Multifunctional brownmillerite KBiFe2O5: Structural, magneto-dielectric, optical, photoelectrochemical studies and enhanced photocatalytic activity over perovskite BiFeO3

Brownmillerite KBiFe2O5 (KBFO) absorbs large part of the solar spectrum due to its smaller bandgap. This optical response has immense potential in photocatalytic applications. In this work, KBFO was successfully synthesized using citrate combustion method. X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS) as well as Mössbauer spectroscopic studies, identify the valence state of Iron (Fe) as Fe3+. The strong magneto-dielectric coupling in KBFO was demonstrated by integrating both magnetization (M) and dielectric constant (ε) characteristics as a function of temperature. Magnetic and dielectric transitions were observed in close proximity in temperature range ∼780 K–760 K respectively. To the best of our knowledge, the photoelectrochemical properties of as developed KBFO were analyzed for the first time revealing a significant photoresponse with an average photocurrent density of 0.1 μA cm−2. The photocatalytic properties of KBFO were investigated by degrading organic effluent methylene blue (MB) under direct sunlight followed by a comparison with the photodegradation performance of perovskite BiFeO3 (BFO). KBFO showed enhanced photocatalytic performance as compared to BFO due to its enhanced structural and optical properties. [Display omitted] •Multifunctional brownmillerite KBiFe2O5 developed using citrate combustion method.•Strong magneto-dielectric coupling in KBiFe2O5.•Photoelectrochemical properties of KBiFe2O5 analyzed for first time and average current density found to be ∼0.1 μA/cm2•Enhanced photodegradation efficiency of KBiFe2O5 (Eg = 1.67eV), over regular perovskite BiFeO3 (Eg = 2.1 eV).