Pyridine-functionalized mesoporous silica as an efficient adsorbent for the removal of acid dyestuffs

Pyridine-functionalized mesoporous silica was prepared via direct condensation of tetraethoxysilane (TEOS) and N-(3-(triethoxysilyl)propyl)isonicotinamide using the copolymer P123 as structure-directing agent, and employed as adsorbent for the removal of alizarin red S, reactive brilliant red X-3B and reactive yellow X-RG from waste water. The adsorption measurements showed that, due to the large surface areas and the high affinity of pyridine groups, the prepared adsorbents exhibit a high adsorption capacity and an extremely rapid adsorption rate for acid dyestuffs. Using the linear forms of Langmuir, Freundlich and Redlich-Peterson isotherms, the experimental equilibrium data were analyzed. It is found that the experimental data for the adsorption of alizarin red S and reactive brilliant red X-3B can fit the Langmuir isotherm, while the Freundlich model is very suitable for describing the adsorption behavior of reactive yellow X-RG. On the basis of the Langmuir analysis, the monolayer adsorption capacities were determined to be 143.8, 891.1 and 3369.3 mg of dye per gram of adsorbent for alizarin red S, reactive brilliant red X-3B and reactive yellow X-RG, respectively. Since the pyridine unit is known as a good ligand for various metal ions, a hydrogen-bonding donor as well as an organic base, pyridine-functionalized mesoporous silica should be a promising absorbent not only for acid dyestuffs, but also for other organic and inorganic pollutants.