Herein, two-dimensional (2D) TiO2 mesoporous nanosheets with three to four C3N4 layers grown in situ are employed to design a core–shell 2D/2D van der Waals heterojunction (TiO2/C3N4). Edge-terminated zero-dimensional (0D) Ti3C2 MXene quantum dots (TCQD) are subsequently integrated in the C3N4 surface via electrostatic interactions. The constructed 2D/2D/0D TiO2/C3N4/Ti3C2 composite heterojunction photocatalyst exhibits enhanced CO2 reduction activity compared to TiO2, C3N4, TiO2/C3N4, C3N4/Ti3C2 for CO and CH4 production. A step-scheme (S-scheme) charge transfer mechanism operates for the prepared samples during CO2 reduction, as authenticated by in situ X-ray photoelectron spectroscopy and electron paramagnetic resonance analysis. This study provides a paradigm of a rational structural design for regulating the number and type of heterointerfaces and further insights into the mechanism of multijunction photocatalysts.

2D/2D/0D TiO2/C3N4/Ti3C2 MXene composite S-scheme photocatalyst with enhanced CO2 reduction activity

Photocatalysis is a green technology to use ubiquitous and intermittent sunlight. The emerging S-scheme heterojunction has demonstrated its superiority in photocatalysis. This article covers the state-of-the-art progress and provides new insights into its general designing criteria. It starts with the challenges confronted by single photocatalyst from the perspective of energy dissipation by borrowing the common behaviors in the dye molecule. Subsequently, other problems faced by single photocatalyst are summarized. Then a viable solution for these problems is the construction of heterojunctions. To overcome the problems and mistakes of type-II and Z-scheme heterojunctions, S-scheme heterojunction is proposed and the underlying reaction mechanism is summarized. Afterward, the design principles for S-scheme heterojunction are proposed and four types of S-scheme heterojunctions are suggested. Following this, direct characterization techniques for testifying the charge transfer in S-scheme heterojunction are presented. Finally, different photocatalytic applications of S-scheme heterojunctions are summarized. Specifically, this work endeavors to clarify the critical understanding on curved Fermi level in S-scheme heterojunction interface, which can help strengthen and advance the fundamental theories of photocatalysis. Moreover, the current challenges and prospects of the S-scheme heterojunction photocatalyst are critically discussed. 

Emerging S‐Scheme Photocatalyst

Step-scheme (S-scheme) photocatalytic system has been considered as an effective method for solar energy conversion by utilizing broadband solar energy, realizing easy separation of photoexcited carriers and strong redox ability. Herein, the novel ternary Ni2P cocatalysted two-dimensional (2D)/2D SnNb2O6/CdS-diethylenetriamine (SNO/CdS-D) system was designed and fabricated. The S-scheme SNO/CdS-D heterostructure gives photocatalytic hydrogen production of 7808 μmol g−1 h−1, which is about 130.13 and 2.35 times stronger than that of SNO and CdS-D. Further, noble-metal-free Ni2P cocatalyst is decorated into SNO/CdS-D heterostructure, the photocatalytic hydrogen evolution performance could be enhanced to 11,992 μmol g−1 h−1. Additionally, XPS analysis and DFT calculation revealed the carriers moves from CdS-D to SNO and then to Ni2P in the Ni2P-SNO/CdS-D nanocomposite. This work will give a reliable and clear insight into the interface and surface design of the 2D catalysts and offer a broadband photocatalytic hydrogen evolution process without noble metal cocatalysts.

Noble-metal-free Ni2P modified step-scheme SnNb2O6/CdS-diethylenetriamine for photocatalytic hydrogen production under broadband light irradiation

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.

/pdf/nanostructured-cds-for-efficient-photocatalytic-h-2-4jzzdho2wh.pdf

Nanostructured CdS for efficient photocatalytic H 2 evolution: A review

A review on 2D MoS2 cocatalysts in photocatalytic H2 production

Constructing low-cost Ni3C/twin-crystal Zn0.5Cd0.5S heterojunction/homojunction nanohybrids for efficient photocatalytic H2 evolution

In Situ Fabrication of Robust Cocatalyst-Free CdS/g-C3N4 2D–2D Step-Scheme Heterojunctions for Highly Active H2 Evolution

Developing an inexpensive and high-efficiency hydrogen-production cocatalyst to replace the noble metal Pt remains a big challenge in the fields of sustainable photocatalytic hydrogen evolution. He...

Carbon Nanotube-Supported Cu3P as High-Efficiency and Low-Cost Cocatalysts for Exceptional Semiconductor-Free Photocatalytic H2 Evolution

Different mechanisms of selective electrochemical decarboxylation of acetic acid and butyric acid in aqueous solution and at room temperature.

Yingna Ding

Papers

Nanostructured CdS for efficient photocatalytic H 2 evolution: A review

Constructing low-cost Ni3C/twin-crystal Zn0.5Cd0.5S heterojunction/homojunction nanohybrids for efficient photocatalytic H2 evolution

In Situ Fabrication of Robust Cocatalyst-Free CdS/g-C3N4 2D–2D Step-Scheme Heterojunctions for Highly Active H2 Evolution

Carbon Nanotube-Supported Cu3P as High-Efficiency and Low-Cost Cocatalysts for Exceptional Semiconductor-Free Photocatalytic H2 Evolution

Enhancing the selectivity of hydrocarbons during the Kolbe electrolysis of biomass-derived short-chain carboxylic acids by anionic surfactants