Degradation of aqueous ketoprofen by heterogeneous photocatalysis using Bi2S3/TiO2–Montmorillonite nanocomposites under simulated solar irradiation

Abstract

The photocatalytic degradation of Ketoprofen (KP), 2-(3-benzoylphenyl)-propionic acid was studied under near UV–Vis irradiation (NUV-Vis) using supported photocatalysts. Bi2S3/TiO2-montmorillonite (Bi2S3/TiO2-Mt) photocatalysts were synthesized using a two- step ion exchange and impregnation method, and characterized using different techniques: Fourier transform infrared spectra (FTIR), X-ray fluorescence (XRF), X-ray diffraction (XRD), UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS) and photo-electrochemistry. Successful intercalation of TiO2 and Bi2S3 in the montmorillonite (Mt) was carried out, and the corresponding energy diagram for the Bi2S3/TiO2 heterojunction has been proposed. The resulting Bi2S3/TiO2-Mt nanocomposites were able to degrade KP under NUV–Vis irradiation. KP photodegradation was monitored by HPLC. The kinetics of photocatalytic transformation followed the Langmuir-Hinshelwood kinetic model. Pseudo-first-order kinetics adequately fitted the experimental data (t½ca. 17 min at pH 11, t½ca. 44 min at pH 3. 0.5 g·L−1 Bi2S3/TiO2 (25/75)-Mt nanocomposite). Factors affecting the kinetics of the process, such as the different Bi2S3/TiO2 ratio and initial pH solution have been discussed. KP photoproducts were identified using HPLC-MS, and the corresponding reaction mechanism has been proposed. Photodegradation of KP over Bi2S3/TiO2-Mt nanocomposites under NUV-Vis irradiation starts with the decarboxylation of KP and subsequent hydroxylation by HO• and oxidation by HO• and other reactive oxygen species (ROS) leads to the formation of photoproducts. TiO2 and Bi2S3 intercalated in the montmorillonite are cheap and efficient nanocomposites for the abatement of persistent organic pollutants (POP), such as KP, using NUV-Vis light.