Abstract

The synthesis and characterization of sodium titanates (ST), and their evaluation in the photocatalytic reduction of nitric oxide (NO) are described herein. The materials were synthesized by a hydrothermal route using 5 M NaOH as the mineralizer agent and a TiO2 content of 0.06 mg/mL (expressed as the mass ratio of TiO2/mL of NaOH), at 170 °C for 48 h, resulting in sodium tri- and hexa-titanates. A nanotubular morphology was observed for the ST, as proved by scanning electron microscopy (SEM); a subsequent heat-treatment at 400 °C allowed a complete transformation of sodium tri- to hexa-titanates and an increase in bandgap. The obtained ST were impregnated with Ag+ and Zn+ cations, ST-Ag and ST-Zn, respectively, to tune the materials' bandgap. XPS analysis of the ST-Ag materials showed evidence of metallic Ag, pointing to the formation of silver nanoparticles, whereas for ST-Zn oxide phases were mainly spotted. The materials were evaluated for the photocatalytic reduction of NO using a reactor fed with a continuous flow rate of NO, generated in situ at a flow of 280 mL/min using nitrogen and a 253-nm UV irradiation source. The photocatalytic tests showed that pristine ST (tri- and hexa-titanates) displayed better performance in the reduction of NO with respect to the impregnated samples (ST-Ag, ST-Zn). Maximum degradation efficiencies of 80% were achieved when 1 g of photocatalyst was used with a flow of 280 mL/min and a 253 nm UV lamp.

Highlights

  • Photocatalysis is a process with important applications in environmental remediation and energy production

  • A nanotubular morphology was observed for the sodium titanates (ST), as proved by scanning electron microscopy (SEM); a subsequent heat-treatment at 400 °C allowed a complete transformation of sodium tri- to hexa-titanates and an increase in bandgap

  • Other attempts include the use of titaniumbased inorganic perovskites, such as SrTiO3 decorated with SrCO3, which was tested to degrade nitric oxide (NO) by photocatalysis (Jin et al 2018)

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Summary

Introduction

Photocatalysis is a process with important applications in environmental remediation and energy production. Other modifications involve doping with noble metals to degrade organic matter (El Rouby et al, 2017) Their morphology is appropriate to increase the catalytic and photocatalytic activity due to tubular structure and surface areas >200 m2/g (Machorro López et al, 2021). Ibukun and Jeong (2020) achieved the TiO2 modification with silver to avoid the abovementioned issues These authors reported that the modified TiO2 was active in the visible region; degradation kinetic of methyl blue was increased. Turkten and Bekbolet (2020) achieved the modification of TiO2 with ZnO to avoid the recombination of (e−-h+) pair and to shift the bandgap of the photocatalyst to the visible region. Modification of titanium-related materials such as ST with Ag+ and Zn+ has been investigated and tested in environmental remediation studies; their use in as photocatalyst to degrade NOx has not been implemented

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