Preparation Of ?-cyclodextrin-based Nanospheres And Their Decolorization To Printing And Dyeing Wastewater

With the rapid development of modern industry,a large amount of printing and dyeing wastewater has been discharged into the water,which aggravated the pollution level of water resources.The characteristics of printing and dyeing wastewater include large discharge,complex components,high chromaticity,high toxicity,relatively stable chemical properties of pollutants,and not easy to be degraded,which seriously hinders the national health and sustainable development of economy and society.Therefore,the decolourisation of printing and dyeing wastewater has become one of the priorities in environmental remediation research.Among the commonly used methods for decolorization of printing and dyeing wastewater,the adsorption method is widely used in industry because of its low cost,simple operation process,ideal effect and no secondary pollution.At the same time,with the emergence of more inexpensive,efficient and renewable new adsorbents,the adsorption method has a greater development potential in the decolorization of printing and dyeing wastewater.Currently,adsorbents commonly used in industry include clay/zeolite,activated carbon(AC),activated alumina and agricultural solid waste adsorbents.However,these traditional adsorbents have poor adsorption effect on pollutants in printing and dyeing waste and are difficult to regenerate.Therefore,in order to achieve efficient and low-cost adsorption of printing and dyeing wastewater,many scholars have developed numerous new adsorbents on the basis of traditional adsorbents.As a cyclic oligosaccharide macromolecule with a special cavity structure(hydrophilic outside and hydrophobic inside),?-cyclodextrin(?-CD)can form a host-guest envelope with organic or inorganic compounds.It has the advantages of low cost,easy to get and biodegradable,so it can be used to decolorize printing and dyeing wastewater.However,its application in the field of wastewater decolorization is limited because it is easily soluble in water and can not be separated from wastewater after adsorbing dyes.Therefore,it is necessary to modify ?-CD to achieve its water insolubility,thus improving the availability of ?-CD.In this paper,two ?-CD-based nanospheres(?-CDN and ?-CDN@PEI)were prepared by a nucleophilic substitution reaction using N,N dimethylformamide(DMF)as the solvent,hexachlorocyclotriphosphonitrile(PNC)as the cross-linking agent and polyethyleneimine(PEI)as the surface modifier.The structure and morphology of the two nanospheres were systematically characterized using solid-state NMR spectroscopy,Fourier transform infrared spectroscopy,field emission scanning electron microscopy and zeta potential-particle size analyzer.Their water solubility was also investigated.The prepared ?-CD-based nanospheres were also used as adsorbents for the adsorption studies of two cationic dyes(methylene blue and basic red 14)and three anionic dyes(acid yellow 11,direct red 81 and methyl orange)respectively,and the adsorption properties were compared with those of AC,leading to the following conclusions.(1)the two kinds of ?-CD-based nanospheres made in this thesis can overcome the disadvantage of the former being soluble in water on the basis of guaranteeing the original cavity structure of ?-CD.At the same time,the surface of the nanospheres is rough and has a high specific surface area,which is helpful for the efficient adsorption of various pollutants.(2)The p H of the simulated dye solution plays an important role in the adsorption capacity of the adsorbent.With the increase of p H value of the simulated dye solution,the adsorption rate of the two adsorbents for cationic dyes increased gradually,while the adsorption rate for anionic dyes decreased gradually.The adsorption of dyes by the two adsorbents and AC was in accordance with Langmuir isothermal adsorption model and pseudo-second-order adsorption kinetics model.The fitting results show that among the three adsorbents,?-CDN has the best adsorption effect on cationic dyes,AC is the second best,and ?-CDN@PEI is relatively poor.The saturation adsorption of ?-CDN on cationic dyes can reach about 2 times that of AC.?-CDN@PEI has the best adsorption effect on anionic dyes,followed by ?-CDN,and AC is the worst.The saturation adsorption of ?-CDN@PEI on anionic dyes can reach 2-3 times that of activated carbon,and the adsorption rate can reach 8-42 times that of AC.Based on the above results,?-CDN is more suitable for the adsorption of cationic dyes,while ?-CDN@PEI is more suitable for the adsorption of anionic dyes.(3)After 10 consecutive adsorption-desorption cycles,the dye adsorption performance of ?-CDN and ?-CDN@PEI remained stable.The results show that the prepared ?-CD nanospheres have excellent cyclic adsorption for dyes and can be easily regenerated,which can realize the rapid reuse of adsorbents.(4)Both ?-CDN and ?-CDN@PEI adsorbents showed higher adsorption rates for both dyes in the mixed system of methylene blue-methyl orange(MB-MO)compared to the single system.This result can be attributed to the electrostatic interactions between the different electrical properties of the two dyes,creating a synergistic adsorption effect between them.In addition,under acidic conditions,both adsorbents showed relatively good adsorption capacity for both dyes in the MBMO mixed system.