Molecular and reactive adsorption of dimethyl methylphosphonate over (0 0 1) and (1 0 0) anatase clusters

Interaction of dimethyl methylphosphonate (DMMP) with clean, hydroxylated and hydrated (0 0 1) and (1 0 0) surfaces of TiO2 anatase was qualitatively modeled by ab initio quantum computations. The clean surfaces were represented by clusters Ti4O16H16 and Ti4O14H12, whereas hydroxylated and hydrated ones by clusters Ti4O17H18 and Ti4O15H14, respectively, which were constructed using published relaxed surface geometries. It was found that over clean surfaces molecular adsorption can proceed but dissociative adsorption is strongly endothermic. Over hydroxylated and hydrated surfaces, both molecular and reactive hydrolytic adsorption can proceed. The hydrolysis results in formation of adsorbed methanol or methoxy group and methyl methylphosphonate or methyl methylphosphonic acid. The results underscore the importance of either hydroxylation or hydration of anatase nanopowders applied for air decontamination.