Preparation And Application Of Nanocellulose/Au NPs Nanocomposites

Noble metal nanoparticles have played an important role in a range of applications,such as biological detection,biosensing,and surface enhanced Raman spectroscopy,due to their particular optical,electric,magnetic,or catalytic properties.However,noble metal nanoparticles are generally unstable due to their large active surface areas which may result in self-aggregation.Thus,they are usually encapsulated in polymers and mesoporous matrices,or supported on supporting materials such as graphene oxide,silica oxides etc.As the emphasis of science and technology is gradually shifting towards environmentally friendly and sustainable resources and processes,natural polymer are thought to be one of the best supporting material for the fabrication of inorganic-organic nanohybrids.Nanocellulose,derived from natural cellulose fibers,have been applied as template material、optical material and biomedical material,owing to their unique properties:high specific surface area,outstanding mechanical property,controllable size,easy surface-functionalization properties.Using nanocellulose as a supporting material for noble metal nanoparticles can improve the dispersion of the NPs,and a better-performing nanohybrid matieral is obtained.In this paper,Carboxylated nanocellulose were prepared from cotton pulp by three different methods:TO-NCC:TEMPO-mediated oxidation of nanocrystalline cellulose（which are obtained by sulfuric acid hydrolysis）;AO-NCC:Ammonium persulfate oxidation of cotton pulp;TO-NFC:TEMPO-mediated oxidation-homogenization treatment of cotton pulp.The morphological structure,particle size,crystallinity,chemical structure,thermal stability,and the carboxyl content of nanocellulose were characterized.Thiolate ligand glutathione functionalized fluorescent gold nanoparticles（GSH-AuNPs）which can fluoresce at wavelengths at 630 nm was obtained,and the particle size was 2-3 nm.Two different nanohybrids of nanocellulose and GSH-AuNPs was studied.All the relative studies are outline as follows:（1）visual colorimetric detection of Hg²⁺based on a flexible fluorescent nanofibrillated cellulose（NFC）membrane was prepared for the first time.It is a simple and effective approach,in which GSH-AuNPs were homogeneous-dispersed immobilized both inside and on the surface of fibrous NFC membrane,and the resulting composite membrane were shown to retain the fluorescence properties of GSH-AuNPs and exhibit intensive red fluorescence under the excitation of UV light,being cogent criteria for the production of a visual colorimetric sensor.By utilizing the high-affinity metallophilic and high specific of Hg²⁺-Au⁺interactions,the fluorescence can be effectively quenched,the results indicated that the composite membrane also exhibit good sensitivity towards Hg²⁺,which might be benefit from the large specific surface area of NFC fibrous membrane made of micro-sized fibers.The excellent selectivity of the composite membrane towards detecting Hg²⁺over other environmentally relevant metal ions has been analyzed by its response to other common toxic metal interferences in water.With the outstanding performance of the composite membrane being determined,including green and environmental protection,high stability and selectivity,good sensibility,naked-eye detection,the proposed method could be taken into consideration for the visual detection of Hg2+in aqueous solutions without complicated and time-consuming or other costly labeled probe preparation processes,setting a new trend in membrane-based sensor systems.（2）For the potential practical applications as AuNPs carriers for the fluorescent detection of drug release process,the sulfydryl-modified NCC was successfully designed to react with GSH-AuNPs.The successful modifications of NCC and NCC/GSH-AuNPs composites were detected by FTIR and TEM.