Preparation And Properties Of Metal Nanoparticles Supported On Nanocellulose

Nanocellulose generally refers to cellulosic materials having at least one dimension in the nanometer range.Nanocellulose can be produced by chemical method?such as acid hydrolysis,enzymatic hydrolysis and oxidative method?and mechanical method?like grinding or highpressure homogenization?from different sources of biomass.Owing to its large surface area?150-250 m2/g?,excellent mechanical properties?Young's modulus of 100-140 GPa and tensile strength of 1.7 GPa?,controlled surface chemical modification and its biocompatible,and biodegradable properties,this green material has been used in various applications such as polymer reinforcement,antimicrobial and medical materials,green catalysts,etc.Through selective oxidation,carboxyl,aldehyde and other functional groups could be introduced on the surface of cellulose chain.This functional groups would be beneficial to strengthening the interactions between cellulose and inorganic metal ions,which could be be used for the preparation of metal nanoparticles supported on cellulose.In this study,two kinds of carboxylated nanocellulose?TO-CNC and AO-CNC?were prepared by using ultrasonic assisted 2,2,6,6-tetramethylpiperidinyl-1-oxy radical?TEMPO?oxidation and one-step ammonium persulfate?APS?oxidation,respectively.The effects of sodium hypochlorite?NaClO?and APS content on the yield,carboxyl content,degree of polymerization?DPv?and morphology of the oxidized cellulose in the two methods were studied.Furthermore,the differences of TO-CNC and AO-CNC were evaluated by Fourier transformed infrared spectra?FT-IR?,X-ray diffraction?XRD?and thermogravimetric analysis?TGA?.The results showed that with increase of oxidant content in the two methods,the carboxyl groups on the surfaces of TO-CNC and AO-CNC were both improved.However,a remarkable decline of the DPv of cellulose sample after oxidative treatment was inevitable.Nevertheless,even though AO-CNC showed a lower yield compared with TO-CNC,they exhibited a higher crystlibity and a better thermal stability.Dialdehyde nanocellulose?DNC?was prepared using sodium periodate as an oxidant from TO-CNC.Palladium nanoparticles/NC and gold nanoparticles/NC catalysts were synthesized by using DNC as reducing agent and template,respectively.The preparation conditions,chemical structure and crystal structure of catalysis were characterized by UV-vis?ultraviolet visible?spectra,FT-IR and XRD.In addition,the oxidation state and size of palladium and gold nanoparticles on the surface of cellulosic carrier were determined by X-ray photoelectron spectroscopy?XPS?and transmission electron microscopy?TEM?,respectively.Results showed that the higher the concentration of DNC,the smaller the average particle sizes of metal particles are.The average particle size of nano palladium obtained was 14 nm and the average particle size of nano gold was 40 nm.The catalytic performances of the gold nanoparticles/NC and palladium nanoparticles/NC catalysts were investigated by Suzuki coupling rection and the reduction of 4-nitropheol?4-NP?,respectively.It was found that the product yield of the Suzuki coupling reaction between aryl bromides and phenyl boronic acid can reach more than 90% when the reacting time was 1 h and the adding amount of catalysts was 0.1% mol.The fact suggested that palladium nanoparticles/NC had an efficient catalytic activity to the Suzuki coupling reaction.For the gold nanoparticles/NC catalysis,the conversion ratio of 4-NP could be up to 94% after reacting for 55 min,and the catalytic rate constant of catalysis in the reaction was calculated to be 0.073 min^-1.