Piroxicam Adsorption over Graphene OXIDE Nanosheets: A DFT-ONIOM Study

A theoretical study of piroxicam (PIR) adsorption over graphene (G) and graphene oxide (GO) sheets was made to find out whether these nanomaterials could be integrated as an additional element into the existing hybrid methodologies of water treatment, to eliminate this contaminating drug. The G-sheet was modeled starting from a polycircumcoronene cluster of 78 carbon atoms, which facilitated the good accommodation of the PIR drug over the sheet; to minimize edge effects, a chemical environment of carbons and hydrogens (C₇₂H₃₀) was added around the initial structure, using the ONIOM methodology, to thus obtain a final cluster of C₁₅₀H₃₀; after this, the G cluster was functionalized to obtain the GO-sheet with a C/O ratio of 5.33. The calculations were performed using the Density Functional Theory formalism implemented in Gaussian09 package. The PIR adsorption energy was about 19-21 kcal mol^-1, with adsorption distances less than 3.00 Å and a significant change of 327 meV in the gap (HOMO-LUMO) of the sheet, after the adsorption process. Some elongations of the bonds in the adsorbed PIR with respect to its free form were also observed. All these results indicated a favored chemisorption process and allowed us to confirm that GO-sheets could be a good adsorbent for this drug. The G-sheet also showed a good behavior as an adsorbent material.