Adsorption Performance And Mechanism Of Defect-rich ZIF-L Materials For Simultaneous Removal Inorganic/Organic Phosphorus From Wastewater

Phosphorus（P）as a non-renewable nutrient element,is essential for the growth of organisms.However,effluent from organophosphorus production plants usually contains large amounts of inorganic/organophosphorus,if discharged into the natural water body,it will not only cause the eutrophication of the water body but also harm human health.Besides,adsorption method has received widely attention due to its characteristics of simple operation,high efficiency and the ability to simultaneously remove multiple target pollutants.Defects,as the specific chemical bonding sites with inorganic/organic phosphorus,played a key role in the P-selective adsorption on zeolitic imidazolate frameworks（ZIFs）.Therefore,in this study,in order to improve the simultaneous removal performance of inorganic/organic phosphorus from wastewater,numerous Zn-defect sites were created by a facile acid-etching/pyrolysis method on leaf-like ZIF（ZIF-L）surface to develop a dual-functional adsorbent.The main work of this paper includes the following aspects:（1）We proposed to treat precursor ZIF-L by acid etching/pyrolysis and successfully obtained rich-defect ZIF-L（ae-ZIF-L and py-ZIF-L）materials.The resulted of XPS peak showed that there were more Zn-OH functional groups in defect-rich ZIF-L（ae-ZIF-L（13.63%）>py-ZIF-L（6.61%）>ZIF-L（6.16%））.The NH₃-TPD calculation showed that the size order of unsaturated Zn²⁺defects in three ZIF-L materials was py-ZIF-L（111629）>ae-ZIF-L（62303）>ZIF-L（3855）,indicating the breaking of Zn²⁺and imidazole coordinate bonds under strong acid/high temperature condition.Meanwhile,thanks to more abundant Zn²⁺defect sites in defect-rich ZIF-L,resulting in the surface of py-ZIF-L（25.5 m V）and ae-ZIF-L（18.0 m V）were positively charged,and the zeta potential was much higher than that of ZIF-L（11.1 m V）.Besides,in the range of pH=4-11,the Zn²⁺leaching of defect-rich ZIF-L were less than 2.0 mg/L,indicating that defect-rich ZIF-L has excellent stability in practical wastewater.（2）Based on the preparation and characterization of adsorbent,the properties and mechanism of phosphate adsorption from water by the obtained defect-rich ZIF-L material were further explored.The phosphate adsorption capacities of acid-etched ZIF-L and pyrolyzed ZIF-L was respectively 164.4 mg/g and 100.8 mg/g,significantly better than the original ZIF-L（73.5 mg/g）,attributing to the specific chemical bonding of richer P-adsorbing-active Zn defects and strong electrostatic attraction from higher surface zeta potential.More importantly,under the interference effect of four 100 mg/L competitive anions,ae-ZIF-L（93.8%-97.5%）and py-ZIF-L（90.2%-98.0%）possessed outstanding capacity retention rates（only 77.2-95.7%for ZIF-L）,mainly thanks to the selective PO₄^3-–adsorbing ability of unsaturated coordinate Zn-defects.The column filtration experiments showed defect-rich ZIF-L could respectively treat actual wastewater of 725 BV and 805 BV,much higher than the 455 BV and 645 BV of ZIF-L,indicating that the defect-rich ZIF-L material has better actual wastewater treatment capacity.（3）Based on the exploration of the adsorption properties and mechanism of phosphate from water by defect-rich ZIF-L materials,the glyphosate and phpsphate adsorption properties as well as mechanism from water by acid-etched ZIF-L and pyrolyzed ZIF-L were further investigated.Compared to ZIF-L,due to the higher surface zeta potential of ae-ZIF-L and py-ZIF-L,the adsorption properties of ae-ZIF-L and py-ZIF-L for glyphosate increased by 1.19 times and 3.28 times,respectively.At the same time,the inparticle diffusion model of the three ZIFs materials showed the acid etching/pyrolysis treatment unchanged the adsorption behavior.Besides,the co-adsorption experiments of phosphate and glyphosate showed that the defect-rich ZIF-L material could achieve complete phosphorus removal in a single system,but the removal rate were only slightly reduced in the coexistence system.Meanwhile,the capacity retention rates of defect-rich ZIF-L could reach more than 83%of the original value,after four co-adsorption and regeneration of NaOH water solution with pH= 12.