I find silver ion can easily change it color at high temperature. Is it because Ag+ reduce to Ag0? But the atmosphere is an oxidized environment, how can it reduce?
Probably Ag(+) is being reduced to Ag(0) and finely divided metals show usually a black colour; on increasing time, temperature and Ag(+) loading, yello2 will become brown and finally black
There could be two possible reasons:
1) The silver oxide is not thermally stable and decomposes readily at ~ 280 C to metallic silver , and as it is photo sensitive, the decomposition could even take place at lower temperatures when exposed to sunlight
2) If the silver source for the ion exchange of the zeolites is not pure, it may contain Cu which readily tarnishes in presence of air and water to a greenish yellow color.
And by the way,which zeolite have you used to load the silver. A type A zeolite could easily break down structurally at high silver loadings and the amorphous alumino silicate may also result in a color change ?
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