The Preparation Of Cucurbit[6]uril Immobilized Resin And Its Application In Water Treatment

Cucurbit[n]uril (CB [n], n=4~12) was a new macrocyclic compounds. It was synthesizedafter the Cyclodextrins, Cryptand, Crown ether and Calixarene in supermolecular chemistry.It composed by a rigid hydrophobic cavity and two hydrophilic ports. The ports were coveredwith carbonyl oxygen atoms. Rigid hydrophobic cavity could selective catch the part ofhydrophobic molecules whose size was match to CB homologue size purposefully. And thetwo electronegative ports could combine with some organic molecules and metal ions throughthe hydrogen bonding interaction and ion-dipole function, forminghost-guest inclusion complex. This special structure resulted in CB[n] having a broadapplication prospect in molecular recognition, supramolecular catalysis, molecular assembly,sewage treatment and other fields.In the1990s, researchers began to use CB[n] in sewage treatment technology, andcarried out some research work. After the pollutants adsorbed on CB[n], we can use themethods such as ozone oxidative CB[n] to realize regeneration. But as the study continues,the defect of CB[n] also exposed. The solubility of CB[n] is very low in water, but in aqueoussolution of acidic solution (such as formic acid, hydrochloric acid, sulfuric acid, etc.) andalkali metal ion, alkaline-earth metals, the solubility of CB[n] is far bigger than in water. Inaddition, the solubility increased with the increase of solution acidity and the concentration ofmetal ions. The characteristics of solubility lead to CB[n] as a new type of functional materialusing in wastewater treatment efficiency is not good, and it can bring secondary pollution.Therefore, it is necessary to immobilize CB[n] on carrier materials, in order to avoid CB[n]homologue dissolution.In this paper, through hydroxyl derivatization, we got the hydroxyCB[6]. In polarorganic solvent--DMF, we used NaH as protons accept agent, chloromethylated polystyrenebeads as the carrier, by the nucleophilic substitution reaction mechanism between chlorinemethyl groups and hydroxyl, the CB[6] immobilized resin was produced. And the productwas characterized by means of IR, NMR, SEM and Zeta potential. The results showed that theimmobilized method was feasible. The optimum reaction conditions of producting CB[6] wasdetermined by the N element analysis. The best reaction ratio of hydroxy CB[6] andchloromethylated polystyrene beads was0.5:1. Under such circumstances, the bonding site onthe surface of the carrier reached saturation. The most appropriate reaction temperature was60℃, and in higher temperature, fixing amount of CB[6] didn’t increase obviously andchloromethylated polystyrene beads was more likely to be broken. The best reaction time wasabout46h. Next, CB[6] immobilized resin adsorption experiment of SMM was did. The resultshowed that CB[6] immobilized resin had a good adsorption effect on SMM. The pseudofirst-order and pseudo second-order kinetic model were used to fit the kinetics process ofSMM adsorption on CB[6] immobilized resin. Adsorption kinetics experiments showed thatthe adsorption of SMM could be best described by the pseudo second-order equation. Theintra-particle diffusion model was used to further analyze the diffusion mechanism of methylorange. The result implied that intra-particle diffusion was not the only rate-limiting step.What’s more, pH had a great influence on the adsorption of SMM. In weakly acidic (pH=6~7) conditions, the adsorption of SMM on CB[6] immobilized resin had the best effect. Whilewith the increase of pH of the solution, the Zeta potential of cucurbiturils immobilized resinwas reduced, the electrostatic attraction weakened, leading to adsorption was reduced slightly.When pH <6, SMM and CB[6] immobilized resin with the opposite charge, resulting inelectrostatic repulsion adsorption was inhibited. The addition of electrolytes would hinderedthe adsorption of SMM, and the negative effect of bivalent cation was larger than monovalentcations’. This was because electrolytes could compress double electric layer on the surface ofCB[6], and make it thinner. At the same time, carbonyl oxygen atoms was surrounded bymetal cation, it weakened the electrostatic force between the adsorption point and SMMmolecules. The adsorption capacity of CB[6] immobilized resin decreased with the increaseof concentration of the metal cation. Adsorption isotherms research showed that Henryadsorption isotherms model is better fitting adsorption process. And adsorptionthermodynamic experimental results showed that the adsorption process of SMM on CB[6]immobilized resin was an exothermic process. Gibbs equation calculation results showed thatthe adsorption entropy change <0, adsorption heat <40kJ/mol. was mainly physicaladsorption, and the adsorption process was based on electrostatic adsorption supplemented,hydrophobic effect the result of joint action.The regeneration of CB[6] immobilized resin after SMM saturated adsorption by HClwas studied. The results proved that using hydrochloric acid solution as the desorptionsolution to achieve regeneration CB[6] immobilized resin was feasible. Desorption with1mol/L HCl solution three times later, CB[6] immobilized resin regeneration remained high as89.5%.