Phase control synthesis of α, β and α/β Bi2O3 hetero-junction with enhanced and synergistic photocatalytic activity on degradation of toxic dye, Rhodamine-B under natural sunlight

Nano particles of a few alpha/beta Bi2O3 hetero-junctions of various compositions synthesized by one-pot hydro thermal method, exhibit exceptional and synergistic photo-catalytic activity for the degradation of Rhodamine-B in aqueous solution under natural sunlight. Pure alpha and pure beta Bi2O3 are also synthesized by control post heating of synthesized hetero-junction. The nano-materials were characterized by diffraction (XRD), microscopic and spectroscopic techniques. The XRD reveals alpha-beta phase hetero junctions of Bi2O3 are made of alpha-Bi2O3 and beta-Bi2O3 with average dimensions within 13-113 and 5-71 nm respectively and having band gap range of 2.4-2.9 eV. The spectrophotometrically determined % degradation of the dye and associated rate constant on the best hetero-junction are increased by 4.5(/12.1) and 3.3(/1.2) times than these on pure alpha (/beta). The effects of operational parameters and trapping agents have been analyzed. The maximum removal of the dye was achieved up to 99.6% in 3 h using 0.5 g/L photo-catalyst at pH 3. The reusability test shows that the photo-catalytic activity is retained excellently due to change in chemical nature of the catalyst from alpha -Bi2O3 to beta-Bi2O3, Bi2O2CO3 and BiOCl. A suitable mechanism is proposed.