Photocatalytic hydrogen evolution over the isostructural titanates: Ba3Li2Ti8O20 and Na2Ti6O13 modified with metal oxide nanoparticles

Isostructural titanates exhibiting rectangular tunnel structure with the general formula Na₂Ti₆O₁₃ and Ba₃Li₂Ti₈O₂₀, were synthesized by solid state and sol-gel methods. The structural, morphological, optical, textural and electrical properties of the materials were characterized by XRD, SEM, UV-vis, BET and EIS. The photocatalytic activity for hydrogen evolution of the materials was evaluated under UV light. Na₂Ti₆O₁₃ exhibited higher activity (120 μmol/gh) than Ba₃Li₂Ti₈O₂₀ (30 μmol/gh), and it was attributed to the distortion of the octahedrons in Ba₃Li₂Ti₈O₂₀, which increases the recombination of charges in the material. Additionally, the 1D dimension obtained in Na₂Ti₆O₁₃ promotes a better charge separation, transport and utilization in this phase. The activity of the materials was enhanced with the incorporation of metal oxide nanoparticles MO (M = Cu, Ni) as cocatalysts. The activity of Ba₃Li₂Ti₈O₂₀ increased 10 times with the addition of CuO (240 μmol/gh), while the activity of Na₂Ti₆O₁₃ increased 3.5 times (416 μmol/gh). This improvement in the photocatalytic activity of the isostructural titanates was attributed to the formation of a p-n heterostructure between n-type titanates and p-type CuO, which promoted an enhanced charge separation, transference and utilization.