Photocatalytic H2 evolution on CdS modified with partially crystallized MoS2 under visible light irradiation

One-pot synthesis of transition-metal-sulfides decorated CdS by low-temperature KSCN flux: An effective route to strengthen the interface for enhanced photocatalytic H2 evolution

The performance of decorated photocatalysts is highly dependent on the interfacial contact between the cocatalyst and the substrate photocatalyst, which is essentially determined by their fabrication routes. Herein, a simple one-pot preparation method based on low-temperature KSCN flux was developed for the synthesis of sulfide photocatalysts with MS/CdS (MS = CoS2, NiS2, Cu1.8S, SnS2, MoS2, and WS2) as prototypes. The results indicate that a sulfidation of Cd2+ and the cocatalyst precursors can be achieved successively in the reaction system, which facilitates the formation of a welded interface as the cocatalysts can grow epitaxially on the formed CdS surface. The KSCN flux serves not only as a reaction medium but also as S2- precursor. Most of the MS (except for WS2) could be successfully fabricated and deposited in situ on CdS. However, only the transition-metal-sulfides (TMSs, MoS2, CoS2, and NiS2) decorated samples showed enhanced photocatalytic H2 evolution reaction (HER) performance and the activities decreased in the order of MoS2 > CoS2 > NiS2. The sample loaded with 1 %MoS2 demonstrated the highest activity, which was 25 times higher than that of the pristine CdS. The superior HER performance could be ascribed to the loading of the active MoS2 sites for HER and the intimate tandem type I (between CdS and 2H-MoS2) and Schottky (between 2H- and 1T-MoS2) junctions for separation of photoinduced charge carriers. Compared to the conventional preparation methods, the developed one-pot flux route demonstrates remarkable advantages in fabricating highly efficient MoS2/CdS photocatalyst besides its convenience, versatility, and scalability. We believe that, in addition to CdS, the developed route can also be applied to synthesize other sulfide-based photocatalysts.

Fabrication of an S-Scheme Heterojunction Photocatalyst MoS2/PANI with Greatly Enhanced Photocatalytic Performance

As a promising catalyst, MoS2 has been widely studied owing to its high chemical reactivity, excellent electrical carrier mobility, good optical properties, and narrow band gap. However, the high recombination rate of photoinduced charge carriers limits its practical application in photocatalysis. In this study, MoS2 was coupled with PANI to fabricate an S-scheme heterojunction MoS2/PANI. The synthesized products were characterized systematically, and their photocatalytic properties were evaluated by photocatalytic degradation of norfloxacin (NOR) and rhodamine B (RhB). The obtained results indicated that the fabricated MoS2/PANI inorganic-organic heterojunction displayed tremendously enhanced photocatalytic activity. The degradation efficiencies for 60 mg L-1 of NOR and RhB are 86 and 100% under the simulated sunlight irradiation for 1 h with 10 mg of catalyst, which are 13 and 47 times higher than those of pure MoS2, respectively. Interestingly, it is superior to the previously reported related materials. The remarkably enhanced photocatalytic activity of MoS2 is assigned to the high charge conductivity feature of PANI and the formed S-scheme heterojunction that result in a steric separation of holes and electrons and conserve the initial powerful redox ability of the parent catalysts. This study provides a facile method to greatly improve the photocatalytic activity of MoS2 and facilitates its application for highly efficient removal of organic pollutants, such as antibiotic drugs and organic dyes, utilizing solar energy.

Ultrafast charge separation in a WC@C/CdS heterojunction enables efficient visible-light-driven hydrogen generation

The rapid recombination of photogenerated carriers and strong photocorrosion have considerably limited the practical application of CdS in the field of photocatalysis. Loading a cocatalyst has been widely utilized to largely enhance photocatalytic activity. In the present work, a WC@C cocatalyst was prepared by a novel molten salt method and explored as an efficient noble-metal-free cocatalyst to significantly enhance the photocatalytic hydrogen evolution rate of CdS nanorods. The WC@C/CdS composite photocatalyst with a 7 wt% content of WC@C showed the highest photocatalytic hydrogen evolution rate of 8.84 mmol g^-1 h^-1, which was about 21 and 31 times higher than those of CdS and 7 wt% Pt/CdS under visible light irradiation. A high apparent quantum efficiency (AQY) of 55.28% could be achieved under 420 nm monochromatic light. Furthermore, the photocatalytic activity of the 7 wt% WC@C/CdS photocatalyst exhibited good stability for 12 consecutive cycles of the photocatalytic experiment with a total reaction time of 42 h. The excellent photocatalytic performance of the photocatalyst was attributed to the formation of a Schottky junction and the loading cocatalyst, which not only accelerated the separation of the photogenerated carrier but also provided a reactive site for hydrogen evolution. This work revealed that WC@C could act as an excellent cocatalyst for enhancing the photocatalytic activity of CdS nanorods.

Research progress in metal sulfides for photocatalysis: From activity to stability

Metal sulfides are a type of reduction semiconductor photocatalysts with narrow bandgap and negative conduction band potential, which make them have unique photocatalytic performance in solar-to-fuel conversion and environmental purification. However, metal sulfides also suffer from low quantum efficiency and photocorrosion. In this review, the strategies to improve the photocatalytic activity of metal sulfide photocatalysts by stimulating the charge separation and improving light-harvesting ability are introduced, including morphology control, semiconductor coupling and surface modification. In addition, the recent research progress aiming at improving their photostability is also illustrated, such as, construction of hole transfer heterojunctions and deposition of hole transfer cocatalysts. Based on the electronic band structures, the applications of metal sulfides in photocatalysis, namely, hydrogen production, degradation of organic pollutants and reduction of CO₂, are summarized. Finally, the perspectives of the promising future of metal-sulfide based photocatalysts and the challenges remaining to overcome are also presented.

MoS2-2xSe2x Nanosheets Grown on Hollow Carbon Spheres for Enhanced Electrochemical Activity

Electrochemical catalysts with high conductivity and low reaction potential are respected. In this paper, hollow carbon spheres (HCSs) were homogeneously coated with Se-doped MoS₂ (MoS_2-2xSe_2x) nanosheets by hydrothermal synthesis. The HCSs reduced the agglomeration of MoS_2-2xSe_2x nanosheets and improved their conductivity. Compared with the MoS₂-modified samples, Se doping increased the interlayer spacing which provided more active catalytic sites and improved the charge transfer. Thus, MoS_2-2xSe_2x-decorated samples revealed enhanced electrocatalytic activity. The composition of MoS_2-2xSe_2x nanosheets was adjusted by changing the ratios of sulfur and selenium precursors. In the case of a Se/S molar ratio of 0.1, the composite of HCS decorated with MoS_2-2xSe_2x nanosheets (C@MoS_2-2xSe_2x) revealed the lowest overpotential and the smallest Tafel slope.

Rare earth material CeO2 modified CoS2 nanospheres for efficient photocatalytic hydrogen evolution

The construction of a heterojunction promoted the separation of electrons and holes, so that CeO2/CoS2 exhibited an excellent hydrogen evolution performance.