Preparation,Surface Modulation Of Magnetic MOFs-based Material And Its Adsorption Performance On Mercury Ions

Environmental degradation cuts across water,air and soil which are components of the environment upon which humans depend for survival.These components of the environment are critical resources which drive economic,agricultural,social and cultural developments that sustain human life.However,these environmental components have continuously and consistently been polluted with hazardous materials due to the increase of population and natural activities.These activities including automobile wastes,agricultural runoffs,mining,discharge of untreated wastewaters,dry and wet depositions,volcanic eruptions,soil erosions and chemical weathering of rocks have continued to release degrading pollutants into the environment which raise issues of health and economic concerns across the globe.Unarguably,providing a corresponding strategy in response to the incessant introduction of water,air and soil pollutants which degrade the environment has remained one of the fundamental issues of emerging concerns facing scientists,environmentalists and the world at large.In order to solve the problem of low removal rate and secondary pollutant,an economical and efficient adsorbent must be developed through a facile and fast route to significantly improve the removal rate of heavy metallic ions.Nanomaterials（NMs）have become the main participants in environmental remediation because of their excellent properties.Considering the above shortcomings of previously used technologies and the fact that researchers are currently focusing severely on developing clean,green and environmentally friendly remediation techniques and adsorbents at low cost,a one pot self-assembled magnetic nano hybrid adsorbent based on ZIF-90 nanoparticles was developed to adsorb and remove mercury ions from aqueous solution.First,based on the synergistic effect of-COOH groupsof polyacrylic acid on the surface of Fe₃O₄nanoparticles and Zn²⁺of ZIF-90,Fe₃O₄nanoparticles were embedded into the shell of ZIF-90,so as to make Fe₃O₄@ZIF-90 nanoparticles.Using the modifiability of aldehyde groups of ZIF-90,-CHO groups and-NH₂groups of cysteine were connected by Schiff base reaction to prepare magnetic nano hybrid adsorbent Fe₃O₄@ZIF-90-C.Among them,the modification of cysteine on the surface of ZIF-90 and the uniform distribution of-SH groups on the surface and internal pores of ZIF-90 make the magnetic nano hybrid adsorbent have good stability in acidic medium.Single nanoparticles and final hybrid nanoparticles were characterized by various characterization methods to confirm the successful synthesis,modification,structural composition,morphology and various physical properties.Cysteine has strong affinity for heavy metal ions such as Hg²⁺,and can be used for adsorption and removal of heavy metal ions in aqueous solution.As expected,the nano hybrid adsorbent Fe₃O₄@ZIF-90-C can efficiently and selectively remove Hg²⁺from aqueous solution and has higher adsorption capacity(900 mg^-1when the initial concentration of Hg²⁺is 500 mg/L),compared with other heavy metal ions(Pb²⁺,Cd²⁺and Cu²⁺).The reasons for the high affinity and selectivity of the adsorbent for Hg²⁺are as follows:（1）after the successful modification of cysteine on the nanocomposites,the-SH groups are densely distributed on the surface and inner pores of the skeleton;（2）The solubility product constant of Hg S is much smaller than that of other sulfides,and-SH group of cysteine has stronger affinity for Hg²⁺.This work not only promotes the application of ZIF-90 based adsorbents in wastewater treatment,but also has the properties of regeneration and reuse.