Adsorption efficiency and photocatalytic activity of Ni- Bi4V2O11 oxide catalyst were correlated well with the variation in phase crystal structures stabilized at room temperature as a function of composition. The best photocatalytic performance exhibited by gamma– stabilized phases of the tetragonal symmetry ( space group I4/m mm) were attributed to their higher specific surface area, narrower band– gap energy and higher oxygen vacancy concentration in the perovskite vanadate layers.

However, in Case of Mn-Bi4V2O11 oxide catalyst The β (orthorhombic) –phase, space group Acam exhibited the highest photocatalytic degradability, indicating that the photocatalytic efficiency of this catalyst is essentially enhanced by the increased number of catalyst active sites, irrespective of the kind of phase stabilized and the increasing photoabsorption ability with Mn dopant content.

To my knowledge, the purpose to dope a specific transition metal onto photocatalyst is to promote separation of charges and decreases the electron and hole recombination rate and thereby increasing the quantum yield of the photocatalytic process, thus favouring the photocatalytic activity. Otherwise, doping leads to the formation of localized states within the band gap, owing to oxygen vacancies, absorbing light with energy lower than the parent photocatalyst.