Magnetic nanoparticles of Nd-Fe3O4 were prepared by hydrothermal synthesis method, using NdCl3·6H2O and FeCl3·6H2O as the starting materials in this paper. The structure and morphology of nanoparticles were investigated by XRD, FTIR, EDS and TEM. The results showed that, while the addition of Nd at 10% in mole ratio, resulted in the formation of Nd2O3 crystal peak in cubic Fe3O4 nanocrystallites by XRD. The absorption bands of Fe‒O, ‒OH, ‒O‒C‒O‒ and ‒CH2‒ were accordant to the correspondent chemical groups by FTIR. The morphology of the prepared nanoparticles exhibited spherical structure and evenly distributed without agglomeration phenomenon by TEM. The elemental composition were mainly consistent with the precursor materials used in the experiment.
Waste chicken feathers are the ideal precursor for the production of low-cost N-enriched biochar. KOH-modified N-enriched biochar (KNB) containing 15.92 wt% N was successfully prepared using waste chicken feathers. The adsorption kinetics results showed that KNB had rapid Cd (2 h) and Pb (1 h) adsorption rates. The Cd and Pb adsorption capacities of KNB (the values of K F were 22.324 (Cd) and 119.654 (Pb) mg 1−(1/n) ·L 1/n ·g −1 ) were 7.07 and 26.52 times higher than those of the original biochar based on the adsorption isotherm results. The KNB was stable at pH 3–6 and had stronger co-adsorption capacities in double-ion systems. Based on the adsorption experiments and various characterization methods, we concluded that the primary Cd and Pb adsorption mechanisms of KNB involved electrostatic interactions, cation-π interactions, complexation, and K + exchange. The precipitation mechanism could partially account for Pb adsorption but not for Cd adsorption. KOH modification enhanced the electronegativity of biochar and then increased the electrostatic attraction. Surface O- and N-containing functional groups were involved in Cd and Pb adsorption. Graphitic-N, oxidised-N, and O C O were the main active adsorption groups, the relative contents of which increased after KOH modification, thus increasing the Cd and Pb adsorption performance. Therefore, KNB can be used as a fast and highly efficient adsorption agent to remove Cd and Pb from wastewater containing either Cd and Pb or a combination of these two metals.
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