Perspective and status of polymeric graphitic carbon nitride based Z-scheme photocatalytic systems for sustainable photocatalytic water purification

Hydrogen (H2) production via solar water splitting is one of the most ideal strategies for providing sustainable fuel because this requires only water and sunlight. In achieving high-yield production of hydrogen as a recyclable energy carrier, the nanoscale design of semiconductor (SC) materials plays a pivotal role in both photoelectrochemical (PEC) and photocatalytic (PC) water splitting reactions. In this context, the advent of two-dimensional (2D) materials with remarkable electronic and optical characteristics has attracted great attention for their application to PEC/PC systems. The elaborate design of combined 2D layered materials interfaced with other SCs can markedly enhance the PEC/PC efficiencies via bandgap alteration and heterojunction formation. Three classes of 2D materials including graphene, transition metal dichalcogenides (TMDs), and graphitic carbon nitride (g-C3N4), and their main roles in the photoelectrocatalytic production of H2, are discussed in detail herein. We highlight the various roles of these 2D materials, such as enhanced light harvesting, suitable band edge alignment, facilitated charge separation, and stability during the water splitting reaction, in various SC/2D photoelectrode and photocatalytic systems. The roles of emerging 2D nanomaterials, such as 2D metal oxyhalides, 2D metal oxides, and layered double hydroxides, in PEC H2 production are also discussed.

Two-dimensional materials in semiconductor photoelectrocatalytic systems for water splitting

Both pristine metal-organic frameworks (MOFs) and graphitic carbon nitride (g-C3N4) displayed outstanding photocatalytic performances toward H2 production, CO2 reduction, Cr(VI) reduction and organic pollutants degradation. To further enhance their photocatalytic performances under visible light or sunlight irradiation, MOFs and g-C3N4 were combined to construct g-C3N4/MOF heterojunctions with the purpose of overcoming their individual disadvantages like fast recombination of pohotogenerated electron-hole pairs. The fabrication methods, characterizations, photocatalytic performances and the corresponding mechanism of some typical g-C3N4/MOF composites were highlighted. Also, the prospective and challenges of this research field were declared.

Powerful combination of MOFs and C3N4 for enhanced photocatalytic performance

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

As the world decides on the next giant step for the renewable energy revolution, scientists have begun to reinforce their headlong dives into the exploitation of solar energy. Hitherto, numerous attempts are made to imitate the natural photosynthesis of plants by converting solar energy into chemical fuels which resembles the "Z-scheme" process. A recreation of this system is witnessed in artificial Z-scheme photocatalytic water splitting to generate hydrogen (H2). This work outlines the recent significant implication of the Z-scheme system in photocatalytic water splitting, particularly in the role of electron mediator and the key factors that improve the photocatalytic performance. The Review begins with the fundamental rationales in Z-scheme water splitting, followed by a survey on the development roadmap of three different generations of Z-scheme system: 1) PS-A/D-PS (first generation), 2) PS-C-PS (second generation), and 3) PS-PS (third generation). Focus is also placed on the scaling up of the "leaf-to-tree" challenge of Z-scheme water splitting system, which is also known as Z-scheme photocatalyst sheet. A detailed investigation of the Z-scheme system for achieving H2 evolution from past to present accompanied with in-depth discussion on the key challenges in the area of Z-scheme photocatalytic water splitting are provided.

https://onlinelibrary.wiley.com/doi/epdf/10.1002/advs.201903171

Z-Scheme Photocatalytic Systems for Solar Water Splitting.

Highly efficient H2 production over NiCo2O4 decorated g-C3N4 by photocatalytic water reduction

2D mesoporous ultrathin Cd0.5Zn0.5S nanosheet: Fabrication mechanism and application potential for photocatalytic H2 evolution

Novel reduced graphene oxide-supported Cd0.5Zn0.5S/g-C3N4 Z-scheme heterojunction photocatalyst for enhanced hydrogen evolution

Enhanced photocatalytic H2 evolution on ultrathin Cd0.5Zn0.5S nanosheets without a hole scavenger: Combined analysis of surface reaction kinetics and energy-level alignment

Wenhua Xue

Papers

Highly efficient H2 production over NiCo2O4 decorated g-C3N4 by photocatalytic water reduction

2D mesoporous ultrathin Cd0.5Zn0.5S nanosheet: Fabrication mechanism and application potential for photocatalytic H2 evolution

Novel reduced graphene oxide-supported Cd0.5Zn0.5S/g-C3N4 Z-scheme heterojunction photocatalyst for enhanced hydrogen evolution

Enhanced photocatalytic H2 evolution on ultrathin Cd0.5Zn0.5S nanosheets without a hole scavenger: Combined analysis of surface reaction kinetics and energy-level alignment

Synthesis of In2Se3 homojunction photocatalyst with α and γ phases for efficient photocatalytic performance