One-Pot Synthesis of Nanoscale Zero-Valent Iron Immobilized with Granular Activated Carbon

Activated carbon has widely been used to adsorb and remove various pollutants, but it is not an adequate treatment solution for degrading pollutants; rather, it merely transforms the pollutants from a liquid-phase to a solid-phase bound in the carbon matrix. In this study, we have investigated the immobilization of nanoscale zero-valent iron (nZVI) on granular activated carbon (GAC) for the purpose of providing redox reactivity towards water pollutants. Two representative processes for nZVI immobilization on granular activated carbon (GAC/Fe) were evaluated, and concluded by the suggestion of optimized conditions for synthesizing GAC/Fe composites. Both total iron content and Fe⁰ content can be significantly influenced by the preparation process; therefore, it was important to avoid oxidation during preparation, to achieve the highest possible reduction capacity. The optimal condition for producing reactive GAC/Fe was determined to be immersing GAC in a Fe²⁺ solution for 24 h, followed by the reduction of Fe²⁺ to Fe⁰ without an intermediate drying step. The reactivity of prepared GAC/Fe was tested by evaluating nitrate reduction; in addition, the effect of acid addition was investigated. A colorimetric assay was applied to quantify the reaction products, whereupon the effectiveness of the colorimetric assay was well verified. Ultimately, the prepared GAC/Fe composite demonstrated a synergistic effect between the adsorption capability of the GAC and the degradation capability of the nZVI, which make this composite a very effective material for environmental remediation.