Wakayama University, Japan
Title: White light emission from solid carbon in water during hydrogen generation by VIS nanosecond laser pulse irradiation
Akimoto has given her PhD from Kyoto University in 2002. She takes responsibility for one research group in Department of Material Science and Chemistry at Wakayama University. She is a member of the Physical Society of Japan, the Japan Society of Applied Physics, and the Society of Electron Spin Science and Technology in Japan. She has wide research backgrounds by using laser light about optical properties of materials from semiconductors to organic phosphors.
We found a novel method of hydrogen generation from a mixture of water and solid carbon by visible nanosecond laser pulse irradiation at room temperature and under ambient atmosphere. The generated gas contains roughly 50% of hydrogen and 20% of carbon monoxide, meaning that the carbon was oxidized by the laser irradiation. Speed of the gas generation was improved by ethanol addition. We tentatively attributed the gas generation mechanism to photochemical reactions of the solid carbon with water, in analogy to the classical coal gasification which usually progress under high pressure and high temperature (HPHT). It has been unclear, however, whether the HPHT condition was achieved at the site and the moment of laser pulse irradiation or not. According to the nonlinear laser power dependence of generated gas volume and pulse width dependence, we have supposed that the photochemical reactions occur by multi-photon absorption and sequential excitation in carbon material in nanosecond duration. In this presentation, we focus on the spectroscopic phenomenon during the hydrogen generation. Optical emission of continuous spectrum was observed over visible range in both sides of the excitation wavelength for excitation power over a threshold. We discuss a possibility of non-equilibrium temperature elevation.