Competitive adsorption between atrazine and methylene blue on activated carbon: the importance of pore size distribution

A series of phenolic resin-based microporous activated carbon fibers (ACF) were used to determine how pore size distribution influences the nature of the adsorption competition mechanism between the micropollutant, atrazine, and a compound similar in size, methylene blue (MB). Experiments consisted of simultaneous adsorption, dye preloading, and atrazine preloading. Direct competition for adsorption sites is the primary mode when the competing adsorbate can access the same pore size region as the target micropollutant. When only a narrow distribution of primary micropores (pore width <8 Angstrom) is present, simultaneous adsorption and dye preloading greatly impacted atrazine adsorption. Increasing the micropore volume and shifting the pore size distribution into the secondary micropore region (8 Angstrom <pore width <20 Angstrom) reduced the degree of competition. The relative impact of preloading with MB on atrazine adsorption decreased with increasing pore volume and pore size. When atrazine was preloaded, the low:level of atrazine desorption from the smallest pore size adsorbent, which contained mainly primary micropores, provided evidence for strong adsorption/slow desorption in these pores. This is consistent with the enhanced adsorption resulting from overlapping pore wall potentials, contributing to non-ideal competitive adsorption. The displacement of pre-adsorbed atrazine by MB in the other four ACFs is primarily associated with direct competition for sites in the secondary micropore region. (C) 2000 Elsevier Science Ltd. All rights reserved.