PEO–Hydrothermal Engineering of VOₓ/TiO₂ Photocatalysts for Efficient Visible-Light Degradation of Methylene Blue

Document Type : Research Paper

Authors

1 Bu-Ali Sina University, Department of Materials Engineering, Faculty of Engineering, Hamedan, Iran

2 Sejong University, Department of Nanotechnology and Advanced Materials Engineering, Seoul 05006, Republic of Korea

Abstract

Visible-light-driven photocatalysis plays a crucial role in sustainable wastewater treatment. In this work, Methylene blue (MB) was employed as a model organic pollutant to evaluate the photocatalytic performance of VOₓ/TiO₂ composite coatings fabricated via plasma electrolytic oxidation (PEO) followed by hydrothermal treatment. The hydrothermal temperature (160–200 °C) was systematically investigated as the key operating variable. Structural and optical properties were analyzed using XRD, SEM, UV–Vis DRS, and PL spectroscopy. The optimized sample synthesized at 180 °C exhibited an apparent optical band gap of ~1.75 eV and a pronounced red-shift compared to pristine TiO₂ (~3.2 eV). Under visible-light irradiation (54 mW cm⁻²), the 180 °C sample achieved 85% methylene blue degradation within 2.5 h, compared to only 23% for pristine TiO₂, corresponding to a 62 percentage-point improvement. Moreover, the apparent reaction rate constant increased from 2×10⁻³ to 11×10⁻³, representing an approximately 5.5-fold enhancement. The degradation efficiency increased from 73% at 160 °C to 85% at 180 °C but decreased to 58% at 200 °C, confirming the existence of an optimal hydrothermal temperature window. The enhanced activity is attributed to improved crystallinity, extended visible-light absorption, and suppressed charge recombination at the VOₓ/TiO₂ interface. These findings highlight the importance of hydrothermal temperature control in engineering efficient visible-light photocatalysts.

Keywords

References

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Journal of Ultrafine Grained and Nanostructured Materials
Volume 59, Issue 1
June 2026
Pages 116-125

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History

  • Receive Date: 24 November 2025
  • Revise Date: 03 May 2026
  • Accept Date: 03 May 2026

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