In Situ Time-Resolved XAFS Studies on Laser-Induced Particle Formation of Palladium Metal in an Aqueous/EtOH Solution

摘要

The reaction kinetics of laser-induced particle formation in an aqueous/EtOH solution of PdCl42- without a photoactivator was investigated by transmission electron microscopy (TEM) and dispersive X-ray absorption fine structure (DXAFS) measurements. Pd particles were generated by the irradiation of a nanosecond pulsed 266 nm laser with a fluence of 19.9-59.7 mJ/cm(2). The TEM observation showed the dependence of the particle size on the laser fluence and the promotion of particle growth by the irradiation of a high-fluence laser. The DXAFS data were analyzed by three methods: deconvolution of the X-ray absorption near-edge structure (XANES) spectrum by a linear combination fitting, model fitting of the extended XAFS (EXAFS) oscillation of the PdCl42- ion, and fitting of the spectrum edge of XANES using an error function. These methods give the ratio of Pd2+, the coordination number of Pd Cl bond, and the edge width of XANES, which are related to the Pd2+ concentration. Temporal changes of the Pd2+ concentration obtained by these three methods were analyzed on the basis of the Finke Watzky two-step mechanism. The analysis elucidates that, in laser-induced particle formation in the absence of a photoactivator, the photons contribute to reduction of the PdCl42- ion by the one-photon process and to the autocatalytic growth of Pd particles by the multiphoton process.