The appropriate interfacial contact of heterojunction photocatalysts plays a critical role in transfer/separation of interfacial charge carriers. Design of two-dimensional (2D)/2D surface-to-surface heterojunction is an effective method for improving photocatalytic activity since greater contact area can enhance interfacial charge transfer rate. Herein, ultrathin 2D/2D WO3/g-C3N4 step-like composite heterojunction photocatalysts were fabricated by electrostatic self-assembly of ultrathin tungsten trioxide (WO3) and graphitic carbon nitride (g-C3N4) nanosheets. The ultrathin WO3 and g-C3N4 nanosheets were obtained by electrostatic-assisted ultrasonic exfoliation of bulk WO3 and a two-step thermal-etching of bulk g-C3N4, respectively. The thickness of ultrathin WO3 and g-C3N4 nanosheets are 2.5–3.5 nm, which is equivalent to 5–8 atomic or molecular layer thickness. This ultrathin layered heterojunction structure can enhance surface photocatalytic rate because photogenerated electrons and holes at heterogeneous interface more easily transfer to surface of photocatalysts. Therefore, the obtained ultrathin 2D/2D WO3/g-C3N4 step-scheme (S-scheme) heterojunction photocatalysts exhibited better H2-production activity than pure g-C3N4 and WO3 with the same loading amount of Pt as cocatalyst. The mechanism and driving force of charge transfer and separation in S-scheme heterojunction photocatalysts are investigated and discussed. This investigation will provide new insight about designing and constructing novel S-scheme heterojunction photocatalysts.

Ultrathin 2D/2D WO3/g-C3N4 step-scheme H2-production photocatalyst

In recent years, nanocrystals of metal sulfide materials have attracted scientific research interest for renewable energy applications due to the abundant choice of materials with easily tunable electronic, optical, physical and chemical properties. Metal sulfides are semiconducting compounds where sulfur is an anion associated with a metal cation; and the metal ions may be in mono-, bi- or multi-form. The diverse range of available metal sulfide materials offers a unique platform to construct a large number of potential materials that demonstrate exotic chemical, physical and electronic phenomena and novel functional properties and applications. To fully exploit the potential of these fascinating materials, scalable methods for the preparation of low-cost metal sulfides, heterostructures, and hybrids of high quality must be developed. This comprehensive review indicates approaches for the controlled fabrication of metal sulfides and subsequently delivers an overview of recent progress in tuning the chemical, physical, optical and nano- and micro-structural properties of metal sulfide nanocrystals using a range of material fabrication methods. For hydrogen energy production, three major approaches are discussed in detail: electrocatalytic hydrogen generation, powder photocatalytic hydrogen generation and photoelectrochemical water splitting. A variety of strategies such as structural tuning, composition control, doping, hybrid structures, heterostructures, defect control, temperature effects and porosity effects on metal sulfide nanocrystals are discussed and how they are exploited to enhance performance and develop future energy materials. From this literature survey, energy conversion currently relies on a limited range of metal sulfides and their composites, and several metal sulfides are immature in terms of their dissolution, photocorrosion and long-term durability in electrolytes during water splitting. Future research directions for innovative metal sulfides should be closely allied to energy and environmental issues, along with their advanced characterization, and developing new classes of metal sulfide materials with well-defined fabrication methods.

Recent advances in metal sulfides: from controlled fabrication to electrocatalytic, photocatalytic and photoelectrochemical water splitting and beyond

Improving the photocatalytic property of g-C3N4 by combined strategies has attracted increasing attention recently. In this work, we realized the structure nanosizing of g-C3N4 and its synchronous compounding with TiO2 nanoparticles in one step, using a facile melamine-involved vapor deposition method coupled with a simple and easy setup. Nanostructured g-C3N4/TiO2 heterojunction was well-established and the resultant nanocomposite demonstrated an excellent visible-light photocatalytic H2 evolution performance 10.8 times higher than that of bulk g-C3N4. The structure nanosizing coupled with the heterojunction construction contributed together to the improvement of photoinduced electron-hole separation and final photocatalytic efficiency. The proposed simple method and setup have the potential to be used for preparing other g-C3N4-based nanocomposites with advanced photocatalytic properties.

One-step synthesis of nanostructured g-C3N4/TiO2 composite for highly enhanced visible-light photocatalytic H2 evolution

Cadmium sulfide (CdS)-based photocatalysts have attracted extensive attention owing to their strong visible light absorption, suitable band energy levels, and excellent electronic charge transportation properties. This review focuses on the recent progress related to the design, modification, and construction of CdS-based photocatalysts with excellent photocatalytic H2 evolution performances. First, the basic concepts and mechanisms of photocatalytic H2 evolution are briefly introduced. Thereafter, the fundamental properties, important advancements, and bottlenecks of CdS in photocatalytic H2 generation are presented in detail to provide an overview of the potential of this material. Subsequently, various modification strategies adopted for CdS-based photocatalysts to yield solar H2 are discussed, among which the effective approaches aim at generating more charge carriers, promoting efficient charge separation, boosting interfacial charge transfer, accelerating charge utilization, and suppressing charge-induced self-photocorrosion. The critical factors governing the performance of the photocatalyst and the feasibility of each modification strategy toward shaping future research directions are comprehensively discussed with examples. Finally, the prospects and challenges encountered in developing nanostructured CdS and CdS-based nanocomposites in photocatalytic H2 evolution are presented.

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Nanostructured CdS for efficient photocatalytic H 2 evolution: A review

Multi-component nanomaterials with intricate multishell architectures hold great potential for the development of advanced photocatalytic materials. However, most of the multishell hollow materials reported so far are single-component, and it is rare to come across multi-component ones with hybrid compositions. Herein, we demonstrate a facile in situ supramolecular self-assembly strategy to synthesize hollow, porous and double-shell octahedron of CdS@C3N4 composition. By virtue of compositional and structural advantages, the CdS@C3N4 composites exhibit outstanding activity and stability in photocatalytic H2 generation and selective oxidation of saturated C H bonds.

Porous double-shell CdS@C3N4 octahedron derived by in situ supramolecular self-assembly for enhanced photocatalytic activity

WS2 nanosheets–CdS nanorods with heterojunctions were prepared by an ultrasonic/exfoliation method using dimethylformamide as the dispersing agent. CdS nanorods were coupled with small WS2 nanosheets as a result of exfoliation. An excellent hydrogen production rate of 1222 μmol h–1 (20 mg of catalyst) was achieved over the WS2–CdS composite with a WS2-to-CdS mass ratio of 1.6:1 under visible-light irradiation (λ ≥ 400 nm). The efficient evolution of hydrogen is attributed to promotion of the separation of photogenerated charge carriers due to the presence of heterojunctions created on the surface.

CdS Nanorods Coupled with WS2 Nanosheets for Enhanced Photocatalytic Hydrogen Evolution Activity

Fabrication of two-dimensional porous CdS nanoplates decorated with C3N4 nanosheets for highly efficient photocatalytic hydrogen production from water splitting

Thiamine derivatives that are cheap, readily available, non-toxic and green are used as heterogeneous catalyst for the generation of cyclic carbonates through cycloaddition of CO2 to epoxides without the need of co-catalyst and solvent. The interaction between thiamine hydrochloride (VB1-Cl) and substrates (CO2 and propylene oxide) was proven by ultraviolet-visible spectroscopy and 1H nuclear magnetic resonance analysis, and it is deduced that the synergistic action among multi-functional groups (hydroxyl, halide anion and amine) is a favorable factor for cycloaddition reaction. A series of VB1/GO aerogels were facilely prepared through the addition of aqueous VB1 derivatives to a suspension of GO in ethanol at room temperature. It was found that the aerogel generated through the interaction of VB1-Cl with GO shows catalytic activity and stability higher than those of VB1-Cl. It is because the electrostatic interaction between GO and VB1-Cl enhances the nucleophilicity and leaving ability of anion. The effects of reaction temperature, catalyst loading, CO2 pressure and reaction time on CO2 cycloaddition to propylene oxide were thoroughly studied.

Green and efficient cycloaddition of CO 2 toward epoxides over thiamine derivatives/GO aerogels under mild and solvent-free conditions

The invention discloses a preparation method and application of regular octahedron cadmium sulfide. The preparation method disclosed by the invention has the characteristics of being cheap in raw material, simple in process, free of organic solvent or surfactant, free of toxic or harmful organic intermediate, controllable in morphology of target products, and the like. The invention further relates to application of the regular octahedron cadmium sulfide as a photocatalyst. As the photocatalyst, the regular octahedron cadmium sulfide can be applied to reaction such as visible photocatalytic water splitting hydrogen production, photocatalytic degradation of organic dyes, photocatalytic composition of organic matters, preparation of organic matters such as methanol through photocatalytic carbon dioxide reduction, photocatalytic selective carbonization of hydrocarbon compounds, and the like. The catalyst is very good in stability, and relatively high photocatalytic activity is still maintained after 100 hours of continuous use.

Preparation method and application of regular octahedron cadmium sulfide

A protocol for the copper-catalyzed oxidative self-coupling of α-amino carbonyl compounds has been developed for the synthesis of tetrasubstituted 1,4-enediones (Z-isomers) in moderate to good yields through the cleavage of four sp3C–H bonds and the simultaneous formation of one C=C double bond in the α-amino carbonyl compound. The strategy has the advantages of using readily available starting ­materials and of high stereoselectivity.

Zi-Qi Yi

Papers

CdS Nanorods Coupled with WS2 Nanosheets for Enhanced Photocatalytic Hydrogen Evolution Activity

Fabrication of two-dimensional porous CdS nanoplates decorated with C3N4 nanosheets for highly efficient photocatalytic hydrogen production from water splitting

Green and efficient cycloaddition of CO 2 toward epoxides over thiamine derivatives/GO aerogels under mild and solvent-free conditions

Preparation method and application of regular octahedron cadmium sulfide

Copper-Catalyzed Oxidative Self-Coupling of α-Amino Carbonyl Compounds for the Synthesis of Tetrasubstituted 1,4-Enediones