Microcystin-LR adsorption by activated carbon

We use a selection of wood-based and coconut-based activated carbons to inv estigate the factors controlling the removal of the hepatotoxin microcystin -LR (m-LR) from aqueous solutions. The wood carbons contain both micropores and mesopores. The coconut carbons contain micropores only, Confirming pre viously published observations, we also find that the wood-based carbons ad sorb more microcystin than the coconut-based carbons. From a combination of a judicious modification of a wood-based carbon's surface chemistry and of the solution chemistry, we demonstrate that both surface and solution chem istry play minor roles in the adsorption process, with the adsorbent surfac e chemistry exhibiting less influence than the solution chemistry. Conforma tional changes at low solution pH probably contribute to the observed incre ase in adsorption by both classes of adsorbent. At the solution pH of 2.5, the coconut-based carbons exhibit a 400% increased affinity for m-LR compar ed with 100% increases for the wood-based carbons. In an analysis of the th ermodynamics of adsorption, using multiple temperature adsorption chromatog raphy methods, we indicate that m-LR adsorption is an entropy-driven proces s for each of the carbons, except the most hydrophilic and mesoporous carbo n, Bl. In this case, exothermic enthalpy contributions to adsorption also e xist. From our overall observations, since m-LR contains molecular dimensio ns in the secondary micropore width range, we demonstrate that it is import ant to consider both the secondary micropore and the mesopore volumes for t he adsorption of m-LR from aqueous solutions. (C) 2001 Academic Press.