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The large overpotential and poor cycle stability caused by inactive redox reactions are tough challenges for lithium–oxygen batteries (LOBs). Here, a composite microsphere material comprising NiCo2O4@CeO2 is synthesized via a hydrothermal approach followed by an annealing processing, which is acted as a high performance electrocatalyst for LOBs. The unique microstructured catalyst can provide enough catalytic surface to facilitate the barrier‐free transport of oxygen as well as lithium ions. In addition, the special microsphere and porous nanoneedles structure can effectively accelerate electrolyte penetration and the reversible formation and decomposition process of Li2O2, while the introduction of CeO2 can increase oxygen vacancies and optimize the electronic structure of NiCo2O4, thereby enhancing the electron transport of the whole electrode. This kind of catalytic cathode material can effectively reduce the overpotential to only 1.07 V with remarkable cycling stability of 400 loops under 500 mA g−1. Based on the density functional theory calculations, the origin of the enhanced electrochemical performance of NiCo2O4@CeO2 is clarified from the perspective of electronic structure and reaction kinetics. This work demonstrates the high efficiency of NiCo2O4@CeO2 as an electrocatalyst and confirms the contribution of the current design concept to the development of LOBs cathode materials.

Activated sludge, which is difficult and expensive to treat and dispose of, is a key concern in wastewater treatment plants. In this study, magnetic sludge biochar containing activated sludge and different sizes (14.3, 40.2 and 90.5 nm) of Fe 3 O 4 nanoparticles was investigated as an effective adsorbent for tetracycline (TC) adsorption. Magnetic sludge-based biochar was prepared by a facile cross-linking method and characterized by transmission electron microscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, X-ray photoelectron spectroscopy (XPS) and zeta potential analysis. The adsorption performances of TC on three kinds of adsorbents were investigated. Although 14.3 nm Fe 3 O 4 nanoparticles could be inclined to aggregate and partially filled with pores of biochar, it turned out that magnetic sludge biochar with 14.3 nm Fe 3 O 4 nanoparticles exhibited optimum performance for TC removal with adsorption capacity up to 184.5 mg g −1 , due to the larger amounts of functional groups and the change of zeta potential. Furthermore, the adsorption kinetics of TC on three kinds of adsorbents were studied, which implied that the pseudo-second-order kinetic model exhibited the better fit for the entire sorption process.

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