Because of spontaneous agglomeration effect and undesirable electronic state of Zr sites on the surface, zirconium (hydro)oxides generally exhibit suboptimal defluoridation capacity. Herein, a template confinement-ligand anchoring strategy is developed by utilizing confined growth of zirconium hydroxide (ZH) inside chitosan hydrogel beads (CHB) and subsequent anchoring of fumaric acid (fm) on its surface Zr sites in a monodentate mononuclear coordination mode. This technique leads to uniform dispersion of ultrafine fmZH (≈3.4 nm) and tunable electron density at the Zr sites. Due to the electron-withdrawing ability of fm, electron-delocalized Zr sites increase the orbital energy level matching and vacate Zr 4d orbitals to promote hybridization with the F 2p orbitals. Ultimately, robust Zr F bond can be formed as a result of reduced the adsorption energy toward fluoride ions. The defluoridation capacity shows positive linear relationship with the electron extraction ability of ligands. The saturation adsorption capacity and dynamic treatment capacity of CHB@fmZH are 10.8 and 45.9 times higher than that of CHB@ZH, respectively, owing to high electron extraction (0.098 e − ) of fm. This study offers a novel insight into the design and synthesis of high-efficiency metal oxide adsorbents by steering its surface metal sites’ electronic state through ligand effect.
Mineralization of lead ions (Pb 2+ ) to pyromorphite using phosphorus-containing materials is an effective way to remediate lead (Pb) contamination. Bone char is rich in phosphorus, but its immobilization of Pb 2+ is limited by poor phosphate release. To utilize the phosphorus in bone char and provide a suitable growth environment for phosphate-solubilizing bacteria, bone char and Pseudomonas rhodesiae HP-7 were encapsulated into bio-beads, and the immobilization performance and mechanism of Pb in solution and soil by bio-beads were investigated. The results showed that 137 mg/g of phosphorus was released from bone char in the presence of the HP-7 strain. Pb 2+ removal efficiency reached 100 % with an initial Pb 2+ concentration of 1 mM, bone char content of 6 g/L, and bio-bead dosage of 1 %. Most Pb 2+ was immobilized on the surface of the bio-beads as Pb 5 (PO 4 ) 3 Cl. The soil remediation experiments showed a 34 % reduction in the acid-soluble fraction of Pb. The bio-beads showed good stability in long-term (30 d) soil remediation. The present study shows that bone char can be turned into an efficient Pb immobilization material in the presence of phosphate-solubilizing bacteria. Thus, bio-beads are expected to be used in the remediation of Pb-contaminated environments.
Qi Li,Xiaolei Yang,Changning Li,Aolei He,Shanmu He,Xuemei Li,Ying Zhang,Tuo Yao
Phosphate materials (PMs) combine with phosphate solubilizing bacteria play an essential roles in lead (Pb) immobilization, but their resulting ability to reduce Pb bioavailability may vary depending on PMs used. In this study, Pseudomonas edaphica GAU-665 and three PMs: tricalcium phosphate, calcium phytate and nano-hydroxyapatite were respectively encapsulated into bio-beads by sodium alginate, which immobilization efficiency of Pb 2+ were 99.11%, 97.76% and 99.02% at initial Pb 2+ concentration of 200 mg L −1 , respectively. The Pb 2+ immobilization performance of bio-beads under different conditions and their organic acids secreted were examined. Most Pb 2+ was immobilized by bio-beads through combined functions of adsorption, precipitation, ion exchange and biomineralization, accompanied by the formation of more stable compounds such as Pb 3 (PO 4 ) 2 , Pb 5 (PO 4 ) 3 OH and Pb 5 (PO 4 ) 3 Cl. Meanwhile, pot experimental results indicated that the inoculation of CPhy (calcium phytate) bio-beads with PSB have highest biomass and root growth of oat ( Avena sativa L.) in Pb-stressed compared with CK, which increased the content of chlorophyll b (167.51%) in shoot. In addition, the CPhy bio-beads enhance the peroxidase, catalase activities and reduce the malondialdehyde content to alleviating lead physiological toxicity in oat, which reductions the Pb accumulation in shoot (52.06%) and root (81.04%), and increased the residual fraction of Pb by 165.80% in soil. These findings suggest the bio-beads combined with P. edaphica GAU-665 and calcium phytate is an efficient Pb immobilization material and provided feasible way to improve safety agricultural production and Pb-contaminated soil remediation.
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