Research paper
Construction of NH2-MIL-125(Ti)/CdS Z-scheme heterojunction for efficient photocatalytic H2 evolution

https://doi.org/10.1016/j.jhazmat.2020.124128Get rights and content

Highlights

  • CdS/NH2-MIL-125 heterojunction was fabricated by an in-situ growth process.

  • This established structure shows excellent Z-scheme charge-carrier separation.

  • The photocatalytic performance with hydrogen evolution was 3.5 times that of CdS.

Abstract

Designing efficient semiconductor-based photocatalysts for hydrogen production is a challenging but promising prospect in energy conversion. Herein, a novel Z-scheme CdS/NH2-MIL-125(Ti) heterojunction is successfully fabricated through a facile solvethermal method. The detailed characterizations reveal that CdS nanoparticles are in-suit archored on NH2-MIL-125(Ti) nanoplates. Benefited from the intrinsic band alignment and intimate contact of two species, this established structure gives a positive effect regarding charge separation. In consequence, the optimal CdS/NH2-MIL-125(Ti) nanocomposites exhibit excellent photocatalytic performance with hydrogen evolution rate of 6.62 mmol·h−1·g−1 under visible light illumination, which was 3.5 times higher than that of the pristine CdS. We believe that this work will provide a new avenue to develop high-efficiency heterojunction catalyst for solar-driven energy conversions and other application.

Introduction

In the past decades, massive burning of fossil fuels has caused serious energy shortage. It is indispensable to find a clean and sustain way to alleviate energy crisis. Recently, photocatalytic hydrogen production from water splitting has engendered tremendous attention because it holds cheap and pollution-free features (Wang et al., 2015a, Wang et al., 2015b, Wang et al., 2015c, Wang et al., 2019b, Wang et al., 2015, Wang et al., 2009, Wang et al., 2019a). To date, many highly efficient photocatalysts have been developed for hydrogen production, such as TiO2, ZnIn2S4 and g-C3N4 (Li et al., 2017, Li et al., 2017, Wang and Ding, 2020, Xie et al., 2018, Yang and Liu, 2013). Although some significant process has been made on the adsorption range of photocatalysts, which extended to visible light from UV light (Kiwi and Grätzel, 1979), their photocatalytic activities are still poor due to low quantum efficiency and rapid charge recombination (Chen et al., 2020a, Chen et al., 2020b, Li and Yu, 2018). Therefore, it is necessary to develop an ideal photocatalyst, which could promote the solar energy utilization and achieve efficient charge spatial separation. In addition, these photoinduced carriers are supposed to effectively migrate to the surface of semiconductor and accumulate enough potential to drive water splitting in thermodynamics and kinetics.

As a typical member of many photocatalysts, cadmium sulfide (CdS) has been regarded as a promising photocatalytic candidate for hydrogen production due to its adsorption region of visible light and suitable conduction band potential (Wolff et al., 2018, Liu et al., 2018a, Liu et al., 2018b, Luo and Hu, 2012). However, severe photocorrosion and fast charge recombination hinder its further development (Marschall, 2014, Chen et al., 2015). Although many strategies, such as precious mental doping and morphology regulation, could obviously enhance photocatalytic activity (Kai et al., 2018, Li et al., 2020, Liu et al., 2020, Zhao et al., 2016), the expensive cost and complicated preparation process restrict its industrial application. Therefore, it is indispensable to explore a new approach to further improve photocatalytic performance.

Metal-organic-frameworks (MOFs), which are consisted of metal ions and organic ligands, have attracted extensive attention owing to their high surface areas, abundant porous structures and flexible component and ratio (Kaneti et al., 2017, Chen et al., 2020a, Chen et al., 2020b, Yang et al., 2011). These distinctive structural features endow MOFs with potential applications in gas adsorption, biology sensors, drug delivery and catalysis (Witherspoon et al., 2018, Zhao et al., 2013, Stassen et al., 2017, Cai et al., 2015, Mahmood et al., 2016, Bi et al., 2018, Zeng et al., 2016). Many researchers reveal that some MOFs possess semiconductor-like properties and could be served as photocatalysts. Among the different types of MOFs, NH2-MIL-125(Ti) is a typical Ti-based MOF, which plays an important role in photocatalytic degradation of organic pollutants and hydrogen evolution due to its suitable band gap (Wang et al., 2019a, Wang et al., 2019b, Hu et al., 2019, Xu et al., 2017, Guo et al., 2019). However, like other semiconductor photocatalysts, it also suffers rapid charge recombination and insufficient structure stability. Therefore, tremendous methods have been attempted to improve photocatalytic activity such as substitution of mental cations or organic ligands and deposition of noble mental (Gómez-Avilés et al., 2019, Yan et al., 2018, Han et al., 2014). Although these efforts have been made to optimize MOF-based photocatalysts, their application is still in the early stage. As is known to us, construction Z-scheme heterojunction is considered as one of the most efficient and facile strategies to improve photocatalytic performance. It not only facilitates effective separation of charge carriers, but also preserves more negative potential and more positive potential related to stronger reduction ability and stronger oxidation ability for some significant applications such as water splitting and CO2 reduction (Jiang and Sun, 2018, Li et al., 2017, Li et al., 2017, Peng et al., 2020).

Herein, a unique CdS/NH2-MIL-125(Ti) Z-scheme heterojunction was fabricated for high-efficiency photocatalytic hydrogen production by loading CdS nanoparticle on NH2-MIL-125(Ti) nanoplates. Benefited from intimate contact interface and well-matched band structure, the novel nanocomposite photocatalysts obviously contributed to the spatial separation of charge carriers. As a consequence, the illustrational CdS/NH2-MIL-125(Ti) nanocomposites exhibited outstanding photocatalytic performance with hydrogen production rate of 6.62 mmol·h−1·g−1 under visible light illumination. This feasibility and flexibility strategy of fabricating intimate heterojunction structure by combining MOFs with nanoparticles semiconductors will provide an alternative venue to design high efficiency photocatalysts for energy conversion and other applications.

Section snippets

Materials

All the chemicals were of analytical grade, purchased from Sino pharm Chemical Reagent Co., Ltd. (Shanghai, China) and used directly without further purification. Thiourea (NH2CSNH2), cadmium nitrate (CdNO3), methanol (MeOH), N,N-dimethylformamide (DMF) were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Tetrabutyl titanate [Ti(OC4H9)4] and 2-amino-4-benzenedicarboxylic (NH2-BDC) was provided by Alfa Aesar, China Co.

Synthesis of NH2-MIL-125(Ti) nanoplates and CdS/NH2-MIL-125(Ti) nanocomposites

Synthesis of NH2-MIL-125(Ti) nanoplates: NH2

Results and discussion

The crystallinity phase of the obtained samples was measured by X-ray diffraction (XRD). As shown in Fig. 1a, the pristine CdS appeared some strong diffraction peaks at 2θ= 24.81°, 26.51°, 28.18°,43.68°, 47.84°, 51.82°, which could be indexed to the (100), (002), (101), (110), (103), (112) planes of hexagonal CdS (JCPDS No.41–1049), respectively (Xu et al., 2018). The XRD pattern of Ti-MOF was consistent with previous reported literatures (Liu et al., 2018a, Liu et al., 2018b, Sun et al., 2015

Conclusion

In conclusion, a novel Z-scheme heterojunction was successfully fabricated by anchoring CdS nanoparticles on NH2-MIL-125(Ti) nanoplates via a facile solvothermal method. Detailed characterizations revealed that well-matched band structure and intimate interface interaction of two species promoted effective separation and transfer of charge carriers. The optimal CM-10 sample exhibited outstanding photocatalytic hydrogen production performance with an excellent hydrogen evolution rate of

CRediT authorship contribution statement

Xiaohui Zhang: Catalyst synthesis, Writing - original draft. Zhiwei Chen: Catalyst synthesis, Writing - original draft. Ying Luo: Catalytic performance test. Xiaole Han: Writing - reviewing & editing. Qingqing Jiang: Writing - reviewing & editing. Tengfei Zhou: Writing - reviewing & editing. Haijian Yang: Writing - reviewing & editing Juncheng Hu: Supervision.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (21673300), China and Fundamental Research Funds for the Central Universities, South Central University for Nationalities, China (CZT19001).

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