Aiping Wu,Chungui Tian,Yanqing Jiao,Qing Yan,Guoyu Yang,Honggang Fu
The visible-light driven, Pt-free photocatalytic H 2 evolution (PHE) is promising for clean and sustainable H 2 production. The construction of the heterojunction structure with intimate contact and good light adsorption ability is important for realizing the high effective PHE. Here, the core-shell structured MoS 2 /CdS hybrids were constructed through “sequential two-step hydrothermal growth” route for Pt-free PHE. In the synthesis, the hierarchical flower-like MoS 2 was firstly obtained through the reaction of ammonium molybdate and excessive thiourea. Subsequently, without need of centrifugation, the cadmium acetate (Cd source) was added into the cooled MoS 2 solution directly followed by a secondary hydrothermal reaction. In the process, the Cd 2+ could react with partially S 2− in MoS 2 (substituted reaction) and with the excessive S 2− ions in solution to generate CdS, resulting in the formation of CdS shell contacted with MoS 2 core. The micro-structure of the composites (such as the thickness and morphology of CdS shell) could be tuned by changing the amount of Mo source and Cd source. In the composites, the CdS on the outside is convenient to absorb the solar light. The intimate contact of CdS and MoS 2 is beneficial to charge transfer. As a result, the MoS 2 /CdS catalyst showed high catalytic activity for PHE under visible light irradiation (λ > 420 nm). The H 2 evolution rate could reach to 775 μmol h −1 (20 mg catalyst), which is much higher than pure CdS (12 μmol h −1 ) and Pt-CdS (64 μmol h −1 ). The good activity should be related with CdS outside shell beneficial for light adsorption and intimate contact of CdS and MoS 2 for easy charge transfer. A series of experiments demonstrate that the formation of the heterojunction can effectively enhance the charge transfer ability and retard the recombination of electron-hole pairs, thus improving PHE activity and alleviating the photocorrosion of CdS component.
In this work, using a synergistic modification strategy of facet engineering and constructing heterojunctions, MoS2/CdS Z-scheme heterojunction catalysts were successfully prepared. The results indicated that CdS-(100) exhibited enhanced photocatalytic benzylamine coupling activity relative to CdS-(002). Compared with pristine CdS, the photocatalytic activity of MoS2/CdS is significantly enhanced. This enhancement can be attributed to the presence of a Z-scheme heterojunction, which improves the separation efficiency of photogenerated carriers. Moreover, even after 5 cycles, the photocatalyst demonstrates a high photocatalytic activity, which proves that the existence of the Z-scheme heterojunction can effectively inhibit the photocorrosion of CdS. In addition, the reaction can be carried out in different reaction pathways under anaerobic and aerobic conditions. This work proposes a systematic approach for constructing MoS2/CdS Z-scheme heterojunction photocatalysts and the green synthesis of imines.
Low-temperature KSCN flux has been used for one-pot fabrication of decorated sulfide-based photocatalysts. However, the reaction system is actually short of S precursor, as it is determined by the decomposition of relatively stable KSCN, which may not be conducive to the production of high-performance catalysts. To this end, a modified KSCN flux route with a dosage of external S source was developed and used for the one-pot preparation of sulfide photocatalyst with 1% MoS 2 /CdS as the prototype. The results indicated that, compared with the sample (MC) prepared in conventional KSCN flux, a highly efficient sample enriched with seldom reported Cd vacancy (V Cd , MC-S) could be readily fabricated under the S 2− -rich environment. Furthermore, both the size of CdS and MoS 2 could be substantially reduced from μm to nm scale as more nuclei could be introduced in the flux, which leads to a few-layer MoS 2 that can be uniformly and tightly anchored on CdS with the average size of only ∼33 nm. Consequently, the resulting MC-S demonstrated an exceptional H 2 evolution activity of 15.01 mmol h −1 g −1 — a significant 6.5-fold improvement over its counterpart (MC) prepared through traditional KSCN flux. The high activity can be mainly ascribed to the introduction of V Cd and the close interface between small CdS and few-layer MoS 2 , which both benefit electron-hole separation. The preparation mechanism of the samples was tentatively compared and discussed from the difference in the nucleation and the development of crystals. We believe that this improved preparation method will also benefit the synthesis of other high-performance sulfide-based photocatalysts.
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