Co 3 O 4 is an attractive earth-abundant catalyst for CO oxidation, and its high catalytic activity has been attributed to Co 3+ cations surrounded by Co 2+ ions. Hence, the majority of efforts for enhancing the activity of Co 3 O 4 have been focused on exposing more Co 3+ cations on the surface. Herein, we enhance the catalytic activity of Co 3 O 4 by replacing the Co 2+ ions in the lattice with Cu 2+ . Polycrystalline Co 3 O 4 nanowires for which Co 2+ is substituted with Cu 2+ are synthesized using a modified hydrothermal method. The Cusubstituted Co 3 O 4 _Cux polycrystalline nanowires exhibit much higher catalytic activity for CO oxidation than pure Co 3 O 4 polycrystalline nanowires and catalytic activity similar to those single crystalline Co 3 O 4 nanobelts with predominantly exposed most active {110} planes. Our computational simulations reveal that Cu 2+ substitution for Co 2+ is preferred over Co 3+ both in the Co 3 O 4 bulk and at the surface. The presence of Cu dopants changes the CO adsorption on the Co 3+ surface sites only slightly, but the oxygen vacancy is more favorably formed in the bonding of Co 3+ −O−Cu 2+ than in Co 3+ −O−Co 2+ . This study provides a general approach for rational optimization of nanostructured metal oxide catalysts by substituting inactive cations near the active sites and thereby increasing the overall activity of the exposed surfaces. ■ INTRODUCTIONCarbon monoxide (CO) emission from transportation and industrial activities is harmful to both human health and the environment. Currently, CO emission is effectively reduced, mainly through catalytic oxidation over catalysts. 1−4 The most active catalysts for CO oxidation are noble metals, but they are expensive and are of limited supply. Co 3 O 4 has emerged as an attractive alternative catalyst for CO oxidation because of its optimal CO adsorption strength, low barrier for CO reaction with lattice O, and excellent redox capacity. 1,5−8 A breakthrough on Co 3 O 4 for catalytic CO oxidation showing that Co 3 O 4 nanorods with predominantly exposed {110} planes exhibit a much higher catalytic activity for CO oxidation and larger resistance to deactivation by water than Co 3 O 4 nanoparticles was reported by Xie et al. 9 The high catalytic activity of Co 3 O 4 {110} planes is attributed to its higher concentration of Co 3+ cations (correspondingly fewer Co 2+ cations) than other crystal planes, since only Co 3+ cations surrounded by Co 2+ ions are active for catalytic oxidation of CO. 10,11 Subsequently, a number of Co 3 O 4 nanostructures, ranging from nanobelts, nanospheres, nanocubes, and nanotubes to nanowires, have been synthesized with the purpose of preferentially exposing Co 3+ cations. 11−14 Nevertheless, regardless of the morphology of the Co 3 O 4 nanostructures, even the highly active Co 3 O 4 {110} planes still contain Co 2+ cations, which have been assumed to be inactive for catalytic oxidation of CO, 9−11 and ultimately limits the catalytic activity of Co 3 O 4 for CO oxidation. Therefore, substituting Co 2+ with...
A rapid, on-site, and accurate SARS-CoV-2 detection method is crucial for the prevention and control of the COVID-19 epidemic. However, such an ideal screening technology has not yet been developed for the diagnosis of SARS-CoV-2. Here, we have developed a deep learning-based surface-enhanced Raman spectroscopy technique for the sensitive, rapid, and on-site detection of the SARS-CoV-2 antigen in the throat swabs or sputum from 30 confirmed COVID-19 patients. A Raman database based on the spike protein of SARS-CoV-2 was established from experiments and theoretical calculations. The corresponding biochemical foundation for this method is also discussed. The deep learning model could predict the SARS-CoV-2 antigen with an identification accuracy of 87.7%. These results suggested that this method has great potential for the diagnosis, monitoring, and control of SARS-CoV-2 worldwide.
ZnS coated on N,S co-doped carbon (ZnS/NSC) composite has been prepared utilizing zinc pyrithione (CHNOSZn) as raw material via calcination. Through activation using NaCO salt, ZnS nanoparticles encapsulated in NSC (denoted as A-ZnS/NSC) with mixed-crystal structure has also been obtained, which reveals much larger specific surface area and more bridges between ZnS and NSC. Based on the existence of bridges (C-S-Zn and S-O-Zn bonds) and the modification of carbon from N,S co-doping, the A-ZnS/NSC composite as an anode for sodium-ion batteries (SIBs) displays significantly enhanced electrochemical performances with a high reversible specific capacity of 516.6 mA h g (at 100 mA g), outstanding cycling stability (96.9% capacity retention after 100 cycles at 100 mA g), and high rate behavior (364.9 mA h g even at 800 mA g).
CoO has been widely studied as a promising candidate as an anode material for lithium ion batteries. However, the huge volume change and structural strain associated with the Li insertion and extraction process leads to the pulverization and deterioration of the electrode, resulting in a poor performance in lithium ion batteries. In this paper, CoO rose-spheres obtained via hydrothermal technique are successfully embedded in graphene through an electrostatic self-assembly process. Graphene-embedded CoO rose-spheres (G-CoO) show a high reversible capacity, a good cyclic performance, and an excellent rate capability, e.g., a stable capacity of 1110.8 mAh g at 90 mA g (0.1 C), and a reversible capacity of 462.3 mAh g at 1800 mA g (2 C), benefitted from the novel architecture of graphene-embedded CoO rose-spheres. This work has demonstrated a feasible strategy to improve the performance of CoO for lithium-ion battery application.
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