Thin Zinc Oxide Layer Passivating Bismuth Vanadate for Selective Photoelectrochemical Water Oxidation to Hydrogen Peroxide.

Selective photoelectrochemical (PEC) water oxidation to hydrogen peroxide is an underexplored option as opposed to the mainstream oxygen reduction reaction. Albeit interesting, selective H2 O2 production via oxidative pathway is plagued by the noncontrollable two-electron transfer reaction and the overoxidation of the thus-formed H2 O2 to O2 . Here, ZnO passivator-coated BiVO4 photoanode is reported for selective PEC H2 O2 production. Both the H2 O2 selectivity and production rate increase in the range of 1.0-2.0 V versus RHE under simulated sunlight irradiation. The photoelectrochemical impedance spectra and open-circuit potentials suggest a flattened band bending and positively shifted quasi-Fermi level of BiVO4 upon ZnO coating, facilitating H2 O2 generation and suppressing the competitive reaction of O2 evolution. The ZnO overlayer also inhibits H2 O2 decomposition, accelerates charge extraction from BiVO4 , and serves as a hole reservoir under photoexcitation. This work offers insights into surface states and the role of the coating layer in manipulating two/four-electron transfer for selective H2 O2 synthesis from PEC water oxidation.

Improving the Fenton catalytic performance of FeOCl using an electron mediator.

FeOCl Fenton-like catalyst has drawn much attention due to its high catalytic activity. Nevertheless, the potential application of FeOCl is significantly hindered by the sluggish reduction kinetics of Fe3+ to active Fe2+. Here, we report that the incorporation of Fe - O-Mo electron mediator into FeOCl via forming a FeOCl/MoS2 composite can facilitate the Fe2+ regeneration through the oxidation of Mo4+ to Mo6+, which boosts the hydroxyl radicals yields, thus leading to a significantly improved catalytic performance. The removal efficiency of methylene blue (MB, 50 mg L-1) achieves ∼100% within 2 min. with low dosage of FeOCl/MoS2 (0.2 g L-1) and H2O2 (0.6 mM). FeOCl/MoS2 not only has broad working pH range (∼3 - 9) and high salinity tolerance (100 mM), but also capable to degrade various organic pollutants. For practical application, the fabricated FeOCl/MoS2 membrane effectively degrades continuous MB flow. This study demonstrates that incorporating an electron mediator is an effective way to improve the catalytic performance of heterogeneous Fenton-like catalysts.

Graphene oxide and carbon nanodots co-modified BiOBr nanocomposites with enhanced photocatalytic 4-chlorophenol degradation and mechanism insight.

Non-metallic graphene oxide (GO) and carbon nanodots (CDots) co-doped BiOBr ternary system (GO/CDots/BiOBr) were successfully synthesized via a simple one-step solvothermal process. The compositional characterization, optical and electrical properties of photocatalysts were investigated in detail. The prepared ternary photocatalysts possessed the excellent visible-light driven photocatalytic 4-chlorophenol (4-CP) degradation. Additionally, the 4-CP removal efficiencies decreased in the order of GO/CDots/BiOBr (88.9%) > CDots/BiOBr (62.9%) > GO/BiOBr (60.5%) > pristine BiOBr (46.9%) in 6 h under visible light irradiation. The dissolved organic carbon (DOC) removal and the dechlorination efficiency by the GO/CDots/BiOBr were 58.4% and 78.2%, respectively, much higher than pristine BiOBr. The co-existence of GO and CDots on the BiOBr greatly promoted visible light harvesting and utilizing ability and inhibited the recombination of photogenerated electron/hole pairs. The synergistic effect between GO, CDots and BiOBr was expounded, and the photocatalytic reaction mechanism was proposed in detail via the band structure analysis and free radical trapping experiments.