Absorbents for water purification: functionalized ordered mesoporous silcate for the removal of 2,4-Dinirophenol and activated carbon filters for the removal of lead (II) from water

摘要

Imidazole functionalized ordered mesoporous silicate (MCM-IM) with high surface area was synthesized by the co-condensation of tetraethylorthosilicate, and n-[3 - (triethoxysilyl)propyl ]-4,5-dihydroimidazole, using cetyltrimethvlammonium bromide, CTAB, as a structure-directing agent in basic solution. Nitrogen porosimetry showed that MCM-IM exhibited typical Type IV adsorption-desorption isotherm, narrow average pore size distribution of 2.25 nm, surface area of 343 m2//g, and pore volume of 0.21 cm3 /g. MCM-IM exhibited a high affinity for 2,4-dinitrophenol and an adsorption capacity of 1.85 mmol/g was achieved. The adsorption was pH dependent with significant increase in adsorption capacity below pH 4. The sorption of 2,4-dinitrophenol on MCM-IM followed the Freundlich isotherm model, meaning, non-ideal, multiple, non ideal, multi-layer adsorption on heterogeneous surfaces. Asorption studies of Pb2+ on sulfonated and phosphonated activated carbon filters (ACF) were conducted in batch adsorption experiment. Kinetic experiment showed that lead (II) absorption reached equilibrium after 55 hours. Adsorption isotherm experiments showed that sulfonated activated carbons, S-ACF#1 and S-ACF#2 reached equilibrium capacities of 84.9 mg/g and 73.2 mg/g respectively, while phosphonated activated carbon. PVA-ACF, reached capacity of 66.2 mg/g. The adsorption was pH dependant and increased with pH. The sorption of Pb2+ on S-ACF#1 closely follows the Langmuir isotherm model, which means the sorption is monolayer and homogeneous surface. Sorption of Pb2+ on S-ACF#2 follows both Freundlich and Langmuir models and suggesting monolayer coverage on homogeneous surface or multi-layer on heterogeneous surfaces. Lead adsorption was not significantly affected by the prescene of competing alkali and alkali earth cations. except for Mg2+. In the presence of Mg2+ Pb2+ uptake was below 80%.