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Activated carbons from plum stones as efficient adsorbents for the removal of phenol and bisphenol A from aqueous solutions
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.
Activated carbons prepared from stump wood of various tree species by chemical activation and their application for water purification
AbstractActivated carbons (ACs) were produced from stump wood of different tree species, such as pine, bearded birch, and American black cherry using chemical activation with KOH and NaOH. The activated carbons were characterized and evaluated as adsorbents for eliminating bisphenol A (BPA) from aqueous solutions. The kinetics of adsorption and equilibrium adsorption, as well as the impact of solution pH and ionic strength, were examined. The kinetics were analyzed using the pseudo-first-order, pseudo-second-order, intra-particle diffusion, and Boyd kinetic models. The findings suggest that the adsorption kinetics followed the pseudo-second-order model. Additionally, the film diffusion was found to be the rate-determining step for the adsorption of BPA on all of the activated carbons. The data for adsorption equilibrium were tested using the Langmuir, Freundlich, and Sips equations, with results indicating that the Langmuir model was the most applicable. The capacity of activated carbons to adsorb BPA was dependent on their surface area. Higher BET surface areas resulted in increased adsorption. The birch-derived AC activated by NaOH had a monolayer adsorption capacity of 1.980 mmol/g, while the AC from black cherry activated with KOH had 2.195 mmol/g. The adsorption of BPA was pH-dependent, and no effect of ionic strength was observed. The activated carbons had very high adsorption capacities, indicating that stump wood is an excellent precursor for the production of highly effective adsorbents.
KOH-activated tire pyrolysis char as an adsorbent for chloroorganic water pollutants
Activated carbons (ACs) produced from end-of-life tires with different tire pyrolysis char (TPC)-to-activator (KOH) ratios of 1:2, 1:3, and 1:4 were prepared and characterized. These materials were used as adsorbents for the removal of two common chloroorganic water contaminants such as 2,4-dichlorophenol (DCP) and 2,4-dichlorophenoxyacetic acid (2,4-D). The adsorption kinetics, equilibrium adsorption, and effects of solution pH were investigated. The adsorption of both adsorbates was found to be pH-dependent and preferred in acidic environments. The adsorption kinetics was evaluated using pseudo-first-order and pseudo-second-order kinetic models and mechanism - using Weber-Morris and Boyd models. Results demonstrated that the adsorption of DCP and 2,4-D on all ACs followed the pseudo-second-order model and was controlled by film diffusion. The Langmuir isotherm described the equilibrium data better than the Freundlich isotherm model. The maximum adsorption capacity of DCP adsorbed on AC1:2, AC1:3, and AC1:4 at equilibrium was 0.582, 0.609, and 0.739 mmol/g, respectively, while the maximum adsorption capacities for 2,4-D were 0.733, 0.937, and 1.035 mmol/g, respectively. The adsorption rate and efficiency were closely correlated with the porous structure of the tested adsorbents. The results showed that the activated carbons obtained from the scrap of end-of-life tires as raw materials could be used as a low-cost and alternative adsorbent for the removal of chlorinated organic pollutants from water.
Activated Carbons Derived from Different Parts of Corn Plant and Their Ability to Remove Phenoxyacetic Herbicides from Polluted Water
In this study, the adsorption of phenoxyacetic acid (PAA) and its chlorinated derivatives, including 4-chlorophenoxyacetic acid (4CPA) and 2,4-dichlorophenoxyacetic acid (2,4-D), on activated carbons (ACs) from corn kernels (AC-K), corn leaves (AC-L), and corn silk (AC-S) were investigated. The adsorption kinetics followed the pseudo-second-order model, and the film diffusion was the rate-limiting step. The adsorption rate increased in the order PAA < 4CPA < 2,4-D and was correlated with the porous structure (mesopore volume) of these ACs. The Langmuir isotherm models best fit the experimental data; PAA was adsorbed least and 2,4-D most preferentially. The observed trend (PAA < 4CPA < 2,4-D) was positively correlated with the molecular weight of the adsorbates and their hydrophobicity while being inversely correlated with their solubility in water. The adsorption for 2,4-D, according to the Langmuir equation, is equal to 2.078, 2.135, and 2.467 mmol/g and SBET 1600, 1720, and 1965 m2/g, respectively. The results for other herbicides showed a similar correlation. The adsorption of phenoxy herbicides was strongly pH-dependent. The ACs produced from corn biomass can be an eco-friendly choice, offering sustainable products that could be used as efficient adsorbents for removing phenoxyacetic herbicides from water.