m-Phenylenediamine-modified polypyrrole as an efficient adsorbent for removal of highly toxic hexavalent chromium in water

The aim of this work was to develop m-phenylenediamine (mPD)-modified polypyrrole (PPy–mPD) as an efficient adsorbent for the removal of highly toxic hexavalent chromium [Cr(VI)] from industrial wastewater. PPy–mPD was synthesised by in situ oxidative polymerisation and characterised using various techniques. The effects of pH, adsorbent dose, initial concentration, temperature, and co-existing ions on Cr(VI) removal by PPy–mPD were investigated in batch studies. The results showed that PPy–mPD had a high specific surface area of 183 m²/g, and a maximum Cr(VI) adsorption capacity of 526 mg/g at 25 °C and initial pH 2. XPS and IC–ICP–MS studies confirmed that some of the adsorbed Cr(VI) was reduced to Cr(III) by PPy–mPD. Cr(VI) removal by PPy–mPD followed pseudo-second-order kinetics, and the removal was highly selective for Cr(VI) in the presence of co-existing ions in solution. Desorption studies showed that Cr(VI) removal by PPy–mPD was decreased approximately 30% after third treatment cycle. In summary, PPy–mPD was shown to have potential as a novel adsorbent for the highly selective adsorption for Cr(VI) with high capacity although structural integrity of the polymer matrix would be needed if enhanced desorption characteristic is required for specific applications.