The Study Of Adsorption Properties For Dyes Onto Zeolitic Imidazolate Frameworks

Zeolitic imidazolate frameworks(ZIFs)are a new type of porous crystal materials with the zeolite topology constructed from transition metal ions bridged by imidazolate.These materials have attracted much attention for their pore size can be adjusted,large specific surface area,composition diversity and novelty,etc.Owing to the excellent performance of ZIFs,more and more researchers pay much more attention to the study for ZIFs,such as the capture and store of CO2,the separation of mixture of gases,and successively open up many frontier research directions.Based on the hydrophobicity performance and higher chemical stability of ZIFs,in this paper,we choose three different topology structure of the ZIFs as the adsorbents,those are the topology structure of SOD,zni and GIS,to study the discoloration and adsorption properties for three different nature dyes onto ZIFs from aqueous solutions.Through the adsorption process,to investigate the absorption performance and determine the adsorption isotherm of the ZIFs for dyes,adsorption kinetics models were also being estimated.At the same time,we disscussed the adsorption-desorption properties for ZIFs which were loaded dyes.Firstly,we chosed the topological structure of SOD of the ZIF-8 and ZIF-67 as the adsorbents,and studied the adsorption performance onto AB40 dye.The results showed that the maximum adsorption capacity of ZIF-8 and ZIF-67 were 27.92 mg/g and 79.18 mg/g,respectively,in the optimum initial concentration of 50 mg/L and 90 mg/L,respectively,and within the equilibrium time for 360 min,and the difference in the adsorption capacity between ZIF-8 and ZIF-67 may be due to the low-coordination metal ions Zn(?)and Co(?)in the external surface of ZIFs,which has different affinity to the SO3-.As to the ZIF-67,the experimental results corresponded well with the Langmuir isotherm,as the ZIF-8,Langmuir and Freundlich isotherm all could well fitted to the experimental results.The experimental results corresponded well with those of the pseudo second-order kinectic model.Moreover,the topological structure of zni and GIS also had adsorption properties to AB40 dye to some extent.The order of the adsorption capacity between the three structures were:ZIF(SOD)>ZIF(zni)>ZIF(GIS).What's more,the study of desorption efficiency for ZIF-8 and ZIF-67 which loaded dyes in the H2O?EtOH?H2O-NaOH and EtOH-NaOH medium were investigated.Through magnetic stirrers,the adsorbents loaded of the dye showed a predominant desorption behavior in the EtOH-NaOH medium at 60?for 30 min.The ZIF-8 and ZIF-67 keep a good framework after recycling.Finally,we studied the adsorption capacity of ZIF-8 and ZIF-67 to the methylene blue(MB)and acidic red 151(AR151),and the research showed that the AR151 was better than that of MB in the aspects of decoloring.The reason may be proposed as the repulsive force existed between the ZIFs and basic dye MB,while between the ZIFs and acidic dye AR151 was the affinity.Consequently,ZIF-8 and ZIF-67 to two different nature of the dye had different adsorption capacity.