Abstract:
Both inorganic and organic pollutants in water result in damages on the ecosystem due to their toxicity and consumption of dissolved oxygen in the water. Adsorption separation has been regarded as one of the most widely used wastewater treatment methods because of its easy operation, low cost and recyclability. Cyclodextrin (CD) is a commonly used adsorbent material because of its ability for encapsulating of hydrophobic molecules, but its water solubility and low adsorption capacity limit its applications. Here, three different diisocyanates (hexamethylene diisocyanate HDI、1,4-phenylene diisocyanate PDI、diphenyl-methane-diisocyanate MDI) were selected as cross-linking agents to synthesize three CD-polyurethane composites (CD-HDI,CD-PDI,CD-MDI) with different structures. SEM, FT-IR, TG and UV-vis spectroscopy were employed to characterize the synthesized composites. The adsorption kinetic mechanism was studied by using pseudo-first-order model and pseudo-second-order model. The results showed that the pseudo-second-order model fitted better than the pseudo-first-order model, indicating that the adsorptions of the adsorbent against BPA and MB are chemisorption process. To study the adsorption mechanisms of CD-HDI, CD-PDI, CD-MDI toward different pollutants, three different models were applied to fit the equilibrium adsorption data. The results indicated that Sips model described the adsorption performances for BPA and MB very well, and the maximum adsorption capacity of CD-HDI, CD-PDI, CD-MDI was 65.3, 106, 116 mg/g for BPA and 8.90, 26.5, 18.0 mg/g for MB, respectively. The removal efficiency of BPA and MB by the adsorbent decreased by 0.80%—2.40% for BPA and 7.64%—13.4% for MB after 5 cycles, respectively, indicating the good recyclability of the adsorbent.