Mesoporous silica supported bimetallic Pd/Fe for enhanced dechlorination of tetrachloroethylene

Abstract

In this study, mesoporous silica (SiO₂) microspheres were hydrothermally synthesized in the presence of gelatin for the immobilization of bimetallic Pd/Fe nanoparticles (Pd–Fe/SiO₂) to enhance the dechlorination efficiency and dechlorination rate of tetrachloroethylene (PCE) under anoxic conditions. Scanning electron microscopy images and elemental mapping showed that the distribution of nanoscale zerovalent iron (NZVI, Fe) on SiO₂ was uniform and the density of Fe increased as the iron loading increased from 10 to 50 wt%. The optimized 30 wt% Fe/SiO₂ particles were used to fabricate Pd–Fe/SiO₂ microspheres by the electrochemical reduction of Pd ions to Pd⁰ for the enhanced dechlorination of PCE under anoxic conditions. The dechlorination efficiency and rate of PCE by Fe/SiO₂ was significantly enhanced in the presence of 0.5–3 wt% Pd and the pseudo-first-order rate constant (k_obs) for PCE dechlorination by the mesoporous Pd–Fe/SiO₂ microspheres increased by 2–3 orders of magnitude when compared with that of Fe/SiO₂ alone. Ethane was found as the only end product with a carbon mass balance of 95–100%, showing that hydrodechlorination was the main reaction mechanism for PCE dechlorination by the Pd–Fe/SiO₂ microspheres. Column experiments showed the good mobility and permeability of the mesoporous Pd–Fe/SiO₂ microspheres when compared with that of pure NZVI alone. The results obtained in this study clearly show that the immobilization of bimetallic Pd–Fe nanoparticles on the mesoporous SiO₂ microspheres not only increases the reactivity for the dechlorination of PCE but also enhances the mobility and permeability for in situ remediation of chlorinated hydrocarbons in porous media.