Preparation Of Carboxymethylated Cellulose Nanofibiril Adsorbents And Their Cu²⁺adsorption Performance

Water is the source of life and maintains the running of the entire ecosystem on earth.Accompanying with the widespread use of heavy metals in modern society,heavy metal pollution poses increasing threats to the health of human and animals.As a newly-developed biomass adsorption materials,cellulose nanofibrils has emerged as a promising adsorption material for the treatment of heavy metal pollution in water due to its its environmental friendliness and unique physical and chemical characteristics?such as high specific surface area,short diffusion distance,and easy modification?.The application of cellulose naofibrils adsorption materials in the removal of heavy metal ions in water will protect human and animal's life and health,maintain the sustainable development of ecosystem as well as realize the green development strategy of our country.The introduction of active sites into nanocellulose by chemical modification is an important prerequisite for its application in the field of heavy metal pollution treatment.Nonetheless,previous methods for the chemical modification of nanocellulose have disadvantages of complex process and limited number of active sites.This dissertation proposes a two-in-one strategy to prepare CNFs with rich active sites in a facile procedure.Non-selective carboxymethylation along with homogenization is utilized to prepare CNFs with high carboxylate content.By adjusting the dosages of sodium hydroxide and chloroacetic acid,CMCNFs with a highest carboxyl content of 2.7 mmol/g is prepared.TEM and AFM characterizations proved that the shape,diameter and length of CMCNFs accord with the characteristics of CNFs.The adsorption performance of Cu²⁺ions by CMCNFs is then investigated systematically.The effects of p H,carboxylate content,and contact time on adsorption properties are discussed in detail.When the p H is 5.0,CMCNFs with carboxylate content of 2.7 mmol/g exhibit optimum adsorption for Cu²⁺in water.Langmuir adsorption isotherms fitting results show that the highest adsorption capacity of 115.3 mg/g is achieved by CMCNF-2.7.The adsorption dynamics fitting results indicate that the Cu²⁺adsorption kinetic by CMCNFs conforms to the secondary adsorption kinetics,suggesting the adsorption process is chemical adsorption.On the basis of SEM,XPS,AFM characterizations,the mechanism for the Cu²⁺adsorption of CMCNFs involves electrostatic attraction,ion exchange,and complexation.CMCNF-2.7 has the ability to reduce the concentration of Cu²⁺in wastewater to0.1 mg/L that is lower than the drinking water standard?0.5 mg/L?,showing its potential application in heavy metal removal from water.CNFs is usually applied in the treatment of heavy metal pollution in water systems in the form of hydrogels,aerogels and other structures,but the high adsorption capacity of these structures is incompatible with excellent mechanical properties.To overcome this challenge,we use spherical sodium alginate hydrogel beads?Ab?as carrier,CMCNFs are stably loaded on its surface by electrostatic attraction and hydrogen bonding interaction.Firstly,the mechanism for the formation of CAb is uncovered by a variety of characterizations such as ESEM and Na Cl solution penetration test.Secondly,the influence of p H and contact time on Cu²⁺adsorption performance of CAb is explored systematically.The adsorption capacity is as high as 221 mg/g.After that,on the basis of SEM and XPS analysis,Freundlich adsorption isotherm,pseudo-second-order adsorption kinetics,W-M intraparticle diffusion model as well as Elovich models,it is proved that the Cu²⁺adsorption by CAb is achieved by the synergism of physical and chemical adsorption process.The adsorption forces include electrostatic interaction,ion exchange,and complexation and,the kinetics conform to heterogeneous diffusion dynamics.Furthermore,the convenience and usability of CAb are verified by serials of characterizations,CAb possesses excellent compression strength,elasticity,structural stability and resilience.Finally,the result of simulated dynamic column adsorption experiment shows that the Cu²⁺wastewater with a concentration of 100 mg/L is purified to water containing only 0.16 mg/L Cu²⁺,which proves that CAb has the potential to convert Cu²⁺wastewater into drinking water.