Ag-doped ZnO Nanoparticles Synthesized By Using Nanocrystalline Cellulose As Template And Their Adsorption-Photocatalysis Mechanism

This paper was aimed to prepare ZnO-N-Ag nanocomposites by in-situ polymerization with precipitation method and heat treatment,including nanocrystalline cellulose?NCC?as template,zinc acetate as zinc resource and silver nitrate as reaction precursors.The samples were characterized by TEM,FE-SEM,EDS,XRD,BET,FT-IR,XPS and UV-Vis spectroscopy The effects of the weight ratios of Zn?Ac?₂?2H₂O to NCC powder and Zn?Ac?₂?2H₂O to silver nitrate on photocatalytic degradation efficiency of samples for?methylene blue?MB under light irradiation were dicussed.Besides,the photocatalytic reaction mechanism were fitted.On the basis of this,the obtained ZnO-N-Ag nanocomposites were applied to evaluate the photocatalytic degradation efficiency of formaldehyde gas.The influences of the initial concentrations of gaseous formaldehyde,lights and addition of ZnO-N-Ag composites on the photocatalytic degradation activity of ZnO-N-Ag composites were investigated.In addition,the photocatalytic reaction mechanism was preliminary established.In this study,the conclusions were summarized as follows:?1?ZnO/nanocrystalline cellulose?NCC?nanocomposites were synthesized via in-situ polymerization with precipitation method,in which NCC was as the template,and zinc acetate as zinc resource.The results of ZnO/NCC nanocomposites characterization showed that the formation and growth of ZnO crystallite was controlled obviously by the NCC due to the strong interaction between the NCC and ZnO nanoparticles.Meanwhile,ZnO nanoparticles were uniformly dispersed on the surface of NCC.As expected,ZnO/NCC nanocomposites exhibited higher photocatalytic degradation activity on MB than pure NCC,which could be caused by the synergistic effect between adsorption performance of the NCC and photocatalytic property of ZnO nanoparticles.Among all prepared ZnO/NCC nanocomposites,ZnO/NCC0.5nanocomposites exhibited the highest photocatalytic degradation efficiency after 90 min UV light irradiation.However,the content of Zn in nano-ZnO is higher than the content of Zn in ZnO/NCC nanocomposites,and the ZnO nanoparticles in ZnO/NCC nanocomposites were partly covered by NCC,resulting in the degradation rate of ZnO/NCC nanocomposites to MB was slightly lower than pure nano-ZnO.?2?ZnO-N nanomaterials were prepared by heat treatment of ZnO/NCC nanocomposites at550°C,and the optimal process conditions were obtained eventually.ZnO-N nanomaterials better retained the template effect of NCC,showing rod-like nanomaterials assembled from single ZnO nanoparticles,which significantly improved the agglomeration of pure ZnO.In addition,the smaller particle size of ZnO-N nanomaterials could facilitate the decrease of the recombination rate of the carrier.The photocatalytic activity of ZnO-N nanomaterials is generally higher than pure ZnO and commercial ZnO.Furthermore,the highest photocatalytic degradation rate of ZnO-N0.5 nanomaterials after 90 min UV light irradiation was 99.8%,which was due to the fact that ZnO-N0.5 nanomaterials were provided with smaller particle size and large specific surface area.Besides,stronger light absorption intensity is conducive to the improvement of the photocatalytic activity.?3?In the process of preparing ZnO-N-Ag nanocomposites via in-situ polymerization with precipitation method combined with heat treatment,in which silver nitrate was used as doping source.ZnO-N-Ag nanocomposites retained the template effect of NCC better,showing rod-like nanomaterials assembled from single ZnO nanoparticles.Meanwhile,spherical Ag⁰ nanoparticles were uniformly dispersed on the surface of NCC and ZnO nanoparticles.Compared with ZnO and ZnO-N0.5 nanomaterials,ZnO-N-Ag nanocomposites extended absorption in the visible-light region,which could be attributed to the charge transfer between the Ag3d state as well as to the ZnO nanoparticles conduction or valance bands,leading to the generation of electron-hole pairs and prolonged their lifetime,which enhanced the photocatalytic properties of ZnO-N-Ag nanocomposites.Meanwhile,the photocatalytic degradation rate of ZnO-N-Ag nanocomposites was higher than pure ZnO and ZnO-N0.5 nanomaterials.Furthermore,the highest photocatalytic degradation efficiency of ZnO-N-Ag1 nanocomposites after 120 min under visible light irradiation was 99.2%.?4?When the atmospheric conditions with a temperature of 15±3°C and a relative humidity of 55±5%,the prepared ZnO-N-Ag1 nanocomposites were successfully applied to evaluate the photocatalytic degradation activity of formaldehyde gas in self-made experimental device.when the addition of ZnO-N-Ag1 nanocomposites was 200mg and the initial concentration of gaseous formaldehyde is 32.83 mg/m³,the photocatalytic degradation efficiency of ZnO-N-Ag1 composite to gaseous formaldehyde after 18 h was 70.4%,which was better than40.5%under visible light.