Evaluation of electroless gold deposited on porous silica for ligand attachment for metal ion-exchange

A novel ion-exchange system was developed by tethering a small, monofunctional metal ligand, 3-mercaptopropionic acid (MPA), through thiol linkages onto a glass substrate overlaid with gold, using electroless deposition of Au onto 100 mesh controlled pore glass (CPG) particles. Two different CPG glass pore sizes of 22.6 and 104.9 nm were used in an attempt to optimize Au deposition and ligand coverage. It was found that the Au was present on both of the substrates as a nonuniform deposit, possibly existing as small multilayer islands, throughout the CPG particles. The deposit also did not fill the intricate CPG pore network.Au-CPG is a reasonable substrate for the support of small metal binding ligands such as the monofunctional MPA. Typical metal binding capacities were in the range of 7-24 μmol metal/g column, with the smaller pore system binding approximately twice as much metal as the larger pore system due to increased surface area and fractional ligand coverage. The immobilized binding systems were also found to remain chemically and structurally stable in pH environments ranging from pH∼9 to <1 (viz. 1 M HNO₃).