The activity of heterogeneous photocatalytic H2 O2 activation in Fenton-like processes is closely related to the local electron density of reaction centre atoms. However, the recombination of electron-hole pairs arising from random charge transfer greatly restricts the oriented electron delivery to active center. Here we show a defect engineered iron single atom photocatalyst (Fe1 -Nv /CN, single Fe atoms dispersed on carbon nitride with abundant nitrogen vacancies) for the activation of H2 O2 under visible light irradiation. Based on DFT calculations and transient absorption spectroscopy results, the engineered nitrogen vacancies serve as the electron trap sites, which can directionally drive the electrons to concentrate on Fe atoms. The formation of highly concentrated electrons density at Fe sites significantly improves the H2 O2 conversion efficiency. Therefore, the optimized single atom catalyst exhibiting a higher ciprofloxacin degradation activity, which was up to 18 times that of pristine CN.

Regulating Local Electron Density of Iron Single Sites by Introducing Nitrogen Vacancies for Efficient Photo-Fenton Process

Photothermal synergistic catalytic oxidation of toluene over single-atom Pt catalysts was investigated. Compared with the conventional thermocatalytic oxidation in the dark, toluene conversion and CO2 yield over 0.39Pt1/CuO-CeO2 under simulated solar irradiation (λ = 320-2500 nm, optical power density = 200 mW cm-2) at 180 °C could be increased about 48%. An amount of CuO was added to CeO2 to disperse single-atom Pt with a maximal Pt loading of 0.83 wt %. The synergistic effect between photo- and thermocatalysis is very important for the development of new pollutant treatment technology with high efficiency and low energy consumption. Both light and heat played an important role in the present photothermal synergistic catalytic oxidation. 0.39Pt1/CuO-CeO2 showed good redox performance and excellent optical properties and utilized the full-spectrum solar energy. Light illumination induced the generation of reactive oxygen species (•OH and •O2-), which accelerated the transformation of intermediates, promoted the release of active sites on the catalyst surface, and improved the oxidation reaction.

Photothermal Synergistic Effect of Pt1/CuO-CeO2 Single-Atom Catalysts Significantly Improving Toluene Removal.

Electrostatic self-assembly of 2D/2D CoWO4/g-C3N4 p—n heterojunction for improved photocatalytic hydrogen evolution: Built-in electric field modulated charge separation and mechanism unveiling

To overcome the main challenge of low photocatalytic efficiency and high energy consumption of thermocatalysis in the oxidation of volatile organic compounds (VOCs), MOF-derived mesoporous disk-like y Pd/ x N-TiO 2 ( x = 3.2, 5.5, 7.7 wt%, and y = 0.26 wt%) were prepared by ball milling-calcination method for photothermal catalytic oxidation of ethyl acetate. Morphological and pore structure characterization indicated that Pd/N-TiO 2 had abundant pore structure and large specific surface area, which facilitated the adsorption of pollutants on the active sites. Among the catalysts, 0.26 Pd/3.2N-TiO 2 exhibited optimal photothermal catalytic performance. The corresponding temperature required for 50 and 90% conversion of ethyl acetate was 192 and 212 o C, with the specific reaction rate of 0.95 µmol/(g Pd s) at 150 o C. Doping of N and loading of Pd nanoparticles enhanced the light absorption capacity, promoted the charge separation, and the adsorption capacity of ethyl acetate, resulting in a high photothermal catalytic oxidation activity. The detection of free radicals indicated that the photothermal synergy was associated with the generation of reactive oxygen species over 0.26 Pd/3.2N-TiO 2 under light irradiation condition, which directly participated in the catalytic removal of ethyl acetate. A proper increase in temperature could also promote the migration of carriers. The photothermal catalytic oxidation of VOCs over MOF-derivatives had great potential application for environmental protection. • MOF-derived mesoporous disk-like Pd/N-TiO 2 is prepared by a simple ball milling-calcination method. • The Pd/N-TiO 2 catalyst shows better photo-thermo catalytic performance for ethyl acetate oxidation. • The Pd/N-TiO 2 catalyst exhibits the excellent adsorption capacity of ethyl acetate and optical property. • OOH species due to the introduction of water improves the photo-thermal performance. • Photo-thermal synergy is due to more reactive oxygen species generation under light conditions. 

Photothermal synergistic catalytic oxidation of ethyl acetate over MOFs-derived mesoporous N-TiO2 supported Pd catalysts

Direct selective methane photooxidation to liquid oxygenates with high productivity and selectivity under mild reaction conditions is highly urgent but remains challenging. Herein, a Cu and W codoped TiO2 (Cu–W–TiO2) photocatalyst was fabricated to enable aerobic oxidation of methane into oxygenates with limited formation of CO2 under ambient temperature. A high oxygenate productivity of 34.5 mmol g–1 with a remarkable selectivity of 97.1% was achieved over the Cu–W–TiO2 photocatalyst. Based on structural characterizations and mechanism studies, it was suggested that the Cu species acted as hole traps, while oxygen vacancies and the W6+-dopant state worked as electron traps. The inhibited recombination of photogenerated carriers contributed to enhanced photocatalytic efficiency. The modulated electronic and band structure promoted the activation of methane and hindered the overoxidation of oxygenates. 

Selective Photocatalytic Oxidation of Methane to Oxygenates over Cu–W–TiO2 with Significant Carrier Traps

Hydroxyl radicals (•OH) generated in the photocatalytic process are crucial to the conversion of methane (CH4) to value-added methanol (CH3OH) at room temperature. However, utilizing noble metal-free catalysts and low-energy photons of solar light, such as visible and near-infrared light (vis-NIR), is difficult to provide more electron states to form •OH radicals. Here, we developed FeOOH/Li0.1WO3 core-shell nanorods via a two-step in/out co-modification of hexagonal tungsten oxide (h-WO3): (1) lithium ions intercalating into the hexagonal tunnels of h-WO3 to form Li0.1WO3 nanorods and (2) using FeOOH-wrapped Li0.1WO3 to obtain FeOOH/Li0.1WO3 core-shell nanorods. Introduction of lithium induces polaron transition in Li0.1WO3, enabling the absorption of vis-NIR light. Interestingly, FeOOH-based Fenton-like reaction when H2O2 is selected as an oxidant favors the generation of more •OH radicals available for CH4 oxidation to CH3OH. Meanwhile, FeOOH with FeIII as an "electron sink" highly improves the separation of photoinduced electrons and holes in Li0.1WO3. Eventually, efficient selective formation of CH4OH is achieved with remarkable generation rates up to ∼342 and ∼160 μmol g-1 at visible light (420-700 nm) and NIR light (≥800 nm), respectively. Our finding opens up new possibilities for developing noble metal-free catalysts for solar energy-driven CH4 conversion to CH3OH under ambient conditions.

Noble Metal-Free FeOOH/Li0.1WO3 Core-Shell Nanorods for Selective Oxidation of Methane to Methanol with Visible-NIR Light.

Atomic-scale metals as active center have been widely investigated for efficient photocatalysis. Understanding the specific electronic structure of atomic-scale center is of frofound fundamental importance for superior catalytic performance. Here, we report an atomically dispersed gold on tungsten trioxide (Au1/WO3) catalyst for photocatalytic oxidation of methane toward value-added methanol. The Au1 species reveal a specific tip-enhanced local electrons field which favors the C-H dehydrogenation of methane and thus form methanol (up to 589 µmol g-1 h-1). Both experimental and theoretical results demonstrate such tip-enhanced effect-dependent activity of methane oxidation. The theoretical calculations further reveal a lower adsorption energy of product methanol on Au1, in contrast to Au particles, which suppresses the overoxidation of methanol, and thus promotes its selectivity. Establishing the electric structure-activity may create a platform for designing efficient atomic-scale catalysts for C1 catalysis and green chemistry.

Anhua Huang

Papers

Noble Metal-Free FeOOH/Li0.1WO3 Core-Shell Nanorods for Selective Oxidation of Methane to Methanol with Visible-NIR Light.

Photocatalytic Oxidation of Methane to Methanol by Tungsten Trioxide-supported Atomic Gold at Room Temperature