AgBr/SrTiO3 was photoreduced in a methyl orange solution under visible light for 50 seconds. The powder color turned from whitish to dark brown indicating the successful reduction of AgBr to Ag/AgBr. The presence of metallic Ag was confirmed by XPS, however, no XRD peaks for metallic Ag were observed. Such phenomenon has also been observed by others e.g.
1.L. Ye, J. Liu, C. Gong, L. Tian, T. Peng and L. Zan, ACS Catal., 2012, 2,
1677-1683; 2. Y. Zhang, Z.-R. Tang, X. Fu and Y.-J. Xu, Appl. Catal., B, 2011, 106, 445-452.
Can it be because of very small particle size of metallic Ag which is formed on the surface of AgBr? Or some other reasons?
The concentration of the species may be low and longer x-ray irradiation needed in addition to the possibility of small sized particles. I'd also look very carefully for the presence of silver oxide (Ag2O). Brown color is usually indicative of this species whereas black is expected for metallic Ag. In what oxidation state was the Ag from XPS? It may only be shifted 0.7 or 0.8 units (indicating an oxidation state nominally of +1) from that expected for Ag metal.
Thank you very much for the insightful answer Dr. Rawle. The XPS spectrum shows +1 and 0 oxidation states for Ag. More specifically, two peaks at 373.5 and 367.5 eV can be assigned to Ag 3d3/2 and Ag3d5/2 of Ag+1, respectively. Similarly, two peaks at 374.0 and 368.0 eV are assigned to Ag 3d3/2 and Ag3d5/2 of Ag0, respectively.
Dear Dr. Zameer Hussain Shah
Hi,
Do not worry about that. It is a usual case in many papers. Due to low content of metallic silver, we cannot see any peak for this component; because detection limit of XRD is not very high. If you want to see the peaks of metallic silver, you can simply increase the irradiation time to increase production of metallic silver.
Dear Dr. Zameer Hussain Shah
If the amount of Ag is blow 5%, it is impossible to detect by XRD. XPS is better to measure Ag and AgBr.
Hello
good evening
Perhaps If the thickness of the metallic Ag film which is formed on the surface of AgBr film is very small , it may be too small to produce a sufficient signal for "bulk" material characterisation techniques (XRD). In contrast, XPS surface analysis technique, allows the analysed thickness to be reduced to only 3 nm.
Have a nice day
Kind regards
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