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

## TL;DR

This paper presents a sustainable, low-cost sensor made from rice husk to detect the herbicide diuron in water, offering high accuracy and selectivity.

## Contribution

The use of rice-husk-derived biosilica as a sustainable and effective modifier for voltammetric sensors is introduced.

## Key findings

- Sensors with 10% rice husk biosilica showed high sensitivity and a detection limit of 3.31 mg L–1.
- The sensors remained stable for 30 days and were reusable for at least four cycles.
- No interference was observed from common pesticides and metal ions in river water samples.

## Abstract

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, R
2 = 0.9925) and MCM-4110-CPS (LOD = 8.07, LOQ = 26.91, R
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.