Construction And Properties Of Bacterial Cellulose Hierarchical Nanocomposites

Bacterial cellulose（BC）is a natural three-dimensional nanomaterial secreted byAcetobacter xylinum.Even at the molecular level,BC is identical to plant-derived cellulose.However,BC has excellent mechanical properties,thermal stability,high crystallinity,high purity,low density,high specific surface area,excellent permeability,high porosity,and other characteristics.BC has unique advantages in the construction of hierarchical nanocomposites.In the increasingly mature environment of nanomaterials technology,how to make nanofibers with these characteristics play the most role in practical applications is a hot and difficult point in current research.In this paper,BC nanofibers were used as the main research unit.With the help of technologies such as wet-spinning and vacuum-assisted filtration,the structure construction of hierarchical nanocomposites was completed through the controllable assembly of nano-functional units and the design of their unit structures.The active role of BC nanofibers in energy conversion,storage,and sensors was investigated by digging deeper into the inherent physicochemical properties of materials.The main research contents include:（1）2,2,6,6-Tetramethylpiperidine-1-oxyl-oxide bacterial cellulose（TOBC）nanofiber filaments with ionic cable structure were prepared by blending wet-spinning,and an emerging nanofluidic transport platform for osmotic energy conversion was constructed.Through the addition of graphene oxide,one-dimensional nanochannels with high charge density and two-dimensional sub-nanoscale fluid channels were coupled.The osmotic energy conversion properties of natural TOBC nanofibers were improved,enabling fast ion migration and optimizing ion selectivity.Under a 50-fold concentration gradient,the power density of the TOBC/graphene oxide fibers-based osmotic energy conversion device is 0.35 W m^-2,the ion mobility is 0.94,and the energy conversion efficiency is 38%.It produces a high power density of 0.53 W m^-2 in artificial seawater and river water,and maintained a stable power density for 15 days.This research proposes a simple and scalable method to enhance the ionic conductivity,ionic selectivity,and power density of BC-based nanofluidic systems,thereby improving their osmotic energy conversion performance.Compared with membranes,the fibers with ionic cable structures are dimensionally stable and can be produced on a large scale,which is of great significance for the development of clean,abundant,and sustainable energy for mankind and modern society.（2）By integrating one-dimensional BC nanofibers and two-dimensional nanosheets（graphene oxide and layered double hydroxide）,negatively charged BC/graphene oxide membranes and positively charged BC/layered double hydroxide membranes were prepared by vacuum-assisted filtration.Both membranes contain nanofluidic channels for ion transport and a pair of oppositely charged membranes were combined into an ion osmotic generator for continuous output of osmotic energy.The coupling of one-dimensional bacterial nanofibers and two-dimensional nanosheets emerges as a novel strategy to construct nanocomposite membranes,which can significantly improve the output power density by balancing ion selectivity and permeability.For a pair of energy harvesting systems,superposed electrochemical potential difference and ionic flux were created by complementing the diffusion of oppositely charged ions,which achieved an output power density of up to 0.70 W m^-2 using artificial sea water and river water.This work demonstrates the practical feasibility and viability of ion-pair laminar membranes as essential platforms for high-performance osmotic power generators by combining nanoconfined coupling surface charge and size effect.For the first time,layered double hydroxide was demonstrated to be a suitable platform to study and exploit ion transport in nanofluids.（3）The TOBC nanofibers with excellent performance were combined with two-dimensional graphene oxide,and TOBC/graphene oxide suspension was aggregated into fibers by blending wet-spinning.The dispersion mechanism of TOBC on graphene oxide and the effect of the content of reduced graphene oxide on the fiber structure and electrochemical performance after fibers were reduced by hydriodic acid were investigated.The pseudo-capacitive substance polypyrrole was assembled on the surfaces of TOBC and graphene oxide by in-situ polymerization to form flexible,binder-free,high-performance fiber electrodes and all-solid-state fiber-based supercapacitors.The study shows that TOBC not only improves the electrolyte wettability of the electrode but also acts as a spacer for the self-stacking of graphene oxide.In addition,TOBC can also serve as an electrolyte storage site and shorten the ion transport distance.For the synergistic effect of three components,the all-solid-state fiber-based supercapacitor exhibits a high energy density of 8.8 m Wh cm^-3 at the power density of 49.2 m W cm^-3 and a high-power density(429.3m W cm^-3 at the energy density of 4.1 m Wh cm^-3),excellent cycling stability and bending resistance.It achieves an ideal combination of excellent electrochemical performance and good flexibility,which has application prospects in various portable,miniaturized,and wearable electronic devices.（4）Thermoplastic polyurethane was used as the elastomer,carbon nanotubes and graphene were selected as the conductive fillers,and TOBC nanofibers were used as the dispersant and binding agent.The subsequent flexible fiber strain sensors were prepared by multi-component blending wet-spinning.The research shows that the introduction of TOBC can effectively improve the interaction between the polymer matrix and the conductive fillers,and bear a part of the stress and the supporting force during the fiber-forming process,to form the porous structure,which can efficiently carry and transfer the tensile force.Under the synergistic effect of various components,the fiber strain sensor with a wide response range（0-230%）,high gauge factor values of 17.8（0-70%）,326.6（70-150%）and 1501.0（150-230%）,fast response time,and recovery time（≈100ms）and long-term cyclic stability（>10000 cycles）are prepared.In the fiber sensor,the ideal combination of excellent strain sensing performance and flexible wearable characteristics has been realized which will be of great significance in the field of weaving,lightweight,and foldable electronic devices.