Adsorption Of Congo Red From Aquatic Solution Using Zeolitic Imidazolate Framework-8 And Its Characteristics

Metal-organic framework materials(MOFs)possessed excellent features,including high specific surface area,pore size and stable skeleton structure,which lead widespread research interest on it.Zeolitic imidazolate framework-8(ZIF-8)material is a typical MOF,which has a significant feature of high chemical stability and good thermal stability in the boiling water,NaOH solution,and organic solvents conditions.The material has now been widely used in many applications.Congo red dye wastewater is a typically effluent with indigenous toxic,mutagenic and carcinogenic characteristics.It is ineffective for directly using the traditional method of biochemical and physicochemical treatment.This paper used Zeolitic imidazolate framework to remove Congo red in aquatic solution.It aims at resolving dye wastewater problem and providing a theoretical basis for practical engineering applications through studying the impact of different factors on the adsorption process and adsorption reaction mechanism.In current study,using zinc acetate and dimethyl imidazole as a raw material,methanol as solvent,ZIF-8 was synthesized under certain conditions.Its physico-chemical property was characterized for revealing the nature of the material,such as scanning electron microscopy(SEM),X-ray diffraction(XRD),Fourier infrared spectroscopy(FTIR),the specific surface area and porosity analysis.The structural properties for ZIF-8 are consistent with previous synthesis.The dye adsorption ability of ZIF-8 was firstly compared with other two traditional adsorbent materials(activated carbon and zeolite)and then was investigated under different conditions,such as mixing time,initial concentration,temperature,initial pH and varios salt ions.ZIF-8 material was found to have obvious advantages for industrial applications.Fitting the experimental data to adsorption isotherm equation and adsorption kinetics equation found that better than pseudo-first order model,pseudo-second order model fitted the experimental results very well.It referred that the reaction process was a chemi-sorption process.Meanwhile,Langmuir equation is more suitable for the adsorption process,and adsorption reaction happened as monolayer adsorption of dye molecules on ZIF-8 surface.The maximum adsorption capacity of the ZIF-8 material for conge red was estimated as 1250 mg g-1 in the pH = 7.8,and 2000mg g-1 at pH = 4.This showed that the material of the Congo red dye molecules have a strong adsorption capacity,and has broad application prospects in industrial wastewater treatment.Characterization of the results before and after the use of the material can be analyzed fro revealing the adsorption mechanism.The surface structure and shape did not change significantly for ZIF-8 material before and after the adsorption.Meanwhile,the reaction mechanism can be inferred that a large amount of external active sites Zn-OH produced in ZIF-8 through the dissociative adsorption of water with subsequently forming an inner-sphere complex with CR molecule at-SO3 and-N=N-sites.The ion exchange between Zn-OH in ZIF-8 and negatively charged-SO3 in the dye molecule and hydrogen bonding between hydroxyl group of ZIF-8 and electro-negative residues-N=N-in the dye molecule existed,respectively.Furthermore,the?-? interaction between the benzene and naphthalene rings of CR and the aromatic imidazole rings of ZIF-8 is also the proposed interaction mechanism.