Study On The Construction And Adsorption Of Konjac Glucomannan Gel Based On ZIF-8

To study the mechanism of interaction among konjac glucomannan(KGM),zeolitic imidazolate framework-8(ZIF-8)and ghatti gum(GG)and its applications,as well as effectively reduce or detect some specific components in foods,KGM was used as base material and the synthetic ZIF-8 crystals was used as the disperse phase,the konjac glucomannanbased composite aerogel was prepared by sol-gel and vacuum freezedrying method,and it was used to study the adsorption of ciprofloxacin(CIP).The effects of ionic strength,pH and other factors on adsorption were investigated.Adsorption kinetics model and thermodynamic model were used to study the adsorption mechanism.In order to study the effect of other polysaccharides on adsorption,GG/KGM/ZIF-8 composite gels and aerogel were prepared by adding different proportions of GG,then their rheological and adsorption properties were investigated,aming to prepare a composite aerogel with efficient adsorption proporties.The main research contents and results of this paper were as follows:1.The Construction and Rheological Study of Konjac Glucomannan/ZIF-8 Composite GelZIF-8 crystals were successfully prepared by hydrothermal method and KGM/ZIF-8 composite gels(HKZO,HKZO.5,HKZO.75,HKZ1)were prepared by sol-gel method.The rheological properties of composite gels with varying proportions of ZIF-8 crystals were investigated with a rheometer.The results showed that the addition of ZIF-8 crystals was conducive to enlarge the linear viscoelastic region of KGM/ZIF-8 composite gel.HKZ0.5 exhibited good plasticity in high frequency region,and the temperature resistance of HKZ0.5 was relatively strong.HKZ0.5 also showed the best solid-phase gel properties and better anti-resistance and recovery capability.With the increase of shear rate,KGM/ZIF-8 composite gel showed typical phenomenon of shear thinning,indicating that KGM/ZIF-8 composite gel was a pseudoplastic fluid.2.Synthesis and Adsorption Mechanism of Konjac Glucomannan/ZIF-8 Composite AerogelsThe KGM-ZIF-8 aerogels(KZ0、KZ0.5、KZ0.75、KZ1)were synthesized by composing of konjac glucomannan with ZIF-8 crystals for removal of CIP from water.The structure morphology and properties were studied by SEM(Scanning Electronic Microscopy),Transmission electron microscope(TEM),Fourier Transform infrared spectroscopy(FTIR),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS)and Thermogravimetric Analysis(TGA).Several effects such as pH,ionic strength,contact time and temperature were investigated.The results showed that the addition of ions has a negative effect on the adsorption of CIP and when pH=7.0,the adsorption of CIP by KZ0.5 was maximized.The adsorption kinetics followed pseudo-second-order and fitted well with Langmuir model(R2>0.99).The maximum adsorption capacity for CIP based on Langmuir model at 303k was 812.35mg/g.△G,△H and △S are the thermodynamic parameters which indicate that the adsorption KZ0.5 on CIP was an endothermic process.There was no significant decrease in the adsorption amount of KZ0.5 in the six cycles after adsorption and elution,indicating that the KGM/ZIF-8 composite aerogel may be a promising adsorbent.3.Construction and Rheological Study of Ghatti Gum/Konjac Glucomannan/ZIF-8 Composite GelThe GG/KGM/ZIF-8 composite gels(HGKZ0,HGKZ0.4,HGKZ0.6,HGKZ0.8,HGKZ1)were prepared by sol-gel method.Rheometers were used to investigate the rheological properties of the composite gel which contained different proportions of GG.Studies have shown that the appropriate amount of GG was beneficial to the widening of the linear viscoelastic region.HGKZ0.6 had the best plasticity in the high frequency region and good heat resistance.With the increase of shear stress,the solid gel performance was better,and its resistance to deformation and recovery was better than others.The GG/KGM/ZIF-8 composite gel showed a typical shear thinning phenomenon,indicating that the GG/KGM/ZIF-8 composite gel was a pseudoplastic fluid.4.Synthesis and Adsorption Properties of Ghatti Gum/Konjac Glucomannan/ZIF-8 Composite AerogelsGG/KGM/ZIF-8 composite aerogels(GKZ0,GKZ0.4,GKZ0.6,GKZ0.8,GKZ1)were synthesized by combining GG,KGM and ZIF-8,and used for CIP adsorption.The structure,morphology and properties of aerogels were investigated by SEM,TEM,FTIR,XRD and TGA.The effects of GG addition,pH and ionic strength on the adsorption effect were studied.Studies have shown that ZIF-8 crystals are randomly dispersed on the aerogel surface.In the 1000 mg/L CIP solution,the adsorption amount of GKZ0.6 was the largest,and the adsorption amount of CIP at the equilibrium can reach to 1035.4 mg/g.The addition of ions has a negative effect on the adsorption of CIP.When the pH in the solution is 7.0,the adsorption of CIP by GKZ0.6 was the greatest.By repeatedly eluting GKZ0.6 with methanol,GKZ0.6 had a good adsorption effect on CIP when the number of cycles was fewer,and it was a good adsorbent.