Sol-gel synthesis of efficient p-type Ca2+@Bi-ferrites for gas sensing and photocatalytic applications

Herein, we report the sol-gel synthesis and characterizations of pure and Calcium (Ca) doped Bismuth ferrites (BiFeO₃) for H₂S gas sensing and Cr (VI) pollutant reduction. X-ray diffraction confirmed the rhombohedral structure along the RC3 space group of synthesized ferrites. Raman analysis and EDX spectroscopy confirmed the cooperation of Ca²⁺ ions in the host lattice. Contraction in optical bandgap was observed with increasing concentration of Ca²⁺ dopants. Sensitivity towards the reducing gas (H₂S) recorded increased from ∼4.5 for pure BiFeO₃ to ∼ 226 for 18 % Ca²⁺ doped BiFeO₃. The response time of 18 % Ca²⁺ doped BiFeO₃ remained very fast 1–2 s in 5 ppm–25 ppm exposure of H₂S gas. The gas-responsive curves exhibited the p-type behavior of ferrites and such fast and improved response time was not reported in p-type semiconductors. Furthermore, the Cr (VI) dye degradation was recorded under the illumination of visible light and the 35W Xe arc lamp is taken as the source of visible light. The photodegradation of Cr (VI) improves significantly from 58 % for pure BiFeO₃ to 90 % for 18 % Ca²⁺ doped BiFeO₃. The photostability of 18 % Ca²⁺ doped BiFeO₃ is well because the reduction of Cr (VI) recorded up to ∼64 % for 20 cycles. Substitution of Bi³⁺ with Ca²⁺ causes the oxygen vacancies and the amount of Fe³⁺ valance potentials altered significantly as well as 18 % Ca²⁺ doped BiFeO₃ illustrated the iron (IV) higher amount state (Fe⁴⁺) with valence band at 2.47 eV and conduction band at 0.61 eV vs. normal hydrogen electrode. These findings depict that the 18 % divalent (Ca²⁺) doped BiFeO₃ is an excellent candidate for H₂S gas sensing and photocatalytic applications.