No abstract

Due to its unique structure and high porosity, metal–organic frameworks (MOFs) can act not only as nanozyme materials but also as carriers to encapsulate natural enzymes and thus have received extensive attention in recent years. However, a few research studies have been conducted to investigate MOF as a template to generate and tune nanozymes in the structure and performance. In this work, the “raisin pudding”-type ZIF-67/Cu0.76Co2.24O4 nanospheres (ZIF-67/Cu0.76Co2.24O4 NSs) were obtained by rationally regulating the weight ratio of ZIF-67 and Cu­(NO3)2 in the synthesis process. Here, ZIF-67 not only acts as a template but also provides a cobalt source for the synthesis of cobalt copper oxide on the surface of ZIF-67/Cu0.76Co2.24O4 NSs with multiple enzyme-like activities. The ZIF-67/Cu0.76Co2.24O4 NSs can mimic four kinds of enzymes with peroxidase-like, glutathione peroxidase-like, superoxide dismutase-like, and laccase-like activities. Based on its laccase-like activity, an online electrochemical system for continuous monitoring of 3,4-dihydroxyphenylacetic acid with good linearity in the range of 0.5–20 μM and a detection limit of 0.15 μM was established. Furthermore, the alteration of DOPAC in the brain microdialysate before and after ischemia of the rats’ brain was also successfully recorded. This work not only raises a new idea for the synthesis of nanozyme materials with multiple enzyme activities but also provides a new solution for the detection of neurotransmitters in living brains.

Although the mature Haber–Bosch process has become the main method for ammonia production, its high energy consumption nature has motivated people to learn about nitrogenases, which can fix N2 in the atmosphere to NH3 under ambient conditions. Here we show that Bi-CeO2 nanorods with oxygen vacancies can effectively fix N2 to NH3 under ambient conditions by an electrocatalytic nitrogen reduction reaction (NRR). Bismuth has a certain electrocatalytic nitrogen reduction effect because of the strong force between the Bi 6p band and the N 2p orbital. The subsequent one-pot solvothermal method ensure the successful doping of Bi into the CeO2 structure, and the catalyst material Bi-CeO2 has sufficient adhesion with the substrate carbon paper, thereby ensuring electrode stability. Meanwhile, the introduction of a Bi atom to CeO2 is an effective strategy to increase the abundance of oxygen vacancies in CeO2 for the rate-determining step and hence better promote NRR activity compared with classic transition-metal catalysts because the electrons trapped by the oxygen vacancies present in the catalyst material can be injected into the counterbond orbitals of N2 adsorbed on the catalyst material, thereby weakening the NN triple bond for later activation and hydrogenation. The catalyst achieves a high R NH3 of 6.29 μg h–1 cm–2 with a Faradaic efficiency (FE) of 8.56% at −0.5 V (vs RHE) in 0.5 M K2SO4 at room temperature. This Article provides a new avenue for the design and development of efficient catalysts for the electrocatalytic NRR.

Metal–organic frameworks (MOFs) are recently reported with promising perspective to catalyze oxygen evolution reaction (OER) directly, while their wide applications are generally limited by its unsatisfied catalytic activity and stability during the reaction process. Herein, we synthesized Fe and Ni based bimetallic MOFs on 3D nickel foam (NF), i.e. MIL-100­(FeNi)/NF, via a solvothermal process to serve directly as highly efficient OER electrocatalysts. The obtained MIL-100­(FeNi)/NF requires a low overpotential of 243 mV to deliver the current density of 100 mA cm–2 under a small Tafel slope value of 30.4 mV dec–1. Density functional theory (DFT) calculations reveal that the metal–metal coupling effect plays a crucial role in determining the pronounced OER performance of the formed MIL-100­(FeNi). Hopefully, the synthetic strategy and proposed model of bimetallic electrocatalysts (MIL-100­(FeNi)) could simulate the exploration of more novel bimetallic or multimetallic MOFs toward energy storage/conversion application.

Hydrogen peroxide (H2O2) is the main product of enzymatic reactions and plays an important role in biological processes.