Adsorptive removal of heavy metal ions in water using poly(m-phenylenediamine) synthesized by laccase

The polymer of m-phenylenediamine (poly(m-PDA)) which was synthesized by mild laccase catalysis in an aqueous buffer (10 mM citrate phosphate, pH 3) was investigated for the adsorption of several heavy metal ions including Pb2+, Cu2+, Co2+, and Cr3+. In the preliminary study for the adsorption of Pb2+ by poly(m-PDA), the adsorbed amount of Pb2+ was strongly influenced by solution pH being the highest in distilled water and decreased as solution pH was lowered from 5 to 2. The adsorption isotherms of the four heavy metal ions on poly(m-PDA) were well described by Langmuir equation. Poly(m-PDA) shows high maximum adsorption capacities (qmax) for Cu2+, Pb2+, and Cr3+ with the values of 556, 526, and 476 μmol g−1, respectively. This study proposes that the synthesis of polymeric absorbents to remove heavy metal ions from water can be accomplished through simple and environmentally friendly enzymatic methods.