An answer is not straightforward.

First of all, bimetallic nanoparticle can be characterize by FT-IR, but the application in complex matrices like soil or water is quite complicated (maybe, even useless).

For example, oxide-supported bimetallic nanoparticles can be characterized using FT-IR, in transmission mode or DRIFT, by means of probe molecule adsorption (such as, CO). In this case you can focus your attention on specific frequencies related to adsorbed carbonyls on the top of metallic sites. This kind of characterization has been performed for decades to date and it is very useful in Material Science: it is very helpful in determining the oxidation state of metallic sites, the "grade of isolation" (isolated ions, clusters, etc.), the alloy formation, and so on.

However, soil and water contain several other elements that could interfere with the analysis. So, this kind of approach couldn't be very helpful, but it strongly depends on the concentration of your bimetallic species.

I never analyzed such samples, but in liquid-phase (i.e. water) you could be able to detect bimetallic nanoparticle, by means of MES-DRIFTS setup, by removing the contribution of spectator species and noise. However, I don't know which concentration of spectator species you should have. This is up to you. If these samples are prepared in your lab, you could make up a protocol by measuring different samples at different concentration of bimetallic NPs and other spectator species.

Thank you so much Pierfrancesco Ticali . Actually, on general basis how to identify bimetallic nanoparticles have been formed from FTIR Characterization?

As I mentioned, for solid samples, like oxide-supported metal NPs, you could use probe molecules.

For examples, you could put you sample in DRIFTs cell (e.g. Praying Mantis cell) or in a suitable cell for transmission spectroscopy (e.g. pelletized sample in a cell to connect to a gas/vacuum line). By injecting CO it can be adsorbed on your sample generating peaks at different frequencies according to the bonded metallic sites.

Bear in mind that soils are very complex matrices and it could be very difficult (maybe impossible) to characterize the bimetallic species.

In liquid-phase it is a complete different story, because you have to focus on other typical features of the bimetallic species. Solvents and spectator species could make your analysis useless. As I said, I never performed measurements in liquid-phase, so I cannot really help for it.

In the end, it depends on what kind of topic you want to study. If you are studying bimetallic NPs to put in soils to catalyze the degradation of pollutants then you can reproduce it on a laboratory scale by analyzing the NPs without any other species.