Chunlin Zhu

Flexible cathodes and multifunctional interlayers based on carbonized bacterial cellulose for high-performance lithium-sulfur batteries

A three-dimensional (3D) carbonaceous aerogel derived from sustainable bacterial cellulose (BC) is introduced as a flexible framework for sulfur in lithium–sulfur batteries. The 3D carbonized BC (CBC) with highly interconnected nanofibrous structure exhibits good electrical conductivity and mechanical stability. The intrinsic macroporous structure of CBC contributes to a high sulfur loading of 81 wt%. Microstructure and morphology characterization results demonstrate that the sulfur species wrapped around CBC nanofibers are well dispersed. Even at such a high loading, the S/CBC composite still contains sufficient free space to accommodate the volume expansion of sulfur during lithiation. Furthermore, with an ultralight CBC interlayer inserted between the sulfur cathode and separator, significant improvement is achieved in active material utilization, cycling stability, and coulombic efficiency. The CBC interlayer can provide an extra conductive framework and adsorb migrating polysulfides to a certain degree. The CBC interlayer can also act as an additional collector for sulfur and thus could prevent the over-aggregation of insulated sulfur on the cathode surface. The good electrochemical performance reported in this work can be ascribed to the flexible 3D-interconnected nanostructure of the carbon framework and the rational design of battery configuration.

Recent progress in 2D or 3D N-doped graphene synthesis and the characterizations, properties, and modulations of N species

Nitrogen (N)-doped graphene (N-substituted or nitrogenated graphene) (NG) has become a new class of graphene material due to its modified properties such as the tunable work function, n-type semiconductivity, increasing biocompatibility, and, in particular, the synergistic function with various functional materials. However, the preparation of NG by a simple and effective method is still lacking. The modification of NG mainly depends on the N species and the N content. Thus, we focus on the recent progress in preparing methods of 2D NG and the respective key modulating parameters to modulate the N species and the N content. Furthermore, many effective charactering techniques are covered to accurately analyze the properties of N species, and the distribution and topography of N atoms. Also, we review the effect of N species on graphene, especially, the optical and electronic properties. Since constructing 3D structure is considered a promising strategy to prevent the restacking of 2D NG, the summary for preparing 3D NG is made on the basis of methodology of 2D NG. In a word, this review provides a reference for preparing 2D or 3D NG, modulating and characterizing N species, which are greatly contributed to the NG application.

Three-Dimensional BC/PEDOT Composite Nanofibers with High Performance for Electrode-Cell Interface.

There is an increasing need to synthesize biocompatible nanofibers with excellent mechanical and electrical performance for electrochemical and biomedical applications. Here we report a facile approach to prepare electroactive and flexible 3D nanostructured biomaterials with high performance based on bacterial cellulose (BC) nanofibers. Our approach can coat BC nanofibers with poly(3,4-ethylenedioxythiophene) (PEDOT) by in situ interfacial polymerization in a controllable manner. The PEDOT coating thickness is adjustable by the monomer concentration or reaction time during polymerization, producing nanofibers with a total diameter ranging from 30 to 200 nm. This fabrication process also provides a convenient method to tune different parameters such as the average pore size and electrical conductivity on the demands of actual applications. Our experiments have demonstrated that the 3D BC/PEDOT nanofibers exhibit high specific surface area, excellent mechanical properties, electroactive stability, and low cell cytotoxicity. With electrical stimulation, calcium imaging of PC12 neural cells on BC/PEDOT nanofibers has revealed a significant increase in the percentage of cells with higher action potentials, suggesting an enhanced capacitance effect of charge injection. As an attractive solution to the challenge of designing better electrode-cell interfaces, 3D BC/PEDOT nanofibers promise many important applications such as biosensing devices, smart drug delivery systems, and implantable electrodes for tissue engineering.

Biointerface by Cell Growth on Graphene Oxide Doped Bacterial Cellulose/Poly(3,4-ethylenedioxythiophene) Nanofibers

Highly biocompatible advanced materials with excellent electroactivity are increasingly meaningful to biointerfaces and the development of biomedicine. Herein, bacterial cellulose/poly(3,4-ethylene dioxythiophene)/graphene oxide (BC/PEDOT/GO) composite nanofibers were synthesized through the in situ interfacial polymerization of PEDOT with the doping of GO. The abundant free carboxyl and hydroxy groups offer the BC/PEDOT/GO film active functional groups for surface modification. We demonstrate the use of this composite nanofiber for the electrical stimulation of PC12 neural cells as this resultant nanofiber scaffold could closely mimic the structure of the native extracellular matrix (ECM) with a promoting cell orientation and differentiation after electrical stimulation of PC12 cells. It is expected that this biocompatible BC/PEDOT/GO material will find potential applications in biological and regenerative medicine.

Novel Cu@SiO2/bacterial cellulose nanofibers: Preparation and excellent performance in antibacterial activity.

The antibacterial composite based on bacterial cellulose (BC) was successfully prepared by in-situ synthesis of SiO2 coated Cu nanoparticles (Cu@SiO2/BC) and its properties were characterized. Its chemical structures and morphologies were evaluated by Fourier transformation infrared spectrum (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results demonstrated that the SiO2 coated Cu particles were well homogeneously precipitated on the surface of BC. The Cu@SiO2/BC was more resistant to oxidation than the Cu nanoparticles impregnated into BC (Cu/BC) and then Cu@SiO2/BC could prolong the antimicrobial activity against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli).

Synthesis and characterization of hydroxypropyl cellulose from bacterial cellulose

Bacterial cellulose produced by Acetobacter xylinum has been reacted with propyleneoxide to synthesize hydroxypropyl cellulose (HPC) under different reaction conditions while diluted by toluene. The effects of mass ratio of bacterial cellulose to propyleneoxide, dilutability of toluene, reaction temperature (T) and time (t) were investigated by series of experiments. The degree of substitution (DS), hydroxypropyl content (A) and yield (η) were compared. The optimized product exhibited cold-water solubility and hot-water gelatinization in aqueous medium. Further study was carried out with FTIR, TGA, XRD, SEM and 13C-NMR for characterization. The water/air contact angle measurement reveals that it is a good hydrophobic material with good mechanical properties.

Modified PEDOT by benign preparing N-doped reduced graphene oxide as potential bio-electrode coating material

We have successfully prepared poly (3,4-ethylenedioxythiophene) (PEDOT)/N-doped reduced graphene oxide (N-rGO) by electrodeposition, post-reduction, and doping N atoms with a microorganism (as a green reagent) to modify PEDOT and resolve the exfoliation and fragmentation problems of pristine PEDOT. This modification greatly improves the electrochemical properties of PEDOT, showing great potential for a bio-electrode coating material, which should have excellent electrochemical properties, stability and biocompatibility. The as-prepared PEDOT/N-rGO shows lower impedance, and higher capacitive performance and cyclical stability than pristine PEDOT due to the doping of N-rGO. An MTT assay demonstrates this modified PEDOT has good adhesion, cell viability and proliferation, similar to pristine PEDOT. This indicates that the modification process does not restrain the good biocompatibility of pristine PEDOT, which results from the doping of highly biocompatible N-rGO by this green method. The wrinkled structure, residual oxygen containing functional groups and dopant N atoms of N-rGO lead to the formation of a fluctuating surface and an increase in the hydrophilicity of PEDOT, which increase the specific surface area and cell adhesion in cell culture, respectively. Consequently, this modified PEDOT improves the electrochemical properties, and resolves the exfoliation and fragmentation problems of pristine PEDOT, while still retaining the high biocompatibility of pristine PEDOT, which is promising for a bio-electrode coating material.

Novel Nitrocellulose Made from Bacterial Cellulose

Nitrocellulose (NC) is useful in several industrial segments, especially in the production of gun, rocket, and missile propellants. The conventional way to prepare NC is done through the nitration of plant cellulose with nitric acid. In this work, bacterial cellulose nitrate (NBC) is synthesized by bacterial cellulose (BC) and nitro-sulfric acid under heterogeneous conditions. NBC with the degree of substitution (DS) of 1–2.85 was obtained, and the effects of sulfuric to nitric ratio, reaction temperature, and reaction time on the value of DS of NBC are discussed. The samples are also characterized by elemental analysis, thermal analysis, Fourier transform infrared (FT-IR) spectroscopy, and X-ray diffraction.

Biosynthesis approach to nitrogen doped graphene by denitrifying bacteria CFMI-1

Here we present a novel approach to prepare N-doped graphene under ambient conditions by denitrifying bacteria CFMI-1. The N element can be effectively introduced into graphene and 8.2% (atom %) N doping level can be achieved. N-doped graphene possesses a size around 300–600 nm and an average thickness of 1–2 nm.

Microbial oxidation of graphite by Acidithiobacillus ferrooxidans CFMI-1

Graphite oxide was prepared by a simple and environmentally-friendly bio-oxidation strategy using Acidithiobacillus ferrooxidans CFMI-1 bacteria. The obtained graphite oxide nanosheets have a few layers with 1.5–1.7 nm (about 3–4 layers of sheets) height and 150–900 nm size.