One-Pot Fabrication of High Coverage PbS Quantum Dot Nanocrystal-Sensitized Titania Nanotubes for Photoelectrochemical Processes

Abstract

Lead sulfide quantum dot nanocrystal (QDNC) sensitized TiO2 nanotubes have been fabricated using a simple, wet chemical method that is both time- and cost-effective. A single precursor source containing both Pb and S has been employed, with oleylamine as a linker molecule to synthesize the PbS under an ambient pressure based approach. This approach serves to assemble the QDNCs on a TiO2 nanotube surface. Surface characterization was performed using electron microscopy, X-ray diffraction, and elemental analysis, indicating the formation of PbS quantum dots along the nanotube walls and intertubular spacing. The optoelectronic, photoelectrochemical, and photocatalytic properties of the composite heterostructure have been characterized using absorbance spectroscopy, electrochemical studies (including efficiency measurements), and methylene blue conversion as a probe. A 24-fold increase in the photocurrent of TiO2–PbS heterostructure over bare TiO2 nanotube has been observed. Electrochemical impedance measurements of the TiO2 nanotube sample indicate donor density of ∼4.5 × 1019 cm–3 while TiO2/PbS heterostructure shows an n-n photoactive heterojunction with a donor density of ∼2.3 × 1020 cm–3. A 12% increase in photocatalytic activity and theoretical estimates suggesting almost 40-fold enhancement toward value-added product synthesis with PbS inclusion are presented.