Synthesis And Hydrogen Storage Properties Of Silver Sulfide Nanostructures With Different Morphologies

Ag₂S nanostructures and their nanocomposites have significant potential for applications in photoluminescence, optical limiting, solar energy cell, non-volatile memory, nano-switch, photocatalyst for H2 production, organic degradation, cancer therapy, sterilization, sensors, liquid lubrication, etc. Focused on the existcence of some disadvantages in Ag₂S nanostructure research, we designed a series of experimental studies to obtain nanostructures with uniform morphologies and sizes as well as to explore, investigate and control their hydrogen storage properties.The surfactant CTAB-assisted routes were used to synthesize 0D and 1D Ag₂S nanostructures in aqueous solution. The S₂O₃^2-/Ag⁺ molar concentration ratios, the dosage of HNO₃ and reaction time determined morphologies and phase compositon of the obtained nanoparticles at 45 oC. When the molar concentration ratios of S2O₃2-/Ag⁺ were 3.2:1, faceted-spherical and polyhedral Ag₂S/Ag₃SBr hybrid nanoparticles as well as spherical Ag₂S nanoparticles decorated with small nanoparticles were obtained at 0.2, 0.5 and 1.0 mL HNO₃ for 2.0, 1.0 and 0.5 h, respectively. By decreasing the molar concentration ratios to 2.2:1, hexagonal and cubic Ag₂S hollow nanoparticles, as well as capsule-like Ag₂S/AgBr composite nanoparticles, were prepared with 0.2, 0.8 and 2.0 mL HNO₃ for 10.0, 2.5 and 1.0 h, respectively. After the molar concentration ratios were decreased to 1.8:1, rhombic Ag₂S hollow nanoparticles and ellipsoidal Ag₂S/AgBr composite nanoparticles were formed by using 0.2 and 0.5 mL HNO₃ for 12.5 and 5.0 h, respectively. Hollow and hybrid nanoparticles could spontaneously assemble into ordered arrays. The Ag₂S nanorod arrays were prepared with S2O₃2-/Ag⁺ molar concentration ratio of 10:1 for 12.0 h at 90 oC in aqueous solution. It was not benifical for the formation of 1D nanostructures to increase or decrease the S2O₃2-/Ag⁺ molar concentration ratios.Ag₂S nanorods were synthesized by decomposing the Ag-Tu complex with 0.4 mL NaOH for 96.0 h at room temperature in aqueous solution. With the assistance of 0.25 g PVP, nanopartilce-assembled Ag₂S nanorods were formed by employing 0.8 mL NaOH in the same reaction system. If reaction temperature was elevated or NaOH dosage was slightly changed, aggregated or non-homogeneous sized nanoparticles were obtained. Ag₂S nanorods were fabricated with 0.0006 mol AgNO₃ and 0.003 mol S powder for 3.0 h at 120 oC in organic oleylamine solution. Both the temperature variations and the dosage decrease of S powder favored the formation of nanoparticles. Ag₂S nanowires were obtained in the mixture of oleylamine and octadecylamine with 1:9 molar ratio for 4.0 h at 120 oC. When octadecylamine in mixture was replaced with equimolar oleamide, tri-n-octylamine or octadecyldimethylamine, short Ag₂S nanorods, nanopaticles and nanorods, and nanoparticles were prepared for 30 min, respectively. With the increase of reaction time, all 1D nanostructures in organic amines would gradually dissolve and evolve into 0D nanoparticles. Ag₂S nanotubes decorated with cubic Ag nanoparticles were synthesized in ethanol with the presence of S powder by using Ag nanowires as sacrificial templates at room temperature.The electrochemical hydrogen storage properites of the synthesized Ag₂S nanostructures were investigated. The morphologies of Ag₂S nanostructures had obvious effects on their hydrogen storage properties. Rhombic, hexagonal and cubic Ag₂S hollow nanoparticles showed the hydrogen storage capacities of 6.95, 6.58 and 6.95 mg/g and the cycle efficiencies of 90%, 86% and 90%, respectively. The hydrogen storage capacities of faceted-spherical and polyhedral Ag₂S/Ag₃SBr hybrid nanoparticles as well as spherical Ag₂S nanoparticles decorated with small nanoparticles were 3.36, 4.82 and 3.07 mg/g with the cycle efficiencies of 44%, 63% and 40%, respectively. Ellipsodial and capsule-like Ag₂S/AgBr composite nanoparticles had the hydrogen storage capacities of 7.13 and 2.08 mg/g with the cycle efficiencies of 92% and 27%, respectively. Ag₂S nanorod arrays, nanorods and nanoparticle-assembled nanorods, synthesized in aqueous solution, exhibited the hydrogen storage capacities of 7.53, 7.65 and 6.87 mg/g and the cycle efficiencies of 98%, 99% and 90%, respectivley. The Ag₂S nanorods and nanowires obtained in organic amines showed the hydrogen storage capacities of 6.95 and 2.85 mg/g with the cycle efficiencies of 90% and 37%, respectively. The hydrogen storage capacity and the cycle efficiency of Ag₂S nanotubes decorated with Ag nanoparticles were 6.73 mg/g and 88%, respectively. Hollow Ag₂S nanoparticles, ellipsoidal Ag₂S/AgBr composite nanoparticles, Ag₂S nanorods, nanoparticle-assemble nanorods, nanorod arrays and nanotubes had exhibited better hydrogen storage properties, indicating their potential applications in hydrogen storage field.