Studies On Preparation Of Composite-Type Solid Adsorption Materials For Chromate Ion Based On Polyethyleneimine And Their Adsorption Properties

Heavy metal Cr(â…¥) is intensely carcinogenic,and it is a important work in water environment governing to remove Cr(â…¥) from industrial wastewater.There are several methods to take off Cr(â…¥),and among these methods,the adsorption method is more effective and simple.It is a key problem to prepare solid adsorbents with high performance.In this work,three composite-type solid adsorption materials for chromate ion based on functional polymer polyethyleneimine were prepared,and their adsorption properties and mechanism for chromate ion were also studied in depth.Firstly,Polyethyleneimine was grafted onto the surfaces of silica gel particles via the coupling action ofγ-chloropropyl trimethoxy silane,and the grafted particles PEI/SiO₂ with stronger adsorption ability for chromate was prepared.The infrared spectrum of PEI/SiO₂ was determined and its chemical structure was characterized.The adsorption property of PEI/SiO₂ for chromate was studied with static method,and the effects of various factors on the adsorption property were examined.The elution behaviour of chromate from PEI/SiO₂ also was tested.The experimental results show that the grafted polyamine macromolecules PEI are protonated in water,and PEI/SiO₂ produced stronger adsorption action by right of electrostatic interaction for chromate ions.The isothermal adsorption is suited to Langmuir equation.The pH value of the medium has a great effect on the adsorption capacity.The lower the pH value,the greater adsorption capacity is.In the neutral and alkaline solution,the adsorption capacity decrease obviously.The adsorption capacity is decreased with the increase of the temperature,and it is increased with the increase of the graft degree of PEI on PEI/SiO₂.The chromate adsorbed on the particles PEI/SiO₂ is easy to be desorbed by the aqueous solution of NaOH as eluent,and it is convenient for the reuse of PEI/SiO₂.In ordcr to ovcrcomc thc disadvantage that the adsorption property of the grated particles PEI/SiO₂ is severely dependent of the pH value of the medium,in this work, another compote-type solid adsorption material were prepared.The tertiary amination reactions of the primary and secondary amine groups of the grafted PEI were conducted using propylene oxide as tertiary amination reagent,and then the quaterisation was performed using benzyl chloride.The grafted PEI was transformed into ammonium salt-type polyelectrolyte QPEI,and the functional composite particles QPEI//SiO₂ were obtained.The infrared spectrum of QPEI/SiO₂ was determined and its chemical structure was characterized.The Zeta potential of the particles QPEI/SiO₂ was also determined,and the electrical property of its surface was also evaluated.The adsorption property of QPEI/SiO₂ against chromate radical anions was studied with static method.The effects of various factors on the adsorption property of QPEI/SiO₂ were examined.The experimental results show that the particles QPEI/SiO₂ have very strong adsorption ability by right of strong electrostatic interaction,and the saturated adsorption amount can reach 0.14g/g. The isotherm adsorption is suited to Langmuir equation.The major factor which affects the adsorption property of QPEI/SiO₂ for chromate radical anions is the quatemization degree of QPEI/SiO₂,and the particles QPEI/SiO₂ with higher quaternization degree has high adsorption capacity.The pH value of the medium influences on the adsorption property of QPEI/SiO₂ hardly.The dynamic desportion experimenta result shows that QPEI/SiO₂ adsorbed chromate ions has excellent desorption property.As a mixed solution of NaOH and NaCl was used as eluant and the volume of the effluent was 20 BV,the desorption ratio got up to 97.3%.The functional particles QPEI/SiO₂ and the grafted particles PEI/SiO₂ not only have strong adsorption ability towards chromate ions,but also have many excellent properties of the inorganic particles of silica gel particles,such as high specific area,strong mechanical property,fine thermal and chemical stability and low cost.The result indicates that to graft functional macromolecules on inorganic particles is a promising route for preparing solid adsorption materials with high performance.The functional particles QPEI/SiO₂ are lack of adsorption selectivity.In order to overcome this shortcoming,in this work the ion imprinting material was prepared finally. By adopting the novel surface molecular imprinting technique set up by us,the ionic imprinting process was carried out on the surface of PEI/SiO₂ particles with chromate ion as template and ethylene glycol diglycidyl ether(EGGE) as crosslinker,and the ionic imprinted material IIP-PEI/SiO₂ was prepared.The binding characteristic of IIP-PEI/SiO₂ was studied in depth using both static and dynamic methods with phosphate ion and borate ion as contrast ions.The results indicate that the surface imprinting material IIP-PEI/SiO₂ possesses excellent binding affinity and recognition selectivity for chromate ion.With respect of phosphate ion and borate ion,the selectivity coefficients of the non-imprinting material PEI/SiO₂ for chromate ion were 1.39 and 1.79,respectively.However,the selectivity coefficients of the imprinting material IIP-PEI/SiO₂ reached 22.93 and 26.14, respectively,displaying good recognition selectivity towards chromate ion.The imprinting material IIP-PEI/SiO₂ has fine desorption property.As a mixed solution of NaHCO₃ and NaCl was used as eluent and the volume of the effluent got up to 22 BV,the desorption ratio was reached 98.26%%.