Fabrication And Properties Of Highly Ordered,Red-Emission Carbon Dots Hybridized Chitosan/Polyvinyl Alcohol Nanofibers

Chitosan(CS)is a product formed by the partial deacetylation of chitin and can be dissolved in acidic aqueous solutions,which in turn allows for simple aqueous solution processing.In recent years,chitosan has received much attention as an environmentally friendly piezoelectric material for applications in sensors and energy harvesting.As a new member of the carbon nanomaterial family,red-emitting carbon quantum dots(R-CQDs)have attracted increasing interest in biomedical and optoelectronic devices,due to their high photostability,low cytotoxicity,water dispersibility,excellent biocompatibility,and controllable biodegradability.Using chitin-derived chitosan,this study presents the first demonstration that luminous carbon quantum dots direct a large-scale preferred alignment of biocrystalline piezo-phase,thus significantly enhancing the piezoelectric properties of natural biopiezoelectric polymers.In this thesis,a R-CQDs hybridized chitosan/polyvinyl alcohol(CS/PVA)nanofiber with uniaxial orientation was prepared using an electrostatic spinning method.The combination of R-CQDs with the natural piezopolymer resulted in excellent fluorescence and piezoelectric properties for the elecrospun hybrid bionanofibers.The CQDs/CS/PVA nanofibers were systematically studied in terms of fiber morphology,crystalline structure,fluorescence properties,piezoelectric properties,device assembly,and device applications.The main conclusions are drawn as follows.1.Highly ordered electropsun CQDs/CS/PVA hybrid nanofibers can be obtained with proper spinning speed,working voltage,receiving distance,receiving mode and R-CQDs content.In particualr,a very small,yet moderate amount of R-CQDs allows for a highly preferential alignment of CQDs/CS/PVA nanofibers and a highly preferential alignment of internal chitosan piezo-phase crystalline lamellae.Meanwhile,the CQDs/CS/PVA nanofibers maintain the very valuable long-wavelength photoluminescence response of the encapsulated,monodispersed R-CQDs.The piezoelectric voltage output and piezoelectric current output of hybrid bionanofibers reach up to 125 V/cm~3 and 1.5μA/cm~3,respectively.Notably,they are more than 5 and 6 times higher than those of pristine ones,respectively.The remarkable improvement of piezoelectric output should be ascribed to the R-CQDs-directed preferential microscopic piezo-phase alignment and preferential macroscopic nanofiber alignment.2.The proof-of-concept piezoelectric nanogenerator(PNG)based on the red-emission bionanofibers shows a highly durable,highly stable,and highly reproducible piezoresponse in over 10 000 uninterrupted load cycles.As a more reliable renewable energy source,the bio-PNG device is capable of charging external capacitors within a very short period of time.Also,it instantly operates commercial light emitting diodes without using any external storage units.Especially,the mechanically flexible,shape adaptable,highly reproducible,and red emissive biodevice is further used as a self-sustainable wearable tactile healthcare sensor.It attains ultrahigh mechanosensitivity in sensing a broad range of biophysiological pressures and strains,meeting the practical requirements of transient optoelectronics.