Chiral Nanostructured Ag Films for Multicarbon Products from CO2 Electroreduction.

The formation of multicarbon products from CO2 electroreduction is challenging on materials other than Cu-based catalysts. Ag has been known to be a typical metal catalyst, producing CO in CO2 electroreduction. The formation of C2+ products by Ag has never been reported because the carbon-carbon (C-C) coupling is an unfavorable process due to the high reaction barrier energy of *OCCO. Here, we propose that the chirality-induced spin polarization of chiral nanostructured Ag films (CNAFs) can promote the formation of triplet OCCO by regulating its parallel electron spin alignment, and the helical lattice distortion of nanostructures can decrease the reaction energy of *OCCO, which triggers C-C coupling and promotes subsequent *OCCO hydrogenation to facilitate the generation of C2+ products. The CNAFs with helically lattice-distorted nanoflakes were fabricated via electrodeposition using phenylalanine as the symmetry-breaking agent. C2+ products (C2H4, C2H6, C3H8, C2H5OH, and CH3COOH) with a Faradaic efficiency of ∼4.7% and a current density of ∼22 mA/cm2 were generated in KHCO3 electrolytes under 12.5 atm of CO2 (g). Our findings propose that the chiral nanostructured materials can regulate the multifunctionality of catalytic performance in the catalytic reactions with triplet intermediates and products.

DNA-Assisted Creation of a Library of Ultrasmall Multimetal/Metal Oxide Nanoparticles Confined in Silica.

Supported ultrasmall metal/metal oxide nanoparticles (UMNPs) with sizes in the range of 1-5 nm exhibit unique properties in sensing, catalysis, biomedicine, etc. However, the metal-support and metal-metal precursor interactions were not as well controlled to stabilize the metal nanoparticles on/in the supports. Herein, DNA is chosen as a template and a ligand for the silica-supported UMNPs, taking full use of its binding ability to metal ions via either electrostatic or coordination interactions. UMNPs thus are highly dispersed in silica via self-assembly of DNA and DNA-metal ion interactions with the assistance of a co-structural directing agent (CSDA). A large number of metal ions are easily retained in the mesostructured DNA-silica materials, and their growth is controlled by the channels after calcination. Based on this directing concept, a material library, consisting of 50 mono- and 54 bicomponent UMNPs confined within silica and with narrow size distribution, is created. Theoretical calculation proves the indispensability of DNA with combination of several organics in the synthesis of ultrasmall metal nanoparticles. The Pt-silica and Pt/Ni-silica chosen from the library exhibit good catalytic performance for toluene combustion. This generalizable and straightforward synthesis strategy is expected to widen the corresponding applications of supported UMNPs.

DFT study on Ag loaded 2H-MoS2 for understanding the mechanism of improved photocatalytic reduction of CO2.

Transition metal modified molybdenum disulfide to improve the performance of photocatalytic reduction of carbon dioxide has been receiving much attention. Herein, a novel high-efficiency photocatalytic composite Ag/2H-MoS2 has been constructed and simulated using density functional theory (DFT) for unveiling the mechanism of improved photocatalytic reduction of CO2 in our experimental research. Our calculations about the band structure and electronic and optical properties indicate that the loading of Ag atoms enhances the photocatalytic performance of 2H-MoS2 nanosheets by transferring the photogenerated electrons from the valence band of 2H-MoS2 to the loaded Ag atoms. Furthermore, 20 wt% Ag loaded 2H-MoS2 is the most suitable for the thermodynamic requirement of reducing CO2 to CH4 among the catalysts with different Ag loadings, and the formation of *CHO in 20 wt% Ag/2H-MoS2 is the potential-determining step, whose Gibbs free energy reduces from 2.830 eV of 2H-MoS2 to 0.925 eV. Meanwhile the thermochemical results predict the best path for reducing CO2 on such a photocatalyst as CO2 → *COOH → *CO → *CHO → *CH2O → *OCH3 → *CH3OH → CH4. The photocatalytic performance of pristine 2H-MoS2 in CO2 reduction is therefore significantly improved by loading silver. This research provides a theoretical reference for transition metal modified 2H-MoS2 nanosheets.

The Z-scheme transfer of photogenerated electrons for CO2 photocatalytic reduction over g-ZnO/2H-MoS2 heterostructure.

Effective separation of the photogenerated electrons and holes is critical to improve photocatalytic efficiency. To achieve this, we design a Z-scheme g-ZnO/2H-MoS2 heterostructure to spatially separate the photogenerated carriers promoting the reduction of CO2 on the surface of the heterostructure, through density functional theory (DFT) calculations. The g-ZnO/2H-MoS2 heterostructure has a narrow band gap, which is beneficial to speed up the transport of carriers. Simultaneously, the designed heterostructure forms a built-in electric field between the layers to cause band bending, which is very conducive to separate the photogenerated electrons on g-ZnO and the photogenerated holes on 2H-MoS2, and suppress their recombination effectively. Furthermore, the reaction mechanism of photocatalytic reduction of CO2 to CH4 on g-ZnO/2H-MoS2 is studied. The calculation results show that the Z-scheme charge transfer mechanism reduces the barrier of the potential energy control step compared with pristine g-ZnO and 2H-MOS2. Our calculations lay a theoretical foundation for designing and developing high performance photocatalysts for the photocatalytic reduction of CO2.

Cobalt-based ZIF coordinated hybrids with defective TiO2-x for boosting visible light-driven photo-Fenton-like degradation of bisphenol A.

Designing heterostructure of photocatalyst as an efficient approach to boost visible light-driven photocatalytic degradation, we prepared a series of cobalt-based ZIF coordinated with defective TiO2-x, denoted as B-TiO2-x@ZIF-67 composites, through wrapping defective B-TiO2-x on ZIF-67 for promoting photocatalytic degradation efficiency of biphenyl A. The B-TiO2-x@ZIF-67 composites displayed superior photocatalytic performance to pure TiO2-x or ZIF-67 because of faster separation of photogenerated charge carriers and more suitable redox potentials. Such a novel photo-Fenton-like system composed of B-TiO2-x@ZIF-67/H2O2/visible light accelerated the peroxidative degradation of biphenyl An up to a removal efficiency of 95.30%, which is also higher than that of photocatalysis or Fenton-like reaction alone. In addition, the degradation efficiency of biphenyl A is unchanged after catalyst reuse of four cycles. Integrating the trapping experiments and electrochemical analysis, we found the oxygen vacancy on B-TiO2-x capturing the electrons to promote the separation of photogenerated charges, meanwhile the Co(II) in the composite decomposed hydrogen peroxide (H2O2) to produce more •OH radical. Both of them mutually boosted the removal efficiency. Finally, feasible degradation pathways of biphenyl A were proposed based on the assay of LC-MS spectrometry. This strategy offers a novel insight into fabrication of Co-ZIF-based TiO2-x materials and application to visible light-driven photocatalytic and Fenton-like degradation reaction.