Synthesis of nano-TiO2 assisted by glycols and submitted to hydrothermal or conventional heat treatment with promising photocatalytic activity

Lidiaine Maria Santos,Antonio Eduardo Da Hora Machado

doi:10.7717/peerj-matsci.13

Lidiaine Maria Santos, Antonio Eduardo Da Hora Machado

Open Access

https://doi.org/10.7717/peerj-matsci.13

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Abstract

TiO2 nanoparticles were successfully synthesized by the sol-gel method employing different glycols (ethylene glycol, diethylene glycol or polyethylene glycol 300), which were heat-treated in conventional oven or by hydrothermal via, obtaining photocatalysts with particle sizes and distinct crystalline structures. HRTEM analyses showed that the oxides submitted to hydrothermal treatment featured spherical morphology, being formed by partially aggregated particles with sizes varying between 2 and 5 nm. X-ray diffractograms and Raman spectroscopy confirm that anatase was predominant in all synthesized compounds, with presence of brookite phase for samples that received hydrothermal treatment or were synthesized in the presence of polyethylene glycol with heat treatment in conventional oven. The amount of brookite as well as the cell volume, deformation, network parameters and crystallinity were estimated by Rietveld refinement. The surface area and porosity of the materials were higher when the synthesis involved the use of hydrothermal treatment. These oxides are mesoporous with porosity between 14 and 31%. The oxide synthesized in the presence of ethylene glycol with hydrothermal thermal treatment (TiO2G1HT) exhibited the highest photocatalytic activity in terms of mineralization of azo-dye Ponceau 4R (C.I. 16255), under UV-Vis irradiation. This higher photocatalytic activity can be attributed to the formation of binary oxides composed by anatase and brookite and by its optimized morphological and electronic properties.

Highlights

Titanium dioxide (TiO2) is widely employed in technological applications, including solar energy conversion, chemical sensors for gases, environmental depollution and hydrogen production, among others (Machado et al, 2015; Riyapan et al, 2016)
The use of different glycols in the synthesis influenced the particle size due the increase in the carbon chain (G1
We present the preparation of TiO2 mesoporous nanoparticles using the sol–gel method with different glycols as structural molds

Summary

Introduction

Titanium dioxide (TiO2) is widely employed in technological applications, including solar energy conversion, chemical sensors for gases, environmental depollution and hydrogen production, among others (Machado et al, 2015; Riyapan et al, 2016) It is an n-type semiconductor, with band gap energy of the extended solid (bulk) in the ultraviolet region. The photocatalytic process involves the electronic excitation from the valence (VB) to the conduction band (CB), when irradiated by ultraviolet light This process generates charge carriers (e−/h+ pairs) that react with molecular oxygen and water, forming reactive oxygen species (ROS), such as superoxide radical ion (O2·−) and hydroxyl radical (HO·). These and other secondary-generated radicals promote the degradation of environmental pollutants (Machado et al, 2008; Muthamizhchelvan et al, 2020)

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