From environmental remediation to photoelectrochemical cell applications: Fe⁰/ Fe_xO_y, CdFe₂O₄, and NiFe₂O₄ nanoparticles and the development of an electrochemical system for ammonia oxidation reaction at the international space station

Abstract

Contaminated water bodies have been identified in the industrialized area of the north area of Puerto Rico. The excessive construction without considering the diversity of the ecosystem that encompasses the north area has caused the deterioration of the health of the adjoining communities. Las Cucharillas marsh is one of the zones proposed for environmental protection and remediation. Interdisciplinary efforts have been made to identify the best option to solve the pollution problem without affecting the diversity of this rich ecosystem. Previous studies offer zero-valent iron nanoparticle remediation as a viable option to begin cleaning the area, specifically removing metal ions harmful to human health, flora, and fauna. The vision imparted in this study is the reuse of the iron product after environmental remediation, specifically the reuse of residual iron particles containing cadmium and nickel ions. The comprehensive study of the sequestration of cadmium ions and nickel ions is described herein. The transformation of nZVI exposed to ionic solutions of cadmium and nickel is documented. nZVI is converted to cadmium, and nickel ferrates. In chapter three are discussed the methods and techniques utilized to analyze the residual iron material. In chapters four and five, the chemical reasons for the morphology and chemical structure changes that make iron material suitable for photocatalytic applications are electrochemically described. The chemical causes for the morphology and chemical structure changes make the waste material useful as a photoanode is exposed. The knowledge cultivated through these years of study allows the injection of zerovalent particles in the field to be more guided and practical, taking into account the interaction of the nZVI with the ions to be sequestered from a surface material and interface vision. On the other hand, a different study is described in this thesis. Development of an Electrochemical System for Ammonia Oxidation Reaction at the International Space Station aimed to resolve the inexistence of an approved system to describe the Ammonia Oxidation Reaction in a relevant space environment like the International Space Station. It is pretended to offer a complementary option to the ISS urine processor assembly and expose an alternative within the ISS water processing system for long-term missions. Simultaneously, improve the NASA technology readiness level from TRL 5 to TRL 7 of the AOR project in urine purification. Previous experiments conducted by this group in parabolic flights led to a decrease in the catalytic current of 20-65% under microgravity conditions. This reduction in catalytic current is believed to occur due to the lack of buoyancy-driven mixing at the solution-electrode interface. This project aims to compare the electrochemical oxidation of ammonia in a non-gravity environment with the same reaction on Earth. The developed electrochemical system ran twelve experiments on-orbit. Pt(100) in Vulcan-XC-72 nanoparticles was used as a working electrode to perform cyclic voltammetry and chronoamperometric experiments. The experiment rode to the ISS on NG-14, the 14th cargo flight from Northrop Grumman's Cygnus spacecraft, on October 2, 2020. The anodic current obtained on-orbit experiments was almost a quarter of the current obtained on-ground experiments with the same catalyst.