Covalent Organic Framework Materials For Simultaneous Detection And Removal Of Cd²⁺,Pb²⁺,Cu²⁺,Hg²⁺,Zn²⁺

The presence of cadmium(II,Cd²⁺),lead(II,Pb²⁺),copper(II,Cu²⁺),mercury(II,Hg²⁺),zinc(II,Zn²⁺)and other heavy metal ions（HMIs）can cause humans and other organism kinds of diseases.Therefore,real-time monitoring and removal of HMIs in the environment is particularly important.In order to solve these problems,miniaturized and simplified electrochemical methods were used to realize real-time monitoring of HMIs because of low cost,short time-consuming,and simple operation.The physical adsorption method,which can effectively desorb HMIs without secondary pollution so that the environment can be repaired.However,electrochemical detection and physical adsorption also have certain defects,such as poor sensitivity and reproducibility.Therefore,it is an urgent need to find suitable electrode materials with excellent physical and chemical properties to monitor heavy HMIs in real time,and discover new adsorbents with excellent adsorption properties.In this thesis,a simple solvothermal synthesis method was used to synthesize highly oriented two-dimensional flexible covalent organic framework（COFs）films,and directly modified them on the surface of bare glassy carbon electrodes to construct highly sensitive electrochemical sensors.In addition,we used the powder sample to adsorb HMI in the environment.In order to improve the detection and adsorption performance of these material,the high-temperature carbonized biomass macroporous carbon material kenaf stalk（3D-KSC）and the inexpensive melamine foam（MF）were used as the base materials.COFs were controllably modified on the base materials to realize detection and removal integrated materials.The specific work is as follows:1.The insolubility of porous polymers limits the wide application of covalent organic frameworks.Here,COF_BTLP-1 was produced by the aldehyde condensation reaction between 1,4-benzenedithiol-2,5-diaminohydrochloride and 1,3,5-tricarbonylbenzene,and through controlling the concentration and growth time,we could control growth of COF_BTLP-1 on 3D-KSC.Compared with COF_BTLP-1 powder,COF_BTLP-1 on 3D-KSC can effectively avoid its random orientation.Each unit of COF_BTLP-1contains 24 adsorption sites（12 S atoms and 12 N atoms）and regular pores for HMIs to promote the transfer of HMIs.The large number of adsorption sites can selectively identify and capture HMIs,so the COF_BTLP-1/3D-KSC electrode can simultaneously detect Cd²⁺,Pb²⁺,Cu²⁺and Hg²⁺.This study found that compared with COF_BTLP-1/GCE electrode,COF_BTLP-1/3D-KSC electrode has higher sensitivity and detection limit for Cd²⁺,Pb²⁺,Cu²⁺and Hg²⁺,and the detection limits are 12.3 n M and11.8 n M,18.6 n M,21.4 n M respectively.The sensitivity is 1337.4μA/μM cm²,1389.0μA/μM cm²,886.2μA/μM cm² and 770.0μA/μM cm².The detection of Cd²⁺,Pb²⁺,and Cu²⁺by the two sensors can achieve the standard of drinking water allowed by the World Health Organization（WHO）.The detection of Hg²⁺can also reach the sewage discharge standard allowed by the WHO.In addition,COF_BTLP-1/3D-KSC and COF_BTLP-1/GCE can also be applied to other fields of electroanalytical chemistry.2.Covalent organic frameworks（COFs）have attracted much attention due to their excellent performance in environmental repair,but they still face various challenges in practical applications.In this section we used a simple solvothermal synthesis method to synthesize a new type of covalent organic framework material(COF_TDBA-TPA).The study found that the adsorption capacity of COF_TDBA-TPA-based adsorbents for Cd²⁺,Pb²⁺,Cu²⁺and Hg²⁺were respectively up to 711.62 mg/g,603.44 mg/g,716.94 mg/g and 618.25 mg/g.This material also showed fast adsorption kinetics,and the adsorption kinetic equilibrium can be reached within 10 min.We detected its recycling rate and found that after five cycles of use,its adsorption performance was not lost,which provided a reliable platform for environmental repair.In addition,the electrochemical sensor constructed by COF_TDBA-TPA/GCE can realize the simultaneous detection of Cd²⁺,Pb²⁺,Cu²⁺,Hg²⁺and Zn²⁺five HMIs in drinking water,and the detection of each HMI showed a high sensitivity and lower detection limit.The detection limits of Cd²⁺,Pb²⁺,Cu²⁺,Hg²⁺and Zn²⁺were as low as 0.922 n M,0.309 n M,0.450 n M,0.0.208 n M and0.526 n M,respectively.The sensitivity were as high as 17.8μA/μM cm²,53.2μA/μM cm²,36.6μA/μM cm²,79.1μA/μM cm² and 31.3μA/μM cm².Comparing with other studies,it suggested us that its sensing performance was better.In addition,the sensor has excellent repeatability and selectivity,which would provide a new strategy for COFs used in electrochemical sensing.3.Trace heavy metal ions（HMIs）are very harmful to the environment and organism.Therefore,to develop a multifunctional material with detection and removal functions for effectively controlling and sensitively monitoring the content of HMIs is imperative.Here tripolycyanamide（TPA）and 2,5-dihydroxyterephthalic acid（DDTA）were used to synthesize a highly crystalline covalent organic framework(COF_DDTA-TPA)which was used to sensitively detect and efficiently remove HMIs.COF_DDTA-TPA has abundant N-O-O and N-N-O sites and large specific surface area,can be used as an excellent adsorbent for HMIs.Therefore,COF_DDTA-TPA was used for the removal of Cu²⁺,Pb²⁺,Cd²⁺,Hg²⁺and electrochemical detection of Cd²⁺,Pb²⁺,Cu²⁺,Hg²⁺and Zn²⁺simultaneously.The detection limits were 0.85 n M,0.096 n M,0.14 n M,0.072 n M and0.084 n M,respectively.The COF_DDTA-TPA was also controllably grown on melamine foam（MF）and biomass macroporous carbon（3D-KSC）to effectively remove Cd²⁺,Pb²⁺,Cu²⁺,Hg²⁺,which avoid some defects of traditional COFs powder such as random orientation,easy accumulation and poor reproducibility.The COF_DDTA-TPA/MF and COF_DDTA-TPA/3D-KSC can reach adsorption kinetic equilibrium within 50 min.The COF_DDTA-TPA/MF was prepared as a water filter device to simplify the removal of HMIs.In addition,the material can detect and remove HMIs in sewage,soil and blood serum,and showed great potential in environmental remediation and medicine.