Preparation And Application In Heavy Metal Ions Sorption Of Novel Porous Organic Frameworks

Pollution caused by heavy metal ions has become a serious threat to human health and the aquatic ecosystem.Removal of heavy metal ions,such as Ag+，Cu+,Co2+,Zn2+,and Ni2+,from wastewater has been an important project in the area of environmental protection.Up to date,adsorption methods can be considered as a promising method due to its simple process and convenient operations.Developing effective materials in adsorbing heavy metal ions is a fatal process.Porous organic frameworks(POFs)have recently attracted more attention due to their larger capacity,easier preparation,higher efficiency,and fabrication lower cost.Herein,a nitrogen-rich(19.7 wt%)porous organic frameworks,POF-2,was designed based on DFT using the software Guassian 09,which could be synthesized by melamine and 4,4’-(hexafluoroisopropylidene)diphenol.The changes of enthalpy and Gibbs free energy of POF-2 in the process of adsorbing heavy metal ions were calculated.It indicate that the adsorption of metal ions by the POF-BM occurs spontaneously at 298.15 K under 1 atm.According to Gibbs free energy changes,the selectivity sequence of these heavy metal ions adsorbed by POF-BM is as follows:Ni2+>Hg2+>Zn2+>Cd2+>Cu+>Ag+.Based on the simplified adsorption model,the surface area calculated was 1360 m2g-1.A high removal efficiency,up to 99.99%,was calculated in removing heavy metal ions from wastewater.Three novel porous organic frameworks,POF-1,POF-2 and POF-3,were synthesized by melamine.The structures and properties of the resulting materials were characterized and confirmed by means of the elemental analysis,FTIR spectrum,X-ray diffraction,and SEM etc.The pore properties of the three POFs were characterized by N2 adsorption and desorption.The Surface area were 18.29 m2g-1,47.38 m2g-1 and 5.04 m2g-1 respectively.The pore volume were 0.033 cm3g-1,0.25 cm3g-1 and 0.016 cm3g-1.At pH<7,the adsorption capacity of heavy metal ions,such as Cu2,Ni2+,Zn2+,Pb2+,and Mn2+ were respectively tested at 298.15 K and 1 atm.It results that the POFs have selective adsorption for metal ions.The POF-1 has a good removal efficiency for Ni2+,up to 78.6%.The POF-2 has a good adsorption capacity for Cu2+,up to 2089.29 mgg-1.The POF-3 has a good removal efficiency for Pb2+,about 55.9%.the adsorption capacity of heavy metal ions were also tested at pH = 7.The adsorption capacity tested was much higher than that at pH = 4.The POFs show good adsorption capacity for Ni2+,Zn2+ and Cu2+.The adsorption capacity for the tested heavy metal ions adsorbed by POFs is as follows:Ni2+>Zn2+>Cu2+>Ag+,which is in perfect accordance with the theoretical calculations.The removal efficiency reached99%.