Wanglai Cen

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.

Tailoring Active Sites via Synergy between Graphitic and Pyridinic N for Enhanced Catalytic Efficiency of a Carbocatalyst

Because of the limited characterization methods of the structures and morphology of N-doped carbocatalysts that are available at the atomic level, the detailed promotion mechanism of the catalytic efficiency is unspecific and the particular active sites introduced by the N atoms require further evaluation. Herein, this challenging issue is tackled by extensive theoretical simulation. It is first proposed that the active sites, wherein O2 molecules become adsorbed and activated, be tailored by synergistic graphitic and pyridinic N atoms (GrN and PyN, respectively), which remarkably accelerate the generation of highly chemically reactive O-containing species. The boosted catalytic efficiency is essentially contributed by the electron donor and acceptor of the two active sites, which are induced by PyN and GrN, respectively. These active sites steer the electron transfer between O2 molecules, and the reaction centers in a one-way transmission manner along the PyN → O1 → O2 → C → GrN path. This work provides a feasible protocol for the modification of generally practical carbocatalysts and sheds new light on the understanding of the catalysis mechanism.

Promotion mechanism of pyridine N-doped carbocatalyst for SO2 oxidation

Pyridine N (PyN) doped carbon materials have long been recognized as promising catalysts for SO2 oxidation under mild conditions, but our understanding of what is happening at the atomic level is still limited. Herein, the local structure and promotion mechanism of PyN in carbon materials for the catalytic oxidation of SO2 were investigated on graphene model catalysts by using density functional theory. A type of defect involving three PyN atoms around a single C atom vacancy was found to be active for both the dissociation of O2 and the further oxidation of SO2. It is worth mentioning that both PyN and the adjacent C atoms are primary active sites. Additionally, a switch effect of pyridine N-oxide was identified, which can suppress or enhance the oxidation capacity of surface oxygen species for SO2 oxidation. These results provide a mechanistic explanation for the low temperature catalytic oxidation of SO2 by PyN-doped carbon materials and offer insight for the design of new carbon-based catalysts.

Static and dynamic characteristics of SO2-O2 aqueous solution in the microstructure of porous carbon materials

Porous carbon material facilitates the reaction SO2 + O2 + H2O → H2SO4 in coal-burned flue gas for sulfur resources recovery at mild conditions. It draws a long-term mystery on its heterogeneous catalysis due to the complicated synergic effect between its microstructure and chemical components. To decouple the effects of geometric structure from chemical components, classical molecular dynamics method was used to investigate the static and dynamic characteristics of the reactants (H2O, SO2 and O2) in the confined space truncated by double-layer graphene (DLG). Strong adsorption of SO2 and O2 by the DLG was observed, which results in the filling of the solute molecules into the interior of the DLG and the depletion of H2O. This effect mainly results from the different affinity of the DLG to the species and can be tuned by the separation of the two graphene layers. Such dimension dependence of the static and dynamic properties like distribution profile, molecular cluster, hydrogen bond and diffusion coefficient were also studied. The conclusions drawn in this work could be helpful to the further understanding of the underlying reaction mechanism of desulfurization process in porous carbon materials and other applications of carbon-based catalysts.

Generation and transformation of ROS on g-C3N4 for efficient photocatalytic NO removal: A combined in situ DRIFTS and DFT investigation

Abstract Understanding the performance of reactive oxygen species (ROS) in photocatalysis is pivotal for advancing their application in environmental remediation. However, techniques for investigating the generation and transformation mechanism of ROS have been largely overlooked. In this study, considering g-C 3 N 4 to be a model photocatalyst, we have focused on the ROS generation and transformation for efficient photocatalytic NO removal. It was found that the key to improving the photocatalysis performance was to enhance the ROS transformation from •O 2 − to •OH, elevating the production of •OH. The ROS directly participate in the photocatalytic NO removal and tailor the rate-determining step, which is required to overcome the high activation energy of the intermediate conversion. Using a closely combined experimental and theoretical method, this work provides a new protocol to investigate the ROS behavior on g-C 3 N 4 for effective NO removal and clarifies the reaction mechanism at the atomic level, which enriches the understanding of ROS in photocatalytic environmental remediation.