In situ correlation between washing media and gas-sensing performance of CeO¿ produced by microwave-assisted hydrothermal synthesis.

• Grant number: 25/20607-4
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: February 01, 2026
• End date: January 31, 2027
• Field of knowledge: Engineering - Materials and Metallurgical Engineering - Nonmetallic Materials
• Principal Investigator: Alexandre Zirpoli Simões
• Grantee: Pedro Martorelli Pinheiro
• Host Institution: Faculdade de Engenharia (FEG). Universidade Estadual Paulista (UNESP). Campus de Guaratinguetá. Guaratinguetá , SP, Brazil
• Associated research grant: 13/07296-2 - CDMF - Center for the Development of Functional Materials, AP.CEPID

Abstract

The purpose of this research project is to build upon the technical and scientific foundation developed by the research group (Faculty of Engineering and Sciences of Guaratinguetá - UNESP/Brazil and Universidad Nacional de Mar del Plata - UNMdP/Argentina) in the study of advanced ionic electroceramics with semiconducting properties applied to gas sensors. The goal is to optimize the production and performance of these semiconductors by controlling synthesis parameters, in order to obtain materials with improved usability. The material of interest will be pure cerium dioxide (CeO¿), synthesized via the microwave-assisted hydrothermal (MAH) route. The study focuses on the variation of the washing medium employed during synthesis, while keeping other parameters unchanged, as already consolidated in previous works. The initial product (nanopowders) will be characterized with respect to crystalline phase by X-ray Diffraction (XRD) and morphology by Field Emission Scanning Electron Microscopy (FE-SEM) and Transmission Electron Microscopy (TEM). Optical and electronic properties-band gap energy, Ce oxidation states, and crystalline defects-will be evaluated by UV-Vis, Raman, XPS, and EPR spectroscopies. Subsequently, the powders will be deposited onto alumina substrates with electrodes by the screen-printing method, forming semiconducting films. The porosity of the nanoparticles will be determined by adsorption isotherms (BET method). The sensing response of these films will be tested against different gases in a hermetic chamber patented by the group (PI20150103953 - Mar del Plata/Argentina), using the two-probe technique. Electrical current measurements and conductivity type characterization (p or n) will be obtained by impedance spectroscopy.The central innovation of this project lies in the systematic investigation of the role of different washing media (neutral, acidic, and alkaline) in the microwave-assisted hydrothermal (MAH) synthesis of CeO¿ nanoparticles. The washing medium directly influences oxygen vacancy density, surface charge distribution, and the presence of functional groups in CeO¿. Under neutral conditions, particles are expected to undergo minimal modification, serving as a reference. Acidic washings tend to favor ion leaching, increasing oxygen vacancies and enhancing surface reactivity. In contrast, alkaline washings can stabilize crystal facets and alter the isoelectric point, modulating gas adsorption. The novelty of this project lies in treating the washing medium as a strategic engineering variable, capable of indirectly tuning electronic and structural properties. The hypothesis is that such variations will impact sensitivity, selectivity, response time, and stability under repeated cycles.Thus, the project aims to develop more efficient, responsive, and durable gas sensors. Beyond practical advances, this study may inaugurate a new paradigm, demonstrating that secondary synthesis parameters play a decisive role in advancing semiconductors for emerging sensing technologies. (AU)