Hydrothermal synthesis of a photocatalyst based on Byrsonima crassifolia and TiO2 for degradation of crystal violet by UV and visible radiation

Abstract

This work presents a one-step synthesis methodology for preparing a hydrochar (HC) doped with TiO₂ (HC-TiO₂) for its application on the degradation of crystal violet (CV) using UV and visible radiation. Byrsonima crassifolia stones were used as precursors along with TiO₂ particles. The HC-TiO₂ sample was synthesized at 210 °C for 9 h using autogenous pressure. The photocatalyst was characterized to evaluate the TiO₂ dispersion, specific surface area, graphitization degree, and band-gap value. Finally, the degradation of CV was investigated by varying the operating conditions of the system, the reuse of the catalyst, and the degradation mechanism. The physicochemical characterization of the HC-TiO₂ composite showed good dispersion of TiO₂ in the carbonaceous particle. The presence of TiO₂ on the hydrochar surface yields a bandgap value of 1.17 eV, enhancing photocatalyst activation with visible radiation. The degradation results evidenced a synergistic effect with both types of radiation due to the hybridized π electrons in the sp²-hybridized structures in the HC surface. The degradation percentages were on average 20% higher using UV radiation than visible radiation under the following conditions: [CV] = 20 mg/L, 1 g/L of photocatalyst load, and pH = 7.0. The reusability experiments demonstrated the feasibility of reusing the HC-TiO₂ material up to 5 times with a similar photodegradation percentage. Finally, the results indicated that the HC-TiO₂ composite could be considered an efficient material for the photocatalytic treatment of water contaminated with CV.

Keywords: Crystal violet degradation; Hydrochar composite; Photocatalysis; Titanium dioxide; Visible light photocatalysis.