Regular Article
Fabrication of layered Fe2P-Cd0.5Zn0.5S nanoparticles with a reverse heterojunction for enhanced photocatalytic hydrogen evolution

https://doi.org/10.1016/j.jcis.2020.09.042Get rights and content

Highlights

  • Layered Fe2P-Cd0.5Zn0.5S nanoparticles with 2D-0D heterojunctions were synthesized.

  • 2D-0D Fe2P-Cd0.5Zn0.5S showed excellent photocatalytic activity for H2 production.

  • The layered Fe2P has higher conductivity and lower overpotential than Fe2P particles.

Abstract

In this work, a novel two-dimensional (2D) layered Fe2P modified Cd0.5Zn0.5S (CZS) nanoparticles composites were successfully developed by an environmentally friendly solvothermal method. The Fe2P-CZS photocatalysts were used for noble-metal-free photocatalytic H2 generation under visible light. The rate of H2 evolution of 13 wt% Fe2P-CZS was 24.84 mmol·g−1·h−1, which was 37.6 times that of CZS (0.66 mmol·g−1·h−1). The formation of the 2D-0D reverse heterojunction in the Fe2P-CZS composite photocatalyst improved the transport and separation of photogenerated electron-hole pairs and optimized the kinetics of hydrogen evolution. Compared with Fe2P particles, the layered Fe2P cocatalysts had higher conductivity and lower hydrogen evolution overpotential.

Introduction

Hydrogen (H2) evolution from photocatalytic water splitting under visible light irradiation has been proven to be a potential approach to address current energy and environmental problems [1]. To date, various photocatalysts have been developed, and CdS has been recognized as one of the most promising photocatalysts because of its outstanding visible-light response and high photocatalytic H2 generation [2]. To alleviate the high recombination rate of electron-hole pairs and the extensive photocorrosion of pure CdS, combining CdS with ZnS to construct CdxZn1-xS solid solutions has been developed since its band position and light absorption capacity could be easily reached by tuning the proportion of Cd and Zn [3]. Cd0.5Zn0.5S (CZS) in particular has attracted special attention for its superior H2 evolution and high stability [4].

Several strategies have been employed to modify CZS for optimizing its photocatalytic performance, including morphology control, doping, construction of heterojunctions, etc. [5], [6], [7]. In particular, coupling with nanococatalysts to construct nanoheterojunctions is considered one of the most effective strategies by virtue of the size and confinement effect of nanomaterials, the fast transfer carriers of heterojunctions and the low H2 evolution potential from the cocatalyst [8], [9]. Phosphides, as one of the non-noble metal cocatalysts, has drawn intense interest in the construction of nanoheterojunctions, benefiting from their excellent metallic conductivity, low overpotentials, high stabilities, abundance in the earth and environmental friendliness [10], [11]. Yu et al. [12] reported that the CZS modified with a Ni2P nanoparticle cocatalyst had great performance for photocatalytic H2 evolution because the close contact interfaces between CZS and Ni2P can act as an electron-bridge to provide a channel for electron transfer. Dai et al. [13] developed a novel type of zero dimensional/one dimensional (0D/1D) CoP/CZS photocatalyst, where the surface of CZS nanorods was uniformly covered by CoP nanoparticles. The H2 evolution rate of the CoP/CZS photocatalyst was 14.68 mmol·h−1·g−1, which was approximately 20 times that of pure CZS [13]. It has been reported that the 2D phosphides have a larger specific surface area, shorter electron/carrier transfer distance, lower overpotential and smaller Tafel slope than 0D nanoparticles, which are favourable for the H2 evolution reaction [14], [15]. However, phosphides have been mainly used to modify the CZS in the form of 0D nanoparticles by constructing nanoheterojunctions [16], [17], [18]. Even 2D phosphides are limited to Ni2P and CoP, and their preparation process involves not only the introduction of toxic reagents but also complicated template construction and post-processing [19], [20], [21], [22]. These all restrict the expanded application of 2D phosphides in the field of photocatalysis.

Here, the Fe2P-CZS composite photocatalysts with 2D-0D reverse heterojunctions were successfully prepared by an environmentally friendly solvothermal method for the first time. The photocatalytic H2 evolution performance of Fe2P-CZS was evaluated under visible light irradiation without using any noble metal cocatalysts. The interfacial charge carrier dynamics of the Fe2P-Cd0.5Zn0.5S 2D-0D heterostructures were investigated in detail by using various characterization techniques. Moreover, the electron transfer path and possible reaction mechanism over the Fe2P-Cd0.5Zn0.5S heterojunction catalysts are discussed.

Section snippets

Materials

All chemical reagents were of analytical purity and used directly without further purification, including FeCl3·6H2O, red phosphorus, Cd(OAc)2·2H2O, ethylenediamine, Zn(OAc)2·2H2O, ethanolamine, thioacetamide (TAA), ethanol and isopropanol (IPA).

Synthesis of Cd0.5Zn0.5S (CZS)

The CZS was prepared according to a method reported in the literature [7] with a slight modification. Typically, 10 mmol Cd(OAc)2·2H2O and 10 mmol Zn(OAc)2·2H2O were dissolved in a solution containing 30 mL of ethylenediamine and 30 mL of deionized

XRD analysis

The XRD patterns of CZS, Fe2P-CZS and Fe2P are shown in Fig. 1. Compared to the standard diffraction peaks of cubic phase ZnS (JCPDS No. 05–0566), those of the CZS sample were shifted towards the low‐angle side, and compared to the standard diffraction peaks of hexagonal phase CdS (JCPDS No. 41-1049), those of the CZS sample were shifted towards the high‐angle side. Briefly, CZS was a solid solution made of ZnS and CdS based on the results and analysis rather than a simple mixture [29]. As

Conclusion

A novel Fe2P with a unique 2D structure was synthesized in situ for use as a non-noble cocatalyst to modify CZS nanoparticles to construct a nanoheterojunction for efficient photocatalytic H2 production via an environmentally friendly and effective solvothermal approach. The results revealed that the layered Fe2P exhibited typical multi-layered characteristics, such as a high electron mobility, high electron-capture capability and strong reductive ability. The CZS nanoparticles, which were

CRediT authorship contribution statement

Zhibin Liang: Conceptualization, Investigation, Methodology, Software, Data curation, Writing - original draft. Xinfa Dong: Supervision, Conceptualization, Methodology, Writing - review & editing.

Declaration of Competing Interest

We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (No. 21978098) and the Natural Science Foundation of Guangdong Province, China (No. 2020A151501488). We are thankful to Dr. Cui Jie from the Analysis and Testing Centre of South China University of Technology for his support in the structural characterization and analysis of the catalyst.

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