A facile in situ growth of CdS quantum dots on covalent triazine-based frameworks for photocatalytic H2 production
Introduction
The ever-growing global energy crisis and environmental contamination urges us to seek sustainable technologies to develop green and renewable energy [[1], [2], [3]]. Photocatalytic H2 production from water has been proved to be a useful strategy to utilize solar energy, and effectively provide an abundant, green fuel source [[4], [5], [6], [7], [8]]. However, the low catalytic efficiency of photocatalysts still limits photocatalytic H2 evolution performance. Two strategies have been devoted to solving these problems: one way is to continue to explore novel visible-light-triggered photocatalytic materials, and the other way is to modify known photocatalysts such as by loading with different cocatalysts [[9], [10], [11], [12]], coupling with other semiconductors [[13], [14], [15], [16], [17]], and morphology modification [[18], [19], [20], [21], [22], [23]].
CdS QDs are an excellent visible-light-driven photocatalyst due to their unique small size (<10 nm), suitable band energy structure, and shorter charge transportation length [[24], [25], [26], [27]]. Unfortunately, CdS QDs are easily prone to aggregate to form larger particles, resulting in a higher recombination rate of photoinduced electron-hole pairs, which greatly limits the photocatalytic property of CdS QDs [28]. Recently, some approaches have been proposed to conquer these drawbacks such as combining CdS QDs with other semiconductors (TiO2, CeO2, ZnO etc.) [[29], [30], [31], [32], [33], [34]]. However, the tedious synthesis process and the undesirable anchoring ability of supported materials still leads to aggregation of CdS QDs. Seeking a facile synthesis process and efficient supporting materials for CdS QD-based photocatalysts is especially appealing and challenging.
Covalent triazine-based frameworks (CTFs) are a novel type of conjugated polymer semiconductor that has been widely used in the application of photocatalysis [[35], [36], [37], [38]]. Previous research has indicated that the π-conjugated cyclic aromatic rings and π-stacked structure of CTFs is beneficial for visible light absorption and charge transfer [39,40]. We have developed a kind of CTF material (CTF-1) as an efficient photocatalyst for the evolution of H2, and our previous reports have also demonstrated the coordination capability of triazine to nanoparticles or metal ions, with the confinement effect of CTF-1 found to be very favorable for the immobilization of nanoparticles [41,42]. Moreover, the band position of CTF-1 is well-matched with CdS [42,43]; thus, CTF-1 is supposed to be a promising supporting material for the stabilization of CdS QDs for development of an efficient photocatalytic system.
Herein, we report in situ growth of CdS QDs with high dispersion and stability on CTF-1 by a facile photoreduction strategy, as shown in Scheme 1. Compared to that of pure CTF-1 and bulk CdS, the photocatalytic H2 evolution performance of CdS QD-loaded CTF-1 is effectively enhanced under visible light irradiation, which is mainly ascribed to the efficient separation of photogenerated carriers resulting from synergistic QD-on-sheet interactions between CdS QDs and CTF-1.
Section snippets
Synthesis of CTF-1
CTF-1 was prepared via a previous method [42]. Trifluoromethane acid (10 mL) was placed into 1,4-dicyanobenzene (1.28 mg) in a boiling flask. The mixture was then stirred at 30 °C to form a solid and subsequently reserved under a static state for 3 d. The collected product was washed by dichloromethane and NH3•H2O several times. Then, the appropriate amount of NH3•H2O was added at room temperature and left overnight. After being centrifuged and washed with excess deionized water and methanol,
Characterization
The growth of CdS QDs on CTF-1 was prepared by a facile in situ photoreduction method. The layered stacking structure of CTF-1 in the CdS/CTF-1 composite could be observed from SEM (Fig. 1a and b) and TEM images (Fig. 1c and d). The formation of CdS QDs on CTF-1 was confirmed by TEM images. CdS QDs (∼5 nm) with high dispersion were grown onto CTF-1 (Fig. 1d). The HRTEM images showed clear lattice fringes on CTF-1 with a d spacing of ca. 0.316 nm and 0.336 nm corresponding to the (101) and (002)
Conclusion
In summary, a CdS/CTF-1 composite with visible light photocatalytic H2 evolution activity was synthesized via a facile in situ photoreduction method. An enhanced photocatalytic activity was observed that is mainly attributed to a synergic effect between CTF-1 and CdS resulting from their well-matched band positions, which can effectively enhance the generation, separation, and transport of photoinduced charges. This facile one-pot strategy based on CTFs support will enable the development of
CRediT authorship contribution statement
Huimin Huang: Conceptualization, Methodology, Writing - original draft. Bin Xu: Methodology, Data curation. Zunkun Tan: Data curation. Qianqian Jiang: Investigation. Shengqiong Fang: Conceptualization, Writing - original draft. Liuyi Li: Resources, Supervision. Jinhong Bi: Project administration, Supervision, Funding acquisition, Writing - review & editing. Ling Wu: Resources, Supervision.
Declaration of competing interest
There are no conflicts to declare.
Acknowledgments
This work is supported by the National Natural Science Foundation of China (51672047, 51672046, 21403238), the Program for New Century Excellent Talents in the University of Fujian Province and the Natural Science Foundation of Fujian Province (2019J01648, 2019J01226).
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2022, Journal of Physics and Chemistry of SolidsCitation Excerpt :It is also worth mentioning that the quantum confinement effect can change the Eg of QDs in a manner that may be advantageous for PHE with the CB and the VB shifting towards more optimal potentials [46–48]. Furthermore, QDs have a large specific surface area (SSA) and high dispersion capacity, resulting in a higher number of active sites on the surface [49–52]. Based on these observations, we hypothesize that the modification of 1D CSNRs with 0D CSQDs could lead to higher PHE under visible light.