Dechlorination of 2,4‐dichlorophenoxyacetic acid using biochar‐supported nano‐palladium/iron: Preparation, characterization, and influencing factors

Abstract

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.

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

“…Also, Zhang et al 72 confirmed that the fresh nZVI with high reductive and adsorptive activity had a low crystallinity in the metal phase. After the reaction, the peak related to Fe 0 significantly weakened, and the peaks of iron oxides appeared, which suggested that redox reaction happened on the surface of nPd/Fes 73 . However, compared with nPd/Fe after the reaction, obvious Fe 0 peak was still observed in BC alk ‐nPd/Fe, and the peaks of iron oxides were rarely detected in BC alk ‐nPd/Fe.…”

“…After the reaction, the peak related to Fe 0 significantly weakened, and the peaks of iron oxides appeared, which suggested that redox reaction happened on the surface of nPd/Fes. 73 However, compared with nPd/Fe after the reaction, obvious Fe 0 peak was still observed in BC alk -nPd/Fe, and the peaks of iron oxides were rarely detected in BC alk -nPd/Fe. It proved that nZVI tended to be stable, and the passivation on Pd/Fes surface was not easy to form during the reaction due to the presence of BC alk .…”

“…The biochar-supported nPd/Fe composites (BC raw -nPd/Fe) and nPd/Fe in this study were prepared in accordance with our previous study. 41 First, FeSO 4 Á7H 2 O dissolved in water and BC alk (mass ratio of Fe:C was 1:1) were placed in a three-necked flask under N 2 atmosphere and stirred for 30 min for making evenly dispersed biochar in solution. Subsequently, NaBH 4 dissolved in water by dropwise addition to ensured that the molar ratio of Fe 2+ to BH 4 À in the mixture was 1:2.…”

The removal of 2,4,6-trichlorophenol in water by Ni/Fe nanoparticles

“…Zhou et al used a complexing agent EDTA to optimize the degradation of organic chloride in water by Pd/Fe bimetallic nanoparticles. Their results showed that EDTA could complex iron ions and prevent the formation of a passivation layer on the catalyst surface, thereby improving the degradation efficiency [11]. Zhao et al used activated carbon particles to increase the stable specific surface area of the prepared Pd/Fe bimetallic nanoparticles, thereby effectively improving their removal efficiency of PCBs [10,16].…”

“…In response to the above problems, nanoscale iron-based zero-valent bimetallic metals came into being. The nanoscale bimetallic metals composed of iron and other transition metals (such as Pd, Mg, Ni), which is used to dechlorinate and degrade chlorine-containing organic compounds, and their dechlorination degradation rate are much higher than that of nano-zero-valent iron [9][10][11]. Ni/Fe bimetallic nanoparticles are more widely used for the degradation of chlorine-containing organic compounds than other bimetallic systems.…”