Preparation Of Modified Fruit Perecarps And Their Adsorption Properties For Methyl Orange And Cr(?) In Wastewater

Heavy metals and dyes are two common types of pollutants that are seriously harmful to the ecological environment and human health.The adsorption method to remove pollutants from aqueous solution has the advantages of high efficiency,simple operation,low cost and well reusability.The development of various new adsorbents has become one of the research hotspots of adsorption methods.This study synthesized four Polyethyleneimine(PEI)modified pericarps(LC@PEI-30,LC@PEI-65,LG@PEI-30 and LG@PEI-65)at two temperature(30? and 65?)via a simple one-step modification by using natural lychee pericarp(NLC)and natural longan pericarp(NLG)as raw materials which are common in southern China.Pericarp biadsorbents were characterized by scanning electron microscope(SEM),X-ray energy spectrum analysis(EDS),X-ray diffraction(XRD),Zeta potential analysis and Fourier Transform Infrared Spectrometer analysis(FTIR).The removal efficiency of MO and Cr(?)from wastewater were investigated.The specific results are as follows:(1)After PEI modification,the color of lychee pericarp and longan pericarps deepened to red and the surface wrinkle increased.The results of EDS,XRD,FTIR showed that the amino group and imino group in PEI were successfully grafted onto NLC and NLG,and the introduction of amino group and imino group enhanced the positive electricity of pericarps.(2)The adsorption capacity of lychee pericarp and longan pericarp to remove MO were greatly improved after modified by PEI.The MO adsorption onto LC@PEI-30,LC@PEI-65,LG@PEI-30 and LG@PEI-65 was suitable described by pseudo-second-order and Freundlich model which meaning chemical adsorption was the rate-limiting step and the adsorption process was dominated by irregular multilayer adsorption.Theoretical adsorption capacity of the four modified pericarps for MO was in order of LC@PEI-65(349.37 mg/g),LG@PEI-65(321.68 mg/g),LC@PEI-30(257.77 mg/g),LG@PEI-30(242.85 mg/g)from largest to smallest.Five times adsorption-desorption experiments proved that LC@PEI-65 has well reusability and stability.The adsorption of MO on PEI modified pericarps was a complex process,in which may including electrostatic interaction,intermolecular hydrogen bond,?-? dispersion interaction and pore filling.(3)After PEI modification at 65 ?,the adsorption of LC@PEI-65 was increased by 136.1% when compared to NLC.The adsorption of Cr(?)was best described by Elovich kinetic and Langmuir isotherm models.The adsorption capacity of six materials for Cr(?)removal was in the order of large to small: LC@PEI-65(156.82 mg/g),LG@PEI-65(142.74 mg/g),LC@PEI-30(122.95 mg/g),LG@PEI-30(110.97 mg/g),NLG(70.37 mg/g)and NLC(66.41 mg/g).The Cr(?)adsorption process was mainly heterogeneous and belong to molecular layer adsorption.The adsorption of Cr(?)by LC@PEI-65 was an endothermic entropy increase process that can be carried out spontaneously.The possible adsorption mechanism of Cr(?)on pericarp modified by PEI include electrostatic attraction,reduction reaction,surface complexation and porous physical adsorption.In conclusion,the PEI thermochemical modification process of lychee and longan pericarp has the advantages of simple steps,short time consumption and environmental protection.The modified pericarp materials can effectively remove MO and Cr(?)from wastewater.The whole process carried out the principle of "treating waste with waste" and realized the resource utilization of agricultural and forestry waste.