Preparation Of Crosslinked Chitosan Microspheres And Its Adsorption To Organic Dye

In our daily life,more than 100,000 types of commercial dyes are used with a production of over 7×105 tons annually.About 15%of dyes produced are lost during dyeing processes and released into wastewaters,resulting in a considerable amount of colored water as effluent.These dyes can cause irreversible damages to environment,aquicolous organisms and human health.Therefore,the removal of these dyes from water is very important from an environmental point of view.Many methods such as ion exchange,precipitation,adsorption,and membrane processes have been used for the removal of toxic dye wastewaters.In particular,adsorption is recognized as an effective and economic method for the removal of dye pollutants from wastewaters.Activated carbon,as a traditional adsorbent,has been used extensively in industry.However,it is expensive and difficult to regenerate.From this point on,low-cost sorbents have been given increasing attention as they can significantly reduce the cost of an adsorption system.From this point on,much attention has recently been focused on sorbent materials,those that are not expensive,can be obtained from renewable resources,and are harmless to nature.The abundant,natural non-toxic organic polymer chitosan have become the focus in the current wastewater treatment.The macromolecules of chitosan contain numerous active functional groups including amino(-NH2)and hydroxyl(-OH)groups and exhibit unique adsorption,chelating,interactions with other functional groups for all kinds of dyes,proteins,heavy metal ions and so on.Pure or modified chitosan and chitosan composites have been widely used as economical adsorbents are drawing great attention and showing significant adsorption potential for removal of various dyes since amino and hydroxyl functional groups on chitosan chains can serve as electrostatic interaction and coordination bonds,respectively.However,the major limitation of chitosan,is its solubility in most dilute mineral and organic acid solutions,chitosan is easy to dissolve and run off in most dilute mineral and organic acid solutions.Cross-linking can change the crystalline nature of chitosan and enhance the resistance of chitosan against acid,alkali and chemicals and also increase the sorption abilities of chitosan.Chitosan can be cross-linked with different crosslinking agents such as glutaraldehyde(GLA),epichlorohydrin(ECH),ethylene glycol diglycidyl ether(EGDE),genipin and triphosphate(TPP)and so on.The aim of this work is to evaluate the use of chemically crosslinked chitosan micro spheres as sorbent,using Methyl Orange(MO)as a model compound for the adsorption and desorption studies.In this study,with the chitosan powder as the raw material,the dilute acetic acid solution as the solvent,the chitosan powder was dissolved in acetic acid solution,the glutaraldehyde as the crosslinking agent,the Span-80 as the emulsifier,the liquid paraffin as the dispersant,crosslinked chitosan microspheres were prepared by emulsion crosslinking method.The structure and morphology of the chitosan and the crosslinked chitosan micro spheres were characterized by Fourier Infrared Spectro me ter(F TIR),X-Ray Diffractometer(XRD),and Scanning Electron Microscopy(SEM).The influence factors of the preparation of crosslinked chitosan microspheres were investigated.To get the best adsorption conditions,it discussed the affect on adsorpt effect by the dosage of crosslinking agent,the pH of reaction system during the preparation.The influences of the dosage of crosslinked chitosan microspheres,initial concentration of methyl orange solution,temperature of methyl orange solution,pH value of methyl orange solution were studied.The results show that in the preparation of crosslinked chitosan microspheres,the concentration of crosslinking agent and the pH of reaction system during the preparation are the important factors for the adsorption quality and function of chitosan microspheres.When the dosage of crosslinking agent is 2mL,the dosage of NaOH is 6 mL,the crosslinked chitosan microspheres had a good spherical shape,the surface of the crosslinked chitosan microspheres were smooth,and the diameter of microspheres were about 100 ?m.The crosslinking reactions happened between chitosan with glutaraldehyde,and generate a new carbon-nitrogen double bond(Schiff's base).The crystallinity of crosslinked chitosan microspheres decreased.The pH value of methyl orange solution has significant effect on adsorption and a weak acid environment conducive to the adsorption.When the pH value of methyl orange solution is 3,the adsorption rate is the fastest.Adsorption rate increased and adsorbing capacity decreases with the increase of dosage of sorbent.Adsorption rate decreases and adsorbing capacity increased with the increase of initial concentration of methyl orange.The temperature of methyl orange solution has effect on the adsorption,from 5 to 45 ?,the higher the temperature is,the faster the adsorption is.However,little influence on adsorption performance would present when the temperature is much higher than 35 ?.The research results show that the adsorption process conforms to the secondary adsorption dynamic equation model and Langmuir isothermal adsorption model.The crosslinked chitosan microspheres can be reused after eluted by NaCl solution.