In this paper, the enhanced adsorption of methylene blue (MB) dye ion on the activated carbon (AC) modified by three surfactants in aqueous solution was researched. Anionic surfactants—sodium lauryl sulfate (SLS) and sodium dodecyl sulfonate (SDS)—and cationic surfactant—hexadecyl trimethyl ammonium bromide (CTAB)—were used for the modification of AC. This work showed that the adsorption performance of cationic dye by activated carbon modified by anionic surfactants (SLS) was significantly improved, whereas the adsorption performance of cationic dye by activated carbon modified by cationic surfactant (CTAB) was reduced. In addition, the effects of initial MB concentration, AC dosage, pH, reaction time, temperature, real water samples, and additive salts on the adsorption were studied. When Na⁺, K⁺, Ca²⁺, NH⁴⁺, and Mg²⁺ were present in the MB dye solution, the effect of these cations was negligible on the adsorption (<5%). The presence of NO^2- improved the adsorption performance significantly, whereas the removal rate of MB was reduced in the presence of competitive cation (Fe²⁺). It was found that the isotherm data had a good correlation with the Langmuir isotherm through analyzing the experimental data by various models. The dynamics of adsorption were better described by the pseudo-second-order model and the adsorption process was endothermic and spontaneous. The results showed that AC modified by anionic surfactant was effective for the adsorption of MB dye in both modeling water and real water.

Polyacrylonitrile fiber (PANF)-derived activated carbon fibers (PACFs) were successfully prepared using a one step carbonation–activation, and were used for the sorption of perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA). High specific surface areas (SSAs) of 1782 m² g⁻¹ and micro/mesoporous structures of the PACFs were obtained by optimizing the preparation conditions of the PANF-based pre-oxidized fibers (PANOFs)/KOH ratio of 1 : 2 and an activation temperature of 800 °C. The as-prepared PACFs exhibited flexibility and endless forms, and sorption capacities of 1.52 mmol g⁻¹ for PFOS and 0.73 mmol g⁻¹ for PFOA, much higher than the commercially available coal-based powder activated carbon (PAC) and granular activated carbon (GAC), which was also indicated by the site energy distributions. The sorption system followed a pseudo-second-order kinetic model and a Freundlich isotherm model. The intra-particle diffusion and Boy’s film-diffusion models were also used to verify that intra-particle diffusion is the main rate-controlling step. It was assumed that the multilayer sorption most probably occurs through electrostatic attraction and hydrophobic interaction, and some micelles and hemi-micelles form on the ACF surfaces. The PACFs show good reusability over five sorption–desorption cycle studies.

The biochar produced by pyrolysis at 600°C from powdered mango bark impregnated with iron, namely Fe₂O₃/biochar, was recognized as a multifunctional material for environmental applications. This work aims at using the above material for the removal of pyridine and quinoline from aqueous solutions. The physico-chemical properties of synthesized biochars were studied systematically with several commonly used material characterization methods including scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and Fourier transform infrared spectrometer (FTIR). Structural and morphological analyses of the biochars showed that Fe₂O₃ particles were nanosized and distributed evenly on the surface of biochar, and thus exhibited great adsorption capacity for the removal of pyridine and quinoline. In addition, the results suggested that the main magnetic phase is maghemite (Fe₂O₃). The modified biochar showed high removal capacity (99%) for quinoline, but the removal capacity of pyridine was only 73%. The pH experiment in this passage indicated that both pyridine and quinoline reached a maximum adsorption amount at pH near 9.0. Adsorption kinetics suggested that the pseudo-second-order was well fitting the experiment data. The equilibrium study showed that the Langmuir model can adequately describe the adsorption process for pyridine and quinoline. The main mechanism of pyridine and quinoline removal was possibly electrostatic interactions and π–π interactions between the modified biochar and the adsorbate.