Fabrication of Z-scheme Cd0.85Zn0.15S/Co9S8dual-functional photocatalyst for effective hydrogen evolution and organic pollutant degradation

A Z-scheme Cd_0.85Zn_0.15S/Co₉S₈(CZS-CS) photocatalyst was reasonably fabricated by a simple solvothermal method for the effective visible-light-driven H₂evolution and organic pollutants degradation. The precise construction of the CZS-CS composites provided an efficient heterogeneous contact interface and abundant reaction sites for the proposed photocatalytic reaction. The homogeneous Co₉S₈nanocrystals were uniformly wrapped on the surface of Cd_0.85Zn_0.15S nanorods, forming an intimate-contact interface, markedly contributed to the light collection and effectively inhibited the charge-carrier recombination. The optimized CZS-CS-15 composites exhibited a special H₂production rate reaching 19.15 mmol·h^-1·g^-1, roughly 1915 and 4.5 times of pure Co₉S₈and Cd_0.85Zn_0.15S samples and 85% of tetracycline (TC) molecule within 15 min was degraded. Furthermore, trapping experiments confirmed that h⁺was the main active species for TC photodegradation. Moreover, the obtained photocatalysts manifested stability without apparent activity declines during the proposed reactions. Finally, the Z-scheme photocatalytic mechanism was verified to illustrate the characteristics of efficient charge transfer and high redox ability. This study provided a rational and learnable strategy for designing dual-functional Z-scheme heterojunction photocatalysts.

Simple one-pot, high-yield synthesis of 2D graphitic carbon nitride nanosheets for photocatalytic hydrogen production

2-Dimensional (2D) graphitic carbon nitrate (g-C₃N₄) nanosheets are particularly interesting photocatalytic materials because of their large surface area and excellent photoelectric properties. However, it remains challenging to synthesize 2D g-C₃N₄ nanosheets with high yield and high activity simultaneously. In this work, a urea-assisted one-pot method was developed in which the decomposition of urea released NH₃ gas which exfoliated bulk g-C₃N₄ into thin nanosheets and generated pores and wrinkles on their surface. The product g-C₃N₄ nanosheets therefore possessed abundant surface active sites for interaction with reactants and showed enhanced light utilization efficiency, giving rise to their improved hydrogen production activity which was 3.36 times higher than that of their bulk counterpart. Importantly, the yield of g-C₃N₄ nanosheets using this method was almost doubled compared to a previously reported ammonium chloride (NH₄Cl) assisted method. Given that g-C₃N₄ nanosheets are building blocks for various photocatalysts, the current synthetic method which produces g-C₃N₄ nanosheets with high yield and high activity shall pave the way for high-performance photocatalytic applications such as hydrogen production and more.

Non-Metal-Doped Porous Carbon Nitride Nanostructures for Photocatalytic Green Hydrogen Production

Photocatalytic green hydrogen (H₂) production through water electrolysis is deemed as green, efficient, and renewable fuel or energy carrier due to its great energy density and zero greenhouse emissions. However, developing efficient and low-cost noble-metal-free photocatalysts remains one of the daunting challenges in low-cost H₂ production. Porous graphitic carbon nitride (gCN) nanostructures have drawn broad multidisciplinary attention as metal-free photocatalysts in the arena of H₂ production and other environmental remediation. This is due to their impressive catalytic/photocatalytic properties (i.e., high surface area, narrow bandgap, and visible light absorption), unique physicochemical durability, tunable electronic properties, and feasibility to synthesize in high yield from inexpensive and earth-abundant resources. The physicochemical and photocatalytic properties of porous gCNs can be easily optimized via the integration of earth-abundant heteroatoms. Although there are various reviews on porous gCN-based photocatalysts for various applications, to the best of our knowledge, there are no reviews on heteroatom-doped porous gCN nanostructures for the photocatalytic H₂ evolution reaction (HER). It is essential to provide timely updates in this research area to highlight the research related to fabrication of novel gCNs for large-scale applications and address the current barriers in this field. This review emphasizes a panorama of recent advances in the rational design of heteroatom (i.e., P, O, S, N, and B)-doped porous gCN nanostructures including mono, binary, and ternary dopants for photocatalytic HERs and their optimized parameters. This is in addition to H₂ energy storage, non-metal configuration, HER fundamental, mechanism, and calculations. This review is expected to inspire a new research entryway to the fabrication of porous gCN-based photocatalysts with ameliorated activity and durability for practical H₂ production.

Enhanced light harvesting and charge separation of carbon and oxygen co-doped carbon nitride as excellent photocatalyst for hydrogen evolution reaction

Solar-driven water splitting has been regarded as a promising strategy for renewable hydrogen production. Among many semiconductor photocatalysts, graphitic carbon nitride (g-C₃N₄) has received tremendous attention due to its two-dimensional structure, appropriate band gap and decent photocatalytic activity. However, it suffers severe charge recombination problems, affecting its practical performance. In this work, we demonstrated that dual heteroatoms (C and O) doped g-C₃N₄ can exhibit about 3 times higher catalytic performance for hydrogen evolution than that of the normal g-C₃N₄ with a hydrogen evolution rate reaching 2595.4 umol g^-1h^-1 and an apparent quantum efficiency at 420 nm of 16.6%. The heteroatoms (C and O) doped g-C₃N₄ photocatalyst also exhibited superior removal performance when removing Rhodamine B (RhB) . X-ray photoelectron spectroscopy (XPS), solid-state nuclear magnetic resonance (ssNMR) and X-ray absorption near-edge structure (XANES) spectroscopy reveal that the carbon and oxygen dopants replace the sp² nitrogen and bridging N atom, respectively. DFT calculations demonstrate the codoping of carbon and oxygen- induced the generation of mid-gap state, leading to the improvement of light harvesting and charge separation.

Unveiling the charge transfer behavior within ZSM-5 and carbon nitride composites for enhanced photocatalytic degradation of methylene blue

ZSM-5/graphitic carbon nitride (g-C₃N₄) composites were successfully prepared using a simple solvothermal method. By varying the amount of ZSM-5 and g-C₃N₄ in the composites, the charge carrier (electrons and holes) transfer within the materials, which contributes to the enhanced photocatalytic performance, was unraveled. The X-ray diffraction (XRD), Fourier-transform infrared (FTIR), and scanning electron microscopy (SEM) analysis revealed that more ZSM-5 component leads to a stronger interaction with g-C₃N₄. The photocatalytic performance test toward methylene blue (MB) degradation shows that more ZSM-5 in the composites is beneficial in enhancing photocatalytic activity. Meanwhile, the impedance electron spectroscopy (EIS) and photoluminescence (PL) analysis revealed that ZSM-5 facilitates the charge carrier transfer of photogenerated electrons and holes from g-C₃N₄ to the catalyst surface due to its lower charge transfer resistance. During the charge carrier migration, the interface between g-C₃N₄ and ZSM-5 particles may induce higher resistance for the charge carrier transfer, however after passing through the interface from g-C₃N₄ to ZSM-5 particles, the charge carrier can be efficiently transferred to the surface, hence suppressing the charge carrier recombination.

Conjugated Cationic Pp-x Formed on g-C3N4 for Photocatalyzed Water Splitting

Polycationic Pp-x@g-C₃N₄ composite was synthesized through an in situ polymerization process of N-alkylpyridinium acetylenic alcohol bromide (p-x) above the surface of g-C₃N₄. The structure of p-0 and the Pp-x@g-C₃N₄ properties were checked by modern technologies. Photocatalytic tests of Pp-x@g-C₃N₄ in water splitting unveiled much better Pp-x@g-C₃N₄ hydrogen evolution activities by comparison with both g-C₃N₄ and Pp-0. The hydrogen production by Pp-0@g-C₃N₄ was 1654.5 μmol h^-1 g^-1, which is ∼26- and 22-fold greater in relation to what g-C₃N₄ and Pp-0 produced (62.7 and 75.0 μmol h^-1 g^-1, respectively), suggesting strong bilateral and synergistic interactions of g-C₃N₄ with Pp-0. Although the lengthening methylene chain in the polymers weakened the hydrogen generation ability of Pp-x@g-C₃N₄, the conjugated double bonds, solubilization, and dispersion of Pp-x polycationic surfactants made Pp-x@g-C₃N₄ superior to g-C₃N₄ in water splitting. Due to the readily available raw materials, a simple way of preparation (starting chemicals to p-0 to Pp-0@g-C₃N₄), high photocatalysis efficiency, light irritation stability, recyclable ability, and low toxicity, Pp-0@g-C₃N₄ is a good candidate for water splitting.

A dual polymer composite of poly(3-hexylthiophene) and poly(3,4-ethylenedioxythiophene) hybrid surface heterojunction with g-C3N4 for enhanced photocatalytic hydrogen evolution

A surface heterojunction catalyst of g-C₃N₄–PEDOT/P3HT with P3HT and PEDOT as the polymer sensitizer and hole transport pathway is successfully prepared. The as constructed g-C₃N₄–PEDOT/P3HT composite exhibits a photocatalyst H₂ evolution rate up to 427703.3 μmol h⁻¹ g⁻¹ which is 1059 times higher than that of g-C₃N₄, 118 times higher than that of g-C₃N₄–PEDOT with ascorbic acid as sacrificial reagents. What's more, the g-C₃N₄–PEDOT/P3HT can even show an obviously enhanced photocatalytic H₂ evolution rate which is 6.1 times higher than that of pure g-C₃N₄ in pure water without any sacrificial reagent. Combining the experimental results and molecular dynamic (MD) simulation results, a possible mechanism can be drawn that the existed PEDOT possesses relatively higher hole mobility and can be used as a hole conductor between g-C₃N₄ and P3HT. Then, the photogenerated holes migration can be accelerated by PEDOT from the VB of g-C₃N₄ to the VB of P3HT. All those factors may benefit the synergy among g-C₃N₄, PEDOT and P3HT, which finally facilitates the rapid migration of photoinduced electron–hole pairs and eventually improves the photocatalytic H₂ activity process of g-C₃N₄–PEDOT/P3HT with visible light. The present work may provide useful insights for designing a surface heterojunction composite photocatalyst with high photocatalytic activity for H₂ production.

A surface heterojunction catalyst of g-C₃N₄-PEDOT/P3HT with P3HT and PEDOT as the polymer sensitizer and hole transport pathway is successfully prepared. The as prepared photocatalyst with much improved photocatalytic activity for H₂ production.