Abstract
In this study, the amount of phenol adsorbed between 0 and 10 mmol∙L−1 during an immersion calorimetric experiment is compared with the adsorption that takes place once phenol adsorption reaches the solid–solution equilibrium. The activated carbons used were prepared by impregnation of one obtained from coconut shell with solutions of nitric and phosphoric acid, nitric acid with subsequent reflux in ammonium hydroxide solution, and carbonisation in a nitrogen atmosphere at 1073, 1173, and 1273 K. The phenol/activated carbon interactions during the calorimetric experiment and in equilibrium were studied using a modified Langmuir model. The values of the BET surface area for the samples were between 469 and 1113 m2∙g−1, micropore volumes were between 0.18 and 0.43 cm3∙g−1, and the distribution of pore size was between 0.3 and 1.4 nm. The interactions between water and activated carbons determined by immersion enthalpies were between −11.0 and −24.8 J∙g−1, which showed that the treatments modified the surface chemistry of activated carbon. The results show that the presence of nitrogen as a different heteroatom to oxygen on the activated carbon surface favors the phenol adsorption rate, and this process is 97% complete during the calorimetric experiment, indicating that it is an enthalphy-driven processes.
Highlights
Activated carbons are materials characterised by a porous internal structure that gives them great surface area, volume, and distribution of pore size; they have functional groups that are prepared at the edges of grapheme layers and have been used in industrial processes that involve the adsorption of contaminants at the liquid-solid interface [1]
The polar groups in molecules tend to interact with polar groups on the activated carbon surface using hydrogen bonds, permanent dipoles, and permanent
The following activated carbons were identified: activated carbon produced from coconut shell, used as a starting material (G); granular activated carbon impregnated with nitric acid solution (GN); granular activated carbon impregnated with nitric acid solution and subsequent reflux in ammonium hydroxide solution (GNA); granular activated carbon impregnated with phosphoric acid solution (GP); and granular activated carbons treated thermally in a nitrogen atmosphere to 1073, 1173 1273 K, as
Summary
Activated carbons are materials characterised by a porous internal structure that gives them great surface area, volume, and distribution of pore size; they have functional groups that are prepared at the edges of grapheme layers and have been used in industrial processes that involve the adsorption of contaminants at the liquid-solid interface [1]. The surface of activated carbon is heterogeneous, composed of both hydrophobic and hydrophilic regions, with a variety of functional groups that are mainly oxygenated. The process of adsorption has been described using different mechanisms, such as van der Waals interactions, hydrogen bonds, electrostatic interactions, ion exchange, and hydrophobic links. Many organic molecules like phenol possess hydrophilic and hydrophobic regions. The polar groups in molecules tend to interact with polar groups on the activated carbon surface using hydrogen bonds, permanent dipoles, and permanent
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