Tuning Local Coordination Environments of Manganese Single-Atom Nanozymes with Multi-Enzyme Properties for Selective Colorimetric Biosensing.

Single-atom nanozymes (SAzymes) are promising in next-generation nanozymes, nevertheless, how to rationally modulate the microenvironment of SAzymes with controllable multi-enzyme properties is still challenging. Herein, we systematically investigate the relationship between atomic configuration and multi-enzymatic performances. The constructed MnSA -N3 -coordinated SAzymes (MnSA -N3 -C) exhibits much more remarkable oxidase-, peroxidase-, and glutathione oxidase-like activities than that of MnSA -N4 -C. Based on experimental and theoretical results, these multi-enzyme-like behaviors are highly dependent on the coordination number of single atomic Mn sites by local charge polarization. As a consequence, a series of colorimetric biosensing platforms based on MnSA -N3 -C SAzymes is successfully built for specific recognition of biological molecules. These findings provide atomic-level insight into the microenvironment of nanozymes, promoting rational design of other demanding biocatalysts.

Effective Screening Route for Highly Active and Selective Metal-Nitrogen-Doped Carbon Catalysts in CO2 Electrochemical Reduction.

To identify high-efficiency metal-nitrogen-doped (M-N-C) electrocatalysts for the electrochemical CO2 -to-CO reduction reaction (CO2 RR), a method that uses density functional theory calculation is presented to evaluate their selectivity, activity, and structural stability. Twenty-three M-N4 -C catalysts are evaluated, and three of them (M = Fe, Co, or Ni) are identified as promising candidates. They are synthesized and tested as proof-of-concept catalysts for CO2 -to-CO conversion. Different key descriptors, including the maximum reaction energy, differences of the *H and *CO binding energy (ΔG*H -ΔG*CO ), and *CO desorption energy (ΔG*CO→CO( g ) ), are used to clarify the reaction mechanism. These computational descriptors effectively predict the experimental observations in the entire range of electrochemical potential. The findings provide a guideline for rational design of heterogeneous CO2 RR electrocatalysts.

Annealing effect on the microstructure and electrochemical properties of Fe2O3/H-TiNT/FTO thin film.

A layer of titanate nanotubular (H-TiNT) particles between Fe2O3 film and FTO substrate was inserted and heat-treated to improve electrochemical property of Fe2O3 for water splitting. Heat-treatment of the synthesized F2O3/H-TiNT/FTO thin film was found to significantly affect photoelectrochemical properties of the film through electrochemical impedance analysis. The film showed larger oxidation-reduction peaks of I-V characteristics and capacitive properties under UV-Vis light illumination with heat treatment temperatures during transformation of H-TiNT into anatase TiO2 phase. The overall results showed an appropriate heat treatment was a promising way to improve the electrochemical property of the photoanode film.

Enhanced water splitting by Fe2O3-TiO2-FTO photoanode with modified energy band structure.

The effect of TiO2 layer applied to the conventional Fe2O3/FTO photoanode to improve the photoelectrochemical performance was assessed from the viewpoint of the microstructure and energy band structure. Regardless of the location of the TiO2 layer in the photoanodes, that is, Fe2O3/TiO2/FTO or TiO2/Fe2O3/FTO, high performance was obtained when α-Fe2O3 and H-TiNT/anatase-TiO2 phases existed in the constituent Fe2O3 and TiO2 layers after optimized heat treatments. The presence of the Fe2O3 nanoparticles with high uniformity in the each layer of the Fe2O3/TiO2/FTO photoanode achieved by a simple dipping process seemed to positively affect the performance improvement by modifying the energy band structure to a more favorable one for efficient electrons transfer. Our current study suggests that the application of the TiO2 interlayer, together with α -Fe2O3 nanoparticles present in the each constituent layers, could significantly contribute to the performance improvement of the conventional Fe2O3 photoanode.

Preparation of hydrogen titanate nanotube/FTO glass thin film obtained by the layer-by-layer-self assembling method for water splitting.

Hydrogen titanate nanotube (H-TiNT) particles were coated porously on a fluorine-doped tin oxide glass using the layer-by-layer self assembling method and then heat-treated at temperatures below 600 degrees C for 10 min in air. The microstructure, crystallinity, and optical absorbance of the heat-treated H-TiNT thin film were investigated using scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and UV-vis spectroscopy, respectively. Also, I-V characteristics of the fibrous H-TiNT particles in the thin film using linear cycle voltammetry under ultraviolet-A irradiation were analyzed to have a maximum current value at applied voltages with the increase in heating temperature for economic water splitting.

Crystalline characterization and photodecomposition properties of rod-shaped Na2Ti6O13 powder prepared by molten salt process.

To prepare one-dimensional nanostructured Na2Ti6O13 powder, the starting materials of TiO2, NaCl and Na2CO3 were mixed and then heat-treated at 1000 degrees C for 2 hrs in air under molten state of NaCl. Changes in shape and phase, photo absorbance and photocatalytic ability of TiO2 particle were observed controlling added amount of Na2CO3 under constant weight ratio of TiO2 to NaCl using SEM, X-ray diffractometer, Raman spectroscopy, and UV-Vis spectroscopy. The TiO2 particle was changed into rod-shape Na2Ti6O13 with the addition of Na2CO3, showing increase in optical energy band-gap of the powder as well as gradual decrease of the photo-decomposition ability.