface area are prepared via a hydrothermal/annealing method. The presence of surface coarsened nanobelt structure enhances the light absorption through reflection/refraction of light. The TiO₂(B)/anatase hetrophase junctions can efficiently promote the separation of photoinduced electrons and holes pairs and therefore decrease the charge recombination. The large BET surface area provides abundant active sites for the absorption and diffusion of reactants. As a consequence, the obtained TiO₂ nanobelts exhibit an enhanced photocatalytic H₂ evolution activity at the optimal annealing temperature (450 °C) with Pt as co-catalysts (0.786 mmol h⁻¹g⁻¹), exceeding that of pure anatase TiO₂ nanobelts (TiO₂ nanobelts-600 °C, 0.265 mmol h⁻¹g⁻¹). Interestingly, TiO₂ nanobelts-450 °C still show a high hydrogen evolution rate of 0.601 mmol h⁻¹g⁻¹ in the absence of co-catalysts.

Graphical abstract

Introduction

Photocatalytic water splitting for H₂ evolution using sustainable solar energy is an attractive clean technology to solve environmental and energy issues [1]. Titanium dioxide (TiO₂) is one of the most studied semiconductor photocatalysts in the field of H₂ production due to its non-toxicity and inertness [2]. However, from the viewpoints of practical applications, TiO₂ is limited owing to its sensitivity only in the UV region and the easy recombination of carriers [3]. Morphology engineering is a promising approach to enhance the photocatalytic activity of TiO₂ [4]. So far, 0D TiO₂ nanoparticles [5], 1D TiO₂ nanobelts or nanorods [6], 2D TiO₂ nanosheets [3] and even 3D TiO₂ nanoflowers [7] have been successfully obtained. Especially, 1D TiO₂ nanobelts have the advantage of very high carrier transport speed along its axial direction, which is beneficial for carrier separation [8].

By utilizing semiconductor heterojunction concepts, such as p–n junctions, Schottky junctions, band-structure matching heterojunctions were constructed to improve the separation of photoinduced carriers [9]. TiO₂ has four polymorphs (anatase, TiO₂(B), brookite, and rutile) [10]. TiO₂ with heterojunctions of two or three polymorphs have been widely investigated to enable charge carrier migration, such as anatase and rutile in TiO₂ nanoparticles (Degussa p25) exhibit different band structures and band edge positions, which can form a heterophase junction and is beneficial for the transfer of photoexcited electrons and holes [11]. As a minor phase, TiO₂(B)'s photocatalytic performance is lower than anatase [12]. However, TiO₂(B) owns a different electronic energy level with anatase, and can form a well matched heterophase junction with anatase [13]. The photoexcited electrons and holes could migrate to anatase and TiO₂(B), respectively. Therefore, the electrons will statistically accumulate in the anatase phase and holes in TiO₂(B), thus suppressing recombination [14].

Herein, we propose a strategy for the fabrication of surface coarsened TiO₂ nanobelts with TiO₂(B)/anatase hetrophase junctions and large BET surface area via a hydrothermal/annealing treatment. Detailed characterizations and tests confirm that the formation of TiO₂(B)/anatase hetrophase junctions in the surface coarsened TiO₂ nanobelts and large BET surface area can effectively enhance the light harvesting, increase the absorption and diffusion of reactants, as well as enable the separation of photo-generated carriers. Therefore, the obtained TiO₂ nanobelts at the optimal annealing temperature (450 °C) exhibit remarkably enhanced photocatalytic H₂ evolution activity (0.601 mmol h⁻¹g⁻¹) even without cocatalysts.

Section snippets

Structure and morphology

XRD was utilized to investigate the changes of phase structure of the prepared TiO₂ nanobelts. As shown in Fig. 1, after annealing at 300 °C, the diffraction peaks at about 2θ = 14.19°, 28.60°, 43.49°, 44.50° and 58.33°correlate closely with the (001), (002), (003), (601) and (711) crystal planes of monoclinic TiO₂(B) (JCPDS card no. 46-1238). Additionally, the diffraction peaks at about 2θ = 25.28°, 48.05°, 55.06°, 62.69° and 76.02°are ascribed to the (101), (200), (211), (204) and (301) plane

Conclusion

In conclusion, surface coarsened TiO₂ nanobelts with TiO₂(B)/anatase hetrophase junctions are successfully synthesized. With the merits of better light harvesting aroused by surface coarsened nanobelt structure, promoted carrier transfer by TiO₂(B)/anatase hetrophase junctions, and adsorption of water on the exposed active sites by large BET surface area, the photocatalytic H₂ generation rate of TiO₂ nanobelts with an optimized annealing temperature (450 °C) with Pt as co-catalysts (0.786 mmol h

Acknowledgments

The authors are thankful for fundings from the National Natural Science Foundation of China (No. 51872173 and 51772167), Taishan Scholarship of Young Scholars (No. tsqn201812068), Natural Science Foundation of Shandong Province (No. ZR2017JL020), Taishan Scholarship of Climbing Plan (No. tspd20161006), and Key Research and Development Program of Shandong Province (No. 2018GGX102028).

References (26)

Z. Wang et al.
Vertically-heterostructured TiO₂-Ag-rGO ternary nanocomposite constructed with {001} facetted TiO₂ nanosheets for enhanced Pt-free hydrogen production
Int J Hydrogen Energy
(2018)
J. Du et al.
Highly efficient hydrogen evolution catalysis based on MoS₂/CdS/TiO₂ porous composites
Int J Hydrogen Energy
(2018)
X. Hu et al.
The selective deposition of MoS₂ nanosheets onto (101) facets of TiO₂ nanosheets with exposed (001) facets and their enhanced photocatalytic H₂ production
Appl Catal B Environ
(2019)
Y. Li et al.
Ti₃C₂ MXene-derived Ti₃C₂/TiO₂ nanoflowers for noble-metal-free photocatalytic overall water splitting
Appl Mater Today
(2018)
J. Shao et al.
In situ synthesis of carbon-doped TiO₂ single-crystal nanorods with a remarkably photocatalytic efficiency
Appl Catal B Environ
(2017)
J. Tian et al.
RuO₂/TiO₂ nanobelt heterostructures with enhanced photocatalytic activity and gas-phase selective oxidation of benzyl alcohol
Sol Energy Mater Sol Cells
(2016)
H. Xing et al.
(001)-exposed TiO₂ microcrystals decorated with few-layer nanobelts for enhanced photocatalytic activity
Mater Res Bull
(2019)
P. Voepel et al.
Photocatalytic activity of multiphase TiO₂ (B)/anatase nanoparticle heterojunctions prepared from ionic liquids
J Photochem Photobiol, A
(2018)
Y. Wang et al.
Fabrication of TiO₂ (B)/anatase heterophase junctions in nanowires via a surface-preferred phase transformation process for enhanced photocatalytic activity
Chin J Catal
(2018)
J. Lu et al.
In situ synthesis of mesoporous C-doped TiO₂ single crystal with oxygen vacancy and its enhanced sunlight photocatalytic properties
Dyes Pigments
(2017)

Z. Liang et al.

Full solar spectrum photocatalytic oxygen evolution by carbon-coated TiO₂ hierarchical nanotubes

Appl Catal B Environ

(2019)

X. Liu et al.

Integrating the Z-scheme heterojunction into a novel Ag₂O@rGO@reduced TiO₂ photocatalyst: broadened light absorption and accelerated charge separation co-mediated highly efficient UV/visible/NIR light photocatalysis

J Colloid Interface Sci

(2019)

J. Tian et al.

High yield production of reduced TiO₂ with enhanced photocatalytic activity

Appl Surf Sci

(2016)

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Remarkable charge separation and photocatalytic efficiency enhancement through TiO2(B)/anatase hetrophase junctions of TiO2 nanobelts

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Structure and morphology

Conclusion

Acknowledgments

Int J Hydrogen Energy

Int J Hydrogen Energy

Appl Catal B Environ

Appl Mater Today

Appl Catal B Environ

Sol Energy Mater Sol Cells

Mater Res Bull

J Photochem Photobiol, A

Chin J Catal

Dyes Pigments

Appl Catal B Environ

J Colloid Interface Sci

Appl Surf Sci

Remarkable charge separation and photocatalytic efficiency enhancement through TiO₂(B)/anatase hetrophase junctions of TiO₂ nanobelts