Synthesis And Properties Of Cu²⁺ Ion-imprinted Magnetic Chitosan Beads For Selective Recognition Of Cu²⁺ Ion In Aqueous Solution

Heavy metal ions in wastewater is one of the most pressing environmental problems. It is difficult to deintegrate, serious damage to the ecological environment and the healthy on human, so removal heavy metal ions from wastewater needs much more attention. Copper and its compounds are common pollutant of wastewater. The potential sources of copper from industrial effluents include mineral processing, metal fabrication, mechanical manufacturing. Although copper is one of the essential elements for human body, excessive intake of copper can causes abdominal pain, vomiting and cirrhosis. Moreover, the separation and purification of copper in wastewater needs much more attention. The Cu2+ ion-imprinted magnetic chitosan (IIMPs) were prepared by crosslinking-imprinting-recrosslinking reaction of the multi-step required, using chitosan as functional monomer, Cu2+ as template ions, epichlorohydrin and glutaraldehyde as cross-linker. The IIMPs can be used for the selective removal of Cu2+ ions from wastewater.The influencing recation condition synthesis of Cu2+ ion imprinted magnetic chitosan (IIMPs) were optimzed by single factor analysis in order to its best adsorption capacity. The results showed that the aptimum prepared conditions were chitosan-acetic acid concentration of 2%, the dosage of Fe3O4 of 0.1 g/g chitosan, the dosage of ECH of 0.5 mL/gchitosan, the dosage of imprinted ions of n(Cu2-):n(-NH2)=0.3 at 25℃ for 8 h, the dosage of crosslinker of 0.4 mL/chitosan at 60℃ for 2 h.The structure and properties of Cu2+ ion imprinted magnetic chitosan beads were analyzed by SEM, TEM, BET, VSM, FTIR and XRD, the results showed that the Cu2+ ion imprinted magnetic chitosan beads have a 3-dimension network structure with the specific surface area of 13.3 m2·g-1, aperture bore diameter of 4.737 nm. The composition of Fe3O4 were distributed evenly and no agglomeration. The magnetic properties were measured by vibrating sample magnetometer and the saturation magnetization of 10.8 emu·g-1.The adsorption performance of Cu2+ ion on IIMPs was studyed by static adsorption method, which including the influence of pH, adsorption kinetic, adsorption isotherm and adsorption thermodynamics.The results are the optimum adsorption pH value of 5. The adsorption relatively fast and the time required to reach equilibrium conditons was about 2 h. The kinetic study showed that the adsorption process followed the pseudo-second-order kinetic equations. The adsorption isotherm study indicated that the Langmuir isotherm equation was best fitted for the monolayer adsorption processes. The adsorption processes was a chemical one with single molecular layer as main characteristics. Adsorption thermodynamics study showed that the adsorption is spontaneous endothermic process. The IIMPs can be regenerated and reused for 10 times without a significantly decreasing in adsorption capacity.Selective adsorption of IIMPs were performed in Cu2+/Zn2+, Cu2+/Ni2+, and Cu2+/Co2+ binary systems. The results showed the IIMPs have a high selectivity toward Cu2+ion in the binary systems. The selection recognition ability of IIMPs were evaluated by the relative selectivity coefficient (K’) in an multi-solution. The results showed that the relative selectivity coefficient (K’) of IIMPs for Cu2+/Zn2+, Cu2+/Ni2+and Cu2+/Co2+of Cu2+ were 2.07、2.59 and 3.44. The order of selectivity adsorption capacity of heavy metals in solution on IIMPs in turn was Cu2+>Zn2+> Ni2+> Co2+.Thermodynamic study on selectivity recognition process using ⅡMPs was investigated by static adsorption method. Changes of entropy, enthalpy and Gibbs free energy in the process of selectivity recognition were analyzed. The results showed that the entropy play an important role in the selectivity recognition process. Further, studies showed that the selectivity recognition of Cu2+ mainly depended on how well, the geometric cavity structures of ⅡMPs, suited the structure of the Cu2+. The adsorption of Cu2+ on ⅡMPs were characterized by FTIR and XPS, the results indicated that the amine groups in the hole structure on ⅡMPs play a major role in the recognition process.The adsorption experiments of ⅡMPs were studied in the wastewater of a precious metal and chemical industry. The results indicated that the Cu2+ removal rate reached 86.96%, and the adsorption rate of Zn2+ was lower, which can get the selective separation of Cu2+ and Zn2+ in wastewater.