Porous Silicon Working as Immobilizer of TiO2 Decorated with Metal Nanoparticles Analyzing the Absorber and Photocatalytic Activity for Dexamethasone

Abstract

In this investigation, we report the fabrication of heterostructures based on porous silicon (PS) obtained by Metal-Assisted Chemical Etching and titanium dioxide synthesized by the solvothermal method decorated with Au or Ag nanoparticles obtained by chemical reduction of metallic salts. Four different heterostructures were obtained, which were labeled as PS, PS/TiO2, PS/TiO2-Ag, and PS/TiO2-Au, and their morphological, structural, and optical characteristics were analyzed, as well as the interaction with dexamethasone (adsorption and photodecomposition). The morphological characterization of PS showed that the pore size is around 95 nm, 20 μm in length with cylindrical form. The titanium dioxide was synthesized and deposited on PS using the solvothermal method, resulting in a conformal deposit on the surface area. The structural analysis demonstrated the vibration modes of porous silicon and titanium dioxide. This analysis determined the predominance phase, and no evidence of the metallic particles was found. Diffuse reflectance was used to obtain the bandgap (BG) of the heterostructures by using the Kubelka–Munk method. These energies were 1.54 eV for PS and 3.2, 2.88, and 2.71 eV for PS/TiO2, PS/TiO2-Ag, and PS/TiO2-Au, respectively. The decoration with Ag and Au nanoparticles did not exert a considerable effect on the optical properties of the materials. The heterostructure with Ag showed the highest degradation percentage compared to the others. This could be due to the BG (2.88 eV) and the distribution of the Ag nanoparticles. The PL spectra displayed the emission light above 2.4 eV of the heterostructures. All heterostructures showed adsorption of dexamethasone, but only three heterostructures displayed photodegradation (the samples with TiO2) with percentages of 5, 18, and 7% for PS/TiO2, PS/TiO2-Ag, PS/TiO2-Au, respectively. The photodegradation tests were performed using a UV light source of 390 nm separated 20 cm between the source and the heterostructure and 40 ml of aqueous dexamethasone with an initial concentration of 1 mM. The UV source was used because the excitation of the material is in the UV range.