Sustainable Voltammetric Sensors Based on Rice-Husk-Derived Biosilica for Rapid, Low-Cost, and Selective Determination of Diuron in Water

Diuron is a widely used herbicide that frequently contaminates soils and surface waters, posing risks to aquatic ecosystems and human health. Reliable and selective monitoring of diuron in environmental waters is therefore essential. In this work, we design carbon paste electrodes modified with rice-husk-derived biosilica and mesoporous MCM-41 as sustainable platforms for the voltammetric determination of diuron, and we benchmark their performance against commercial silica modifiers. Conventional carbon paste sensors (CPS) offer a versatile electroanalytical platform but often exhibit sluggish electron transfer and moderate sensitivity. The incorporation of biomass-derived silica promotes diuron preconcentration at the electrode-solution interface and markedly enhances the oxidation current. CPS containing 10% rice husk biosilica (rice husk₁₀-CPS) and 10% rice-husk-derived MCM-41 (MCM-41₁₀-CPS) exhibited the best performance, attributable to the increased electroactive surface area, mesopore-facilitated diffusion, and improved charge-transfer properties. Two linear dynamic ranges were obtained; the high-concentration range (0.08-2.0 mg L^-1) was used to estimate limits of detection and quantification for rice husk₁₀-CPS (LOD = 3.31, LOQ = 11.05, <i>R</i> ² = 0.9925) and MCM-41₁₀-CPS (LOD = 8.07, LOQ = 26.91, <i>R</i> ² = 0.9979). The sensors retained their analytical response after 30 days of storage and remained reproducible for at least four reuse cycles. Interference tests in river water showed no measurable effect on the diuron signal from common pesticides and metal ions at 100-fold excess, and satisfactory recoveries (≈90-110%) were obtained by standard addition. These results demonstrate that rice-husk-derived silica is an effective, sustainable, and economical modifier for carbon paste electrodes, enabling robust voltammetric screening and determination of diuron in environmental water samples.