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Effective Adsorption of Phenoxyacetic Herbicides by Tomato Stem-Derived Activated Carbons
Six activated carbons from tomato (Solanum lycopersicum L.) stems (TS-AC) were synthesized by carbonization and chemical activation using potassium hydroxide (KOH) and sodium hydroxide (NaOH) at temperatures of 550, 650, and 750 °C. These TS-ACs were then evaluated as adsorbents to remove 2,4-dichlorophenoxyacetic acid (2,4-D) and 2-methyl-4-chlorophenoxyacetic acid (MCPA) from aqueous solutions. The adsorption kinetics of both herbicides followed the pseudo-second-order model, closely correlating with the mesopore volume of the TS-AC. The Langmuir isotherm accurately described the adsorption process for both 2,4-D and MCPA. The porous structure of TS-AC, characterized by micropore volume and specific surface area, significantly influenced the maximum adsorption capacities. The adsorption of both herbicides was pH dependent, but ionic strength had no significant effect. Regeneration testing, conducted over three cycles, showed less than a 15% reduction in herbicide adsorption capacity. This study demonstrates that agricultural waste, specifically tomato stems, can be effectively valorized by using simple activation techniques in TS-AC that are efficient adsorbents to remove organic pollutants, such as herbicides, from aqueous media.
The Adsorptive Removal of Paracetamol as a Model Pollutant from an Aqueous Environment Using Activated Carbons Made from Selected Nutshells as Agricultural Waste
In this study, carbon adsorbents obtained from agricultural waste, i.e., walnut, hazelnut, and pistachio nutshells, were investigated for the removal of paracetamol (acetaminophen, 4-hydroxyacetanilide) (PAR) from aqueous solutions. Activated carbons (ACs) were produced via a two-step procedure. In the first step, the carbonization of nutshells was carried out at 600 °C, and in the second step, the chemical activation was carried out at 750 °C using alkaline activators, i.e., NaOH and KOH. For all of the ACs obtained and characterized, PAR adsorption kinetics, the adsorption at equilibrium, and the effects of the solution pH were investigated. All results obtained for each nutshell depend on the type of activating agent used. However, in the case of a given activator, there are differences resulting from the type of raw material. Kinetic and isothermal studies revealed that PAR adsorption follows the pseudo-second-order and the Langmuir models, respectively. The adsorption capacities of the ACs were very high and ranged from 332.2 to 437.8 mg/g. This study highlights the remarkable potential of nutshells as valuable and cost-effective precursors for the production of ACs that can effectively remove paracetamol from water.