Adsorption Behavior And Mechanism Of Iron-based Metal Organic Frameworks For Arsenicals In Groundwater

Arsenic pollution does great harm to the natural environment and human health.Therefore,removing arsenic pollutants from water is extremely important.Adsorption is considered to be one of the most promising method for arsenic pollution treatment because of simple operation and low cost.The preparation of adsorbent is the key of adsorption method.Metal-organic frameworks（MOFs）are considered as effective adsorbents for the removal of arsenic pollutants.Based on this,this experiment used iron-based materials MIL-88A to study the adsorption of arsenic,and the effects of different synthesis conditions on the preparation of MIL-88A for different kinds of arsenic were systematically studied.The main research results are as follows:（1）MIL-88A materials were prepared under different synthesis conditions,characterized by Scanning electron microscopy（SEM）,X-ray diffraction（XRD）and Brunner-Emmet-Teller（BET）,and p-ASA removal rate on the prepared materials,adsorption kinetics,adsorption isotherm and the effects of ionic strength were studied.After optimization,MIL-88A-85°C/12 h was the material with the best arsenic when water was used as the synthetic solvent.Adsorption experiments showed that the adsorption kinetics of MIL-88A to p-ASA conformed to the pseudo-second-order model,the adsorption isotherm conformed to the Langmuir model,and the adsorption was not affected by the ionic strength.Therefore,the adsorption of MIL-88A to p-ASA was a monolayer chemisorption,forming an inner sphere complexation.（2）Activated MIL-88A was synthesized by annealing the optimized material,and characterized by thermogravimetric（TGA）,SEM,XRD and BET.The adsorption of different kinds of arsenic and the reuse efficiency of activated MIL-88A were studied.It was found that annealing treatment could significantly improve the adsorption performance of MIL-88A.The maximum adsorption capacities at room temperature（25℃）of activated MIL-88A for p-ASA,ROX,As（V）and DMA were813 mg·g^-1,942 mg·g^-1,347 mg·g^-1 and 177 mg·g^-1,respectively.The adsorption capacity of activated MIL-88A for arsenic pollutants was the largest among the metal skeleton materials reported at present.The activated MIL-88A still had a excellent adsorption capacity after four cycles.（3）Through the Zeta potential,Fourier transform infrared（FTIR）and X-ray photoelectron（XPS）characterization analysis of activated MIL-88A before and after the adsorption of different kinds of arsenic,the results showed that coordination was the main removal mechanism of As（V）and DMA by activated MIL-88A,while the main removal mechanism of p-ASA and ROX by activated MIL-88A was coordination and hydrogen bonding.In this study,by optimizing the synthesis conditions of MIL-88A and carrying out post-annealing activation material on the basis of green synthesis,competitive arsenic adsorption performance was obtained.This study provides a new idea for the synthesis of MOFs and provides a theoretical basis for the adsorption of arsenic compounds by MIL-88A.