Photoelectrochemical reduction and electrochemical detection of Cr(VI) using TiO₂ nanosheet electrodes

Abstract

TiO₂ nanosheet electrodes were successfully fabricated on fluorine-doped tin oxide (FTO) substrates via a hydrothermal method using a TiCl₄–HCl–NH₄F system. The obtained hierarchical nanosheet morphology provides a high surface area and abundant active sites, which are favorable for electrochemical and photoelectrochemical processes. The electrochemical performance of the TiO₂ electrodes was investigated for both detection and reduction of hexavalent chromium (Cr (VI)), a highly toxic and hazardous pollutant in water systems. Cyclic voltammetry revealed enhanced cathodic currents and the appearance of a reduction peak in the presence of Cr (VI), confirming its electrochemical reduction. Chronoamperometric measurements demonstrated a rapid and concentration-dependent current response, with a linear detection range of 0.01–0.8 mM and a sensitivity of 0.213 mA·mM⁻¹, and a limit of detection (LOD) of approximately 0.003 µM. Under UV illumination, a decrease in photocurrent was observed after the addition of Cr (VI), indicating the consumption of photogenerated electrons in the photoelectrochemical reduction process. This behavior confirms that Cr (VI) acts as an efficient electron acceptor, undergoing reduction to less toxic Cr (III). The combined electrochemical and photoelectrochemical results demonstrate that TiO₂ nanosheet electrodes can serve as multifunctional platforms for simultaneous detection and detoxification of Cr (VI). This work highlights the potential of TiO₂-based systems for sustainable water purification and environmental remediation, contributing to the development of clean water technologies.

Keywords: TiO₂ nanosheets, photoelectrochemical reduction, Cr (VI); electrochemical detection, water purification.