Electrostatic Adsorption with Metal Respeciation

The explanation for this behavior draws on electric double-layer theory [26] the local pH is a function of the distance from the adsorption plane and can vary quite considerably (several pH units) from the bulk. Presumably the local chloride concentration reduces in the same way, as the Pt anion-filled surface is approached. It can be argued that the respeciation of Pt evidenced in Table 3.1 is simply in response to the local solution conditions at the adsorption plane. 

Sample Target wt%Pt Surface loading (m /l) NaCI (mol/l) Initial pH CN Cl liquid Final pH CN Cl solid Actual vrt.%Pt 

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The uptake-pH surveys of a number of other metals (Ru(II), Ru(III), Co, and Ni beyond Cu, Pt and Pd) over amorphous and mesoporous silica have recently been reported [24]. It is beheved in all cases that adsorption is all or mostly electrostatic, with minor deviations due to metaldispersed particles form (with the exception once again of Co since Co ammines reduce on silica only at temperatures in excess of 700 C, where sintering cannot be prevented). DI, on the other hand, yielded much larger particles for all metals over both types of supports. 

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