Study On The Adsorption Of Several Pollutants From Solution By Modified Polyvinyl Alcohol Composite Films

Because of easy separation characteristics,membrane materials are used in adsorption filed increasingly.In this paper,polyvinyl alcohol which are non-toxic,high thermal stability and high mechanical strength was blended with polyethyleneimine which are contain rich amino functional groups to prepare a kind of membrane,and the membrane was further modified with FeCl3 and ZrOCl2·8H2O to prepare adsorbents,which can adsorb anionic dyes light green(LG),Cr(VI),phosphate(PO43-),2,4-Dichlorophenoxyacetic acid(2,4-D)and catechol from solution.The adsorbents were characterized by infrared spectroscopy(FT-IR),point of zero charge,scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),and x-ray photoelectron spectroscopy(XPS),etc.The adsorption property was presented using batch adsorption and nonlinear regressive analysis was applied to obtain the parameters of isotherm and kinetic models.Furthermore,thermodynamic parameters were calculated and mechanisms were discussed.Finally,adsorption regeneration experiments were carried out.The adsorption results of PVA/PEI toward LG and Cr(VI)showed that the adsorption capacity of LG and Cr(VI)at 303 K and pH=3 was 420 mg·g-1 and 85 mg·g-1,respectively;the existence of Cl-was not conducive to adsorption.Isotherm Langmuir model and Freundlich model can be used to predict the equilibrium adsorption process while Elovich model can be used to describe LG and Cr(VI)adsorption.Thermodynamic parameters showed that the adsorption of LG and Cr(VI)were endothermic reaction which were spontaneous and entropy increase.The mixed solution of ethanol and CaCl2 and 0.1 mol·L-1 NaOH solution have good desorption and regeneration effects about LG or Cr(VI)loaded adsorbent,respectively.The adsorption of PO43-and 2,4-D by PVA/PEI-Fe film show that the adsorption capacity of PO43-and 2,4-D at pH 5.36 and 3.47 at 303 K was 20 mg·g-1 and 86 mg·g-1,respectively;the existence of HCO3-and SO42-was unfavorable for adsorption.Isotherm Langmuir model and Freundlich model were used to describe the adsorption process of PO43-and 2,4-D,respectively.Both Pseudo-second-order kinetics model and Elovich model can be used to describe the adsorption of PO43-and 2,4-D.Thermodynamic parameters show that the adsorption of PO43-was an endothermic process which were spontaneous and entropy increase,while the adsorption of 2,4-D was an exothermic process which were spontaneous and entropy increase.0.1 mol-L-1 NaOH solution can desorb PO43-and 2,4-D several times from spent or exhausted adsorbent.The adsorption results of catechol by PVA/PEI-Zr film showed that the adsorption capacity of catechol at 303 K and pH=4.98 was 28.5 mg·g-1.There was little effect of adsorption quantity about the change of solution pH and the existence of coexisting ions Cl-and SO42-.Isotherm curves can be described by Freundlich model and Temkin model.Kinetic process can be described by Double Constant model and Elovich model.Thermodynamic parameters showed that the adsorption process was an endothermic reaction which was spontaneous and entropy increase.Because catechol was combined with adsorbent closely,there was not property of the desorption and regeneration.The films used in this study are promising to effectively remove some pollutants from solution.