Preparation Of EDTA-modified Cyclodextrin-polyurethane Materials And Its Adsorption Performance

In recent years, combined pollution has been an increasingly concern in the environmental field. Heavy metal ions, pesticides, antibiotics and water disinfection by-products etc., exist in aquatic environment, and they commonly present at low concentrations. These mixed pollutants are generally of higher accumulation, toxicity and endocrine disrupting effect. They may influence each other and raise a potential risk to ecological systems and human health. A multitude of wastewater treatment methods including conventional treatment processes do not completely remove these pollutants, because of the occurrence of environmental matrix effects. Cyclodextrins (CDs), representatives of macromolecules, possess a characteristic of "flask" effect and can enrich trace hydrophobic pollutants in waters. However, they lack active sites to bind inorganics such as heavy metals. Here, a ligand-like cyclodextrin adsorben was developed to simultaneously remove heavy metals and PAHs.To this end, a novel EDTA-modified cyclodextrin-polyurethane material was self-synthesized, and its adsorption performance toward heavy metal ions and polycyclic aromatic hydrocarbons was investigated. The results are as follows:(1) Based on the theory of nucleophilic substitution reactions, two reactive intermediates, mono-6-OTs-β-CD and mono-6-en-β-CD, were prepared by the replacement of the specific hydroxyl of β-CD with p-toluenesulfonate and ethanediamine, respectively. Then an EDTA-substituted cyclodextrin derivative (mono-6-EDTA-en-β-CD) was achieved by the amidation of EDTA, and the yield was54%. An EDTA-modified cyclodextrin-polyurethane material (EDTA-appended-(3-CDPU) was obtained by polymerization with six-methylene diisocyanate as a crosslinking agent. The material was amorphous particle, with high mechanical strength and better sedimentation-separation.(2) The adsorption behavior of EDTA-appended-β-CDPU for five heavy metal ions Cu(Ⅱ), Pb(Ⅱ), Ni(Ⅱ), Cd(Ⅱ) and Zn(Ⅱ) were studied using batch adsorption experiments.. The results showed that the adsorption isotherms of heavy metal ions fitted Langmuir adsorption isotherm model welll. With respect to the heavy metals, the maximum adsorption capacities were2.544,2.482,1.250,0.558,0.746mg/g, and adsorption constants were2.200,1.140,0.309,0.610,0.692L/mg, respectively. Adsorption dynamics of heavy metal ions followed a pseudo-second-order model, and chemical adsorption process was a rate determining step. The FTIR measurements demonstrated that-COO and-NH-in materials were active groups, suggesting that ion exchange and coordination interaction be predominantly adsorption forces.(3) The adsorption of polycyclic aromatic hydrocarbons (PAHs) onto EDTA-appended-β-CDPU was investigated in the absence or presence of cupric ion. Adsorption distribution constant Kd of PAHs varied from0.82L/g to5.71L/g in the absence of Cu(Ⅱ). The adsorption distribution constants and adsorption capacities of PAHs was markedly enhanced in the presence of Cu(II). Comparisons of adsorption constants obtained from different batch adsorption experiments showed that adsorption sites of heavy metal ions and PAHs were not overlapped, in accordance with the FTIR measuremtns of adsorbents with Cu (Ⅱ), PAHs and both. The material can adsorb both copper ion and PAHs, showing the occurrence of synergism adsorption between them.