Jiayuan Chen

Excellent low temperature performance for total benzene oxidation over mesoporous CoMnAl composited oxides from hydrotalcites

Mesoporous CoMnAl mixed metal oxide catalysts with various Co/Mn atomic ratios have been obtained by calcination at 450 °C of layered double hydroxide (LDH) precursors prepared by the NH4OH co-precipitation–hydrothermal method without distinct MnCO3 peaks. The catalysts exhibited high efficiency for total oxidation of volatile organic compounds (VOCs). The physicochemical properties of the catalysts were characterized using several analytical techniques. Among them, CoMn2AlO shows the optimal activity and the temperature required to achieve a benzene conversion of 90% (T90) was about 238 °C, with a reaction rate and activity energy (Ea) of 0.24 mmol gcat−1 h−1 and 65.77 kJ mol−1 respectively. This temperature was 47 °C lower than that on the Co3AlO sample with a lower reaction rate of 0.19 mmol gcat−1 h−1 and a higher Ea 130.31 kJ mol−1 at a high space velocity (SV = 60 000 mL g−1 h−1). The effects of calcination temperature on the textural properties and catalytic activity of the CoMn2AlO catalyst were further investigated. The as-prepared CoMn2AlO-550 sample displayed superior catalytic activity, with T90 at 208 °C, compared CoMn2AlO-450. The formation of a solid solution with high surface area, rich oxygen vacancies, high Mn4+/Mn3+ and Co3+/Co2+ ratios and low-temperature reducibility made a great contribution to the significant improvement of the catalytic activity.

Hierarchical hollow ZnO cubes constructed using self-sacrificial ZIF-8 frameworks and their enhanced benzene gas-sensing properties

Novel hierarchical ZnO hollow cubes are constructed using the interpenetrated 0D nanoparticles through directly decomposing the Zn-based metal–organic frameworks (Zn-MOF, ZIF-8). After decomposition at 450 °C for 1 h, the as-prepared ZnO well maintains the original ZIF-8 shape with relatively high surface area (45 m2 g−1), thereby realizing fast surface reaction kinetics of benzene molecules. In contrast to singular 0D ZnO nanoscale counterparts, the unique ZnO nanostructure assembly renders the well exposed surfaces and defect states, enhancing significantly chemical sensitivity towards gaseous benzene. The present work provides a facile and versatile approach for designing the high-performance chemical sensing materials.

General Synthesis of Transition‐Metal Oxide Hollow Nanospheres/Nitrogen‐Doped Graphene Hybrids by Metal–Ammine Complex Chemistry for High‐Performance Lithium‐Ion Batteries

We present a general and facile synthesis strategy, on the basis of metal-ammine complex chemistry, for synthesizing hollow transition-metal oxides (Co3 O4 , NiO, CuO-Cu2 O, and ZnO)/nitrogen-doped graphene hybrids, potentially applied in high-performance lithium-ion batteries. The oxygen-containing functional groups of graphene oxide play a prerequisite role in the formation of hollow transition-metal oxides on graphene nanosheets, and a significant hollowing process occurs only when forming metal (Co2+ , Ni2+ , Cu2+ , or Zn2+ )-ammine complex ions. Moreover, the hollowing process is well correlated with the complexing capacity between metal ions and NH3 molecules. The significant hollowing process occurs for strong metal-ammine complex ions including Co2+ , Ni2+ , Cu2+ , and Zn2+ ions, and no hollow structures formed for weak and/or noncomplex Mn2+ and Fe3+ ions. Simultaneously, this novel strategy can also achieve the direct doping of nitrogen atoms into the graphene framework. The electrochemical performance of two typical hollow Co3 O4 or NiO/nitrogen-doped graphene hybrids was evaluated by their use as anodic materials. It was demonstrated that these unique nanostructured hybrids, in contrast with the bare counterparts, solid transition-metal oxides/nitrogen-doped graphene hybrids, perform with significantly improved specific capacity, superior rate capability, and excellent capacity retention.

Designed synthesis of ultrafine NiO nanocrystals bonded on a three dimensional graphene framework for high-capacity lithium-ion batteries

The rational design and controllable synthesis of novel nanostructured metal oxide/graphene hybrid materials have attracted extensive attention for next-generation lithium ion batteries (LIBs). In this work, three dimensional (3D) graphene framework bonding ultrafine NiO nanocrystals are fabricated in situ through hydrothermal treatment and a subsequent thermal annealing strategy. During the material design process, the 2D bark-like Ni precursor which duplicated the morphology of GO was formed firstly by adjusting the amount of the structure-directing agent. Meanwhile, the 3D interconnected framework of graphene can be obtained via π–π interaction. Subsequently, thermal treatment was performed to transform the Ni precursors into NiO nanocrystals with an average particle size of 6.38 nm. The chemical bonding between the NiO nanocrystals and the graphene framework was confirmed by Raman and XPS analysis. Benefiting from the unique architecture, the hybrid anode material exhibits an ultrahigh reversible capacity of 1104 mA h g−1 at a rate of 0.2C after 250 successive cycles, and an outstanding rate capability (440 mA h g−1 at 3.0C). Moreover, superior capacity retention is also demonstrated.