Infrared light dual excitation of Ni-phytate-sensitized ZnIn2S4 with sulfur vacancies for enhanced NIR-driven photocatalysis.

Near-infrared (NIR) light accounts for about half of the solar spectrum, and the effective utilization of low-energy NIR light is an important but challenging task in the field of photocatalysis. Molecular semiconductor photocatalytic systems (MSPSs) are highly tunable, available and stable, and are considered to be one of the most promising ways to achieve efficient NIR hydrogen production. Here, we demonstrate efficient dual-excitation in MSPS consisting of ZnIn2S4-x (ZIS1-x) with sulfur vacancies and phytic acid nickel (PA-Ni), which differs from other NIR-responsive photosensitized systems. The system achieves a hydrogen evolution reaction (HER) of 119.85 µmol h-1 g-1 at λ > 800 nm illumination, which is an excellent performance among all reported NIR catalysts and even outperforms the noble metal catalysts when compared to the reported literature. The superior activity is attributed to the unique charge dynamics and higher carrier concentration of the system. This work demonstrates the potential of dual-excitation systems for efficient utilization of low-energy NIR light.

A NIR-Responsive Phytic Acid Nickel Biomimetic Complex Anchored on Carbon Nitride for Highly Efficient Solar Hydrogen Production.

A challenge in photocatalysis consists in improving the efficiency by harnessing a large portion of the solar spectrum. We report the design and realization of a robust molecular-semiconductor photocatalytic system (MSPS) consisting of an earth-abundant phytic acid nickel (PA-Ni) biomimetic complex and polymeric carbon nitride (PCN). The MSPS exhibits an outstanding activity at λ=940 nm with high apparent quantum efficiency (AQE) of 2.8 %, particularly λ>900 nm, as it outperforms all reported state-of-the-art near-infrared (NIR) hybrid photocatalysts without adding any noble metals. The optimum hydrogen (H2 ) production activity was about 52 and 64 times higher with respect to its pristine counterpart under the AM 1.5 G and visible irradiation, respectively, being equivalent to the platinum-assisted PCN. This work sheds light on feasible avenues to prepare highly active, stable, cheap NIR-harvesting photosystems toward sustainable and scalable solar-to-H2 production.

Multiple Doped Carbon Nitrides with Accelerated Interfacial Charge/Mass Transportation for Boosting Photocatalytic Hydrogen Evolution.

The interaction of water molecule with catalysts is crucial to photocatalysis, but the surface property manipulation still remains a great challenge. In this study, we report an in situ multiple heteroelement (sodium, oxygen, and iodide) doping strategy based on a molten salt-assisted route to prepare a green-colored carbon nitride (GCN). The as-prepared GCN yields 25.5 times higher H2 evolution rate than that of bulk polymeric carbon nitride under visible light. Experimental characterization data demonstrate that the GCN delivers upshift of the conduction band and increased specific surface area and hydrophilicity. As confirmed by time-resolved PL spectra, DMPO spin-trapping EPR analysis, and so on, the excellent activity is dominantly ascribed to the greatly enhanced hydrophilicity and, subsequently, efficient interfacial charge transfer and hydrogen liberation. Moreover, through surface charge modification, the GCN also shows an increased degradation activity of rhodamine B. This work highlights the importance of surface modulation through multiple earth-abundant element incorporation for designing of advanced and practical photocatalysts.

One-Step Nickel Foam Assisted Synthesis of Holey G-Carbon Nitride Nanosheets for Efficient Visible-Light Photocatalytic H2 Evolution.

Graphitic carbon nitride (g-C3N4) with layered structure represents one of the most promising metal-free photocatalysts. As yet, the direct one-step synthesis of ultrathin g-C3N4 nanosheets remains a challenge. Here, few-layered holey g-C3N4 nanosheets (CNS) were fabricated by simply introducing a piece of nickel foam over the precursors during the heating process. The as-prepared CNS with unique structural advantages exhibited superior photocatalytic water splitting activity (1871.09 µmol h-1 g-1) than bulk g-C3N4 (BCN) under visible light (λ > 420 nm) (≈31 fold). Its outstanding photocatalytic performance originated from the high specific surface area (240.34 m2 g-1) and mesoporous structure, which endows CNS with more active sites, efficient exciton dissociation, and prolonged charge carrier lifetime. Moreover, the obvious upshift of the conduction band leads to a larger thermodynamic driving force for photocatalytic proton reduction. This methodology not only had the advantages for the direct and green synthesis of g-C3N4 nanosheets but also paved a new avenue to modify molecular structure and textural of g-C3N4 for advanced applications.

Facile synthesis of CdS/Bi4V2O11 photocatalysts with enhanced visible-light photocatalytic activity for degradation of organic pollutants in water.

The development of Z-scheme heterojunction photocatalytic systems is a promising strategy to produce hydrogen and for pollutant degradation. In this study, the direct Z-scheme CdS/Bi4V2O11 photocatalysts were synthesized via a two-step solvothermal method. The photocatalytic properties of the samples were measured by ciprofloxacin (CIP), tetracycline (TC) and rhodamine B (RhB) degradation under visible light (λ > 420 nm). In addition, a probable reaction mechanism for organic pollutants over CdS/Bi4V2O11 photocatalysts was also proposed based on the analysis of electron spin resonance (ESR) and active species capture experiments. The enhanced photocatalytic activity of CdS/Bi4V2O11 photocatalysts was ascribed to the efficient electron transfer of direct Z-scheme CdS/Bi4V2O11 photocatalysts.

Precisely tunable thickness of graphitic carbon nitride nanosheets for visible-light-driven photocatalytic hydrogen evolution.

Graphitic carbon nitride (GCN) nanosheets with unique physicochemical properties have received increasing attention in the area of photocatalysis, yet tunable thickness for the straightforward production of this graphite-like two-dimensional (2D) nanomaterial remains a challenge. In this work, GCN nanosheets with different thicknesses were firstly prepared by a direct calcination of melamine supramolecular aggregates (MSA) obtained from a hydrochloric acid (HCl)-induced hydrothermal assembly approach. The resultant nanosheets over nanometer scale thickness could be precisely controlled via simply adjusting the HCl concentration. Compared to the bulk GCN (BGCN), the thinner nanosheets possessed a high specific surface area, a large electronic-band structure, and fast charge separation ability. The thinnest nanosheets with a thickness of approximately 4 nm exhibited excellent visible-light-driven photocatalytic water splitting performance in hydrogen evolution (524 µmol h-1 g-1), which is over 9-fold higher than the BGCN powder. This work provides a thickness-dependent strategy for the preparation of metal-free GCN nanosheets and develops a promising 2D photocatalyst for application in solar energy conversion.

Highly efficient visible-light-driven photocatalytic degradation of tetracycline by a Z-scheme g-C3N4/Bi3TaO7 nanocomposite photocatalyst.

Spatial separation of photogenerated electron-hole pairs is one of the most important factors that determine the efficiency of a photocatalyst. It is well acknowledged that the fabrication of heterogeneous photocatalysts with two different inorganic semiconductors is a good strategy to effectively improve the charge separation of electrons and holes. This study describes a novel visible light-induced g-C3N4/Bi3TaO7 composite photocatalyst with superior photocatalytic properties toward the degradation of tetracycline (TC) by visible light irradiation. The formation of heterojunctions significantly improves the separation efficiency of photogenerated carriers, which is confirmed by the photocurrent density and electrochemical impedance spectroscopy. Electron spin resonance examination and trapping experiments confirm that the photoinduced active species (˙OH and ˙O2-) are responsible for the degradation of tetracycline. Based on the experimental results, a possible Z-scheme system reaction mechanism for the g-C3N4/Bi3TaO7 composite towards the degradation of TC under visible light was proposed.

Ag-Decorated ATaO3 (A = K, Na) Nanocube Plasmonic Photocatalysts with Enhanced Photocatalytic Water-Splitting Properties.

Tantalate semiconductor nanocrystals have been at the forefront of the photocatalytic conversion of solar energy to supply hydrogen owing to their favorable and tunable optical and electronic properties as well as advances in their synthesis. However, a narrow band gap is required for response to improve the efficiency of the photocatalysts. Here we propose an efficient enhancement of the H2 generation under simulated sunlight and visible light irradiation by a dispersion of Ag-decorated KTaO3 and NaTaO3 nanocubes. X-ray diffraction and UV-vis diffuse reflectance spectra are used to characterize the products. Transmission electron microscope (TEM) and high-resolution high-angle annular dark-field scanning TEM (HAADF-STEM) images show that the Ag nanoparticles (NPs) are uniformly loaded on the surfaces of KTaO3 and NaTaO3. The photocatalytic water-splitting results over Ag-decorated KTaO3 and NaTaO3 show that the rate for H2 evolution from aqueous CH3OH solutions is up to 185.60 and 3.54 µmol/h·g under simulated sunlight and the rate for H2 evolution is more than 2 times than that of pure NaTaO3 and KTaO3 materials. However, under purely visible light illumination the highest H2 evolution of 25.94 and 0.83 µmol/h·g is observed in the case of Ag-decorated KTaO3 and NaTaO3 nanocubes. To the best of our knowledge, this is the first time that the photocatalytic water-splitting activity of the prepared Ag-decorated KTaO3 and NaTaO3 nanocubes has been reported.

Fabrication of a Ag/Bi3TaO7 Plasmonic Photocatalyst with Enhanced Photocatalytic Activity for Degradation of Tetracycline.

A novel Ag/Bi3TaO7 plasmonic photocatalyst has been prepared by a simple photoreduction process. The as-prepared Ag/Bi3TaO7 photocatalyst exhibited an enhanced photocatalytic activity for the degradation of tetracycline (TC) compared to that of a bare Bi3TaO7 catalyst. The 1 wt % Ag-loaded Bi3TaO7 sample showed the highest photocatalytic efficiency for TC degradation (85.42%) compared with those of the other samples. The enhanced photocatalytic activity could be ascribed to the synergistic effect of the surface plasmon resonance caused by Ag nanoparticles. Electrochemical impedance spectroscopy demonstrated that the incorporation of silver nanoparticles onto the Bi3TaO7 surface promoted the separation of photogenerated carriers. In addition, an electron spin resonance (ESR) and trapping experiment revealed that the photoinduced active species hydroxyl radical and superoxide radical were the main active species in the photocatalytic process of TC degradation. The photocatalytic reaction mechanism was discussed by active species trapping and ESR analysis.