Raman imaging towards in-situ visualisation of perchlorate adsorption

Raman imaging can directly visualise perchlorate adsorption, and even enables in-situ monitoring, because water has a low Raman activity and generates almost no interference, which is demonstrated herein. The Raman signal enhancement of perchlorate on the porous silver surface provides a possibility to monitor the adsorption of perchlorate at low level. From this initial adsorption assembly of (i) porous silver-perchlorate, we test several more, including (ii) porous silver-perchlorate-sand, (iii) porous silver-perchlorate-microplastic-sand, (iv) porous silver-perchlorate-microplastic-sand-river water etc. The introduction of microplastic, another emerging contaminant, can provide extra insights into the co-adsorption process. Particularly the composite structure of microplastic-sand can simultaneously visualise the adsorption of perchlorate on the silver surface, the plastic/organic surface and the sand surface. We note that the water can modify the configuration of perchlorate in-situ towards the adsorption on silver surface; the adsorption of perchlorate can benefit from co-adsorption with organic matter, and the rough surface plays an important role as well. Overall, Raman imaging provides an effective approach to directly visualise the adsorption of emerging contaminants.