WEB Structural, microstructural and optical characterization of Bi2O3-Cu2O heterojunctions for photocatalytic applicationsWednesday (23.09.2020) 16:10 - 16:25 F: Functional Materials, Surfaces, and Devices 1 Part of:
Spherical nanoparticles of tetragonal β-Bi2O3 synthesized by flame spray were used as an n-type semiconductor to obtain Bi2O3-Cu2O heterojunctions to enhance their photocatalytic properties. Cu2O is a p-type semiconductor that exhibits high photocurrent density and remarkable photoactivity for hydrogen generation by water splitting. Analytical grade Cu2O powder was used without further purification. Bi2O3-Cu2O heterojunctions were synthesized by high energy ball milling as a function of time to study the physical coupling of both semiconductors as well as structural defects and thus their correspondent optical properties. The structural parameters were measured as a function of milling time by X-ray diffraction and Rietveld refinement to evaluate their effect on photoabsorption (PA), photoluminescence (PL) and thus photocatalytic properties. Scanning electron microscopy (SEM) and BET surface area evidenced that as prepared Bi2O3 powder has a nanometric size distribution while commercial Cu2O powder shows a micrometric particle size with irregular morphology. From reflectance spectra and Tauc plot using Kubelka Munk theory, the band gap energies of Bi2O3 and Cu2O were 2.27 eV and 2.0 eV, respectively showing that both catalysts can be activated under visible light irradiation. UV-vis-NIR spectrophotometry evidenced an enhancement on the PA in the Bi2O3-Cu2O heterojunction presenting two shoulders in the reflectance spectra respect to the present phases. This effect seems to be attributed to the efficient coupling of both catalysts that promote charge carrier transport. PL spectra of Bi2O3 shows that photorecombination can be reduced by coupling with Cu2O. These results evidenced that Bi2O3 with a narrow band gap semiconductor heterojunction stimulates the photoinduced charge transport and separation which increases the photoactivity of the composite. Moreover, the photorecombination of the electron-hole pair as seen in the PL spectra decreased with increasing milling time on the synthesis of Bi2O3-Cu2O generating thus an efficient coupling of both semiconductors. If the number of emitted electrons resulting from the recombination between excited electrons and holes is increased, the PL intensity increases and consequently, the photoactivity decreases.