Co-modification of amorphous-Ti(IV) hole cocatalyst and Ni(OH)2 electron cocatalyst for enhanced photocatalytic H2-production performance of TiO2

doi:10.1016/j.apsusc.2016.06.108

Applied Surface Science

Volume 391, Part B, 1 January 2017, Pages 259-266

https://doi.org/10.1016/j.apsusc.2016.06.108 Get rights and content

Highlights

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TiO₂ was simultaneously modified with amorphous Ti(IV) and Ni(OH)₂.
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Amorphous Ti(IV) and Ni(OH)₂ traps holes and electrons respectively.
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Improved photocurrent response and significant hydrogen evolution were observed.
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The photocatalyst was stable during the recycling tests.

Abstract

Highly efficient TiO₂ photocatalysts co-modified by amorphous-Ti(IV) hole cocatalyst and Ni(OH)₂ electron cocatalyst (referred to as Ni(OH)₂-Ti(IV)/TiO₂) were prepared by facile two-step process which was the initial formation of amorphous Ti(IV) on the TiO₂ surface via hydrolysis method and the following formation of Ni(OH)₂ via precipitation reaction. It was found that the Ni(OH)₂-Ti(IV)/TiO₂ showed obviously high hydrogen-production performance. When the amount of Ni(OH)₂ and Ti(IV) was 1 wt% and 0.1 wt%, respectively, the hydrogen-production rate of the resultant Ni(OH)₂-Ti(IV)/TiO₂ reached 7280.04 μmol h⁻¹ g⁻¹, which was significantly higher than that of TiO₂, Ti(IV)/TiO₂ and Ni(OH)₂/TiO₂ by a factor of 215, 63 and 1.8, respectively. Moreover, it was found that Ni(OH)₂-Ti(IV)/TiO₂ photocatalyst preserved a steady and highly efficient H₂-production performance during repeated tests and also exhibited a high transient photocurrent density. The enhanced hydrogen-production performance of Ni(OH)₂-Ti(IV)/TiO₂ can be attributed to the synergistic effect of Ti(IV) hole cocatalyst and Ni(OH)₂ electron cocatalyst to simultaneously accelerate the interfacial transfer of photogenerated holes and electrons. The present surface modification of dual cocatalysts can be regarded as one of the ideal strategies for the preparation of highly efficient hydrogen-production materials in view of their abundance, low cost and facile method.

Graphical abstract

Introduction

Photocatalytic hydrogen evolution over semiconductor by solar energy offers a promising way for clean and environmentally friendly production of hydrogen [1], [2], [3], [4], [5], [6]. In the past decades, TiO₂ has attracted enormous interest in photocatalytic hydrogen-production due to its good biological and chemical stability, low cost and nontoxicity [7], [8], [9]. Unfortunately, the previous studies found that bare TiO₂ exhibited low active for hydrogen-production from pure water [10], [11]. Thus, numerous methods have been developed to enhance the photocatalytic hydrogen-production performance of TiO₂, such as morphology control [12], [13], composite photocatalysts between TiO₂ and other semiconductors [14], [15], element doping [16], [17] and cocatalyst modification [18], [19]. Among them, highly efficient cocatalyst-modification is considered as one of the most ideal strategies in the field of photocatalytic hydrogen-production via accelerating transfer of photogenerated charges on the surface and promoting the interfacial photocatalytic reaction [20], [21]. Generally, cocatalysts can act as active sites for the interfacial transfer of photogenerated electrons to enhance the photocatalytic activity due to the rapid transfer of electrons, and the well-known electron cocatalysts include noble metals (such as Pt, Au and Ag) [22], [23], [24], transition metal ions (such as Fe(III), Cu(II), and Cr(III)) [25], [26], [27], transition metal oxides (such as NiO, RuO₂, CoO_X and NiO_X) [28], [29], [30], [31], and transition metal sulfides (such as MoS₂ and CoS₂) [32], [33].

Recently, some transition metal hydroxides (such as Ni(OH)₂ and Co(OH)₂) were also found to be new and effective electron cocatalysts [34], [35], [36]. For example, Yu et al. [34] reported that the TiO₂ modified by Ni(OH)₂ clusters exhibited a maximum of 223-fold increase of H₂-production activity compared to pure TiO₂. Owing to the rapid transfer of photogenerated electrons by cocatalysts, the half-reaction rate can be improved. However, the overall-reaction rate of the photocatalytic materials is still limited by loading single cocatalyst. To further improve photocatalytic activity, it is highly expected to develop new hole cocatalysts to rapidly transfer of holes. Interestingly, amorphous Ti(IV) oxide nanoclusters have been demonstrated to act as hole cocatalyst on the surface of TiO₂ to efficiently oxidize organic contaminants [37], [38]. In our recent works, it was also proved that the amorphous Ti(IV) worked as a hole-cocatalyst to enhance the photocatalytic activity of CdS and Ag-based photocatalysts [39], [40]. It is highly desirable to study the possible synergistic effect of amorphous Ti(IV) hole cocatalyst and the well-known electron cocatalyst (such as Ni(OH)₂) to further improve the H₂-evolution activity of TiO₂ photocatalyst.

In this paper, highly efficient TiO₂ photocatalyst with co-modification of Ti(IV) hole cocatalyst and Ni(OH)₂ electron cocatalyst were prepared by a facile two-step method_. The main synthetic strategy for the Ni(OH)₂-Ti(IV)/TiO₂ photocatalyst was the initial formation of amorphous Ti(IV) via hydrolysis method and the following formation of Ni(OH)₂ on the TiO₂ surface via precipitation reaction. The photocatalytic activities of the samples were investigated by photocatalytic H₂-production from aqueous solution containing ethanol and water under UV-light irradiation. It was found that Ni(OH)₂-Ti(IV)/TiO₂ photocatalysts exhibited significantly enhanced performance compared with pure TiO₂ and TiO₂ modified by single cocatalyst. This work may provide some new insights for the development of highly efficient photocatalytic materials for hydrogen production.

Section snippets

Preparation of TiO₂ photocatalyst

TiO₂ was synthesized by a simple hydrothermal method. Briefly, 70 mL of tetrabutyl titanate (Ti(OC₄H₉)₄,TBOT) was dropwise added into 1000 mL of distilled water at 60 °C with magnetic stirring. After 2 h, the obtained white precipitate was centrifuged, rinsed with distilled water for three times, and then transferred to a 500 mL Teflon autoclave. The autoclave was heated at 180 °C for 8 h. When the autoclave was cooled naturally to room temperature, the collected precipitate was washed with distilled

Strategy for the synthesis of Ni(OH)₂-Ti(IV)/TiO₂

Fig. 1 showed the graphical illustration for the synthesis of various TiO₂ samples. Obviously, Ti(IV)/TiO₂, Ni(OH)₂/TiO₂ and Ni(OH)₂-Ti(IV)/TiO₂ were facilely and controllably synthesized by hydrolysis and precipitation reaction at low temperature. For Ti(IV)/TiO₂ sample (Fig. 1b), the surface of TiO₂ was modified through the hydrolysis of Ti(SO₄)₂ solution at 75 °C. Furthermore, Ni(OH)₂-Ti(IV)/TiO₂ sample (Fig. 1d) was prepared by the reaction of Ni(NO₃)₂ and urea solution at 75 °C. In this

Conclusion

In conclusions, highly efficient TiO₂ photocatalysts co-modified by Ti(IV) hole cocatalyst and Ni(OH)₂ electron cocatalyst were prepared by facile two-step process. When the amount of Ti(IV) and Ni(OH)₂ was 0.1 wt% and 1 wt%, respectively, the resultant Ni(OH)₂-Ti(IV)/TiO₂ showed a high H₂-evolution rate (7280.04 μmol h⁻¹ g⁻¹), which was significantly higher than that of TiO₂, Ti(IV)/TiO₂ and Ni(OH)₂/TiO₂. Moreover, it was found that Ni(OH)₂-Ti(IV)/TiO₂ photocatalyst preserved a steady and highly

Acknowledgements

This work was supported by the National Natural Science Foundation of China (21477094, 61274129, and 21277107). This work was also financially supported by program for Fundamental Research Funds for the Central Universities (WUT 2015IB002).

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Citation Excerpt :
In the second approach, TiO2 supported dual reduction–oxidation cocatalysts are successfully proposed and fabricated with enhanced significance the photocatalytic H2 evolution, as shown in Fig. 4b. In typical, many candidates, including TiO2-Co3O4-Pt [55], Cu2O/TiO2/Bi2O3 [56], CoOx/TiO2/Pt [57], RuO2@TiO2@Pt hollow spheres [58], Ni(OH)2-Ti(IV)/TiO2 [59], CuO/Al2O3/TiO2 [60],O-Co3O4/TiO2 [61], Co-Ni/TiO2 [62], MOx@TiO2@Pt [63], CoOx/TiO2/CdS [64], and 1 T-MoS2/P25/NiOx [65], have been reported to demonstrate the advances on improving the efficiency of H2 evolution. In another approach, enormous efforts have been made recently toward exploring TiO2 supported plasmonic metal cocatalyst, as shown in Fig. 4c.
TiO₂-based photocatalysts have been maintained as the most prominent candidate for solar-driven hydrogen (H₂) evolution over the past decades. However, poor separation of generated electron-hole pairs has been considered the bottle-neck issue, restricting the TiO₂ activity. Coupling a TiO₂ photocatalyst to cocatalyst(s) turns out to be the ideal strategy to suppress the charge recombination and offer robust active centres, boosting the H₂ evolution performance. This review aims at providing the frontier investigations of cocatalysts-integrated TiO₂ for photo-induced H₂ evolution. Four types of cutting-edge development of cocatalysts, including metal (noble metal, non-noble metal, bimetallic), metal sulfides and metal phosphides, 2D-MXenes, and dual materials-based cocatalysts, have been successfully highlighted and discussed. The systematically provided cocatalysts, which remarkably promote the charge separation and facilitate the surface reactions, bring out a roadmap to inspire the preparation of superior TiO₂-based materials for H₂ evolution shortly. We expect this review could provide enriched information to tailor the TiO₂ supported active sites of cocatalysts for highly photo-induced H₂ evolution.

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Co-modification of amorphous-Ti(IV) hole cocatalyst and Ni(OH)2 electron cocatalyst for enhanced photocatalytic H2-production performance of TiO2

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Preparation of TiO2 photocatalyst

Strategy for the synthesis of Ni(OH)2-Ti(IV)/TiO2

Conclusion

Acknowledgements

Renew. Sustain. Energy Rev.

J. Photochem. Photobiol. A: Chem.

Appl. Surf. Sci.

Appl. Surf. Sci.

Curr. Appl. Phys.

Int. J. Hydrogen Energy

Powder. Technol.

Catal. Lett.

J. Catal.

J. Catal.

Int. J. Hydrogen Energy

Catal. Today

Phys. E: Low-dimens. Syst. Nanostruct.

Appl. Catal. B: Environ.

J. Colloid Interface Sci.

Electrochim. Acta

Appl. Catal. B: Environ.

Chin. J. Catal.

Appl. Surf. Sci.

Mater. Lett.

Appl. Catal. B: Environ.

J. Mol. Catal. A: Chem.

Carbon

J. Mol. Catal. A: Chem.

Co-modification of amorphous-Ti(IV) hole cocatalyst and Ni(OH)₂ electron cocatalyst for enhanced photocatalytic H₂-production performance of TiO₂

Preparation of TiO₂ photocatalyst

Strategy for the synthesis of Ni(OH)₂-Ti(IV)/TiO₂