Photostimulated Synthesis of Noble Metals Nanoparticles

Abstract

Nowadays, one of the most relevant areas of modern materials science is the science of nanoparticles and nanomaterials, as well as nanotechnology. Composition, size and shape of nanomaterials at the nanoscale determines its electronic, optical, magnetic, catalytic, etc. properties. Due to the unique optical and catalytic properties, noble metals nanoparticles (silver and gold ones) today are one of the most intensively studied types of nanoobjects. The properties of silver and gold nanoparticles are extremely important and promising for technological use in such areas as electronics, optics, solar energy, information storage, communications, biomedicine, environmental research and others. A number of promising applications of noble metal nanoparticles are due to the effect of localized surface plasmon resonance, which consists in the collective oscillation of conduction electrons relatively to the ions in metallic crystal lattice bounded by the nanoparticle surface at the resonant excitation frequency. The dimensional dependence of the basic physical and chemical properties of nanoparticles makes specific demands on the synthesis, which should provide the necessary particles’ diameter and size distribution, the possibility of surface functionalization, particles’ stability in the manufacturing process, subsequent storage and operation for its further practical application. Existing methods for obtaining noble metals nanoparticles, including physical, thermal, chemical, photochemical, electrochemical, etc. do not provide the required reproducibility or are too expensive for mass use. In addition, most currently known methods allow to obtain metal nanoparticles only with a wide distribution of shapes and sizes. Careful control of the reaction parameters, such as time, process temperature, stirring rate, concentration of reactans and stabilizing additives, allows to narrow the size distribution of nanoparticles, but not always to the desired limits. According to recent studies, monodisperse colloidal solutions of noble metals nanoparticles can be obtained by excitation of plasmon-stimulated reactions in the reaction mixture. This review, based on a rage of experimental studies, demonstrates how light can be used to control the processes of growth, shape and size of noble metals nanoparticles, and to convert heterogeneous populations of metal nanoparticles into populations with high monodispersity. The manifestation of localized surface plasmons in the optical spectra of metal nanoparticles of different sizes and shapes was also considered. In addition, there were also discussed photophysical processes, associated with the excitation of localized surface plasmon resonance in metal nanoparticles, which allow to control chemical reactions at the nanoscale, namely the photothermal effect; concentration of light near the surface of nanoparticles, which leads to an increase in the electromagnetic field and the intensity of the photon flux for molecules near the particles and the generation of hot electron-hole pairs that can participate in charge transfer between nanoparticles and nearby molecules.