Ondřej Zobač

Ag-Cu colloid synthesis: bimetallic nanoparticle characterisation and thermal treatment

The Ag-Cu bimetallic colloidal nanoparticles (NPs) were prepared by solvothermal synthesis from metalloorganic precursors in a mixture of organic solvents. The nanoparticles were characterized by dynamic light scattering (DLS) and small angle X-ray scattering (SAXS). The properties of metallic core and organic shell of the nanoparticles were studied by direct inlet probe mass spectrometry (DIP/MS), Knudsen effusion mass spectrometry (KEMS), double-pulse laser-induced breakdown spectroscopy (DPLIBS), and differential scanning calorimetry (DSC). The transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used for particle characterization before and after thermal analysis. The experiment yielded results that were for AgCu nanoparticles for the first time. The detected liquidus temperature has been compared with the prediction obtained from calculation of the phase diagram of Ag-Cu nanoalloy. The experimental results show that of near-eutectic composition AgCu nanoparticles possess the fcc crystal lattice. Surprisingly, spinodal decomposition was not observed inside the AgCu nanoparticles at temperatures up to 230°C. The depression of the eutectic AgCu melting point was calculated but not observed. The eutectic AgCu microparticles are formed before melting.

AgCu Bimetallic Nanoparticles under Effect of Low Intensity Ultrasound: The Cell Viability Study In Vitro

The effects of metallic nanoparticles as cytotoxicity or antibacterial activity are widely known. It is also obvious that ultrasound is one of the most widely used therapeutic modalities in medicine. The effect of application of therapeutical ultrasonic field in the presence of metallic nanoparticles AgCu <100 nm modified by phenanthroline or polyvinyl alcohol was examined on human ovarian carcinoma cells A2780. Metallic nanoparticles were characterized by electron microscopy and by measuring of zeta potential. The cell viability was tested by MTT test. The experimental results indicate a significant decrease of cell viability, which was affected by a combined action of ultrasound field and AgCu nanoparticles. The maximum decrease of cells viability was observed for nanoparticles modified by phenanthroline. The effect of metallic nanoparticles on human cell in presence of ultrasound exposure was found—a potential health risk or medical advantage of targeted therapy in the future.

Spinodal decomposition of Ag-Cu nanoparticles

Ag-Cu nanoparticles (NPs) of near-eutectic composition were prepared by solvothermal synthesis at 230C from metallo-organic precursors in organic solvent. The nanoparticle size was measured by both dynamic light scattering (DLS) and small angle X-ray scattering (SAXS) method. The size and shape were evaluated by electron microscopy (SEM, TEM and HRTEM), the thermal properties were investigated by differential scanning calorimetry (DSC) and temperature controlled Xray diffraction method (XRD). HRTEM results show that AgCu nanoparticles with face centered cube (fcc) crystal lattice exist as a substitutional solid solution in contrast to bulk AgCu system, which reveals spinodal decomposition under eutectic temperature. The phase diagram respecting size of the AgCu NPs was calculated by the CALPHAD method using surface tension of the bulk Ag-Cu alloy in liquid and solid (fcc) states. The predicted eutectic melting point depression was not experimentally observed when the nanoparticles were melted by DSC. The samples melt at eutectic temperature exactly as bulk AgCu alloy. The microparticles consisting of the eutectic copper and silver rich phases were observed by SEM after melting. A spontaneous separation of copper and silver atoms was observed by temperature controlled X-ray diffraction method (XRD). The temperature treatment of the AgCu NPs showed that a spinodal decomposition and crystallinity changes (size evaluation using Scherrer equation) occur at a narrow range of temperature. The reason for the phenomenon observed can be the metastable state of the nanoparticles but there are also other unknown effects at the nano-scale level that hinder the Cu- and Ag-rich phase separation at low temperatures. The open question is also if the general equilibrium thermodynamics can be used to describe the AgCu NPs system under view.