Enhancement of the adsorptive properties of commercial activated carbons by simple surface modifications using chemical agents and their application to methylene blue, bemacid blue N-TF dyes, and nickel(II) ion removal from their aqueous solutions was the aim of this study. Impregnations in 10% KOH (MAC-K) for 24 h and concentrated H₂SO₄ (MAC-S) for 2 h, applied to Merck activated carbon, and NaOH (RHAC-N) with different strength applied to Riedel- de Haen activated carbon in order to functionalize and to modify their surfaces were investigated. These treatments were found to increase the adsorption capacity of the considered pollutants significantly relative to their untreated state of up to 250.00 mg/g for methylene blue, 11.47 mg/g for nickel(II) ions, and 312.00 mg/g for bemacid blue ET-L by MAC-K, MAC-S, and RHAC-N, respectively. Three well-known model equations namely Langmuir, Freundlich, and Temkin were used to analyze the adsorption equilibrium data. Parameters influencing adsorption capacity such as contact time, adsorbent dosage, pH, and temperature were studied. FT-IR and DRX analysis were performed for chemical functionalities; pH_zpc, methylene blue accessible area, iodine number, and morphological analysis by scanning electron microscopy determination were also performed to characterize the prepared adsorbents. Adsorption kinetics was found to comply with the pseudo-second-order with a good correlation factor (R² = 0.99) and with intra-particle diffusion as the rate-determining steps. This study showed that surface functionalization of activated carbon could prove to be a very useful method in removing toxic substances from wastewater and the environment.

The ability of an activated carbon prepared from sawdust-based activated carbon to remove phenol and its compounds from aqueous solutions has been investigated. Activation was achieved by impregnating sawdust in phosphoric acid with concentrations ranging from 20 to 85% and heating the sawdust-acid mixture starting from 600 to 800°C. The results showed that the Brunauer–Emmett–Teller (BET) surface area exhibited by the prepared material varied significantly with experimental conditions such as impregnation time, solution pH, adsorbent dose, initial concentration, and pyrolysis temperature, and attained a value of 2,257 m² g⁻¹ in comparison to the as-supplied Merck commercial activated carbon (Merck-AC) attaining 1,030 m² g⁻¹. Characterization of the prepared materials was carried out through the determination of the BET surface area, functional groups, and surface area accessible to small and fairly large molecules (iodine and methylene blue). Batch adsorption tests were performed and the experimental data analyzed using the Langmuir, Freundlich, and Temkin models. The estimated adsorption capacities from the fitting of the Langmuir model to the equilibrium data are 200, 334, and 500 mg g⁻¹ for phenol, parachlorophenol, and pentachlorophenol, respectively. The application of the pseudo-first-order, pseudo-second-order, and intraparticle diffusion models to the experimental data showed that pseudo-second-order model is more representative. Thermodynamic tests revealed a spontaneous (ΔG < 0) but an endothermic sorption process (5.10/127 kJ/mol) for all the phenolic compounds investigated.

The rising concentration of CO₂ in the atmosphere is approaching critical levels, posing a significant threat to life on Earth. Porous carbons derived from biobased materials, particularly waste byproducts, offer a viable solution for selective CO₂ adsorption from large-scale industrial sources, potentially mitigating atmospheric CO₂ emissions. In this study, we developed highly porous carbons from lemon peel waste through a two-step process, consisting of temperature pretreatment (500 °C) followed by chemical activation by KOH at 850 °C. The largest specific surface area (2821 m²/g), total pore volume (1.39 cm³/g), and micropore volume (0.70 cm³/g) were obtained at the highest KOH-to-carbon ratio of 4. In contrast, the sample activated with a KOH-to-carbon ratio of 2 demonstrated the greatest micropore distribution. This activated biocarbon exhibited superior CO₂ adsorption capacity, reaching 5.69 mmol/g at 0 °C and 100 kPa. The remarkable adsorption performance can be attributed to the significant volume of micropores with diameters smaller than 0.859 nm. The Radke–Prausnitz equation, traditionally employed to model the adsorption equilibrium of organic compounds from liquid solutions, has been shown to be equally applicable for describing the gas–solid adsorption equilibrium. Furthermore, equations describing the temperature dependence of the Radke–Prausnitz equation’s parameters have been developed.