posted on 2023-08-07, 17:06authored byRené Hafner, Peter Klein, Herbert M. Urbassek
The presence of pharmaceuticals in drinking water has
generated
considerable scientific interest in potential improvements to polymeric
membranes for water purification at the nanoscale. In this work, we
investigate the adsorption of diclofenac and its ultraviolet (UV)
phototransformation products on amorphous and crystalline poly(vinylidene
difluoride) (PVDF) membrane surfaces at the nanoscale using molecular
modeling. We report binding affinities by determining the free energy
landscape via the extended adaptive biasing force method. The high
binding affinities of the phototransformation products found are consistent
with qualitative experimental results. For diclofenac, we found similar
or better affinities than those for the phototransformation products,
which seems to be in contrast to the experimental findings. This discrepancy
can only be explained if the maximum adsorption density of diclofenac
is much lower than that of the products. Overall, negligible differences
between the adsorption affinities of the crystalline phases are observed,
suggesting that no tuning of the PVDF surfaces is necessary to optimize
filtration capabilities.