Study On The Preparation Of Ni(Ⅱ), Pb(Ⅱ) And Hg(Ⅱ) Ion Imprinted Polymers And Their Application In Selective Removal From Waste Water

Heavy metals contamination has attracted extensive attention due to its persistent and highly toxic ability to environment and bioaccumulate. Conventional adsorbents, which are not eco-friendly, hold disadvantages of resource waste, poor selectivities for heavy metals, and would make pollutant transfer, leaving potentially hazardous residues. To solve these defects, ion-imprinting polymer provides a versatile and powerful method of remarkable recognition for template ions. In this study, we have prepared novel ion-imprinted polymers for potential utilization in removal of Ni（Ⅱ）, Pb（Ⅱ） and Hg（Ⅱ） in wastewater, which produced favourable selectivity, excellent reusability, high stability and rebinding ability towards heavy metals, and analyse adsorption mechanism. The details are summarized as follows:1. Ni（Ⅱ）-ⅡP was synthesized for the selective removal of Ni（Ⅱ） from aqueous samples, by precipitation polymerization, using 1-vinyl imidazole as functional monomer and Ni（Ⅱ） as template ions. SEM shows that Ni（Ⅱ）-ⅡP is lamellar structure. BET curve belonges to a distinct hysteresis H3-type loop, which is consist with SEM. The optimum pH for adsorption occurrs at pH 6-7. The maximum adsorption capacity of Ni（Ⅱ）-ⅡP and Ni（Ⅱ）-NIP is 39.16 and 13.28 mg/g, respectively. The adsorption process fits well with the Langmuir adsorption isotherm, which indicates the active adsorption sites of Ni（Ⅱ）-ⅡP are effectively homogeneous, leading to a monolayer binding. Kinetics studies show that the adsorption approaches equilibrium approximately 6 min, the initial adsorption rate is 65.317 mg·g-1·min-1 and the process obeys a pseudo-second-order kinetic model. The linker ratio of Ni（Ⅱ）/1-vinyl imidazole can be figured out to be about 1:4 by XPS and EDS. The Ni（Ⅱ）-ⅡP has an excellent selectivity for Ni（Ⅱ） with the selectivity coefficients with respect to Ni（Ⅱ）, Pb（Ⅱ）, Cu（Ⅱ）, Co（Ⅱ） and Cd（Ⅱ） are 633, 41, 23, 45 and 34, respectively. There is no significant decrease（11.2%） in rebinding capacity up to the 5th desorption-regeneration cycles, demonstrating that the Ni（Ⅱ）-ⅡP is stable and reusable.2. Pb（Ⅱ）-ⅡP, which is observed of about 177 nm without obvious reunion, is synthesed for the selective removal of Pb（Ⅱ） from samples through a precipitation polymerization method using 2-（Allylthio）nicotinic acid（ANA） as a thio-functionalized monomer, which can synergistically coordinate with Pb（Ⅱ） and have a double bond for further polymerization to avoid additional grafts. The adsorption kinetics of Pb（Ⅱ）-ⅡP featured a particularly rapid initial step to approached equilibrium within 16 min, and the experimental datas fit well with the pseudo-second-order kinetic model. The saturation adsorption capacity（29.67 mg/g） is two times lager than Pb（Ⅱ）-NIP, and the adsorption process obeys the Langmuir isotherm model. The Pb（Ⅱ）/ANA linker ratio in Pb（Ⅱ）-ⅡP can be figured out to be approximately 1:2 by XPS and EDS. Pb（Ⅱ）-ⅡP exhibited favourable selectivity and prominent effectiveness towards Pb（Ⅱ） in the presence of co-existing ions. The practical application shows that Pb（Ⅱ）-ⅡP can effectively remove Pb（Ⅱ） from industrial wastewater with a removal rate for Pb（Ⅱ） of more than 97.2% to well below the state standards for wastewater discharge, which indicates it is a great potential adsorbent in selectively removing Pb（Ⅱ） from industrial wastewater.3. A novel magnetic ion-imprinted polymer（MⅡP） with incorporated Fe₃O₄@SiO₂ nanoparticles was synthesized via a surface imprinting technique using allylthiourea（ATU） as a functional monomer. The MⅡP has an excellent saturation magnetization of 15.9403 emu/g. The adsorption of MⅡP for Hg（Ⅱ）（78.3 mg/g） was approximately twice that of magnetic non-ion-imprinted polymer（39.5 mg/g）. The adsorption indicated that the adsorption mechanism closely agreed with a pseudo-second-order adsorption process, with a correlation coefficient R2 of 0.998. Adsorption energy（E） calulated by D-R isotherm model is about 10.2 kJ mol-1, which could be attributed to the soft acid-soft base interaction of Hg（Ⅱ） and allylthiourea. The relative selectivity coefficients of MⅡP for Hg（Ⅱ）/Ni（Ⅱ）, Hg（Ⅱ）/Cu（Ⅱ）, Hg（Ⅱ）/Co（Ⅱ） and Hg（Ⅱ）/Cd（Ⅱ） were 556, 334, 556 and 155, respectively. The recovery in rebinding capacity for Hg（Ⅱ） was found to be decreased by only approximately 10.4% up to 6th cycle, which suggests an excellent stability of MⅡP. The application of MⅡP in real samples shows a removal efficiency for Hg（Ⅱ） of more than 99% to well below U.S. EPA mercury limits for wastewater, indicating that the MⅡP is an effective adsorbent for Hg（Ⅱ） removal in environmental water samples.