Effect of pore size on the liquid-phase pore diffusion of nickel nitrate

The diffusion coefficient of nickel nitrate dissolved in water in porous silica plates with different pore size was measured to investigate the effect of pore size on the liquid-phase diffusion resistance. The pore-diffusion coefficient of nickel nitrate varied with the pore size of the silica gel. In pores of diameter > 5 nm, the diffusion resistance can be ignored, and the pore-diffusion coefficient varies proportionally to the porosity of the silica plates. In pores of diameter < 5 nm, however, the diffusion resistance increases rapidly with decreasing pore diameter. A microporous silica shows the largest diffusion resistance: the pore-diffusion coefficient in micropores is less than 0.01 of the diffusion coefficient in an unbounded system.