Preparation Of Chitin-composite For The Treatment Of Wastewater

The rapid development of industry has brought a lot of water contamination,such as heavy metals and organic micro-pollutants,which seriously harm the ecological environment and human health.Therefore,people developed diverse methods such as membrane separation,catalytic degradation,co-precipitation,ion exchange and adsorption for treating sewage.The adsorption,in comparison to other methods,has attracted more attentions because of its advantages of simple operation,high efficiency and low cost.Chitin（CT）is the most abundant natural polysaccharide polymer except cellulose on the earth.With the characteristics including wide source,low price and biodegradable,chitin mainly exists in crustaceans or fungi.The beibu gulf region of guangxi province is rich in waste seafood shell,a chitin resource,providing the advantage of regional resource in the development of chitin-based functional materials.Based on these,this work intends to develop a series of chitin-based composites with different morphologies（including spherical and sponge-like）by the functional modification of chitin.These composites are then appliedin the adsorption of heavy metals or organic micropollutants in aqueous solution.The main research contents are as follows:（1）Poly（m-phenylenediamine）/chitin composite beads（CT-Pm PD）were prepared by in situ polymerization of m-phenylenediamine on chitin beads.The Fourier Infrared Spectroscopy（FT-IR）,X-ray diffraction（XRD）and Scanning electron microscope（SEM）characterization showed that CT-Pm PD was successfully prepared,and a large number of poly-m-phenylenediamine nanoparticles were anchored on chitin beads.Subseqently,the CT-Pm PD was used to adsorb the hexavalent chromium ion Cr（VI）in the aqueous solution.The results showed that the CT-Pm PD had the largest adsorption capacity at p H=2.0.The adsorption process conformed to the quasi-second-order kinetics and the Langmiur model,indicating that the adsorption was a single-molecule layer adsorptionand dominated by chemisorptions.In addition,the adsorption was an endothermic,spontaneous and entropy increasing process.At 25℃,the maximum theoretical adsorption capacity of CT-Pm PD toward Cr（VI）was 185.4mg·g^-1.The co-existing anions,including Cl^-,NO₃^-and SO₄^2-,conld be competitively adsorbed with Cr（VI）,which inhibited the adsorption of Cr（VI）.The X-ray diffraction（XPS）results showed that the electrostatic attraction between protonylated amine groups and Cr（VI）and the reduction of Cr（VI）by amine/hydroxyl groupswere the main adsorption mechanism of CT-Pm PD toward Cr（VI）.Furthermore,CT-Pm PD can be recycled.CT-Pm PD maintained77.4%of its first adsorption capacity at the fifth adsorption-desorption cycle,indicating that it has a good prospect in the treatment of wastewater containing Cr（VI）.（2）In order to promote the active sites of the chitin-based functional materials for meeting the demand of different objects,β-cyclodextrin（β-CD）with hydrophobic cavities and polyethyleneimine（PEI）with amine functional groups were simultaneously fixed on CT,which resulted in a sponge-like composite material（β-CD-g-PEI/CT）.The results of Hydrogen spectrum nuclear magnetic resonance（¹H NMR）and FT-IR indicated the successful synthesis ofβ-CD-g-PEI/CT.The XRD results showed that the crystal structure ofβ-CD and CT disappeared in the XRD pattern ofβ-CD-g-PEI/CT,indicating that every component was evenly dispersed in the product and the reaction was sufficient.The SEM results showed that theβ-CD-g-PEI/CT presented a porous structure,which benifited the diffusion of the process object.In addition,the content of hydrophobic cavities ofβ-CD-g-PEI/CT was tested to be 0.11 mmol·g^-1.（3）Bisphenol A（BPA）and Cu²⁺were used as models to study the adsorption properties ofβ-CD-g-PEI/CT in the mono-component and bi-component solutions.The results showed that in the mono-component system,both BPA and Cu²⁺were adsorbed well at p H=5.0.The adsorption processes ofβ-CD-g-PEI/CT toward BPA and Cu²⁺conformed to the quasi-second-order kinetic model and the Langmuir isothermal model.At 30℃,the maximum theoretical adsorption capacities ofβ-CD-g-PEI/CT toward BPA and Cu²⁺were149.3 and 178.6 mg·g^-1,respectively.In the bi-component system,the adsorption mechanisms ofβ-CD-g-PEI/CT toward BPA and Cu²⁺were the clathration of cavity to BPA and the complexation between amine groups and Cu²⁺,respectively.The two mechanisms were independent and did not affect each other.β-CD-g-PEI/CT has good regeneration and reusable performance.It maintained 89.5%and 83.6%of its first adsorption capacities at the sixth adsorption-desorption cycle for BPA and Cu²⁺,respectively.β-CD-g-PEI/CT was expected to be used in the treatment of wastewater containing heavy metals and organic micropollutants.