Preparation Of ZIFs Composites And Their Application In The Adsorption And Detection Of Azo Dyes

Azo dyes are organic compounds containing azo groups,about 70%of the annual production of dyes are azo dyes in industry.A variety of azo dyes are harmful to human organs and even can induce cancer,such as Sudan I,which has been classified as a class-Ⅲcarcinogen,it is strictly prohibited to add any Sudan dyes in food products.In addition,most of azo dyes are also used in printing,textile,paper and other industrial fields.The resulting wastewater contains a large amount of azo dyes,such as Congo red,which will pose a serious threat to aquatic ecosystems and human health even at a very low concentration.Therefore,it is of great significance to construct functional materials for detecting and adsorbing azo dyes.Zeolite imidazole frameworks（ZIFs）,as one of the metal-oganic framworks（MOFs）materials with zeolite topological structure,has both the thermal stability and chemical stability of zeolite and the properties of MOFs with large surface area,high porosity,regular pore size,adjustable pore size and so on.It is widely used in sensing,catalysis,degradation,adsorption,energy storage and other fields.In recent years,many researchers have combined ZIFs materials with other functional materials to develop a variety of ZIFs composites,such as magnetic ZIFs composites,fluorescent ZIFs composites,biomass-based ZIFs materials and various ZIFs composite membrane materials.In this paper,three kinds of ZIFs composites were synthesized for the detection and adsorption of SudanⅠand CR respectively,and a series of studies were carried out.The details are as follows:1.According to the ultraviolet absorption spectrum of SudanⅠ,green fluorescent CDs were designed and prepared by microwave-assisted method and encapsulated into ZIF-8 to prepare fluorescent probe CDs@ZIF-8.The fluorescence properties of CDs@ZIF-8 were further investigated and used for the detection of SudanⅠ.The detection range of SudanⅠwas 0.25-70μM and the detection limit was 76.56 n M.Compared with CDs,it has better stability against p H in the range of 2-12,wider detection range and lower detection limit.The prepared CDs@ZIF-8 was applied to the determination of SudanⅠin chili powder,tomato sauce and garlic hot sauce,the recoveries were 95.6%-105.5%.2.Green fluorescent CDs which can be used for CR detection are synthesized directively.Magnetic multi-walled carbon nanotubes（MMWCNTs）and the as-prepared CDs were added to the preparation system of ZIF-8 to obtain a magnetic fluorescent ZIFs composite material（MMWCNTs@CDs@ZIF-8）.The as-prepared MMWCNTs@CDs@ZIF-8 was applied for the detection of CR,with the detection range of 0.25-5μM and the detection limit of 17.46 n M.The mechanism of fluorescence quenching was further investigated,which was attributed to the internal filtration effect.The probe was used to detect CR in acture water samples,and the recoveries of CR were 92.0%-105.4%.The preparation method of MMWCNTs@CDs@ZIF-8 is very simple,which can not only realize the detection of CR in polluted water,but also can be used as an adsorption material for the adsorption and removal of CR due to its rapid magnetic separation function and the adsorption function of ZIF-8.It shows certain practical application value in the detection,adsorption and removal of azo dyes.3.A magnetic hollow ZIF composite material（MH-ZIF）was prepared by combining magnetic MMWCNTs with hollow ZIF（H-ZIF）and aplied for CR adsorption.Compared with the H-ZIF material without magnetic component and the magnetic solid core-shell ZIF material（MS-ZIF）,the adsorption performance was improved.In addition,the effects of adsorption dose,initial CR concentration,p H value and temperature on adsorption properties were furher investigated.The adsorption behavior of CR by MH-ZIF followed the pseudo-second-order kinetic model and Langmuir isothermal adsorption model,and the adsorption process was monolayer chemisorption.The adsorption capacity of CR was up to 1167.9 mg g^-1 at 293 K.In addition,MH-ZIF has excellent selectivity and good regeneration for CR.Based on the above experimental results,it is proved that MH-ZIF is an excellent adsorption material for CR removal.