Sensitive detection of 4-nitrophenol based on pyridine diketopyrrolopyrrole-functionalized graphene oxide direct electrochemical sensor

A diazonium-functionalized silver electrode for the sensitive amperometric detection of p-nitrophenol in water over a wide range of concentrations

This work presents a novel approach for the electrochemical detection of p-nitrophenol (pNP) focusing on the development of a simple and efficient strategy to overcome pNP adsorption. The proposed method involves the functionalization of a silver (Ag) electrode with an electrografted, thin diazonium film. After characterization by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry, the as-functionalized electrode allowed a wide linear detection range to be established in aqueous solutions, spanning from 1 to 500 μM pNP. This outcome indicates that the diazonium film effectively addresses any issues related to adsorption with good repeatability and reproducibility. Furthermore, the sensor's analytical performances were evaluated yielding a sensitivity and a limit of detection of 0.3819 μA cm-2 μM-1 and 600 nM, respectively. The sensor was also found to exhibit a good selectivity towards pNP and phenolic compounds and was successfully tested on a real water sample.

FeCx-coated biochar nanosheets as efficient bifunctional catalyst for electrochemical detection and reduction of 4-nitrophenol

Herein, we present the exceptional performance of FeCx-coated carbon sheets (FC) derived from the pyrolysis of waste biomass as a bifunctional catalyst for electrochemical detection and catalytic reduction of 4-nitrophenol (4-NP). Despite having a lower surface area, larger particle size, and lesser N content, the FC material prepared at a calcination temperature of 900 °C (FC900) outperforms the other samples. Deeper investigations revealed that the FC900 efficiently facilitates the charge transfer process and enhances the diffusion rate of 4-NP, leading to increased surface coverage of 4-NP on the surface of FC900. Additionally, relatively weaker interactions between 4-NP and FC900 allow the facile adsorption and desorption of reaction intermediates. Due to the synergetic interplay of these factors, FC900 exhibited a linear response to changes in 4-NP concentration from 1 μM to 100 μM with a low limit of detection (LOD) of 84 nM (S/N = 3) and high sensitivity of 12.15 μA μM-1 cm-2. Importantly, it selectively detects 4-NP in the presence of five times more concentrated 2-aminophenol, 4-aminophenol, catechol, resorcinol, and hydroquinone and ten times more concentrated metal salts such as Na2SO4. NaNO3, KCl, CuCl2, and CaCl2. Moreover, FC900 can accurately detect micromolar levels of 4-NP in river water with high recovery values (99.8-103.5 %). In addition, FC900 exhibited outstanding catalytic activity in reducing 4-NP to 4-aminophenol (4-AP), achieving complete conversion within 8 min with a high-rate constant of 0.42 min-1. FC900 also shows high recyclability in six consecutive catalytic reactions due to Fe magnetic property.