Preparation Of Hydroxyethyl Cellulose And Broad Bean Straw Based Hydrogels And Their Adsorption Performance To Methylene Blue Dye

Discharge of a great deal of organic dye wastewater in the industry,such as paper-making,textile,and printing have seriously harmed eco-environment.Nowadays,the popular techniques for removing dyes mainly include biological treatment,adsorption and electrochemical method.Among them,the adsorption has become one of the most effective methods because of its low cost and operability.In this thesis,hydroxyethyl cellulose and broad bean straw of wide source,low cost and excellent biocompatibility were respectively selected as the basic raw materials to synthesize a series of hydrogels through a graft copolymerization method with functional monomer.These hydrogels showed excellent swelling performances in aqueous solution and high adsorption capacity to high concentration of methylene and had good application potential in water conservation agriculture and treatment of dye wastewater of high concentration.The thesis consists of five chapters as follows:The first chapter briefly reviewed significance,preparation methods and application advances of hydrogels and introduced main techniques for preparing activated carbon using biomass.In the second chapter,a serious novel superabsorbent hydrogels of hydroxyethyl cellulose-g-poly(acrylic acid)/attapulgite/sodium humate(HEC-g-PAA/APT/SH)were prepared by graft copolymerization of acrylic acid(AA),attapulgite(APT)and sodium humate(SH)onto hydroxyethyl cellulose in aqueous solution.The factors,included the degree of neutralization of acrylic acid,the amounts of crosslinking agent,initiator,attapulgite and sodium humate,influencing water swelling capacity and adsorption capacity to methylene blue(MB)were investigated.The results showed that the prepared super water-absorbing hydrogel possessed a maximum swelling capacity of 1104.06 g/g in distilled water,excellent salt-resistance and wide pH application range,and the prepared highly adsorptive hydrogel had a maximum adsorption capacity to MB of 2337.09 mg/g.The adsorption process obeyed Langmuir isotherm adsorption model and the adsorption kinetic showed a synergistic effect of the pseudo-first-order kinetic and the pseudo-second-order kinetic.In the third chapter,three kinds of broad bean straw based activated carbons were prepared using broad bean straw as raw materials at 300,400,500 ? carbonization temperature,respectively.Their structure and surface morphology were characterized by employing Fourier transform infrared spectroscopy(FT-IR),scanning electron microscopy(SEM)and thermogravimetric analysis(TG)and the adsorption behaviors of methylene blue dye were studied in detail.The results showed the product obtained at 300? carbonized temperature had the highest yield and higher adsorption capacity to MB.The maximum adsorption capacity of methylene blue on the activated carbon reached 207.79 mg/g when pH = 8.The adsorption process fitted in with the pseudo-second-order kinetic model and Langmuir isotherm adsorption model indicating that it was chemically controlled monolayer adsorption process.In the fourth chapter,a kind of novel broad bean straw activated carbon based hydrogels,with 3D network porous structure,were prepared by using a graft copolymerization of acrylic acid onto the pre-synthesized broad bean straw activated carbon in aqueous solution,and applied in water conservation and adsorption to MB.The results displayed that the hydrogel had a good water-absorbing property,excellent salt-resistance and wide pH application range,and the maximum swelling capacity was 619.13 g/g in distilled water.At the same time,it still showed an excellent sorption performance to MB dye and the maximum adsorption capacity to MB reached 1703.68 mg/g.The adsorption isotherm fitted in with the Langmuir model and the kinetic process was consistent with pseudo-second-order kinetic model.Besides,we combined the prepared broad bean straw activated carbon based hydrogels and the broad bean straw activated carbon to treat gradedly high concentration of MB wastewater.After respectively treated three times with these two adsorbents,the removal rate of MB reached 99.73%.In the fifth chapter,some three-dimensional network structure of broad bean straw based hydrogels were prepared by direct grafting copolymerization of functional monomer acrylic acid onto broad bean straw.Under the optimal experimental conditions,the prepared broad bean straw based hydrogel showed higher water swelling rate and higher adsorption capacity to MB than broad bean straw activated carbon based hydrogel,and its maxmum swelling capacity was 669.15 g/g in distilled water and the maxmum adsorption capacity to MB was 1736.39 mg/g.The corresponding adsorption dynamic obeyed Langmuir isotherm model,the kinetic obeyed pyseudo-first-order kinetic model and the adsorption process was physically-controlled monolayer adsorption.