Preparation And Rapid Adsorption Properties Of Polycatecholamines And Their Composites

Polycatecholamine is a kind of functional polymer synthetic resin,which is made of catechol based materials and amine based materials.The material has good adsorption and adhesion functions,due to the large amount of catechol and amine groups.Use low-cost,naturally extractable plant catechol to react with polyamine to prepare polycatecholamine adsorption material.In addition,molecular sieve@polycatecholamine composite was synthesized by modification of molecular sieve with amino group to remove Congo Red（CR）.The surface morphology of the materials was characterized through environmental scanning electron microscopy（SEM）and transmission electron microscopy（TEM）.The composition and thermal stability of the materials are characterized by Fourier transform infrared spectroscopy（FI-IR）,Thermal gravimetric analyzer（TG）and X-ray photoelectron spectroscopy（XPS）,respectively.The influence of various factors on the removal rate has also been explored.The mechanism of adsorption of the materials was explored through the intra-particle diffusion,kinetics and isothermal adsorption model.In this paper,it is mainly divided into three tasks:（1）Poly（tannic acid-butanediamine）（PTBA）is synthesized by a simple one-step method by tannic acid and butanediamine for the treatment of Cr（Ⅵ）-containing wastewater.It was found that the polymers had similar thermal stability,and the materials synthesized with the ratio of 1:10（tannic acid:butanediamine）had better adsorption properties.When the concentration of Cr（Ⅵ）is below 100 mg/L,the adsorption equilibrium can be reached within 30 min,the removal rate is more than99%,and the adsorption capacity is 256 mg/g.PTBA showed the best adsorption performance in the p H=2.5 solution.The presenc of NO₃^-had no significant effect on the removal of Cr（Ⅵ）,but the presence of a large amount of SO₄^2-in the solution will decrease Qe value.The Qe calculated by pseudo-second order kinetic model（317 mg/g）and Langmuir isothermal adsorption model are close to the experimental Qe（310 mg/g）,which indicates that PTBA is carrying out a monolayer chemical adsorption.The experimental results show that the removal mechanism of PTBA may be the reduction of Cr（Ⅵ）to Cr（III）by–OH,the electrostatic adsorption of Cr（Ⅵ）、Cr（III）by-NH₃⁺and-NH₂respectively.（2）We further expand the research of adsorption materials on the basis of the above work.Comparing polycatecholamine materials synthesized by tannic acid with1,4-butanediamine,diethylenetriamine,and tetraethylenepentamine,respectively.The polymers synthesized by tannic acid and 1,4-butanediamine,diethylenetriamine and tetraethylenepentamine are named poly（tannic-1,4-butanediamine）（PTBA）、poly（tannic-diethylenetriamine）（PDTA）、poly（tannic-tetraethylenepentamine）（PTPA）,respectively.It was found that the thermal stability of the three adsorption materials are similar,and PTPA has been found has the best removal performance,which further proves that the increase of amino group content is beneficial to the removal of Cr（Ⅵ）.The results of XPS analysis show that the removal of Cr（Ⅵ）is achieved by the synergistic effect of physical adsorption and chemical reduction.Under the same experimental conditions,PTPA shortened the time from the original 5 h（PTBA）to 30min,which significantly increased the removal rate,indicating that increasing the number of amino groups was conducive to improving the removal rate.（3）The molecular sieve（MSU-H）was surface modified by polycatecholamine to synthesize a new composite adsorption material polycatecholamine@MSU-H（C20#）for the removal of Congo red（CR）.The specific surface area of C20#is increased to 2.4m²/g from 1.77 m²/g（pure polycatecholamine）.Compared with the polycatecholamine,the removal rate of Congo red by C20#increased from 45%to 94%in the same treatment time.The increase in removal rate benefits from the increased specific surface area,which promotes the capture of adsorbates by the active sites.The p H value in the range of 3-7 has little effect on the Qe of the composite material,and the addition of inorganic salt has no significant effect on the Qe.In addition,CR can be separated from the adsorbent by simple ethanol desorption to realize the recycling of the adsorbent.In conclusion,polycatecholamine materials prepared from plant catechol and polyamines show good removal performance for Cr（Ⅵ）and CR.In addition,the removal rate can be increased rapidly by increasing the amine group content in the material or increasing the specific surface area by compounding with molecular sieves.