Microwave-mediated synthesis, photocatalytic degradation and antibacterial activity of α-Bi 2 O 3 microflowers/novel γ-Bi 2 O 3 microspindles

Abstract The present article portray the microwave (MW) synthesis of alpha bismuth oxide microflowers ( α -Bi 2 O 3 MFs) and novel gamma bismuth oxide microspindles ( γ -Bi 2 O 3 MSs) using bismuth nitrate pentahydrate [Bi(NO 3 ) 3 .5H 2 O], and polyvinylpyrrolidone (PVP) as a surfactant. The structural, BET surface area, morphological, photocatalytic activity under ultraviolet (UV) light and antibacterial performance was investigated with varying MW irradiation time. XRD study confirmed the formation of monoclinic ( α -phase) and body-centered cubic ( γ -phase) of Bi 2 O 3 with variation of MW irradiation time for 10 min and 15 min respectively. SEM images revealed the formation of microflowers for α -Bi 2 O 3 and microspindles for γ -Bi 2 O 3 . Further HR-TEM illustrated the appearance of nanoflakes (19–35 nm) and the rose-flowers, and back-bending man (15–30 nm) like structures for α -Bi 2 O 3 MFs and γ -Bi 2 O 3 MSs correspondingly. Interestingly, the comparative photocatalytic activity of α -Bi 2 O 3 MFs and γ -Bi 2 O 3 MSs were evaluated under UV-light irradiation for the degradation of five different dyes viz. malachite green (MG), eriochrome black-T (EBT), methyl thymol blue (MTB), bromophenol blue (BPB), and congo-red (CR). The α -Bi 2 O 3 MFs show enhanced photocatalytic activity than γ -Bi 2 O 3 MSs under UV light without decreasing efficiency up to four consecutive cycles and fallows the pseudo-first order reaction kinetics and degradation order: MTB>MG>EBT>CR>BPB. Furthermore, antibacterial assay of α -Bi 2 O 3 MFs and γ -Bi 2 O 3 MSs was carried out against gram-positive ( Staphylococcus aureus ( S a) and Pseudomonas aeruginosa ( P a)) and gram-negative ( Escherichia coli ( E c), and Klebsiella Pneumonia ( K p)) human pathogenic bacteria using agar well diffusion method. The α -Bi 2 O 3 MFs show comparatively better antibacterial activity against P a than γ -Bi 2 O 3 MSs . The current study provides a simple approach to design the α -Bi 2 O 3 MFs and novel γ -Bi 2 O 3 MSs as a photocatalyst for the environmental remediation of organic pollutants (OPs).