Modification Based On UIO-66 Metal-organic Framework Material And Adsorption Studies On Pb(Ⅱ)

Pb(Ⅱ)is one of the most common heavy metal pollutants,which can cause serious harm to human health and damage aquatic ecosystems,resulting in inactivation of aquatic organisms.In this study,highly stable UIO-66-like metal organic framework adsorbent materials with selective adsorption functions were synthesized and post-modified to provide a theoretical basis for the treatment of Pb(Ⅱ)-containing wastewater and to open up new avenues for the modification and utilization of MOFs.In this study,UIO-66 materials were synthesized by the solvothermal method,and surface modification was performed by hydrothermal method using ethylenediaminetetramethylenephosphonic acid and 1,3,5-benzenetricarboxylic acid.Two new MOFs materials were prepared separately and the static adsorption experiments of Pb(Ⅱ)were performed.The adsorption behavior,influencing factors and recycling performance of modified UIO-66 on Pb(Ⅱ)were investigated.The mechanism of Pb(Ⅱ)adsorption treatment by modified UIO-66 was investigated using SEM-EDS,FT-IR,XRD,XPS,TGA and other analytical methods,combined with adsorption kinetics,thermodynamics and isotherm models.The main findings of the study are as follows.(1)UIO-66-EDTMP was synthesized by hydrothermal method using ethylenediaminetetetramethylenephosphonic acid rich in O,P and N groups as the modifying agent.The synthesized material has excellent chemical and thermal stability,and the skeleton structure remains intact at 300 °C.The equilibrium time and maximum theoretical adsorption capacity of UIO-66-EDTMP for Pb(Ⅱ)were 480 min and 381.195 mg/g at p H 5 and 298 K,respectively.The adsorption mechanism of UIO-66-EDTMP on Pb(Ⅱ)is the chelation,ion exchange and electrostatic interaction between O,N and P containing groups and Pb(Ⅱ).The coexisting ions and the resolution experiments indicate that the adsorbent has better selectivity for Pb(Ⅱ)and high regeneration capacity.The adsorption process of Pb(Ⅱ)is a heat absorption reaction.The adsorption of Pb(Ⅱ)on UIO-66-EDTMP is a chemisorption process with multimolecular involvement and favorable.(2)UIO-66-COOH was synthesized by hydrothermal method using1,3,5-benzenetricarboxylic acid containing carboxyl group as the modifying agent.The synthesized material has strong negatively charged ions and multiple coordination modes,which improve the stability and structural diversity of the material.The adsorption studies showed that the adsorption process saturated at 120 min with a maximum adsorption capacity of 322.213 mg/g.The maximum theoretical adsorption capacity of UIO-66-COOH for Pb(Ⅱ)was 799.600 mg/g at p H 5 and 298 K.The Langmuir,R-P isothermal model and PSO kinetic model can describe the adsorption process well.The adsorption mechanism of UIO-66-COOH on Pb(Ⅱ)is a multi-molecular physicochemical adsorption with chelation,pore filling,ion exchange and electrostatic interactions as the mechanisms.Coexisting ions and resolution experiments indicate that the adsorbent has better selectivity for Pb(Ⅱ)and high regeneration capacity.Thermodynamics suggests that the adsorption of Pb(Ⅱ)is an exothermic reaction with stochastic growth and that the driving force of Pb(Ⅱ)adsorption on UIO-66-COOH is both enthalpic and entropic.