Low temperature hydrothermal synthesis, evaluation of band gap energies and catalytic performance for Biginelli reactions of Sr2-xAxNb2O7+δ (A=Eu3+ and Nd3+) (x = 0.01 and 0.05) nanomaterials

Nano powders Eu3+ and Nd3+ - doped Sr2Nb2O7 were prepared by a low temperature hydrothermal method at 120 ºC for 48 h followed by annealing at 400 ᵒC for 3 h among Sr(NO3)2 and Nb2O5, Eu2O3 and Nd2O3 raw materials at stoichiometric 1:1 Sr:Nb molar ratio. Characterization of the synthesized materials was performed by X-ray powder diffraction (XRPD) technique. FullProf program employing profile matching with constant scale factors was employed for structural analysis. The results showed that the patterns had a main Sr2Nb2O7 orthorhombic crystal structure with space group . FESEM images showed that the synthesized nanomaterials had flower morphologies. Ultraviolet-visible spectra analysis showed that the synthesized Eu3+ and Nd3+ - doped Sr2Nb2O7 nanomaterials had light absorption in the ultraviolet light region. The direct optical band gap energies obtained from UV-Vis absorption spectra were 3.45, 3.50 and 3.80 eV for pure Sr2Nb2O7, S2 and S4, respectively. The catalytic activity of the obtained materials in the one-pot synthesis of the heterocyclic compounds 3,4-dihydropyrimidin- 2(1H)-ones (DHPMs) in Biginelli reaction is investigated. The optimized 0.03 g of the catalyst, 95 ºC reaction temperature, and 60 min reaction time are used for the other Biginelli reactions in this work.