Plasmon-enhanced electrochemical sensing of 2,4,6-trichlorophenol and photocatalytic degradation of methylene blue by green-synthesized Au-doped SnO2 nanostructures using Delonix regia flower extract

Abstract

The present study comprehensively investigates the structural, electrical, optical, and electrochemical sensing properties of pure and Au-doped SnO₂ nanoparticles (NPs) synthesised by a green synthesis method using Delonix regia flower extract. X-ray diffraction (XRD) confirms the successful formation of tetragonal SnO₂ nanoparticles with an average crystallite size of ∼4.66 nm for pure SnO₂ and ∼6.56 nm for Au-doped SnO₂ NPs. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) reveal the uniform and spherical morphology consistent with the tetragonal phase. The UV-visible (UV-vis) results exhibit enhanced absorption in the visible region for Au–SnO₂ NPs compared to pure SnO₂ NPs. Photoluminescence (PL) spectra exhibit several defect-related peaks, such as blue (∼474 nm), green (∼552 nm), and red (∼701 nm) emissions. These emissions can be attributed to oxygen and tin vacancies. The photocatalytic efficiency of the prepared samples is assessed by the degradation of methylene blue (MB) dye under visible light irradiation. The SnO₂ NPs doped with Au sample demonstrates superior activity compared to the pure one, which may be due to enhanced charge separation and plasmonic effects. In electrochemical sensing, the performance is evaluated for the detection of the environmental pollutant 2,4,6-trichlorophenol (TCP). The Au–SnO₂-modified electrode exhibits improved sensitivity of 0.4416 µA µM⁻¹ cm⁻² for the concentration range of 5–100 µM and increases to 1.872 µA µM⁻¹ cm⁻² for the range of 100–300 µM, with a lower detection limit of 0.60 µM, benefiting from increased active sites that improve electron transport. These results demonstrate the multifunctional potential of green-synthesised Au–SnO₂ nanostructures for environmental remediation and the detection of toxic pollutants.