CC BY
17LM-I-11
Laser-induced plasma in water as an origin of chemical reactions
V.V. Kononenko, V.M. Gololobov, K.H. Ashikkalieva, N.R. Arutyunyan and V.I. Konov
Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, Russia
e-mail: [email protected]
The laser plasma in water is a problem of great interest in solution chemistry, biology, and medicine [1,2]. One of the most attracting technique based on the plasma-assisted processes is a photochemical reduction of metal salts. Recently, intense femtosecond laser radiation was demonstrated to effectively ionize solution and drive the formation of metal nanoparticles (NPs) in aqueous media [3]. This approach is "green", i.e. requires the minimum number of chemical reactants, and seems to provide precise control over the size and shape of synthesized nanoparticles. Here we present an experimental study of laser induced plasma in the gold aqueous solution (HAuCU 3H2O) and explore the correlation between its properties and a rate of the gold NPs synthesis.
Ionization of water was carried out in a strong optical field of the Ti:sapp femtosecond laser (pulse duration ~ 100 fs, wavelength 800 nm, intensity > 1012 W/cm2). Both the refractive index and absorbance
of the ionized zone were measured in the time window of ~ 1.5 ns using a pump-probe interferometric technique which was developed for temporally and spatially resolved observation in solids. The measurements allowed quantifying the induced processes: ionization of water and solvation of excess electrons, geminate recombination and development of cavitation. Besides interferometric measurements the scattering of pump radiation on aqueous plasma was studied. The dependence of the intensity of the scattered light on the pulse energy allowed characterizing the plasma induced at high laser intensity (> 1013 W/cm2) when the laser power exceeded remarkably the critical power and beam propagated in a quite nonlinear manner.
For the photochemical experiments the salt solutions were irradiated for times ~10 minutes. The pulse energy was varied for each series. The kinetics of Au ions reduction and formation of Au NPs was measured monitoring (i) the absorption spectra of the solutions (a Perkin Elmer UV-vis-NIR double-beam spectrophotometer) and (ii) particle size distribution by a dynamic light scattering technique (an Zetasizer Nano analyzer). We discuss the relationship between the different regimes of water ionization and productivity of the metal ions reduction in laser-induced plasma. Presented data provide an experimental basis for theoretical models that describe the plasma-assisted processes in aqueous media.
This work was supported by the Russian Science Foundation (grant 19-12-00255).
[1] V. K. Meader, M. G. John, C. J. Rodrigues, K. M. Tibbetts, The Journal of Physical Chemistry A, 121~(36), 6742~(2017).
[2] A. Vogel, J. Noack, G. Huttman, G. Paltauf, Applied Physics B, 81~(8), 1015~(2005).
[3] C. Zhao, S. Qu, J. Qiu, C. Zhu, J. Mater. Res., 18, 1710~(2003).
