Bio-based hierarchical vertically aligned 2D ZnO nanostructures for ultra selective electrochemical sensing of p-Chloroaniline

Abstract

Herein, we report synthesis of hierarchical 2D vertically aligned nanostructures (VANs) of ZnO onto the surface of FTO glass via bioinspired route for targeted electrocatalytic sensing of p-Chloroaniline (p-CA). The phytochemicals present in vegetal extract of Sechiun edule were employed to grow and form stable ZnO VANs onto FTO (ZnO-VANs(bio)/FTO). The morphological characterizations of ZnO-VANs(bio)/FTO showed the formation of vertical nanostructures (length ∼ 820 nm) with high density and good crystallinity. It exhibited an increased surface roughness 2.2-fold higher than seeded FTO (ZnO@seed/FTO). The ZnO-VANs(bio)/FTO@pH7 electrode showed a decrease in electron transfer resistance from 7.78 to 3.02 MΩ with 1.2-fold increase in effective surface area than FTO(bare). The oxidation of p-CA included an irreversible one-electron oxidation mechanism with formal potential (E0) of 0.978 V vs. Ag/AgCl and standard heterogeneous rate constant (k) of 0.737 s−1. ZnO-VANs(bio)/FTO@pH7 exhibited remarkable electrocatalytic sensing of p-CA with low limit of detection (0.021 µM) and excellent sensitivity (0.194 µA·µM−1·cm−2) between a linear window of 2–200 µM. The detection limit of fabricated sensor for p-CA sensing was about 2-fold lower than FTO(bare). Chlorobenzene, carbendazim, profenofos, nitrite, 4-nitrophenol, bisphenol a, and mercury could not interfere p-CA sensing, and only 4.7% reduction in peak current was observed upto 9th cycle. The ZnO-VANs(bio)/FTO@pH7 could efficiently sense p-CA in spiked river and residential water samples, comparable with HPLC (max 4.6% deviation). Therefore, ZnO VANs synthesized in a bio-based route is a potential electrocatalyst for binder-free sensor development with high stability and low detection limit for sensing pesticides and their intermediates.