Design Of Zirconium Based Environmental Nanomaterials For The Synergistic Removal Of Typical Pollutants From Aqueous Solution

The pollution-induced water scarcity is formed with the emission of various pollutants during the process of civilization,industrialization,and agricultural activities,and threatens the sustainable development of human.The conventional water treatment processes are not able to address adequately the removal of contaminants in raw water.Currently,nano-adsorbents are promising materials for the effective and advanced removal of pollutants due to their short intraparticle diffusion distance,tunable pore size and extremely high specific surface area and associated sorption sites.However,nano-adsorbents are often prepared in the form of fine powders which cause problems in separation/regeneration processes and potential safety concerns due to leaching into water bodies.The mono-functionalization and high cost of nano-adsorbents is unavoidable.To overcome the above shortages,the immobilization and multi-functionalization of nano-adsorbents were explored.Moreover,the advanced treatment of heavy metals and phosphate was also profoundly investigated.Owing to its better stability,eco-friendly,and specific adsorption toward heavy metals and phosphate,HZO was studied as a representative of nano-adsorbents.The main research contents and conclusions are presented as follow.（1）Fe₃O₄@HZO yolk-shell nanospheres were synthesized via a two-step process and further examined as adsorbents for the removal of Pb（II）.Specifically,the preformed monodispersed Fe₃O₄spheres were used as cores for subsequent deposition of silica layer and HZO layer to obtain core-shell Fe₃O₄@SiO2@HZO,Fe₃O₄@HZO yolk-shell nanospheres were generated with etching the silica layer by NaOH.The as-obtained samples were characterized by XRD,FESEM,TEM,N₂ adsorption,Zeta potential meter,and vibrating sample magnetometer.The results demonstrated that the resultant HZO can be evenly deposited on Fe₃O₄ surface with a large cavity between the HZO layer and the Fe₃O₄core.The magnetic saturation（Ms）values of the Fe₃O₄@ HZO is 11.9 emu g-1.The prepared samples can be separated easily from solution with the help of an external magnetic force.The Pb（II）sorption capacity of Fe₃O₄@HZO is 310.8mg/g after normalized by the weight of Zr.Fe₃O₄@HZO exhibited 41.6%higher Pb（II）adsorption capacity as compared to that of Fe₃O₄@SiO2@HZO.STEM-EDS results revealed that the existence of cavities between Fe₃O₄cores and HZO shells is responsible for the improved adsorption performance.The removal efficiency of Pb（II）was maintained above 90%in five consecutive adsorption-desorption cycles.（2）Furthermore,the novel catalytic-adsorption reaction was developed for removing the EDTA-chelated Pb（II）（Pb-EDTA）from aqueous solution.Specifically,the Fe₃O₄ core of Fe₃O₄@HZO is served as Fenton-like catalyst for decomplexation of Pb-EDTA,and the Zr（OH）x shell of Fe₃O₄@HZO is used as adsorbent to remove the free Pb（II）generated during the decomplexation.The total Pb removal efficiencies of Fe₃O₄@HZO towards 0.1 mM Pb-EDTA was determined to be 89.8%at pH 5.Meanwhile,65.3%of total organic carbon was eliminated.The major intermediates were identified by HPLC-MS and IC.The adsorption of Pb（II）ions on the Fe₃O₄@HZO shell was confirmed by STEM-EDS and XPS.Moreover,the exhausted Fe₃O₄@HZO could be easily refreshed for cyclic runs with less capacity loss.（3）The porous HZO sphere（PHZO）was subsequently functionalized by electrostatic interaction of poly（ethylenimine）（PEI）,to produce a high surface coverage of amino groups on their surfaces（PEI-PHZO）.FESEM,N₂ adsorption,XPS,FT-IR,and Zeta potential meter were used to characterize the as-obtained samples.The modifications with PEI appeared to give fairly stable amino-functionalizations for PHZO.The PEI functionalization was able to shift the isoelectric zero point of PHZO from pH6.2to pH 10.5.The PEI-PHZO has high sorption capacity of 2.49mmol P/g at pH7,47.5%higher as compared to that of PHZO,and strong selectivity for phosphate in presence of competing ions and humic acid.In a real treated wastewater effluent with phosphate concentration of 1.5mg P/L and 10mg/L humic acid,0.15 g PEI-PHZO enhanced with ultrafiltration membrane efficiently reduced 1 L wastewater when the breakthrough point was set as 0.2mg P/L,the 10mg/L humic acid is also completely rejected by ultrafiltration membrane.The exhausted PEI-PHZO could be efficiently regenerated with 1 M NaOH,where the P was enriched in the desorption effluent and could be recovered as struvite.（4）A novel concept of dual-functional ultrafiltration（DFUF）membrane is demonstrated by entrapment of hollow porous HZO nanospheres（HPZNs）into the finger-like pores of ultrafiltration（UF）membrane and seal with polydopamine,rather than in the membrane matrix in previous reports of blend membranes,resulting in an exceptionally high active content and simultaneous removal of multiple pollutants from water due to the dual functions of rejection and adsorption.HPZNs were immobilized in polyethersulfone（PES）UF membranes with a high content of 68.9 wt%.The decontamination capacity of DFUF membranes towards multiple model pollutants（colloidal gold,polyethylene glycol（PEG）,Pb（II））was evaluated against a blend membrane.Compared to the blend membrane,the DFUF membranes showed 2.1-fold increase in the effective treatment volume for the treatment of Pb（Ⅱ）contaminated water from 100 ppb to below 10 ppb（WHO drinking water standard）.Simultaneously,the DFUF membranes effectively removed the colloidal gold and PEG below instrument detection limit,however the blend membrane only achieved 97.6%and 96.8%rejection for colloidal gold and PEG,respectively.Moreover,the DFUF membranes showed negligible leakage of HPZNs during testing;and the membrane can be easily regenerated and reused.