Fabrication of highly efficient water splitting CoxNi1-xTa2O6 (x = 0-1) photocatalysts with high crystallinity and surface nanostructure

Porous CoxNi1-xTa2O6 mesoporous nanomaterials were synthesized through a sol-gel route using the spray-dried method. They had high photocatalytic activity for water splitting into H2 and O2 under visible light. The X-ray diffraction (XRD) patterns of CoxNi1-xTa2O6 revealed that Co atoms could displace Ni atoms in the NiTa2O6 bulk lattice to form a solid solution. A field emission scanning electron microscope (FE-SEM, JSM-6700F) image showed that the microspheres were constructed of irregular nanoparticles randomly stacked to form a mesoporous structure. UV-Vis diffuse reflection spectroscopy (DRS) was used to determinate the band gap changes of CoxNi1-xTa2O6 samples, which extended towards the visible light region. However, the photocatalytic activity did not have a linear relationship with the band gap, even when the effect of the s urface area was considered. The distortion index of the TaO6 octahedral lattice was found to be an important influencing factor, and Co0.8Ni0.2Ta2O6 showed high photocatalytic efficiency with a maximum of 1367 μmol h−1 g−1 for H2 yield, which made it a promising candidate for splitting water.