KCl-mediated dual electronic channels in layered g-C3N4 for enhanced visible light photocatalytic NO removal

The solvent-driven formation of multi-morphological Ag-CeO2 plasmonic photocatalysts with enhanced visible-light photocatalytic reduction of CO2

Ag-CeO2 plasmonic photocatalysts with multiple morphologies were synthesized via a simple solvent-driven method. The phase compositions, morphologies and optical properties of the samples were systematically investigated. A combination of noble metal Ag and semiconductor CeO2 in certain solvents (such as methanol and ethylene glycol) enhanced surface plasmon resonance (SPR), which was attributed to the good dispersion of Ag particles on CeO2 and high Ag0 ratios on the surface. The enhanced SPR effect boosted absorption of incident light and facilitated charge carrier separation and transport efficiency caused by the formation of Schottky barriers, thus promoting VLPCR performance. The optimum ACG sample (ethylene glycol was adopted as the solvent) exhibited the maximum VLPCR activity, achieving a CH4 yield of 100 μmol and a CH3OH yield of 35 μmol per gram of catalyst per hour during 6 h visible-light irradiation.

One-step facile synthesis and high H2-evolution activity of suspensible CdxZn1-xS nanocrystal photocatalysts in a S2-/SO32- system

For a CdS-based photocatalyst, both the photocorrosion resistance and the rapid H₂-production reaction are highly required for improving its photocatalytic H₂-production performance. In this study, a facile strategy was reported to simultaneously realize an improved photocorrosion resistance and rapid interfacial H₂-evolution reaction of Cd_xZn_1-xS solid-solution photocatalysts in a sulfur-rich S^2-/SO₃^2- solution. Here, the suspensible Cd_xZn_1-xS nanocrystal photocatalysts are prepared by a one-step co-precipitation route through the direct introduction of Zn²⁺/Cd²⁺ mixing ions in a sulfur-rich Na₂S-Na₂SO₃ solution, and the resultant Cd_xZn_1-xS nanocrystals (ca. 5 nm) display a suspensible structure owing to the numerous and selective adsorption of S^2-/SO₃^2- on the surface of these Cd_xZn_1-xS nanocrystals. It is found that the bandgap structure of Cd_xZn_1-xS (from 2.25 to 3.52 eV) nanocrystals can be easily controlled by adjusting the Cd²⁺/Zn²⁺ molar ratio. The photocatalytic experimental results suggested that the suspensible Cd_xZn_1-xS nanocrystal photocatalysts clearly displayed an excellent photocatalytic H₂-production performance, and the suspensible Cd_0.6Zn_0.4S nanocrystals exhibit the highest photocatalytic H₂-generation performance of 717.19 μmol h^-1, a value higher than that of the sole CdS (320.99 μmol h^-1) and ZnS (5.89 μmol h^-1) by a factor of 2.2 and 121.8 times, respectively. Based on the experimental results, a possible S^2- active site-mediated mechanism accounted for the high H₂-production activity of the suspensible Cd_xZn_1-xS nanocrystals, namely the numerous adsorbed S^2- ions not only function as efficient hole scavengers to rapidly consume the photogenerated holes, resulting in an improved photocorrosion resistance of suspensible Cd_xZn_1-xS nanocrystals, but also serve as effective H⁺-capturing active sites to accelerate the interfacial H₂-production reaction. Meanwhile, an optimum bandgap structure of suspensible Cd_xZn_1-xS nanocrystals is also extremely required for promoting the photocatalytic H₂-production activity. This research may provide advanced insights for developing stable and high-activity photocatalytic materials.

Converting CO2 into fuels by graphitic carbon nitride-based photocatalysts

A metal-free photocatalyst, graphitic carbon nitride (GCN) with a moderate band gap catering for visible-light excitation, shows amazing potential in various photocatalytic applications. Carbon dioxide reduction using diversified photocatalysts has been attracting increasing public attention and the extensively studied GCN is one of the most promising photocatalysts. However, because of the low concentration and high recombination rate of photogenerated carriers, and some other disadvantages of the pristine GCN photocatalyst, the solar-to-fuel conversion efficiency is too low for practical use. Modifications or optimizations of GCN are therefore important to enhance its CO₂ photocatalytic conversion performance. This review summarizes the research progress made during the past five years on GCN-based photocatalysts in two main areas, which includes pristine GCN and its molecular modifications, and heterostructure composite photocatalysts based on GCN, for CO₂ reduction. It is expected that this review may benefit the development of GCN-based photocatalysts for CO₂-to-fuel conversion.

Simultaneous introduction of oxygen vacancies and Bi metal onto the {001} facet of Bi3O4Cl woven nanobelts for synergistically enhanced photocatalysis

In order to relieve air pollution problems via photocatalytic NO purification, we prepared Bi3O4Cl (BOC) woven nanobelts with exposed {001} facets by a one-pot hydrothermal method. The as-prepared catalysts were modified by a simple chemical reduction to introduce oxygen vacancies (OVs) and plasmonic Bi metal on their surfaces. The photocatalytic performance was strongly dependent on the OVs and surface plasmon resonance (SPR) effect induced by Bi metal. DFT calculations and in situ DRIFTS study were closely combined to show that the OVs could not only induce the formation of a middle-gap in BOC which increases the production of the ˙OH species by introducing more holes on the valence band, but also promote the generation of ˙O2- species by activating the adsorbed O2 on the surface. Meanwhile, the Bi metal can serve both as an electron donor and a bridge for charge transfer to promote charge separation. As a result, the OVs and Bi metal could synergistically tailor the charge transfer pathway and enhance the photocatalytic performance significantly. Moreover, the reaction intermediates were revealed and the mechanism of photocatalytic NO oxidation was proposed based on in situ DRIFTS spectra. The design concept of modifying the catalyst surface via simultaneous introduction of OVs and Bi metal on the catalyst surface could offer a novel strategy to enhance the photocatalytic performance of other nanomaterials for environmental and energy-related applications.

Confining the polymerization degree of graphitic carbon nitride in porous zeolite-Y and its luminescence

Graphitic carbon nitride (g-C₃N₄) has aroused broad interest in the field of photocatalysis and luminescence as a kind of metal-free semiconductor with a suitable band gap of ∼2.7 eV. The properties largely depend on the polymerization degree of g-C₃N₄. This research exploits the nanocages of zeolite-Y to confine the polymerization of the melamine monomer to form g-C₃N₄. The composites are achieved via a facile two-step method, i.e., melamine–Na⁺ ion exchange reaction in the cage of the zeolite and subsequent calcination. BET measurement and transmission electron microscopy (TEM) confirm that the g-C₃N₄ is encapsulated in zeolite-Y, and the polymerization degree can be controlled by the melamine contents exchanged with Na⁺ in the cages of zeolite-Y. Photoluminescence and vibration spectroscopy also show the features of g-C₃N₄ with different polymerization degrees in the zeolite-Y composites. This research gives a perspective of fabricating subnanoscale g-C₃N₄ in porous zeolite, which may find potential applications in photocatalysis and optoelectronics.

The composites of porous zeolite-Y and graphitic carbon nitride can be synthesized via a facile two-step method, and the polymerization degree of the latter can be confined by the former.

Efficient and stable photocatalytic NO removal on C self-doped g-C3N4: electronic structure and reaction mechanism

The unique electronic structure of C self-doped g-C₃N₄ enables highly enhanced photocatalytic NO removal efficiency.