The high photocatalytic activity and reduced band gap energy of La and Mn co-doped BiFeO3/graphene nanoplatelet (GNP) nanohybrids

Abstract

Recently, bismuth ferrites have attracted great interest in the field of photocatalysis due to their magnetic nature and narrow band gap. Herein, nanohybrids of lanthanum (La) and manganese (Mn) co-doped BiFeO₃ (BLFMO)/graphene nanoplatelets (GNPs) have been synthesized. The hybrids were prepared by two different but simple and low-cost synthesis routes: (i) co-precipitation (namely the C-series), and (ii) hydrothermal (namely the H-series) methods. This article details a comparison of the C-series and H-series BLFMO/GNP nanohybrids based on their photocatalytic activity and band gap. The H-series nanohybrids showed a more crystalline structure, reduced band gap and less dye removal compared to the C-series nanohybrids. The enhanced dye removal (92%) of the C-series nanohybrids is attributed to their high surface area (55 m² g⁻¹) due to GNP incorporation inside the BLFMO/GNP nanohybrids. The higher surface area enables more adsorption of dye molecules over the catalyst surface under dark conditions. In addition, the band gap of the BLFMO/GNP nanohybrids was reduced from 2.04 eV (pure BiFeO₃) to 1.40 eV (BLFMO/GNPs) because of the presence of new donor energy levels with Mn loading. The calculated particle sizes from Scherrer’s formula were 19.3–23.5 nm (C-series) and 22.5–26 nm (H-series). The estimated particle size calculated via transmission electron microscopy (TEM) is approximately 31 nm for the C-series nanohybrids. The graphene based nanohybrids significantly enhanced dye removal compared to pure BiFeO₃ (44%) under visible light irradiation. The low cost, easy preparation and higher catalytic activity of the BLFMO/GNP nanohybrids reported here make nanohybrids suitable candidates for practical applications.