Date of Award

31-8-2024

Document Type

Thesis

School

School of Chemical & Biotechnology

Programme

Ph.D.-Doctoral of Philosophy

First Advisor

Dr.K.Arockia Jayalatha

Keywords

Pesticides, Imidacloprid, Carbendazim, Chlorpyrifos

Abstract

Intentional and unintentional events of pesticide poisoning and their accidental exposure have significantly raised the concerns of global organizations to classify these chemical compounds based on their toxicity, to assign permissible limits, and to appoint task force for periodic monitoring of their presence in water bodies.

In this context, researchers are continually seeking potential alternatives to develop water quality sensors with higher selectivity to obtain the desired performance during real-time assessment. Electrochemical sensors involving interface materials of distinguishing capacity at elevated matrix complexity are desirable. However, there remains a challenge in designing suitable techniques, methodologies, and appropriate validations to support the grounds for the selection of interface materials.

The ability to monitor imidacloprid, carbendazim, and chlorpyrifos pesticides in water matrix using interface materials of suitable states is the major focus of this work. To achieve the same, composites of functionalized multiwalled carbon nanotubes (f-MWCNTs) and ethylenediamine tetraacetic acid (EDTA), nitrilotriacetic acid trisodium salt monohydrate (NTAA Na3.H2O), and N-(2-Hydroxyethyl) ethylenediaminetriacetic acid trisodium salt hydrate (N-(2-C2H5O) ED(CH3COONa)3) were prepared and utilized for the surface modification of screen-printed carbon electrodes.

A systematic synthesis follow-up was achieved from the investigations on structural, morphological, optical, and electrochemical analysis of these interface materials. The electrochemical sensing characteristics of the surface modified electrodes were analyzed using Cyclic Voltammetry (CV) and Differential Pulse Voltammetry (DPV) techniques. The design parameters such as different loading volume, loading concentration, scan rate, pH, and accumulation time were optimized based on the systematic control studies.

The selective charge transfer characteristics of the developed sensors toward the target pesticides were decoded with the aid of electrochemical, optical, and DFT studies in-turn the electrochemical sensing mechanism. The developed sensors exhibited a wide linear window and lower detection limit for all the three pesticides (Imidacloprid: 0.001 nM-0.04 mM & 3.1×10-3 pM; Carbendazim: 0.5 nM-500 μM & 5.54 pM; Chlorpyrifos: 0.5 nM-500 μM & 9.7 pM) respectively.

Further, these sensors exhibited similar type of electrochemical behaviour as witnessed in the case of analytical standard compounds, which reveal the excellent recognition capacity over their respective active ingredients present in pesticide formulations. The observed repeatability, reproducibility, and stability of these sensors with low percentage deviations suggest their high performance metrics.

Moreover, the real-time performance of these sensors was investigated using samples collected along the Kaveri River and validated with High Performance Liquid Chromatography (HPLC) technique. All the three sensors showed excellent recoveries in the ranges of 93-107%, 93-110%, and 92-120% for imidacloprid, carbendazim, and chlorpyrifos, respectively. Thus, the sensors can be taken for deployment in water bodies for the selective real-time quantification of these pesticides.

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