Adsorption of Acid Red 114 and Basic Fuchsin from Aqueous Solutions on Mesoporous Carbon Materials

In this work the adsorption of basic fuchsin and acidic red on mesoporous carbon materials C-KS and C-KC was examined. Carbon materials were obtained applying softtemplating method in environment of hydrochloric acid and citric acid. For examined adsorbents low-temperature nitrogen adsorption isotherms were determined, used next for porous structure parameters calculations. Obtained isotherms can be categorized as IV type according to IUPAC classification. Studied adsorbents have large surface area SBET: 650 m2/g (C-KS) and 760 m2/g (C-KC); large total pore volume Vt: 0.59 cm 3/g (C-KC) and 0.89 cm3/g (C-KS). Mesopores participation in total porosity of examined carbons is 83% for C-KS and 71% for C-KC. This confirms that examined carbons are mesoporous materials with significant advantage of mesoporosity over microporosity. Mesopores dimension, for maximum of distribution function (in the mesopores range) were estimated using KrukJaroniec-Sayari (KJS) method. Mesopores dimension for C-KC carbon is 6 nm and for C-KS carbon is 8.7 nm. Adsorbates concentrations, before and after adsorption, were estimated using spectrophotometric method. Adsorption studies were carried out at 25°C. The adsorption equilibrium for studied mesoporous systems: carbon material dye solution, was achieved after 8 hours. Studies of the adsorption process kinetics showed that in three cases adsorption kinetics proceeded in compliance with model of apparent II order of reaction: C-KC (acidic red 114) and C-KS (basic fuchsin and acidic red 114). In one case adsorption kinetics proceeded in compliance with model of apparent I order of reaction: C-KC (basic fuchsin). Obtained adsorption isotherms were applied to Langmuir and Freundlich equations. Adsorption process of fuchsin on both examined carbons and adsorption of acidic red on C-KC carbon was carried out in agreement with adsorption model described by Langmuir equation. However, acidic red adsorption on C-KC carbon is better described by Freundlich adsorption model. Adsorption abilities, of examined mesoporous carbon materials, are significantly higher in relation to fuchsin than to acidic red 114; e.g. for C-KS adsorbent, it is 1.289 mg/g (acidic red 114) and 10.661 mg/g (fuchsin). Applying K constant value from Langmuir equation, free enthalpy ∆G was calculated. Obtained values change in range of –25 to –34 kJ/mol. Negative values of ∆G show that studied adsorption process is spontaneous.