Sodium titanate nanomaterials: structure, morphology and photocatalytic properties

Author(s)

Isabela Marcondelli Iani

• Document type: Master's Dissertation
• Press: Araraquara. 2021-07-27.
• Institution: Universidade Estadual Paulista (Unesp). Instituto de Química. Araraquara
• Defense date: 2021-07-13
• Advisor: Leinig Antonio Perazolli

Abstract

Sodium titanate nanotubes have been studied as important alternative materials for applications such as photocatalytics. This is mainly due to phenomena related to electronic structure, charge transport mechanisms and surface defect states. Such characteristics can be related to its complex stoichiometry (NaxH2-xTi3O7, 0 ≥ x ≥ 2). In this work, the structural and electronic factors of these titanates were demonstrated in more detail, as well as the characterization of the materials in relation to the compositional variation between H+ and Na+ . The Microwave Assisted Hydrothermal Synthesis (HAM) method was used, varying the final parameters of the synthesis - washing of the particles and a post heat treatment. The washings of the nanoparticles were carried out in order to obtain different pHs from neutral to acid: 7, 5 and 1; followed by different heat treatments: without further heat treatment, and at 300°C/2h, 450°C/2h and 600°C/2h. The samples obtained were characterized as to their structural, optical, electronic, and morphological properties in relation to the compositional variation between H+ and Na+ , by means of spectroscopic techniques (Raman scattering, UV Vis absorption and X-ray energy dispersion), X-ray diffraction and scanning and transmission electron microscopy. Furthermore, the materials were characterized as to their photocatalytic activities. It was established that acid washing favored the cation exchange process and promoted the formation of the Na2Ti3O7/H2Ti3O7 heterojunction, with the coexistence of these two phases. The thermal treatments that the materials were submitted caused the elimination of H+ from the structures, and promoted the structural rearrangement for the formation of the Na2Ti6O13 and TiO2 anatase phases. The photocatalytic results showed that acid washing influences the band structure and proposed mechanisms. The lower the Na+ concentration in the structure, the better the photoactivity under UV radiation. The sample that showed the best photocatalytic activity under these conditions were the nanoparticles from the group washed at pH 1, which demonstrated a photocatalytic reaction with a half-life equal to 6 minutes, a result comparable to the already known P-25. In addition to the conventional charge transfer mechanism for type II heterostructures, the influence of the Z-scheme mechanism in samples with heterojunctions was identified, according to the observed staggered gap band alignment. (AU)

• FAPESP's process: 19/12114-7 - Nanomaterials of sodium titanate: structure, morphology and photocatalytic and sensor properties
• Grantee: Isabela Marcondelli Iani
• Support Opportunities: Scholarships in Brazil - Master