Fabrication And Applications Of Cellulose-based Fluorescent Composite Materials

Based on natural renewable biomass, nanofibrillated cellulose(NFC) shows excellent properties including low density, high aspect ratio, high mechanical strength, highly ordered crystal structure, good biocompatibility and biodegradation, which can be a promising replacement for petroleum based polymers applied to transparent film, flexible electronics, biological medicine, tissue engineering and other fields. Currently, the preparation and surface modification of NFC has become one of the advanced and interested research focuses. Thus the extractin and preparation, controlled morphology and surface modification of NFC, as well as the construction of the novel cellulose-based nano-composites by grafting with functional materials become a new and crucial research subject. Herein, nano-cellulose was successfully prepared by the acid hydrolysis and high pressure homogenization from various biomasses, respectively. And then nanocellulose based fluorescent nano-composite materials were assembled after different surface modification process.1) NFC was prepared by acid hydrolysis using garlic skin, kelp, enteromorpha and hemp as source materials, and the morphological and structural change of the samples in the successive stages of the acid hydrolysis process compared with that of high pressure homogenization.The obtained NFC has fibrillar morphology with 10~50 nm in diameter and several micrometers in length. The aspect ratio was calculated to exceed 50. The NFC from garlic skin has high crystallinity of 74.2 %. The NFC extracted from acid hydrolysis has better thermal stability, while the NFC extracted from high pressure homogenization has larger aspect ratio. Finally, the surface carboxylation was performed using TEMPO as a catalyst with the primary oxidant such as hypochlorite to oxidize the hydroxyl groups on the surface of NFC.2) CDs were successfully prepared via one-step hydrothermal method by employing white melon juice(WMJ) as raw material. Then CDs grafting on NFC were carried out after TEMPO-oxidation of NFC to obtain the NFC/CDs composites. The photoluminescent CDs 4.5~5 nm in diameter and rich in function groups, showed strongest luminescence intensity when excited at 360 nm, and the maximum emission peaks located at 448 nm. CCK-8 cytotoxicity and bio-imaging test of hep G2 cells indicated that the CDs were nontoxic and biocompatible. The obtained NFC/CDs composites can be applied to Cu2+ detection and the porous structure of freeze-dried NFC/CDs promoted the dsorption, and the maximum detectable concentration was 1μM.3) An efficient epoxidation treatment was developed to enhance the activity of the UCNPs. The UCNPs after epoxidation reacted with NFC to form the nano-composite NFC/UCNPs. The assembled fluorescent NFC/UCNPs hybrid nanopaper obtained through the extrusion process showed the synergistic properties of transparency of NFC nanopaper and luminescence property of UCNPs. The transpareny and luminescent property under the 980 nm excitation of the nanopaper were mainly depended on the ratio of UCNPs to NFC. Of importance here is that, the interlaced heterogeneous network of NFC/UCNPs provided a benefit to the excellent photostability of fluorescent nanopaper.