Highly Efficient Degradation of Toxic Congo Red Dye under Sunshine Using a Mesoporous BiZnO3/g-C3N4 Nanocomposite

Abstract

The presence of toxic Congo red (CR) dye in water has significant impacts on human health and the environment. The development of a cost-effective and efficient technique for CR degradation is essential. In this study, mesoporous BiZnO₃/g-C₃N₄ nanocomposites were synthesized via thermal decomposition for the degradation of CR dye under sunshine. Powder X-ray diffraction analysis revealed the formation of pure phases of the materials, with the average crystallite size of BiZnO₃ being 20.89 nm. The Fourier transform infrared spectrum shows the presence of different functional group such as Bi–O, Zn–O, C–N, and C═N. The surface morphology of the sample showed BiZnO₃ nanorods (100–300 nm) embedded in g-C₃N₄ sheets. The high-resolution transmission electron microscopy image showed the formation of lattice fringes with an interplanar spacing of 0.200 nm, corresponding to the (431) plane of BiZnO₃. The specific surface areas of mesoporous BiZnO₃, g-C₃N₄, and BiZnO₃/g-C₃N₄ were 14.02, 17.30, and 45.82 m² g^–1, respectively. The direct band gaps of BiZnO₃, g-C₃N₄, and BiZnO₃/g-C₃N₄ were found to be 3.37, 2.90, and 3.43 eV, respectively. The BiZnO₃/g-C₃N₄ nanocomposite exhibited 99.79% removal of CR dye within 1 h and followed a first-order reaction kinetic model, with a rate constant of 0.0470 min^–1. The degradation efficiency decreased with an increase in the pH of the solution, with the maximum efficiency observed at pH 2. The presence of coexisting anions affected the degradation efficiency in the following order: IO₃^– > Cl^– > Br^– > NO₃^– > PO₄^3–. Scavenger experiments indicated that ^•OH and h⁺ are the active species involved in CR degradation. Furthermore, after six recycling runs, the catalyst performance showed only a 6% decrease, indicating the stability of the BiZnO₃/g-C₃N₄ nanocomposite. This study demonstrates that the synthesized BiZnO₃/g-C₃N₄ nanocomposite holds significant potential for the effective removal of toxic CR dye from wastewater.