On stability of hydroxyl groups on substituted titania

The present study reports the stability of hydroxyl groups involving the surface coordinated oxygens of Pd, C, N-doped, Pd/C and Pd/N-codoped anatase TiO2, probed using DFT calculations. Two unique surface planes, (001) and (100), were chosen for the analysis of stability of hydroxyl groups and their activities were studied from the net oxygen activation analysis. Hydroxyl group formation energies ranged between -6.16 to -7.88 eV for C,N-doped, Pd/C and Pd/N-codoped TiO2 (001) and (100) planes. The order of hydroxyl stability was observed to be TiO2 (001) > TiO2 (100) > Pd/C-codoped (001) > Pd/N-codoped (100) > Pd/C-codoped (100) > N-doped (001) > C-doped (100) > N-doped (100) > Pd/N-codoped (001) > C-doped (001) plane of TiO2. Although, the formation energies of Pd/C and Pd/N-codoped TiO2 were marginally higher compared to that of pure TiO2 (001) and (100) planes, they exhibited higher net oxygen activation of 32.1% and 28.9% over surface exposed (100) plane which indicated the better feasibility of reversible exchange of lattice oxygen. Electron density maps displayed the surface reconstruction phenomenon corresponding to the rearrangement of surface atoms and the transfer of electrons between O-H over (001) and(100) planes of C, N, Pd/C and Pd/N-codoped TiO2.