Astudy On The Preparation And Application Of Imido-Acetic Acid-type Composite Chelating Adsorption Material IAA-PEI/SiO₂ Based On PEI

Chelating adsorption material is a kind of solid （particulate） material, on which surface chelating functional groups were bonded. It was applied extensively in many science and technology field, such as environment protection, reclaiming and reusing metal resource, bioseparation, and catalyzer science. Chelating functional groups include imido-acetic acid-type, Schiff base type, salicylic acid type, 8-hydroxyquinoline type, and amidoxime type. Among these chelating functional groups, imido-acetic acid-type possesses strong chelating interaction towards heavy metal ions, noble metal ions, and rare earth ions. So, imido-acetic acid-type chelating material has important application in analyzing and testing metal ions, removing heavy metal ions, enriching and distilling noble metal ions and rare earth ions, separating and purifying protein, and catalytic oxidation of metal complex compound. Apparently, it has important scientific value to develop imido-acetic acid-type chelating material.With elaborate molecular design, imido-acetic acid-type chelating material IAA-PEI/SiO₂ was prepared via coupling grafting and macromolecular reaction. The structure and morphology of Imido-Acetic Acid-type Composite Chelating Adsorption Material IAA-PEI/SiO₂ were characterized by means of various of methods, including FTIR, SEM, TGA, Chemical analysis, and so on. The influence of main factor on preparation process was studied and reaction mechanism was discussed. The adsorption abilities and mechanism of IAA-PEI/SiO₂ towards heavy metal ions and rare earth ions were studied, and the adsorption thermodynamics was discussed. Immobilized imido-acetic acid-Cu（Ⅱ） complex compound catalyzer was obtained through the coordination reaction between IAA-PEI/SiO₂ and Cu（Ⅱ）. This immobilized complex compound was used in the oxidation reaction of ethylbenzene and benzyl alcohol by molecular oxygen, and the catalytic oxidation mechanism was investigated. IAA-PEI/SiO₂ possesses not only strong chelating ability of imido-acetic acid-type chelating material, but also excellent properties of silica gel, such as higher mechanical intensity, and excellent thermal and chemical stability. The preparation of this high-powered composite chelating material has distinct science signification. It could be anticipated that this chelating material will has important applied value.Firstly, polyamine polyethyleneimine （PEI） was grafted onto micron-sized silica gel particles withγ-chloropropyltrimethoxysilane as intermedium, forming the grafted particles PEI/SiO₂. Then the nucleophilic substitution reaction between chloroactic acid and the amino groups of PEI/SiO₂ was performed, resulting in the bonding of imido-acetic acid （IAA） groups onto grafted particles PEI/SiO₂ and obtaining the composite chelating particles IAA-PEI/SiO₂ with polydentate ligand. The influence of main factor on nucleophilic substitution reaction was studied, reaction mechanism was discussed, and reaction condition was optimized. The experimental results show that the nucleophilic substitution reaction between chloroactic acid （CAA） and the amino groups of PEI/SiO₂ has a reaction mechanism of S_N2. The fitting temperature is 60℃, and the appropriate amount of acid acceptor NaHCO₃ is equal to CAA. Under fitting reaction condition, the prepared IAA-PEI/SiO₂ has a bonding ratio of 72%.Subsequently, the chelating adsorption ability of IAA-PEI/SiO₂ towards heavy metal ions was examined, and the adsorption mechanism and thermodynamics were investigated in depth. The experimental results showed that the composite chelating material IAA-PEI/SiO₂ possesses strong adsorption ability towards heavy metal ions by right of the synergism of electrostatic interaction and coordination chelating action between imido-acetic acid groups and heavy metal ions. Especially, IAA-PEI/SiO₂ possesses very strong adsorption ability towards Ni2+, and the adsorption capacity could reach 10g/100g（0.59mol/100g）. The adsorption ability order of IAA-PEI/SiO₂ for heavy metal ions is Ni²⁺>Pb²⁺>Cu²⁺>Cd²⁺. The adsorption process of IAA-PEI/SiO₂ towards heavy metal ions is exothermic, and the adsorption capacity decreases with raising temperature. The adsorption is a process driven by enthalpy. In the pH range, in which the hydrolysis of the heavy metal ions can be inhibited, the chelating adsorption ability of IAA-PEI/SiO₂ increases with increasing pH value.The chelating adsorption ability of IAA-PEI/SiO₂ towards rare earth ions was also examined, and the adsorption mechanism and thermodynamics were investigated in depth. The experimental results showed that the composite chelating material IAA-PEI/SiO₂ possesses strong adsorption ability towards rare earth ions by right of the synergism of electrostatic interaction and coordination chelating action between imido-acetic acid groups and rare earth ions. The main force is ionic coordination bond between imido-acetic acid-type chelating groups and rare earth ions, and the stability of this interaction is weaker. So, the adsorption capacity of IAA-PEI/SiO₂ towards rare earth ions is lower than that of IAA-PEI/SiO₂ towards heavy metal ions.. IAA-PEI/SiO₂ possesses similar adsorption ability towards Nd³⁺, Ce³⁺, and Eu³⁺ because of the very similar physical and chemical properties, and the adsorption capacity could reach 0.11mol/100g. The adsorption process of IAA-PEI/SiO₂ towards rare earth ions is endothermic, and the adsorption capacity increases with raising temperature. The adsorption is a process driven by entropy. In the pH range, in which the hydrolysis of the rare earth ions can be inhibited, the chelating adsorption ability of IAA-PEI/SiO₂ increases with increasing pH value.Finally, the immobilized imido-acetic acid-Cu（Ⅱ） complex compound Cu（Ⅱ）-IAA- PEI/SiO₂ was obtained via the coordination reaction between IAA-PEI/SiO₂ and Cu（Ⅱ）. This immobilized complex was used in the oxidation reaction of ethylbenzene and benzyl alcohol by molecular oxygen as a heterogenous catalysis, and the catalytic activities and the mechanisms of the catalytic oxidations were investigated. The experimental results show that as a heterogenous catalyst, Cu（Ⅱ）-IAA-PEI/SiO₂ can efficiently catalyze the oxidation process of ethylbenzene by molecular oxygen, and the main product is acetophenone. Catalytic oxidation reaction follows the radical chain mechanism. Ethylbenzene was high selectively oxidized to acetophenone with mutual transformation of different valence of Cu elements. Under the suitable temperature （130℃） and time （10h）, the yield of acetophenone could reach 40%. Additional, the catalyst has well reusability.The composite catalyst consisted of 2,2,6,6-tetramethyl-piperidinyloxyl （TEMPO） and Cu（Ⅱ）-IAA-PEI/SiO₂ was used in the oxidation reaction of benzyl alcohol by molecular oxygen. The experimental results show that the composite catalyst can highly efficiently catalyze the oxidation reaction of benzyl alcohol to benzaldehyde with molecular oxygen. Under the mild conditions （with oxygen at atmospheric pressure and at the temperature of 80℃）, the yield of benzaldehyde could reach 75%.