Studies On Preparations And Properties Of Pomelo Peel Microcrystalline Cellulose Based Heavy Metal Adsorbents Synthesized Through ATRP

With the acceleration of modern urbanization,environmental issues have been received serious attentions.Heavy metal pollution is one of the most harmful water pollution problems.Heavy metals are highly toxic,easily enriched by organisms,and are less susceptible to degradation than organic pollutants.After diffusion and transfer,they can slowly accumulate into the human body through the food chain,causing devastating effects on human health.Therefore,heavy metal pollution has become a prominent problem of environmental protection.Biosorption has many advantages in this area,including better adsorption effect,lower implementation cost and higher selectivity etc,which make biosorption a wide application prospect.In this work,the cellulose in the pomelo peel was separated and extracted by a chemical separation technique.The influences of NaOH concentration,H₂O₂ concentration,reaction temperature and reaction time on the cellulosic yield were studied.Response Surface Methodology（RSM）was used to design a three-factor and three-level experimental scheme and the optimum extraction process was obtained by regression equation analysis.The surface morphology,chemical structure and crystallinity of the cellulose were characterized by SEM,FT-IR and XRD.It was proved that the cellulosic yield reached the highest when NaOH concentration,H₂O₂ concentration,reaction temperature and reaction time were 8%,8%,30℃and 120 min,respectively.The optimum conditions of cellulose extraction were as follows by RSM:NaOH concentration was 8%,reaction temperature was 34°C,reaction time was 124min,and the experimental result was 62.06%.FT-IR and XRD further identified that the cellulose was the main content of the sample from the functional group,structure and crystal type.The results of SEM showed that the long chain of pomelo peel cellulose was not destroyed,and its surface was smooth.Pomelo peel microcrystalline cellulose was prepared by acidolysis of pomelo peel cellulose.Glycidyl methacrylate（GMA）was grafted onto the surface of microcrystalline cellulose by Atom Transfer Radical Polymerization（ATRP）and amino groups were introduced into the surfaces by ring-opening polymerization.The effects of grafting time on the grafting yield and aminization time on the adsorption of Cu（II）were studied and characterized by SEM,FT-IR and XPS.This work proved that the optimum reaction time of ATRP is 2.5h and the optimum aminization reaction time is 64h.The surface morphology,functional groups,elements and chemical bonds of pomelo peel microcrystalline cellulose were characterized by SEM,FT-IR and XPS.It was further proved that GMA were successfully grafted onto the surface by ATRP and amino groups were successfully introduced,thus providing a large number of sites for the adsorption of Cu（II）.The adsorption behaviors including adsorption kinetics,isotherms,pH effect and ATRP reaction time effect were investigated.This work proved that the adsorption equilibrium of Cu（II）and Pb（II）was achieved within 7h and 3h on the PGMA-grafted pomelo peel cellulose.According to the Langmuir fitting,the maximum adsorption capacities of Cu（II）and Pb（II）on the aminated adsorbent were 2.52mmol/g and 1.46mmol/g,respectively,higher than many adsorbents reported in the literature.When the solution pH is 2.5³,the aminated adsorbent had almost no adsorption capacity for Cu（II）and Pb（II）.Then the adsorption capacities both increased with the increasing solution pH.When the solution pH is more than 5.5,hydroxide precipitation will be formed,so the optimal pH value is 5⁵.5.The adsorption capacity of aminated adsorbent increased rapidly with the reaction time of ATRP and reached equilibrium at 2.5h.