S-Scheme heterojunction of Cs2SnBr6/C3N4 with interfacial electron exchange toward efficient photocatalytic NO abatement.

Photocatalytic technology is of great significance in environmental purification due to its eco-friendly and cost-effective operations. However, low charge-transfer efficiency restricts the photocatalytic activity of the catalyst. Herein, we report Cs2SnBr6/C3N4 composite catalysts that exhibit a robust interfacial electron exchange thereby enhancing photocatalytic nitric oxide (NO) oxidation. A comprehensive study has demonstrated the S-scheme electron transfer mechanism. Benefiting from the interfacial internal electric field, the C-Br bond serves as a direct electron transfer channel, resulting in enhanced charge separation. Furthermore, the S-scheme heterojunction effectively traps high redox potential electrons and holes, leading to the production of abundant reactive oxygen radicals that enhance photocatalytic NO abatement. The NO removal rate of the Cs2SnBr6/C3N4 heterogeneous system can reach 86.8 %, which is approximately 3-fold and 18-fold that of pristine C3N4 and Cs2SnBr6, respectively. The comprehensive understanding of the electron transfer between heterojunction atomic interfaces will provide a novel perspective on efficient environmental photocatalysis.

Defect-poor BaSn(OH)6 enhanced charge separation for efficient photocatalytic degradation of toluene.

Crystal defect is well-known to have a significant effect on the photocatalytic performance of semiconductors. Herein, defect-rich and -poor BaSn(OH)6 (BSOH-Sn and BSOH-Ba) photocatalysts were synthesized by exchanging the addition order of Ba and Sn. Results show that the defect-poor BSOH-Ba exhibited more efficient toluene degradation under ultraviolet (UV) light, which could attribute to the great suppression of photogenerated electron-hole (e--h+) pairs recombination by tuning the defect concentration. The low defect concentration in BSOH-Ba finally promotes the charge separation efficiency, the generation of reactive oxygen species (ROS), and the photocatalytic toluene degradation reactions. This work not only provides an effective way to inhibit the recombination of photogenerated carriers and improve the photocatalytic performance, but also promotes the understanding of defective perovskite-type hydroxide for more photoreactions.

Enhance the stability of oxygen vacancies in SrTiO3 via metallic Ag modification for efficient and durable photocatalytic NO abatement.

Oxygen vacancy engineering is an appealing strategy in the direction of photocatalytic pollutant purification. Unfortunately, the short lifetime of oxygen vacancies significantly limits photocatalytic efficiencies and their application. Herein, we report that such a scenario can be resolved via plasmonic silver metal modification SrTiO3 containing oxygen vacancies, which can achieve a high NO removal rate of 70.0% and long stability. This outstanding photocatalytic activity can be attributed to the increased optical response range and carrier separation by metallic Ag with the unique character of localized surface plasmonic resonance (LSPR) effect. Moreover, the intrinsic mechanism of how the plasmonic metal could enhance the stability of oxygen vacancies is proposed. The plasmon-driven hot carriers inject SrTiO3 support that promotes the regeneration of oxygen vacancies around the interface, meanwhile, the introduction of Ag nanoparticles prevents the oxygen vacancies from being filled by the reactant. This work elucidates the unique role of plasmonic metal in photocatalysis, providing an innovative idea for improving catalytic stability.

Promote hydroxyl radical and key intermediates formation for deep toluene mineralization via unique electron transfer channel.

The degradation and mineralization of volatile organic compounds (VOCs) in gas-solid phase photocatalytic systems suffer great challenges due to the low electron transfer efficiency and slow benzene ring-opening kinetics. Hence, a heterojunction photocatalyst of Bi2SiO5/TiO2 has been synthesized by a facile method. Bi2SiO5/TiO2 shows the ability of mineralizing toluene to CO2 with a degradation rate of 85.5%, while TiO2 is 49.0% and presents a continuous deactivation. Experimental characterizations and theoretical calculations indicate that a unique electron transfer channel of Bi/Si-O-Ti can be established in the heterojunction sample due to the coupling of the interface. The channel facilitates electron transfer to the catalyst surface, generating •OH radicals with strong oxidation and ring-opening ability. Moreover, in-situ DRIFTS reveal that the selective generation of benzoic acid on Bi2SiO5/TiO2 heterojunction plays a critical role in the ring-opening of toluene. This work discloses a novel paradigm to obtain the deep and durable photocatalytic mineralization of toluene.

Highly active Cs2SnCl6/C3N4 heterojunction photocatalysts operating via interfacial charge transfer mechanism.

In this study, a novel lead-free perovskite heterojunction Cs2SnCl6/C3N4 composite was constructed and applied for photocatalytic NO purification. After design optimization, the Cs2SnCl6/C3N4 heterojunction exhibit excellent and stable photocatalytic NO purification ability under visible-light irradiation, which is significantly better than pristine Cs2SnCl6 and C3N4. Combined in-situ DRIFTS and electron spin resonance spin-trapping, the mechanism of Cs2SnCl6/C3N4 photocatalytic NO removal was revealed. Under visible-light irradiation, the photo-generated electrons on the conduction band of C3N4 would spontaneously migrate to the CB of Cs2SnCl6, leaving holes (h+) on the valence band of C3N4, contributing to efficiently segregated charge carriers and improved photocatalytic NO purification. Density functional theory calculations also revealed the directional electron transfer at the C3N4 and Cs2SnCl6 interface, in which the charge was migrated from C3N4 to Cs2SnCl6 induced by the internal electric field. This research sheds fresh light on the fabrication of Cs2SnCl6/C3N4 heterojunctions as well as its effective interfacial charge separation.

Efficient NO removal and photocatalysis mechanism over Bi-metal@Bi2O2[BO2(OH)] with oxygen vacancies.

Photocatalysis technology prevails as a feasible option for air pollution control, in which high-efficiency charge separation and effective pollutant activation are the crucial issues. Here, this work designed Bi-metal@ Bi2O2[BO2(OH)] with oxygen vacancies (OVs) catalyst for photocatalytic oxidation of NO under visible light, to shed light on the above two processes. Experimental characterizations and density functional theory (DFT) calculations reveal that a unique electron transfer covalent loop（[Bi2O2]2+ → Bi-metal → O2-）can be formed during the reaction to guide the directional transfer of carriers, significantly improving the charge separation efficiency and the yield of active oxygen species. Simultaneously, the defect levels served by OVs also play a part. During the NO purification process, in-situ DRIFTS assisted with DFT calculations reveal that Bi metals could be functioned as electron donors to activate NO molecules and form NO-, a key intermediate. This induces a new reaction path of NO → NO- → NO3- to achieve the harmless conversion of NO, effectively restraining the generation of noxious intermediates (NO2, N2O4). It is expected that this study would inspire the design of more artful photocatalysts for effective charge transfer and safe pollutants purification.

Reheat treatment under vacuum induces pre-calcined α-MnO2 with oxygen vacancy as efficient catalysts for toluene oxidation.

Engineering α-MnO2 with abundant oxygen vacancies is efficient to enhance its catalytic activity towards toluene oxidation. A simple and facile method was introduced to fabricate oxygen vacancies on α-MnO2 surface by reheating the pre-calcined samples under vacuum condition. The reheat treatment especially at 180 °C is beneficial for the formation of oxygen vacancies on α-MnO2 surface, enhancing the oxidation of toluene. The toluene conversion is up to 100% at 270 °C, which is 30 °C lower than that of α-MnO2 without reheat treatment. The apparent activation energy (16.8 kJ mol-1) of MnO2-180 catalyst is lowest among these catalysts, which is essential for accelerating the oxidation of toluene. In-situ DRIFTS results indicate that the MnO2-180 sample promotes the formation of benzaldehyde and the occurrence of ring-opening reaction, thus effectively improving the catalytic performance for toluene oxidation. A possible catalytic oxidation mechanism of toluene over α-MnO2 catalysts after reheat treatment was proposed.

Efficient α-MnO2 with (2 1 0) facet exposed for catalytic oxidation of toluene at low temperature: A combined in-situ DRIFTS and theoretical investigation.

The α-MnO2 catalysts with (1 1 0), (2 1 0) and (3 1 0) crystal facets exposed were prepared via hydrothermal method and studied for the catalytic oxidation of toluene. Some characterization technologies and DFT theoretical calculation were combined to analyze the as-synthesized catalysts. The α-MnO2 catalyst exposed with the (2 1 0) plane displayed best catalytic performance and attained complete toluene conversion at 140 °C. The O2-TPD and XPS results exhibited the amount of surface lattice oxygen on α-MnO2-210 catalyst was largest. Lower accumulation and faster disintegration of intermediates which was characterized by in-situ DRIFTS could be discovered on the surface of α-MnO2-210 catalyst. The results of DFT calculation showed that the unique atomic arrangement of α-MnO2-210 catalyst enhanced the charge separation and conversion, promoting the formation of active oxygen and the activation of toluene. The Ea of α-MnO2-210 catalyst was 24.75 kJ mol-1, lowest among the three catalysts. This work highlights the facet effects on catalytic property and provides new insight into the understanding of catalytic oxidation reaction mechanism of toluene.

Effect of redox state of Ag on indoor formaldehyde degradation over Ag/TiO2 catalyst at room temperature.

Ag/TiO2 catalysts were prepared via in-situ synthesis and impregnation methods. The effect of redox state of Ag species on catalytic activity of Ag/TiO2 catalysts was studied. The Ag-i-300 catalyst with partially oxidized state of Ag species shows superior catalytic activity, keeping HCHO removal efficiency at an extraordinary level of 100% during the 200 min's reaction. The Ag/TiO2 catalysts were characterized by XPS, UV-Vis, BET, XRD, TEM, and in-situ DRIFTS technologies. XPS and TEM results exhibit that the partially oxidized state of Agδ+ (0 < δ < 1) and high dispersion of Ag species are beneficial for the oxidation of HCHO over Ag/TiO2 catalysts. According to the above results, a reaction pathway for HCHO oxidation over Ag-i-300 catalyst was also proposed.