Research On Performance And Mechanism Of Bamboo Cellulose-based Conductive And Adsorbent Materials

With the increasing shortage of global resources and the increasing environmental pollution,the research on converting sustainable lignocellulosic biomass into various high value-added products is a very important topic now.This research is supported by“National Key R&D Program of China(2017YFD0600804)”.In view of the low utilization rate,the single product category and the low added value of the product of moso bamboo,a preliminary study on the high-value conversion and utilization of bamboo cellulose has been carried out,and several new bamboo cellulose-based materials with energy storage and adsorption functions have been developed.The nanocellulose/graphene aerogel(CGA)was successfully synthesized by a one-step hydrothermal method.When the mass ratio of nanocellulose to graphene is 1:1,CGA supercapacitors with excellent electric double layer capacitance characteristics can be prepared by reacting at 180°C for2 hours.When the scan rate is 5 m V·s^-1,the CGA supercapacitor has an excellent specific capacitance of 125.5 F·g^-1,and its specific capacitance retention rate is as high as 98.3%,after 5000 cycles of charging and discharging.In CGA,nanocellulose can effectively prevent the aggregation between graphene sheets and form a stable 3D network structure with graphene sheets,which not only be well used as an electrolyte reservoir,but also provides an effective transmission path for ion diffusion during charging and discharging.The nanocellulose/graphene/Mn O₂aerogel(MCGA)was successfully prepared.The obtained MCGA_1:1:4shows the best electrochemical performance when the mass ratio of nanocellulose,graphene and Mn O₂is 1:1:4.When the scan rate is 5 m V·s^-1,the MCGA_1:1:4supercapacitor has a good specific capacitance of 212.73 F·g^-1,and its specific capacitance retention rate is as high as 86.5%,after 5000cycles of charging and discharging.In the MCGA electrode,the micron-scale network structure constructed by nanocellulose and graphene can continuously and stably transport electrolyte ions,and the introduction of metal oxide Mn O₂increases the specific surface area and specific capacitance of the electrode,so the capacitance performance and the cycle stability of the MCGA electrode has been improved at the same time.Nanocellulose/graphene oxide/sodium alginate aerogel beads(CGS)were synthesized to adsorb MB in wastewater.Among them,SA acts as a cross-linking agent in the ternary system,and combines with nanocellulose and graphene oxide through hydrogen bonds.Studies have shown that the adsorption capacity of CGS on MB reaches 588.24 mg·g^-1,because it has abundant active centers.The adsorption isotherm and adsorption kinetics of CGS on MB conform to the Langmuir isotherm model and the pseudo-second-order kinetic model respectively.Therefore,the adsorption process of CGS on MB is mainly a single-layer chemical adsorption.Carbon microspheres CM_APSwere quickly prepared by adding ammonium persulfate(APS)during the hydrothermal reaction of cellulose.Studies have shown that the addition of APS significantly speeds up the carbonization reaction process.When the hydrothermal reaction is carried out for 2 h,carbon microspheres with a yield of 23.79%and an average particle size of 5?m can be obtained.Compared with CM,the reaction time of CM_APSwas shortened by 10 h,the carboxyl content increased by 1.08mmol·g^-1,the oxygen content increased to 38.74%,and the particle size distribution was more concentrated.After adding APS in the hydrothermal reaction process,the hydroxyl radicals decomposed by APS can not only promote the formation of organic acids,but also catalyze the dehydration and polycondensation reactions of HMF.At the same time,the oxygen released by the hydrolysis of APS greatly increases the pressure in the reactor,accelerates the accumulation of carbon nuclei,and enables the rapid formation of carbon microspheres in a short time.CM_APSwas activated and carbonized by Zn Cl₂to obtain ACM_APS-Zn Cl₂.The specific surface area and pore volume of ACM_APS-Zn Cl₂are684.19 m²·g^-1and 0.3 m³·g^-1,respectively.The ACM_APS-Zn Cl₂is assembled into a supercapacitor,which has a specific capacitance of 152.73 F·g^-1at a scan rate of 5 m V·s^-1,and its specific capacitance retention rate reached 95.2%after 1000 cycles of charging and discharging.Carbon microspheres CM_APS+AAwere prepared by adding APS and a small amount of acrylic acid(AA)in the cellulose hydrothermal process.The addition of AA significantly increases the carboxyl groups of the carbon microspheres,which is beneficial to the adsorption performance of the carbon microspheres on MB.Studies have shown that p H 8 is the best p H value for the adsorption of MB by ACM_APS+AA.The initial concentration of MB,adsorption temperature and adsorption time are positively correlated with the MB adsorbed,and the amount of CM_APS+AAadded is negatively correlated with the MB adsorbed.The Langmuir isotherm model can accurately describe the adsorption process of ACM_APS+AAon MB,and its theoretical maximum adsorption capacity(Qmax)is as high as 892.86mg·g^-1at 45°C.The adsorption process of ACM_APS+AAon MB is more in line with the pseudo-second-order kinetic model,so the adsorption of MB by ACM_APS+AAis mainly chemical adsorption.