Characterization of cadmium-doped nZVI residuals: Structure, morphology, and photoelectrochemical properties

Abstract

This study explores a novel approach to reuse the residual material generated after environmental remediation processes using nanoscale zero-valent iron (nZVI) nanoparticles. While nZVI has been evaluated for the removal of heavy metal ions in contaminated areas, it has yet to provide a definitive solution. We propose utilizing the residual nZVI material for photo-harvesting in photoelectrochemical cells. Here, we report on the material's transformation into a Fe⁰/Fe_xO_y Cd_1−xFe_xO_y catalyst and investigate its potential through X-ray photoelectron spectroscopy (XPS), inductively coupled plasma (ICP), transmission electron microscopy (TEM), and X-ray diffraction (XRD). On the other hand, traditional characterization methods were also employed to validate the versatility of the Cathodic Particle Coulometry (CPC) technique. This method is especially sensitive to conductive and semiconductive particles, such as metal oxides or corrosion products, as they generate distinct current signals when reduced or oxidized under cathodic conditions. CPC permits the sizing of the particle, and the obtained results are discussed hereinafter. Interestingly, a staircase response was also obtained for the most concentrated sample of particles suggesting a blocking mechanism. The inclusion of cadmium (Cd) in the nZVI residual material resulted in structural changes, shifting from a hexagonal hematite lattice to a face-centered cubic CdFe₂O₄ phase. Incident photon-to-current efficiency measurements revealed a 10-fold increase in efficiency compared to the original nZVI material. Furthermore, photovoltage measurements as a function of Cd content suggest that Cd alters the semiconductor properties of the Fe_xO_y structure. This study highlights the potential of cadmium-doped iron residual materials (Cd-IR) in enhancing the performance of photoelectrochemical solar cells (PSC) and provides insights into the changes in material properties and structure due to Cd incorporation.