Response surface optimization of hydrothermal synthesis of Bismuth ferrite nanoparticles under supercritical water conditions: Application for photocatalytic degradation of Tetracycline

Abstract

Ultrafine bismuth ferrite (BiFeO3) powders have been successfully synthesized through supercritical water hydrothermal technique, in a batch type reactor. A Box–Behnken three-level experimental design was used to optimize the process variables affecting the BiFeO3 efficiency includes pH of starting solution (1.5–12.5), reaction time (1–2 h), and reaction temperature (450–550 ℃). The samples were characterized via X–ray powder diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The model was validated by analysis of variance (ANOVA) and conducting an experiment at optimal design conditions (temperature of 522 ℃, pH of 3.25 and 1.3 h). The maximum BiFeO3 production efficiency which obtained at optimum condition was about 45%. The attained results showed good correlation between the predicted model and experimental data (Model P-Value = 0.0052). The present work confirmed that the supercritical water hydrothermal method is a suitable way to produce BiFeO3 nanoparticles with a mean grain size of 60 nm and narrow size distribution. Moreover, the optical property of the product was investigated by Ultraviolet-visible diffuse reflectance spectroscopy (DRS). The attained nanostructures showed a narrow band gap of 1.96 eV, indicating that BiFeO3 powders can be applied as a novel visible-light-responsive photocatalyst for degradation of tetracycline (TC). Photocatalytic experiments revealed that using BiFeO3 nanoparticles, TC degradation efficiency of 80.3% and 87.5% could be reached under UV and visible light radiations, respectively. Furthermore, it was found the degradation of TC follows the pseudo-second-order kinetics by BiFeO3.