Synthesis of α-β Bi2O3 heterojunction photocatalyst and evaluation of reaction mechanism for degradation of RhB dye under natural sunlight

A few biphasic nano composites containing alpha and beta Bi2O3 of varying composition were synthesized by facile solvothermal method without using any capping agent and further calcination. X-ray diffraction, microscopic and spectroscopic techniques were employed for characterization of the as synthesized catalysts which are used as photocatalysts in degradation of pollutant, Rhodamine B (RhB) dye. The band gap of the nanocatalysts as calculated from tauc plot varies within 2.35-2.58 eV for beta-form and 2.85-3.19 eV for alpha-form in the alpha-beta Bi2O3 hetrojunctions. The operational parameters that influence the degradation process were optimized. The best catalyst dosage and pH are 0.5 gL(-1) and 4 respectively and the best concentration of H2O2 when added is 2 mM for 10 ppm aqueous solution of dye. Among different heterojunctions, the best catalyst which is produced from bismuth nitrate concentration of 0.05 M, degrades RhB up to 99.6% at pH 4 under 120 min sunlight irradiation. The effects of addition inorganic salts in RhB dye solution were also examined. The radical trapping experiments have been applied to explore the involved and main species responsible for degradation. The identification of degradation products of RhB was analyzed and the plausible mechanistic pathway is drawn from HPLC and HRMS. It shows that the degradation of RhB proceeds via initial generation of N-deethylated products followed by ring opening ones, which indicates the photosensitization induced photocatalytic mechanism of the reaction.