Zhimin Ao

Bio: Zhimin Ao is an academic researcher from Guangdong University of Technology. The author has contributed to research in topics: Catalysis & Graphene. The author has an hindex of 43, co-authored 166 publications receiving 7167 citations. Previous affiliations of Zhimin Ao include Jilin University & University of Technology, Sydney.

MoS2/Graphene Composite Anodes with Enhanced Performance for Sodium‐Ion Batteries: The Role of the Two‐Dimensional Heterointerface

Abstract: Graphene has been widely used as conformal nanobuilding blocks to improve the electrochemical performance of layered metal sulfides (MoS2, WS2, SnS, and SnS2) as anode materials for sodium-ion batteries. However, it still lacks in-depth understanding of the synergistic effect between these layered sulfides and graphene, which contributes to the enhanced electroactivity for sodium-ion batteries. Here, MoS2/reduced graphene oxide (RGO) nanocomposites with intimate two-dimensional heterointerfaces are prepared by a facile one-pot hydrothermal method. The heterointerfacial area can be effectively tuned by changing the ratio of MoS2 to RGO. When used as anode materials for sodium-ion batteries, the synergistic effect contributing to the enhanced reversible capacity of MoS2/RGO nanocomposites is closely related with the heterointerfacial area. The computational results demonstrate that Na prefers to be adsorbed on MoS2 in the MoS2/RGO heterostructure rather than intercalate into the MoS2/RGO heterointerface. Interestingly, the MoS2/RGO heterointerfaces can significantly increase the electronic conductivity of MoS2, store more Na ions, while maintaining the high diffusion mobility of Na atoms on MoS2 surface and high electron transfer efficiency from Na to MoS2. It is expected that the efforts to establish the correlation between the two-dimensional heterointerface and the electrochemical sodium-ion storage performance offer fundamental understanding for the rational design of layered metal sulfides/graphene composites as high-performance electrode materials for sodium-ion batteries.

Nitrogen-Doped Graphene for Generation and Evolution of Reactive Radicals by Metal-Free Catalysis

Abstract: N-Doped graphene (NG) nanomaterials were synthesized by directly annealing graphene oxide (GO) with a novel nitrogen precursor of melamine. A high N-doping level, 8–11 at. %, was achieved at a moderate temperature. The sample of NG-700, obtained at a calcination temperature of 700 °C, showed the highest efficiency in degradation of phenol solutions by metal-free catalytic activation of peroxymonosulfate (PMS). The catalytic activity of the N-doped rGO (NG-700) was about 80 times higher than that of undoped rGO in phenol degradation. Moreover, the activity of NG-700 was 18.5 times higher than that of the most popular metal-based catalyst of nanocrystalline Co3O4 in PMS activation. Theoretical calculations using spin–unrestricted density functional theory (DFT) were carried out to probe the active sites for PMS activation on N-doped graphene. In addition, experimental detection of generated radicals using electron paramagnetic resonance (EPR) and competitive radical reactions was performed to reveal the PMS...

Occurrence of radical and nonradical pathways from carbocatalysts for aqueous and nonaqueous catalytic oxidation

Abstract: Metal-free activation of superoxides provides an efficient and environmentally benign strategy for heterogeneous catalytic oxidation. In this study, nanocarbons with varying carbon-conjugation structures and functional groups were investigated for peroxymonosulfate (PMS) activation. It was discovered that radical and nonradical oxidations could occur on different carbocatalysts depending on the carbon structure. Radical oxidation occurs exclusively on MWCNTs and CMK-3, similar to a metal oxide, MnO2. Both radical and nonradical oxidations are very pronounced in nanodiamond (AND-900)/PMS whilst nonradical oxidation is dominated in reduced graphene oxide (rGO-900)/PMS. Density functional theory (DFT) calculations were employed to explore the PMS adsorption and O O bond activation on the different carbon configurations for an in-depth probe of the activation mechanism. The intact sp2-conjugated π system in MWCNTs and electron-rich ketonic groups (as Lewis basic sites) in CMK-3 can stimulate PMS dissociation to generate SO4 − and OH, similar to metal-based catalysts. However, the defective edges at the boundary of carbon network are able to facilitate the organic degradation without generation of the reactive radicals, which is well supported by both experiments and the DFT calculation. The emerging nonradical oxidation induced by the carbocatalysis is superior to the radical oxidation on most metal oxides for effective degradation of various organics. The influences of solution pH, various anions (H2PO42−, HCO3− and Cl−) and background organic matters (humic acid) on the nonradical oxidation were further evaluated. The nonradical oxidation on carbocatalysts can be utilized as a green and effective oxidation strategy for aqueous environmental remediation and nonaqueous phase oxidation.

Core-shell magnetic Fe3O4@Zn/Co-ZIFs to activate peroxymonosulfate for highly efficient degradation of carbamazepine

Abstract: A core-shell metal-organic framework encapsulated Fe3O4 magnetic particles (Fe3O4@Zn/Co-ZIFs) was designed and synthesized successfully to activate peroxymonosulfate (PMS) for carbamazepine (CBZ) degradation. It exhibits superior catalytic performance since the unique interior structure and synergistic effect between ZIFs shell and Fe3O4 core, achieving 100% removal of CBZ (5 mg/L) within 30 min. The outer wrapping structure of ZIF-8 can stabilize the ZIF-67 and Fe3O4 under intricate reaction conditions to restrain the leaching of Co ions (as low as 0.067 mg/L). Further investigation found that both SO4 – and OH contribute to the degradation of CBZ at initial stage, and SO4 – gradually plays a pivotal role with the reaction time prolonging. The acceleration of electron transfer between Fe3O4 and cobalt active sites of Zn/Co-ZIFs could induce the redox cycling of Co2+ and Co3+. The possible degradation pathway was proposed by analyzing intermediates. This work extends the development of MOFs materials for environmental remediation.

Graphene: The New Two-Dimensional Nanomaterial

Abstract: Every few years, a new material with unique properties emerges and fascinates the scientific community, typical recent examples being high-temperature superconductors and carbon nanotubes. Graphene is the latest sensation with unusual properties, such as half-integer quantum Hall effect and ballistic electron transport. This two-dimensional material which is the parent of all graphitic carbon forms is strictly expected to comprise a single layer, but there is considerable interest in investigating two-layer and few-layer graphenes as well. Synthesis and characterization of graphenes pose challenges, but there has been considerable progress in the last year or so. Herein, we present the status of graphene research which includes aspects related to synthesis, characterization, structure, and properties.

Sodium-ion batteries: present and future

Abstract: Energy production and storage technologies have attracted a great deal of attention for day-to-day applications. In recent decades, advances in lithium-ion battery (LIB) technology have improved living conditions around the globe. LIBs are used in most mobile electronic devices as well as in zero-emission electronic vehicles. However, there are increasing concerns regarding load leveling of renewable energy sources and the smart grid as well as the sustainability of lithium sources due to their limited availability and consequent expected price increase. Therefore, whether LIBs alone can satisfy the rising demand for small- and/or mid-to-large-format energy storage applications remains unclear. To mitigate these issues, recent research has focused on alternative energy storage systems. Sodium-ion batteries (SIBs) are considered as the best candidate power sources because sodium is widely available and exhibits similar chemistry to that of LIBs; therefore, SIBs are promising next-generation alternatives. Recently, sodiated layer transition metal oxides, phosphates and organic compounds have been introduced as cathode materials for SIBs. Simultaneously, recent developments have been facilitated by the use of select carbonaceous materials, transition metal oxides (or sulfides), and intermetallic and organic compounds as anodes for SIBs. Apart from electrode materials, suitable electrolytes, additives, and binders are equally important for the development of practical SIBs. Despite developments in electrode materials and other components, there remain several challenges, including cell design and electrode balancing, in the application of sodium ion cells. In this article, we summarize and discuss current research on materials and propose future directions for SIBs. This will provide important insights into scientific and practical issues in the development of SIBs.