Modifications And Functional Properties Of Gellan Gum

Gellan gum(GG)is a new microbial polysaccharide derived from gram-negative bacterium Sphingomonas paucimobilis.Due to its functional properties such as high transparency and resistance to heat and acidic environments,GG has been widely used in food,pharmaceutical production,and chemical engineering applications.GG contains hydroxyl,carboxyl and other hydrophilic groups,making it as a good source of adsorption materials.In this paper,GG was modified by the introduction of different monomers and crosslinker,and the adsorption properties and adsorption mechanism were studied by the adsorption model of crystal violet(CV)and methylene blue(MB).In addition,GG/GO aerogels were prepared by introducing nanophase materials graphene oxide(GO),and the adsorption properties were studied.The main results are as follows:(1)In this paper,the modified gellan gum(GGTTE)was prepared by acrylamide(AM)as monomer,three hydroxymethyl propane three glycidyl ether(TTE)as a crosslinker,and potassium persulfate(K2S2O8)as an initiator.The structure and morphology of GGTTE were characterized by Fourier transform infrared(FT-IR)spectroscopy,X-ray diffraction(XRD),Differential scanning calorimetry(DSC)and Scanning electron microscopy(SEM).Compared with GG,FT-IR data showed that GGTTE had the absorption peaks of N-H(2788 cm-1),C-N(1411 cm-1)and NH2(1117 cm-1),and the absorption peak(3448 cm-1)of O-H and N-H broadened,indicating that the acryl group had been introduced into GG,XRD data showed that the intramolecular and intermolecular hydrogen bond forces of GGTTE strengthened,making the crystal structure more orderly.DSC data indicated that the thermal stability of GGTTE was improved.SEM analysis showed that GGTTE had porous microstructure,the crosslinking and reticular structure of GGTTE made it to have adsorption properties.(2)GGTTE as an adsorbent,the effect of operational parameters including adsorbent dose,initial pH,contact time,contact temperature and initial dye concentration were studied in batch adsorption experiments.The results showed that the optimum conditions for the adsorption of CV were as follows:At the temperature of 30?,80 mg GGTTE was added to pH 6 60 mg/L CV solution,after adsorption of 60 min,the adsorption and removal rate of CV on GGTTE were 33.87 mg/g and 55.89%,respectively.The adsorption kinetics and thermodynamics of GGTTE on CV showed that:The adsorption of CV complied with the pseudo-second-order kinetic model,and the adsorption isotherm model was Langmuir adsorption model.The thermodynamic parameters of ?G,?H and ?S indicated that the adsorption process was spontaneous exothermic.FT-IR results showed that the active sites such as hydroxyl and carboxyl groups in GGTTE could interact with CV.XRD results showed that the crystal structure of GGTTE was more disorder after CV adsorption.(3)On the basis of GGTTE,acrylic acid(AA)was added to prepare pH sensitive Gellan gum-acrylic acid-acrylamide-three hydroxymethyl propane three glycidyl ether hydrogel(AAAMGG).To improve the adsorption properties of AAAMGG.Single factor and response surface methodology were combined to optimize the synthesis conditions of AAAMGG.The structure and morphology of AAAMGG were characterized by FT-IR,DSC,XRD and SEM.AAAMGG as an adsorbent,the effect of operational parameters including adsorbent dose,initial pH,contact time,contact temperature and initial dye concentration were studied in batch adsorption experiments.The experimental results showed that the optimum synthesis conditions of AAAMGG were as follows:30 g AA:AM with the mass ratio of 2:1,meanwhile,the AA neutralization degree was 80%,2%TTE and 2%K2S2O8 reacted 4 h at 70 ?.The results of FT-IR showed that AAAMGG had been successfully crosslinked.The results of XRD showed that the crystal structure of AAAMGG was more orderly.The results of DSC showed that the thermal stability of AAAMGG was improved,and the results of SEM showed that AAAMGG had a honeycomb porous structure.The optimal conditions for adsorption of MB by AAAMGG were:At the temperature of 25 ?,20 mg AAAMGG was added to 120 mg/L pH 6 MB soltion,after adsorption of 60 min,the adsorption and removal rate of MB on AAAMGG were 163.66 mg/g and 96.06%,respectively.The adsorption kinetics and thermodynamics of AAAMGG on MB showed that:The adsorption of MB complied with the pseudo-second-order kinetic model,and the adsorption isotherm model was Langmuir adsorption model.The thermodynamic parameters of ?G,?H and ?S indicated that the adsorption process was spontaneous exothermic.(4)On the basis of GG,GG/GO aerogel was prepared by sol-gel freeze drying method.The structure and morphology of GG/GO was characterized by FT-IR,DSC,XRD and SEM.The FT-IR results showed that the GG/GO aerogels prepared at different freezing temperatures(-20 ? and-80 ?)were not different,but the DSC experimental results showed that the freezing temperature at-20 ? had a more stable structure,and SEM showed that the freezing temperature at-20 ? was more loose and more distinct than the GG/GO aerogels prepared at-80?.At the temperature of 25 ?,6 mg GG/GO-6 aerogels was added to 50 mL 30 mg/L MB soltion of pH 6,after adsorption of 120 h,the adsorption and removal rate of MB on GG/GO-6 aerogels were 192.49 mg/g and 72.56%,respectively.