Molecularly Engineered Covalent Organic Frameworks for Hydrogen Peroxide Photosynthesis.

Synthesizing H2 O2 from water and air via a photocatalytic approach is ideal for efficient production of this chemical at small-scale. However, the poor activity and selectivity of the 2 e- water oxidation reaction (WOR) greatly restricts the efficiency of photocatalytic H2 O2 production. Herein we prepare a bipyridine-based covalent organic framework photocatalyst (denoted as COF-TfpBpy) for H2 O2 production from water and air. The solar-to-chemical conversion (SCC) efficiency at 298 K and 333 K is 0.57 % and 1.08 %, respectively, which are higher than the current reported highest value. The resulting H2 O2 solution is capable of degrading pollutants. A mechanistic study revealed that the excellent photocatalytic activity of COF-TfpBpy is due to the protonation of bipyridine monomer, which promotes the rate-determining reaction (2 e- WOR) and then enhances Yeager-type oxygen adsorption to accelerate 2 e- one-step oxygen reduction. This work demonstrates, for the first time, the COF-catalyzed photosynthesis of H2 O2 from water and air; and paves the way for wastewater treatment using photocatalytic H2 O2 solution.

Sterilization of Escherichia coli by Photothermal Synergy of WO3-x/C Nanosheet under Infrared Light Irradiation.

The application of photocatalytic sterilization technology for the sterilization of water has been broadly studied in recent years. However, developing photocatalysts with high disinfection efficiency remains an urgent challenge. Tungsten trioxide with coexisting oxygen vacancies and carbon coating (WO3-x/C) has been successfully synthesized toward the photothermal inactivation of Escherichia coli. Oxygen vacancies and carbon coating bring WO3-x/C strong absorption in the infrared region and enhance the carrier separation efficiency. As a result, a higher sterilization rate is obtained compared to WO3. WO3-x/C can completely inactivate E. coli under infrared light within 40 min through photothermal synergy process. During the process of inactivating bacteria over WO3-x/C, E. coli is killed by the destruction of their cell membrane to decrease the activity of enzymes and release the cell contents, which can be ascribed to the efficient generation of reactive oxygen species (O2•- and •OH) and thermal effect. This work demonstrates a novel approach for engineering efficient and energy-saving catalysts for water sterilization.

A Metal-Free Donor-Acceptor Covalent Organic Framework Photocatalyst for Visible-Light-Driven Reduction of CO2 with H2 O.

Visible-light-driven CO2 reduction to valuable chemicals without sacrificial agents and cocatalysts remains challenging, especially for metal-free photocatalytic systems. Herein, a novel donor-acceptor (D-A) covalent organic framework (CT-COF) was constructed by the Schiff-base reaction of carbazole-triazine based D-A monomers and possessed a suitable energy band structure, strong visible-light-harvesting, and abundant nitrogen sites. CT-COF as a metal-free photocatalyst could reduce CO2 with gaseous H2 O to CO as the main carbonaceous product with approximately stoichiometric O2 evolution under visible-light irradiation and without cocatalyst. The CO evolution rate (102.7 µmol g-1 h-1 ) was 68.5 times that of g-C3 N4 under the same conditions. In situ Fourier-transform (FT)IR analysis indicated that CT-COF could adsorb and activate the CO2 and H2 O molecules and that COOH* species may be a key intermediate. DFT calculations suggested that nitrogen atoms in the triazine rings may be photocatalytically active sites.