Preparation And Adsorption Properties Of Modified Cellulose Beads

In order to solve the problem of shortage of fossil resources,the development and utilization of renewable resources have attached great attention from governments around the world.Cellulose is an extremely rich natural resource on the earth.The annual global production of cellulose is up to trillion tons,far exceeding the existing oil reserves.It is inexpensive,biodegradable,renewable,and of good performance.In this paper,cellulose was used as the main raw material,and it was combined with cheap and readily available sepiolite,chitosan and magnetic nanoparticles to create cellulose composite beads with good adsorption properties through physical modification.In addition,the cellulose beads were chemically modified by β-cyclodextrin grafting reaction or 2,2,6,6-tetramethyl-1-piperidinyloxy(TEMPO)oxidized system.The adsorption capacity of malachite green,heavy metal ions,bisphenol A and organic dyes on modified cellulose beads were examined in turn,and various factors affecting the adsorption performance of the beads were discussed to determine the best adsorption conditions.The specific research work of this paper is as follows:(1)Using abundant naturally-occurring sepiolite and cellulose as raw materials,a physically modified cellulose bead capable of efficiently adsorbing malachite green(MG)was prepared.The morphology,structure,thermal stability,and adsorption performance of the composite beads were studied to evaluate their potential applications in removing organic dyes.The results showed that when sepiolite/cellulose mass ratio was 3:4,adsorption time was 4h,adsorption temperature was 30℃,solution pH was 7.0,and malachite green concentration was 400 mg/L,the maximum adsorption capacity of the sepiolite/cellulose composite beads to malachite green can reach up to 382 mg/g.The adsorption process fitted well with the Langmuir isotherm model and the pseudo-second-order kinetic model.Compared with the pure cellulose bead,the surface of composite beads exhibited more folded and rough structure and the thermal stability was improved.(2)Fe3O4 nanoparticles were carboxylated by citric acid(CA)to prepare Fe304@CA nanoparticles,which were combined with cellulose and chitosan to prepare a novel adsorbent for the adsorption of heavy metal ions.The effects of adsorbent dosage,pH value,time and solution concentration on the adsorption of heavy metal ions were investigated carefully.The results showed that the maximum adsorption capacity of chitosan/cellulose magnetic composite beads to Cu2+,Cd2+ and Pb2+ was 74.44 mg/g、40.38 mg/g、90.59 mg/g respectively,and the adsorption process fitted well with the Langmuir isotherm model and the pseudo-second-order kinetic model.(3)The β-cyclodextrin is grafted on the surface of cellulose beads under alkaline conditions.By utilizing the unique hydrophobic cavity ofβ-cyclodextrin,bisphenol A can form host-guest interaction with the modified cellulose bead to achieve high efficient adsorption.XRD,NMR,FE-SEM etc.analysis revealed that the cellulose and cyclodextrin were combined by the covalent bonds,and their thermal stability was slightly lower than that of pure cellulose.The adsorption process of bisphenol A was fitted to the Langmuir isotherm model and the pseudo-second-order kinetic model.And the maximum adsorption capacity of bisphenol A on the grafted cellulose bead can reached 30.77mg/g.After four adsorption/desorption cycles,the adsorption capacity could still maintain 20.96mg/g.(4)In the neutral TEMPO/NaClO/NaClO2 system,cellulose beads were chemically modified by a simple microwave-assisted oxidation reaction.Only 6 hours of oxidation time is required,and the carboxylate content can reach 1.28mmol/g.The resulting oxidized cellulose beads were characterized by scanning electron microscopy,solid state 13C-NMR spectroscopy and X-ray diffraction.Four organic dyes(rhodamine B,auramine O,malachite green,and methylene blue)were used as simulated contaminants to evaluate the adsorption characteristics of cellulose beads treated with microwave-assisted oxidation.The adsorption performance and kinetics,as well as the recyclability of oxidized cellulose beads,were investigated to verify that a cellulose-based adsorbent with high adsorption capacity and good recyclability had been successfully prepared.