(Photo)catalysis by ferric (hydr)oxide nanoparticles (NPs) in water underlies many important geochemical processes and environmental remediation technologies. These heterogeneous reactions have been extensively studied using batch kinetic measurements which suffer from the intrinsic limitations originated from the aggregation of NPs.  Using a new method that combines in situ FTIR spectroscopy and ex situ XPS to overcome this limitation, we study the effect of size on the (photo)catalytic oxidation of Mn(II) and Fe(CN)62- on hematite (a-Fe2O3) and ferrihydrite NPs. We find that both the oxidative catalytic and photocatalytic performances of these NPs per surface area degrade with decreasing their size. Given the nanosize-induced changes in the electronic properties of ferric (hydr)oxides and the thermodynamic properties of the system, we demonstrate that the catalytic reaction proceeds through the electrochemical pathway, in contradiction to the conventional chemical paradigm. We explain the found correlation between catalytic and photocatalytic properties of the NPs. The new mechanistic insights suggest new interpretation of literature data, open up new possibilities for manipulating technological performance of metal oxides, and conceptually broaden our general understanding of (bio)chemical activity of metal oxide NPs.

What can we learn from combination of in situ FTIR spectroscopy and ex situ XPS about (photo)catalytic reactions at mineral-water interfaces?

245th National Meeting (2013)

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