The adsorption of oxyanions unto metal oxides surfaces and nanoparticles is a common and critical reaction that influences the transport of contaminants and nutrients as well as the reactivity and behavior of these materials in conjunction with their use as catalysts and in ion batteries. Here, we present investigations of oxyanions adsorption on ferrihydrites (chloride, nitrate, sulfate, phosphate, and arsenate) and lithium cobalt oxide (phosphate) nanoparticles using operando and in situ flow microcalorimetry. In both cases, and in addition to obtaining the net adsorption enthalpy, peak shapes analyses reveal that oxyanions reactions differed kinetically in that heat evolution and reaction times were not uniform suggesting underlying reactions occurring at different times. Combining the thermodynamic measurements with a time-sequence in situ ATR−FTIR with two-dimensional correlation analysis, a method adapted from Prof. Grassian’s earlier work, clarifies the spectroscopic signatures of phosphate adsorption and indeed reveals two underlying processes that occur sequentially. This mechanistic insight is extended to the other oxyanions and analyzed in the context of the energetic implications of these adsorption reactions.

Temporal evolution of oxyanions adsorption studied by operando flow microcalorimetry and time-sequential FTIR with correlation analysis

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