Hydrothermal synthesis of bismuth niobates and their application in azo-dyes photo-discoloration

Combined experimental and DFT approach to BiNbO4polymorphs

“…The increased structural complexity of β-BNO lowers its symmetry as compared to α-BNO; hence extra Raman peaks are observed at 101, 459, and 697 cm −1 which are consistent with the findings in ref. 29 and 36 .…”

“…The observed minute differences in the FTIR absorbance among these two phases are due to the slight difference in the way the [Bi 2 O 2 ] layers are formed in these two polymorphs. 36 Since both polymorphs are made up of stacking layers of alternating [Bi 2 O 2 ] and [NbO 4 ] units, the bond vibrations have their origins in NbO 6 octahedra, Nb–O–Nb, Nb–O, Bi–O, and Bi–O–Bi. The stretching vibrations in Bi–O bonds are detected near 400 to 500 cm −1 .…”

“…The observed minute differences in the FTIR absorbance among these two phases are due to the slight difference in the way the [Bi 2 O 2 ] layers are formed in these two polymorphs. 36…”

“…34,35 The co-precipitation methods yield both pure a-BNO and mixed phases at ∼700 °C. [36][37][38] By varying the calcination temperature from 600 to ∼800 °C in the hydrothermal process, mixed, a-BNO and b-BNO phases were synthesized. 36,39 The sol-gel methods produced similar phases of BNO as the calcination temperature was varied across ∼600 °C (b-BNO), ∼700-900 °C (mixed a-b-BNO) and ∼900-1020 °C (a-BNO).…”

“…[36][37][38] By varying the calcination temperature from 600 to ∼800 °C in the hydrothermal process, mixed, a-BNO and b-BNO phases were synthesized. 36,39 The sol-gel methods produced similar phases of BNO as the calcination temperature was varied across ∼600 °C (b-BNO), ∼700-900 °C (mixed a-b-BNO) and ∼900-1020 °C (a-BNO). 21,21,24,25,29,40,41 The most widely used solid-state reaction technique stabilized the a-BNO and b-BNO at ∼1020 °C and ∼1040 °C respectively.…”