Adsorption of Diclofenac and Its UV Phototransformation Products in an Aqueous Solution on PVDF: A Molecular Modeling Study

The presence of pharmaceuticals in drinking water hasgeneratedconsiderable scientific interest in potential improvements to polymericmembranes for water purification at the nanoscale. In this work, weinvestigate the adsorption of diclofenac and its ultraviolet (UV)phototransformation products on amorphous and crystalline poly(vinylidenedifluoride) (PVDF) membrane surfaces at the nanoscale using molecularmodeling. We report binding affinities by determining the free energylandscape via the extended adaptive biasing force method. The highbinding affinities of the phototransformation products found are consistentwith qualitative experimental results. For diclofenac, we found similaror better affinities than those for the phototransformation products,which seems to be in contrast to the experimental findings. This discrepancycan only be explained if the maximum adsorption density of diclofenacis much lower than that of the products. Overall, negligible differencesbetween the adsorption affinities of the crystalline phases are observed,suggesting that no tuning of the PVDF surfaces is necessary to optimizefiltration capabilities.