Modification Of Nanocrystalline Cellulose And Its Absorption Behavior Of Heavy Metal Ions

With the rapid development of the economic society and industry,water pollution of heavy metal ions had become one of the most serious environmental problems facing the world.In the methods of removing heavy metal ions,adsorption method was found to be superior to other techniques in terms of flexibility and simplicity of design,initial cost,insensitivity to toxic pollutants and ease of operation.Conventional adsorbents are usually limited by the lack of selectivity and lower adsorption kinetics due to the limited surface area or active sites.In recent years,nanomaterials,due to their higher surface area and greater active sites for interaction with pollutants,are increasingly used in heavy metal ion removal.In this paper,nanocrystalline cellulose?NCC?,extracted from kraft pulp by acid hydrolysis,was firstly oxidized by sodium periodate to obtain dialdehyde nanocellulose?DANC?.Then,through the Schiff base reaction and nucleophilic replacement reaction,DANC was grafted with diethylenetriamine?DETA?and jing bark tannins respectively to get amino-functionalized nanocrystalline cellulose?ANCC?with free amino groups on the surface and tannin nanocrystalline cellulose composition?TNCC?.Finally,ANCC and TNCC were applied as adsorbents to adsorb the heavy metal ions Cu???,Pb???and Cr???.The adsorption isotherms and kinetics were investigated.Firstly,NCC was prepared by 64% of sulphuric acid hydrolysis of bleached hardwood kraft pulp?BHKP?.NCC was then oxidized by sodium periodate to yield DANC.Finally,DANC was grafted with DETA to obtain ANCC with free amino groups through Schiff base reaction.The influences of DETA dosage on yield,amino group content and Zeta potential of ANCC were investigated.With the increasing of DETA dosage,the amino content and Zeta potential of ANCC gradually increased.The properties of ANCC were characterized by FT-IR,element analysis,color reaction,TGA,XRD and AFM.It was further evidenced by FT-IR,element analysis,and ninhydrin color reaction that DANC was grafted with DETA successfully.TGA results showed that comparing with DANC,the thermal stability of ANCC was increased.XRD analysis proved that ANCC still kept crystal structure of cellulose-I.It was observed by AFM that NCC,DANC and ANCC were rodlike structure,and the particle size of DANC and ANCC were decreased comparing with NCC.Subsequently,ANCC was used as adsorbent to remove heavy metal ions Cu???,Pb???and Cr???in aqueous solutions,and the adsorption capacity,adsorption isotherms and kinetics were investigated.The results showed that the optimum adsorption p H of Cu???and Pb???is p H 6,while Cr???is pH 2.Under the testing metal ions concentration range,the adsorption capacity of ANCC increased with the increase of initial ions concentration of Cu???,Pb???and Cr???.The adsorption of Cu???,Pb???and Cr???by ANCC all followed the pseudo second order kinetics equation and Langmiur adsorption isotherm.The maximum adsorption capacity of ANCC on Cu???,Pb???and Cr???was 26.28 mg/g,28.89 mg/g and 38.39 mg/g,respectively.DANC was grafted with jing bark tannin to prepare TNCC through nucleophilic replacement reaction.The influences of reaction p H,jing bark tannins dosage and reaction time on tannin loading and tannin quality ratio of TNCC were investigated,Results showed that the optimal reaction pH value was about 4.5,and the tannin quality ratio in TNCC increased gradually with the increase of jing bark tannins dosage and reaction time.TNCC was characterized by color reaction,TGA,XRD and AFM.FeCl₃ color reaction proved the existence of active hydroxyl on TNCC.TGA analysis showed that comparing with DANC,the thermal stability of the TNCC was increased.XRD analysis proved that TNCC still kept crystal structure of cellulose-I,as NCC and DANC.It was observed by AFM that NCC,DANC and TNCC were all Rodlike structure.TNCC was applied as sorbent to remove heavy metal ions Cu???,Pb???and Cr???in aqueous solutions,and the adsorption capacity,adsorption kinetsc and isotherms were investigated.The results showed that the optimum adsorption p H of Cu???and Pb???is pH 6,while Cr???is pH 2.All the adsorption equilibrium could be achieved within 4 h.Under the testing metal ions concentration range,the adsorption capacity of TNCC increased with the increase of initial ions concentration of Cu???,Pb???and Cr???.It was found that the adsorption of Cu???,Pb???and Cr???by TNCC all followed the pseudo second order kinetics and Langmiur adsorption isotherm.The maximum adsorption capacity of TNCC on Cu???,Pb???and Cr???was 46.14 mg/g,49.53 mg/gand 101.442 mg/g,respectively.