Regulation Of Ion Transport Properties And Applications Of Bacterial Cellulose Based Membranes/Gels

There are many ion transport and their regulatory processes in biological systems,including plants,animals and humans,especially energy harvesting systems based on ion transport.Ion transport mobility and selectivity are determinants in such systems,so scientists often adapt materials and/or devices to meet different application needs by changing their multiscale structure.Bacterial cellulose（BC）has attracted widespread attention for its high purity,high crystallinity,high aspect ratio and its excellent properties.And BC nanofibers are composed of hierarchical structures,namely nanofiber scale,nanofibril scale and molecular chain scale.Due to its hierarchical structure,abundant modifiable surface functional groups,and sustainability,BC-based materials are considered to be a promising ion transport regulation platform.However,how to achieve efficient ion transport and develop new applications of BC hierarchical structure through structural design has become a hot spot and difficult point in current research.In this paper,BC is the main research object,and the design and optimization of BC hierarchical structure are realized by surface modification,in situ culture and network recombination,and BC membrane and gel materials with excellent ion regulation ability with adjustable surface electrical properties and ion channels are prepared,and they are applied to the fields of osmotic energy conversion and thermoelectric conversion.The main research contents include:（1）Based on the weak charge density on the surface of BC and the weak ability of BC to regulate ion transport due to the disordered distribution of BC nanofibers.Positive and negative charged BC films with high charge density and narrow BC nanochannels were obtained by etherification process and 2,2,6,6-tetramethylpiperidine-1-oxyl（TEMPO）mediated oxidation method and combined with physical mechanical stretching,respectively.And the surface charge densities were 3.13 m C m^-2 and?2.66 m C m^-2,respectively,so as to realize the selective transport process of ions in the positively and negatively charged BC films.It is further applied to the osmotic energy conversion,and under the concentration gradient of simulated seawater（0.5 M Na Cl）/river water（0.01 M Na Cl）,the power density of the osmotic energy conversion device based on the positively and negatively charged BC film is 0.23 W m^-2,the ion mobility is 0.83,and the energy conversion efficiency is 32%.In this work,BC film is applied to osmotic energy conversion for the first time,and the transport behavior of ions in BC film is preliminarily established,which lays a foundation for subsequent research.（2）To further improve the osmotic energy conversion capacity of BC membrane, negatively charged carboxymethylcellulose BC composite membrane（BC-CMC）and positively charged quaternated chitosan BC composite membrane（BC-HACC）with adjustable charge density and nanochannels were prepared by in situ culture.Based on the continuous process of BC nanofibrils secretion by Xylenacetobacter,a continuous BC nanochannel structure with high charge density was successfully constructed,and its surface charge and nanochannel structure could be adjusted by the adhesion amount of CMC or HACC on the surface of BC nanofibrils,thereby improving the permeability conversion ability of BC composite film.When BC-CMC membrane and BC-HACC membrane are applied to osmotic energy harvesting device,the output power density based on BC-CMC composite membrane and BC-HACC membrane can reach 2.25 W m^-2 and 0.42W m^-2,respectively,and the highest energy conversion efficiency can reach 35.9%.A further 15-cell BC permeation energy converter device is connected in series with an output voltage of up to2.53V to directly power electronic devices.This work highlights the advantages of large-scale preparation by biosynthesis,which can simultaneously adjust the surface properties and nanochannel size of BC to regulate ion transport behavior.（3）Based on the problem that electrolyte ions are difficult to penetrate into BC molecular chains,BC hydrogels（Ca BC）with Ca²⁺synergistic coordination were prepared by in situ culture using calcium gluconate as a carbon source.The molecular simulation results showed that the presence of Ca²⁺destroyed the accumulation of cellulose chains,increasing the interchain distance of BC molecules from 0.51 nm BC to 0.97 nm of Ca BC,which was conducive to ion diffusion into the sub-nanoscale channel composed of its molecular chain.When the Na Cl（1 M）solution is immersed,the ratio of the ionic diffusion coefficient between Cl^-and Na⁺increases from 1.21 BC to 1.52 Ca BC.Ca BC/Na Cl hydrogels were applied to ionic thermal supercapacitors to obtain a Seebeck coefficient of–27.6 m V K^-1 ion and an ionic conductivity of 204.2 m S cm^-1.This work expands the practical application of nanochannel-based materials in thermoelectric conversion,and provides a new option for the preparation of materials with high ionic conductivity and high Seebeck coefficient.（4）Deep eutectic solvent is introduced to destroy the strong hydrogen bond between BC nanofibers,BC/PAM composite gel is prepared by macromolecular network recombination,and thermogen cells for thermoelectric conversion are constructed by introducing redox system.In the structure of BC nanofiber-macromolecular composite network,BC nanofibers act as"ion high-speed transport pathway"in which effectively reduce the resistance of the gel electrolyte and improve the ionic conductivity of the composite gel.Furthermore,by optimizing the content of guanidine hydrochloride in the system,a high-performance ionic thermoelectric conversion gel with a Seebeck coefficient of 3.84 m V K^-1,an ionic conductivity of 108.5 m S cm^-1,and a specific output power density of 1761.7μW m^-2K^-2 was obtained.This work provides a new method for attenuating hydrogen bonding between BCs,which is expected to play a role in sustainable green energy and self-powered wearable electronics.