| Cellulose is the most abundant biomass resource on earth,with the advantages of being degradable,renewable,non-toxic and cheaply available,and can replace petroleum-based resources to produce a variety of high value-added functional materials.Currently,the functionalization of cellulose fibers(CFs)using various nanostructures has become an important development trend.Among them,a new type of metal-organic framework(MOFs)is used to functionalize CFs to obtain new materials.On the one hand.MOFs endow CFs with many new functions(such as fluorescence,antibacterial,flame retardant,and photocatalysis).On the other hand,CFs provide suitable flexible substrates for full utilization of MOFs,and therefore have broad development value and application prospects.However,due to the drawbacks of CFs such as small specific surface area and few nucleation sites,the efficient insitu growth and anchorage of MOFs on CFs still faces great challenges.This paper breaks a new path,CFs are first made into porous regenerated cellulose hydrogel(RCH)using the "dissolution-regeneration" strategy,and then MOFs nanoparticles are in situ embedded,firmly anchored and uniformly distributed based on the "nano confinement" effect of the RCH pore channel.On this basis,five high-value cellulose-based bioplastics with UV-blocking function are obtained using hot pressing or natural drying processes.That is,using RCH and carboxymethyl cellulose hydrogel(CRCH)with high nanometer pores as substrates,MOFs as functional modification components,and using in-situ synthesis and hot pressing or natural drying combined processes to prepare regenerated cellulose-anchoraged MOFs functional bioplastics.The functional application and mechanism of their function in UV shielding is studied.The growth and immobilization mechanisms of MOFs on cellulose substrates and the influence mechanism of MOFs on the performance of new cellulose-based functional materials are explored,which provid scientific basis and research ideas for the in-depth development and comprehensive utilization of celluloseanchoraged MOFs functional materials.The paper mainly includes the following aspects:Regenerated cellulose hydrogels(RCH)with a nanoporous structure were prepared by dissolving cellulose fibres(filter paper)using a green solvent system-LiOH/urea aqueous solution.Using this RCH substrate,MIL-68(In)-NH2 nanoparticles were in situ embedded and anchored within its pores at room temperature,and then transparent MIL-68(In)NH2@cellulose bioplastic(M(In)CBP)was prepared by hot pressing MIL-68(In)-NH2@RCH.RCH has a large number of nanopores inside,and the surface of cellulose is rich hyroxyl group.The nanopore of RCH can be used as a " nanoreactor" of MIL-68(In)-NH2,and the hydroxyl group can be used as anchorage sites.The size of MIL-68(In)-NH2 is restricted within the"nano confinement" space of the RCH,resulting in the in situ growth and anchorage of small sized MIL-68(In)-NH2 within the RCH pore channel,suggesting that the "nano confinement"effect of the nanopores can effectively regulate the size of MIL-68(In)-NH2.Meanwhile,MIL68(In)-NH2 nanoparticles can be uniformly distributed in the cellulose matrix.MIL-68(In)-NH2 nanoparticles as a modified component endow the bioplastics with excellent UV shielding performance and as a reinforcing agent to improve the mechanical strength.In addition,the hot-pressed M(In)CBP exhibits high resistance to penetration by aqueous and non-aqueous liquids.Meanwhile,M(In)CBP still has excellent UV shielding ability after being in contact with the aqueous solution for 12 hours,which shows that the MIL-68(In)-NH2 nanoparticles are firmly anchored in the cellulose matrix.M(In)CBP has a single function,which may not be conducive to its application in more advanced fields.For example,harmful light also includes high-energy blue light,and cellulose materials have high flammability.To address these issues,MIL-125(Ti)-NH2 nanoparticles were in situ embedded and anchored in the pores of RCH at room temperature,and then the MIL-125(Ti)-NH2@cellulose composite bioplastic(M(Ti)CBP)was prepared by hot-press drying.The introduction of MIL-125(Ti)-NH2 nanoparticles gives M(Ti)CBP high-efficiency UV shielding performance.More importantly,it is found that when the deposition amount of MIL-125(Ti)-NH2 increases,M(Ti)CBP shows high-efficiency shielding against harmful blue light,and M(Ti)CBP still has good transparency.Meanwhile,it was found that MIL-125(Ti)NH2 can be used as a flame retardant and reinforcing agent,and the limiting oxygen index and mechanical strength of M(Ti)CBP were significantly increased.To address the low transparency and high haze of M(Ti)CBP and to further promote the firm anchorage of MIL-125(Ti)-NH2 in the cellulose matrix,carboxymethyl cellulose fibres were prepared by the reaction of cellulose fibers and sodium chloroacetate using sodium hydroxide as a catalyst,and CRCH were obtained after dissolution-regeneration.MIL-125(Ti)NH2@CRCH was prepared by in situ synthesis strategy using the nanopores of CRCH as"nanoreactor" and the carboxyl groups as anchor sites.Highly transparent,low haze multifunctional composite bioplastic(M(Ti)CCBP)was prepared by hot-press drying.On the one hand,the carboxymethylation modification greatly improves the transparency and reduces the haze of the bioplastic.M(Ti)CCBP has highly efficient UV and blue light shielding properties,while also exhibiting high transmittance(79%-92.8%)and low haze(2.6%-7.2%).On the other hand,the introduction of carboxyl groups improves the binding strength between MIL-125(Ti)-NH2 and cellulose.The incorporation of MIL-125(Ti)-NH2 improved the flame retardancy and mechanical strength of M(Ti)CCBP.In addition.the construction of CRCH provides a powerful platform for the preparation of highly transparent and low-haze functional composite materials.In response to the previous work involving the use of organic solvent DMF and high energy consumption due to hot pressing,highly transparent and low haze MIL-8 8A@carboxymethyl cellulose composite film(M(Fe)CCF)was prepared by in-situ synthesis and natural drying at room temperature using CRCH as the substrate and water/ethanol as the reaction solvent.The M(Fe)CCF exhibits excellent UV shielding ability,while the M(Fe)CCF has high transparency(81.5%-85.3%)and low haze(2.5%-4.9%).Moreover,M(Fe)CCF exhibits stable UV shielding performance under high temperature,UV irradiation,acidic or alkaline conditions,providing M(Fe)CCF with a long-term use capacity.Meanwhile,the UVshielding ability of the M(Fe)CCF do not decrease even after 30 days of immersion in aqueous solution,demonstrating the high stability of MIL-88A(Fe)and its strong anchoraged in the cellulose matrix.Due to the three MOFs used in the previous work are somewhat photocatalytic,this may risk the sacrifice of some inherent properties(e.g.physical,mechanical and chemical)during the long-term use of the composites.To address this issue,Cu-MOF@CRCH was obtained by in situ synthesis strategy using CRCH as the substrate and water as the reaction solvent under room temperature.Then,the transparent Cu-MOF@carboxymethyl cellulose composite bioplastic(Cu-CCBP)was prepared by hot-press drying.Due to Cu-MOF nanoparticles do not have photocatalytic effect under ultraviolet light or visible light,therefore,Cu-CCBP has high photostability and the UV shielding ability of Cu-CCBP can be maintained even after 12 h of continuous UV irradiation.Meanwhile,Cu-MOF as an antibacterial agent gives excellent antibacterial properties to Cu-CCBP. |
