**4. Conclusions**

Carboxylate groups are important functionalities for metal ion adsorption for the biomaterial *Datura innoxia*. Esterification of these functionalities was observed to reduce metal binding capacity 30-40%. Three metals of similar binding affinity to the biomaterial (Cd2+, Ni2+, and Zn2+) were exposed sequentially to both the native esterified biomaterials immobilized within a polysilicate matrix. Removal of surface carboxylates significantly impacted the binding of each metal ion and the impact of each metal bound on the binding of the others. A model involving at least 16 binding sites for these metal ions revealed a majority of binding to involve species-independent or common sites and the presence of cooperativity for some metal-ion binding environments
