In this study, the size-controlled synthesis of silver nanoparticles (Ag NPs) via chemical reduction method by NaBH 4 as a reducing agent and poly(vinyl pyrrolidone) or PVP as a stabilizing agent is reported. Changing of ratios between reducing agent and stabilizing agent relative to AgNO 3 -optimized conditions for synthesis of stable Ag NPs was studied. The formation of Ag NPs was tracked by UV-Vis spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectroscopy. Particle size distribution was studied by particle size analyzer, and the morphology was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The optical properties of the synthesized Ag NPs were also investigated. The optimized Ag NPs were very stable even after 1 month that was due to effective stabilization by PVP molecules. The mechanism of Ag NPs formation and stabilization is discussed in detail.

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In this work, ?-Fe2O3 nanoparticles (NPs) have been synthesized by using a simple Pechini sol-gel method from iron nitrate, citric acid as complexing agent and ethylene glycol as polymerization agent. The calcined ?-Fe2O3 NPs were fully characterized by different techniques. It was confirmed that ultrafine and highly crystalline ?-Fe2O3 NPs with high purity and mesoporous nature can be obtained after calcination at 550?C for 3 h. In addition, the results of electrical resistance measurements of the fabricated Fe2O3 thick films showed that ?-Fe2O3 thick films have stable electrical properties which are beneficial for electrical applications such as gas sensing and field effect transistors.

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Ag@α-Fe2O3 nanocomposite having a core–shell structure was synthesized by a two-step reduction-sol gel approach, including Ag nanoparticles synthesis by sodium borohydride as the reducing agent in a first step and the subsequent mixing with a Fe+3 sol for α-Fe2O3 coating. The synthesized Ag@α-Fe2O3 nanocomposite has been characterized by various techniques, such as SEM, TEM and UV-Vis spectroscopy. The electrical and gas sensing properties of the synthesized composite towards low concentrations of ethanol have been evaluated. The Ag@α-Fe2O3 nanocomposite showed better sensing characteristics than the pure α-Fe2O3. The peculiar hierarchical nano-architecture and the chemical and electronic sensitization effect of Ag nanoparticles in Ag@α-Fe2O3 sensors were postulated to play a key role in modulating gas-sensing properties in comparison to pristine α-Fe2O3 sensors.

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