Molecular and reactive adsorption of dimethyl methylphosphonate over (001) and (100) anatase clusters

Interaction of dimethyl methylphosphonate (DMMP) with clean, hydroxylated and hydrated (001) and (100) 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.