FeC_x-coated biochar nanosheets as efficient bifunctional catalyst for electrochemical detection and reduction of...

Herein, we present the exceptional performance of FeC_x-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.