Preparation and optical properties of silica@Ag–Cu alloy core-shell composite colloids

Wide spectrum photocatalytic activity in lanthanide-doped upconversion nanophosphors coated with porous TiO2 and Ag-Cu bimetallic nanoparticles

Approaches towards maximum utilization of solar light spectrum for photocatalysis have currently attracted great interest. The combination of profoundly different properties, such as, upconversion, semiconducting and plasmonic properties can produce a favorable path in efficient utilization of the different regions of solar light reaching to earth. In this regard, design and fabrication of microstructures consisting of upconverting lanthanide doped nanophosphors coated with porous semiconducting material, TiO₂ and decorated with plasmonic Ag-Cu bimetallic nanoparticles is presented in this work. These microstructures display great stability and exceptional photocatalytic activity by absorbing wide spectrum from ultraviolet to near infrared. The photocatalytic activity could be attributed to the synergistic effects between the different components and the efficient energy transfer between them. The development of such sort of hybrid microstructures could pave way for the development of new materials for the efficient utilization of the wide spectrum of sunlight.

A simple robust method of synthesis of copper-silver core-shell nano-particle: evaluation of its structural and chemical properties with anticancer potency

A simple method of synthesis of a stable bimetallic copper-silver nano-particle (CuAg-NP) was developed by successive reduction of Cu(NO₃)₂ and AgNO₃, using hydrazine hydrate as the reducing agent and gelatin and poly-vinyl pyrrolidone (PVP) as the capping agents. The round-shaped particles were of a core-shell structure with a core of Cu⁰ atoms surrounded by a shell of Ag⁰ atoms. The size and the mol. wt. of the NPs were (100 ± 10) nm and (820 ± 157) Kd, respectively; the particles were crystalline in nature and 90% of the precursors Cu(NO₃)₂ and AgNO₃ were converted to the NPs. The particles were more toxic to cancer cells than normal cells; the dose of the NPs (4-5 μg ml^-1), that killed about 75% of the different human cancer cell lines viz, HepG2 (liver cancer), A549 (lung cancer) and AGS (stomach cancer), killed only about 22.5% of the normal cell lines viz, WRL68 (liver) and WI38 (lung). Therefore, the NP may be developed as a potent anticancer drug in future. The more detailed study on the cytotoxicity of the CuAg-NP on the HepG2 cell line revealed that the particles caused cell cycle arrest in a G2/M phase, depolarization of mitochondrial membrane potential, translocation of phosphatidylserine residues from inner to outer leaflets of cell membrane and DNA degradation; these phenomena confirmed that the NP-induced cell death was apoptotic in nature.

Highly shape-selective synthesis, silica coating, self-assembly, and magnetic hydrogen sensing of hematite nanoparticles

The open forced hydrolysis method and controllable silica growth based on bound water to polyvinylpyrrolidone molecules have been developed for the highly shape (including rhombohedra, semispheres, and rods) selective synthesis, self-assembly, and uniform silica coating (in the unprecedented range of 5-200 nm) of hematite nanoparticles. The open system realizes the direct short-range self-assembly of hematite semispheres in their growth process. The bound water method has been extended to coat gold nanoparticles with tunable silica shell and directly assemble the cores into one-dimensional, dimer, and trimer nanostructures during the coating process. The silica coating increases the particle stability and monodispersity even as hematite is modified into ferromagnetic Fe(3)O(4). The hematite@silica core-shell spheres are assembled into long-range ordered structures with considerable photonic bandgap for the first time due to their high monodispersity. By exploiting the hematite antiferromagnetism caused by the superexchange interaction via intervening oxygen ions that are sensitive to hydrogen, a novel hydrogen sensing based on magnetization variations is achieved in the hematite assemblies. Weakening the antiferromagnetism by reducing the hematite size and/or covering the hematite surface by silica coating suppresses the sensitivity to hydrogen, showing that the antiferromagnetic spin variations on the hematite surface are responsible for the gas sensing.

Gold, palladium, and gold-palladium alloy nanoshells on silica nanoparticle cores

The synthesis of gold, palladium, and gold-palladium alloy nanoshells (approximately 15-20 nm thickness) was accomplished by the reduction of gold and palladium ions onto dielectric silica core particles (approximately 100 nm in diameter) seeded with small gold nanoparticles (approximately 2-3 nm in diameter). The size, morphology, elemental composition, and optical properties of the nanoshells were characterized using field-emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and ultraviolet-visible spectroscopy. The results demonstrate the successful growth of gold, palladium, and gold-palladium alloy nanoshells, where the optical properties systematically vary with the relative content of gold and palladium. The alloy nanoshells are being prepared for use in applications that stand to benefit from photoenhanced catalysis.

Preparation, characterization, and optical properties of gold, silver, and gold-silver alloy nanoshells having silica cores

This report describes the structural and optical properties of a series of spherical shell/core nanoparticles in which the shell is comprised of a thin layer of gold, silver, or gold-silver alloy, and the core is comprised of a monodispersed silica nanoparticle. The silica core particles were prepared using the Stöber method, functionalized with terminal amine groups, and then seeded with small gold nanoparticles (approximately 2 nm in diameter). The gold-seeded silica particles were coated with a layer of gold, silver, or gold-silver alloy via solution-phase reduction of an appropriate metal ion or mixture of metal ions. The size, morphology, and elemental composition of the composite nanoparticles were characterized by field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, thermal gravimetric analysis (TGA), dynamic light scattering (DLS), and transmission electron microscopy (TEM). The optical properties of the nanoparticles were analyzed by UV-vis spectroscopy, which showed strong absorptions ranging from 400 nm into the near-IR region, where the position of the plasmon band reflected not only the thickness of the metal shell, but also the nature of the metal comprising the shell. Importantly, the results demonstrate a new strategy for tuning the position of the plasmon resonance without having to vary the core diameter or the shell thickness.