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In the present study, peanut shell, a green waste raw material, was used to prepare biochar (BC) and to obtain BC‐supported nano‐palladium/iron (BC‐nPd/Fe) composites for removing 2,4‐dichlorophenoxyacetic acid (2,4‐D) from water. Characterization analysis demonstrated that nPd/Fe particles were well dispersed on the BC surface with weakened magnetic properties. The average particle diameter and specific surface area of nPd/Fe were 101.3 nm and 6.7 m2 g−1, whereas the corresponding values of the BC‐nPd/Fe materials were 88.8 nm and 14.8 m2 g−1, respectively. Several factors were found to influence the dechlorination of 2,4‐D, including the weight ratio of BC to Fe, Pd loading ratio, initial solution pH, 2,4‐D concentration, and reaction temperature. Dechlorination results indicated that the 2,4‐D removal and phenoxyacetic acid (PA) generation rates were 44.1% and 20.1%, respectively, in the nPd/Fe system, and 100.0% and 92.1%, respectively, in the BC‐nPd/Fe system. The dechlorination of 2,4‐D was well described by the pseudo‐first‐order kinetic model (R2 > 0.97), and the observed rate constants kobs were 0.0042 min (nPd/Fe) and 0.0578 min (BC‐nPd/Fe), respectively. The reaction mechanism indicated that the dechlorination hydrogenation was the main process to remove 2,4‐D from water in the BC‐nPd/Fe system. In addition, BC inhibited the formation of a passivation layer on the particle surface during the reaction, thus maintaining the high reactivity of BC‐nPd/Fe. The easy preparation technique, high 2,4‐D dechlorination capacity, and mild reaction conditions suggest that BC‐nPd/Fe may be a promising alternative composite to remove 2,4‐D from water.

Nanoscale zero‐valent iron (nZVI) has high removal efficiency and strong reductive ability to organic contaminants, but this reactivity soon ceases and is attributed to rapid passivation of the nZVI surface due to the formation of iron oxides. In the present study, bimetallic palladium‐zero valent iron nanoparticles were activated with sodium citrate (SC‐nPd/Fe) to enhance 2,4‐D dechlorination from aqueous solutions. FTIR and XRD analyses showed that there was no passivation layer on the surface of nZVI after the addition of SC, and XPS analysis confirmed the nZVI after the reaction still maintained high reactivity and surface Pd ratio. The existence of SC facilitated the transfer of electrons from Fe0 to contaminants, thus accelerating the reductive dechlorination of 2,4‐D. The dechlorination efficiency of 2,4‐D on nPd/Fe was only 56.4% in 210 min, while complete dechlorination could be achieved on SC‐nPd/Fe under the same conditions, and simultaneously 97.1% of phenoxyacetic acid (PA) was generated. Moreover, the effect of reaction conditions on the dechlorination such as Pd ratio, SC dosage, initial pH and temperature was also investigated, and it was well described by pseudo‐first‐order kinetic model. In particular, The chelating abilities of SC is similar to EDTA, but it is an environmentally‐friendly chelating agent. Findings from the present study suggested that the SC could be a promising substitute for application in the remediation of 2,4‐D contained water.

Environment-friendly iminodisuccinic acid (IDS) has been recognized to enhance the reactivity of Pd/Fe nanoparticles (nPd/Fe) for the effective dechlorination of 2,4-dichlorophenoxyacetic acid (2,4-D). In this study, the improving effects of IDS and other experimental parameters, such as IDS concentration, initial pH, Pd ratio and reaction temperature, on the reduction of 2,4-D were investigated. Characterization analyses of nPd/Fe with and without IDS were performed, and the mechanism of the improvement by IDS of nPd/Fe reactivity was also elucidated. Results revealed that IDS not only removed the passivation layer on nanoscale zero-valent iron (nZVI) surface, but also inhibited the iron ions from forming nZVI surface passivation layer through complexation.As a result, nPd/Fe maintained their reactivity throughout the reaction. In the presence of IDS, the removal efficiency of 2,4-D by nPd/Fe was significantly increased from 32.5 to 99.2%, and nearly 96.2% phenoxyacetic acid (PA) was simultaneously generated. The findings from the present study demonstrate that IDS could be a promising alternative complexing agent for inhibiting surface passivation and enhancing the effective utilization of nPd/Fe for dechlorination.

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