From isolated Ag+ ions to aggregated Ag0 nano-clusters in silver-exchanged ETS-10 molecular sieve: a reversible behavior

Recently it has been shown that ETS-10, a crystalline microporous titanosilicate, is an inverse-shape-selective photocatalyst. The main drawback in the extensive use of this material was its band-gap value, located in the UV, that don’t allow the use of solar light. In this work we succeed to shift the ETS-10 light absorption down to the visible region of the electromagnetic spectrum by introducing Ag+ cations inside the ETS-10 channels. Thermal-, chemical- and UV-photo-treatments have been applied to Ag-ETS-10 to tune, in a controlled and progressive way, the aggregation of isolated Ag+ counterions into metal nanoclusters of increasing nuclearity. This is a direct mean to tune the frequency of silver nanoparticle plasmon resonance and thus the light absorption properties of the material. It is further reported that transformation of isolated Ag+ ions into aggregated Ag0 nano-clusters, is almost reversible. Cycles of H2-chemical reduction/O2-chemical oxidation and of UV-photo-reduction/Vis-photo-oxidation are reported. UV-Vis, Ag K-edge EXAFS and FTIR spectroscopy of adsorbed CO are the main techniques used to monitor the evolution of the silver aggregation along the different reduction/oxidation treatments.