Wen Cui

Highly Efficient Performance and Conversion Pathway of Photocatalytic NO Oxidation on SrO-Clusters@Amorphous Carbon Nitride

This work demonstrates the first molecular-level conversion pathway of NO oxidation over a novel SrO-clusters@amorphous carbon nitride (SCO-ACN) photocatalyst, which is synthesized via copyrolysis of urea and SrCO3. The inclusion of SrCO3 is crucial in the formation of the amorphous carbon nitride (ACN) and SrO clusters by attacking the intralayer hydrogen bonds at the edge sites of graphitic carbon nitride (CN). The amorphous nature of ACN can promote the transportation, migration, and transformation of charge carriers on SCO-ACN. And the SrO clusters are identified as the newly formed active centers to facilitate the activation of NO via the formation of Sr-NOδ(+), which essentially promotes the conversion of NO to the final products. The combined effects of the amorphous structure and SrO clusters impart outstanding photocatalytic NO removal efficiency to the SCO-ACN under visible-light irradiation. To reveal the photocatalytic mechanism, the adsorption and photocatalytic oxidation of NO over CN and SCO-ACN are analyzed by in situ DRIFTS, and the intermediates and conversion pathways are elucidated and compared. This work presents a novel in situ DRIFTS-based strategy to explore the photocatalytic reaction pathway of NO oxidation, which is quite beneficial to understand the mechanism underlying the photocatalytic reaction and advance the development of photocatalytic technology for environmental remediation.

Directional electron delivery via a vertical channel between g-C3N4 layers promotes photocatalytic efficiency

Suffering from inefficient charge separation and random charge transfer between its planes, the photocatalytic efficiency of g-C3N4 is still unsatisfactory. Herein, this challenging issue is tackled via intercalating alkalis into the interlayer space in g-C3N4 to create a vertical channel between the layers for directional electron delivery, which is a novel strategy to effectively quench charge recombination and promote electron transfer. Using a close combination of theoretical and experimental methods, the alkalis intercalated in g-C3N4 have been designed and fabricated. The alkali species could suppress random charge transfer between the planes of g-C3N4 and enable the electrons to directionally migrate between adjacent layers in a one-way transmission manner. In an unprecedented result, the photocatalytic efficiency of g-C3N4 is significantly improved by 115.0% via alkali intercalation and it is also stable for recycled usage. This work could provide a feasible protocol for the modification of a wide range of 2D materials, and shed new light on the understanding of photocatalytic mechanisms.

Pt quantum dots deposited on N-doped (BiO)2CO3: enhanced visible light photocatalytic NO removal and reaction pathway

In order to achieve efficient photocatalytic NO removal, N-doped (BiO)2CO3 hierarchical superstructures deposited with Pt quantum dots (2–4 nm) were fabricated by a one-pot hydrothermal method using ammonium bismuth citrate and H2PtCl6 as precursors. In such a combined way, visible light absorption and charge carrier separation can be simultaneously enhanced. The as-prepared Pt/N-doped (BiO)2CO3 catalysts exhibited a highly enhanced visible-light photocatalytic performance for NO removal and phenol degradation, which can be ascribed to the N doping that narrows the band gap, the formation of a Schottky barrier because of Pt that promotes electron/hole separation, and scattering and surface reflecting effects (SSR) caused by the hierarchical architecture. To reveal the reaction mechanism of photocatalytic NO oxidation, in situ DRIFTS investigation was applied to probe the reaction process, and a new intermediate, NO+, was firstly discovered during photocatalysis. Pt quantum dot deposition could change the reaction pathway via the inhibition of NO2 production. Based on ESR trapping and time-dependent observation of the reaction products, a new photocatalytic reaction pathway was proposed for photocatalytic NO oxidation with Pt/N-doped (BiO)2CO3. The present work could provide new perspectives for advancing the photocatalysis efficiency, offer a new insight into the photocatalytic NO oxidation process and promote large-scale environmental applications of high-performance photocatalysts.

In situ growth of Au nanoparticles on 3D Bi2O2CO3 for surface plasmon enhanced visible light photocatalysis

Novel plasmonic photocatalysts were fabricated by the modification of 3D Bi2O2CO3 microspheres with Au nanoparticles (NPs) via a facile one-pot in situ method for the first time. The as-obtained 3D Au/Bi2O2CO3 heterostructures (Au/BOC) were characterized by XRD, XPS, SEM, TEM, EDX, N2 adsorption–desorption isotherms, UV-vis DRS and PL. The results revealed that the Au NPs were produced by in situ reduction of Au3+ by the citrate ions and deposited on the surface of Bi2O2CO3 microspheres. The photocatalytic activity of Au/BOC was evaluated by the removal of NO under visible light with pure Bi2O2CO3 as reference. The pure Bi2O2CO3 microspheres displayed decent photocatalytic activity due to surface scattering and reflecting (SSR) that resulted from their special hierarchical architecture. Au/BOC exhibited highly enhanced visible light photocatalytic performance in comparison with pure BOC because of the co-contribution of the SSR effect, the Schottky barrier and the surface plasmon resonance (SPR) effect endowed with metallic Au NPs. The integration of the SSR effect and SPR effect in one system for enhancing photocatalysis could provide a new scope in the architectural design and mechanistic understanding of other noble metal-based plasmonic photocatalysts.

Enhanced Visible Light Photocatalytic Activity of Br-Doped Bismuth Oxide Formate Nanosheets

A facile method was developed to enhance the visible light photocatalytic activity of bismuth oxide formate (BiOCOOH) nanosheets via Br-doping. The as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, the Brunauer–Emmett–Teller surface area, UV-vis diffuse reflectance spectroscopy, photoluminescence spectra, and N2 adsorption-desorption isotherms measurement. The Br− ions replaced the COOH− ions in the layers of BiOCOOH, result in a decreased layer distance. The photocatalytic activity of the as-prepared materials was evaluated by removal of NO in qir at ppb level. The results showed that the Br-doped BiOCOOH nanosheets showed enhanced visible light photocatalytic activtiy with a NO removal of 37.8%. The enhanced activity can be ascribed to the increased visible light absorption and the promoted charge separation.

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

Although graphitic carbon nitride (g-C3N4, CN) has been widely studied for its photocatalytic applications in environmental remediation and solar energy conversion, the electronic structure of CN has not been optimized in terms of reactant activation and ROS generation. In this work, C self-doped g-C3N4 (CN-C) was prepared by co-pyrolysis of urea and saccharose and showed highly enhanced photocatalytic NO removal efficiency in comparison with the pristine CN. Theoretical and experimental methods were highly combined to illustrate the geometric structures of CN-C and reveal the promotion mechanisms in terms of enhanced optical and electron transfer properties. The unique electronic structure of CN-C allows NO and O2 to be more easily activated for the production of reactive radicals to participate in the photocatalytic redox reaction. The enhanced production of reactive radicals and the boosted separation rate of photogenerated carriers could promote the photocatalysis efficiency, leading to efficient and stable photocatalytic oxidation of NO over C self-doped g-C3N4. Importantly, the conversion pathways of photocatalytic NO oxidation over CN and CN-C have been elucidated based on the results of DFT calculations, ESR spectra and in situ DRIFTS spectra. A new absorption band at 2175 cm−1 associated with the NO+ intermediate is discovered for CN-C. The present work could offer new insights into the understanding of the electronic structure and photocatalytic NO oxidation mechanism on typical photocatalysts.