Alkaline Earth Niobates as New Photocatalysts: Interplay between Structure, Ferroelectric Nature, and Photocatalytic Activity

A series of alkaline earth niobates, ANb2O6 (A = Ba, Sr, and Ca), was synthesized with the aim of probing the effect of A-site alteration in columbite structures. The prepared materials were thoroughly characterized to understand the structural, morphological, and physicochemical properties. The Rietveld refinement and Raman spectroscopy reveal that CaNb2O6 (CNO) crystallizes into a regular columbite structure; however, SrNb2O6 (SNO) and BaNb2O6 (BNO) deviate from the columbite structure owing to their bigger A-site ions. The prepared products were utilized for the photocatalytic reduction of Cr6+ and the degradation of several types of antibiotics, like ciprofloxacin, doxycycline, and metronidazole. The photocatalytic activity of the synthesized catalysts is in the order of SNO > BNO > CNO in all the pollutants. This can be attributed to the higher band gap and the lower rate of recombination in SNO. Additionally, these niobates exhibit ferroelectric behavior in the order of SNO > BNO > CNO. The projected density of states (PDOS) reveals a stronger p–d hybridization and higher empty d states, facilitating better ferroelectric behavior in SNO. This significantly lowers the charge recombination rate and boosts its photocatalytic activity. Therefore, this study correlates photocatalytic activity with the intrinsic ferroelectric nature of these niobates and opens up the scope for exploring these materials as a new class of ferroelectric photocatalysts.