Preparation Of Salicylhydroxamic Acid Type Surface-imprinted Materials And Research On Its Recognition Property

In this study, Lead ions and quercetin molecules surface-imprinted materials wereprepared by the novel ion (molecule) surface imprinting technique. The binding selectivityproperty of the surface imprinting materials for their target ions (molecules) were studied byadopting both static and dynamic methods. The surface imprinting materials obtained werecharacterized by strong chelating and multiple hydrogen bonding sites of hydroxamic acidgroup, high mechanical strength and good thermal stability of silica gel particles and the finebinding affinity and obvious recognition selectivity of surface imprinting material, so theycould be used in separation and recovery of toxic lead ions and the separation and purificationof quercetin, which would have great significance in the governance of the waterenvironment and the extraction of flavonoids drugs.First, silica gel particles were surface-modified by γ-aminopropyltrimethoxysilane(AMPS) to obtain the modified particles AMPS-SiO2. After that the grafted particlesPHEMA/SiO2was prepared by virtue of the surface-initiated graft-polymerization of2-hydroethyl methacrylate (PHEMA) on silica gel particlesan with and the persulfate as theinitiator. Then salicylhydroxamic acid (SHA) was chloromethylated with1-4-bis(hloromethoxy) butane (BCMB) as chloromethylation reagent, and5-chloromethyl-salicylhydroxamic acid (CMSHA) was obtained. Subsequently, salicylhydroxamic acid(SHA)-functionalized composite chelating adsorbing material SHA-PHEMA/SiO2wasprepared via the nucleophilic substitution reaction of CMSHA with PHEMA/SiO2in thepresence of deacid reagent. The chemical structures of SHA-PHEMA/SiO2and PHEMA/SiO2were characterized by the infrared spectrum. The effects of main factors, such as theconcentration of alcoholic hydroxyl groups in PHEMA/SiO2, reaction temperature andsolvent polarity on the nucleophilic substitution reaction were examined, and the reaction mechanism was discussed. Experimental results show that the reaction has a reactionmechanism of SN1between the alcoholic hydroxyl groups of grafted particles PHEMA/SiO2and the chloromethyl of CMSHA, and the higher reaction temperature and the solvent withstronger polarity are helpful to the reaction. SHA can be bonded onto the grafted particlesPHEMA/SiO2successfully with a bonding rate of31.4%.The chelating adsorption ability of SHA-PHEMA/SiO2for lead ions was examined. Theexperimental results show that SHA-PHEMA/SiO2possesses a very strong chelatingadsorption property for Pb2+ions and the adsorption capacity of it for Pb2+ions at35℃reaches57.2mg/g. The adsorption process of SHA-PHEMA/SiO2for Pb2+ions can bedescribed better by pseudo-second-order kinetics model. The adsorption behavior of it forPb2+ions follows Langmuir isothermal and is a monomolecular adsorption. The pH value ofthe medium has a great effect on the chelating adsorption ability of SHA-PHEMA/SiO2, andthe optimum pH value is5.5~6. The adsorption capacity of SHA-PHEMA/SiO2for Pb2+ionsincreases with the raising temperature, and is a chemical adsorption process driven byentropy.Then the lead ion imprinting was conducted with Pb2+ion as the template ion andethylene glycol diglycidyl ether (EGDE) as crosslinker via the ion surface imprintingtechnique, and the lead ion surface-imprinted material Pb2+-IIP-SHA-PHEMA/SiO2（shortened to Pb2+-IIP-SHA/SiO2）was obtained through the ring-opening reaction. Thebinding selectivity property of Pb2+-IIP-SHA/SiO2for Pb2+ions were studied by means ofboth static and dynamic methods with Cu2+and Cd2+ions as contrast ions. The experimentresults show that Pb2+-IIP-SHA/SiO2has a fine binding affinity and an obvious recognitionselectivity for Pb2+ions. The adsorption capacity of Pb2+-IIP-SHA/SiO2for Pb2+ions at40℃reaches62.7mg/g. The selectivity coefficients of Pb2+ion over Cu2+ion and Cd2+ion are4.3/0.57and5.3/1.18, respectively. Moreover, the crosslinking reaction conditions have agreater impact on the selectivity coefficient of Pb2+-IIP-SHA/SiO2for Pb2+ions.Pb2+-IIP-SHA/SiO2with fine recognition and selectivity properties can be obtained whenn(SHA)：n(EGDE) is1:0.5, the crosslinking reaction temperature is45℃, and the reaction time is10h. Lead ions adsorpted by Pb2+-IIP-SHA/SiO2can be removed with a dilutedaqueous solution of HCl (pH=1) as the eluent. The percentage of Pb2+ions removed fromPb2+-IIP-SHA/SiO2after13bed volumes was99.42%. Besides, the adsorption capacity isalmost the same after9times consecutive adsorption-desorption experiments ofPb2+-IIP-SHA/SiO2for Pb2+ions, indicating that Pb2+-IIP-SHA/SiO2has an excellentreusability.Finally, the quercetin molecule surface-imprinted material Qu-MIP-SHA-PHEMA/SiO2(shortened to Qu-MIP-SHA/SiO2) was prepared using quercetin as the template molecule andEGDE as the crosslinker. The binding selectivity property of Qu-MIP-SHA/SiO2towardsquercetin were also studied via both static and dynamic methods with genistein as contrastmolecule. The experiment results show that Qu-MIP-SHA/SiO2has a fine binding affinityand an obvious recognition selectivity for the quercetin molecule. The adsorption capacity ofQu-MIP-SHA/SiO2for quercetin at25℃reaches0.37mmol/g. The selectivity coefficients ofQu-MIP-SHA/SiO2and SHA-PHEMA/SiO2for the quercetin over genistein are4.54and1.1,respectively. Qu-MIP-SHA/SiO2has a good desorption performance and the percentage ofquercetin removed from Qu-MIP-SHA/SiO2after22bed volumes was96.8%. The adsorptioncapacity is almost the same after9times consecutive adsorption-desorption experiments ofQu-MIP-SHA/SiO2for quercetin, indicating that Qu-MIP-SHA/SiO2has excellentregeneration and reusability.