Application of Metal-organic Framework Materials (MOFs) in the photocatalytic CO2 Reduction：A mini review

In recent years, the effective use of CO2 has become one of the research hotspots worldwide to solve environmental pollution and energy shortage, whose excessive emission led to increasingly serious global environmental problems. Metal-organic frameworks (MOFs), with extraordinary specific surface areas, tunable surface chemistry, fast electron migration rate, large CO2 adsorption capacity, etc． are a new class of functional materials composed of metal ions/clusters and organic ligands, which have broad application potential in CO2 photocatalytic reduction. This paper systematically generalized the composition of the structure, discussed the methods of synthetics and expounded the photocatalytic properties and photocatalytic mechanism of MOFs. In addition, the application and research progress of MOFs functional materials in recent research are reviewed. The article also summarized challenges and prospects for the large-scale photocatalytic applications of MOFs catalysts. It guides the preparation of novel modified MOFs photocatalysts for high-efficiency applications in the field of CO2 reduction and photocatalytic degradation of dyes.

Study on Photocatalytic Desulfurization and Denitrification Performance of Cu- and Cr-Modified MWCNT

Carbon nanotubes are a promising adsorbent for desulfurization and denitrification. In this paper, Cu- and Cr-doped TiO2 supported by multi-walled carbon nanotubes (MWCNTs/Cu-Cr-TiO2) were synthesized by the sol-gel method. Characterizations of the samples were performed by TEM, XPS, XRD, DRS, and BET. The experiments of simultaneous desulfurization and denitrification were conducted in a fixed-bed reactor. The results showed that the adsorbent with a Cu to Cr molar ratio of 3 displays excellent adsorption property. The SO2 and NO adsorption capacity of MWCNTs/Cu-Cr-TiO2 (Cu/Cr = 3) were 36.83 and 12.34 mg/g under the optimal experimental operating parameters (SO2 content: 1575 mg/m3, NO content 736 mg/m3, O2 content 8%, H2O content 5%, and space velocity 1003 h−1). The adsorption capacity of MWCNTs/Cu-Cr-TiO2 was significantly better than that of the adsorbent doped with Cu or Cr alone (MWCNTs/Cu-TiO2 and MWCNTs/Cr-TiO2). Compared with single metal doping, bimetallic multivalent states accelerate the electron migration and separation from holes, which increase the number of oxygen vacancies and enhance the adsorption of SO2 and NO. The kinetic models and the reaction mechanism of the desulfurization and denitrification were also analyzed in this work.

Filming movies of attosecond charge migration with high harmonic spectroscopy

Electron migration in molecules is the progenitor of chemical reactions and biological functions after light-matter interaction. Following this ultrafast dynamics, however, has been an enduring endeavor. Recently, it has been suggested that high-harmonic spectroscopy (HHS) is able to probe dynamics with attosecond temporal and sub-˚angstr¨om spatial resolution. Still, real-time visualization of single-molecule dynamics continues to be a great challenge because experimental harmonic spectra are due to the coherent averages of light emission from individual molecules of different alignments. Here we demonstrate that the uniting of machine learning (ML) algorithm and HHS in two-color laser pulses enables us to retrieve the complex amplitude and phase of harmonics from single fixed-in-space molecule. From the complex single-molecule dipoles for different harmonics, we construct a movie of electron migration after tunnel ionization of the molecules at time steps of 50 attoseconds. Moreover, the angular dependence of molecular charge migration is fully resolved. By examining the movie, we observe that electron holes do not just “migrate” along the laser direction, but may “swirl” around the atom centers. Our ML-based HHS establishes a general reconstruction scheme for studying ultrafast charge migration in molecules, paving a way for further advance in tracing and controlling photochemical reactions by femtosecond lasers.

Fabrication of Highly Textured 2D SnSe Layers with Tunable Electronic Properties for Hydrogen Evolution

Hydrogen is regarded to be one of the most promising renewable and clean energy sources. Finding a highly efficient and cost-effective catalyst to generate hydrogen via water splitting has become a research hotspot. Two-dimensional materials with exotic structural and electronic properties have been considered as economical alternatives. In this work, 2D SnSe films with high quality of crystallinity were grown on a mica substrate via molecular beam epitaxy. The electronic property of the prepared SnSe thin films can be easily and accurately tuned in situ by three orders of magnitude through the controllable compensation of Sn atoms. The prepared film normally exhibited p-type conduction due to the deficiency of Sn in the film during its growth. First-principle calculations explained that Sn vacancies can introduce additional reactive sites for the hydrogen evolution reaction (HER) and enhance the HER performance by accelerating electron migration and promoting continuous hydrogen generation, which was mirrored by the reduced Gibbs free energy by a factor of 2.3 as compared with the pure SnSe film. The results pave the way for synthesized 2D SnSe thin films in the applications of hydrogen production.

Filming movies of attosecond charge migration with high harmonic spectroscopy

Ultrafast electron migration in molecules is the progenitor of all chemical reactions and biological functions after light-matter interaction [1–4]. Following this ultrafast dynamics, however, has been an enduring endeavor [5, 6]. Recently, it has been shown that high-harmonic spectroscopy (HHS) is able to probe dynamics with attosecond temporal and sub-angstrom spatial resolution [7–10]. Still, real-time visualization of single-molecule dynamics continues to be a great challenge because experimental harmonic spectra are due to the coherent averages of light emission from individual molecules of different alignments. Here, we show that from high harmonics generated with single-color and two-color probe lasers in a pump-probe experiment, the complex amplitude and phase of harmonics from a single fixed-in-space molecule can be reconstructed using modern machine learning (ML) algorithm. From the complex single-molecule dipoles for different harmonics, we construct a series of film clips of hole density distributions of the cation at time steps of 50 attoseconds (1 as=10^{−18} s) to make a classical “movie” of electron migration after tunnel ionization of the molecule. Moreover, the angular dependence of molecular charge migration is fully resolved. By examining these clips, we observed that holes do not just “migrate” along the laser direction, but they may “swirl” around the atom centers. The ML-based HHS proposed here establishes a general reconstruction scheme for studying ultrafast charge migration in molecules, paving a way for further advance in tracing and controlling photochemical reactions by femtosecond lasers.

Co-Zn-MOFs Derived N-Doped Carbon Nanotubes with Crystalline Co Nanoparticles Embedded as Effective Oxygen Electrocatalysts

The oxygen reduction reaction (ORR) is a crucial step in fuel cells and metal-air batteries. It is necessary to expand the range of efficient non-precious ORR electrocatalysts on account of the low abundance and high cost of Pt/C catalysts. Herein, we synthesized crystalline cobalt-embedded N-doped carbon nanotubes (Co@CNTs-T) via facile carbonization of Co/Zn metal-organic frameworks (MOFs) with dicyandiamide at different temperatures (t = 600, 700, 800, 900 °C). Co@CNTs- 800 possessed excellent ORR activities in alkaline electrolytes with a half wave potential of 0.846 V vs. RHE (Reversible Hydrogen Electrode), which was comparable to Pt/C. This three-dimensional network, formed by Co@CNTs-T, facilitated electron migration and ion diffusion during the ORR process. The carbon shell surrounding the Co nanoparticles resulted in Co@CNTs-800 being stable as an electrocatalyst. This work provides a new strategy to design efficient and low-cost oxygen catalysts.

Construction of a 3D/2D g-C3N4/ZnIn2S4 hollow spherical heterostructure for efficient CO2 photoreduction under visible light

The 3D/2D g-C3N4/ZnIn2S4 hollow spherical heterostructure can greatly increase visible light absorption and improve the efficiency of photo-generated electron migration and conversion, resulting in an excellent CO generation rate.