Application of CdTe quantum dots sensitized titanate nanotubes in photocatalytic degradation of organic pollutants under visible light irradiation

The use of solar-driven photocatalysis for the degradation of recalcitrant organic waste from water is a promising and environmentally friendly technology to meet the challenge of mitigating increasing global pollution. This paper presents a new composite of layered H2Ti3O7 hydrothermal nanotubes (TNT) with cadmium telluride quantum dots prepared by the simple mixing suspensions of both components in TNT/CdTe-QDs ratios in the range of 1:0.005-1:0.03. The products were characterized by X-ray diffraction, spectroscopic techniques such as Fourier transform infrared, Raman scattering, UV-visible diffuse reflectance, photoluminescence, and X-ray photoelectron spectroscopy, as well as by scanning and transmission electron microscopy. The photocatalytic performance of the products was tested by photocatalytic degradation of two molecular models of contaminants, methyl orange (MO) and 4-chlorophenol (4-CP). Nearly 100 % removal of organic contaminants was achieved and the degradation rate of MO and 4-CP under simulated sunlight in the presence of QDs was approximately five and four times faster than using TNT alone, respectively. The degradation rate response in the presence of specific radical scavengers corresponds to a direct Z-scheme photocatalysis. Recycling experiments demonstrated a structurally stable catalyst that maintains its efficiency after five irradiation cycles. Photoelectrochemical and photocurrent measurements validated the synergistic effect observed, reflecting that heterojunction promotes the transfer of photogenerated electrons and holes, decreasing recombination changes and improving photocatalytic activity.