Limitation of adsorptive penetration of cesium into Prussian blue crystallite

The adsorption of cesium (Cs) onto Prussian blue (PB) with different crystallite sizes is investigated to examine the limitations of the adsorptive penetration of Cs⁺ into PB crystallite. The adsorption of Cs⁺ onto soluble PB occurs via ion exchange with a charge-compensation cation like K⁺, which originally resides in the crystalline lattice. The ratio of the compensation cation sites that are replaced by Cs⁺ after adsorption time of 2 weeks significantly increases with decreasing crystallite size, meaning that the adsorption occurs only near the surface of the crystallite during the adsorption time. The depth of Cs⁺ penetration after 2 weeks is only within approximately 1–2 nm (or 1–2 units of the crystalline lattice) from the external surface of the crystallite at ambient temperature, regardless of the crystallite size. Hence, the crystallite size is the most important factor governing the adsorption performance.