Preparation And Application Of Cellulose Nanofibers From Wheat Straw

With the improvement of human quality of life,the problems of energy crisis and environmental pollution are becoming increasingly serious.The development of new environmentally friendly biomass materials and energy storage devices is imminent.Cellulose,as the most renewable and abundant natural biomass material,has the advantages of large specific surface area,excellent mechanical properties,high thermal stability and biodegradability,etc.As a by-product of wheat cultivation,wheat straw is an abundant agricultural residue with a high cellulose content among all crop straws.Its resourceful utilization contributes to alleviate the environmental problems caused by its incineration.In this paper,nanocellulose(CNF)was prepared using 2,2,6,6-tetramethylpiperidin-1-yloxy(TEMPO)oxidation to investigate the recycling of wheat straw to produce biomass materials.Its application in a new green energy storage device,supercapacitor was also studied.(1)The TEMPO oxidation was chosen to produce CNF from wheat straw.The morphology of CNF was characterized.The results showed that the diameter of CNF was about 5-10 nm.The FTIR results proved that the lignin and hemicellulose in the CNF were effectively removed without changing the structure of cellulose.The hydroxyl group at the C6 position of the cellulose was oxidized to carboxyl group.The Zeta potential of CNF suspension was-49.7 m V.The XRD results showed that the type I structure of cellulose was not changed during the preparation process.The crystallinity of WS,WS-1.4%and CNF were calculated as 48.5%,53.7%and 63.2%.The preparation of CNF from wheat straw is of great significance in the recycling of crops by-products.(2)The wheat straw was pretreated with Na OH solution under different reaction conditions.The experimental results showed that the carboxyl content of nanocellulose was optimal when the concentration of Na OH solution was 7 wt%.Then the pretreated wheat straw was oxidized by TEMPO to prepare CNF.The dosage of Na Cl O was 3.0,6.0 and 9.0(mmol/g pulp).The carboxyl content of the CNF was 0.73 mmol/g,0.95 mmol/g and 1.27mmol/g respectively.CNF-MWCNTs dispersions with different carboxyl content were prepared using the CNF and multiwalled carbon nanotubes(MWCNT).According to the formula calculation,the concentrations of multiwalled carbon nanotubes in the CNF-MWCNTs dispersions were 45.9 mg/L,94.7 mg/L and 137.2 mg/L.Finally,CNF-MWCNTs/CC electrode was constructed together with carbon cloth(CC).The electrochemical performance of electrodes with different carboxyl content was investigated through electrochemical tests.The results showed that the area specific capacitance of the electrode was significantly improved with the increase of carboxyl content.(3)A novel multi-walled carbon nanotube-modified nickel foam(NF)electrode was prepared using cellulose from wheat straw with different contents.The prepared CNF was used to facilitate the uniform dispersion of MWCNT and favor the formation of a stable CNF-MWCNTs membrane on the NF skeleton.The influence of dispersing materials and content of CNF on the electrochemical performance of electrodes was investigated.It was revealed that the incorporation of CNF can improve the electrochemical stability of electrodes was superior to that of chitosan adhesive electrode.Moreover,it also exhibited optimum capabilities(70.2%capacitance retention from 1 to 40 m A/cm~2)when CNF:MWCNT=1:0.7.The area specific capacitance of the CNF-MWCNT/NF electrode for a scanning rate of 5 m V/s was twice that of the MWCNT/NF electrode and 30 times that of the NF electrode.The low-cost biomass materials prepared have certain development and application potential in supercapacitors.It is of great significance in the synchronous development of green environment and energy.