Preparation of zeolitic imidazolate framework-8 and its adsorption performance on Congo Red
Objective In order to solve the problem that printing and dyeing wastewater is harmful to the environment and difficult to treat,this research aims to prepare an economical and environmentally friendly adsorbent with excellent adsorption effect,and the adsorption performance of ZIF-8 on azo dyes represented by anionic Congo Red dyes was investigated.Method In this research,2-methylimidazole and Zn(NO3)2·6H2 O were used as raw materials,and deionized water was used as solvent.The proportion of 2-methylimidazole,Zn(NO3)2·6H2 O and deionized water was adjusted and they mixed by mechanical stirring to prepare the homogeneous and clear particles of zeolitic imidazolate framework-8(ZIF-8)material under normal temperature and normal pressure conditions.The structure of the ZIF-8 material was tested by scanning electron microscopy(SEM),infrared spectrometry,X-Ray diffraction,thermogravimetry,BET and other characterization methods.The adsorption performance of the material on dyes was evaluated by the water-bath constant-temperature shaking method,and the factors affecting the adsorption and the adsorption mechanism were analyzed.Results It was found from SEM images that the ZIF-8 section was smooth,and that the particles were uniform and had a polyhedral structure.Infrared spectra analysis and X-Ray diffraction results showed that the ZIF-8 material was consistent with the finding reported in docoments.Thermogravimetric analysis and specific surface area tests revealed that the thermal cleavage temperature of the ZIF-8 material was 258℃,and the ZIF-8 had a good thermal stability.The specific surface area of BET was 869.63 m2/g,the specific surface area of Langmuir was 1 140.03 m2/g,and the average pore size was 3.27 nm.The adsorption equilibrium was reached in a shorter time at the lower initial concentration,and the adsorption amount reached the maximum when the initial concentration was 95 mg/L.It was found that the adsorption would first rise,then fall and finally tend to equilibrium with the increase of ion concentration,and the adsorption amount could reach the maximum when pH was neutral.It was also revealed that the adsorption rate of ZIF-8 could still be maintained at 69%after 4 cycles.The adsorption of ZIF-8 on Congo Red was more in line with the pseudo-second-order model through the fitting of kinetic model,which was dominated by chemical adsorption.The adsorption isotherm model fitting showed that the adsorption of ZIF-8 on Congo Red was in line with the Langmuir model,which belonged to the adsorption of the monolayer molecules.It was believed that the whole adsorption process was an exothermic reaction,and the low temperature was favorable for the adsorption.Under the conditions of 20℃and pH=7,the adsorption effect of ZIF-8 on 95 mg/L Congo Red solution was the best,and the maximum adsorption rate was 671.41 mg/g.Conclusion ZIF-8 prepared using deionized water as the solvent is found to reduce cost compared to the situation with methanol as the solvent,and the operation is simple and safe compared to other preparation methods.The ZIF-8 particles prepared are uniform and clear,with good thermal stability and large specific surface area.ZIF-8 has better adsorption performance on anionic dyes represented by Congo Red,so it can be applied to the treatment of general anionic dye waste liquid.
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