Detailed structural and optical studies of the microwave synthesized β-Bi2O3 nanostructured photocatalysts: Photocatalytic applications on anionic and cationic organic dyes

Abstract

Photocatalytic degradation is a popular technique, has been used to degrade toxic and harmful chemicals like organic dyes, usually released from industries. For decades, research has been conducted to develop appropriate photocatalysts that can degrade these harmful dyes efficiently when irradiated with light sources such as ultraviolet and visible radiations; sometimes direct Sun light can also be used. Out of many semiconductor oxide materials used as photocatalysts, the most important material is Bi2O3 as it is active in the visible region. Keeping that in mind, in this work, Bi2O3 was prepared through microwave method of synthesis by rapidly heating the sample. This has resulted in the formation of β-phase Bi2O3 with tetragonal structure that was confirmed by X-ray diffraction and Raman spectroscopy. The scanning electron microscopy analysis showed that the Bi2O3 sample has a nanosheet like morphology and the sheet structure possessed large surface area of 7.58 m2/g for adsorption of dye molecules during photocatalysis. Photodegradation studies were performed on two cationic dyes namely Malachite green (MG), and rhodamine B (RhB) and two anionic dyes namely Methyl orange (MO), and Congo red (CR) under sunlight irradiation. A maximum degradation efficiency of 97.2%, and 90.7% were obtained for MG and RhB for 240 min of sunlight irradiation. Whereas, upon 60 min of sunlight irradiation, the degradation efficiency of 91.8% and 93.7% were obtained for MO and CR respectively. The β-Bi2O3 photocatalyst was found to be structurally stable as well as photostable when used in continuous photodegradation experiments. A systematic study on the structural, optical and microstructure characteristics of Bi2O3 was performed and its application for the photocatalytic degradation of four different organic dyes is presented in this work.