Measurement of the diffusion coefficient of nickel nitrate in wet silica gel using UV/VIS spectroscope equipped with a flow cell

A novel technique for the measurement of the diffusion coefficient of a solute in a transparent wet-gel monolith was developed by analyzing the decay behavior of the absorbance of the gel plate in a flow cell. The diffusion coefficient of a Ni(NO3)2 in a wet silica gel is estimated by fitting the absorbance–time data with an exponential function. The efficiency of the technique was ensured by testing the effects of several measurement conditions, such as the flow rate of the external solution and the thickness of the gel plate. The diffusion coefficient of Ni(NO3)2 in wet silica gel is 6.0×10−10 m2 s−1 at 20°C, which is ca. 60% of that in bulk solution. The data suggest that the silica gel network allows relatively fast transport of the liquid phase.