The role of graphene and europium on TiO2 performance for photocatalytic hydrogen evolution

Highly efficient Eu-TiO2/graphene composites were synthesized by a two-step method such as sol-gel and hydrothermal process. The synthesized photocatalysts were characterized by XRD, TEM, XPS, UV-vis diffuse reflectance spectroscopy and photoluminescence (PL) spectroscopy. The results confirmed that anatase Eu-TiO2 nanoparticles with average 10 nm sizes were successfully deposited on two-dimensional graphene sheets. The UV-visible spectroscopy showed a red shift in the absorption edge of TiO2 due to Eu doping and graphene incorporation. Moreover, effective charge separation in Eu-TiO2/graphene composites was confirmed by PL emission spectroscopy compared to TiO2/graphene, Eu-TiO2 and pure TiO2. The photocatalytic activity for H2 evolution over prepared composites was studied under visible light irradiation (λ ≥ 400 nm). The results demonstrate that photocatalytic performance of the photocatalysts for hydrogen production increases with increasing doping concentration of Eu upto 2 at%. However, further increase in doping content above this optimum level has decreased the performance of photocatalyst. The enhanced photocatalytic performance for H2 evolution is attributed to extended visible light absorption, suppressed recombination of electron-hole pairs due to synergistic effects of Eu and graphene.