Preparation Of ZIF-8 And Its Study On The Treatment Of Printing And Dyeing Wastewater

Metal-Organic Frameworks(MOFs)are characterized by high controllability,large specific surface area and reproducibility,and ZIF-8 as a typical MOF has been of great interest and widely used in many fields.Dye wastewater is a typical high-color and high-concentration wastewater,and the current process has been unsatisfactory for its treatment.Rhodamine B and methyl orange are typical dyestuffs as cationic and anionic dyestuffs,respectively,and the study of the adsorption effect of ZIF-8 on these two dyestuffs was conducted to find out the optimal conditions for the adsorption of dyestuffs by ZIF-8,aiming to solve the difficult problems in the treatment of dye wastewater.In this experiment,ZIF-8 was prepared using two different precursors by the ambient stirring method,and its characterization revealed that the adsorbent with zinc nitrate hexahydrate as the precursor exhibited a regular dodecahedral structure with a smaller particle size and larger specific surface area,and had a higher adsorption capacity and shorter adsorption equilibrium time.The adsorption experiments were further carried out with five adsorbents prepared in different molar ratios,and the maximum adsorption capacity of 103.5 mg/g was found at a molar ratio of 1:8.The effects of the initial dye concentration,adsorbent dosage,solution p H,temperature and ion concentration on the adsorption of dyes by ZIF-8 were subsequently investigated.The results showed that the adsorption treatment of 50 ml,50 mg/L of rhodamine B solution with the optimal dosage of 30 mg,the experiment reached the adsorption equilibrium at 60 min,when the decolorization rate reached 92.5%;the adsorption treatment of 50 ml,50 mg/L of methyl orange solution with the optimal dosage of 40 mg and the equilibrium time of 420 min,the decolorization rate reached94.3%.Among them,methyl orange was more affected by p H,which was due to the fact that p H changed the surface charge of ZIF-8,and the adsorption was weaker under the condition of p H>9 when the adsorbent was negatively charged and methyl orange molecules repelled each other,and the adsorption effect was better when the adsorbent surface was positively charged and methyl orange attracted each other at p H<9.And rhodamine B is less affected by p H,because its adsorption process is electrostatic adsorption and chemisorption coexist.By comparison,the adsorption effect of ZIF-8on rhodamine B was better than that of methyl orange when the dye concentration exceeded 50 mg/L.By analyzing the mechanism of dye adsorption,both dyes conformed to the pseudo-secondary kinetic model and the Langmuir isotherm model,indicating that the adsorption process was mainly electrostatic adsorption,which was a spontaneous heat absorption reaction,but the chemisorption was more obvious during the adsorption of rhodamine B.The adsorption equilibrium time of ZIF-8 increased by50% and the adsorption amount of adsorbent decreased but the decolorization rate of the dye could still be maintained at 74% after 10 adsorption and desorption experiments.Overall,the adsorption effect of the prepared adsorbent in the real water background reached the expected level,and subsequent improvements are still needed to improve the adsorption effect in the real water.