表面酸性官能基の有無が活性炭の鉛イオン吸着におよぼす影響

抄録

Influence of solution temperature and acidic surface factional groups on lead(II) ions adsorption onto activated carbons (ACs) were studied. ACs with no surface oxygen, OG-ACs were made by heating at 1273 K under helium flow, and those introduced acidic surface factional groups were prepared with nitric acid, Ox-ACs. The amount of proton released from carbon was measured after the lead(II) ions adsorption was completed. Adsorption of lead(II) ions onto OG-ACs were caused by electrostatic interaction between Cπ electrons on the graphene layer and lead(II) ions, whereas the adsorption onto Ox-ACs were took place by ion exchange. The thermodynamic parameters such as Gibbs free energy change (ΔG⁰), enthalpy change (ΔH⁰), and entropy change (ΔS⁰) were calculated from van′t Hoff plots. Adsorption onto OG-ACs resulted in spontaneous and exothermal process. Though the adsorption by Ox-ACs was also spontaneous from ΔG⁰, the ΔH⁰ was nearly equal to zero because temperature dependence could not be observed for the adsorption onto oxidized carbons. The adsorption kinetics was examined using the Langmuir type rate equation, indicating that adsorption rate constants were greater for Ox-ACs than for OG-ACs. The adsorption kinetic constants were significantly enhanced with increasing solution temperature and/or decreasing in particle size, revealing that the rate determining step of adsorption onto Ox-ACs could be effectively shifted from inter-particle diffusion to collision between adsorbate and adsorption sites.