Dye-affinity microbeads for removal of phenols and nitrophenols from aquatic systems

Alkali Blue 6B attached poly(2-hydroxyethyl methacrylate) (PHEMA) microbeads were investigated as dye-affinity adsorbents for the removal of phenol and nitrophenols (i.e., 2-nitrophenol, 4-nitrophenol, and 2,4-dinitrophenol) from aqueous solutions. PHEMA microbeads were prepared by radical-suspension polymerization of HEMA in the presence of azobisisobutyronitrile as the initiator. These microbeads with a swelling ratio of 55% and carrying 23.6 mumol Alkali Blue 6B/g polymer were then used in the removal of phenol and nitrophenols from aqueous media. The adsorption was fast in all cases (20-min equilibrium time). The maximum adsorptions of phenols onto the microbeads carrying Alkali Blue 6B were 145.2 mumol/g for phenol, 87.8 mumol/g for 2,4-dinitrophenol, 112.6 mumol/g for 4-nitrophenol, and 104.3 mumol/g for 2-nitrophenol. The affinity order was phenol > 4-nitrophenol > 2-nitrophenol > 2,4-dinitrophenol. The adsorption of nitrophenols decreased with increasing pH. Desorption of nitrophenols was achieved using a 30% (v/v) methanol solution. The microbeads carrying Alkali Blue 6B are suitable for repeated use for more than five cycles without a noticeable loss of adsorption capacity. (C) 2002 John Wiley Sons, Inc.