SnO2(β-Bi2O3)/Bi2Sn2O7 nanohybrids doped with Pt and Pd nanoparticles: applications in visible light photocatalysis, electrical conductivity and dye-sensitized solar cells

Abstract

Bi₂O₃–SnO₂ nanocomposites formed at a nominal molar ratio of 3 : 1 and loaded with Pd/Pt nanoparticles synthesized by a sol gel-hydrothermal method with the aid of a template were thoroughly characterized by X-ray diffraction, TEM-EDX, N₂ sorptiometry, diffuse reflectance UV-Vis, FTIR, photoluminescence and electrical conductivity. It has been shown that Pd and Pt stimulate the existence of β-Bi₂O₃ and SnO₂, respectively together with the key component Bi₂Sn₂O₇. The photocatalytic results indicate that Pd/β-Bi₂O₃–Bi₂Sn₂O₇ revealed a remarkable performance for the degradation of methylene blue (MB) dye as compared to the Pt/SnO₂–Bi₂Sn₂O₇ and Bi₂O₃–SnO₂ samples in both the UV and visible regions. The enhanced photocatalytic activity of the Pd/β-Bi₂O₃–Bi₂Sn₂O₇ nanocomposite is primarily attributed to the broad contact between the β-Bi₂O₃ and Bi₂Sn₂O₇ phases, which indicates high mesoporosity and heterojunction structures resulting in separation efficacy between photo-induced electron–hole pairs. Specifically, the photosensitive β-Bi₂O₃ is easily excited and released electrons to be accepted by Bi₂Sn₂O₇ and Pd that might be deposited in the interlayer between β-Bi₂O₃ and Bi₂Sn₂O₇. The degradation mechanism of MB over Pd/β-Bi₂O₃–Bi₂Sn₂O₇ in the visible region showed that the dye degradation proceeds through evolution of ˙O₂⁻ and ˙OH radicals as evaluated using photoluminescence and free radical trapping experiments. An insight into the electrical properties including the dielectric constant and impedance of the materials indicates that Pd/β-Bi₂O₃–Bi₂Sn₂O₇ has the highest conductivity based on increasing the ionic transport and defects at the β-Bi₂O₃/Bi₂Sn₂O₇ heterojunction. This material displayed an improved photocurrent response of a higher power conversion efficiency, exceeding that of Pt/SnO₂–Bi₂Sn₂O₇ and SnBi₃ by 50% and 250%, respectively, in dye-sensitized solar cells. Picosecond-resolved photoluminescence (PL) and polarization gated PL anisotropy measurements were combined to clarify the process of FRET from the excited Pd/β-Bi₂O₃–Bi₂Sn₂O₇ to SD N719. This indicates that the latter structure can be proposed as a multifunctional candidate for use in dye-sensitized solar cells, as an electrical material and as an efficient photocatalyst based on its versatile structure.