Novel BiOIO3/Bi12O17Cl2 heterostructure for improved photocatalytic degradation of dye pollutants under low energy visible light irradiation
Osemeikhian Ogbeifun, Shepherd M. Tichapondwa, Evans M. N. Chirwa
Abstract
• Calcination of BiOIO 3 and Bi 12 O 17 Cl 2 precursors resulted in BiOIO 3 /Bi 12 O 17 Cl 2 -x:y heterostructures of various compositions (y:x mass ratio). • The BiOIO 3 /Bi 12 O 17 Cl 2 –1:1 heterostructure possesses the highest degradation capacity towards cationic and anionic dyes. • The higher redox potential and separation of holes and electrons in the material explained the better degradation performance reported for the material. • BiOIO 3 /Bi 12 O 17 Cl 2 –1:1 showed good stability after four cycles. Dye pollution resulting from industrial waste poses a substantial threat to both human health and the environment. The potential of advanced oxidation photocatalysis technology employing Bi 12 O 17 Cl 2 and BiOIO 3 semiconductor materials was explored. The inherent challenges of using individual materials for visible-light photocatalysis include the rapid recombination of photogenerated electron-hole pairs in Bi 12 O 17 Cl 2 and the limited photon utilisation of the visible light wavelengths by BiOIO 3 . Bi 12 O 17 Cl 2 displays visible light activity due to its narrow band gap energy, while BiOIO 3 possesses an internal electric field that promotes the separation of charge carriers. The combination of these materials was hypothesised to produce a more potent photocatalyst that synergises the ability of Bi 12 O 17 Cl 2 to respond to visible light and the capacity of BiOIO 3 to separate electrons and holes. Heterostructure composites with varying mass ratios (BiOIO 3 /Bi 12 O 17 Cl 2 -x:y) were fabricated to enhance the effectiveness of individual materials in combating dye pollution. Material characterisation by Electrochemical Impedance Spectroscopy (EIS), Photoluminescence (PL), and cyclic voltammetry (CV) revealed that the BiOIO 3 /Bi 12 O 17 Cl 2 –1:1 heterostructure exhibited the highest charge separation efficiency and redox potential amongst other heterostructures and individual materials. The average degradation rate constant, k , for dyes (rhodamine B and methyl orange) on BiOIO 3 /Bi 12 O 17 Cl 2 –1:1, BiOIO 3 and Bi 12 O 17 Cl 2 are 0.43 h −1 , 0.09 h −1 and 0.15 h −1 , respectively. These results translate to 4.7 times performance of BiOIO 3 /Bi 12 O 17 Cl 2 –1:1 over BiOIO 3 and 2.9 times over Bi 12 O 17 Cl 2 , which underscored the contribution of heterostructure formation in the photocatalytic degradation process. The proposed photocatalytic degradation mechanism highlights •OH and •O 2 – as the main participating species. Furthermore, BiOIO 3 /Bi 12 O 17 Cl 2 –1:1 exhibited good photocatalytic stability after four degradation cycles, with 96 % efficiency retention. Therefore, BiOIO 3 /Bi 12 O 17 Cl 2 –1:1 heterostructure material is promising in addressing the challenges posed by dye pollution in particular and organic pollutants in general.