Synthesis,performance And Mechanisms Of Poly(m-phenylenediamine)-based Adsorbents For The Removal Of Pollutants From Aqueous Solution

With the rapid development of economy and industry,various environmental pollutions have become increasingly serious,which affect human health and ecological environment.Efficient removal of pollutants from environment especially from wastewater is becoming an urgent problem.Adsorption is considered to b e one of the alternatives for wastewater treatment because of its high efficiency,economic feasibility,simplicity and adaptive over a wide concentration range.Poly(m-phenylenediamine)(PmPD),an amine-containing conjugated polymer,can be easily prepared via oxidation polymerization.PmPD has excellent adsorption performance in water purification owing to its powerful redox properties and adsorption abilities.However,PmPD particles tend to aggregate together resulted ing low specific aurface area.PmPD suffers from weak recyclability.It is difficult to be separated from wastewater after adsorption.In addition,the surface positive charges result in weak affinity of PmPD toward positively charged pollutants due to electrostatic repulsion.These drawbacks limit the application of PmPD in the wastewater treatment.In this study,matrix introduction and surface functionalization were used to overcome these natural drawbacks of PmPD.The performance and mechanism of removing emerging pollutant and heavy metals from water by modified PmPD adsorbents were also investigated.This study attempts to lay the theoretical foundation for the application of PmPD in practical wastewater treatment and provides new methods and ideas for constructing high-efficiency on PmPD based adsorbents.The main contents and main conclusions are as follo ws:(1)In order to prevent the agglomeration of PmPD and increase the specific surface area,the LDH-PmPD composites were prepared via simple chemical oxidation polymerization and used for removing DCF from wastewater.The addition of LDH decreased the accumulating density of PmPD and increased the specific surface area of LDH-PmPD,which improved the adsorption capability of LDH-PmPD toward diclofenac sodium(DCF).The as-prepared material had the highest adsorption capacity of 588.9 mg/g for DCF.The adsorption of DCF was mainly controlled by the strong electrostatic attraction,followed by hydrogen bonding and?-?stacking.The natural and artificial aging experiments indicated that the LDH-PmPD had good anti-aging performance.Significantly,LDH-PmPD had a satisfactory performance in the actual medical wastewater treatment.Overall,its facile fabrication and superior sorption ability indicate that LDH-PmPD has the potential for practical applications in DCF wastewater treatment.(2)In order to prevent the agglomeration of PmPD and obtain easy separation property,3D PmPD/melamine foam(MF-P)was synthesized.The m-phenylenediamine was in situ chemical oxidation polymerized on a polyvinyl alcohol modified melamine foam.The 3D MF-P was characterized and used for DCF removal.Compared with PmPD,MF-P have a higher specific surface area.In the adsorption study,the addition of polyvinyl alcohol increased the adsorption ability of MF-P toward DCF.The adsorption kinetics and isotherms of DCF were well fitted with the pseudo-second-order model and Langmuir model,respectively.The highest adsorption capacity of MF-P was 115.7 mg/g for DCF.Meanwhile,MF-P could effectively remove nearly 70%50mg/L DCF within 5 min and be easily separated from water after adsorption.It has great potential for practical applications.The main adsorption forces of MF-P were electrostatic attraction and hydrophobic force.(3)In order to change the surface electronegativity and increase the specific surface area of PmPD,a novel and highly efficient adsorbent(MnO2@PmPD)was designed through the redox reaction between KMnO 4 and PmPD and used for the application of heavy metals removal.The adsorption properties of Pb²⁺onto MnO2@PmPD under different conditions were investigated.Results indicated that the MnO2@PmPD possessed a saturated adsorption capacity of 446.4 mg/g for Pb²⁺,largely exceeding the pristine PmPD.The removal of Pb²⁺was mainly due to the increased surface area and altered surface electronegativity.The possible adsorption mechanism of MnO2@PmPD was proposed based on the experimental results and DFT calculations.Pb adsorption at the surface of MnO2@PmPD was achieved by the electrostatic attraction and ion exchange between Pb and Mn²⁺.DFT calculations revealed the facet-dependent adsorption of?-MnO2 toward Pb.The adsorption affinity of facets toward Pb was in the order of(311)>(111)>(400)>(440).Meanwhile,the internal adsorption of Pb was attributed to the amine groups and newly formed carboxy groups on PmPD.(4)To provide the PmPD with easy separation property,a unique MnO2@Fe3O4/PmPD core–shell hybrid with high adsorption ability and inherent paramagnetic property have been successfully fabricated by adding magnetic-core material,Fe3O4.The adsorption properties of heavy metals onto MnO2@Fe3O4/PmPD under different conditions were investigated.MnO2@Fe3O4/PmPD had more negative surface charges,more available exposed active sites and larger specific surface area compared with PmPD,resulting in a high adsorption capacity and affinity toward heavy metal ions.Due to the electrostatic attraction,ion exchange and coordination interaction between MnO2@Fe3O4/PmPD and heavy metals,the maximum adsorption abilities of MnO2@Fe3O4/PmPD were 438.6 mg/g for Pb(II)and 121.5 mg/g for Cd(II).Furthermore,the column experiment proved that wastewater with low level Pb(II)can be effectively treated upon single passage through the MnO2@Fe3O4/PmPD containing filterable column.MnO2@Fe3O4/PmPD has high adsorption capacity and easy separation property that enables it to remove heavy metal pollutants at large scale.Also,it can be a potential candidate for filter element.