Synthesis and sensing efficiency of CN-wrapped ZnFe2O4 microsphere–ionic liquid composites towards ultra-high sensitive arsenic(iii) monitoring of ground drinking water

Abstract

Arsenic(III) poisoning may lead to neurological disorders, heart diseases or carcinogenic effects due to long-term exposure. The presence of arsenic in drinking water is a widespread problem and presents an important analytical challenge. Among the methods for As(III) monitoring, electrochemical analysis offers fast response, low detection limits and high sensitivity. Here we report a novel system, which achieves exceptional performance without use of expensive noble metals by exploiting a metal oxide rich in oxygen vacancies (OVs). Novel OV-rich spinel ZnFe₂O₄ microspheres (ZF-Ms) were synthesized and applied to electrochemical monitoring of As(III) in underground drinking water by square wave anodic stripping voltammetry (SWASV) in acetate buffer (pH 6.0). To boost sensing capability, the surface of ZF-Ms was further wrapped with carbon and nitrogen rich nanodots (CNs) and modified with benzimidazolium-1-acetate ionic liquid (IL). The designed CN-wrapped IL-modified ZF-Ms (CN@ZF-Ms-IL) sensor offered an ultra-low detection limit of 0.0006 ppb (based on the 3σ method), high sensitivity (41.08 μA ppb⁻¹) and a wide linear range (∼1–60 ppb) including the World Health Organization (WHO)'s desirable range (10 ppb). To the best of our knowledge, the system outperforms most alternatives based on noble metal electrodes and almost all those based on the reported metal-free electrochemical sensors. A possible sensing mechanism is proposed and supported with experimental evidence. Additionally, the system has been successfully applied to monitor arsenic-contaminated real ground drinking water collected from a flood-affected area, Muzaffargarh, Punjab, Pakistan.