Butterfly cluster like lamellar BiOBr/TiO2 nanocomposite for enhanced sunlight photocatalytic mineralization of aqueous ciprofloxacin.Sci Total Environ. 2019 May 15; 665:668-677.ST
The present study for the first time reports facile in-situ room temperature synthesis of butterfly cluster like lamellar BiOBr deposited over TiO2 nanoparticles for photocatalytic breakdown of ciprofloxacin (CIP). The butterfly cluster arrangement of BiOBr resulted in an increase in surface area from 124.6 to 160.797 m2·g-1 and subsequently increased incident light absorption by the composite photocatalyst. The XRD indicated the existence of TiO2 as spherical ≈10-15 nm diameter particles with  preferential growth planes of anatase phase while the lamellar BiOBr showing growth along  and  preferential planes that were also confirmed by the HR-TEM images. DRS data implicated 2.76 eV as the energy band gap of the synthesized nanocomposite while PL spectroscopic analysis predicted it to be 2.81 eV. XPS measurements examined the chemical oxidation states of the constituents among the nanocomposite samples. The lameller structure of BiOBr in 15%BiOBr/TiO2 acts as a manifold promoting both visible light (λ > 420 nm) and direct sunlight catalytic degradation of 25 mg·L-1 aqueous CIP up to 92.5% and 100%, respectively within 150 min. The rate constant values suggested that the visible light photocatalysis of CIP with 15%BiOBr/TiO2 was 5.2 and 9.4 times faster compared to pristine TiO2 and BiOBr, respectively. The free radical scavenging study demonstrated that although photogenerated superoxide ions and holes contribute to the overall photocatalytic activity, yet, hydroxyl radicals predominantly control the CIP oxidation. The synthesized nanocomposite was re-used up to five cycles and retained 82.98% efficiency even after 5th use cycle showing a decline of only 12%. The catalyst stability and easy recovery adds to its reusability and value of the photocatalytic process.