Effect of Fe doping on the Structural, Optical, Magnetic, and H2 Sensing Properties of Fe-doped TiO2 Nanoparticles
De la Torre Pari, Sonia Alina 1; Vilca Huayhua, Carlos Adolfo 1; Marcos da Silva, Wellington 1; Ichihara Sado, Mariana Lumi 2; Almeida Silva, Alysson Martins 2; Huamani Coaquira, José Antonio 1,3
1 Universidade de Brasília, Instituto de Física, Núcleo de Física Aplicada, Brasília DF 70910-900, Brazil 2 Mechanical Engineering Department, Faculty of Technology, Campus Universitário Darcy Ribeiro, University of Brasília, DF – 70.910-900, Brazil 3 Facultad de Ciencias Universidad Nacional de Ingeniería, Av. Túpac Amaru 210, Lima 15333, Perú
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Abstract
Fe-doped TiO2 nanoparticles (NPs) were synthesized using a microwave-assisted method. X-ray diffraction (XRD) patterns confirmed the formation of a predominantly anatase crystalline structure for all samples, with no secondary phases associated with iron oxides. The formation of the anatase phase was corroborated by Raman spectroscopy measurements. Furthermore, the Eg1 Raman active mode shows some peak position shifts, which were assigned to lattice strain effects likely induced by the incorporation of the Fe3+ ions. Diffuse reflectance spectra data analysis revealed a shift of the absorption edge toward the visible region, which indicates a reduction in the optical band gap from 3.09 eV corresponding to the undoped TiO2 to a value close to 2.90 eV determined for the % Fe-doped TiO2 NPs. High-resolution X-ray photoelectron spectroscopy (XPS) spectra evidenced an increase in the concentration of oxygen vacancies upon Fe doping, which arise to compensate the charge imbalance generated by the substitution of Ti⁴⁺ by Fe³⁺. Room-temperature Mössbauer spectroscopy revealed two doublets, which evidence the absence of long-range magnetic order in the Fe-doped TiO2 NPs. The isomer shift values of δ ≈ 0.29 – 0.38 mm/s suggest the presence of Fe³⁺ ions likely in a high-spin configuration occupying cation sites with distinct chemical environments. The absence of sextets is consistent with the magnetic measurements, which indicated that Fe-doped TiO2 NPs show only paramagnetic behavior for all Fe contents. On the other hand, the sensing response of the % Fe-doped TiO2 NPs to the presence of H2 gas reaches a value of 29 ± 1 % at room temperature, demonstrating the influence of Fe doping on their sensing performance. These results suggest that the Fe solubility reaches a limit at which the adsorption/desorption processes are more effective.
Keywords: Fe-doped TiO2 NPs; Mössbauer spectroscopy; room-temperature H2 gas sensor