Mingbo Ruan

Growth Mechanism Deconvolution of Self-Limiting Supraparticles Based on Microfluidic System

The synthesis of colloidal supraparticles (SPs) based on self-assembly of nanoscopic objects has attracted much attention in recent years. Here, we demonstrate the formation of self-limiting monodisperse gold SPs with core-shell morphology based on the building blocks of flexible nanoarms in one step. A flow-based microfluidic chip is utilized to slow down the assembly process of the intermediates, which surprisingly allows for observation of ultrathin gold nanoplates as first intermediates. Notably, these intermediate cannot be observed in traditional synthesis due to their rapid rolling-up to form the second-order nanostructure of flexible hollow nanoarms. The growth mechanism of SPs can then be deconvoluted into two seed-mediated steps. Monte Carlo simulations confirm that the self-limiting growth of binary SPs is governed by a balance between electrostatic repulsion and van der Waals attraction.

Single-molecule chemical reaction reveals molecular reaction kinetics and dynamics

Understanding the microscopic elementary process of chemical reactions, especially in condensed phase, is highly desirable for improvement of efficiencies in industrial chemical processes. Here we show an approach to gaining new insights into elementary reactions in condensed phase by combining quantum chemical calculations with a single-molecule analysis. Elementary chemical reactions in liquid-phase, revealed from quantum chemical calculations, are studied by tracking the fluorescence of single dye molecules undergoing a reversible redox process. Statistical analyses of single-molecule trajectories reveal molecular reaction kinetics and dynamics of elementary reactions. The reactivity dynamic fluctuations of single molecules are evidenced and probably arise from either or both of the low-frequency approach of the molecule to the internal surface of the SiO2 nanosphere or the molecule diffusion-induced memory effect. This new approach could be applied to other chemical reactions in liquid phase to gain more insight into their molecular reaction kinetics and the dynamics of elementary steps.

Catalytic properties of graphitic and pyridinic nitrogen doped on carbon black for oxygen reduction reaction

Pure graphitic nitrogen (G-N) was doped on carbon black by Hummers method and a following heat treatment was used to transform the G-N to pyridinic (P)-N. An oxygen reduction reaction (ORR) study showed that the G-N site doped on carbon gave a two-electron ORR with H 2 O 2 as the main product, while the P-N site gave the four-electron process of ORR and decreased the production of H 2 O 2 . The results help the understanding and design of doped N-based ORR electrocatalysts.

Theoretical Study of Resorufin Reduction Mechanism by NaBH4

In the current work, the whole reduction mechanism of resorufin by sodium borohydride (NaBH4) has been investigated completely using quantum chemical theory for the first time. The possible pathways for each step were considered as much as possible. The calculated results reveal that the reduction mechanism for resorufin undergoes a nucleophilic addition with BH4(-), a synchronous proton abstraction from a carbon (C) atom, a protonation in a nitrogen (N) atom, and then a final hydrolysis process to obtain final reduced product dihydroresorufin. Interestingly, it was found that the protonation of N atom could induce a reduced product molecule with a Λ-type structure rather than a planar one, and the large alteration in geometry will induce different optical properties, such as fluorescent or nonfluorescent. More importantly, countercation Na(+) and solvation effect of H2O play important roles in reducing the activation energy in elementary steps, and their stabilization effect has been confirmed by NBO analysis. The detailed theoretical investigation for the reduction reaction of resorufin by NaBH4 will support some guidance for the similar reduction reaction for organic compounds like aldehydes and ketones.

A Bifunctional Highly Efficient FeNx/C Electrocatalyst

Herein, a type of Fe, N-codoped carbon electrocatalyst (FeNx /C, Fe-N-BCNT#BP) containing bamboo carbon nanotubes and displaying bifunctional high catalytic efficiency for both oxygen reduction reaction (ORR) and carbon dioxide reduction reaction (CO2RR) is reported. It shows high electrocatalytic activity and stability for both the ORR process with onset potential of 1.03 VRHE in alkaline and the CO2RR to CO with high faradic efficiency up to 90% and selectivity of about 100% at low overpotential of 0.49 V. For CO2RR to CO, it is revealed that Fe3 C is active but the activity of FeNx centers is lower than that of C-N-based centers, contrary with that observed for ORR. Due to its low cost and high electrocatalytic performance for these two reduction reactions, the obtained catalyst is very promising for extensive application in future. The revealed huge activity difference of the same types of active sites for different reactions can efficiently guide the synthesis of advanced materials with multifunction.