In-situ sampling of nitrophenols in industrial wastewaters using diffusive gradients in thin films based on lignocellulose-derived activated carbons

Nitrophenols (such as o-nitrophenol (ONP), p-nitrophenol (PNP), and 2,4-dinitrophenol (DNP)) are priority environmental pollutants. Their toxicity is pH dependent, and these molecular species of nitrophenols exhibit higher toxicity than their anionic counterparts. Herein, for the first time, a method for the in situ measurement of nitrophenols in acidic industrial wastewater was developed using diffusive gradients in thin films (DGT) with lignocellulose hazelnut shell-derived activated carbons (HSACs) as the binding agents. Nylon membranes (0.1 μm rated) with diffusion coefficients of (2.02 ± 0.13) × 10−6 cm2 s−1 for ONP, (1.39 ± 0.09) × 10−6 cm2 s−1 for PNP and (1.20 ± 0.08) × 10−6 cm2 s−1 for DNP at 25 °C were used as the DGT diffusion layers. The accumulation of ONP, PNP, and DNP in DGT samplers based on the HSAC and nylon membranes (HSAC-DGT) agreed well with the theoretical curves predicted by the DGT equation in synthetic solutions with 200 μg L−1 nitrophenol. The uptake of the HSAC-DGT samplers for ONP, PNP, and DNP was found to be independent of the ionic strength of pNaNO3 (−log [NaNO3] (mol L−1)) in the range of 0.7–3 and the pH range of 3–7 for ONP and PNP and 3–6 for DNP, which is beneficial for their accumulation. The matrices of the tested water samples exhibited no notable interference during nitrophenol analysis by the HSAC-DGT samplers. The results of field deployments in acidic industrial wastewater containing 268.3 ± 79.2 μg L−1 DNP were satisfactorily accurate, thus demonstrating that the HSAC-DGT samplers are good candidates for use in the in situ measurement of nitrophenols in acidic aqueous solutions.