The application of cyclic voltammetry coupled with surface plasmon resonance measurements to thiol-collector interactions with gold surfaces

摘要

Cyclic voltammetry coupled with surface plasmon resonance (SPR) spectroscopy has unexpectedly proved to be a useful tool for studying the interaction between thiol collectors, such as xanthate, and a gold surface. Sensor metal surfaces such as silver and copper may also be used. Strong responses have been obtained, especially for a longer chain xanthate, or for a trithiocarbonate collector. The SPR responses obtained for the various collectors appear to be mostly in accord with the accepted model referred to above. There is no increase in the SPR response until the electrode potential reaches the values where chemisorption and xanthate oxidation occur simultaneously. In that region the SPR response increases as expected. An interesting observation, however, is that when reduction of the dithiolate occurs, the SPR angle is still rather high, and that it does not decrease as expected from the electrode current. It might mean that xanthate is still adsorbed, although that seems to differ from observations that chemisorbed thiol layers result in adequate hydropho-bicity for flotation (Gardner and Woods, 1974), and that hydrophobicity is not detected at these negative potentials. Contact angle measurements could be used to investigate this potential region. The SPR response may be differentiated for more efficient comparison with cyclovoltammetry responses. This comparison shows current responses that do not affect the SPR response, i.e. those that do not involve the collector species. In this respect the SPR response is similar to other techniques such as SERS, FTIR, etc. The SPR response seems to be a very sensitive indicator of thiol species on the gold surface, although it cannot distinguish between e.g. chemisorbed collector species and oxidized collector species. It thus appears that SPR in this application is complementary to other spectroscopic techniques. The sensitivity of SPR has the promise of studying in more detail the initial phases of collector adsorption. It is known that sub-monolayer chemisorbed material can induce sufficient hydrophobicity for flotation (Woods et al., 2000). Thus a study of the initial formation of such layers can be of importance in better understanding the mechanism of flotation. Another strength of SPR combined with cydovoltammetry is that the measured response is proportional to the amount of thiol on the gold surface, and that it follows changes in this immediately. Thus the differentiated SPR response may be directly compared to the electrochemical response. This approach has proved useful in generally confirming the present model of thiol-gold interaction.