Photoelectrochemistry of Nano Zerovalent Fe Based CdFe2O4 / FexOy Produced from Cd2+ Water Remediation

Iron nanoparticles are a new generation of materials for environmental remediation. Various metallic ions including Pb²⁺, Cr⁶⁺, Ni²⁺, As³⁺, As⁵⁺, Cd²⁺, Cu²⁺, Zn²⁺ and Ba²⁺ had been fixated from water using this new technology.¹ Nanoscale zero-valent iron (nZVI) had been studied as an alternative for decontamination processes.  In nZVI reaction, metallic iron is oxidized in presence of water. During this reaction, other metal ions can be removed from the aqueous media by chemical absorption.⁴ In this process, iron oxides such as hematite (α-Fe₂O₃) are produced.⁵ This α-Fe₂O₃ have been broadly study for catalytic applications due to its highly active photochemical properties and resistance to corrosion, but the excited electrons have a short lifetime and the charge mobility is low.⁶ Approaches such as doping with other metals and changing the structural arrangement of the system had been employed to overcome α-Fe₂O₃ challenges regarding to the electron transfer processes. Previous studies from our group proves that the incorporation of cadmium (Cd) ions in the oxidized nZVI produce a changes in the structure of the system associated to iron oxides species (Fe_xO_y) and cadmium ferrite (CdFe₂O₄) formation. This can be done without using high temperatures to complete the preparation of the material, a common practice in the literature. Additional to these changes, cadmium species have been also studied for their photochemical applications. Regardless of all this information, there are few reports, which employ these particles as photocatalysts. nZVI particles were used in Cd²⁺ remediation as a proof of concept for further use at the Las Cucharillas Marsh. Our group had done experiments in Cd²⁺ concentrations between 1 and 6ppm. This led us to explore the effect of higher Cd²⁺ concentration on the nZVI. Moreover, an alternative use of the remediation nZVI product was evaluated. This led to its possible use in photoelectrochemical cells. A challenge in this device is to optimize the quantum conversion efficiency, which is affected by the electron transfer processes in the system. We used the CdFe₂O₄ / Fe_xO_y produced from nZVI in a photoelectrochemical cell to further understand their properties. The Cd concentration employed is similar to contaminated area with this heavy metal at Las Cucharillas Marsh, Cataño, Puerto Rico. The soil in this region is mainly acidic, i.e. between pH 2 and 5. Soil analysis, using ICP following the EPA 6010B method; have shown Cd²⁺ concentrations between 1 and 33ppm (mg/kg) in different regions of the marsh. The nZVI have been treated in different Cd²⁺ solution between 1 and 30 ppm, based on the concentrations found in the Las Cucharillas Marsh. The nZVI treated in a Cd²⁺ 30ppm solution were evaluated as anode materials for photoelectrochemical cells. This materials was characterized by different techniques such as XPS, XRD, electron microscopy, FT-IR, UV-Vis, cyclic voltammetry, and electrochemical impedance spectroscopy.