Functionalized Persimmon Tannins Biosorbents And Research On Its Application In Sewage Treatment

In modern society,water pollution has become increasingly serious,causing great harm to the environment and human health.In this paper,persimmon tannin?PT?being extracted from persimmon was used as the raw material,and three different PT-based biosorbents were obtained through functional modification.The adsorption performance of precious metal ions,heavy metal ions and organic dyes in sewage was studied.The micro-information including the structure and morphology were investigated by means of Fourier transform infrared spectrometer?FTIR?,scanning electronic microscope?SEM?,thermogravimetric analysis,Zeta potential,Brunner-Emmet-Teller measurements?BET?,X-ray photoelectron Spectroscopy?XPS?and X-Ray diffractomer?XRD?.The optimum adsorption conditions were obtained by the single-factor adsorption experiment.The adsorption mechanism was analyzed deeply by the fitting of experimental data by the isotherm and kinetic models and calculating the enthalpy.The competitive adsorption and recycling experiments were used to evaluate the adsorption characteristics and stability of the three modification PT-based biosorbents.The main contents as following:1.The PT-GO biosorbent was successfully prepared by functionalization PT with graphene oxide?GO?and the effective adsorption behaviour of Au³⁺,Pd²⁺and Ag⁺ions from aqueous solution was investigated.The PT-GO was characterized by FTIR,SEM,TGA and Zeta potential.Adsorption experiment results showed that the maximum adsorption capacity for Au³⁺,Pd²⁺and Ag⁺were 1325.09 mg/g,797.66 mg/g and 421.01mg/g,respectively.The isothermal adsorption process of Au³⁺and Ag⁺on PT-GO were suitable to be described by Langmuir model,while the Freundlich model fitted better for Pd²⁺.The adsorption removal of Au³⁺,Pd²⁺presented relatively fast adsorption kinetics with pseudo-second-order equation as the best fitting model,while the pseudo-first-order kinetic model was suitable for describing the adsorption of Ag⁺.Combination of ion exchange,electrostatic interaction and physical adsorption are the mechanism for adsorption of Au³⁺,Pd²⁺and Ag⁺on PT-GO biosorbent.All the results showed that PT-GO may be an ideal biosorbent for removing precious metal ions and extends the potential application of persimmon tannin biosorbent in wastewater treatment.2.The PT-CS biosorbent has been successfully prepared by functionalization PT with chitosan?CS?and the effective adsorption behaviour of Pb?II?from aqueous solutions was investigated.FT-IR,XRD,SEM,BET,XPS and Zeta potential were used to elucidate the adsorption mechanism.The results showed that the adsorption process of Pb?II?ions by PT-CS including oxidation reaction,chelation reaction and electrostatic interaction.Equilibrium isotherm for the adsorption of Pb?II?was analyzed by the Langmuir,Freundlich and Temkin models and the Langmuir isotherm models was the best.The maximum adsorption capacity was 179.3 mg/g.The pseudo-second-order kinetic model was fitted well of the process of Pb?II?adsorption onto PT-CS.Moreover,thermodynamic parameters including?G⁰<0,?H⁰>0 and?S⁰>0 showed that the process of Pb?II?adsorption onto PT-CS was spontaneous and endothermic.All these results illustrated that PT-CS would be a promising and low-cost alternative bioadsorbent of Pb?II?in wastewater treatment.3.The PT-PEI biosorbent was successfully prepared by functionalization PT with polyethyleneimine?PEI?and the effective adsorption behaviour of anionic dye-methyl orange?MO?in aqueous solution was investigated.The properties of PT-PEI were characterized by FT-IR,SEM,Zeta potential and TGA.Batch adsorption experiments were carried out systematically to optimize the adsorption process.Kinetic models analysis revealed that the adsorption processes of MO followed a pseudo-second-order model and that the internal diffusion was the rate-determining step for the adsorption of MO on the surface of PT-PEI.The equilibrium isotherm was well fitted to the Freundlich model with the maximum adsorption capacity of 225.74 mg/g.Thermodynamics data revealed the adsorption nature of MO onto PT-PEI was feasible,spontaneous and endothermic.A possible adsorption mechanism has been proposed where electrostatic interaction,hydrogen bonding and?-?interaction dominated the adsorption of MO onto PT-PEI.All those results indicated that PT-PEI may be a high-performance and promising candidate for effective removal anionic dyes from aqueous solution.