Microwave Modification Of Chitosan And Its Application In Wastewater Treatment

Chitosan is a reproducible natural polymer, due to its rich sources, cheap, good nature, safe, non-toxic, it is most concerned increasingly, become an increasing attention and gradually is widely used in chemical industry, environmental protection, medicine, materials, and so on. But chitosan has lower solubility, could only be dissolved in some diluted acid, insoluble in water, alkaline solution and most organic solvents, which greatly limits the application of it. However, the chitosan molecules contain a large number of -NH2 and -OH, can be modified by physical and chemical methods in order to improve the physical and chemical properties of it through introduction of chemical groups. Microwave heating has the characteristics of uniform, conservation, accelerating the reaction, improving the yield and selectivity. Combining the advantages of both, microwave chemical modification of chitosan can find a new technology for the application of chitosan material and expand its scope of application. And it has important theoretical and applied significance on the reaction rule of understanding microwave, the content and the major results of the study are as follows:1. The microwave preparation of maleic anhydride modified chitosan and its adsorption propertiesA chitosan-based adsorbent (CCTM) was synthesized by the reaction between epichlorohydrin O-crosslinked chitosan and maleic anhydride under microwave irradiation. The chemical structure of this new polymer was characterized by infrared spectra analysis. Their adsorption characteristics were reviewed by static adsorption method from the adsorption equilibrium, adsorption kinetics and adsorption thermodynamics, etc. Initial concentration, time and temperature on the adsorption were discussed. The adsorption properties of its regeneration were studied.(1) Its adsorption for metal ions the results show that CCTM have a higher adsorption capacity for the metal ion such as Pb²⁺,Cu²⁺,Cd²⁺,Zn²⁺ and Co²⁺ than chitosan. In particular, the adsorption capacities for Pb²⁺ and Cu²⁺ are 246.3 mg·g^-1 and 132.1mg·g^-1 respectively. The results of adsorption of CCTM for Pb²⁺ and Cu²⁺ ions indicate that the adsorption is consistent with Langmuir isotherm at low concentrations, the corresponding Langmuir constant is 247.0 and 263.8L?mol^-1, Dubinin-Kaganer-Radushkevich isotherm at a high concentration. The adsorption kinetics are well described by pseudo-second-order equation models. At different temperatures,ΔH<0,ΔS<0, adsorption process is exothermic, cooling is favorable to adsorption. The reused results show that the desorption rate of metal ions is more than 93%, and the desorption rate and absorption capacity have little change after the use of several times.(2) Its adsorption for 2,4-dinitrophenol The results show that the appropriate pH of the adsorption for 2,4–dinitrophenol is 3.6 and the adsorption capacities is 209.5mg·g^-1. The adsorption is consistent with Freundlich isotherm; adsorption kinetics is consistent with the proposed second-order reaction kinetics model; the adsorption of CCTM for 2,4-dinitrophenol is measured at different temperature, thermodynamic parameters of adsorption process are calculated, we use Freundlich equation to fit the experimental data and find that the equation applies to the study of the adsorption system. Thermodynamic is closely related to adsorption mechanism, the adsorption process is exothermic, the entropy of system is reduced, cooling is favorable to adsorption. Desorption rate increases with the increase of the microwave time, and reach 91.60% after 5min.2. The microwave preparation of TiO₂ modified magnetic chitosan microspheres and its photocatalytic degradation for methyl orangeSelf-made TiO₂, magnetic Fe3O4 and chitosan in the appropriate proportion were added to the acetic acid solution, stirring, overnight, and then crosslinked chitosan microspheres were prepared by using formaldehyde and epichlorohydrin as crosslinking agent under microwave, the chemical structure of this new polymer was characterized by infrared spectra analysis, thermo gravimetric analysis and surface area analysis. The effects of pH, initial concentration of methyl orange, time and temperature on the photocatalytic degradation of methyl orange were studied in general illumination of Fluorescent lighting. The results show that the initial pH have a greater impact on degradation rate of methyl orange, in acidic conditions, the photodegradation of methyl orange is faster, photo degradation rate has a downward trend with the increase of the pH; the degradation rate of methyl orange reduce with the increase of initial concentration. when the pH is 3, methyl orange concentration of 10mg·L^-1 and the photocatalytic after 120min, methyl orange has been basically colorless, the degradation rate of 89.58%, photocatalytic degradation of nanoparticle for methyl orange solution is in line with the bleaching reaction pseudo-first-order kinetics equation, the reaction rate constant reduce and half-life extend with the increase of the initial concentration.3. The microwave preparation of dicyandiamide modified chitosan microspheres and its adsorption of Cu²⁺A novel chitosan microspheres resin was microwave synthesis from chitosan through hydroxpropy–chloridization and amination. The adsorption performance of the adsorbent for Cu²⁺ was investigated. The results show that the appropriate pH of the adsorption for Cu²⁺ is 5, The adsorption isotherm data is consistent with Langmuir isotherms model. The saturated adsorption capacity of modified chitosan microspheres for Cu²⁺ is 165.4 mg·g^-1. The adsorption kinetics is well described by pseudo-second-order equation models, the adsorption capacity slightly increase with the increase of temperature.