Multifunctional alkali-modified biochar-nPd/Fe composites for enhanced removal of 2,4-D: Preparation, characterization, and mechanism

In this study, nPd/Fes were dispersed on peanut shells-derived alkali-modified biochar (BC_alk) to obtain BC_alk-nPd/Fe composite for overcoming the instability, agglomeration, and oxidation of nPd/Fes. Results demonstrated that the dispersion stability and thermal stability of nPd/Fes were improved and the surface passivation layer was thinned by nanoparticles loading onto the alkalized biochar. Characterization analyses revealed of the improved 2,4-D dichlorination by BC_alk-nPd/Fe. After biochar alkalization, more Si-O-Si sites on BC_alk responsible for supporting nZVI particles were formed and coupled with nZVI to generate Si-O-Fe. Hence, nPd/Fes were immobilized on BC_alk, while the increased oxygen-containing surface functional groups promoted electron transport between nPd/Fes and 2,4-D. Therefore, the BC_alk-nPd/Fe exhibited higher dechlorination efficiency toward 2,4-D than that of nPd/Fe and BC_raw-nPd/Fe. About 99.25% and 89.11% of the 2,4-D removal and dechlorination, respectively, were achieved after 150 min. Kinetic studies revealed that the removal of 2,4-D using nPd/Fe, BC_raw-nPd/Fe, and BC_alk-nPd/Fe fitted well in the Langmuir–Hinshelwood kinetic model, and the order of rate constants was as follows: BC_alk-nPd/Fe > BC_raw-nPd/Fe > nPd/Fe. This study suggested that the prepared composites promoted detoxification and harmlessness of 2,4-D contaminated wastewater and exhibited promising prospect in the efficient treatment of wastewater containing chlorinated organics.