Study On Selectivity And Anti-Interference Performance Of Palladium And Lithium Ion-Imprinted Polymers

This paper selects new type of metal pollutants with Li(I)and Pd(Ⅱ)in industrial wastewater as the research object,functional monomers were prepared through bringing a unsaturated double bond to a strong chelating ligands,the monomers can rapidly and selectively adsorb target metal ion,which obtain a material with good selectivity.Moreover,in order to come true the property of anti-interference and anti-block in industrial wastewater to the imprinted material,the adsorbents with surface grafting polymer brushes were synthesized by further RAFT-surface grafting polymerization.The main content includes:1.In order to obtain the strong selective functional monomers to Li(I)and Pd(Ⅱ),two new functional monomers were prepared by bringing a double bond to ligand to improve the selective adsorption ability of Li(I)and Pd(Ⅱ).At the temperature of50℃ with continuous stirring,3-Allyl-2-hydroxybenzaldehyde thiosemicarbazone(AHTB)was prepared through schiff based reaction with thiosemicarbazide and3-Allylsalicylaldehyde as the reactants;2-(allyloxy)methyl-12-crown-4 also was synthesized by through nucleophilic substitution reaction step between allyl bromide and 2-(Hydroxymethyl)-12-crown 4-Ether.Two functional monomers have been successfully synthesized by some characterization methods of nuclear magnetic resonance(NMR),infrared spectra(FT-IR),element analysis.2.Palladium ion-imprinted polymer was prepared through the bulkpolymerization by Pd(Ⅱ)as template ion,AHTB as functional monomer,EGDMA as crosslinking agents.Which were analyzed by SEM,specific surface area,TGA,element analysis.The new imprinted polymer posses rough surface,high stability with decomposition temperature(280℃)and the size of particles is 200 nm in diameter.The functional monomer was fixed in the polymer.Additionally,the specific surface area of imprinted material reached 26.24 m2 g-1,which is obvious higher than the non-imprinted material(13.19 m2 g-1).The new imprinted polymers posses high adsorption capacity(59.39 mg g-1 in pH 3.0)and high stability with six recycles nearly 90%,affording selective capture and rapid identification with the selectivity coefficient higher than 5.Adsorption behavior was fully discussed with corresponding kinetic,isotherm models and thermodynamic parameters,indicating that adsorption is endothermic and chemistry adsorption is the main adsorption behavior.Furthermore,the coordination mechanism of the AHTB to Pd(Ⅱ)was investigated based on FT-IR and XPS,chelating with third amines(-N=)and S atoms to Pd(Ⅱ)rather than electrostatic interaction should be mainly attributed to strong adsorption manner.3.Four kinds of different sizes of imprinted microspheres were synthesized by changing the initiator(AIBN)dosage through reversible addition fragmentation chain transfer(RAFT)precipitation polymerization method with Li(I)as template,2-(allyloxy)methyl-12-crown(2AM12C4)as functional monomer,EGDMA as crosslinking agents,2-phenylpropan-2-yl benzodithioate(CDB)as a chain transfer agent,95% methanol and water as the solvent.After polymerization,furtherRAFT-surface grafted poly 2-hydroxyethyl methacrylate(PHEMA)polymer brushes.Disperse microspheres can be observed using SEM.Compare the ungrafted ⅡPs,grafted ⅡPs beyond better dispersion in water,higher kinetic rate constants,which speed up the ability that Li(I)enters the imprinted cavity.Based on the analysis of GPC,specific surface area and mass gain of grafting,it can be proved that the different grafting densities of lithium ion-imprinted polymer have been prepared.Their grafting densities of the microspheres were 1.43,1.31,1.17 and 1.06 chains nm-2 for the grafted ⅡP1,grafted ⅡP2,grafted ⅡP3 and grafted ⅡP4,respectively.The molecular weight of PHEMA molecular brushes was 20 thousand.According to varieties of model fitting,indicating that the imprinted material is a single layer of chemical adsorption;thermodynamic studies show that adsorption of Li(I)is an endothermic process.The adsorption experiments were executed in model wastewater,which shows that the grafted polymer brushes have good anti-interference ability,and the suitable grafting density has a greater anti-interference intensity.SEM-EDS and XPS data revealed anti-interference and anti-blockage mechanisms in which hydrophilic PHEMA brushes could effectively adhere to fine particles and flocculants through Van der Waals force interactions,which make the imprinted cavities well protected in a complex wastewater environment.