Construction Of Metal Catalysts Supported On Chitin Microspheres And Its Efficient Gas Phase Catalysis

With the increasingly serious environmental pollution and the continuous consumption of non-renewable fossil fuels,the development and utilization of renewable biomass resources to manufacture environment-friendly materials becomes more urgent than ever.Chitin,a renewable and abundant natural polymer,is widely found in crustaceans,fungi,algae,etc.It is composed of various with showing excellent biodegradability,making it as an ideal raw material for building novel functional materials.Additionally,the hydroxyl and acetylamino groups on the chitins molecular chain can interact with many metal nanoparticles.Therefore,chitin polymers as a support material for metal and anionic particles has broad application prospects in the area of water treatment,"green"catalysis,gas adsorption,etc.It is well known that air pollution,one of the serious problems in big cities,is threatening seriously harms human’s life and health.Therefore,it is pressing to search for a simple and“green”material which can be use to effectively reduce the gas pollutants.This paper presents an innovative approach to treat gaseous pollutants by using chitin-loaded metal catalysts.It is conducive to the purification of atmospheric pollutions while conserving resources and compliance with“green”chemistry and sustainable developments strategy.In this work,based on the chitin dissolved in NaOH/urea aqueous solution at low temperature,chitin microspheres containing nanofiber structure were prepared by an emulsion method,and the abundant hydroxyl and acetamide groups in the chitin chain were used to immobilize effectively the metal catalysts.The structure and properties of these composite materials were characterized by scanning electron microscope（SEM）,transmission electron microscope（TEM）,Fourier transform infrared VI spectroscopy（FT-IR）,wide angle X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,nitrogen adsorption,etc.The correlation between structures and properties of composite was also studied.Furthermore,the application prospect in the field of gas purification were evaluated.The main innovations of this work are as follows.（1）A series of chitin/metal catalyst composite microspheres with nanofiber structure were successfully constructed,and the metal nanoparticles catalysts were uniformly dispersed on the surface microspheres,which effectively improved the efficiency of gas phase reaction with the metal catalyst.（2）Pd/TiO₂@carbon nanofiber microspheres were prepared for the first time by emulsification,thermal induction and carbonization,processes and was proved that it exhibited excellent catalytic activity in catalytic degradation of volatile organic compounds.（3）A stable Ru@chitin catalyst was successfully made,which indicated excellent catalytic activity for the oxidation reaction of carbon monoxide.The main contents and conclusions of this thesis are summarized below.The NaOH/urea aqueous solution was used to dissolve chitin at low temperature,and the chitin microspheres with nanofiber structures were constructed by the method thermal induction.Based on the large surface area and abundant functional groups of the chitin microspheres,highly dispersed TiO₂ nanoparticles and metal cocatalyst were steadily immobilized on the microspheres.The results of SEM and nitrogen adsorption indicated that the TiO₂ nanoparticles（in the average diameter 15 nm）of chitin/titanium dioxide composite microspheres（TNCM）were evenly dispersed on the nanofibers.It was found that multilevel pore structure and interconnected 3D network architecture was beneficial to the diffusion and adsorption of volatile organic compounds.The results of photocatalytic degradation of volatile benzene and toluene showed that the metal cocatalyst can improve the photocatalytic degradation efficiency of the TiO₂catalyst,and the catalytic activity of different metal cocatalyst indicated that chitin/titanium dioxide/palladium composite microspheres（Pd TNCM）had the highest catalytic degradation efficiency.TiO₂/nanofibrous microspheres were constructed from chitin/NaOH/urea aqueous solution by blending with TiO₂ through emulsification and thermal induction method.Then,the TiO₂/chitin microspheres were carbonized and followed by immobilizing Pd nanoparticles to obtain Pd/TiO₂@carbon microspheres（PCTNCM）.The examination of TEM indicated that the composite microspheres were composed of carbon nanofibers.The TiO₂ nanoparticles with mean size of 15 nm and ultra-small Pd nanoparticles with mean size of 1 nm were well immobilized and distributed.The SEM,FT-IR,TG and XRD results showed the strong physical interaction between the metal nanoparticles and the carbon nanofibers,which was beneficial to the fixation and uniform distribution of the metal nanoparticles.Multilevel pores and interconnected 3D network architecture of PCTNCM provided a large number of active sites for the metal catalyst TiO₂,and the Pd nanoparticles as cocatalyst can further improve the efficiency of TiO₂catalytic degradation of volatile organic compounds.The Pd/TiO₂@carbon microspheres were used for the gas phase photodegradation of VOCs.The study demonstrated that the conversion of toluene and benzene to CO₂ and H₂O reached 96.4%and 91.7%,respectively,which was higher than that reported.Moreover,the Pd/TiO₂@carbon microspheres could be recycled and reused afterwards.This work provided a new approach to eliminate VOCs,which would contribute to a cleaner and a sustainable world.Ru@carbon nanofibrous microspheres（CRNCM）with multilevel pores and interconnected 3D network structure were constructed by immobilizing Ru nanoparticles on the chitin microspheres,followed by the treatment of carbonizing.High resolution transmission electron microscopy（HRTEM）results showed the ruthenium nanoparticles had a narrow size distribution,and the average diameter was1.5 nm.Meanwhile,scanning transmission electron microscope（HAADF）proved the presence of highly dispersed ruthenium nanoparticles in the microspheres.The results of FT-IR,TG and XRD indicated that strong physical interaction between the metal nanoparticles and the carbon nanofibers,which was beneficial to the fixation and uniform distribution of the metal nanoparticles,as well as the catalytic activity.The composite catalyst was used for the CO oxidation reaction,and the test showed that CRNCM has excellent activity and stability.A series of chitin/metal composite microspheres as catalysts were constructed,and the formation mechanism of nanocatalysts was clarified.Also,the relationship between the structure and properties of the materials was investigated through various characterization methods.These studies can provide valuable"green"materials for the purification of gaseous pollutants.This research involves interdisciplinary fields of polymer,inorganic nanoparticle and catalysis.Thus,these fundamental research not only have important academic value and potential application prospects,but also meet the needs of“green”chemistry and sustainable development strategy.