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AbstractThis paper investigates the optimal ventilation mode for double fires in a typical interchange subway station. Numerical simulations were carried out in a full-scale subway station with different heat release rates, ventilation modes, and fire source locations. Results demonstrate that when double fires occur, activating ventilation systems in one line may affect the smoke spread in other lines due to the existence of transfer channels. For the platform-tunnel mixed exhaust mode, when the fire size is small, the optimal TVF exhaust volume range exists. There is no optimal smoke exhaust volume for double fires with the large fire size or near the ends of the platform. Under such circumstances, the subway staff should take some measures to hinder the unwanted smoke flow path.

Addressing the secondary contamination associated with advanced oxidation processes based on sulfate radicals (SR-AOPs) is the primary challenge in developing efficient cobalt-based catalysts. In this study, a simple two-step hydrothermal procedure was used to successfully prepare hollow sea urchin-like Co3O4@CuO/CuMoO4(CCM) polymetallic composite catalysts to rapid activate peroxymonosufalte (PMS) for phenanthrene (PHE) degradation with less amount of catalyst and PMS. Mo doping effectively enhanced the redox cycle between Co-Cu bimetals and could achieve 100% degradation of PHE within 10 min with a higher kinetic-rate constant (k= 0.402 min−1), it was 3.2 times higher than that of Co3O4@CuO (CoCu). Quenching experiments, XPS, and EPR confirmed that the incorporation of Mo facilitated CoOH+formation and altered the production of reactive oxygen species, the oxidative degradation of PHE changed from a non-radical (1O2) dominated to a combination of multiple reactive oxygen species (SO4•−, •OH, and 1O2). The toxicity of the intermediates was evaluated using T.E.S.T. and lettuce germination experiments to verify the superior mineralization capacity of the CCM/PMS system for PHE degradation. Also, the efficiency and stability of the catalysts in actual wastewater treatment provided significant value for the practical application of SR-AOPs.

Elements doping has been used to improve the electrochemical performances of O3-type layered transition metal oxide cathodes for sodium-ion batteries. However, their roles and the improvement mechanism have not been clearly understood. Herein, the effects of Mg substitution for Mn on the structure and electrochemical performances of NaMn0.48Ni0.2Fe0.3Mg0.02O2have been comprehensively investigated and some new insights into the roles of Mg in improving the rate capability and cycling stability have been presented. (1) The substitution of Mg for Mn enlarges the interlayer spacing, which not only enhances Na+diffusion and the rate capability but also alleviates the lattice strains induced by Na+intercalation/deintercalation. (2) The substitution of Mg by Mn also shrinks TM–O bond and TMO2slabs, which enhances the layered structure stability. (3) The Mg substitution also mitigates the structure distortion or volume change of the crystal lattices and suppresses the irreversible phase transitions. (4) The substitution of low-valence Mg2+for Mn3+reduces Mn3+and minimizes Jahn–Teller effect, which also further alleviates the irreversible phase transformations and improves the layered structure stability. This study not only unveils the roles of Mg but also presents some insights into designing the cathode materials with both high rate capability and high cycling stability through the lattice structure regulation.