Preparation Of β-CD Based Adsorbent And Its Adsorption Of Heavy Metal Ions In Printing And Dyeing Wastewater

As a common textile industry wastewater,printing and dyeing wastewater has the characteristics of large discharge,complex water quality and toxicity.As one of the most harmful pollutants in printing and dyeing wastewater,heavy metal ions cannot biodegrade and stably exist in water,and can continuously accumulate in aquatic organisms and even lead to their death.In the long run,they will not only lead to the deterioration of water environment,but also may enter the human body through the food chain and seriously threaten life safety.Therefore,before printing and dyeing wastewater discharge,it must be treated to reduce the concentration of heavy metal ions in wastewater,in line with industrial discharge standards.Among the commonly used heavy metal ion treatment methods for printing and dyeing wastewater,adsorption method is widely used in industry because of its advantages such as low cost,simple operation,good efficacy and no secondary pollution.With the emergence of a variety of cheap,efficient and renewable new adsorbents,the adsorption method has a greater development space in the treatment of heavy metal ions in printing and dyeing wastewater.At present,the commonly used adsorbents in industry are activated carbon,clay,zeolite and biological adsorbents.Their adsorption effect on heavy metal ions needs to be further improved,and it is difficult to regenerate.Therefore,it is necessary to develop an adsorbent with high efficiency,low cost,green environmental protection and strong renewable ability.Metal organic frameworks（MOFs）are a new kind of porous materials,which are composed of organic ligands and required metal ions or metal clusters through self-assembly.Its adjustable pore size,multilayer structure,and modifiable sites make MOFs ideal for water treatment.β-cyclodextrin（β-CD）is a cheap and easily available biomass material,with a wide range of sources,natural green,good biocompatibility and low price,its structure contains hydrophobic cavities,can be used with the size and polarity of the matching organic molecules host guest package,chelate with metal ions,coordination.There are a large number of hydroxyl groups around and on the surface,with high polarity and hydrophilicity,which is conducive to cross-linking reaction and modification.After modification,the modification groups on the surface can generate electrostatic attraction and complexation on heavy metal ions.These advantages makeβ-CD and its derivatives can be used to absorb various pollutants in wastewater.Meanwhile,the synthesis of MOFs usingβ-CD as organic ligand also conforms to the concept of environmental protection,low cost and excellent adsorption performance of adsorbent.However,β-Cd-based MOFs are easily dissolved in water,and the collapse of crystal structure leads to a sharp decrease in their adsorption properties.Therefore,post-treatment is needed to improve their stability in water.In this paper,β-CD organic matrix material（β-CDMOF）was synthesized by hydrothermal method withβ-CD as organic ligand and KCl as corresponding metal salt.Then citric acid（CA）was used as crosslinking agent,1,4-dioxane as solvent,and potassium dihydrogen phosphate（MKP）as catalyst.Three kinds ofβ-CD based adsorbents（β-CDMOF@CA）with good water stability were prepared.The structure and morphology ofβ-CDMOF andβ-CDMOF@CA were studied by scanning electron microscope（SEM）,Fourier transform infrared spectrometer（FTIR）and X-ray diffractometer（XRD）.At the same time,the adsorption of Sb³⁺,Pb²⁺,Cu²⁺and Cr⁶⁺simulated wastewater and printing and dyeing wastewater real water were studied.The main research contents are as follows:1.The yield ofβ-CDMOF was the highest at 20 wt%ofβ-CD,the feeding ratio ofβ-CD to water was 1:2.21,crystallization temperature was 10℃,crystallization time was 12 h,and the yield was close to 80%.2.The adsorbentsβ-CDMOF@CA（1:1）,β-CDMOF@CA（1:2）andβ-CDMOF@CA（1:3）,which were prepared by CA cross-linking modification,overcame the shortcomings ofβ-CDMOF soluble in water,and the solubility in water were 0.034,0.031 and 0.025g/L,respectively.3.With the increase of pH value of heavy metal ion solution,the adsorption rate of Sb³⁺,Pb²⁺,Cu²⁺increased gradually,but the adsorption rate of Cr⁶⁺decreased gradually.4.The adsorption processes of the three adsorbents for Sb³⁺and Pb²⁺conform to the Langmuir isothermal adsorption model and pseudo-second-order adsorption kinetics model.The adsorption processes of Cu²⁺and Cr⁶⁺were consistent with Freundlich isothermal adsorption model and pseudo-second-order adsorption kinetics model.The results showed thatβ-CDMOF@CA（1:3）had the highest saturation adsorption capacity of Sb³⁺,whileβ-CDMOF@CA（1:2）had the lowest.β-CDMOF@CA（1:3）had the highest saturation adsorption capacity of Pb²⁺,whileβ-CDMOF@CA（1:1）had a relatively low saturation adsorption capacity.β-CDMOF@CA（1:3）on the saturated adsorption amount of Cu²⁺was much higher than that ofβ-CDMOF@CA（1:1）andβ-CDMOF@CA（1:2）;β-CDMOF@CA（1:3）had the highest saturation adsorption capacity of Cr⁶⁺,whileβ-CDMOF@CA（1:2）had the lowest.β-CDMOF@CA（1:3）has the highest adsorption efficiency for four kinds of heavy metal ions,indicating that the increase of the amount of CA crosslinking agent is helpful to improve the adsorption performance ofβ-CDMOF@CA heavy metal ions.5.After 5 times of adsorption-desorption cycles,the adsorption properties of the three adsorbents for the four metal ions remained stable,especially the cyclic adsorption ofβ-CDMOF@CA（1:3）is the most prominent,indicating that the prepared adsorbents show good cyclic adsorption of heavy metal ions,and can realize the rapid reuse of adsorbents.6.Within a certain pH range,the adsorption removal rates of heavy metal ions Sb³⁺,Pb²⁺,Cd²⁺,Co³⁺,Fe^（2+,3+）and Hg²⁺in the real water of printing and dyeing wastewater increased with the increase of the pH value of the wastewater.The adsorption effect was the best when pH=6,which was consistent with the adsorption results of simulated metal ion solution.With the increase of the amount of adsorbent,the adsorption performance of adsorbent is also improved.After five times of adsorption-desorption cycles,the adsorbents still maintained good adsorption properties for the above six metal ions.The above results show that theβ-CDMOF@CA adsorbent synthesized in this paper has good adsorption performance for heavy metal ions in printing and dyeing wastewater,and has a good application prospect in the treatment of heavy metal ions in printing and dyeing wastewater.