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Background: Magnetic nanoparticles are attracting much attention toward easyoperation and size controllable synthesis methods. We develop a method to synthesize MnO, Co,CoO, and Ni nanoparticles by thermal decomposition of metal 2,4-pentanedionates in the presenceof oleylamine (OLA), oleic acid (OA), and 1-octadecene (ODE). Methods: Similar experimental conditions are used to prepare nanoparticles except for the metalstarting materials (manganese 2,4-pentanedionate, nickel 2,4-pentanedionate, and cobalt 2,4-pentanedionate), leading to different products. For the manganese 2,4-pentanedionate startingmaterial, MnO nanoparticles are always obtained as the reaction is controlled with differenttemperatures, precursor concentrations, ligand ratios, and reaction time. For the cobalt 2,4-pentanedionate starting material, only three experimental conditions can produce pure phase CoOand Co nanoparticles. For the nickel 2,4-pentanedionate starting material, only three experimentalconditions lead to the production of pure phase Ni nanoparticles. Results: The nanoparticle sizes increase with the increase of reaction temperatures. It is observedthat the reaction time affects nanoparticle growth. The nanoparticles are studied by XRD, TEM,and magnetic measurements. Conclusion: This work presents a facile method to prepare nanoparticles with different sizes,which provides a fundamental understanding of nanoparticle growth in solution. 

Disordered aggregated porous nanoparticles of KCMS are highly efficient and have exceptionally high sorption capacity in removing Ag⁺and Pb²⁺following the exchange of K⁺and Co²⁺ions bonded electrostatically and covalently in KCMS, respectively. 

Non-noble metal based electrocatalysts for the hydrogen evolution reaction (HER) hold great potential for commercial applications. However, effective design strategies are greatly needed to manipulate the catalyst structures to achieve high activity and stability comparable to those of noble-metal based electrocatalysts. Herein, we present a facile route to synthesize layered Co 9 S 8 intercalated with Co cations (Co 2+ -Co 9 S 8 ) (with interlayer distance up to 1.08 nm) via a one-step solvothermal method. Benefiting from a large interlayer distance and efficient electron transfer between layers, the Co 2+ -Co 9 S 8 hybrid shows outstanding electrocatalytic hydrogen evolution performance in an acid electrolyte. The electrocatalytic performance is even better than that of 20% Pt/C at the <−0.54 V region with an overpotential of 86 mV at a current density of 10 mA cm −2 in 0.5 mol L −1 H 2 SO 4 . More importantly, the system can maintain excellent stability for more than 12 h without obvious decay. This study not only presents a novel and efficient approach to synthesize cobalt sulfide intercalated with Co cations for stable electrocatalytic HER but also provides an avenue for the design of intercalated materials used in other energy applications.