Design of C3 N4 -Based Hybrid Heterojunctions for Enhanced Photocatalytic Hydrogen Production Activity

Atomic-level investigation on significance of photoreduced Pt nanoparticles over g-C3 N4 /bimetallic oxide composites

Designing an effective photocatalyst for solar-to-chemical fuel conversion presents significant challenges. Herein, g-C3 N4 nanotubes/CuCo2 O4 (CN-NT-CCO) composites decorated with platinum nanoparticles (Pt NPs) were successfully synthesized by chemical and photochemical reductions. The size distribution and location of Pt NPs on the surface of CN-NT-CCO composites were directly observed by TEM. Extended X-ray absorption fine structure (EXAFS) spectra of Pt L3-edge for the above composite confirmed establishment of Pt-N bonds at an atomic distance of 2.09 Å in the photoreduced Pt-bearing composite, which was shorter than in chemically reduced Pt-bearing composites. This proved the stronger interaction of photoreduced Pt NPs with the CN-NT-CCO composite than chemical reduced one. The H2 evolution performance of the photoreduced (PR) Pt@CN-NT-CCO (2079 μmol h-1  g-1 ) was greater than that of the chemically reduced (CR) Pt@CN-NT-CCO composite (1481 μmol h-1  g-1 ). The abundance of catalytically active sites and transfer of electrons from CN-NT to the Pt NPs to participate in the hydrogen evolution are the primary reasons for the improved performance. Furthermore, electrochemical investigations and band edge locations validated the presence of a Z-scheme heterojunction at the Pt@CN-NT-CCO interface. This work offers unique perspectives on the structure and interface design at the atomic level to fabricate high-performance heterojunction photocatalysts.

Segmented Structure Design of Carbon Ring In-Plane Embedded in g-C3 N4 Nanotubes for Ultra-High Hydrogen Production

The photocatalytic water splitting capability of metal-free graphitic carbon nitride (g-C₃ N₄ ) photocatalyst is determined by its microstructure and photoexcited electrons transfer. Herein, a segmented structure was developed, consisting of alternant g-C₃ N₄ nanotubes and graphitic carbon rings (denoted as C_r -CN-NT). The C_r -CN-NT showed ordered structure and ultralong length/diameter ratio of 150 nm in diameter and a few microns in lengths, which promoted electron transport kinetics and elongated photocarrier diffusion length and lifetime. Meanwhile, the local in-plane π-conjugation was formed and extended in C_r -CN-NT, which could improve charge carrier density and prohibit electron-hole recombination. Accordingly, the average hydrogen evolution rate of C_r -CN-NT reached 9245 μmol h^-1  g^-1 , which was 61.6 times that of pristine CN, and the remarkable apparent quantum efficiency (AQE) of C_r -CN-NT reached up to 12.86 % at 420 nm. This work may provide a pathway for simultaneous morphology regulation and in-plane modification of high-performance photocatalysts.

An Artificial Photosystem of Metal-Insulator-CTF Nanoarchitectures for Highly Efficient and Selective CO2 Conversion to CO

It is of pivotal significance to explore robust photocatalysts to promote the photoreduction of CO₂ into solar fuels. Herein, an intelligent metal-insulator-semiconductor (MIS) nano-architectural photosystem was constructed by electrostatic self-assembly between cetyltrimethylammonium bromide (CTAB) insulator-capped metal Ni nanoparticles (NPs) and covalent triazine-based frameworks (CTF-1). The metal-insulator-CTF composites unveiled a substantially higher CO evolution rate (1254.15 μmol g^-1  h^-1 ) compared with primitive CTF-1 (1.08 μmol g^-1  h^-1 ) and reached considerable selectivity (98.9 %) under visible-light irradiation. The superior photocatalytic CO₂ conversion activity over Ni-CTAB-CTF nanoarchitecture could be attributed to the larger surface area, reinforced visible-light response, and CO₂ capture capacity. More importantly, the Ni-CTAB-CTF nanoarchitecture endowed the photoexcited electrons on CTF-1 with the ability to tunnel across the thin CTAB insulating layer, directionally migrating to Ni NPs and thereby leading to the efficient separation of photogenerated electrons and holes in the photosystem. In addition, isotope-labeled (¹³ CO₂ ) tracer results verified that the reduction products come from CO₂ rather than the decomposition of the photocatalysts. This study opens a new avenue for establishing a highly efficient and selective artificial photosystem for CO₂ conversion.

Silver based photocatalysts in emerging applications

The infinite availability of solar energy grants the potential of fulfilling the energy demands and environmental sustainability requirements with more feasible and reliant renewable energy forms through photocatalysis. In the past decade, the intensive plasmonic effect, suitable work function, superior electrical conductivity and physiochemical properties have made Ag-based photocatalysts attractive components for emerging applications. The local surface plasmon resonance effect (LSPR) provides extra hot-carriers to participate in the photocatalytic process, and Schottky/Ohmic contacts would facilitate charge transfer. Here, recent studies focused on Ag-based photocatalysts for emerging applications are reviewed. Notably, the mechanisms of LSPR, the Schottky barrier and ohmic contacts are introduced together with urgent issues in CO₂ reduction, antibacterial application, H₂ generation, and environmental hazard removal. Additionally, some perspectives and directions on more comprehensive designs on material system, band alignment and functionalization are given to further the exploration in this research area.

Engineering of g-C3N4-based photocatalysts to enhance hydrogen evolution

The technology of photocatalytic hydrogen production that converts abundant yet intermittent solar energy into an environmentally friendly alternative energy source is an attractive strategy to mitigate the energy crisis and environmental pollution. Graphitic carbon nitride (g-C₃N₄), as a promising photocatalyst, has gradually received focus in the field of artificial photosynthesis due to its appealing optical property, high chemical stability and easy synthesis. However, the limited light absorption and massive recombination of photoinduced carriers have hindered the photocatalytic activity of bare g-C₃N₄. Therefore, from the perspective of theoretical calculations and experiments, many valid approaches have been applied to rationally design the photocatalyst and ameliorate the hydrogen production performance, such as element doping, defect engineering, morphology tuning, and semiconductor coupling. This review summarized the latest progress of g-C₃N₄-based photocatalysts from two perspectives, modification of pristine g-C₃N₄ and interfacial engineering design. It is expected to offer feasible suggestions for the fabrication of low-cost and high-efficiency photocatalysts and the photocatalytic mechanism analyses assisted by calculation in the near future. Finally, the prospects and challenges of this exciting research field are discussed.

Borophene and Boron Fullerene Materials in Hydrogen Storage: Opportunities and Challenges

Two-dimensional materials have led to a leap forward in materials science research, especially in the fields of energy conversion and storage. Borophene and its spherical counterpart boron fullerene represent emerging materials that have attracted much attention in the whole area of advanced energy materials and technologies. Owing to their prominent features, such as electronic environment and geometry, borophene and boron fullerene have been used in versatile applications, such as supercapacitors, superconductors, anode materials for photochemical water splitting, and biosensors. Herein, one of the most promising applications/areas of hydrogen storage is discussed. Boron fullerenes have been considered and discussed for hydrogen-storage applications, and recently borophene was also included in the list of materials with promising hydrogen-storage properties. Studies focus mainly on doped borophene systems over pristine borophene due to enhanced features available upon decoration with metal atoms. This Review introduces very recent progress and novel paradigms with respect to both borophene derivatives and boron fullerene based systems reported for hydrogen storage, with a focus on the synthesis, physiochemical properties, hydrogen-storage mechanism, and practical applications.