Studies On Recognition And Separation Of Chromate Anions By Constituting Tailored Caves With Novel Surface-Ion Imprinting Technique

The water contamination caused by heavy metals is a serious environmentalproblem because of their toxicity to many life forms. Among various heavy metals,chromium, especially chromate（Cr（Ⅵ））, is highly toxic and has a powerful carcinogeniceffect. In this paper, vinylimidazole （VI） was grafted on micron-sized silica gel particlesin a manner of“grafting from”in a solution polymerization system by right of themediation of the coupling agentγ-methacryloxypropyl trimethoxysilane （MPS）,resulting in the chromate anions adsorption particles PVI/SiO₂. The adsorptionbehaviours of PVI/SiO₂towards the chromate anions were examined and the preparationof surface imprinting materials, which was performed with chromate anions as templateion, was done. Then, both static and dynamic methods were adopted to study therecognition property for chromate anions and the separation ability towards chromateand phosphate anions in the hybrid aqueous solution. This adsorbent excogitated in thispaper showed high selection affinity and high adsorption capacity towards the chromateanions, and would have great significance and good application prospect in the Cr（Ⅵ）remove and recycling from aqueous solution.Firstly, Micron-sized silicon particles were chemically surface-modified withcoupling agent KH570, and bonding particles MPS/SiO₂were obtained. The graftpolymerization of vinylimidazole （VI） on the surfaces of particles MPS/SiO₂wasperformed in the solution polymerization system. The grafting particles werecharacterized with FTIR, TGA and SEM methods. The effects of the main factors on thegraft polymerization of VI were examined. The experimental results showed that in the graft polymerization process, the best reaction conditions are as follows: Time=8h, T=70℃, the used amount of initiator=1.4%, Monomer concentration=16.7%. The graftingdegree of PVI can get up to 21.51g/100g under the best reaction conditions.Subsequently, the behaviours of the graft particles PVI/SiO₂against the chromateanions were examined, the adsorption mechanism was mainly studied in this reserach.The experimental results showed that the tertiary amine groups has strong adsorptionability for the chromate anions by right of the electronic interaction, the adsorptioncapacity can get up to 120 mg/g at 25℃. With the pH values increased, absorptioncapacity would decrease. Because the adsorption process is phisical adsorption, raisingtemperature would weaken the adsorption process and decrease the adsorption capacity.Salinity has the shielding effect between the graft particles PVI/SiO₂and adsorbate, assalinity increased, the adsorption capacity decreased. Finally, adsorption capacityincreases with the degree of the grafting degree increased.Finally, the ion imprinting was carried out towards the grafted PVI grafted on thesurface of the silica gel particles with the chromate anions as template ion and1,6-dibromohexane as crosslinking agent, using the novel surface-molecular imprintingtechnique established by our research group. Then obtained the chromate ion-imprintedmaterial IIP-PVI/SiO₂. With the contrast compound phosphate anions, both static anddynamic methods were adopted to study the recognition property for chromate anionsand the separation ability towards in the hybrid aqueous solution. The experiment resultsshowed that IIP-PVI/SiO₂have obvious recognition selectivity and fine binding affinityfor chromate anions, and the selectivity coefficient is equal to 7.78 with respect to thephosphate anions. Besides, IIP-PVI/SiO₂has excellent elution property, with 0.1 MNa2CO3and 1 M NaCl as the mix eluent, the desorption ratios of chromate anions reach97.4 % in 11 BV. The conditions of crosslinking all affected the selectivity coefficient.The optimal preparation conditions of imprinted polymers for chromate anions isdetermined: Time=6h, T=55℃, pH value is 4.0 and the ratio of amount of crossing agentand amount of VI is 1:3.