Dual-function UiO-66/AgNPs/TiO2 SERS substrate with photocatalytic self-cleaning for recyclable detection of thiram

Abstract

Thiram, a cost-effective pesticide widely used for disease control in agricultural produce, poses potential health risks, necessitating the development of rapid surface-sensing techniques. Herein, a recyclable ternary surface-enhanced Raman scattering (SERS) substrate was developed by combining UiO-66/AgNPs with TiO₂ nanoparticles. The optimized UiO-66/AgNPs composite (S10) demonstrated excellent SERS performance, achieving a detection limit of 10⁻¹¹ M for rhodamine 6 G (R6G), with a wide linear range (10⁻⁶ to 10⁻¹¹ M, R² > 0.99), high signal uniformity (relative standard deviation < 10 %), and good temporal stability. The enhancement mechanism is attributed to the synergistic effects of analyte enrichment by the porous UiO-66, electromagnetic enhancement from AgNPs via localized surface plasmon resonance and nanogap effects, and chemical enhancement through charge transfer at the Ag–UiO-66 interface. Practical detection capabilities of S10 were confirmed with thiram detection limits of 10⁻⁹ M in laboratory conditions, 10⁻⁸ M in lake water, and 1 mg/L on apple surfaces. Further incorporation of TiO₂ nanoparticles yielded the S10T substrate, which not only improved SERS activity but also enabled photocatalytic self-cleaning. The S10T substrate maintained high performance over three consecutive detection-degradation cycles, retaining 89.2 % of the thiram characteristic peak intensity at 560 cm⁻¹ after the third cycle, thereby demonstrating excellent recyclability and great potential for practical applications.